The bottom line to me is how long it takes to get from one place on the ground to another place on the ground. All the ‘knobs’ available to a given type (altitude capability included) are fair game to minimize the elapsed time between those points on the ground. If one type shows a low number on the airspeed indicator as a result of being able to go higher and faster over the ground, is that anything other than a side issue?
I think unless you presume that high altitude flight is forbidden or inconvenient, the number on the airspeed indicator does not provide much useful information in terms of elapsed time between two points on the ground. And I think if that were the case, no oxygen on board, limited power or whatever, you’d just compare true airspeed for different types at whatever altitude you’d choose for each. Seems like common sense to me.
Alt is 8000 feet. It’s a kind of “industry standard” for cruising performance.
I don’t think so. Maybe for Rotax engined aircraft. But anybody who can get a higher TAS higher will go for it. Mooney and Cirrus for example use FL200 plus to get their 200kt+ figures on their turbo aircraft.
I am not sure where the TB20 (non turbo) achieves the highest possible speed at say 75% power, but I know it gets the best MPG at about FL120, because one can run at 2200rpm and wide open throttle. TAS there would be about 140-145.
For my NA Mooney….the max TAS (171kts) is achieved at 8000’ according to the POH….higher is slower, but specific fuel consumption improves…
Goes a bit funny using work airplane
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I always see performance data WITH altitude, and for non-turbo a/c it’s mostly 8000 ft at ISA.
Mooney and Cirrus for example use FL200 plus to get their 200kt+ figures on their turbo aircraft.
Isn’t FL200 an altitude? :-) I mean if it says 200 KTAS at FL200 – what’s wrong with that?
Am I the only one who thinks the shape of the surface in post #04 looks wrong? Not to mention #25…
Am I the only one who thinks the shape of the surface in post #04 looks wrong? Not to mention #25…
It looks rather like a Mercator projection so the scale increases with latitude (Sec^2) and never reaches the poles.
I don’t know how to paste my map in here, but for the Teal, Mid James Bay to North Carolina, and Maine to Minnesota (though the Teal is not allowed in the USA). The C 150 has a somewhat smaller circle, which can include the USA. But there’s lots of Canada for me in the Teal, so the “merican’s” are just missing my tourism dollar!
I don’t think so. Maybe for Rotax engined aircraft. But anybody who can get a higher TAS higher will go for it.
I think you misunderstand. Besides, O-540s are no Rotaxes, and the 914 is a Turbo in any case 
What I mean is that 8000 feet has become an “industry standard” of sorts for reporting cruising performance. Everybody use that number. We can of course discuss why and the merits etc. but it doesn’t really matter. With TAS at 8000’ this can be used to compare most aircraft on an even basis.
8000’ is after all a good cruising altitude for a non pressurized aircraft. You can still breath up there and the engine will run at approximately 75% power WOT (best efficiency). With Turbo/turbine and cabin pressure, 8000’ makes no particular sense, but most private aircraft do not have turbo and/or cabin pressure.
www.gcmap.com has this function, too. For my AA-5B at 8000 ft I would just type 665nm@LKBU in the entry box:
By default, the map is barely large enough to accommodate the request, but one can scale it down, too:
