SOH P-61 project

[warchild]

Changes include modifications to the mach tuck tables, and we now have compressability. You go too fast over 525 mph and you aint got no control no more >. I'm loving it.. Great work Tom ..

[warchild]

http://www.flyingmandocumentary.com/

the story of Johnny Myers, Northrop test pilot and one of the main people behind making the P-61 fly ( as well as a whole buncha other ones )..

[warchild]

thanks Robert..

[Whitehawk]

Sweet animations back up?

[warchild]

Most. Flaps arent working but i know they will be .. Robert was focusing on the gear tonight.
I'm beginning to put everything in the project tracker and using this space for commentary and public interest stuff such as the link to the upcoming documentary of Johnny Myers life. Let me know if you have any problems geting into the project tracker or using it and i'll do what i can to get it fixed..

[modelr]

Glad you got it working, Pam.

Don't want to spend tight cash on just a bad connection, lol.

Watching patiently.

[Ferry_vO]

"Caught in the Black Widow's web!"

http://3.bp.blogspot.com/_EDThwIXZ6B...0-h/P-61-1.jpg

[warchild]

::chuckles:; Thats cute.. I'm sorry i dont speak that language but the meaning is pretty evident none the less .. Thanks for posting ..

[warchild]

could you P-61 officienado's please watch the below film. it shows a mossie losing power on one engine during a climbm and crashing. its not easy to watch, but i need to know if you think the P-61 would behave in the same manner.. Lke i said, its a really hard video to watch. but i appreciate any input i can get on it..
Thanks..

http://www.youtube.com/watch?v=Ag5ut3tP3ZM

[Whitehawk]

Well from reading the accident report it appears the Mosquito suffered a temporary powder loss from the left engine at the apex of the final wingover (to the right). With the right engine at full power and reduced airspeed the aircraft yawed left and stalled, entering a spin. After that power appeared to be restored but recovery was no longer possible due to the height at which control was regained..

In terms of the Widow, in a similar situation i.e. low airspeed banked approx. 90 degrees to the right, a sudden failure of the left engine with the right delivering high power would of course create a yawing force to the left. However, due to the very different designs, and not knowing the exact speed the accident flight was at (referencing VMCA) when power was lost it is impossible to tell if a Widow would react the same to that yaw. It is worth noting that the Mosquito does have a rather high VMCA due to the small rudder surface outside of the propeller slipstream, while the Widow has significantly more rudder placed in the propeller slipstream.

In summery I would say that in the same circumstances (low speed, 90 degree bank, higher engine failing) the Black Widow would definately yaw towards the dead engine if uncorrected, and the pilots ability to maintain control would be directly tied to airspeed at engine failure and pilot reaction time. If uncorrected the yaw would produce roll towards the dead engine (secondary effect of yaw being roll in the direction of yaw), which would produce yet more yaw (secondary effect of roll is yaw in the direction of roll) leading to spin entry depending on the aircraft's susceptability to spin entry.

This is why red line (VMCA) in a twin is so important, if close to VMCA it is imperative to maintain control, even if that means reducing power on the live because the alternative is yaw-skid-roll-spin..

[roger-wilco-66]

could you P-61 officienado's please watch the below film. it shows a mossie losing power on one engine during a climbm and crashing. its not easy to watch, but i need to know if you think the P-61 would behave in the same manner [...]

Just curious, did you try to refly this situation in the project P-61, and if yes, how did it behave?

Cheers,
Mark

[warchild]

yup.. I reflew it, and made adjustments accordingly to bring the widow into a state where she would duplicate the crash. unfortunattely, with her high lift wing design, i was never able to duplicate the crash. what i got however is telling..

in a standard stall at low speed with an engine cut, the plne shows no appreciable stall characteristics or spin characteristics. it has the stall characteristics of a butterfly, which pretty much agrees with the manual and training film.
in a low speed pass with full power to one engine and the other engine cut, the plane will slowly rol towards the cut engine and begin a banking turn during which her nose drops about 80 degrees through the 180 degree arc.

in both cases, control can be reacquired by countering the roll with the spoilers, adjusting for level flight and re-trimming the rudder. once the dead engine is back online, re-trim and aresume normal flight.

i must have run fifteen to twenty tests. Each time i varied either yaw, roll on yaw or rudder efficiency, and each time, it reacted the same, even when the rudder efficiency was lowered to 35%. Now, fliger and i have been doing our best to make this plane as real as we can possibly make it, and we may be succeeding, but with as little documentation as there is this one area continues to raise a question in my head. What little evidence we have is circumstantial at best. for example, we know that during his demonstration flights in the Pacific, Johnny Myers would find a flight of F4F's or F6f's, cut an engine, and proceed to fly aerobatics around them. That tells me that its single engine handling wasnt that much different that its twin engine handling: probably due in part to the twin tail some how.. but it doesnt give us anough data to extrapolate a curve. Other data shows that most crashes that werent combat oriented in the p-61 were caused either by excessive speed, or raising the flaps too soon. of those two, raising the flaps too soon was the biggest contributor.
Still, ( and i hate to say this ) this is the FSX world, where "real" is an ideal we each have between our ears, and it doesnt always coincide with the actual plane.. I'm being extremely cautious on this one aspect because it is the accumulation of a great many other things, and i've already re-engineered a great deal of the FM, so that the performance and behaviour we had achieved in all the other areas wasnt changed, but this one area began to have an effect. No other plane i've ever flown has ever had the real POH state that the plane had no stall characteristics, like thus one does, and Its difficult for me to accept that. Every plane can fall down. If this one doesnt, its the first one ive ever heard of..
The closest relative we have for data, is the P-38, and it uses a completely different wing plan, but with its twin boom design, it might give us enough of a general idea to work with.. Thats still kind of a big "if" though.

[SADT]

Pam,

For a plane with no stall characteristics, how does she spin?

BTW - What time is it in Bend, Oregon right now? 10:00 PM here in NZ!

[warchild]

;;chuckles;; its 3:45am.
well, the book can tell me it doesnt spin all it wanrs, but the laws of physics contradicts that.. However, i can understand it if the spin characteristics are minimal. I thibk it was the Germans who built an entire plane based on asymmetrical thrust. it was twin boomed but one boom had the engine and the other held the cockpit. afraid i dont know anything more about thatplane though.. Just thinking that if it could be stable, there's little reason to think either this one or the P-38 would be while operating with an engine out,,

[txnetcop]

Well from reading the accident report it appears the Mosquito suffered a temporary powder loss from the left engine at the apex of the final wingover (to the right). With the right engine at full power and reduced airspeed the aircraft yawed left and stalled, entering a spin. After that power appeared to be restored but recovery was no longer possible due to the height at which control was regained..

In terms of the Widow, in a similar situation i.e. low airspeed banked approx. 90 degrees to the right, a sudden failure of the left engine with the right delivering high power would of course create a yawing force to the left. However, due to the very different designs, and not knowing the exact speed the accident flight was at (referencing VMCA) when power was lost it is impossible to tell if a Widow would react the same to that yaw. It is worth noting that the Mosquito does have a rather high VMCA due to the small rudder surface outside of the propeller slipstream, while the Widow has significantly more rudder placed in the propeller slipstream.

In summery I would say that in the same circumstances (low speed, 90 degree bank, higher engine failing) the Black Widow would definately yaw towards the dead engine if uncorrected, and the pilots ability to maintain control would be directly tied to airspeed at engine failure and pilot reaction time. If uncorrected the yaw would produce roll towards the dead engine (secondary effect of yaw being roll in the direction of yaw), which would produce yet more yaw (secondary effect of roll is yaw in the direction of roll) leading to spin entry depending on the aircraft's susceptability to spin entry.

This is why red line (VMCA) in a twin is so important, if close to VMCA it is imperative to maintain control, even if that means reducing power on the live because the alternative is yaw-skid-roll-spin..

Yep sounds and looks exactly like that is what happened! Dang that's horrible because you have just long enough to know you're gonna die!

[Snave]

;;chuckles;; its 3:45am.
well, the book can tell me it doesnt spin all it wanrs, but the laws of physics contradicts that.. However, i can understand it if the spin characteristics are minimal. I thibk it was the Germans who built an entire plane based on asymmetrical thrust. it was twin boomed but one boom had the engine and the other held the cockpit. afraid i dont know anything more about thatplane though.. Just thinking that if it could be stable, there's little reason to think either this one or the P-38 would be while operating with an engine out,,

You're thinking of the Blohm and Voss BV141



http://en.wikipedia.org/wiki/Blohm_%26_Voss_BV_141

Also there were the Rutan versions of asymmetric flight:
http://www.aviastar.org/air/usa/rutan_boomerang.php
and
http://www.aviastar.org/air/usa/rutan_ares.php

[warchild]

Thats the one all right.. very weird, but amazing aircraft. Not jus the BV but all of them. I would honestly love to see the notes from the engineers and see what they learned, especially Dick Rutans.

[warchild]

Yep sounds and looks exactly like that is what happened! Dang that's horrible because you have just long enough to know you're gonna die!

Gods know the man was doing everything he could think of not to die. and then that guy standing near the camera says "oh ****" and you know its all over with.

I know that for the pilot there was no escaping it, but i cant help but wonder if there wasnt something he could have done that would have at least given him a couple extra moments to bail out.. Since i wasnt in he cockpit, its all speculation, but you see something like that and it sticks with you, and its hard not wo wonder and look for options he may have missed.

[warchild]

here's what i'm seeing..
The mosquito is over all somewhat smaller than the widow. ten feet less wingspan and 10000 pounds lighter on average. Its effective tail area is less than half of a widows ( respectively, and in size ). i wish i knew more about its exact wing plan. That is the crucial factor here.
In the widow, as the engine stalls, the remaining engine surges its wing forward yawing and rolling towards the dead engine. The yaw itself is violent enough that in a lighter plane, the roll could go un-noticed until it was too late. The only things that save the widow are the wing plan, and the weight of the engine ( greater inertia to overcome to start the roll ). The widows wing plan is very similar to a B-17s, which had an inordinate amount of lift. I dont know what the mosquito's wing plan was like. In the widow, things happen with this queasy horror film slowness like the B-17, the Mosquito obviously doesnt give you any time to be queasy.
In the video, the accident would have been a confused and terrifying cluster f***, especially with no ejection seat.
I do hope that that accident was able to do more somewhere, than to just give this not so humble modeler the data to make her little plane more realistic.

[Whitehawk]

Possibly.. My actions in that situation, if I could plan it ahead of time and execute the plan instantly when power was lost, would be to boot in right rudder whilst chopping BOTH throttles to idle. That would kill the yaw left then releasing the right rudder to bring it back to co-ordinated flight, then roll it level lowering the nose to maintain/attain best glide speed and THEN worry about the engine. Either you could apply power, (from what I've read it was a momentary fuel flow interruption caused by the left carburettor cutting off flow when it experienced negative 'g' as the pilot stopped the roll in the vertical, so the left might have come back, as it appeared to do during the final dive - in fact noting that the crash examination showed evidence of SYMMETRICAL power at impact this appears to be the case) if power was restored fly it back carefully in case it goes again, if not fly it back assymetric and worst case a forced landing on the nearest field depending on height speed and power available..

BTW for anyone who cares lol the last thing you want to do at stall speed with un-commanded roll is to pick it up with aileron, that is just asking for spin entry as the down going aileron increases the angle of the mean chord line, effectively increasing Angle of Incidence, serving to increase Angle of Attack on the down going wing which already has an increased AoA since it is moving downwards. This could exceed the critical angle at the aileron causing the outer wing to stall (as well as the inner wing which is probably already stalled since it is dropping, washout causing the outer wing to keep flying initially) and with the whole wing stalled, and creating more drag because of it, yaw increases, roll increases, and the aircraft enters an autorotative state i.e. spin.. Now with spoilerons it should be a little different as the spoiler on the down going wing would remain retracted, and deploy on the upgoing wing, increasing drag and decreasing lift on that wing so that should counter the yaw and roll and allow an effective recovery.

Hmm from what I've just typed I would say that use of spoilerons close to the stall speed could be a very bad thing - Increase drag + decrease lift on the down going wing in a commanded roll could well induce a wing-drop stall as in the above situation..

I love this aeroplane lol it's making me think so much more about flight dynamics and its handling!

Oh re. the no stall characteristics in the AFM, possibly this could indicate the stall was gentle with little more than a slight pitch forward to counter it, and no tendency to drop a wing? Just guessing on that one lol! Thanks for all the hard yards you're putting into this FM!

[warchild]

Oh re. the no stall characteristics in the AFM, possibly this could indicate the stall was gentle with little more than a slight pitch forward to counter it, and no tendency to drop a wing? Just guessing on that one lol! Thanks for all the hard yards you're putting into this FM!

Those characteristics are also what is demonstrated in the training video, but thats with normal power from both engines. The mosquito video gave me a wake up call..
Remember, the widow didnt have spoilerons or ailerons. it had spoilers. they werent large ( six inches high and curved ) but they were somewhat long. It's probably a lot more detailed than i can be, but going on their length, their inside distance from the cacoon/crew nacelle, and their estimated applied lateral force ( as opposed to the force needed to overcome the tail planes inertia ) the estimated apex/fulcrum of the generated critical angle would be somewhere between the cacoon, and the powered engine. This would result in a very shallow yaw towards the unpowered wing, but not anything dramatic. of course, i'm doing this all in my head and half guessing, but as much as i hate guessing, sometimes it's all i have..

[fliger747]

From what I could gather , the widow had a reasonably gentle one engine stall, as long as the engine was not at WEP! And of course the recovery would be as described above. In almost all WWII twins, reduction of thrust and landing straight ahead was the prescribed course of action if engine failure occured after liftoff but before a safe single engine speed was obtained. The critical ingredient was to have either speed or altitude, even better both!

Modern light twins share the same vunerabilities even today, leading to a safety record poorer than one might expect.

Cheers: T

[Whitehawk]

Hang on I think I'm getting a little lost lol, are we talking about the yaw induced by the live engine or adverse yaw caused by using the spoiler to roll?

[Whitehawk]

The critical ingredient was to have either speed or altitude, even better both!

Modern light twins share the same vunerabilities even today, leading to a safety record poorer than one might expect.

Yeah what a lot of people don't realise is in a twin engine failure = loss of 50% of thrust, but having a dead engine sitting on the wing doing nothing increases drag by 30%, giving an overall performance loss of 80%!

[fliger747]

Live engine.... Spoiler would help if it were not for the drag, best technique in this plane is to use almost all rudder. The rudder (at least one) being in the slipstream is more effective than the Mossie's which was not.

Problem with using ailerons is that the adverse yaw adds to the yaw moment. In most spoiler planes we use mostly rudder. In an aileron equipped light twin, or even the widow with some speed, a small amount of roll away from the dead engines reduces the amount of sideslip and moves the center of thrust (slightly) toward the CG/Center of drag. However not a great idea at a high AOA!

T