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Bleed air to airplane from ground source

Bleed air to airplane from ground source

I have come into a problem in which I need help in understanding and identifying problems and situations to avoid.

The problem: A military aircraft is to be parked in a new hanger and its pneumatic systems charged so crews can conduct training exercises in and on the plane. Normally the pneumatics systems are charged/powered by bleed air from the aircraft's engines in flight, with the plan sitting on the ground, this would be an obvious waste of fuel and create unwanted noise issues. Use of an AGE (Aircraft Ground Equipment) cart is not desirable with the aircraft being parked in a hanger, noise and exhaust issues. With these options 'off-the-table' client requested that the building's compressed air system be used to charge/power the pneumatic systems on the plane.

The hanger has been built and the designed and installed compressed air system are not meeting the aircraft's needs. My job now is to evaluate, validate and propose solutions.

My questions:
1) Is a bleed air requirement of 150 Lbm/min typical? Does this sound reasonable (units)?
2) What is the typical temperature range of bleed air as it comes off an aircraft's engine? From an AGE cart?
3) Do AGE carts providing bleed air to an aircraft typically a pre-cooler?
4) If answer to #3 is yes, what is typical temperature range bleed air is provided to the aircraft's pneumatic systems?
5) How critical is the temperature of the air entering the bleed air system of on aircraft?

In a typical building compressed air system (powering pneumatic tools), the air is compressed to 120 psig and provided in SCFM (Standard Cubic Feet per Minute). This is too high for an aircraft and I have been given a pressure requirement of 35 psig. I have made some calculations trying to convert the Lbm/min to SCFM, but as I've learned more about bleed air systems for aircraft, I've learned that my assumption are likely grossly wrong especially in regard to air temperatures.

Since this does involve military hardware, you'll excuse me if I'm hesitant to provide too many details and talk in more general terms.

RE: Bleed air to airplane from ground source


Suggest You get a copy of following SAE documents just to be fully litterate regarding this subject. May be much harder to do than expected.

SAE ARP217 Testing of Airplane Installed Environmental Control Systems (ECS).

SAE ARP1270 Aircraft Cabin Pressurization Criteria

These ARP discusses roughly what You are tasked to-do.

Pressurization system testing is no big deal from a ground cart; however full pneumatic system testing requires a lot of air IN and OUT [system flow-thru]... hence it is a lot harder to do in a hangar environment.

Does this acft have an internal APU that You could 'operate' in an open hangar or ramp environment special vent systems required?

I suspect that this testing may require a bleed-air APU, located outside of the hangar with hard ducting to the vicinity of the acft, a short section of flexible duct to the acft service connection and a lot of instrumentation to ensure the system is meeting acft requirements. Also need to ensure that the airflow vents safely from the acft and from the hangar.

What does the Pneumatic system T.O. say about this subject?

May pay for You to 'have-a-peek' at how ATC trains Pneumatic system technicians on system operation!

IF they have a full system set-up already designed for training, then You're in luck! Plagerize!

IF they have an 'Iron Bird' then Your stuck.. unless elements could be adapted SAFELY.

Personnel and aircraft SAFETY will be a major issue for You!

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

RE: Bleed air to airplane from ground source

Possibly applicable in the 'lessons learned' department: (famous KC-135 Pressure Test)

In your case, perhaps just leave the doors open, especially until the procedures are de-bugged.

RE: Bleed air to airplane from ground source

Nice article VE1BLL. Although we are having a problem with not getting enough air to the aircraft with a 125 HP compressor rated to 615 CFM FAD at 125 psig.

Thanks for the referrals wktaylor, I'll look them up and take a look through. When you refer to the "system T.O." what does T.O. stand for? In my facilities world it means "Task Order".

RE: Bleed air to airplane from ground source

T.O. [USAF] = Technical Order = USN = NAVAIR or Army TM = Technical Manual

On the USAF aircraft I work on, the T.O.(s) for the pneumatic system [Environmental Control System (ECS)] are 1X-XXX-2-3-1 and 1x-xxx-2-3-2 and also the 1X-XXX-2-16-1 [pneumatic start APU].

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

RE: Bleed air to airplane from ground source

Thank you for clarifying Wil.

RE: Bleed air to airplane from ground source

Hi dbill74,

The bleed system or pneumatic system is a supplier system that provides air in a certain temperature and pressure depending upon the consumers needs - air conditioning, engine starting, anti-ice. Therefore, the flow, pressure and temperature would depend on your application - based on your explanation, I assume you will need bleed air to run air conditioning packs (air cycle machine) in the hangar. In this case a flow of 150 lb/min seems to be more than sufficient but depends upon the pressure ( normally a pressure of 35-40 psig is sufficient). Another option is to use ground cart to directly provide air to run the air conditioning system (high pressure ground equipment) or to directly provide conditioned air to the occupied zone (similar to a portable air conditioning system). Answering uour questions:
1) see above
2) bleed air tapped from engine may reach temperatures up to 500 Deg Celsius. From AGE Cart will be lower than that (~ 150 Deg Celsius)
3) normally AGE does not have a precooler.

Hpe this may help you. Good luck!

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