Flaps deployment

[Pilum]

If the hydraulic system is malfunctioning then there will be structural damage. There is a very good reason why it gets tested on a regular basis.

 

Why are you stating the obvious? But if you want a comment I agree! :)

[Pilum]

Holtzauge,

 

The thermal relief valve will open at 1400 to 1600 psi and return the excess fluid to the reservoir.

 

Take a close look at the path it takes to get there. When that pressure hits the system, the pressure relief valve will open.

 

It works as described.

 

 

We have the P-51 hydraulic schematics in the pdf Friedrich posted now, please refer to which figure you mean and how you mean this works as described. Walk us through it.

 

Take the example of the pilot moving the lever to the 50 deg position at a speed below 165 mph IAS at altitude. I assume we can agree that the flaps will deploy down to the full 50 deg right? Now do you agree with my description of how this comes about and how the valves operate? I say they are open until they reach the target angle at which time the follow up arm closes them. Agree or disagree? If you don't agree then please provide alternative description of the system state at this point and which valves are open and which are closed.

 

Now if we have come so far we can assume the flaps are down and the pilot dives.

 

I guess we both agree that the speed will build up and the force on the flap actuation cylinder goes up?

 

Now what happens? Does the flap start to move? If so the piston in the actuator is pushed back and through which part of the hydraulic circuit does the hydraulic fluid flow on it's way to the relief valve? Please point out which figure you are refering to and which path the pressure takes? Which valves are open and which are closed?

Edited January 25, 2015 by Pilum
Clarified that speed is IAS to avoid TAS/IAS discussion

[KLR Rico]

I'm with Pilum, that's the same conclusion I came to when I saw the hydraulics schematic.

 

If the flaps are down and *then* the speed limitations are exceeded the fluid won't bypass through any designed mechanism, the flaps are effectively locked.

 

However, the flaps could blow up 'gently' if hydraulic fluid escaped from the plumbing between the actuating strut and the control valve, the fluid leaked past the piston, or leaked past the control valve. (The latter two options seem to be the most likely, IMHO)

 

If there was zero leakage (internal or external) on the flap actuating strut, the control valve, or the plumbing between, the flaps would only retract as a consequence of mechanical failure.

[Crumpp]

However, the flaps could blow up 'gently' if hydraulic fluid escaped from the plumbing between the actuating strut and the control valve, the fluid leaked past the piston, or leaked past the control valve. (The latter two options seem to be the most likely, IMHO)

 

If there was zero leakage (internal or external) on the flap actuating strut, the control valve, or the plumbing between, the flaps would only retract as a consequence of mechanical failure.

 

According to the flap control valve description, the thermal relief valve will open and send fluid to the reservoir at 1400 psi.

 

A thermal relief valve is on the system because it is a closed system with the flap selector valve in the desired position. It is there to relieve pressure as the fluid pressure increases with temperature. While it called a thermal relief valve, it is just a pressure relief valve like any other and is triggered when the flap circuit pressure exceeds 1400 psi.

 

When the flap circuit pressure exceeds 1400 psi, that valve will open and push fluid to the reservoir to relieve the pressure.

 

That 1400 psi is dumped on the return line side downstream from the reservoir. That will cause the pressure relieve valve on the main circuit to open further protecting the system.

 

The dynamic pressure on the flaps and hydraulic pressure will move to equilibrium at a pressure below that 1400psi dumping excess pressure and fluid into the main circuit.

 

It works just like Yo-Yo modeled it and The Fighter Collections mechanics say......

[sobek]

The Fighter Collections mechanics say......

 

I wouldn't call Nick Grey a mechanic...

[KLR Rico]

According to the flap control valve description, the thermal relief valve will open and send fluid to the reservoir at 1400 psi.

 

 

Ah yes... Right you are! I was basing my stance from my interpretation of the posted schematic, but I've gone back to see Friedrich's T.O. and I see the thermal relief valve now.

[Crumpp]

I wouldn't call Nick Grey a mechanic...

 

OOPS...yep He is a pilot...That is what I get for assuming.

 

Don't ask pilot's about mechanical stuff...ask the Mechanics!!! :smartass:

 

 

Ah yes... Right you are! I was basing my stance from my interpretation of the posted schematic, but I've gone back to see Friedrich's T.O. and I see the thermal relief valve now.

 

:thumbup:

[MiloMorai]

Testing and adjusting unloading and relief valve (pg 268 )

 

Why would the pressure reach 1400psi when the adjustment screw is set for 1250psi max?

[IIIJG52_Otto_]

...Now if we have come so far we can assume the flaps are down and the pilot dives.

 

I guess we both agree that the speed will build up and the force on the flap actuation cylinder goes up?

 

Now what happens? Does the flap start to move? If so the piston in the actuator is pushed back and through which part of the hydraulic circuit does the hydraulic fluid flow on it's way to the relief valve? Please point out which figure you are refering to and which path the pressure takes? Which valves are open and which are closed?

 

In that situation, several things will occur:

- The drag increase rapidly with speed.

- The plane would take an attitude of "heavy nose" and recover the dive will be more difficult ..

- When the speed becomes high enough, the flaps and actuators will bend, the hydraulic pipes burst, or the flaps will be ripped from its hinges.

 

- And the pilot will be fired, or he will goes to a martial court :)

Edited January 26, 2015 by III/JG52_Otto_+

[NineLine]

Well... I am no expert in the field, but I hope it works like its modeled in the sim, it doesnt make much sense to have a system that would rather there was damage to the flaps if over-speeding occurred, than to have them forced closed by the forces placed upon them... just my opinion of course.

 

Least that sounds most logical to me... having to replace maybe some fluid instead of replacing mechanical parts of the flaps...

[Crumpp]

Testing and adjusting unloading and relief valve (pg 268 )

 

Why would the pressure reach 1400psi when the adjustment screw is set for 1250psi max?

 

:doh:

 

 

Is not the flap thermal valve......

 

Let Yo-Yo handle it.

Edited January 26, 2015 by sobek

[Crumpp]

I've gone back to see Friedrich's T.O.

 

I would post the entire maintenance manual but it would take up almost all my document space. I actually zipped it into 15 5Mb parts to share.

 

Any suggestions?

[KLR Rico]

Maybe post to Google drive? I for one would love to have a copy. Mx manuals go into system details a whole lot more than the -1's, interesting reading.

[MiloMorai]

Maybe post to Google drive? I for one would love to have a copy. Mx manuals go into system details a whole lot more than the -1's, interesting reading.

 

Try here, http://www.scribd.com/doc/34812228/P51D-Mustang-Maintenance-Manual#scribd

[Friedrich-4B]

Maybe post to Google drive? I for one would love to have a copy. Mx manuals go into system details a whole lot more than the -1's, interesting reading.

 

It's also possible to join Avialogs for about $15 US:

 

http://www.avialogs.com/index.php/en/aircraft/usa/northamericanaviation/p-51mustang/Page-6.html

[Echo38]

Speaking of mechanics, perhaps its time we stopped asking the pilots and started asking the folks who maintain the bird. Surely someone up top is able to contact the the Fighter Collection's mechanics about this question?

[sobek]

Speaking of mechanics, perhaps its time we stopped asking the pilots and started asking the folks who maintain the bird. Surely someone up top is able to contact the the Fighter Collection's mechanics about this question?

 

It would seem that Nick Grey knows his stuff.

[NineLine]

It would seem that Nick Grey knows his stuff.

 

I would imagine Yo-Yo had access to anyone he needed to talk to. And I agree, I would imagine Nick Grey knows the Mustang inside and out... that said, some of these functions that would cause damage to the aircraft are hard to get good data on, as far as I know, most real pilots dont have an F2 feature :)

[sobek]

Neither do they have a "restart mission" feature. :)

[NineLine]

Neither do they have a "restart mission" feature. :)

 

Yes, nobody would be here to talk about this stuff if we were all flying real aircraft :)

[Crumpp]

Yes, nobody would be here to talk about this stuff if we were all flying real aircraft

 

:thumbup:

 

Exactly, I don't want to find out would will happen if I overspeed the flaps on any airplane I have flown.

 

Two things you never want to hear from a pilot:

 

"Hey Watch This!!"

 

"Why did it do that??!?"

[Friedrich-4B]

Here are the material specs for such things as the flaps' brackets/hinges and control rods etc.

 

 

Presumably ED has to take such information as this into account when developing their models.

Edited February 22, 2015 by Friedrich-4/B

[MiloMorai]

Is not the flap thermal valve......

 

Some of us are able to man up and say 'Oops, my mistake'.:music_whistling:

 

It would be nice to see a graphic (photo or sketch) showing where this thermal relief valve is installed.

[Echo38]

It would seem that Nick Grey knows his stuff.

 

I don't doubt this at all! But, if I'm interpreting the posts aright, we have a case of two real P-51 pilots disagreeing about one of the finer points of the hydraulic system, or something like that. Not surprising, given how often pilot input diverges, especially with something like this that cannot easily be tested. Perhaps going directly to the people whose job it is to maintain that hydraulic system would be better than talking to the pilots.

[Pilum]

To get a second opinion on the question of how the flaps operate on the P-51, I consulted a retired engineer I know who spent his entire working career designing hydraulics in the mining industry. He was actually quite interested in this question since he used to be a private pilot himself and especially liked the Mustang which it turned out he himself had seen as a kid when a delivery flight passed over Stockholm shortly after the war.

 

Anyway, this is what he had to say: He was impressed and thought it was a neat system and he especially liked the mechanical linkage controlling the flaps which he thought was both simple and smart. He also confirmed that they functioned so that at rest, the valves in the wing flap control valve would be all closed, effectively locking the flap in position and cutting it off from the rest of the system.

 

On the subject of the thermal control valve he said that it was difficult to make any call on this since it was both missing from the schematics and he could neither see it in the sectioned drawing (Fig 331 in Friedrich's pdf) so it was difficult to judge any potential impact. However, since the amount of fluid that needs to be vacated from the closed flap circuit to relieve a thermal overload would be miniscule, the thermal valve itself could be very small so it was in his opinion difficult to say if the flow through such a valve would in practice have any impact on the flap movement at all.

Edited January 27, 2015 by Pilum