the newer digital autopilots will hold the speed very precisely
I understand that an autopilot will hold the speed accurately.
I would agree that it’s not an authoritative source, but this page gives a chart showing the l/d of a cessna 172.
http://uk.mathworks.com/help/aerotbx/examples/calculating-best-glide-quantities.html
Best glide is about 72 knots, but at 67 or 77 knots, it’s only a few percent less.
If you’re high up and you can glide 10 miles, a 3% advantage in l/d will only increase your potential landing area by 6%. But assuming there’s any wind aloft you will be able to go further if you’re flying at a speed other than Vbg anyway. And unless you know the winds fairly precisely you won’t be able to calculate it anyway. So why get hung up on trying to maintain a precise speed that doesn’t matter too much and may not be correct anyway?
Also these autopilots will never stall the airplane, because of their “envelope protection” features.
But you want to stall the plane in order to land at the lowest possible speed. You just want to do it when you’re a few inches up rather than a few hundred feet. So at the most critical phase of the whole procedure shouldn’t you be keeping eyes out and slipping, turning, or doing whatever else it takes to get the touchdown spot right rather than fiddling with the autopilot to turn it off? Conversely, at altitude you should have enough altitude to recover from an upset anyway.
I’ll confess I’ve never flown anything very slippery so perhaps it’s much harder to hold speed in an SR22 or TB20 than a Cessna or Piper trainer?
Yep, I’m with Achimha and Flyer59 and always climb in IAS mode adjusting the speed selected as I get higher.
kwlf,
of course I’d switch off the A/P before landing :-)
And in the Cirrus, if at 2000 ft AGL i realize I won’t make the airport, I’d use CAPS anyway, just because it’s more likely nobody will be injured.
And you can always use cruise climb speeds down low then lower it for performance as you get higher
Yep, I’m with Achimha and Flyer59 and always climb in IAS mode adjusting the speed selected as I get higher.
We do that even in a Citation.
BUT the VS is much nicer mode to use at high level, although it requires vigilance to avoid getting anywhere near the stall..
