My highest is Gunnison, Colorado, one up in a Pa28-161, departing with half fuel. The engine was at the end of its life – I got a discount for using up it’s last hours. 7,600’, the air felt comfortably cool in a T-shirt so temp was above the standard atmosphere.
As a student was doing circuits in a C182, I used the same runway direction, towards the mountains, and made a low level turn away from them as the ground was rising faster than my climb rate.
Plan was to land straight ahead if not at a reasonable height 200 metres after lift off, turn round, and, after talking to the C182, take off towards the valley. The runway is long, and not busy outside the skiing season.
Obviously this is why a turbo is a popular accessory for high altitude operations, but most of the aircraft types which are popular for these (mostly taildraggers) don’t have turbos.
What I find is that the general performance of the plane is quite important to consider. If you have a low power SEP which has a service ceiling of 10’000 ft, you can just about imagine what will happen if you try to take off at 8000 ft DA. Mine for instance has 17’000 ft SC and will climb quite nicely even at 8000 ft DA at max power, even though it’s only got a carburetted O360. With the same engine, other planes only have maybe 12k ceiling.
Still, even with long runways, take off roll is often considerable. At Samedan, calculated ground roll can approach 1000 m. Once you are airborne and cleaned up, your climb rate is likely to be covered by the POH. I usually see about 500 fpm during climb until reaching the crossing heights for most passes. Usually I fly in direction East and cross at the Flüela, with take off 03 it usually works out well enough.
In places like Samedan, your problem is not the takeoff roll. With these long runways, you will get airborne at some point. The problem is the anemic climb performance, often in a confined space with mountains all around. And where there are mountains, there are downdraughts, like the Malojawind, which has hit several low performers in past years.
Takeoff roll increases about 10% for every additional 1,000 feet of density altitude.
My POH does not cover my high DA operations (and my previous plane did not have a POH in any comprehensive sense).
How do people plan their takeoff performance, when going to these high altitude airports? The POH may or may not cover it.
Mooney_Driver wrote:
I always found it irritating that while auto mixture is something you can find in rotary engines quite a lot (the AN2 has it and I understand also quite a few western engines) this was never attempted for GA airplanes. It should be feasible, so why has nobody ever bothered to do it?
Autolean is existing and STC for many common types, even for your M20C:
http://flightenhancements.com/auto-lean.html
Silvaire wrote:
The Bing CV carb equipped Rotax will adjust mixture with density altitude to a degree all of its own, so there is no strong reason for a manual mixture control.
I always found it irritating that while auto mixture is something you can find in rotary engines quite a lot (the AN2 has it and I understand also quite a few western engines) this was never attempted for GA airplanes. It should be feasible, so why has nobody ever bothered to do it?
The Bing CV carb equipped Rotax will adjust mixture with density altitude to a degree all of its own, so there is no strong reason for a manual mixture control. The technology was developed by SU in England in the 1920s, and used on cars from then. In the late 60s-on implementations (Bing, Keihin, Stromberg, all introduced at that time) the slide is sealed with a rubber diaphragm instead of the original SU close clearance fit, and if the rubber diaphragm does split the throttle closes regardless of throttle position. That’s why the Rotax has two carbs – when one carb fails you still have 50% power (or close).
I wholeheartedly agree with Silvaire here.
Of course I understand that for some aircraft and engines, engine monitors are vital, but this cannot be generalised as a requirement.
What would I do if I took off with a Rotax powered A210 from an airport with a DA of say 8000ft? The A210 has no manual mixture control. It has a variable pitch propeller though.
I have never departed from an airport situated higher than 300ft AMSL, so I’m genuinely wondering how one would handle such high DA operations without influence on the mixture.
