As the altitude (OK, technically not the MSL but the pressure-altitude) increases the air get thinner aand the power the engine can produce at a given RPM is lower... despite the carbs trying to compensate and get the right mixture as the altitude changes... and I'll have a lower indicated airspeed at the same throttle setting than at a lower altitude.
On other hand air resistance (drag) is less, and, for example, at 8500 feet an accurate indicated airspeed of 100mph results in a true airspeed of about 113mph.
So I will be traveling further in an hour of fuel consumption than at a lower altitude.
So is there an approximate altitude where the gain of true airspeed due to altitude with a Rotax 912 gets you the most miles per gallon?
For example, it's known the sweet spot on altitude efficiency for jet engines is about 35,000 feet, for turboprops (if I got this right) it's about 25,000 feet.
Any idea where approximately it is for an aircraft powered by a Rotax 912?
(Let's for the moment ignore the practical complicating question/factor/issues rolleyes of on a given flight the extra fuel used to climb up to the optimal cruise altitude could offset the fuel saving from cruising at the optimal altitude, different winds aloft, need for oxygen, etc. And let's assume a fixed pitch propeller to keep things simple.)
A.
Note that this question was already posted in the Four-stroke technical questions section, but since we got no solid answers there, with the Moderator (Rodger) permission am posting here to see if anyone browsing here dares take on this slippery one. ;-)
On other hand air resistance (drag) is less, and, for example, at 8500 feet an accurate indicated airspeed of 100mph results in a true airspeed of about 113mph.
So I will be traveling further in an hour of fuel consumption than at a lower altitude.
So is there an approximate altitude where the gain of true airspeed due to altitude with a Rotax 912 gets you the most miles per gallon?
For example, it's known the sweet spot on altitude efficiency for jet engines is about 35,000 feet, for turboprops (if I got this right) it's about 25,000 feet.
Any idea where approximately it is for an aircraft powered by a Rotax 912?
(Let's for the moment ignore the practical complicating question/factor/issues rolleyes of on a given flight the extra fuel used to climb up to the optimal cruise altitude could offset the fuel saving from cruising at the optimal altitude, different winds aloft, need for oxygen, etc. And let's assume a fixed pitch propeller to keep things simple.)
A.
Note that this question was already posted in the Four-stroke technical questions section, but since we got no solid answers there, with the Moderator (Rodger) permission am posting here to see if anyone browsing here dares take on this slippery one. ;-)
