A question about Hydraulic Preasure.

[PSC13]

I had tried to fly F-4E with no fuel, and engine malfunction, compressor stall.

Then I can see the PC-1 and PC-2 are zero, and Engine RPM is also zero.

But I can still fly the plane, everything controllable. Every parts move as normal.

I am not sure if this is a problem, since I had already made many mistakes, something are just designed to be like that.

But I don't know why it is controllable. Did any one know that?

PS：Once I landed it, I will be unable to control soon, no parts can move any more.

[Jef Costello]

My guess this is not normal, no hydraulic pressure no flight controls and Martin Baker is your friend!

[Ivandrov]

So, first of all, the hydraulic pressure gauges require generator power to function. You can test this by turning off both generators in flight and the hydraulic gauges will drop to zero despite the engines still being on and providing hydraulic pressure. The Gens don't provide enough voltage while just windmilling and so the pressure reading also drops to zero.

There's an electrically driven pump that is supposed to provide some hydraulic pressure to the PC-1 side of the Stabilator in the event that hydraulic pressure drops below about 1000 psi.

Even then, if you are in the air, it is likely the engines are windmilling and providing some hydraulic pressure through that avenue as well.

Rudder control is still possible even without hydraulic pressure.

Edited 23 hours ago by Ivandrov

[PSC13]

9 hours ago, Ivandrov said:

So, first of all, the hydraulic pressure gauges require generator power to function. You can test this by turning off both generators in flight and the hydraulic gauges will drop to zero despite the engines still being on and providing hydraulic pressure. The Gens don't provide enough voltage while just windmilling and so the pressure reading also drops to zero.

There's an electrically driven pump that is supposed to provide some hydraulic pressure to the PC-1 side of the Stabilator in the event that hydraulic pressure drops below about 1000 psi.

Even then, if you are in the air, it is likely the engines are windmilling and providing some hydraulic pressure through that avenue as well.

Rudder control is still possible even without hydraulic pressure.

Thank you for your information, I will try it later, but, I actually set engine malfunction, and from F2 view, the engine rpm is 0%. So I guess windmill is not work.

I don't know much about electrically driven pump, ChatGPT told me that it will fail soon after engine down. I don't know how long it can support, the start point is 33000 feet in the air, until I landed it, I didn't found any problem about control, maybe 5 minutes.

[Ivandrov]

2 hours ago, PSC13 said:

Thank you for your information, I will try it later, but, I actually set engine malfunction, and from F2 view, the engine rpm is 0%. So I guess windmill is not work.

I don't know much about electrically driven pump, ChatGPT told me that it will fail soon after engine down. I don't know how long it can support, the start point is 33000 feet in the air, until I landed it, I didn't found any problem about control, maybe 5 minutes.

Well, I tried the no fuel engine malfunction as well and the engine rpm gauges in the plane were still reading an engine RPM, about 20-30% at 300 knots.

ChatGPT is not likely to help you here all that much.

 

It's safe to say to that, it is likely that you were in fact windmilling and that provided enough hydraulic pressure until you finally slowed down on the runway since that is when your flight controls stopped working.

Edited 13 hours ago by Ivandrov

[PSC13]

1 hour ago, Ivandrov said:

Well, I tried the no fuel engine malfunction as well and the engine rpm gauges in the plane were still reading an engine RPM, about 30-35% at 300 knots.

ChatGPT is not likely to help you here all that much.

 

It's safe to say to that, it is likely that you were in fact windmilling and that provided enough hydraulic pressure until you finally slowed down on the runway since that is when your flight controls stopped working.

Wow, thanks for try it, did you tried the malfunction option "seized" or something like that? I am not beside my game gear, but I guess that is an option can stop engine from rolling?

[PSC13]

I tried it again, with dynamic pause, and the seized option of engine malfunction. Yes, it stop the engine from rolling, and the APU support the hydraulic pressure. But PC-1 and PC-2 read 0. If I move the stick a lot, it will finally run out of pressure, and the aircraft will become a brick fall out of the sky. If engine is not seized, rpm below than 10% will lead to the same thing. However, once the aircraft regain speed during falling, rpm will increase, and regain control again. Now I understood!