windmilling A320
 

HI,
I'm looking for the speeds (CFM & IAE) needed by those engines to be able in windmilling to provide sufficient hydraulic power to supply the flight controls

I have tried it in the sim and I had enough windmilling power for hydraulics at 280knots. I was even able to put the autopilot on. The autopilot disconnected at about 230 knots, that was when there was not enough windmilling to keep green and yellow hydraulics on, so I suppose, that if the aircraft works like a sim, it would be close to that.

With or without half your engine blades missing? ;)

I would be very surprised if you would not have sufficient hydraulic power for partial flight controls down to approach speed of about 130-140 kts. The CFM engines on the 737 supplied this for a few glide approaches in the early days! You might lose elevator authority during flap extension, but if the minimum was about 280kts, you effectively have an unflyable aeroplane in the event of total engine failure!

a cfm 56-5 engine using apu bleed air and running at about 5% N1 (not so sure about n2 value.. i´ll check it next time i do a dry run) provides enough energy to run the engine driven pump to 3000psi.

That's what the RAT is for. It gives 2500psi to the blue system, which leaves you with all control surfaces operative down to 125 knots.

thanks for the info about the RAT.
But that day the RAT door is bent by birds impact, and the RAT stays home.

makes a helluv a difference what blades are missing.

assuming that the hydraulics run off the N2 then you pretty much don't care what's going on in the N1 subject to the following.

The N2 is actually a drag condition when windmilling with all the compressor blades and needs it's turbine to actually windmill as intended. Of course it helps to have air get to the N2 so that's another side of the story.

Now if you actually want to produce thrust you do need another set of circumstances balanced in the equations.(like balanced pressures between the N1 and N2)

Near enough what I was going to say, as I couldn't believe anyone would consider the N1's 'windmilling action' as a reliable form of emergency power. That's what the RAT and APU are for, and as correctly stated (I didn't know the numbers) the RAT will provide you with full hydraulics to the essential control surfaces right down to the numbers.

That's good enough for me :ok:

Off topic, but the 747 doesn't have a RAT and it utilizes windmilling RPM to provide hydraulic pressure for flight controls.

GF

CFM-56 question about N1/N2
 

In the CFM-56, is N1 geared to anything...? (Besides N1 RPM) -
Just have limited experience (and recollection) of the CFM-56.
Flew a few 100s of hours with them in DC8-70s... Mid-1980s.
My old head tells me that the accessory gearbox was on N2.
Or am I getting too old...? Please re-educate this old fart...
:{
Happy contrails

The CFM 56 LP spool (N1) is not geared to anything. It could be windmilling at 100% but if your HP spool (N2) has minimal rotational speed or is seized, you have little or no drive into the accessory gearbox and therefore no hydraulic pressure from the EDP.

7 per cent N2 is required for single engine taxi NOT to start PTU, i.e. sufficient for all flt controls. Observed regularly after engine shutdown for single engine taxi in. IAS=0.

FD