Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Noah17 on August 05, 2010, 06:02:53 AM
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I didn't want to "hijack" the F6F thread but, I've heard that the F4U could drop flaps up to 300-310MPH. Is that true?
I know F4U flaps and their modeling have been discussed before but don't remember if the top speed for a drop was discussed.
:salute
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First notch of flaps for the F4U in our game come down at 250mph IAS.
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Yes, in game it's 250. I had heard that the real aircraft could drop higher than that.
I wasn't sure if that was true or not.
Thanks
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Oh if only... We d never hear the end of it.
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Oh if only... We d never hear the end of it.
What difference would it make? The machine is above corner speed at 300 anyway, so the extra lift would account for naught.
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Yes, in game it's 250. I had heard that the real aircraft could drop higher than that.
The thing that I always wonder about is how many Gs could the plane pull without damaging the flaps. I am quite sure that the handbook speed limit on deployment assumes G~1, with some tolerance. In the game we lower 30 deg flaps at 250mph and then pull 6G...
The stress on the flap will depend on the lift and induced drag that scale close to linearly with G, and there is an additive term due to parasitic drag. Since lift and induced drag scale like V^2, my guess is that for a given limiting stress on the flap the speed limit will go like V_limit ~ V_book / sqrt(G), at least for G>1. So if the manual says 250mph is the safe limit, then you have to be doing less than 100mph to pull 6G without breaking them (6G at 100mph is of course impossible).
I wish the auto retract (or alternatively, jam flaps) feature would kick in for a speed modified by G load. This way manuevering flaps will be useful only at very low speeds and only the first few notches and we will see a bit less of the flap-fest that flight sims have become.
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That is an interesting note, Bozon. The issue of load factors on flaps hasn't really been discussed before huh?
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The Corsairs have an over speed prevention set up which actually prevents the flaps from coming down (or staying down) at to high a speed. I have met pilots that have said they dropped their flaps at 350 kts and I believe it. THe only thing is, that they dropped the flaps in the cockpit only, and the flaps attempt to deploy to be stopped by the over speed prevention.
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Here's what my Pilot's Flight Operating Instructions says.
"flap control shall not be place in position for lowering flaps at speeds in excess 200 knots even though the flaps are protected by an overload release mechanism."
The flaps on a corsair really do "blow up" like in the game. That is the overload release mechanism mentioned.
So no, a real corsair couldn't lower it's flaps at 300 mph at least not a -1, or -1A. (The models my book covers)
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bozon I see no G limitation on use of the flaps only a speed limitation.
There is this in the Operating Instructions:
"The flaps are also designed for use in maneuvering the airplane in combat. With typical maneuvering flap deflections of 20* or less the airplane may be maneuvered at equivalent limiting "flaps up" accelerations up to 200 knots."
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I remember an account of Ike Kepford being chased by a bunch of Zeke's just above the water. He apparently told Tommy Blackburn that at a high speed he dropped flaps and caused an overshoot of a Zeke. I know that he had been travelling well over 300mph during most of the chase but can't say for sure at that specific time what his speed was.
An interesting side note for me was that apparently his WEP water/methanol mix was used up and his engine was not running that well. Then end result was that he was barely able to out run the Zeke's. Something we do here with ease without WEP in any model F4U.
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bozon I see no G limitation on use of the flaps only a speed limitation.
There is this in the Operating Instructions:
"The flaps are also designed for use in maneuvering the airplane in combat. With typical maneuvering flap deflections of 20* or less the airplane may be maneuvered at equivalent limiting "flaps up" accelerations up to 200 knots."
This is quite a low speed and moderate flap deflection. At these speeds the ability to pull G is very limited anyway. That is exactly my point - flaps as a maneuvering aid are designed to operate at a moderate deflection angle and quite slow speeds. At higher speeds, not only the 1G stress on the mechanism increase, but the ability to overload it by more G also increase. By 250mph, most planes are capable to pulling 6G but at 200mph very few can. I would be very surprised if the flap blow-up mechanism really was controlled by speed and not the actual load on the flap. In that case, the blow-up speed would change with G load.
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iirc the "blow up" mechanism is based purely on speed. The air pushing on the flap literally blows it "back up" that is why at a given speed only a flap setting not exceeding that speed can be achieved even if the flap lever is in the full down position.
Bodhi would know more about this than I do since all my info comes just from books.
Noah I remember the story you are referencing. It comes from Tom Blackburn's book "The Jolly Rogers". I don't recall the dropping flaps at hi speed part but I will look it up and see what it says.
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Airflow (created by speed) pushes the flap back, preventing damage. You can still bend the pushrods and attach fittings. The gear is different in that it unloads when it is delpoyed as a dive brake. Both have built in overspeed protection.
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iirc the "blow up" mechanism is based purely on speed. The air pushing on the flap literally blows it "back up" that is why at a given speed only a flap setting not exceeding that speed can be achieved even if the flap lever is in the full down position.
Airflow (created by speed) pushes the flap back, preventing damage. You can still bend the pushrods and attach fittings.
The flaps do not read the speed gauge in the cockpit. The force acting on the flap depend on the speed... and on the attitude of the flap relative to the airflow (and the whole wing section near the flap as well). This changes with the angle of attack and for a given speed this means G load. The speeds everyone quote must be for conditions between unloaded and level flight, which are the normal conditions at which flaps are used.
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The airspeed gauge in the cockpit is driven by air pressure differential. So why can't the flap "blow up" function be controlled in the same way?
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The airspeed gauge in the cockpit is driven by air pressure differential. So why can't the flap "blow up" function be controlled in the same way?
If you mean it has a pitot tube that activates it, that is possible.
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Bodhi would know since he works on them, but I suspect that there's some sort of mechanical assembly that is deflected back by the air stream. You could use certain size springs to make that happen simply, for example.
But, Bozon, most control surface assemblies are designed to withstand the same amount of G forces as the rest of the airplane. If, for example, the flap assembly couldn't withstand a 6-g load in the deflected position, it wouldn't withstand a 6-g load in the retracted position. I would expect that the flap assembly wouldn't be damaged by any g-load that didn't damage the remainder of the wing.
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Bodhi would know since he works on them, but I suspect that there's some sort of mechanical assembly that is deflected back by the air stream. You could use certain size springs to make that happen simply, for example.
From what I understand of the Corsair's flaps, this is PRECISELY how it works: The springs are designed to allow the airstream to "blow" the flaps up above a certain airspeed.
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If you mean it has a pitot tube that activates it, that is possible.
No, I mean that as part of an airfoil there is a pressure differential between the upper and lower surfaces. So as long as the wing is flying there has to be a pressure differential between the upper and lower surfaces. If pressure was equal I don't believe you would be able to blow the flap up. So at a given velocity there is x amount of pressure pushing against the bottom of the flap surface, and on the top surface there is less. At a given point the pressure differential reaches a point where it will cause the flaps to retract.
This is all supposition on my part, maybe one of the engineer types can come blow my theory apart. From what I understand though the blow up mechanism is purely mechanical,(springs and levers).
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No, I mean that as part of an airfoil there is a pressure differential between the upper and lower surfaces. So as long as the wing is flying there has to be a pressure differential between the upper and lower surfaces. If pressure was equal I don't believe you would be able to blow the flap up. So at a given velocity there is x amount of pressure pushing against the bottom of the flap surface, and on the top surface there is less. At a given point the pressure differential reaches a point where it will cause the flaps to retract.
If it measured the pressure difference between two position on the wing, it will depend strongly not only in the speed but on the lift/G/AoA whatever you want to call it. Speed is measured by the difference between kinetic and static pressure in a pitot tube away from the wing and fuselage. That is why it it usually installed at the end of a long stick.
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First I don't believe that anything is actually measured. Again I defer to bodhi here, but if I understand what I've read. there is a pushrod attached to the flaps on one end and to the "blow up" valve on the other. When the flaps are down and the plane is flying within airspeed limits there is not enough air pressure pushing on the flaps and the pushrod to activate the valve, but when the plane exceeds the airspeed limits the force of the air on the flap surface applies pressure to the pushrod actuating the valve and the flaps retract.
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In that case, the blow-up speed would change with G load.
It's the air load on the flap that causes it to "blow up". G doesn't bother the flaps. The issue with G and flaps is that you can generate higher G at a specific speed which may lead to structural damage/failure.
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Not that it probably matters, but...
Wouldn't increasing G's make the flaps appear "heavier", and (maybe?) more difficult to blow back up? As in, if the flap weighs 100#, at 6G's wouldn't it "seem" to weigh 600#?
Then, with the increased pressure on the bottom of the flap, forcing it up, opposed to the increased "weight" of the flap, what would the net result be?
I have no idea really, just thought I'd throw something crazy into the pot.
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I am using G here as a measure of the lift. The actual factor that increase the stress on the flap at a given speed is a change in the angle of attack and the resulting lift.
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First I don't believe that anything is actually measured. Again I defer to bodhi here, but if I understand what I've read. there is a pushrod attached to the flaps on one end and to the "blow up" valve on the other. When the flaps are down and the plane is flying within airspeed limits there is not enough air pressure pushing on the flaps and the pushrod to activate the valve, but when the plane exceeds the airspeed limits the force of the air on the flap surface applies pressure to the pushrod actuating the valve and the flaps retract.
I don't think there is an actual lever that operates the so called "blow up valve" I think its just a bypass valve in the hydrolic line that vents the hydrolic fluid from the cylinder back into the resevoir when the cylinder is over loaded.
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I don't think there is an actual lever that operates the so called "blow up valve" I think its just a bypass valve in the hydrolic line that vents the hydrolic fluid from the cylinder back into the resevoir when the cylinder is over loaded.
According to the manual I have and the schematic within there is a separate "blow up" valve actuated by a push rod. It even has it's own separate hydraulic line.
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According to the manual I have and the schematic within there is a separate "blow up" valve actuated by a push rod. It even has it's own separate hydraulic line.
Post it, mines blurry.
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Here you go.
(http://i238.photobucket.com/albums/ff266/Radcam/F4Uflaphydraulics.jpg)
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Here you go.
(http://i238.photobucket.com/albums/ff266/Radcam/F4Uflaphydraulics.jpg)
Those push rods are connected to the lever, not any valve. The flaps are two piece and require a seperate push rod for each. This diagram shows it somehow senses an over pressure (probably a spring and ball set up) and ports the hydrualic fluid back to the manifold. The equalizing valve would sense this also and provide an equal pressure to the opposite strut. If it didn't do this one flap would retract and the other would stay down if the pressure on one flap was greater than the other. If bohdi works on them lets wait and see what he says. The lines are hard for me to trace.
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ok fine
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From what I understand of the Corsair's flaps, this is PRECISELY how it works: The springs are designed to allow the airstream to "blow" the flaps up above a certain airspeed.
It's a spring loaded arm that keeps the flaps down below a certain speed and the blow up device is supposed to be sensitive to pressure as well as equalize the flaps, as they have separate actuators.
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Sorry, corrected the above answer as it was incomplete.
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Wow, this is good stuff. I'm glad I asked the question it's just like reading a book on the F4U!
See......everybody was going to groan and whine....."oh not another F4U magic hover flap posting." I can't hover in them anyway.......
Thanks guys!
:salute
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Hover class will be available soon as my connection is fixed at home.
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Hover class will be available soon as my connection is fixed at home.
:pray for lightning to strike your connection. I've been running into enough F4Us hovering in the air then magically following me in a high g turn to get a pilot kill when I'm E+ on them.
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:pray for lightning to strike your connection. I've been running into enough F4Us hovering in the air then magically following me in a high g turn to get a pilot kill when I'm E+ on them.
Some of those f4u guys can cloak the E in that thing pretty good. If its mtnman it only looks like hes following you and there is no escape.
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hey jamdive did you win the lotto or something? go to work.... ya it looks like the hydrolic lines are conected to the
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hey jamdive did you win the lotto or something? go to work.... ya it looks like the hydrolic lines are conected to the
margarita blender?
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Here's what my Pilot's Flight Operating Instructions says.
"flap control shall not be place in position for lowering flaps at speeds in excess 200 knots even though the flaps are protected by an overload release mechanism."
The flaps on a corsair really do "blow up" like in the game. That is the overload release mechanism mentioned.
So no, a real corsair couldn't lower it's flaps at 300 mph at least not a -1, or -1A. (The models my book covers)
200 knots is not 300 mph. 200 knots is 230.116 mph. 1 knot = 1.15077945 mph
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Some of those f4u guys can cloak the E in that thing pretty good. If its mtnman it only looks like hes following you and there is no escape.
I'm pretty sure Mtnman is an F4U
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Hover class will be available soon as my connection is fixed at home.
I'm ready for that!
:salute
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200 knots is not 300 mph. 200 knots is 230.116 mph. 1 knot = 1.15077945 mph
Yeah I know this, Your point is?
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My point is 200 Kn is approximately where the flaps come out in game and where they could be deployed according to your manual.
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I never said the flaps should be able to be deployed at 300mph. Actually if the flaps come down at 250mph then they are coming out at a slightly higher speed than they should.