Forum: General F-22A Raptor forum

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).

That's what I thought. It would be an unusual "physiological incident" for a pilot to not notice a loud BANG from the engines.

That_Engine_Guy wrote:

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

According to the AIB, What happen in the Alaska crash was an indicated DUAL BLEED AIR failure, that shut down the supply to the OBOGS, and the OBOGS itself shut down and caused a suffocating feeling by the pilot before he crashed.

The OBOGS shutoff, with ICAWS, is different to the physiological incidents which came to light after the crash, that are a different cause, and apparently have not resulted in any ICAWS faults being recorded. These ICAWS are recorded to the CSFDR.

Thanks for your insight TEG

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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

Hi pale. I am saying not the compressor stall. let's say if the f-119 ENGINE have a compression ratio of 20. and subject to low or still air speed with only 10% of sea level air pressure. Then the bleed air can reach only 200% or 300% of sea level air pressure.
But this still enough to make the engine run normally.(Provide much much less thrust of course)

jamesli wrote:

Hi pale. I am saying not the compressor stall. let's say if the f-119 ENGINE have a compression ratio of 20. and subject to low or still air speed with only 10% of sea level air pressure. Then the bleed air can reach only 200% or 300% of sea level air pressure.

James,
I was the one who posted that I doubted that it was insufficient airflow into the engines causing problems with the OBOGS, because in a case of insufficient airflow to the engines, there would be a compressor stall well before the loss of bleed air would cause the OBOGS to fail. If bleed air supply is compromised, a very noticeable "BLEED AIR" caution warns the pilot before OBOGS failure. The Crash Survivable Fight Data Recorder would record both the BLEED AIR & OBOGS failure. This is what happened in the Alaska crash.

jamesli wrote:

But this still enough to make the engine run normally.(Provide much much less thrust of course)

The engines wouldn't run normally. When an engine has a reduction in thrust due to disrupted airflow(or malfunction, low fuel flow) it is called a "roll back" and engine RPM is reduced. If the disrupted airflow is not corrected quickly it will result in a compressor stall and flameout. The F119 engine has excellent airflow characteristics compared to earlier engines (eg. TF-30 in the F14A) so even high altitude/slow flight wouldn't cause a rollback, much less bleed air problems.

As posted previously, I think the theory about the Combat Edge flight gear being improperly fitted is quite possible.

Hey guys. It's jamesLi here again. After so many months and the F-22's oxygen problem is still no totally addressed. You know why is this? Because I just don't have the phone No. of the F-22 project manager or some generals of USAF. If Give me 2 minutes to talk to some of these guys. I can make them get it right in minutes. any way the reason I am here back again to post is there is news came out saying I made it very right. Almost proved my theory in someway.
here it is go ahead and read this please:

http://www.military.com/daily-news/2012 ... ckpit.html

"As the aircraft descends and the pilot puts eight Gs on the aircraft, the percentage of oxygen produced by the Obogs is reduced," the report says. "As the pilot reduces the G load, the Obogs begins to recover and then the percentage of oxygen produced by the Obogs is reduced again when the pilot reapplies the Gs."

The report says, "The amount of oxygen being produced does decrease to between 60 percent and 70 percent."

I am not an arrogant man. BUT I JUST WANT TO SAY A BARE TRUTH HERE: FOR THE f-22 oxygen problem. ONE CHINESE GUY HAD JUST BEAT THE ENTIRE LOCKHEED ENGINEERING TEAM in 3 minutes.

I'm sure Gen. Mike Hostage, USAF, Commander of Air Combat Command who is qualified to fly a F-22, also checks his email. A smart guy can often figure out what email address is for even senior USAF personnel are Very Happy

If the Gen. responds, thats another story in itself.

I see a flaw in your comment. It was not HIGH and SLOW flight that induced the OBOGS output deficit. A F-22 can manoever at high altitude and not bleed airspeed like other jets. This is due to having thrust vectoring engines. The problem wasn't technically "extreme" altitude related, but related to the OBOGS "oxygen" output under high G loads.

Saying "Use LOX bottles would solve the problem" is technically correct except that operationally, when a F-22 (Or any fighter pilot) goes to emergency Oxygen supply, that is a knock-it-off event except for real combat emergencies. The pilot at that point ceases pulling High-Gs

The short version is something like this. Air contains a mixture of primarily nitrogen and oxygen. OBOGS enhances the oxygen concentration in the bleed air by filtering mechanism. If the oxygen concentration into the oxygen mask is reduced, the effect is difficult for humans to handle. The pilot(human) will become hypoxic. It is fatal for a human to inhale 100% nitrogen for any length of time. Due to the lack of inhaled CO2, the human doesn't feel breathless, they pass out. An SpO2 alarm will alert the pilot, in time to switch to 100% [emergency] oxygen and recover the jet.

In the F-22 case, some smart people decided NOT to mix the OBOGS air. The report says. "Unlike most other aircraft oxygen generation systems, the breathing air to the F-22 pilot is not diluted with cockpit air to obtain the appropriate oxygen partial pressure (PPO2) necessary to maintain physiological function at a particular altitude". That is fine, except that it places additional demands on the OBOGS, compared to previous jets. What the problem is that under medium altitude, high G conditions, the OBOGS is still cycled to maintain software scheduled PPO2 but isn't matching the demanded PPO2 at the pilots mask, after the regulator. That is a combination of software regulating PPO2 and the design used.

I suspect that your confusing two major issues here;
1) The "raptor cough" etc. was substantially caused by the Breathing regulator/anti-g (BRAG) valve. This has been addressed with replacement valves and education on Combat Edge vest fitting instructions.
2) Neuro-physiological issues that remain. This is what I commented on above.

neurotech wrote:

I'm sure Gen. Mike Hostage, USAF, Commander of Air Combat Command who is qualified to fly a F-22, also checks his email. A smart guy can often figure out what email address is for even senior USAF personnel are Very Happy

If the Gen. responds, thats another story in itself.

I see a flaw in your comment. It was not HIGH and SLOW flight that induced the OBOGS output deficit. A F-22 can manoever at high altitude and not bleed airspeed like other jets. This is due to having thrust vectoring engines. The problem wasn't technically "extreme" altitude related, but related to the OBOGS "oxygen" output under high G loads.

Saying "Use LOX bottles would solve the problem" is technically correct except that operationally, when a F-22 (Or any fighter pilot) goes to emergency Oxygen supply, that is a knock-it-off event except for real combat emergencies. The pilot at that point ceases pulling High-Gs

The short version is something like this. Air contains a mixture of primarily nitrogen and oxygen. OBOGS enhances the oxygen concentration in the bleed air by filtering mechanism. If the oxygen concentration into the oxygen mask is reduced, the effect is difficult for humans to handle. The pilot(human) will become hypoxic. It is fatal for a human to inhale 100% nitrogen for any length of time. Due to the lack of inhaled CO2, the human doesn't feel breathless, they pass out. An SpO2 alarm will alert the pilot, in time to switch to 100% [emergency] oxygen and recover the jet.

In the F-22 case, some smart people decided NOT to mix the OBOGS air. The report says. "Unlike most other aircraft oxygen generation systems, the breathing air to the F-22 pilot is not diluted with cockpit air to obtain the appropriate oxygen partial pressure (PPO2) necessary to maintain physiological function at a particular altitude". That is fine, except that it places additional demands on the OBOGS, compared to previous jets. What the problem is that under medium altitude, high G conditions, the OBOGS is still cycled to maintain software scheduled PPO2 but isn't matching the demanded PPO2 at the pilots mask, after the regulator. That is a combination of software regulating PPO2 and the design used.

I suspect that your confusing two major issues here;
1) The "raptor cough" etc. was substantially caused by the Breathing regulator/anti-g (BRAG) valve. This has been addressed with replacement valves and education on Combat Edge vest fitting instructions.
2) Neuro-physiological issues that remain. This is what I commented on above.

Hey man. So nice to see you again. I am not a neuro scientist and not sure why you are saying is. But you know. The most direct and positive fact the news saying. Is when the aircraft dive (like from 26000feet)and pulling 8G maneuver. the output oxygen of the Obogs is reduced by 40% to 30%.

This is perfectly match to my theoretical prediction. which is : low speed high G high altitude all leads to engine core pressure drop. and leads to obogs output reduction.

(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)

for the obogs. the higher the pressure differential. the better the air separation capacity. Very Happy

you can see. a medium altitude high G maneuver already causes 40% drop in oxygen output. what would it be for a high g maneuver or even stall in 30000 to 40000 feet.

Can we separate "air show" F-22 from a "combat" F-22 please?

Pulling 8Gs in most jets for any length of time(2-30 seconds) seconds isn't a low-speed maneuver, this is true for the F-22 as well. The F-22 just can maintain the maneuver as it has a high t/w and thrust vectoring. Previous jets, like the F-16 in A/A config can do a 8G turn, and actually increase airspeed in certain parts of the flight envelope.

Secondly, they did NOT say that there was a reduction in bleed air output under G load that was the cause. They only said the "oxygen" concentration (Partial Pressure O2) from the OBOGS output was reduced under G load. They have the engine control computer's data recorder to confirm the engine bleed output. A F-22 pilot could be at zero airspeed(post stall thrust vectoring) and still get the full bleed air output at a high altitude.

Third, The neuro-physiological issues currently experienced are not an extreme high altitude (eg. at 60,000 ft) phenomenon, they can and do happen at 25,000 ft to 40,000 ft, which is a more typical fighter jet operating altitude.

Hi there pale. @neurotech

You just didn't get it. What I said in my post is
----------
So why other aircraft have no oxygen problem and the F-22 does?

The answer is clear: They are all not designed to fly at high altitude. They can’t perform

violent maneuver at high altitude like F-22 dose. Especially the high AOA, low speed and post

stall maneuver.
----------
see, ofcourse I know to pull Gs a plane must have enough kinetic energy/air speed. and at

centain altitude a good steedy turn can be achieved without lossen air speed.
Let me explain my theory again.
How much pressure the engine can build inside the engine core is decided by engine RPM/ ambient

pressure/ air speed/ and AOA. This core pressure will decide the bleed air pressure which then

decide the OBOGS output capacity.

1: the higher the engine RPM. they higher pressure the compressor produce
2: if we say it's stall status and 0 airspeed. then no matter how much the engine RPM is. the

max air flow rate/core pressure is only decided by the ambient pressure. The engine is like a

black hole. it sucks in surrounding air. but this suction force is from by the surrounding air

pressure in fact.
3: for a certain low ambient pressure level. the air speed which is the amount of extra air

rushing into the intake channel. will decide the flow rate of the engine compressor/core

pressure
4: the angle of the intake channel to the incoming air. at high G. the AOA of the intake

channel to the incoming air is high. This will reduce the ramming effect by some level. and to

reduce the flow rate of the engine compressor/core pressure.
the other factor is the increased oxygen demand of the pilot during high G maneuver . for

example : the anti G mussel contraction act

To you second question.
They said the OBOGS's output oxygen is reduced by 40%. So if it isn't my theory to explain this

phenomenon. What would you suggest the causes to this phenomenon? they checked every mechanical

parts including the valves. That's not the causes.

And I need to ask that if you know it or not. That what is OBOGS's working principle?

neurotech wrote:

Can we separate "air show" F-22 from a "combat" F-22 please?

Pulling 8Gs in most jets for any length of time(2-30 seconds) seconds isn't a low-speed maneuver, this is true for the F-22 as well. The F-22 just can maintain the maneuver as it has a high t/w and thrust vectoring. Previous jets, like the F-16 in A/A config can do a 8G turn, and actually increase airspeed in certain parts of the flight envelope.
....

And ofcourse the steedy turn can only achieved at certain altitude and condition. For most turns. the plane lose air speed.

jamesli wrote:

So why other aircraft have no oxygen problem and the F-22 does?

The answer is clear: They are all not designed to fly at high altitude. They can’t perform violent maneuver at high altitude like F-22 dose. Especially the high AOA, low speed and post stall maneuver.

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.

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.

jamesli wrote:

----------
see, ofcourse I know to pull Gs a plane must have enough kinetic energy/air speed. and at

centain altitude a good steedy turn can be achieved without lossen air speed.
Let me explain my theory again.
How much pressure the engine can build inside the engine core is decided by engine RPM/ ambient pressure/ air speed/ and AOA. This core pressure will decide the bleed air pressure which then decide the OBOGS output capacity.

1: the higher the engine RPM. they higher pressure the compressor produce
2: if we say it's stall status and 0 airspeed. then no matter how much the engine RPM is. the

max air flow rate/core pressure is only decided by the ambient pressure. The engine is like a

black hole. it sucks in surrounding air. but this suction force is from by the surrounding air

pressure in fact.
3: for a certain low ambient pressure level. the air speed which is the amount of extra air

rushing into the intake channel. will decide the flow rate of the engine compressor/core

pressure
4: the angle of the intake channel to the incoming air. at high G. the AOA of the intake

channel to the incoming air is high. This will reduce the ramming effect by some level. and to reduce the flow rate of the engine compressor/core pressure.
the other factor is the increased oxygen demand of the pilot during high G maneuver . for example : the anti G mussel contraction act

Yes, intake airflow can affect the engine, but it would have to be a really bad disruption to cause ANY PROBLEM with bleed air. The engine will make a loud bang when intake airflow is insufficient, before bleed air output is effected.

jamesli wrote:

To you second question.
They said the OBOGS's output oxygen is reduced by 40%. So if it isn't my theory to explain this phenomenon. What would you suggest the causes to this phenomenon? they checked every mechanical parts including the valves. That's not the causes.

And I need to ask that if you know it or not. That what is OBOGS's working principle?

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.

OBOGS units use zeolite molecular sieve to filter nitrogen out of the supply (bleed) air, which is at a high pressure, and then supply it to the breathing regulator (aka BRAG valve)for the pilot. Part of the problem is the OBOG unit is allowing excessive nitrogen to seep through under high G-load, causing hypoxia in pilots.

The other problem is the software that controls how much oxygen the OBOGS unit produces, according to a programmed schedule based on altitude.

@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.

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?

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.

Not exactly. I'm saying that if the F-22 pulls high-alpha, the engines keep running, complete with bleed air. Disrupted (turbulent) airflow at high-alpha isn't going to induce a compressor stall in a F-22.

The above is not the same for older jets, like the F-14A. A VF-101 F-14A had an ACM mishap due to a dual compressor stall. I don't think the F-14A had OBOGS, but pilot & RIO were a little more concerned with the rapid loss of airspeed and altitude. They ejected safely. Loss of bleed air, preventing a cross-feed restart was a factor in the mishap.

IF the F-22 does have a compressor stall (Has there even been a documented compressor stall in a F-22?) It is obvious to the pilot, and thrust from the engines(s) will be lost. Bleed air supply from the affected engine will be lost. The pilot will get the appropriate ICAW warnings in the HUD if the engines fail, or if Bleed Air is lost, and if a dual bleed failure, within seconds OBOGS warning.

There has not been any evidence to suggest that engine issues is to blame for the F-22 physiological issues. There is a digital recorder in the engine & flight computer which would alerted the investigators if this was the cause.

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.

Forum: General F-22A Raptor forum

Theory about F-22 OBOGS solution