"Yeah. See, we plan ahead, that way we don't do anything right now. Earl explained it to me." - Tremors, 1990
In your 777 trip to Heathrow, the cabin altitude is typically 7,000 to 8,000 feet even with the jet at 40,000'. Everyone gets along fine w/o oxygen masks. Loss of cabin pressure, and you get the rubber jungle in back, lots of screaming and panic.
Military jets also have cabin pressure. An Eagle at 50,000' will have a cockpit ambient equivalent to the high teens IIRC. I can look up the pressurization schedule, but the actual numbers are not important. What is, is the fact that normal operation will have the pilot breathing ambient cockpit air enriched with a bit of pure O2 to keep him physiologically near sea level. Not doing so promotes slow reflexes and reduced performance. And the cockpit air is "turned over" very quickly using bleed air from the engine compressors.
Put a big hole in the canopy, like from a shell, and the cockpit goes unpressurized. The O2 system automatically goes into overdrive, boosting O2 delivered to the pilot. It is in those circumstances that a pilot will begin to pressure breathe in the mid 30's and higher. Above about 50,000', loss of cabin pressure w/o a pressure suit can result in fatal bends regardless of the O2 system, which is why (at least in my day) peacetime flying above 50,000' was prohibited. The risks were too great. This is also why U-2 and SR-71 pilots wear partial or full pressure suits. Without them, it'd be instant death from decompression if the system loses cabin pressure.
Speed has little to do with O2 use and consumption.
Last edited by Chogy; 15 May 12, at 13:34.
From your description, if the cockpit is pressurized to a near constant altitude the problem still has got to be with the OBOGS. What is the source of the air going into the OBOGS?
It's pure speculation on my part but it seems to me also significant that hypoxia problems have not emerged until several years after initial operation. I wonder if there is an actual increase in the rate of hypoxia incidents with aircraft age. If so, it seems to me that if the zeolite material used in the OBOGS was not effectively decoupled from the external environment then continuous operations at high G loading and in a high altitude environment could lead to earlier than expected degradation of the material and unexpected failure modes. On the other hand if this was the case the Air Force should have figured out the problem as soon as they cut apart the zeolite and put it under an electron microscope. So that's probably not it.
Another source of problems could be that there was a very subtle change in the preparation of the material. It could be as simple as somebody switching to a different mine for the starting raw materials. It is possible to get a case where your materials look exactly the same on your manufacturing tests but end up behaving differently than the material used in the original tests. I have heard of these problems occurring in nanotechnology research and the zeolites are class of materials that function at the nanoscale.
A very perplexing problem and one that no doubt needs to be solved if future aircraft systems will continue using these systems.
Last edited by citanon; 15 May 12, at 22:36.
Citanon, I cannot speak with authority on the F-22 system, but I can guess.
Almost all jets use bleed air from one (or both) compressor sections of the engine(s) to provide pressurized air for a number of purposes. Some of it goes into the cockpit ambient air after being cooled and probably filtered to provide cabin pressure. Some of this air gets into the pilot's lungs with each breath during normal operations, mixed with some O2 from the OBOGs, unless 100% O2 is selected, in which case it is ALL OBOGs product.
Possibility: The F-22 may have a more advanced system than earlier jets, whereby ALL air entering the mask may be generated by the OBOGs, none of it being mixed with ambient (cockpit) air.
Additional engine bleed air undoubtedly goes into the OBOG system, whereby nitrogen is removed and the concentrated O2 is injected into the regulator (mask) system, the percentage undoubtedly driven by system demand.
As for the OBOGs itself, I am unsure how (exactly) it operates. I don't think there is any sort of CO2 scrubbing or recirculation... the heart of the machine is the (to me, miraculous) device that concentrates O2. Same sort of system sold to folk with emphysema. Portable O2 concentrators. But you may know far more than I do about these sorts of systems. In the end, the air the pilot breathes gets routed through a number of devices and pipes before it enters his lungs, and any chemical contamination has a number of possible entry routes. Even something as simple as the engine bleed valve may be a culprit... if lubricants or hydraulic fluids leak into the air, it can contaminate the whole works.
The thing about hypoxia symptoms is that they can be pretty obscure. Everyone has different symptoms, everything from dizziness to tingling, numbness, slowed reactions, even some euphoria, and these parallel symptoms from some chemicals, no doubt. That is why I think my suggestion may have some merit. Even if it is only a stopgap - install a small, say 40 cubic foot 3,000 PSI pure aviators O2 bottle in the jet, and have an emergency valve that will allow the sick pilot to bypass all onboard O2 systems and breathe ONLY the bottled air. This will allow recovery of the jet, and give some peace of mind, while the remainder of the system is investigated.
One thing that I don't think has been mentioned is that these jets aren't spending a whole lot of time at 50k+ feet. There's just no reason for it on a training mission. The benefits to altitude are speed and missile range...non-factors in most training sorties where you're not allowed to break the sound barrier anyway and you're just going to burn extra gas getting above the 20/30s.
When I grow up I want to be Ed Harris
Looks like all of our guesses may have been wrong.
Flight suits behind F-22 pilot sickness? - CBS News
June 13, 2012 11:27 PM
Flight suits behind F-22 pilot sickness?
(CBS News) Pilots flying the U.S. military's most advanced fighter jet, the F-22 Raptor, had been getting sick at the controls, and much of the focus toward finding the cause has been on the plane itself.
Now, however, Air Force investigators say the specialized flight suit pilots wear in the F-22 could be at least partially to blame for the oxygen deprivation experienced in flight.
Officials tell CBS News correspondent David Martin that tests carried out in a flight-simulating centrifuge replicated hypoxia-like conditions for pilots wearing the suits. The link to the suits was first reported by CNN on Wednesday.
As "60 Minutes" reported in May (video), the Raptor - the most expensive fighter ever - has been plagued by a mysterious flaw that causes its pilots to become disoriented while at the controls from a lack of oxygen.
Pilots of the stealth fighter have complained that those oxygen-deficit problems have resulted in pilot dizziness, blackouts and other symptoms.
Martin reported that, according to the Air Force, there have been 22 unexplained cases over the past four years in which pilots experienced symptoms of oxygen deprivation.
The F-22 was grounded last year while engineers searched for something that could be contaminating the cockpit air, but the Air Force returned it to flight, sending the F-22s to the Persian Gulf, without finding the cause.
Now, investigators are zeroing in on a part of the flight suit called the "Combat Edge," which "hampers breathing and causes oxygen loss when combined with a physiological condition that collapses air sacs in the lungs," CNN reports.
The Air Force report is also expected to state that another possible problem for pilots is a condition called acceleration atelectasis, which causes a pilot's lungs to not effectively deliver oxygen to the bloodstream. The extreme effects of g-forces along with the pure oxygen breathed by pilots could lead to the condition.
Following the "60 Minutes" report, Secretary of Defense Leon Panetta limited the flights of the F-22 fighter jet to regions where pilots can quickly land the plane if they experience oxygen problems, and also ordered the investigation into the oxygen deprivation problem. The report detailed above is just the first of the monthly updates expected from the Air Force on the problem.
Watch the full "60 Minutes" report below
© 2012 CBS Interactive Inc.. All Rights Reserved.
I don't know about ground crews, but we may have reached the physiological limit for human flesh in an aircraft. Not until the F-15/16 did we have aircraft capable of such sustained g-loads, and what this can do to the human body, long-term, is still a bit of a mystery. I remember the physiological expert at the centrifuge stating "under 9 G, your heart will descend 6 inches in your chest cavity." Uh, we didn't need to hear that.
Combine freakish levels of instantaneous acceleration with "combat edge", a device designed to compress your chest and abdomen while simultaneously forcing pressurized gas into your lungs, and it's a near miracle that more pilots don't simply keel over from embolysms, strokes, and other maladies.
Almost every pilot has had encounters with g-loc, g induced loss of consciousness. I once lost it pitching out in the overhead pattern. 2/3 of the way through a 180 degree turn at 1,200', I blacked out. The only thing that saved my life was the fact that I had a slight upward vector when it happened. I woke up beaming out across the base in a slight climb, with tower asking me where I was going.
Anyway, the F-22 folk need to approach this systematically. Isolate the problem by incrementally removing suspect systems. Take a sample of jets and do the bottled O2 thing. Another sample would leave combat edge behind, go back to the older system. This has gone on long enough!
added: Combat Edge has been around since the late 1980's. Unless the system in the F-22 is different from those in other aircraft, it isn't CE.
Last edited by Chogy; 15 Jun 12, at 13:55.
NASA says F-22 problems are caused by too much Oxygen, not too little.
NASA Decodes Trouble With F-22
September 14, 2012
Rather than receiving too little oxygen, the pilots of one of the world’s most advanced fighter aircraft could be taking in too much, according to a NASA assessment of the F-22 ’s life support system.
Pilots of the Raptor have for years experienced breathing difficulties and something now called “ Raptor cough.” The Air Force launched serious investigations into the problem in 2008, after pilots reported an increasing number of “hypoxia-like symptoms.”
Since that time, the Air Force has pointed to a “mosaic” of interrelated problems in the cockpit.
Independently, the NASA Engineering Safety Center conducted its own assessment, and principle engineer Clinton Cragg presented the findings during a House Armed Services Committee hearing Sept. 13. The assessment found that a high concentration of oxygen at low altitudes can lead to “absorption atelectasis,” in which too much oxygen can wash away necessary nitrogen within the lungs and cause lung tissue to collapse. The effects of high oxygen levels are compounded by the aircraft’s “inevitable acceleration,” Cragg said.
“Inappropriate inflation” of the pilots’ upper pressure garment further restricted breathing and reduced overall cardiac output, Cragg’s testimony said. In addition, “uncharacterized F-22 life support system vulnerabilities, such as pressure drops across components in the cockpit,” contributed to the trouble.
Cragg’s testimony also took issue with the F-22 pilot community’s reaction to the aircraft’s problems. “Differences in pilot breathing in the F-22 from other platforms was widely known and accepted as a normal part of flying the advanced aircraft,” Cragg ’s testimony said. “The acceptance of these phenomena as ‘normal’ could be seen as a ‘normalization of deviance.’” That is a NASA term of art to describe the lower standard of excellence accepted on components of the Challenger before the shuttle’s devastating explosion.....
^^ Makes some sense. The life support / physiology folk are being too clever with all these gadgets. Go back to simplicity - standard G-suit, standard mask, as used since Vietnam. Get rid of combat edge if it is causing problems.
There are systems already tested that recover a fighter in the event of G-LOC. The device senses the G-LOC, engages the autopilot, and executes a perfect recovery to straight and level, allowing the pilot to recover naturally.
There are currently 1 users browsing this thread. (0 members and 1 guests)