Pressurization Performance and issues

[Willis]

This is more or less, a question for Glenn and his 680FP.

As I understand it, Pressurization is accomplished with a fuselage mounted, hydraulically powered Supercharger.  This may also be a source of cabin heat.

1.  Have you tested the pressurization; what altitudes have you flown and what were the cabin altitudes?
2.  any Issues with pressurization?  Door seals, etc?
3. do you know if the hydraulic pumps driving the supercharger are the same as other commanders? (or are they bigger)? 

Ive seen some of the boots used on the foot pedals and the yoke-column.  I hope these are still in supply.

My general curiosity stems from my interest in how much power the supercharger consumes.  The "main" hydraulic system operates at 3000 psig.  This drives the supercharger.  The "Utility" side (flaps, brakes, steering, landing gear) uses a lower pressure (~1000 psig) and there is a step down regulator to do this.

For reference:  1 horsepower = 1500 psig x 1 gpm.

Somewhere in the 680FLP MM is a reference to ~10 gpm of flow to the supercharger.  At 3000 psig thats nearly 20 horsepower being consumed. 

This has two effects.  (1) lower HP from the engines and (2) the hydraulic fluid must absorb 20 HP.  This causes heat. 

The loss of 20 HP from a total of 680 isnt much;  at altitude the power should be set near 60% so the effect is even less.

QQ:  How is heated skydrol cooled?  I haven't found a air-hydraulic oil heat exchanger in the system  so far. 

Im still researching these engines and systems. 



Thanks.

Bud

[ghancock]

So there are 2 hydraulic pumps one on each engine.  I suspect they are larger than other Commanders but they are definitely different as they run skydrol instead of 5606.  They also generate 3000psi to run the hydraulic turbine in the rear of the plane.  One of the reasons skydrol was choose I believe is its ability to deal with the heat and I also am not aware of any cooling unit for the fluid, however there is a coil that I had assumed was only for the air but it could also be for cooling the fluid and most likely is.

The main hydraulic system runs at 1500psi but as you stated is regulated for the different portions of the system.  I believe the brakes as an example are around 400psi.

I also can tell you that currently my left hydraulic pump is not producing and when I turn on the pressurization system it will drag the right pump down to 1500psi from 3000psi when it starts running.  So while both pumps put out 3000psi they evidently can't run the system completely on their own.

I have not currently gone up to altitude as I'm trying to find and fix all the hydraulic leaks before getting involved in the pressurization system.  I'll stay in touch on that as I proceed but currently am hunting a leak someone bottom front.  Hoping to have it identified and fixed soon.

Thanks,

Glenn