I have the TAS subscale on the IAS but it wasn’t set correctly (the reading is showing 155).
Assuming zero instrument and position error, 129 KIAS would be 135 KTAS at 4000 ft and +1°C.
Practically, modern oxygen systems using the MH O2D2 electronic demand regulator work well above 18k, delivering 95% blood oxygen at FL200 (I’ve tested this many times on various people).
Yes they do. Until they don’t. There was a hypoxia related fatality, I think two or three years ago, ago involving a highly experienced flight instructor who habitually flew alone at those altitudes using cannulas (not sure if O2D2 or not) who got away with it for years until one day he didn’t and died.
Also, as is well known, one of the problems with hypoxia is that it is very insidious and, unless you measure your sats regularly, it’s easy for it to creep up on you without you realising that it is affecting you. In addition, different people have different levels of tolerance. For example Reinhold Messner climbed to over 29000 ft to the summit of Everest without supplementary O2.
Apart from the question of O2, if I’m not mistaken, there’s also another issue: aren’t you supposed to have pressurised magnetos above 18000?
Doesn’t that just boil down to a discussion on where to draw the line?
I have flown with an instructor who could not read the altimeter at 12000ft, so making the wearing of a cannula above 18k a criminal offence would not have done him much good. At the other end of the scale, Messner was spectacularly fit (probably in the top 0.01% of the human population) and did years of high altitude climbing before he did that.
Interesting point about mags… I don’t know of such a reg. Does the TB21 (TIO-540-AB1AD, FL250 ceiling) use a pressurised D3000 mag? The need depends totally on the clearances inside the mag. For any given flashover voltage, at 18k (500mb) you need about 2x more clearance than at sea level.
Finally, almost nobody flies unpressurised above about 10k unless
You’re right to say it depends where you draw the line. The problem is you don’t really know where the line is until you cross it and, because hypoxia works in the way it does, you also don’t know when you are approaching it unless you measure your sats.
Finally, almost nobody flies unpressurised above about 10k unless it’s required to stay VMC on top, or you are flying a Mooney Acclaim, on expenses, and want to see the highest possible TAS
Actually, I do fly above that habitually in a SR22 N/A. On a flight of anything over about two hours, I fly at 16000 or 17000 with typical numbers between 10.4 GPH =154 KTAS and 13.1 GPH = 166 KTAS always LOP.
I forgot about terrain also (edited my post).
At what altitude do you get the best speed, and best MPG?
Still air MPG ie TAS / GPH the best I get is between 21.5 and 22.5 (imperial 
) and always high (17000). I am usually happy to sacrifice a few knots for lower consumption and lower temperatures. After all, an extra 15 KTAS only saves about 10 minutes on a two hour flight and the extra couple of GPH I would have to burn costs something like an extra £30 in fuel and I could afford the landing fee at Shoreham for that (you really need a little devil smiley…..)
I log consumption and performance on most of my flights and looking at them now, the top 120 flights for stIll air MPG are all above 10000. My best flight at 10000 gave 12.4 GPH, 161 KTAS and 17.9 MPG.
The best MPG for most non-turbocharged piston aircraft that burn petrol (avgas), stochiometric, should be at 8000-10000ft.
If you are getting it at say 16000ft that is really curious. It would be due to some second order effect but I wonder which one?
I too fly at best economy which is about 140kt IAS low level, and it turns out to be ~ 140kt TAS at higher levels. Higher up, 17000ft and above, one has to go to best-power (130F ROP) and then the MPG drops, at least 10% (I posted some data here recently).
BTW (and I know you were just winding me up about this) the Shoreham landing fee, about £30 and much slagged off on the main Brit anti-Shoreham aviation chat site is not relevant. What is relevant is the difference between that figure and the landing fee of the alternative(s) And there aren’t many alternatives in that part of the UK that are in a good condition. My usual alternate is Biggin which is even more, plus some £100 for a taxi to get back home, plus another £100 for a taxi to collect the aircraft (because Biggin has no useful public transport). Lydd is a £150 taxi (2010 price) each way and is totally in the back of beyond. Bournemouth is 2 trains. Southampton has very little parking (not sure of the exact situation for PPR and longer term parking since they kicked out piston GA some years ago). Shoreham is running at about 75% of its permitted annual movements so there is no scope and no business incentive to reduce prices – whatever one’s opinion is on the landing fee. If Redhill got a hard runway (their application failed; Biggin’s campaign to block the application not helping!) that would transform the situation (which presumably is why, in the best UK GA tradition, Biggin tried to block it ).
My usual alternate is Biggin which is even more, plus some £100 for a taxi to get back home, plus another £100 for a taxi to collect the aircraft
Just a thought, but it’s probably cheaper to rent a car if you can get one delivered.
I was just being a bit devilish about Shoreham. I don’t have a dog in that fight as it’s not somewhere I need to go to and I do follow your logic about the commercial realities there.
As far as the consumption I get goes, the only thing I can think of is that I do fly very lean of peak and the settings I use at the different altitudes may not be comparable. Anyhow, it works for me.
…OK, modest proposal: move the “training wheel” back under the rudder where it belongs, add a decent set of tyres and never pay another landing fee or taxi. Just land where we want to go – everywhere is an airport…BTW (and I know you were just winding me up about this) the Shoreham landing fee, about £30 and much slagged off on the main Brit anti-Shoreham aviation chat site is not relevant. What is relevant is the difference between that figure and the landing fee of the alternative(s) And there aren’t many alternatives in that part of the UK that are in a good condition. My usual alternate is Biggin which is even more, plus some £100 for a taxi to get back home, plus another £100 for a taxi to collect the aircraft (because Biggin has no useful public transport). Lydd is a £150 taxi (2010 price) each way and is totally in the back of beyond. Bournemouth is 2 trains.
Of course, TAS drops to 110 kt or less, so the time we previously enjoyed waiting for and sitting in bus/train/car/taxi is now wasted sitting in an aeroplane watching the world go by. There had to be a catch!
ATB, Peter.
Or get one of these.
I must say, for certain places this would be fun. Just not in Europe, would be utterly useless here.
