CONTROLLABLE PITCH (C/P) AIRSCREW MINI TUTORIAL.

This text file is best displayed (or printed) in a 'fixed format' font such as 'Courier' to preserve layout of handling note sections. This is a complex tutorial aimed at experienced flight simulation enthusiasts already used to using such tutorials and who are already familiar with the 2008 Propliner Tutorial from www.Calclassic.com/tutorials.  Many abbreviations used in this tutorial are explained in the 2008 Propliner Tutorial.  Both the 2008 Propliner Tutorial and this supplementary mini tutorial are designed for on screen 'keyword' or 'key phrase' searching during self training, so that a particular topic can be researched and 'threaded'.


ADDING C/P TECHNOLOGY TO FS9 - LIMITATIONS - Please read very carefully.

The new Calclassic 'propeller pitch controls', (always in association with carefully matched controllable pitch flight dynamics), allow flight simulation enthusiasts to control airscrew pitch as a handling note target, *but they cannot disable other types of airscrew control* that are also valid gauges inside FS9. Nor can the new Calclassic controls disable other types of airscrew related input from keyboards, mapped joystick buttons, RPM levers on yokes, or mapped mousewheels.

To conduct a simulation of c/p technology *all propeller related inputs must be made *ONLY* by mouse clicking, or mouse dragging, the supplied Calclassic prop pitch control*. Calclassic c/p gauges which replicate two position screw pitch management must be mouse clicked to invoke full fine, else full coarse pitch. They default to full fine. In the future Calclassic c/p or a/p gauges which deliver any position screw pitch management must instead be mouse dragged to the % lever or % push rod position cited in the supplied handling notes. Those future Calclassic gauges will also default to full fine.

Since this system is constantly sending commands to FS to adjust the RPM system to achieve a desired prop pitch, the normal multiple-key keystrokes for engine selection and doors would not work.  Thus, we have included Rob Barendregt's Selection Correct gauge (with permission), which will allow such keyboard entries.  The only change from default behavior is that if you press only the E key, after one second all engines will be selected.

Calclassic c/p gauges have no control over the animation (code) of airscrew related levers or push rods in pre existing VCs. This 'technology demonstrator' therefore deliberately makes use of a pre existing CFS2 VC, which has no animated engine levers of any kind, and no relevant supplementary door / hatch commands. Within this release the screw pitch controls are the blue knobs, between the avionics tuners, below the Sperry Blind Flying Unit. No other working propeller control levers, push rods, or engine control unit (ecu), should be added. Mouse clicking between the blue sliders will move both together. Screw pitch asymmetry is available as a failure training mode by clicking a single slider.

When saved flights are loaded the screws will default to full fine causing an input error (in most cases). 

If we make an inadvertent propeller related input using any other control device, or by loading a saved flight, we must 'recycle' the Calclassic 'screw pitch controls' to re-impose a valid c/p pitch selection to cancel our simulation input error. You must also return any hardware RPM control to full fine and leave it there.  Attempts to use the Calclassic pitch controls while the simulation is paused may fail.

If in the future Calclassic c/p gauges, and matched third party c/p flight dynamics from another source, are used with a pre existing VC that has animated engine RPM control levers, those levers must not be used for controlling RPM or prop pitch. They 'may' animate randomly and annoyingly during simulation, but even if they do, they must not be 'moused' after engine start. 

VCs (which do not yet exist) can be developed in the future to have fully animated c/p screw operating controls, not just 'sliders' within the 3D simulation environment. MDLs can be developed to have supplementary door and hatch commands that do not duplicate engine control code. In theory those who own the source code to pre-existing MDLs and VCs can develop a 'c/p control animation' version of that existing VC using the existing 'levers'. This 'FS9 c/p technology demonstration' does not address those future goals and since two position c/p controls are used in flight only twice per sortie it is unlikely many existing VCs will ever be source animation code modified. This 'technology demonstrator' is instead intended to demonstrate that such modification of the original VC animation source code is not 'necessary', but simulation of c/p technology within MSFS will always require self discipline by the user. 


PURPOSE and LIMITATIONS OF *THIS* CALCLASSIC RELEASE.

A 'technology demonstration' must demonstrate the advantages and problems arising from c/p technology, and the means by which the operator of the technology invokes and overcomes them. The aircraft and engines chosen for the demonstration must pose a challenge, but not a difficult challenge. That drove our selection of the Royal Air Force Lockheed L-414 Hudson I as the 'demonstrator' despite the fact that it is not a 'propliner'.
 
However all 351 Hudson Is were manufactured in California, with much of the sub assembly undertaken by Rohr Aircraft in San Diego.  The L-414 Hudson I was an adaptation of the pre existing Lockheed L-14 Super Electra propliner, but almost all L-14 Super Electras were delivered with constant speed screw technology, so the L-14 propliner cannot serve as our c/p screw technology demonstrator.
 
The Calclassic c/p technology demonstration therefore uses unaltered CFS2 Lockheed Hudson files cited in the install.txt. This is *not* an MDL or simulation control interface update, save that the 'Calclassic two position c/p control' files are added, and gauges only available in FS9, such as the Sperry Blind Flying Unit, an appropriate AP of limited functionality, de icing capability etc, are added or substituted for a CFS 2 gauge list which could not include that level of realism. 
 
Use of accurate FS9 gauges, in place of always inaccurate CFS2 gauges, is essential to c/p screw simulation since c/p screw simulation requires detailed attention to, and accurate avoidance of, engine RPM limits, together with accurate control of MAP to avoid 'undersquare' running, (see below). Default CFS2 gauges are simply not accurate enough for that purpose. Consequently we will be using much more accurate (unaltered) gauges by Phil Perrott from within his Avro York VC.
 
Functional FS9 VC lighting has been provided, but CFS2 Hudson MDLs have no embedded functional landing lights. That FS9 functionality can be added only by the owner of the CFS2 source code. During night approaches use the runway lights for course guidance and the altimeter to monitor height. Flare to just negative VSI once below 50 feet. Simulation of wartime operations from the U.K. is assumed and all external lights should be off. Consequently no external lights have been added even though the switches for them are now present in the VC.
 
To avoid the problems that arise from 'harmonising' 2D and 3D simulation control interfaces, and the need for multiple 2D interfaces and bitmaps of differing aspect ratio, this Calclassic technology demonstration is VC only. The supplied code will therefore work on any screen, or in any window, of any aspect ratio, at any resolution, while providing parallax compliance at any consumer chosen zoom, within any consumer chosen Field of View.
 
The supplied Calclassic files will not work in CFS2, and are *not* an update for pre existing Hudson constant speed screw technology and 2 x 1050hp Pratt & Whitney Twin Wasp flight dynamics when simulating operation of a Hudson running on U.S. supplied low density 92 Octane AVGAS. The aliased gauges, flight dynamics, handling notes and this tutorial add the opportunity to understand and simulate the earlier c/p technology of the dual fuel Wright R-1820-G102A Cyclone powered Hudson I, running on British high density 87 Octane AVGAS, or British high density 100 Octane AVGAS, and only in FS9, while using an unmodified CFS2 MDL and textures. 

For a variety of reasons available CFS2 Hudson I models (MDL files) and textures do not mix well with FS9.  Therefore, this demonstrator uses a Hudson Mk III MDL file.  The Hudson III MDL depicts the Hudson as having wing slots and a ventral turret. The Hudson I had neither. That is accounted for within the supplied Hudson I flight dynamics. The Vspeed placard within the VC must be disregarded since it is for a Hudson IV, and anyway the RAF and RCAF used ASIs calibrated in MIAS, not KIAS. We will see airscrew hubs which are obviously constant speed hubs with long domed cylinders, again because this is a Hudson III MDL, but the supplied dynamics are controllable pitch.  
 
The original CFS2 Hudson release supplies no sounds; this demonstrator currently aliases the sound to the default DC-3. FS9 users should alias sounds of their own choice from any appropriate twin engine aeroplane. Remove any stall horn which may be present in the sound.cfg. The Hudson wing is stalled when the tail is down and the inappropriate horn will annoy you if you add one. You may also confuse the bogus stall warning with other warnings (see below). A GEAR warning horn has been added.


WHAT IS A 'CONTROLLABLE PITCH' (C/P) PROPELLER?


Early types of airscrew.

All early airscrews were fixed pitch (f/p). They were highly efficient during only one phase of any flight, but how the engine would rev up and down as MAP was varied with throttle, and as profile = windmill drag = IAS on the screw varied, was very predictable, making design and operation of aero engines simple, and engine overspeed easy to avoid. All series production WW1 aero engines had f/p screws. MSFS can simulate the use of f/p screws.

The next step was to develop airscrew hubs with metal collars, containing removable and rotatable blades, that a mechanic could turn with a tool on the ground, and then lock to any desired pitch. Low = fine if a short take off was required on the next flight, else large = coarse if high efficiency at high velocity (TAS) was needed instead to increase range, or combat radius. The rotatable blades inserted in these or later varieties of metal collars could be metal or wood. These second generation screws were adjustable pitch (a/p) screws. 

If these second generation screws were adjusted to a fine pitch it became easy for the operator to over rev the engine as windmill drag = IAS increased at constant MAP. Fine screws offer less resistance to engine RPM at the same IAS and MAP. The RPM limits of the engine did not change, but avoiding damage was more complex and required more careful attention to both IAS and MAP targeting. MSFS has no support for a/p screws, but at a much later date this technology will also be demonstrated and made available for simulation training, using a slightly different version of the new Calclassic gauge, and new compliantly matched FD.

In real life the third step was to automate a pitch change from fine, (during take off), to coarse for both cruise climb and cruise, at a specified higher IAS. These were automated variable pitch (v/p) screws over which the crew had no control and which could not revert to fine for the approach, (and potential go around), at low IAS. They were more efficient and more dangerous than a/p screws. FS9 can simulate the use of third generation v/p screws.


Controllable pitch airscrews.

The next step was to allow the crew to vary the pitch of the screw between the same two maximum versus minimum pitches using a push rod which actuated hydraulics to move the screw from max to min with no choices in between. These were (two pitch) controllable pitch (c/p) screws. Retail MSFS has no ability to simulate the use of c/p screws. The first practical c/p screw was patented by Hamilton Standard in the USA in 1930, but the early hydraulics worked only with screw blades of low mass and diameter, and across a small max to min pitch range, so that third generation French (Ratier) patent v/p screws were commonplace as new delivery options until about 1935. By 1934 the fourth generation Hamilton Standard two position c/p screws were competitive, but not dominant because they introduced two new and conflicting problems


MIXED BLESSING.

Two position c/p screws introduced a new problem which v/p screws deliberately avoided. At constant MAP and IAS the operator could now suddenly switch the screw from coarse to fine causing the engine to rev up suddenly. This delivered two new engine failure modes to pilots and flight engineers. They could easily rev the engine beyond its RPM limit due to either excess MAP, or excess IAS. Both MAP and IAS now had to be very carefully targeted with the new c/p screws. The point in the approach when a low target IAS had to be achieved became critical for the first time, and low IAS had to be achieved using high MAP!

This was due to a new and more complex problem. With an f/p screw the designer of the aeroplane chooses a screw pitch that never causes 'under square' running of the engine. If the screw pitch is large enough, as throttle is advanced RPM divided by 100 will never exceed MAP, measured in inches by Americans. The designer could protect the operator from that mismanagement possibility if the aeroplane in question actually had engines which were damaged when run 'undersquare'. One such engine was the Wright R-1820 Cyclone. The problem with two position c/p screws was that in order to be useful the new fine pitch had to be so fine that RPM/100 could easily exceed applied MAP in inches.

Since the switch from fine to coarse was no longer automated, engine damage could occur climbing out and again during the approach. The pilot or flight engineer now had the means to select a pitch that could easily cause undersquare running, by suddenly increasing engine RPM, at low and constant MAP.

The shift from coarse to fine during the approach not only had to be made at a low target IAS, it had to be made with substantial MAP so that fine RPM/100 remained less than MAP in inches, even after the engine was 'revved up hard'. The idea of c/p screws had arisen in the era of high co-efficient of drag biplanes with fixed gear. In that biplane pioneer era of aviation history high MAP was compatible with low IAS even with modest negative Vertical Speed Increment (VSI); for instance while descending on final approach. Now suddenly the reality was sleek monoplanes with retractable gear, and early monoplane propliners like the B247 had no flaps.

Remembering to switch to coarse before IAS exceeded a V speed target, (typically Vx), during climb out was no more difficult than complying with any other handling note targeting. It was just like any other variable geometry state change contingent on many new IAS (V speed) targets and limits that aircrew now had to manage as gear became retractable giving rise to Vle limits, and flaps became first present, and then multi stage, giving rise to multiple Vfe limits. 

The critical problem with fourth generation c/p screws was the one that Ratier had carefully dodged with third generation v/p screws. The change from coarse to fine required high MAP and low IAS when the aeroplane was approaching the landing runway. Aircrew had to think further ahead and had to plan their energy state changes much more carefully. The sequencing of variable geometry state changes became critical, due to the need to sustain high MAP while reducing windmill drag (IAS) during the approach to land. The more slippery the aeroplane the bigger the problem, and fourth generation c/p screw technology arrived just as aeroplanes were becoming much more slippery.

To a large extent this tutorial, and the supplied modifications to retail MSFS, are all about understanding that problem and acquiring the skills to overcome it. To have a significant problem to solve we need the aeroplane we train in to be a powerful sleek monoplane, but not too sleek. The Lockheed Hudson I is just about ideal, in part because its pre war Wright Cyclone engines have low RPM limits. 


CONSTANT SPEED (c/s) SCREWS NEEDED.

These were the operating problems that the fifth generation of constant speed (c/s) aircrews, (first available in 1937), were designed to solve. The use of c/s screws can be simulated within retail MSFS, and that easy to control technology is widely misapplied by MSFS flight dynamics authors to many aeroplanes that did not have it, because retail MSFS has no ability to simulate the more difficult to control c/p screw technology they had in real life. The real life problem was also addressed by three pitch c/p screws, and later still by 'any pitch' c/p screws. 

These avoided the sudden 'lurch' from full coarse pitch to full fine pitch that caused a huge surge of engine RPM with 'two position' screws. That surge always stressed the engine, even if it did not actually over rev the engine due to excess MAP, else cause it to run 'undersquare' due to inadequate MAP, at the moment of switching. Remember third generation Ratier v/p screws were automated and could never over rev an engine, because they only ever revved engines down. Consequently they could never invoke undersquare running either.

The arrival of two pitch c/p screw technology made go arounds safer, but made engine damage more common, and after slow accumulation of stress damage that made engine failures more common. Outside the Soviet Union, fourth generation c/p technology was also a transient technology, just like third generation automated v/p screws. Thus the Martin M-130 China Clippers were delivered with two position c/p screws in 1935, but were retrofitted with engines that could drive c/s screws in 1937. 


LOCKHEED HUDSON I

The Wright Cyclone powered Lockheed Hudson I is almost ideal as a 'technology demonstrator' and skills trainer within FS9, but unfortunately that means we need to learn some new things specific to the Lockheed Hudson I before we move on to study the c/p screw issues with numbers attached to the generic concepts explained above. 

*I have taken some liberties with the real values in RAF pilot's notes to better demonstrate the issues and sometimes to simplify operation within FS9*.

Calclassic 'regulars' will be very familiar with the operation of dual fuel engines in propliners ranging from the Grumman Goose through to the Boeing Stratocruiser. That familiarity is more or less assumed in what follows which adds a further level of propulsion realism to FS9. If you have no experience of operating dual fuel engines to the different limits specified in their on screen handling notes, while using the different specified fuels, you should obtain that experience before attempting to add the additional realism of controllable pitch airscrew simulation.

The FS9 handling notes for the Hudson I begin;

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Lockheed L.414 Hudson I Pilot's Handling Notes
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The two Wright R-1820-G102A Cyclone dual fuel engines have automatic mixture controls, and are carburetted with manually applied carb heat controls. These engines drive Hamilton Standard controllable two pitch aircrews optimised for take off and anti submarine patrolling. They are rated 900hp at 2300 RPM at 6700 feet (ISA).

Use of 92 Octane military grade fuel (or better) allows use of full throttle, and below 600 feet (ISA) it is then permissible to generate 43.5 inches MAP, and up to 2350 RPM, thus generating up to 1100hp, for up to five minutes for TOGA and WEP. Conversely while running on airline grade (87 Octane) AVGAS these engines must instead be throttled to 37.5 inches MAP and 2300 RPM. 

These engines need no cowl flaps.

WARNING: Compliance with the relevant MAP limit will not prevent engine overspeed.

WARNING: With military grade fuel (or better) DO NOT EXCEED 2350 RPM. 

WARNING: With airline grade fuel DO NOT EXCEED 2300 RPM.

WARNING: AVOID - RUNNING Cyclone engines UNDERSQUARE (MAP must always exceed RPM divided by 100).

WARNING: CRITICALLY WEAK FLAPS - Vfe = 115 MIAS

This Hudson I is loaded with the maximum possible = normal 4,080lbs of British high lead, high density, 87 Octane AVGAS. Bomb load is therefore restricted to 2 x 250lb anti submarine bombs. 

This aircraft is unpressurised and the five crew have no oxygen supply. Under King's Regulations do not exceed FL100 by day or FL80 by night.

**********************************************

During the 1930s, and well into WW2, the whole issue of dual fuel engines and controllable pitch aircrews overlap to limit the performance of aeroplanes in ways which retail MSFS cannot simulate. The purpose of this Calclassic 'technology demonstrator' is to add that capability, so that we can understand not only the operation of controllable pitch airscrew technology, but how it limited the performance envelope of relevant aircraft.


DUAL FUEL 'REQUIRES' CONSTANT SPEED TECHNOLOGY.

During the 1930s the British Empire and Dominions did not produce 92 Octane 'military grade' AVGAS. They produced 76 Octane 'general aviation grade' AVGAS which was also issued to military and naval training commands, and RAF Army Co-operation Command. 87 Octane, 'airline grade' AVGAS was mass produced for use by airlines and all other military and naval commands. Meanwhile 'weapon grade' 100 Octane AVGAS was produced as quickly as possible, but was stockpiled and not issued. 

When Germany invaded France and the Low Countries in May 1940 the RAF started to issue weapon grade fuel, but only to RAF Fighter Command in the UK. The British Expeditionary Force in France continued to use airline grade fuel. RAF Coastal Command were not authorised to draw upon weapon grade fuel stocks until August 1940. 

RAF Coastal Command squadrons flying aeroplanes with Bristol sleeve valve engines (mostly the Botha and Beaufort), desperately needed fuel better than airline grade to reduce frequent and fatal engine failures. Consequently the limited quantity of weapon grade fuel consumed by Coastal Command during the life span of the Hudson I was directed away from the Hudson I squadrons, because their Wright Cyclone poppet valve engines did not need 'luxury fuel' to avoid early failure. One of the things this 'MSFS technology demonstrator' is designed to illuminate is why aeroplanes with only fourth generation c/p screws were performance limited, even when running on weapon grade fuel, while aeroplanes with c/s screws whose crew could limit or increase RPM, using RPM levers, could benefit much more. 

*Higher quality fuel allowed aero engines to run at significantly higher MAP, but it did not allow them to run at significantly higher RPM*. 

Aeroplanes with propulsion systems that had no means to limit RPM independently from fuel flow barely benefited from better fuel. The decision to issue weapon grade fuel to RAF Fighter Command from May 1940 therefore required all the existing f/p screw and c/p screw Spitfires and Hurricanes to be retrofitted with c/s screws so that they could run at higher MAP *without generating higher RPM*. 

Those c/s screws, so hurriedly retrofitted between June and October 1940, were not needed while Fighter command ran on airline grade fuel. The screw (propulsion technology) upgrade was the explicit consequence of the fuel upgrade. The 'Boys Big Book of Wonderplanes' and the internet are full of 'aviation histories' which fail to comprehend the tightly interlinked upgrade process. 

Most flight simulation releases also contain no comprehension or simulation of dual fuel technology and how it interrelates with propulsion technology. The reality was that better fuel needed the propulsion system to be fitted with a 'governor' or 'constant speed unit' to control (limit) engine RPM at the (much) higher manifold pressures (MAP) that better fuel enabled. The problem everywhere was that constant speed control mechanisms were complex. The necessary precision machine tools were in short supply, and so for a while between 1937 and about 1943, CSUs could not be produced in the same quantities as powerful aero engines. For a while only aircraft with the most critical roles, (for a particular nation), could have c/s propulsion, and without it they could make only limited use of better AVGAS. 

Consequently at a time when the most important aircraft in the RAF were very briefly the daylight interceptors of UK Fighter Command, the Hudson I had no chance of being retrofitted. However the U boat threat would soon become the primary threat to the UK and so from September 1940 RAF Coastal Command terminated delivery of Hudson Is with c/p only technology and insisted on Hudson IIs and Hudson IIIs with c/s technology installed prior to delivery, from October and November 1940 respectively. The Hudson II and III could then make full use of weapon grade fuel because the pilot could limit. or increase, RPM to any value, at any MAP, allowing the engine to produce more power without overspeeding.

More power and better performance from better fuel are only (significantly) available with c/s screw technology. 
 

TAKE OFF and OBSTACLE CLEARANCE.


Trimming for obstacle clearance before take off.

We have no cowl flaps to worry about, but we cannot control or target RPM directly. Instead we control SCREW PITCH and we have only two choices. They are FINE (push rod full forward = up) or COARSE (push rod full aft = down). Take off requires FINE SCREW PITCH so that the engine can spool up to high RPM, so that it can produce high power. That apart, take off proceeds like any other take off. 

We have a specific V speed = IAS target beyond Vr, (usually and also in this case Vx), which we always carefully trim the aeroplane to seek, (hands off = with zero pilot joystick pressure), prior to take off. Carb heat must be OFF = COLD. We must deploy exactly the correct lift augmentation from FLAP at that pre trimmed target IAS = Vx, because every other flap extension value delivers worse lift to drag ratio at the pre take off trimmed IAS = Vx which we are about to seek, and will retain as our operating target until the obstacle clearance phase is completed.


Fowler Flaps in FS9.

In real life the Hudson has Fowler patent flaps whose extension is measured in per cent, not degrees, because slight extension adds only wing area without drooping to increase wing camber. This allows aircrew to increase lift without increasing co-efficient of profile drag. The real pilot can use any % extension. In this release the standard take off, approach, and landing lift to drag augmentation ratios are preconfigured, and in FS9 we shall measure those per cent extensions in fake 'degrees' of 'droop' = aerofoil camber change.


MAP restrictions versus RPM restrictions.

Now remember that these aeroplanes used only 87 Octane fuel in real life. We have two restrictions. Consequently we must not generate more then 37.5 inches of MAP and we must not generate more than 2300 RPM. With no RPM levers, controlling no engine governor, at any given MAP, RPM simply rises according to the profile = windmill drag = IAS we abuse the airscrew with. 

We are all used to the idea that we must restrain our profile drag = IAS so that it does not cause structural failure of the airframe, but without RPM levers we must also restrain windmill drag = IAS so that it does not cause structural failure of the engines. We must still avoid premature detonation of the AVGAS in our engines, by restricting MAP according to the quality (Octane rating) of the fuel we load, but with c/p screws that is the lesser problem. With c/p screws we must restrict both MAP and IAS in concert so that we do not overspeed the engine into structural failure.

In nil wind standing on the runway our windmill drag = 0 MIAS. With 87 Octane AVGAS we are allowed to apply 37.5 inches of MAP and the mediocre fuel will not suffer premature detonation, but the engines will not spool to 2300 RPM at 0 MIAS. Thus they cannot produce 900hp while the aeroplane is static.  Remember how the handling notes begin;

>>>>>>>>>>>>>>>

The two Wright R-1820-G102A Cyclone dual fuel engines have automatic mixture controls, and are carburetted with manually applied carb heat controls. These engines drive Hamilton Standard controllable two pitch aircrews optimised for take off and anti submarine patrolling. They are rated 900hp at 2300 RPM at 6700 feet (ISA).

>>>>>>>>>>>>>>

The handling notes for engines with c/s screws, (with an engine governor), do not mention a specific RPM because the pilots or flight engineer can mix and match any desired horse power with different combinations of MAP and RPM, because they have RPM levers to impose any constant RPM they choose. With no constant (engine) speed unit (governor) we cannot impose that option. 

So when we release the brakes of our Hudson I, windmill drag = IAS on the screws will increase, and that rising windmill drag will windmill the engines (which have no governor) to ever higher RPM, and that RPM will eventually exceed the 87 Octane AVGAS (high power overheat) limit of 2300 RPM even though the engine will not spool to 2300 RPM with windmill drag = 0 MIAS with no wind today and the brakes firmly on.  

Limiting MAP to 37.5 inches is still necessary, but is not at all the point. We will only be able to use 37.5 inches for take off when our squadron converts to the Hudson II or Hudson III, with fifth generation c/s propulsion in the autumn of 1940. Then, and only then, we will be able to demand only 2300 RPM with RPM levers, which we do not have in a Hudson I. While we are flying the Hudson I we must set the MAP which will not cause the engine to exceed its overspeed limit, after we reach our trimmed V speed target. As usual we trim the elevators to make the aeroplane accelerate 'hands off' to IAS = Vx before we enter the runway.

With c/p screws pre take off trimming for IAS = Vx is super critical, because we are about to limit MAP to the value that will not cause engine RPM overspeed at IAS = Vx. The designer of the real propulsion system knows what that MAP is, he knows the value of Vx, and the two values are inserted in the (real) handling notes. Our job is to trim aeroplanes very carefully to seek IAS = Vx before we enter the runway, and then to limit MAP to that which will not overspeed the engines while we take great care not to exceed IAS = Vx.

Using 87 Octane AVGAS, we must limit MAP to no more than 34.5 inches for TOGA, because if we use more the engines will overspeed before (when) we reach Vx = 110 MIAS. Remember Vx is the profile drag = IAS which delivers maximum climb gradient throughout the obstacle clearance phase, which always follows the take off phase. Maximising climb gradient requires low forward velocity, not a high Vertical Speed Increment (VSI). The phase of any flight in which we maximise our VSI is the climb phase, during which we make faster progress down route, not the obstacle clearance phase. During the obstacle clearance phase the last thing we want is progress down route into the obstacle!

We do not need to set 34.5 inches precisely. We can set (just) less than the engine structural failure by overspeed at Vx safety limit.


Dual fuel technology in FS9.

However this is a 'technology demonstrator' release, as well as a 'realistic' simulation of RAF Coastal Command operating criteria, so in order to understand the issues arising from having only c/p propulsion we can instead load British weapon grade 100 Octane AVGAS and make a full throttle take off. When we do that we must be critically aware of the need to throttle the engines to less than 2350 RPM (high power torque limit) even though we have no need to throttle them to limit MAP.

The much higher quality fuel will no longer suffer premature detonation above 37.5 inches MAP, but the engine will suffer high power over-torque at 2350 RPM regardless. The much higher quality fuel only gives us another usable 50 RPM. If we use 43.5 inches for TOGA, with weapon grade fuel, all of our skills must be much sharper, and in particular, we must be able to target IAS = Vx very accurately indeed. The reality was that issuing weapon grade fuel to Hudson I squadrons would have been a waste because it would only have allowed operation from very slightly shorter runways, or steeper climb over nearby obstacles, and there was no need to relocate Hudson I squadrons to aerodromes with critically short runways, and none of them were surrounded by obstacles (such as mountains) anyway. 

Within FS9 we can now (for the first time) impose the super critical problems of a 43.5 inch (full throttle) take off on ourselves, to understand how much skill is required to control RPM, via very precise targeting of IAS, if we use higher quality fuel, without the fifth generation c/s technology that gives us RPM levers to set 2300 or 2350, or whatever the engine (high power overheat or over-torque) limit is, before we take off.


Video and audio warnings in FS9.

Because c/p screws make the issue of variable RPM limits with variable Octane AVGAS super critical this 'Calclassic technology demonstrator' comes with a read out of the fuel loaded. The reminder is positioned just below the port engine MAP and RPM gauges. We click on it to vary the Octane rating of the fuel we load, sortie by sortie. That mouse click also resets the engine overspeed and over-torque warnings to match the fuel we load!

The fully qualified Hudson I pilot had no gauges other than the RPM gauges to warn him of engine overspeed. We need the Calclassic warning gauges to 'represent' a nominated training captain, or our flight commander standing alongside us in the gangway while we are conducting our Hudson I type conversion training. If we are not warned of pilot errors when we commit them, we learn more slowly, and those prompts help us to understand the limitations that fourth generation c/p screws imposed on pilots and flight engineers. There is no FE or P2 in a Hudson. When we overspeed our engines, a warning will appear and a horn will sound in FS9. We can then identify our pilot error, and correct our pilot error, *before* the engines fail. Imposing engine failures for unexplained reasons does not enhance learning.

Although this simulation release provides engine pressure and temperature gauges, as in the real Hudson I they are almost out of sight on the sub panel above the crew gangway. We will not need to monitor CHT if we do not overspeed or over-torque the engines, and we will not need to monitor engine pressures if we supply the MAP required to achieve our IAS compliance targets in the compliant variable geometry states cited in the supplied on screen handling notes. We must concentrate on IAS, RPM and MAP compliance.


IAS controls power and thrust.

Now don't miss the point! In aeroplanes with c/p screws we increase or lose power output from the engines as our IAS varies. This isn't just about avoiding IAS > Vx and avoiding engine overspeed or engine over-torque. If we allow our IAS to drop below windmill drag = Vx the engine spools down and produces less power, and our airscrews spool down and produce less thrust, so our VSI decreases as we conduct obstacle clearance at less than 110 MIAS, and we may impact the critical departure obstacle, (in cloud or a blizzard). With c/p screws we need much better IAS targeting skills, because windmill drag = IAS varies both horse power available, and thrust available, at constant MAP. 

With c/p screws, for each desired dynamic state, (phase of the flight), there is only one IAS that is fully efficient. Once we have relevant experience, simply avoiding structural failure of the engines, by avoiding excess IAS is 'easy enough', but avoiding the IAS that will cause structural failure of the engines by a large margin, may prove fatal too.  

Profile drag on the aeroplane's structure (IAS), which may cause structural failure if we exceed the relevant limit for a particular variable geometry state, is the same thing as windmill drag on the airscrews, which will just as easily cause structural failure of the engines, if that windmill drag = IAS is allowed by pilot error to exceed the current IAS (V speed) limit = Vx = 110 MIAS. Yet we must keep our windmill drag at, or very close below, our V speed target else both power and thrust spool down.

Our engines will not overspeed provided we do not exceed IAS = Vx = 110 MIAS, and provided we impose the compliant MAP for the fuel in use. Once we set the compliant MAP, whether the engines overspeed, and how much power they produce, is a function of our skill to target IAS during two high workload phases of the sortie, in a single pilot aeroplane. It follows that (sim) pilots who were (are) under confident of their ability to pre take off trim for, and then target Vx accurately, must use less MAP for take off and will require longer runways. The important skill to learn within FS9 is avoidance of engine overspeed, if necessary by application of less than maximum safe MAP, (for the AVGAS in use), so that slight exceedence of Vx does not cause engine overspeed. The longer term goal is to acquire the skill to use maximum compliant MAP, without exceeding Vx, and without needing to target an IAS far below Vx, in order to avoid engine overspeed beyond Vx.

The real flight dynamics designer of the Hudson I chose a screw full fine pitch which delivered the full throttle RPM limit of the engine = 2350 RPM, with full throttle applied just above sea level, pumping out 1100hp at 43.5 inches MAP, at the windmill drag = IAS = Vx for the Hudson I = 110 MIAS.  That is the only IAS at which the engine can deliver 1100hp for TOGA, (actually only for Go Around already at 110 MIAS), because 110 MIAS is the only windmill drag that will spool the engines up to 2350 RPM, by windmill action on the screws. However the RAF decided to issue only 87 Octane with a limit of 2300 RPM which had not been pre-associated with the chosen fine screw pitch, so we must use less than the 37.5 inches MAP pressure limit, and never more than 34.5 inches MAP, so that the engine does not exceed 2300 RPM at 110 MIAS.


Prepare to 'rev down hard'.

Even departing an RAF or RCAF coastal aerodrome with no nearby obstructions, the obstacle clearance phase always endures until we are 200 feet AGL, and may endure for much longer. During that phase we must nail Vx = 110 MIAS (for which we elevator trimmed very carefully before entering the runway), and the more MAP we employ to take off the better our IAS targeting skills need to be to avoid engine overspeed.

We retain FULL FINE PITCH until *after* obstacle clearance is completed. The obstacle clearance phase is flown with FLAP = STAGE 1 and at windmill drag = Vx = 110 MIAS, however long it endures. If we are simulating use of weapon grade fuel we will reject TOGA MAP = 43.5 inches as soon as it seems safe to do so, and we will throttle the engines down to (no more than) 34.5 inches (always within five minutes of throttle up). However in real life we would be using 87 Octane airline grade fuel and would already have set (no more than) 34.5 inches, against the brakes, after we lined up. 

When we have met all of the 'cross above' restrictions, within the real ATC departure for the airfield we are departing, (which we download from the internet), we are ready to rev the engines down hard to increase our velocity down route. Only then do we select FULL COARSE PITCH, still maintaining Vx = 110 MIAS, still with FLAP 1 deployed, until after we have revved the engines down hard by invoking that screw pitch change. 

Having completed urgent climb, and having invoked velocity maximising = coarse screw pitch, we retract FLAP, and since that velocity maximising screw pitch is very inefficient at low windmill drag = IAS, we now need to increase our windmill drag = IAS urgently until it is an efficient windmill drag for a screw in coarse pitch.

For the first time since before we entered the runway we alter elevator trim. Now we must elevator trim for profile drag = windmill drag = 135 MIAS = Vy, and so now we pitch the nose down with the yoke to impose close to zero VSI while we do so. If this was an airliner we would have reduced MAP, from rated MAP, to only METO MAP, prior to 'revving down hard', but this is a combat mission and we will retain rated MAP = 34.5 inches for as long as our turbine superchargers can pump it. We want to get up to mission altitude, get the radar on, and test it, as soon as possible, because failure of the search radar is the most likely cause of an aborted maritime patrol in a Hudson I in 1940.  

All of that is much abbreviated in the on screen handling notes which specify our operating targets and how we must sequence them. Make sure you can associate each line of the handling notes below with the tutorial above. The handling notes explain only real life operations with 87 Octane airline grade fuel, but remember the supplied flight dynamics, and Calclassic gauges, fully support dual fuel operation as explained above.


***************************************************************
Take Off and Obstacle Clearance phase: 

PITCH      = FINE        <<<<<<<<<<<<
CARB HEAT = COLD
FLAP       = STAGE 1 (10 degrees)
TRIM       = 9 degrees (45%) UP (to target Vx)
LINE UP

BRAKES     = ON
MAP        = 34.5 inches (87 Octane Fuel)
BRAKES     = OFF

YOKE       = NEUTRAL
ROTATE     = 90 MIAS (Vr)
GEAR       = UP 
ACCELERATE = 110 MIAS 
ACHIEVE    = 200 feet AGL 

Above all local obstacles:

PITCH      = COARSE      <<<<<<<<<<<<
FLAP       = UP
VSI        = minimal or zero
ACCELERATE = 135 MIAS

***************************



Tail up, rotation, unstick and Vmc criteria.

Do not force the tail up with the yoke during the take off roll. Let it come up on its own. We rotate at Vr = 90 MIAS to reduce our rate of acceleration towards our trimmed target of Vx = 110 MIAS. The 9 degrees of elevator tab will force the elevators to seek Vx 'hands off' but we are altering the dynamics vigorously as we rotate the aeroplane and then raise the gear. If everything is happening too fast don't be in a rush to raise the gear. We must not exceed 110 MIAS and although we trimmed for 110 MIAS, during these rapid dynamic changes it will take time for the elevator trim to settle (damp) the aeroplane to Vx = 110 MIAS. We must use the yoke to impose 110 MIAS while the aeroplane 'settles'. Provided we use only 34.5 inches (only rated MAP or a bit less) during TOGA, acceleration to 110 MIAS after rotation at 90 MIAS, should happen at a rate we can control without overshoot of IAS target causing overspeed of the engines.

The early models of Lockheed L-14 Super Electra had been designed and delivered with structurally deficient, and under size, fins and rudders. That problem had been cured before L 414 Hudson production began and so the Hudson I had two big strong fins and rudders, positioned right out in the prop wash. Retaining directional control after engine failure was nowhere near as critical, or impossible, as in many contemporary combat aircraft, and so we are not desperate to accelerate to a very high IAS = Vmc (engine out minimum control IAS). Vmc is below Vx.


MIAS measures the applied drag = force of a passing fluid, not aeroplane speed.

The new idea that even Calclassic 'regulars' must come to terms with is that with c/p screws that allow us to select a very low = fine pitch we can over rev our engines with excess IAS as easily as we can over rev them with excess MAP. With TOGA MAP = 43.5 inches at full throttle using weapon grade fuel we will overspeed the engines if we allow windmill drag to exceed Vx = 110 MIAS. With airline grade fuel, using only 34.5 inches, most 'typical' pilot handling errors causing IAS > Vx will not overspeed = over heat (or over torque) the engines, but our IAS target is still Vx = 110 MIAS. 

Think about how even a gale of profile = windmill drag, (only 34 KIAS = 39 MIAS), might turn the sails of an ancient windmill at an RPM that would shatter the bearings, or connected machinery. Aero engines will happily tolerate more than a gale of windmill drag on their sails, but once we push our abuse beyond hurricane drag, which is identical to F1 tornado drag, (only 64 KIAS = 74 MIAS), into F2 tornado force = drag (98 KIAS = 113 MIAS), if we have full fine screw pitch applied then allowing the windmill drag abuse to rise to F2 tornado force windmill drag can rip the connected bearings or machinery of our aero engine apart. Our aero engine has an RPM limit just like the bearings and machinery of a windmill and the finer we trim our sails the easier it is for any level of operator windmill drag = IAS abuse to spin the sails up to the machinery structural failure RPM. 

Remember IAS has nothing to do with 'aeroplane speed'. Drag is just another way of saying force. IAS measures drag = force. Gale *force* is only 34 KIAS. Hurricane *force* is only 64 KIAS. Speed is something else and is measured in KTS or MPH. A gale 'speed' wind has no meaning. Structures are destroyed by the force = profile = windmill drag = IAS of passing fluids. Any vehicle or vessel impacted by that fluid can have its own speed (measured in MPH) which is very different to the force = drag (measured in MIAS) imposed on it by the passing fluid.

Provided we motor our windmill around, always preventing the windmill drag abuse we apply exceeding 110 MIAS, (just below F2 tornado force = drag), while we are employing FINE SCREW PITCH, that windmill drag abuse won't quite destroy the machinery because it won't quite windmill the engine beyond its safe (high power torque) limit of 2350 RPM using weapon grade fuel, or 2300 RPM (high power overheat) limit using airline grade fuel. 
 


HUDSON I CLIMB PHASE is brief.

As we continue climb at our target windmill drag = Vy = 135 MIAS, to maximise our climb rate instead of our climb gradient, in COARSE PITCH using rated MAP = 34.5 inches, (whatever fuel we loaded), we are in no danger at all of overspeeding the engines. Remember long before c/p screws existed use of full throttle (TOGA power) for climb was forbidden in aeroplanes with superchargers. If we have access to weapon grade fuel we may use unsustainable MAP to take off, but never during either the obstacle clearance phase, or the subsequent climb phase.  

***************************
Climb Phase = Rated Power:

MAP = 34.5 inches
IAS = 135 MIAS

Anti sub patrol typically FL65
****************************

Remember the first paragraph of the handling notes?

>>>>>>>>>>>>>>>

The two Wright R-1820-G102A Cyclone dual fuel engines have automatic mixture controls, and are carburetted with manually applied carb heat controls. These engines drive Hamilton Standard controllable two pitch aircrews optimised for take off and anti submarine patrolling. They are rated 900hp at 2300 RPM at 6700 feet (ISA).

>>>>>>>>>>>>>>

Our RATED ALTITUDE is 6,700 feet (ISA). Our turbines, which can pump 43.5 inches at sea level, can pump only 34.5 inches at FL67. In even thinner air above rated altitude, in level flight, our turbines cannot pump RATED MAP = 34.5 inches and cannot deliver RATED POWER = 900hp, but this is a maritime patrol asset designed to patrol at FL65, just below rated altitude, and climb to that level with 34.5 inches at Vy = 135 MIAS will be swift.

If this was an airliner and our goal was instead to maximise profit we would instead cruise climb at higher windmill drag (IAS) using less MAP, to induce less fuel flow (PPH), while making faster progress down route, (once above all down route obstacles).



MARITIME PATROL.

Our mission is almost always maritime patrol, usually at night, else within or above cloud by day. This is the only aeroplane in the world that can search effectively during those conditions, because the Hudson I is the only aeroplane in existence with airborne surface search radar. 

The aircraft.cfg explains;

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

ui_manufacturer=Lockheed
ui_type=Hudson I
ui_variation= RAF Coastal Command
description=The RAF ordered 350 Hudson Is powered by Wright R-1820-G102A Cyclones rated 900hp at 6700 feet, driving Hamilton Standard two position screws. They were delivered between February 1939 and September 1940. From January 1940 these became the first aircraft anywhere to have surface search radar, hence five crew. Almost all went to RAF Coastal Command and squadron service began in May 1939. They were stationed at Gosport (use Goodwood - EGHR), Bircham Newton (use Marham - EGYM), Thornaby (use Leeming - EGXE), Leuchars (EGQL) and Aldergrove (EGAA). 28 were diverted to 11 Sqn RCAF in October 1939 and were based at Dartmouth (CYAW). Two were diverted to the SAAF for evaluation. One later became an RAF VIP transport. Later marks of Hudson had constant speed screws, most had different engines, and more fuel. These files should not be used with those variants.


>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Our radar search is normally flown at FL65. These are mostly night patrols, else all weather patrols, with IFR departures and IFR approaches, all year round. Whether we are line searching a block of sea which we expect U boats or E boats to pass through on the surface, or whether we are the anti submarine CAP in a drifting race track holding pattern ahead of a progressing coastal or Atlantic convoy, really makes no difference. We patrol. We conserve fuel inbound and outbound, not just on patrol.

****************************
Maritime Patrol: 

IAS   = 135 MIAS
MAP   = as required
RADAR = SEARCH
Plan  = 300 PPH
Yield = 130 KTAS at FL65 
****************************

Our 4,080lbs of high density AVGAS yields a theoretical endurance of 13.6 hours to dry tanks, but in practice we won't be tasked for more than 12 hours airborne in a Hudson I. When simulating RCAF operations from CYAW we fly only maritime patrol. Once we achieve a hostile contact we call for back up, while we shadow the hostile contact until (warship) back up arrives. Our firepower to prosecute hostile contacts is minimal and search radar equipped aircraft were really too rare and valuable to be used for prosecution in 1940. The RAF have not yet invented and deployed the first air deployable depth charges and anti submarine bombs had limited combat utility. 

However if we encounter German maritime patrol aircraft we will always attack. The Luftwaffe is engaged in the never ending political struggle to take maritime patrol budget away from the Kriegsmarine, but is not yet winning that battle. Most of the German maritime patrol aircraft we meet by chance in 1939 - 1940 will be Kriegsmarine hydroplanes, not the very rare land based Luftwaffe Fw 200 Kondor. The RAF's first air to air kill of WW2 was scored by a Coastal Command Hudson I and was over a Dornier 18 north west of Hamburg.

Our radar equipped Hudson is too valuable a night and all weather search asset to be assigned tactical bombing missions unless the need is desperate, and its bomb bay is far too small for mine laying. However attacking enemy harbours, ports, dockyards and even shipyards is the job of RAF Coastal Command, and every so often we may be ordered out on night bombing raids of great importance. We never exceed FL80 by night. Night vision deteriorates quickly as blood oxygen saturation falls and in this 1939 vintage maritime patrol aeroplane we have no oxygen supply. 


BOMBING and MARITIME STRIKE SORTIES.

During the BEF retreat to Dunkirk in May and June 1940 we will be required to fly emergency army co-operation tactical day bombing missions against the main supply routes and choke points along which German motorised and mechanised infantry are advancing. Operating no more than 30 miles beyond the contracting British perimeter we will encounter no Flak at FL100 by day.

****************************
Tactical (day bomber) cruise: 

MAP   =  25 inches
Plan  = 500 PPH
Yield = 174 KTAS at FL100
****************************

Later marks of RAF Coastal Command Hudsons will strike deep into Germany during RAF 'thousand bomber raids', but the Hudson I had been retired from combat duty by then. Our practical combat radius is about 70% of the theoretical light bomber combat radius the planning criteria above disclose. Soon German coastal maritime traffic and infrastructure isn't the only coastal traffic we need to radar search, else attack. RAF Hudson Is are based to reach the furthest coasts of France, Denmark and Norway, and to perform convoy CAP half way to Iceland. RCAF Hudson Is are more concerned with iceberg spotting and drift plotting on the convoy routes, (while operating from forward bases east of Dartmouth), than they are with U-boats, at this stage of the war, The range and endurance of aeroplanes is not a single number as pretended in the 'Boys Big Book of Wonderplanes'. It is what we plan and execute, sortie by sortie.

We use max cruise power to increase fuel burn to battle headwinds and our endurance is greatly reduced. Occasionally we dash at max cruise to prosecute a U-boat or E-boat contact reported by others, typically a convoy, or evacuation beachhead, under attack.

****************************
Max Cruise:

MAP = 29 inches

Typically  670 PPH
Typically  198 KTAS at FL100
***************************



VMAX IS CONTROLLED AND THEREFORE LIMITED BY C/P TECHNOLOGY.

Earlier we studied how the windmill drag = IAS we could abuse the engines with may be limited to only 110 MIAS when we set our airscrew blades full fine. Exactly the same problem exists now that we have set our screw pitch to full coarse. At full throttle there is a higher windmill drag = IAS = Vmax that will again overspeed = overheat (else over-torque) the engines. The real flight dynamics designer must choose the singular coarse pitch very carefully. 

The real FD author would like to choose a pitch which windmills the engine up to RATED = 900hp, (the maximum power allowed after TOGA regardless of fuel loaded), at modest IAS so that all of that potential power is available to climb, but of course if he chooses a coarse screw pitch that windmills the engine to 900hp at Vy = 135 MIAS that would become the maximum IAS for both patrol and cruise. That would be almost ideal if the Hudson I had no secondary tactical bomber, or heavy fighter role, but it did, and so the real FD author must choose a singular coarse pitch which overspeeds the engine at significantly higher windmill drag = IAS than Vy. Whatever pitch he chooses the resulting IAS is Vmax.

If he chooses a very high IAS as Vmax, the RPM to which the engine is windmilled at 34.5 inches MAP, at only IAS = Vy will be low and the power generated will be low during climb. Remember we need high engine RPM to generate high horsepower, and we need high screw RPM to generate high thrust (at low IAS = Vx or Vy). 

The real flight dynamics designer must pick the singular coarse pitch that causes RATED POWER = 900hp to be developed at the RATED ALTITUDE demanded by the customer, when the pilot applies FULL THROTTLE at RATED ALTITUDE. So that condition must windmill the engine to RATED RPM at RATED ALTITUDE. 

We know the handling notes disclose that;

>>>>>>>>>>>>>>>>>

The two Wright R-1820-G102A Cyclone dual fuel engines have automatic mixture controls, and are carburetted with manually applied carb heat controls. These engines drive Hamilton Standard controllable two pitch aircrews optimised for take off and anti submarine patrolling. They are rated 900hp at 2300 RPM at 6700 feet (ISA).

>>>>>>>>>>>>>>>>>

So the coarse pitch the real FD author must employ within the relevant two position c/p prop hub is the singular pitch which causes 2300 RPM, under ISA conditions, in level flight, at FL67, at full throttle.  

That then becomes what the MSFS (or CFS) c/p screw air file for a Hudson I must emulate. The engines must deliver 1100hp at 2350 RPM at FULL THROTTLE and CLIMBING at Vx = 110 MIAS below 600 feet in FINE PITCH, and they must also deliver 900hp at 2300 RPM at Vmax at RATED ALTITUDE = 6700 feet (ISA), at FULL THROTTLE in LEVEL FLIGHT in COARSE PITCH.

In the first case (in thick air) the applied windmill drag = 110 MIAS = Vx spools the gear driven supercharger turbines to pump 43.5 inches MAP. In the second case the much higher windmill drag = Vmax, impacting coarse screws, spools the same turbines to less RPM, even in thinner air, and partly because RPM is lower, but mostly because the air to be compressed is thinner, the same turbine outputs only 34.5 inches MAP at full throttle at Vmax at rated altitude (regardless of the fuel in  use). The real FD author chooses the singular fine and singular coarse pitches which cause those two results. The MSFS FD author must code the c/p air file accordingly. The singular air file must output both complex equations linking those inputs to those outputs for Vx and Vmax. A gauge that allows us to switch between the two relevant pitches is the lesser part of the FS development problem.

Without fifth generation c/s technology we have no RPM levers. We cannot spool the engine independently from our windmill drag = IAS. We cannot control screw RPM to control traction efficiency, or spool engine RPM to max = 2350, to spool the turbines to generate more MAP at will, They all just vary with our applied windmill drag = IAS.

If we begin to descend in full throttle, our IAS will rise, we will instantly windmill the engine to more than 2300 RPM = RATED RPM, and the engine will generate > RATED POWER > 900hp and the exhaust valves will overheat causing premature detonation of the airline grade fuel, and the engines will be damaged. The (poppet) exhaust valves may shatter. Soon afterwards with power rising we will windmill the engine beyond 2350 RPM (its high power torque limit) and it will (eventually) suffer structural failure. In a Hudson I we cannot use an RPM lever to prevent RPM above limit RPM, or to demand those safe limit RPM, to maximise turbine RPM to maximise available MAP. In a Hudson I we only have fourth generation c/p screws and no RPM control levers.

The maximum velocity of the Hudson I is limited by our inability to produce 900hp using different combinations of MAP and RPM. Above 6700 feet MAP falls further, we cannot sustain even 2300 RPM in level flight , and so power falls, and thrust falls, and so our TAS yield falls. We cannot mix and match more MAP and same RPM, even if we have weapon grade fuel. There is no point in issuing it. With c/p screws Vmax is possible at just one altitude (which varies with the weather each day and each night). Consequently Hudson I Vmax was only 225 MIAS = 214 KTAS, (measured using RAF mean cruise weight criteria), and was achieved at FL65 just below rated altitude.


DESCENT PHASE - OVERSQUARE ENGINE OPERATION REQUIRED.

Only out of control descent will generate engine overspeed via total loss of control of windmill drag = IAS. However we must remember that even so the engines will suffer structural failure before the clean airframe, and so Vne also has no relevance while we have only c/p technology. Even with huge holes cut into it for a bomb bay and dorsal turret the Super Electra airframe is very strong, but with c/p screws we cannot exploit that strength. The engines will always overspeed before we reach Vne, while we throttle them to run oversquare.

***************************
Descent phase:

VSI   = vary to deliver
IAS   = prior cruise IAS
MAP   = OVERSQUARE (follow RPM down)

Prior to IAF, hold or circuit:

MAP = OVERSQUARE (follow RPM down)
VSI = 0
IAS = 135 MIAS

****************************


Wright Cyclone engines in particular must not be run undersquare. We must sustain MAP in inches greater than RPM divided by 100. So we can reduce MAP when we descend, but if we intend to dive to almost 2300 RPM, we must not reduce MAP below 23 inches, which is more than we use to cruise during an anti submarine patrol! 

We 'can' descend an aeroplane with only c/p propulsion technology, at 'high' MAP, but only subject to maximum RPM, and since this is a maritime patrol asset, not a fighter, we intend to make all descents with MAP reduced below typical patrol MAP, not well above typical patrol MAP!  

The whole issue of avoiding running undersquare is much more acute with c/p screws than it is with c/s screws. If we allow RPM increase, by allowing windmill drag = IAS increase during descent, we may need to increase MAP, again and again, to stay oversquare, to avoid engine damage and eventually failure, (usually on a later flight).  Eventually we overspeed or over torque the engines instead, while trying to remain oversqaure. Only fifth generation c/s screw technology allows pilots and flight engineers to hold RPM low and constant at cruise RPM, during descent with varying IAS. We do not have that technology in a Lockheed Hudson I. 


Hudson I type conversion training.

During real type conversion training, we would have a nominated training captain, or our flight commander, standing alongside us in the gangway to warn us if we imposed undersquare running, which is even harder to notice than overspeed, since it can occur at any RPM with either grade of fuel. The Calclassic 'technology demonstrator gauges' come to our rescue again! The same gauges which warn us of engine overspeed = overheat, else over torque, will also provide video and audio warning of undersquare running, replicating human supervision of type conversion training in real life.


GEAR as air BRAKE
 
Protecting the engines from overspeeding with only c/p screws prevents steep dives, unless the aeroplane in question has dive brakes, and flaps are not a variety of dive brake. They are far too flimsy and the Hudson I IAS = Vfe = 115 MIAS which will cause structural failure of the FLAPS is far too low.
 
The Hudson I is not an F4U Corsair, nor a DC7. It cannot use its mainwheel landing gear as a *dive* brake. The engines are no more flimsy than the Cyclones powering an L-14W (for Wright) Super Electra airliner serving a few miles way with British Airways or BOAC, but nor are they more durable because the livery changes to military. Those BA and BOAC pilots already have fifth generation c/s screws on their Super Electras.
 
If we have been patrolling with maybe 20 inches MAP applied and maybe 1500 RPM in consequence, (to sustain 135 MIAS in the current weather, at our current weight tonight), if we descend sustaining our patrol windmill drag = 135 MIAS, our RPM will not rise. We must not run the Wrighht Cyclone undersquare. In this example we can only reduce from 20 inches to just above 15 inches. If we have been employing tactical cruise power = 25 inches our RPM will have been in excess of 1900 RPM and we can only reduce to around 20 inches for the descent. If we allow our windmill drag = IAS to rise, our RPM will rise and we must use more MAP to remain oversquare. This just wastes fuel, and it requires us to descend sooner.
 
Although the Hudson I main GEAR cannot be used as *dive* brakes, we may need to use them as *air* brakes. If we apprehend that we may need to shed IAS urgently, or that we may need to increase negative VSI urgently, or both together to 'expedite descent', we will take great care to reduce to less than Vle = 155 MIAS, at Time of Descent, before descending from cruise, even if our cruise IAS was higher. This wastes fuel, but we then have the option to shed IAS, or increase VSI, or both together to maximise our descent gradient, by extending the GEAR.

The extra drag available can double VSI while descending at 135 MIAS. Since we are almost always patrolling at 135 MIAS in a Hudson I this option is usually available without any particular pre planning during 'realistic' Hudson I operations. We always achieve 135 MIAS before we reach our Initial Approach Fix, and we always hold at 135 MIAS, so the main GEAR is always available as a temporary air brake prior to commencing an approach (see later).
 
*If we use the GEAR as a low IAS air brake we must remember to retract it after such use*
 
However final cruise / patrol level is never above FL100 and rarely above FL65 in a Hudson I, so we never have a huge vertical increment to discard between patrol flight level and our allocated altitude in the holding pattern while we await clearance for our NDB or ZZ night / all weather approach. A tutorial concerning NDB and ZZ approaches is contained within the 2008 Propliner Tutorial. The means by which vintage era RDF = GPS en route wireless navigation by the Wireless Operator may be conducted within FS9 is also explained within the 2008 Propliner Tutorial. Use the supplied GPS pop up window only at ten minute intervals accordingly, and then assign a new heading on the comparison compass of the Sperry Blind Flying Unit.


A SPERRY BLIND FLYING UNIT (BFU) is not an AUTOPILOT.

The Hudson I has a primitive autopilot connected to the Sperry BFU, but the BFU is not the AP and the BFU would be present and needed even if the Hudson I had no AP. The simple AP in the Hudson I can hold current heading, (HDG hold), but it cannot capture a different demanded heading. It can hold current flight attitude (ATT hold), using a second Sperry gyroscope, but it has no connection to the altimeter, and has no altitude (ALT hold) mode. Each course change must be manually applied with the AP OFF. HDG hold and ATT hold can then be activated again. 

The HDG knob of the Sperry BFU is *not* an AP control. It is used to 'bug' our heading assigned by NAV to P1 on the upper barrel of the Sperry comparison compass, *whether or not the aeroplane also has an AP*, whether or not an AP is going to be used in an aeroplane that has one. 

The Sperry twin barrel comparison compass within the Sperry BFU is then used to compare current heading deviation from assigned heading, (hence its name). Just before course changes we bug 'next heading' on the upper barrel of our Sperry comparison compass, (using the assigned HDG knob to control the HDG bug), before turning the aeroplane manually until current heading on the lower barrel matches next assigned heading on the upper barrel. 

Then we can choose to turn the primitive Hudson I AP ON and it will hold both *current* heading and *current* aircraft attitude (ATT). *It has no ALT hold mode*. We can however demand a different ATT by tilting the Sperry ATT gyroscope with the PITCH knob that tilts the Sperry ATT gyroscope. A Sperry BFU does not contain an altimeter. It contains only Sperry gyroscopes, from which an AP (if fitted) can also access two axis (deviation) data.


HOLDING PHASE.

In the Hudson I we hold at the same IAS as we patrol. If we allow IAS to rise in descent, or our mission was a tactical bombing mission, or we were battling a headwind with max cruise power, we must achieve stack altitude before the stack because we need to level out (VSI = 0) to achieve our target IAS for holding. We are still hamstrung by c/p screws. We must not run undersquare. As we level out windmill drag decays, RPM decays, and we can 'follow down' with MAP. Trickling MAP down to 'square' is a key component of c/p operation with Cyclone engines, but hamstrung by c/p screws our ability to reduce IAS is limited and slow. We must always plan ahead.

****************************
Holding phase:

FLAP  = UP
IAS   = 135 MIAS
MAP   = as required
Plan  = 300 PPH

HOLD until < 15,650lbs = MLW
****************************

We must not commence an approach until our weight is down to 15,650lbs which is our maximum safe landing weight. Maritime patrol aircraft rarely find a target to attack and unlike bombers they normally land with all weapons still aboard. That being so a Hudson I is only safe to land once half of the maximum = normal fuel has been consumed or dumped. Thus we have an easy way to determine whether we are down to MLW. Take off with weight exceeding MLW was contingent on the fuel dump vales being operational and all de icing systems being operational to prevent weight increase. 

We plan holding at the same fuel burn as patrolling and we hold at patrol IAS. Even if we have no delay to our approach we must achieve 135 MIAS before we reach the Initial Approach Fix (IAF), and so it follows that we need to research where it is and include it in our flight plan!

With c/p screws that becomes more important because we cannot reduce RPM with a lever, and we must not run undersquare, so we cannot reduce IAS in level flight, or constrain IAS in descent, by substantial retardation of the throttle levers either.


APPROACH PHASE.
 
A detailed worked example, using an NDB(A) approach to RAF Aldergrove is provided as a second mini tutorial elsewhere within this release and should be studied only after reading and understanding this mini tutorial. 
 
Critically weak flaps in vintage era aeroplanes:
 
In streamlined monoplanes with c/p screws it is only possible to target the combination of high MAP and low IAS, that will avoid undersquare running of the engines, when we select FINE SCREW PITCH, by deploying substantial FLAP to allow high HIGH MAP to be used in conjunction with LOW IAS. Since we wish IAS to be low (not above 110 MIAS) when we select FINE SCREW PITCH, we wish to select fine screw pitch in level flight, not while descending.
 
The modern concept of 'stable approaches' in which landing flap is deployed, and profile drag is reduced to Vref, before descent from approach Minimum Descent Altitude (MDA) was considered dangerous in the relevant era of aviation history. Vintage era aeroplanes were designed to comply with vintage era procedures. They often had critically weak FLAPS, because it was assumed that FLAP 1 would be deployed in level flight within a visual circuit pattern, preceded by GEAR deployment to achieve Vfe1, and then further reduction of profile drag = IAS, before further deployment of more FLAP. 
 
There was a Hudson I approach procedure compatible with a straight in IFR approach to a 'low' MDA, but it was rarely used and the procedures are very demanding to simulate. That complex procedure *is* explained within the final section of this mini tutorial and is cited at the bottom of the on screen handling notes. However we should avoid straight in approaches and their Vfe limit complications whenever the weather permits.
 
In a Hudson I we have the intention of flying the holding pattern and the subsequent instrument approach FLAP UP and GEAR UP. During any such descent we restrain our profile drag below Vle = 155 MIAS allowing us to deploy our MAIN GEAR as an air brake if we need to do so to expedite descent.
 
However that procedure is utterly incompatible with deployment of FLAP (Vfe = 115 MIAS). This vintage era technique is utterly incompatible with a classic era precision straight in approach down a continuous glideslope; *instrument or visual*. We would never be able to reduce to a profile drag (IAS) compatible with any flap deployment at all!
 
*************************
Approach then Circuit:
 
Before descent to MDA:
 
IAS  = 135 MIAS
FLAP = UP
 
On Descending to MDA:
 
MAP = trickle barely oversquare
IAS < 155 MIAS
 
When maintaining MDA:
 
IAS = reduce to 135 MIAS
MAP = oversquare
Look for landing runway
 
Downwind in Visual circuit:
 
GEAR     = DOWN
WHEN IAS < 115 MIAS 
FLAP     = STAGE 2
IAS      = 110 MIAS
PITCH    = FINE <<<<<<<<<<<<<
 
Final in visual circuit:
 
To achieve Vref = 85 MIAS (at 14,000lbs)
 
FLAP = STAGE 3
MAP  = INCREASE if necessary
 
Cross airfield boundary @ 85 MIAS 
 
MAP = UNDERSQUARE ALLOWED
FLARE and LAND
BRAKES as required
 
Clear of runway:
 
FLAP  = UP
*********************** 
 

Prepare to 'rev up hard'.


The default Hudson I approach always enters a visual pattern and reduction to Vfe = 115 MIAS, and deployment of FLAP, is always preceded by deployment of GEAR *in level flight*. This is all about avoiding use of the critically weak flaps for as long as possible, and avoiding 'revving up' so hard that RPM/100 exceeds MAP in inches. We must allow time to bring our profile drag back to 110 MIAS, and significantly increase our MAP, before we select FINE SCREW PITCH.
 
That action always requires substantial MAP prior to 'revving up hard'. We *calibrate* how much MAP is sufficient to preclude undersquare running upon FINE PITCH selection by sustaining 110 MIAS in level flight with GEAR and FLAP 2 deployed. Only MAP high enough to sustain that configuration is also enough MAP to avoid undersquare running when we move the prop pitch levers to 'rev up hard' in case we need to Go Around. Randomly more MAP could instead cause the engines to overspeed and / or overtorque when we 'rev up hard'. Having no RPM levers to control or limit engine RPM makes life difficult! Our operation of the aeroplane is more restricted and must be more precise. 

When we deploy FLAP 2 downwind in the circuit, our co-efficient of profile drag (Cdp) rises sharply. That is the intention and we must not let it surprise us. The extra Cdp causes us to need a substantial increase in MAP to sustain target IAS = 110 MIAS. We do this explicitly to ensure that MAP is high and IAS is low as the necessary precursor to selecting FINE SCREW PITCH.
 
****************************
Downwind in Visual circuit:
 
GEAR     = DOWN
WHEN IAS < 115 MIAS 
FLAP     = STAGE 2
IAS      = 110 MIAS

PITCH    = FINE <<<<<<<<<<<<<
*****************************
 
There is no specific MAP which will ensure MAP > RPM/100 because RPM will vary with the weather (altitude density) in this particular visual circuit. We 'calibrate' the altitude density by always establishing the target IAS and 'matching' it with the necessary matched MAP for the current weather. 

After our squadron converts to the Hudson II or Hudson III we will no longer need to impose this inconvenient procedure. After we can control engine RPM with a lever we will delay deployment of FLAP 2 until after we begin the final descent to land and we will turn base with only FLAP 1 already deployed. With c/p screws in a Hudson I we must reduce IAS earlier, then invoke a high MAP, so that we can 'rev up hard' without causing undersquare running of Cyclone engines. 

Make sure you begin that sequence in good time so that you do not need to extend a ridiculous distance downwind in order to meet those downwind operating targets before you turn base leg. If necessary begin those actions just before joining the pattern. We must make sure we do not join patterns still descending. It will take too long to achieve 110 MIAS with FLAP 2 deployed in order to make the prop pitch change.
 
The LAST thing we do just before we turn base leg and commence final decent to the landing runway is SELECT FINE PITCH.
 
Because;
 
1) IAS is 110 MIAS restraining RPM, and 
 
2) MAP applied is high enough to sustain 110 MIAS in level flight with GEAR and FLAP 2 
 
when we select FINE SCREW PITCH, and our engines 'rev up hard', our engines will never suddenly be pitched into undersquare running, at any weight, in any weather. RPM/100 will still be less than our MAP in inches, even in FINE PITCH. 
 

Final approach:
 
Thereafter we reduce IAS to Vref = 85 MIAS, by careful timing of FLAP 3, because we cannot simply reduce throttle, because we must keep MAP above RPM/100 even in fine pitch. Only if we misjudge when to deploy FLAP 3, and we deploy it too soon, we may need to increase MAP to sustain the visual glideslope after achieving Vref = 85 MIAS, too soon. 
 
If we are under confident of our ability to judge timing of FLAP 3 versus the headwind today / tonight we may elect to deploy FLAP 3 'too soon' as a deliberate act, knowing that we will need more MAP to sustain the necessary VSI as a result. We always use only elevator (trim) to control IAS. We always use only throttle to control VSI. Many flight simulation enthusists lose control of their final approaches because they fail to obey those two simple rules.
 
Because undersquare running can be invoked at any RPM, we are much less likely to notice that pilot error. The same Calclassic c/p gauges which represent our training captain, or flight commander, standing in the gangway providing supervision during Hudson I type conversion, will warn us if we run undersquare. Avoiding running undersquare on approach is more difficult than avoiding overspeeding or over torquing the engines during obstacle clearance.
 
Just as we close the throttles as we flare for landing we will hear an *allowable* undersquare warning. Do *not* confuse that warning with a stall horn. There should be no stall horn in your chosen sound.cfg to avoid that confusion. The engines will quickly spool down into oversquare ground running. We do need to be able to differentiate an engines undersquare warning from a gear up warning horn!
 
The 2008 Propliner Tutorial explains how to calculate Vref as approach weight varies, but since approach weight cannot be more than 15,650lbs in a Hudson I, Vref won't vary much from 85 MIAS, which is above Vmc for any flap state while weight < MLW.
 
 
LANDING RUNWAY is NOT the INSTRUMENT RUNWAY.
 
During the 1939 - 1940 time frame the runway we intend to land on will rarely be the instrument runway we approach. We will instead fly a visual circuit pattern to land on the into wind landing runway, having earlier approached the only instrument runway, treating MDA as the circuit pattern altitude of the landing runway, which in Coastal Command is always 1000 feet above the elevation of the landing runway, always disclosed by our flight planning tool, (encoded BGL data may vary from real world IAP data). 
 
During the Hudson I era, on most nights, or in most UK / Canadian east coast weather by day, we will be approaching an instrument runway that is not our landing runway. Remember the landing runway will often be on a different nearby airfield, (a satellite airfield). 
 
Normally we descend down the instrument approach, towards the only instrument runway, initially using our crossing needle pilot goniometer for course guidance, to locate the instrument runway visually, descending only to self assigned MDA = visual circuit pattern altitude for the (same or nearby) airfield. Then maintaining visual pattern altitude, 1000 feet above the *relevant* airfield, we must locate and identify our landing runway, if necessary on a different satellite airfield, which is our real destination, and enter the visual pattern for the landing runway at our destination airfield.
 
The search for the only instrument runway, and then the search for the often different landing runway, (landing airfield), is conducted above the relevant visual pattern altitude, and never below the circle to land MDA of the only instrument runway. We conduct that search exactly like a maritime patrol search; clean and at 135 MIAS after we attain level flight at self imposed MDA. 
 
*With c/p screws we cannot approach a visual pattern at random IAS, with random VSI, with random MAP, in a random variable geometry state*. 
 
Having the intention to fly a visual pattern to the landing runway at this master airfield, or a nearby satellite airfield, we approach them from the Final Approach Fix (FAF) of the master airfield descending to self imposed MDA. Then we fly the visual transition to the visual pattern of the landing runway, on the master or satellite airfield, at the relevant pattern altitude. We only vary our VG status as we join, or immediately after we join the correct visual pattern. The *last* thing we do before we turn base leg is SELECT FINE SCREW PITCH, and only after complying with all of our downwind operating targets.
 

VINTAGE ERA WIRELESS NAVIGATION.
 
Remember this is the era of aviation history when only qualified navigators are allowed to look at unobscured arc radio compasses showing all 360 degrees of arc, and only qualified wireless operators are allowed to manipulate D/F loops. Pilots must use only obscured arc goniometers and fixed forward facing D/F loops.  Sometimes the master airfield will have more than one NDB approach, and more than one Final Approach Fix, and we can choose which NDB we tune our obscured arc crossing needle pilot goniometer to receive as we seek the instrument runway of our choice. 
 
Within FS9 our virtual Wireless Operator will leave his manual D/F loop locked forward and our obscured arc crossing needle pilot goniometer will always be active provided we tune a Non Directional Beacon for the manual, but locked, loop to D/F. The avionics tuner is incorrectly labelled ADF. The loop is fixed, not automated. In real life WO tuned the avionics from his seat in the cabin behind the cockpit, and eventually fixed the loop facing forward, so that the pilot could use his short range MFDF crossing needle obscured arc goniometer during the holding and approach phases, but in FS9 we have the necessary avionics tuners below the Sperry BFU.
 
Audio should always be ON during WW2 approaches. We have no MKR lights. We must listen for the outer, middle and inner MKR Morse tones, because they are the closest thing we have to DME in a Hudson I, but not all instrument runways have Marker fans generating MKR tones. 
 

RAF VISUAL PATTERN.
 
So in most cases we select FINE SCREW PITCH just before we turn base in the visual pattern, having flown a downwind leg 1.5 miles abeam the landing runway, 1000 feet above the landing runway, having joined the pattern in level flight at 135 MIAS and having reduced to 110 MIAS before we turn base. 
 
As we turn base we cannot just close the throttles to achieve Vref = 85 MIAS as we descend, and we cannot set RPM. *We must run Wright Cyclones oversquare*. We fly an unstable, unrushed approach, during which we cause IAS to reduce from 110 MIAS to Vref = 85 MIAS with additional FLAP (STAGE 3 = 45 degrees). When this approach doctrine and sequencing is followed compliantly we end up with MAP well above RPM/100 even in fine pitch, but if we begin descent to land in the wrong variable geometry state, or at the wrong IAS, or from a random location, it is very difficult to get things back under control and undersquare running and / or a rushed approach results.
 
Now of course in MSFS that has no negative consequence at all, which is good, because we can train and get this wrong, time and time again, without damaging real engines, until we learn how to get it right. Once the sequence is learned and the approach is unrushed, starting from a stable state, at the compliant IAS, in the compliant VG state, from the compliant location, it is not difficult to repeat, repeat, repeat, but meanwhile we must practice, practice, practice, and we will make various mistakes during practice, but that is what flight simulators are for.
 
With the new Calclassic C/P gauges we will get warnings from our training captain when we make mistakes, so that we can correct them, before the engines fail!
 

GO AROUNDS - Two position C/P SCREWS IMPOSE TWO CASES.
 
Coarse Pitch at MDA.
 
During any instrument approach if we have arrived at MDA, and we still have no visual contact with the instrument runway at our missed approach time, we must enter the missed approach procedure. We must then think very carefully what our MAP limit is with the AVGAS in use. Until we have positively identified our landing runway, and until we start descent from our MDA to that landing runway, we are always in COARSE SCREW PITCH and we can GO AROUND at 110 MIAS even with full TOGA MAP applied, but COARSE PITCH prevents the engines from developing TOGA power and TOGA thrust. Since in that circumstance we are going around from MDA, far above the runway, that is acceptable.
 

Fine Pitch below MDA.
 
Since we never exceed 110 MIAS during or after selection of FINE SCREW PITCH and we have been reducing to Vref = 85 MIAS, before we need to Go Around, we can use 43.5 inches MAP with weapon grade fuel, but just as for Take Off, when we Go Around, in FINE PITCH with 87 Octane fuel we must restrict MAP to RATED MAP = 34.5 inches. 
 
We can increase windmill drag to a maximum of Vx = 110 MIAS, and since we will be progressively retracting GEAR, then FLAP 3, then FLAP 2 as we climb away, we must exercise caution before each retraction, to ensure that IAS is less than 110 MIAS at time of retraction, so that we do not exceed 110 MIAS after each progressive retraction.  We do NOT select coarse pitch. We need high RPM to generate high power and high thrust during a Go Around from below MDA. We are entering another, but unexpected, obstacle clearance phase (studied earlier). We have a cross above (at) ATC restriction at the holding pattern and we are within an obstacle clearance phase until we achieve that ATC restriction.
 

ASYMMETRIC APPROACHES.
 
During an asymmetric final approach the motored screw must be in FINE PITCH while the windmilling screw must be in COARSE PITCH. By definition two position screws have no feathering capability.
 
In a Hudson I Vmc is low and we concentrate on not overspeeding or overheating the surviving engine by using only compliant RPM and compliant MAP. Even with FLAP 3 Vmc is always below Vref. A steeper than normal final approach from Minimum Descent Altitude should be flown.  Remember controlled asymmetric flight in FS9 requires the auto co-ordination cheat mode to be OFF in the realism screen. In the event of an emergency return, following an engine failure after take off, fuel must be dumped to achieve MLW (use the fuel menu). 
 
When flying this Hudson I with 87 Octane fuel we must not exceed 34.5 inches = RATED MAP if we intend to allow 110 MIAS, but once we reduce below 110 MIAS on final approach we will employ up to 37.5 inches = 87 Octane TOGA MAP while monitoring the motoring engine RPM to prevent > 2300 RPM.
 
A Go Around from an asymmetric approach at MLW is possible from low heights, but requires early and simultaneous retraction of GEAR and FLAP 3. With 87 Octane fuel available climb rate will be marginal at MLW with FLAP 2 and we proceed to FLAP 1 as soon as it seems safe to do so. We use TOGA = 37.5 inches, (not RATED = 34.5 inches), and we reduce Vx to 100 MIAS so that 37.5 inches will not overspeed the only motoring engine. We have only five minutes in 87 Octane TOGA MAP = 37.5 inches to complete the asymmetric circle to land, always with our windmill drag pegged at 100 MIAS, until we reduce to Vref on late final approach.
 
During an asymmetric approach, only if runway length is sufficient, it is permissible to use only FLAP 2 for landing with Vref = 95 MIAS. 
 

BACKGROUND INFORMATION.
 
Some other historical issues regarding the evolution of c/p technology not needed to use the Calclassic 'c/p gauges', and the Hudson I c/p flight dynamics within FS9, are addressed within my related forum post at;
 
http://calclassic.proboards.com/index.cgi?board=general&action=display&thread=3662&page=2
 
 
 
STRAIGHT IN APPROCHES - ARE VERY DEMANDING.
 
The problems explained below apply to any straight in approach; instrument or visual.
 
Only attempt this procedure after mastering NDB(A) approaches with transition to a visual circuit and only attempt straight in instrument approaches after mastering the NDB(A) concepts explained in the second mini tutorial within this release. 
 

Before descent to MDA:
 
In order to conduct a straight in approach to 'low' MDA in a Hudson I we must reduce our profile drag below Vfe = 115 MIAS *before we commence descent to MDA*, since we may not be able to maintain MDA for long enough to achieve Vfe, before we must descend again, to achieve the straight in approach, having descended to MDA at an IAS far in excess of Vfe = 115 MIAS.
 
If prolonged flight maintaining MDA is implied by the published procedure, it is then possible to delay FLAP deployment to MDA, else we must target 110 MIAS before we descend from minimum safe holding altitude, in order that we can deploy enough FLAP to sustain less than Vfe = 115 MIAS through out descent *while running our engines with sufficiently high MAP to remain oversquare*
 
At some point we hope to acquire visual contact with the lights of the instrument = landing runway. When we have a tally we wish to switch to FINE pitch, but that imposes all sorts of problems which we must take into account during our prior descent in cloud, (or low visibility). 
If we select FINE pitch at random IAS, or at random MAP, we will 'rev up hard' and RPM/100 with exceed MAP in inches causing undersquare running. With no RPM levers, to avoid that pilot error, we must fly the approach at very precise IAS and with an applied MAP which is matched to our current weight and the current weather, so that when we 'rev up hard' constant MAP is still above RPM/100.
 
Consequently while in level flight, and before we descend below the minimum safe holding altitude for this location, to approach Minimum Descent Altitude for this approach, we must reduce our profile drag below the structural failure limit of our FLAPS, and then we must deploy FLAP 1 while restraining our windmill drag to 110 MIAS, just as we did during obstacle clearance.
 
*********************************
Approach or Circuit:
 
Before descent to MDA:
 
IAS  = 135 MIAS
GEAR   may be used as brake
IAS  = 110 MIAS
FLAP = STAGE 1
IAS  = 110 MIAS
MAP  = as required
*********************************
 
The MAP required varies with weight and weather, but it is also the MAP we need today / tonight to prevent the engines revving up hard' into undersquare running when we later select FINE pitch. we are again 'measuring' the weather  (altitude denisty) around us during this approach which will vary RPM from constant MAP.  
 

The descent to Minimum Descent Altitude (MDA):
 
When the published approach procedure, which we obtained from the internet, calls for us to commence descent from the minimum safe holding altitude we deploy FLAP 2, *we do not alter MAP*, and we always trim our Hudson I to descend in cloud (or not) at minus 600 VSI. By deploying FLAP 2 we reduce the increase in IAS, and therefore RPM, that would occur if we descended at constant prior MAP with only FLAP 1 deployed. Our IAS will not remain constant, but it is restrained. Actually our MAP will not remain constant either since all approaches are above the 600 foot critical altitude of our superchargers, but rate of increase of MAP will also be 'restrained' as we descend at only minus 600 VSI during all approach procedures.
 
Of course we never descend below our MDA, and while we descend in cloud. or low visibility, until MDA, and after we reach and maintain MDA, we continue our attempt to locate the lights of the instrument runway.
 
**************************
On Descending to MDA:
 
FLAP  = STAGE 2
MAP   = do NOT alter 
VSI   = minus 600
UNTIL = MDA
Look for runway lights
 
Only while maintaining MDA:
 
IAS = 110 MIAS
MAP = as required
Look for runway lights
**************************
 

Missed Approach at MDA:
 
If we don't see the lights during descent to MDA at minus 600 VSI, we maintain MDA, and we must then increase MAP just enough to maintain 110 MIAS with FLAP 2. If we never see the lights, and we reach our missed approach time, we will enter the published missed approach procedure. We never revoked COARSE PITCH so we are free to apply up to TOGA MAP for the fuel in use as we Go Around into the missed approach procedure at 110 MIAS. We can reduce FLAP to FLAP 1 when ready. Note that by staying in coarse pitch we can use TOGA = 37.5 inches MAP to Go Around with 87 Octane, if there is an obstacle ahead.
 
This is the vintage era of aviation history. There are as yet no electronic glideslopes at Coastal Command airfields. Every type of approach invokes descent to maintain a Minimum Descent Altitude (MDA) which we maintain, in level flight, until we reach the location where it is appropriate to commence our final descent to land on the landing runway. 
 

The descent from MDA:
 
Usually we will see the lights of the instrument runway in time to make the necessary descent to land from a straight in approach, but since we are still in COARSE PITCH we have more to cope with than a pilot able to set final approach RPM with RPM levers long before.
 
***************************
ONLY IF runway lights acquired:
On descending:
 
GEAR  = DOWN
PITCH = FINE <<<<<<<<<<<<<
 
To achieve Vref = 85 MIAS (at 14,000lbs)
 
FLAP = STAGE 3
MAP  = INCREASE if necessary
 
Cross airfield boundary @ 85 MIAS 
*********************************
 
Before we select FULL FINE PITCH we *decide* whether we have time to complete a safe and unrushed straight in approach. If we decide to land straight in the first thing we must do is extend the GEAR and check for two greens. Only when we have two greens do we select FINE PITCH. 
 
Because;
 
1) IAS is only 110 MIAS, restraining RPM, and 
 
2) MAP applied is never *more* than MAP required for 110 MIAS in level flight at MDA. and
 
3) MAP applied is never *less* than MAP required for 110 MIAS descending at minus 600 VSI with FLAP 2
 
when we select FINE SCREW PITCH, and our engines 'rev up hard', our engines will never be pitched into undersquare running, at any weight, *or* into overspeed, in any weather, and RPM/100 will still be less than our MAP in inches. 
 
Note that the straight in approach (of any kind) may require us to select FINE SCREW PITCH while descending and that invokes the possibility of engine overspeed as well as engine undersquare that was the only problem in level flight during a visual circuit. To fly a straight in approach that will not damage the engines we must target VG status and IAS and VSI with precision and that is much more difficult than the default visual circuit procedure described earlier.
 

Final Straight In Approach:
 
Thereafter we reduce IAS to Vref = 85 MIAS, by careful timing of FLAP 3, because we cannot simply reduce throttle, because we must keep MAP above RPM/100 even in fine pitch. Only if we misjudge when to deploy FLAP 3, and we deploy it too soon, we may need to increase MAP to sustain the visual glideslope after achieving Vref = 85 MIAS, too soon. 
 
If we are under confident of our ability to judge timing of FLAP 3 versus the headwind today / tonight we may elect to deploy FLAP 3 'too soon' as a deliberate act, knowing that we will need more MAP to sustain the necessary VSI as a result. We always use only elevator (trim) to control IAS. We always use only throttle to control VSI.
 
Because undersquare running can be invoked at any RPM, we are much less likely to notice that pilot error. The same Calclassic c/p gauges which represent our training captain, or flight commander, standing in the gangway providing supervision during Hudson I type conversion, will warn us if we run undersquare. Avoiding running undersquare on approach is more difficult than avoiding overspeeding or over torquing the engines during obstacle clearance.
 
So to recap here is the whole of the straight in approach handling note and variable geometry sequencing with all sub phases. 
 
****************************
Approach Phase:
 
Before descending:
 
FLAP = STAGE 1
IAS  = 110 MIAS
MAP  = as required
 
On Descending to MDA:
 
FLAP  = STAGE 2
MAP   = do NOT alter 
VSI   = minus 600
UNTIL = MDA
Look for runway lights
 
Only while maintaining MDA:
 
IAS = 110 MIAS
MAP = as required
Look for runway lights
 
ONLY IF runway lights acquired:
On descending:
 
GEAR  = DOWN
PITCH = FINE <<<<<<<<<<<<<
 
To achieve Vref = 85 MIAS @ 14,000lbs
 
FLAP = STAGE 3
MAP  = INCREASE if necessary
 
Cross airfield boundary @ 85 MIAS 
 
MAP = UNDERSQUARE ALLOWED
FLARE and LAND
BRAKES as required
 
Clear of runway:
 
FLAP  = UP
***********************
 
As soon as we are inside the boundary of our destination airfield we are allowed to run the engines undersquare briefly as we flare for landing. An 'allowable' warning will be generated briefly, but the engines will soon spool down into oversquare ground running.
 
Make sure you can associate those abbreviated, evaluated, and sequenced operating targets with the concepts explained above. The 2008 Propliner Tutorial explains how to calculate Vref as approach weight varies, but since approach weight cannot be more than 15,650lbs in a Hudson I, Vref won't vary much from 85 MIAS, which is above Vmc for any flap state while weight < MLW.
 
FSAviator - March 2011.
