FS2002 (only) flight model notes for the Boeing 247D
These notes explain how to use FS2002 to simulate vintage aspects of the B247D with which you may not be familiar. When the techniques below are combined with the in flight reference notes all aspects of the performance envelope of the Boeing 247D can be simulated to within 3%.
The most unusual aspect of the Boeing 247 was the decision to provide low speed lift via a huge wing without flaps. The 247D has very low profile drag compared to other aircraft of the day and in reality the more Boeing reduced the drag by introducing new concepts like NACA cowls the more it needed those missing flaps. It is essential to reduce speed early to allow the deliberately low aspect ratio wing to produce induced drag. If you do not it will float down the approach and then on down the runway. If you are not used to flying flapless approaches you may find speed control difficult. The problem is however accurately portrayed.
This aircraft was not designed to fly a three degree glidepath under power. It is from a previous era of different techniques. You must reduce to 80 KIAS before beginning final descent much of which will be flown with throttles in flight idle. Reducing to 80 KIAS may take some time and you should plan your circuit or IFR approach accordingly. Plan your turn onto final so that it is flown at not less than 90 KIAS with time to reduce to 80 KIAS before intercepting the glidepath. Once established on the glidepath speeds down to 70 KIAS are safe, but with no flaps to modify the wing camber, (with an accurate panel.cfg), you will lose sight of your touchdown point as AoA increases. If you are not used to flying flapless approaches you will make the mistake of pushing the nose down. If you have judged your approach correctly your touchdown point will re-appear as you sink below the glidepath in a nose up attitude with some distance to run. Then, and only then, you can increase power and IAS to keep the touchdown point in sight. If you lose sight of the far end of the runway you are too slow or too high, or both, to complete the approach safely. Resist any temptation to sideslip an aircraft as big as the Boeing 247. It will not work well in FS2002 anyway.
Failure to control airspeed prior to final descent is the greatest problem you will face when learning to fly the Boeing 247. Give yourself lots of room and lots of time when setting up the approach. Those who flew it in real life had rarely flown an aircraft with flaps and were used to using induced drag from low aspect ratio wings to control descent rate.
Do not attempt to three point an airliner. The stalling angle is much greater than the tail down angle and you will suffer a tail strike. I have been very generous with the strength of the tailwheel, but taildragging airliners must be 'wheeled on'. Aim to put the mainwheels down at just under 70 KIAS, remove any remaining power and when below stalling speed pull the yoke full aft and apply the brakes.
Note that full emergency power is not normally used for take off in the Wasp. The 247D can easily take off from any runway it can realistically land on. The power surplus is so great, and the acceleration after take off so good, that the usual Wasp transition through METO power (33/2100) is normally omitted, power being reduced immediately from normal take off (34/2100) to continuous climb (31/2100). Setting 2100 for take off gives you one less variable to change as you climb away. Go around is however performed at 35.5/2200 (full throttle / fully fine).
The Boeing 247D originally had Hamilton Standard controllable pitch screws (c/p screws). These had multiple pitch settings but did not maintain constant engine or prop speed especially after they hit the end pitch stop. The early c/p props cannot be simulated with accuracy in FS2002, they have to be 'fudged'. These FDE take the process about as far as it can go. the power delivery is accurate, but rpm may vary from real life.
I have not attempted to replicate the S1H1-G gear box as this would have posed problems for simulating vintage c/p props. Despite the lack of gear box simulation the FDE are designed to produce the correct sound.cfg driver cues.
The FDE are written so that any WYSIWYG rpm gauge will read the engine rpm correctly. Use of WYSIWYG (i.e. default or unscaled) gauges is mandatory with these FDE and the supplied handling notes. Beware many third party gauges contain scalars or bitmap repainting errors. The handling notes use engine (not airscrew) rpm as the reference. It is not possible to obtain an accurate flight simulation with inaccurate (power management) gauges.
The FS2002 manual mixture control is fully functional in these FDE, (provided you turn auto mixture off in FS2002). As in real life by careful adjustment of the mixture you may be able to beat the book figures for speed v range. These FDE were however written to deliver certification performance with auto mixture enabled in FS2002.
The in flight check lists and handling notes are 247D_ref. They are called using the F10 key in flight and selecting the 'reference' tab. They should be followed stage by stage in flight. They are sub set of the content of the real aircraft certification and engine manuals with some liberties taken to accommodate the simulation of c/p props in FS2002.
The Sperry AP was the earliest true AP, but it did not have the precision of a modern AP. The tendency to overshoot at low IAS with some wallowing is deliberate. It was used to relieve the tedium and potential loss of concentration arising from en route flying in cloud. It was not a good blind landing aid. They took many more years to develop and in the hands of the Royal Air Force Blind Flying Unit the Boeing 247 played a significant part in that process between 1942 and 1944. Using the pre war Sperry below about 90 KIAS or above 155 KIAS in the Boeing 247 is unwise.
Although the emphasis in these FDE is on vintage realism they permit autolanding from an APR coupled approach using a modern AP provided you use the throttle to maintain between 75 and 80 KIAS throughout the final descent, and provided of course that the ILS is correctly placed in the relevant bgl. Apart from that you only have to close the throttle and apply the brakes.
Unfortunately flapless taildraggers do not work well with the FS2002 AI routines.
By the standards of 1935 the 247D was a difficult aircraft, though once you learn how to fly the flapless approach you will soon appreciate its combination of short field performance, ability to climb over obstacles and stability on the approach.
