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I have a L4P and have been spending a lot of time at FL 240/250. I also investigated this as much as one can before getting comfortable up there. My comments are below. Jim Hergert
table of "Times of Useful Consciousness" <after losing pressurization> on the USAF flight surgeon guide...>
FL 180 20 to 30 Min
FL 220 10 Min
FL 250 3 to 5 Min
FL 280 2.5 to 3 Min
Two things to note are that these are "average" times and also that they are not to total incapacitation.
From listening to you all and reading on the net, I'd guess that most of the IV-P owners cruise between FL220 and FL260. I can't find any specs <anyone> online about the IVP emergency descent rates--I'd bet it was at least 2500 FPM when you drop the flaps, gear, and go up on a wing <of course assuming that you do it the same in a lancair as in a piper or cessna> I'm thinking you'd have plenty of time to get down to where you wouldn't have many problems flying your aircraft. FL200 does seem to be the "magic number" (I don't smoke at all.) But even after that..you would still have to get your bird down on the ground..preferably on an airport w/ paved runways..which brings me back to my original question.
How far could you expect to glide if you had to? Also, have any of you gotten your high altitude sign-off in a chamber? I'd be interested in it eventually if you felt that it was worth it as far as future recognition of the signs of the onset of hypoxia. IT just seems like a good idea but I've spoken to very few GA pilots that have actually gone through the process.
Tom, I'm definately with you on being pumped up on adrenaline--there is nothing quieter than hearing your engine "quit" all of a sudden and then just the whistling wind.
Thank you all for the information,
Adam
Time of useful Consciousness I was told was less than 2 min. at FL250, However, I had the experience of going through the Altitude chamber at Edwards Airforce Base with 25 other folks. I can briefly say that all the woman had to put on the Ox mask at 10K ft. and one guy had his lips turn blue and could not put on his own mask at 11K ft. I was writing and doing OK until about 19K ft. ,put the Ox mask on, and after that they started asking tricky questions. I had my Ox mask on and was stumped on half the questions. I had a fellow friend there that weighs 110 lbs and is just under 5 foot tall that was sharp and could answer all questions up to 28K ft. where they stopped the test and said he won. Then they do a rapid decompression which fogs up the chamber and your ears. But that is why you must take this test in the military so you know your own tolerance. Night time your affected altitude is lower by at least 5K ft.
Another time I was flying my A36 over the Sierra's and while climbing to 14K ft. I wasn't on Ox, I tried to follow a low ravine to give me more terrain clearance. It was more than 15 min. before I noticed that I had turned 90* from my intended track and I was not crossing the mountains, just flying along a ridge. I was looking at heading and Loran and still not aware. Scary thought.
L4P emergency descents? First, I hang the Ox mask around my neck and have it plugged in and tested before I take off into the FL's. With the pressurization controller you can select the rate of cabin altitude change you want from 250 to 1000 fpm. I have mine on 250 fpm. I normally trim descend at 1K to 2K fpm without changing any settings. I have tried 4K fpm descents without changing the engine and guess what? This airplane likes it. There is no problems. You don't come close to the 274 KIAS Vne. They teach you that you can't go over 225 KIAS at FL250 because your Mmo is .6 Mach. However, if you loose an engine and need to get down, don't worry about Mmo. I know two L4 pilots that have seen way over 300 KIAS (they won't tell me how much over). Also, I talked to one pilot/owner who had the door window blow out two different times at FL250. He didn't put on the OX mask just pushed the nose over and got it down to 15K in about 2 min.
The most likely failure to have is either a window break or a Turbo hose fail.
My procedure will be to push over the nose to at least 5K fpm, watch the airspeed, use the speed brakes if needed, close the incoming pressurization valve, and last put on the OX mask.
I know that if you pull the engine back to idle you loose pressurization fast. I think the outflow valve will do -250 fpm but the inlet valve will need to be closed very fast to stop the back flow. Has anyone tried this test on the ground? If anyone is pressure testing on the ground and one is inside the cabin please try to close the inlet and have the outflow set at its lowest rate and see how long it takes for the cabin altitude to go down. I would like to know for sure if closing the inlet value works?
The Gliding distance. In the SFS EFIS you put in a ratio that is displayed at a round circle modified my winds and terrain. I have 11 to 1 in mine but I know that is with the Prop pulled to course pitch. You must have oil pressure to do this. Also, I know that if you have a Full Feathering Prop Stopped, the glide ratio goes up to over 20 to 1. That is a long way when at 250, which I don't want to test.
Inputs appreciated,
Jim Hergert
N6XE, "An Sex Y" L4P
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