F4U highest flap speed?

[SIK1]

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?

[bozon]

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.

[Stoney]

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.

[Saxman]

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.

[SIK1]

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).   

[bozon]

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.

[SIK1]

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.

[colmbo]

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.

[mtnman]

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.

[bozon]

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.

[jamdive]

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. 

[SIK1]

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.

[jamdive]

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.

[SIK1]

Here you go.

[jamdive]

Here you go.

(Image removed from quote.)

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.