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..
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.
Yep, I’m with Achimha and Flyer59 and always climb in IAS mode adjusting the speed selected as I get higher.
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?
However, if the PSS60 is part of an S-TEC autopilot system (60-1 or 60-2), then you cannot engage a vertical mode without also engaging a lateral mode.
It often isn’t, it’s often used as an altitude retrofit for a completely different lateral only autopilot. In all of these installations I’ve seen it is possible do engage each autopilot separately.
Not that I consider this an advantage, really.
I never do climbs without IAS mode. Even in the SR22 NA it works perfectly.
If the temps go up I just dial in a higher speed but it’s almost never necessary.
Like Achim I use IAS for climbs and VS for descents, with the Vnav feature of the 430.
Certainly not Peter. IAS hold is one of the best things and I use it all the time for climbs. It’s the only climb mode that works, VS is too unstable with a bit of weather and our low performance aircraft. A VS control loop is far less stable than an IAS control loop which is rock solid. For descents I use VS. Both modes require manual throttle operation unless you have an electronic wastegate such as the SR22T.
I basically do my climbs by adjusting the IAS knob to yield the desired CHTs because — as with pretty much all high performance piston planes — climbs are CHT limited.
Not true in a turbocharged piston Peter. I always used it in the Mirage for the climbs at best rate then cruise climb.
I assume it is equally useful in an SR22.
And you can always use cruise climb speeds down low then lower it for performance as you get higher.
IMHO IAS hold is of limited use in GA pistons, due to their low performance. And if you set an IAS low enough to “last” in a climb to a reasonable altitude, say FL150, say 95kt, you will overheat the engine low down because 95kt is far too slow for the power then being developed (IO540 case).
As Ultramad has already stated the PSS60 add on does this. I have it and he is right.
However, if the PSS60 is part of an S-TEC autopilot system (60-1 or 60-2), then you cannot engage a vertical mode without also engaging a lateral mode. I believe the statement is still true: an autopilot capable of lateral and vertical modes will never let you engage a vertical mode without also engaging a lateral mode.
