Corsair aircraft “flip on the back behavior”

[daveT]

Information from official accident report: It was noted that when Corsair aircraft was in a pull out, and indicating over 320 knots, it would flip over to the right onto its back. This trouble was experienced previously on several other Corsair aircraft and was corrected by straightening the aileron wipers on those aircraft. The Corsair aircraft in general was known for exhibiting "flip on the back behavior".
Vought, the contractor, was ordered to investigate this problem, as this flight characteristic has been noticed on several occasions on other aircraft of this type from this manufacturer
Does anyone know more about this behavior?

the full story about the accident is available in the stories section
Marine Corps Captain Edward Oliver Shaw – WWII Corsair Double Ace

 

[gumbyk]

Could possibly high-speed stall characteristics, stalling without the usual buffeting being felt leading up to it.

I'm more intrigued by what 'aileron wipers' are.

 

[XBe02Drvr]

I believe your "aileron wipers" are what today would be called gap seals. They would prevent or restrict airflow through the gap between aileron and wing structure, preventing an upward-turned aileron from acting as a trailing edge slat, especially at high angles of attack. If you're turning at 320+ knots indicated, you're almost certainly pulling significant G and angle of attack, and the lift is distributed across your wingspan. If the air under one wingtip suddenly finds a "shortcut" through the aileron gap to the top surface low pressure area, what's going to happen to your spanwise lift distribution? Right, one wing is going to suddenly have A LOT more lift than the other and you're going to bash your helmet against the side of the canopy. And that Zero turning in behind you will find you dead center in his gunsight.
Cheers,
Wes

 

[Shortround6]

Right, one wing is going to suddenly have A LOT more lift than the other and you're going to bash your helmet against the side of the canopy. And that Zero turning in behind you will find you dead center in his gunsight.

Only very briefly as the Corsair then proceeds into the realm of uncontrolled flight which the Zero cannot follow or really predict where the Corsair will end up (recover control).

 

[XBe02Drvr]

Only very briefly as the Corsair then proceeds into the realm of uncontrolled flight which the Zero cannot follow or really predict where the Corsair will end up (recover control).

Sure it will be uncontrolled flight, as the Corsair will be full of 20MM holes and the pilot likely dead, dazed, or disoriented. And if the Zero pilot is experienced, he's probably seen this before, and knows how to counter it.There's nothing like a high speed high G snap roll to kill a lot of your energy and get your bent wing bird down into a speed range where the Zero can exploit its nimbleness. By the time your Corsair reaches or passes inverted attitude, the roll impetus will have decayed, the nose will fall through, and you'll be in an inverted dive, accelerating from a much slower speed than you had before you departed.
Needless to say I've not done this in a Corsair, but I have in a T-34 and have ridden through it in a T-28 (the big-engine version), and have no reason to expect much different from an F4U.
Cheers,
Wes

 

[gumbyk]

I believe your "aileron wipers" are what today would be called gap seals. They would prevent or restrict airflow through the gap between aileron and wing structure, preventing an upward-turned aileron from acting as a trailing edge slat, especially at high angles of attack. If you're turning at 320+ knots indicated, you're almost certainly pulling significant G and angle of attack, and the lift is distributed across your wingspan. If the air under one wingtip suddenly finds a "shortcut" through the aileron gap to the top surface low pressure area, what's going to happen to your spanwise lift distribution? Right, one wing is going to suddenly have A LOT more lift than the other and you're going to bash your helmet against the side of the canopy. And that Zero turning in behind you will find you dead center in his gunsight.
Cheers,
Wes

I'm not sure how much of this behaviour is due to aileron gaps though. I've experienced it in almost all aircraft that I've stalled in a turn, including aircraft that have no aileron gaps. Many aircraft 'flick' when stalled in a turn or at high speed, especially if they're even a little bit out of balance.

 

[XBe02Drvr]

Many aircraft 'flick' when stalled in a turn or at high speed, especially if they're even a little bit out of balance.

Well of course you're going to "flick" if you stall it asymmetric. As the glider pilots say, "Ya gotta keep the string straight". I used to ease into turning stalls with students so the aircraft would roll off gently and not scare them and they could quickly gain confidence in their recovery technique. Once they got the hang of keeping the turn coordinated as the bank angle increased and recovering from any upset that did occur, we progressed to steeper banks, higher speeds and more abrupt stalls. Once a student could show me three "flick free" stalls from 45 to 60 degrees bank and explain accurately what was happening, I figured they were safe enough to move on. After a workout like that, spin avoidance and spin recovery were a piece of cake, and most students were looking forward to spins with anticipation. "Whee, that's like acro, man!"
The more G you're pulling, the more perfectly you have to have that ball centered, or you're going for a ride. Occasionally you will encounter a plane that has had a major airframe repair or is slightly misrigged for some other reason, and is impossible to stall in a "coordinated" turn without rolling one way or the other. Sometimes with those I've found a "sweet spot" with the ball slightly out one way or the other where the bird will stall normally in a turn. When pilots reach a certain experience level, they can roll into a coordinated turn just watching the nose move relative to the horizon, and don't need to break their focus to look inside at the turn coordinator.
As for the presence or absence of gap seals, there are so many variables of airfoil shape, stalling angle, wingtip design, mach range, aileron design, etc, that whether gap seals are needed or even applicable depends on the characteristics of individual designs.
Cheers,
Wes

 

[daveT]

The big question would be did the manufacturer Vought ever correct this "flip on the back behavior" or did they just train pilots about this flight characteristic?
Calling all F4U Corsair pilots out there, what do you know about this characteristic...
I always want to know that something was done to prevent this kind of accident from happening again.

 

[billrunnels]

I am not a Corsair pilot but had a good friend who was. The only complaint I ever herd him state, because of the long nose it was challenging to land on a Carrier. I always thought it was one of the "majestic" looking aircraft in the air during WWII.

 

[XBe02Drvr]

I always want to know that something was done to prevent this kind of accident from happening again.

In your original post it was stated that it was corrected by "straightening the aileron wipers". Sounds like a maintenance issue to me. I've seen aileron gap seals that struck me as not overly robust, and that was on aircraft that didn't live anywhere so strenuous a life as the Corsair. Four years of flying from a coral island has left me with a healthy respect for the erosive and abrasive qualities of coral dust and salt air. And we had mostly paved runways. Imagine flying 2000 HP airplanes off PSP laid directly on crushed coral. I imagine "aileron wipers" became an item of concern in daily inspections.
You used the term "accident" in referring to this behaviour. Did it result in a lot of losses, or just scared/startled pilots? It doesn't sound like the sort of event that's likely to happen close to the ground unless you're dive bombing, so it seems like most times there should be plenty of room for recovery. Hope we dredge up some actual Corsair pilots. Like to see what they would say.
Cheers,
Wes

 

[admiralkit]

The big question would be did the manufacturer Vought ever correct this "flip on the back behavior" or did they just train pilots about this flight characteristic?
Calling all F4U Corsair pilots out there, what do you know about this characteristic...
I always want to know that something was done to prevent this kind of accident from happening again.

Hey Dave, I stumbled across this post trying to look up some details on the F4U and thought I'd add in a couple cents. My grandfather flew Corsairs and while I never heard him speak of high speed stall, I know there was an issue with asymmetric stall during landings. Apparently they eventually retrofitted the planes with stall strips to correct the issue, but during the war the planes were largely relegated to island duty because of this asymmetric stall characteristic. They brought Charles Lindbergh in as a representative of the manufacturer to discover this issue and determine the workaround, which initially was to bring the plane in at high speeds and just use the wheel brakes to slow it down to prevent the plane from flipping over. Sounds like they eventually solved the problem by installing stall strips on the right wing to match its stall speed to that of the left wing.

I'll try to give him a call this week to see if he can shed any more details on it.