I haven’t had to take off from a density altitude between 6000 and 9000 feet. But it may happen this summer. I was wondering how to lean to 125 degree ROP on the ground prior to take off. I can enter the runway, then engage brakes, go full power, full rich, lean until peak EGT, then enrich to 125 ROP. But this procedure may take up to a minute, and it is not advisable to go full power while brakes fully engaged. Not good for prop and engine. Alternatively, I could look up ROP fuel flow for the altitude for 75% power from POH (perhaps rounded up to be on the safe side), which is quicker to lean to, perhaps just 5 seconds. Also, at 6000 feet, I am still able to generate more than 75% power, so I have to be careful not to lean beyond 125 ROP. So how do I go about this? My engine is a Lycoming IO-540. Thank you!
Lean to ROP by fuel flow and after takeoff pitch for cruise climb speed as soon as feasible, else the modern reliable technology of the lycoming will overheat very quickly. Depending on the airport location you may have to choose between an overheat and a mountain face / ridge…
Why not do a full power climb at the planned altitude and figure out the fuel flow. Then at the altiport set that fuel flow. In the summer the density altitude will be even higher so the risk of damaging the engine is very limited and you will probably even need even less fuel flow then in a clear air climb at the same altitude.
I would not worry too much about damaging the engine at those altitudes. You could also just lean until you have a certain EGT like 1300-1400F no matter what the actual peak is.
Lucius wrote:
I haven’t had to take off from a density altitude between 6000 and 9000 feet. But it may happen this summer. I was wondering how to lean to 125 degree ROP on the ground prior to take off.
Should you really lean by temperature in this situation and not to max rpm/MP?
A constant speed prop won’t change RPM when you lean it, will it?
Typical sea level (ISA) takeoff EGT on my TB20 is about 1330F, so setting that will give you about 150F ROP which will be good enough.
Shorrick_Mk2 wrote:
A constant speed prop won’t change RPM when you lean it, will it?
Obviously not. But the MP would increase. Or maybe not. I’ve never had to lean before takeoff with a VP prop.
Obviously not. But the MP would increase. Or maybe not
The MP will not change significantly if you lean. Usually you can only feel the additonal power. At the moment you lean properly engine rpm will increase a bit until the governor adapts the prop and the engine will run much softer.
Where do you want to land this summer? If it is one of the Franch altiports I would not worry too much because at takeoff not much power is needed as you go downhill. If it is LSZS in Switzerland with very high terrain around and a rising valley in the west take great care. Those are the moments all the expenses for a turbo pay of in one single flight…
If it is LSZS in Switzerland with very high terrain around and a rising valley in the west take great care. Those are the moments all the expenses for a turbo pay of in one single flight…
The valley in Samedan is so big that you can easily fly circles in a SEP. It’s only the jets that play Russian roulette in dodgy weather and as a result the SEP pilots get punished. I don’t consider Samedan to be particularly difficult at all, I was there in a C172M in summer with 3 adults, i.e. very marginal performance and it was no problem at all.
The valley in Samedan is so big that you can easily fly circles in a SEP. It’s only the jets that play Russian roulette in dodgy weather and as a result the SEP pilots get punished.
The strange thing is that the jet pilots are not really punished at all! Cat B/C aircraft pilots can just fly there without any kind of checkout if the weather is CAVOK, while cat A pilots always need a local checkout (or mountain rating).
I don’t consider Samedan to be particularly difficult at all, I was there in a C172M in summer with 3 adults, i.e. very marginal performance and it was no problem at all.
I looked at the online briefing for Samedan and I agree that from a SEP perspective it doesn’t look more difficult than any other airfield in the alps. You have to be careful with your performance calculations, of course. I wouldn’t hesitate the least in going there.
