Forum: General F-22A Raptor forum

neurotech wrote:

cerberus wrote:

I think the APU automatically takes over if the engines go out. Wasn't the issue to do with G-suits and winter wear rather than the OBOGS anyway? Didn't they do centrifuge tests to prove this?

I thought procedure in dual engine failure was to switch to emergency oxygen. APU Bleed Air would be primarily used to restart the engines first. I'm not sure if the APU supplies Bleed Air to OBOGS in that case.

The centrifuge tests confirmed a faulty BRAG valve. The replacement BRAG value solved the respiratory issues, such as "raptor cough" but not the neurological issues.

I don't think it's the valve's problem or pressure vest or something. Since may until now. There have been the same type of incidents happens again. They have not yet find the problem.

and your are keep saying a compressor stall. Well it doesn't take a stall to fool the OBOGS. Just if the enough pressure differential is not maintained . The oxygen production capacity is going to be too low for what pilot needed.
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(if the F-119 have max pressure ratio of 36. at full power. the core pressure is 36bar at sea level. but only 3.6bar at 30000 feet. yet another factor remains. only at high speed the engine can reach full power at 30000 feet. this is due to the effect of ram air intaking)
______
a 3.6bar core pressure at sea level is almost a compressor stall. but when ambient pressure is only 0.1bar. This make the engine look good running. Although the bleed air pressure is droped by 10 fold.
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I believe this is what you are still not make right.
And I really doubt if there is a bleed air pressure warning on the F-22. Or how much is the trigger value to send the warning.
So far I seems clear to me. my original guess is right.
The most advanced fighter jet ever. depending solely on an OBOGS that have no big enough buffer tank and no backup oxygen.

in my original post I suggested they use a backup/buffer oxygen tank(if they dont' have one) to make the F-22 safe to fly. Which is just what lockheed martin is doing right now.

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neurotech wrote:

The F-22 can fly at high AoA, low speed and post-stall maneuver and the engines will keep running, and producing bleed air for the OBOGS. That is not the problem, although you originally suggested that it was a bleed air supply problem.

--------------The engine is running but infact the bleed air pressure is dropped by 10 fold at 30 Kft.-------------

Other jets don't have the supersonic agility of the F-22, but they still do high altitude, high-G turns without any problems. They may have to trade some altitude to maintain speed.

--------------but exact how much G, at what speed, and altitude? the flight envelope of F-22 is nothing an f-15 can look at even.--------------------

Your theory said it was a problem with the engine bleed output at high altitude/low-speed. That is incorrect. From the USAF statements, the problem is with not with OBOGS input (bleed air) but with OBOGS output under G-load. The OBOGS warning would come on if it was a OBOGS bleed air supply problem.
--------------------please read this: AF Still Reviewing Oxygen Levels for F-22 Cockpit

by defensetech on October 16, 2012
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---------------------They said " the report says the incidents “merit further analysis and testing.” Which they still believe it's some sort of G force acting on mechanical parts or some thing. From a mechanical point of view. This is just not a little possible. As the G force is not very big on small light weighted parts.
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---------------------They also said: "Oxygen concentration level fluctuations were noted in the Air Force Scientific Advisory Board (SAB) Report on Aircraft Oxygen Generation, which delved into the recent Raptor pilot breathing problems and was released last month."
Which is exactly what I suggested in my original post also. They are now aiming at the right direction but still blind on the target.
----------------------Please note the word "recent". after the replacement of BRAG valve. Things keeps happening. Just like the filter and contaminants claims. That's just so fuzzy to me.-----------------------

f22spec wrote:

@Neurotech

To clarify what you're saying, if the airflow is interrupted to the intakes, the jet will continue to output bleed air and supply the pilot with OBOGS? If that's correct, are you getting this information from your knowledge of engines, or is there a source somewhere saying this? I apologize if this sounds like an accusation because it isn't, I'm just curious.

Well clearly Mr. Neurotech think that if only the engine is still spinning. The bleed air is not stopping. The OBOGS should works fine. Even if the bleed air pressure had dropped by 10 fold.

jamesli wrote:

Well clearly Mr. Neurotech think that if only the engine is still spinning. The bleed air is not stopping. The OBOGS should works fine. Even if the bleed air pressure had dropped by 10 fold.

Actually Yes to the first part. If the engine is still "spinning" then some bleed air will be produced, at a lower pressure. I don't think the OBOGS keeps working during with the engine windmilling on the way down. Having said that, the pilot usually shuts off the bleed air supply valve if the engine flames out, as part of a restart procedure.

I didn't say "OBOGS should work fine", It doesn't work properly, thats the problem. What I had previously said there was no OBOGS ICAW in these incidents.

Do we have any confirmation that an actually "Bleed Air" pressure drop is actually occurring in these "physiological incidents"?? There has not been a "Bleed Air" ICAW displayed in these incidents, yet the pilot is experiencing problems. The recent DefenseTech article didn't mention "Bleed Air". What the DefenseTech article DID say was that the partial pressure Oxygen (PPO2) output from OBOGS was dropping.

The F-22 DOES have a backup Oxygen System. What the Alaska crash AIB determined was that Capt. Haney was unable to activate it. The bottle is now larger, and the activation handle is also larger, and easier for the pilot to access.

Your understanding of Engine Pressure is mistaken, it is typically expressed as a ratio. The Engine Pressure Ratio varies with altitude and thrust. Remember, Bleed Air comes from the first stage COMPRESSOR and even at high altitude (60,000 ft) there is enough airflow to provide more than enough pressure for the Bleed Air for the OBOGS and ECS.

And That_Engine_Guy has previously confirmed my comment about the airflow vs bleed air. Here it is again:

That_Engine_Guy wrote:

I'd say it's not the fault of the motors providing insufficient air flow or pressure. If the engines were running out of air like that at high altitude and high AOA, they would likely compressor stall/stagnate long before bleed-air pressure/flow dropped below specification.

The pilot would know this from the loud BANG, or the loss of power in the motor(s). If anything, a condition like this would be indicated in the CSFDR or in the remaining engine control component memory. (Yes, if still somewhat intact, they can retrieve data from the engine control system chips after a crash!) It would have been obvious with any mishap that the engines had surged/stalled/flamed-out and contributed to situation.

I don't know much about the bleed-air system of the F119/Raptor, but I'm going to assume that both motors feed the common OBOGS? So that a single engine out situation would not affect Oxygen supply? This further reduces the possibilities that the Raptor's propulsion system 'slow/high' would ever be insufficient to supply the OBOGS - feeding from BOTH engines equally.

Shrug

TEG

Am I missing something?

neurotech wrote:

Do we have any confirmation that an actually "Bleed Air" pressure drop is actually occurring in these "physiological incidents"??

-------We don't have yet. What I think is this "Bleed Air pressure drop" is the only logical explanation.----------

neurotech wrote:

There has not been a "Bleed Air" ICAW displayed in these incidents

-------I know very little about these detail desgin. I just now assure that there is no proper ICAW design.-----------

neurotech wrote:

The Engine Pressure Ratio varies with altitude and thrust.

-------No. Technically, The pressure ratio of compressor is only decided by forward air speed/incoming air speed and engine RPM.---------

neurotech wrote:

Bleed Air comes from the first stage COMPRESSOR and even at high altitude (60,000 ft) there is enough airflow to provide more than enough pressure for the Bleed Air for the OBOGS and ECS.

-------I didn't know whether the bleed air is from the LPC or HPC. If it does from the LPC. Then thank you for this lesson. But that doesn't change my theory as I think the pressure drop at the LPC or HPC is both the same situation. "low air speed. high AOA. low ambient air pressure. will reduce the bleed air pressure, No matter it's being taken from the end of LPC or HPC"

neurotech wrote:

And That_Engine_Guy has previously confirmed my comment about the airflow vs bleed air. Here it is again:

-------Well I don't think the airflow have anything to do with air pressure. The OBOGS rely on the pressure to work. And from some point of view. for a fix sized air pipe. the pressure and flow rate is positively linked.

I think at this point the USAF will discover some linkage between the pulling Gs and oxygen drop. whether it's my theory is right or just some mechanical or software fault. What I really doubt is when they do find out. would they keep it secret or disclose it? This could be classified.

neurotech wrote:

cerberus wrote:

I think the APU automatically takes over if the engines go out. Wasn't the issue to do with G-suits and winter wear rather than the OBOGS anyway? Didn't they do centrifuge tests to prove this?

I thought procedure in dual engine failure was to switch to emergency oxygen. APU Bleed Air would be primarily used to restart the engines first. I'm not sure if the APU supplies Bleed Air to OBOGS in that case.

The centrifuge tests confirmed a faulty BRAG valve. The replacement BRAG value solved the respiratory issues, such as "raptor cough" but not the neurological issues.

In that case, I'm not really sure. I know that airflows can be a pain for separating into several flows, each of similar properties.

jamesli wrote:

neurotech wrote:

There has not been a "Bleed Air" ICAW displayed in these incidents

I know very little about these detail desgin. I just now assure that there is no proper ICAW design.

ICAW(S) = Integrated Caution And Warning (System). ICAWS, the System that is, works great, it prioritizes pilot attention to the most safety critical items first.

The Bleed Air pressure warning & leak detection system warning does work properly. The Bleed Air warning in the Alaska crash was resulting from a Center Bleed Air Duct leaking.

The OBOGS output pressure warning does work correctly. What does not work properly is that the OBOGS warning will not warn the pilot in case of a "Partial Pressure O2" drop at the OBOGS output.

jamesli wrote:

neurotech wrote:

And That_Engine_Guy has previously confirmed my comment about the airflow vs bleed air. Here it is again:

-------Well I don't think the airflow have anything to do with air pressure. The OBOGS rely on the pressure to work. And from some point of view. for a fix sized air pipe. the pressure and flow rate is positively linked.

I think at this point the USAF will discover some linkage between the pulling Gs and oxygen drop. whether it's my theory is right or just some mechanical or software fault. What I really doubt is when they do find out. would they keep it secret or disclose it? This could be classified.

The USAF have pretty much confirmed the OBOGS PPO2 drop, they just don't know if it can be fixed in software, requires a OBOGS re-design or other changes to the pilot Oxygen system. I think they'll release a statement regarding the ongoing investigations and solutions. The precise operational details will not be released publicly, as that is either Classified and/or "For official Use Only"

neurotech wrote:

The USAF have pretty much confirmed the OBOGS PPO2 drop, they just don't know if it can be fixed in software, requires a OBOGS re-design or other changes to the pilot Oxygen system.

Well I think the so called PP02 drop is in fact a result of insufficient oxygen production/lower than desired 02 concentration. Which is a result of input air pressure drop?
I really don't think it could a G force induced mechanical or software fault.
I should just wait to say what the air force investigation will find out next.

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The moepheus moon lander has inherent design flaw. It will never be a safe.

Forum: General F-22A Raptor forum

Theory about F-22 OBOGS solution