The problem with non-turbo piston is that you don’t have constant power.
Well, jets don’t either but they have loads of spare power.
IAS mode is good but PIT mod works really well, and inherently compensates for the loss of power with altitude. It won’t fly the plane into a stall either.
you have the perfect set up so you maintain pitch with decreasing IAS down to Vy as power wanes during climb??
Yes; that is what happens.
Constant IAS is actually not optimal due to engine management reasons; you need more IAS at lower levels to manage CHT. At FL180 there is no CHT to manage because there isn’t any air to burn the fuel with 
The KFC225 is a fully “digital” autopilot which is very hard to beat, except for the fimware bugs which burns out the servos. The GFC500, 20 years later, should be better, with brushless servos etc, but if your GPS dies it won’t fly a coupled ILS.
The KFC225 is a fully “digital” autopilot which is very hard to beat, except for the fimware bugs which burns out the servos. The GFC500, 20 years later, should be better, with brushless servos etc, but if your GPS dies it won’t fly a coupled ILS.
How well does the KFC fly the coupled ILS with a servo that is guaranteed to eventually burn? How much does a lack of GPS on final cost in replacement / maintenance bills and how often does it happen?
Peter wrote:
if your GPS dies it won’t fly a coupled ILS.
This is certainly something pilots should be aware of, but given the relative reliabilty of GPS system (satellites, navigator…) and the A/P itself, this is a non-issue to me. But maybe the GFC500 is so much more reliable than older autopilots that it does matter?
As a replacement for a King there’s now the Aerocruze 230. Not many pireps yet but those who are out there seem to be quite positive. They sell it as a slide in replacement for the kfc150, which it isn’t, of course, but it does use the old servos and seems to work with the usual Garmin stuff.
Not many pireps yet but those who are out there seem to be quite positive.
We have probably read the same one and a half pireps on one of the US sites 
Reading between the lines and knowing a bit about avionics, they are scary! The shop was out of their depth installing it, it didn’t work, took best part of 100hrs to get sorted, needed a lot of assistance from HBK, a part of it never worked (IAS mode?) etc. Well, just like some reports on the DFC90 some years ago, most of which didn’t get posted and the early installs of that one (Cessna 182) were a disaster story, never told. Except that the KFC230 installs were done in the US, with local-ish support, whereas all DFC90 support had to be done remotely from the US, and not even from Avidyne; the AP box had to go back to some other place. I reckon a KFC230 install in Europe might be “interesting”.
KFC230 not ready for prime time yet, not by a long way.
But maybe the GFC500 is so much more reliable than older autopilots that it does matter?
That’s a good point, but for me it is a simple case of systems redundancy. The GPS system is of course immensely reliable (unless locally jammed) but the receiving end isn’t anywhere near as reliable, and I have had to fly an ILS to (or close to) minima on quite a lot of flights (returning home), and on those flights not being able to do so would have been disastrous. You are basically going to land. There is not another alternate and then another… I am not a cowboy but the alternate is the last alternate (generally) and you will be flying that ILS all the way to the tarmac. Fancy doing it by hand? I know you can hand fly an ILS on the GFC500 flight director in such a situation, but how much do you want to stack up the odds against yourself, when you are flying the alternate down to the DH (or down to the tarmac) already?
Peter wrote:
I am not a cowboy but the alternate is the last alternate (generally) and you will be flying that ILS all the way to the tarmac. Fancy doing it by hand? I know you can hand fly an ILS on the GFC500 flight director in such a situation, but how much do you want to stack up the odds against yourself, when you are flying the alternate down to the DH (or down to the tarmac) already?
My point is that (unless the GFC500 is much more reliable than older A/Ps) if you have to hand fly an ILS to minimums it is much more likely to be because the A/P failed than because the GPS box (or system) failed.
Airborne_Again wrote:
My point is that (unless the GFC500 is much more reliable than older A/Ps) if you have to hand fly an ILS to minimums it is much more likely to be because the A/P failed than because the GPS box (or system) failed.
Plus you usually have dual GPS box for redundancy thus lowering the possibility that both fail at the same time which leaves only the option of system failing.
Peter wrote:
The problem with non-turbo piston is that you don’t have constant power.Well, jets don’t either but they have loads of spare power.
IAS mode adjusts pitch to any sort of set power. During climb, it will keep IAS current and gradually lower pitch to compensate for the loss of power. That is where it is most valuable. For piston engines in descent, it is problematic because piston engines can’t be brought back very far due to the cooling problem, there probably VS is easier. Even in case of an engine failure, IAS mode will keep the airplane at the selected speed, in that case in a descent. Set V-BG and the AP will fly it.
Pitch mode will keep a fixed pitch. That means in a climb with max power (or climb power) set, IAS will gradually reduce until it eventually stalls. Same as with VS, only a different parameter.
IAS will gradually reduce until it eventually stalls
PIT mode doesn’t actually do that. A plane stalls at a specific AoA. If you climb at a fixed pitch angle, it just climbs to whatever the ceiling is at that AoA. If you set the pitch at say 8 degrees, it will climb a TB20 to ~FL200 (ISA)
VS mode is completely different and the plane will stall. It also isn’t suitable for high altitude climbs because the VS is not controlled precisely enough; you can select the value in 100fpm steps only.
Peter wrote:
PIT mode doesn’t actually do that. A plane stalls at a specific AoA
Ineed, you just need to find max PIT value that give max AoA under various power/config settings
If you stick AP PIT bellow that max PIT, you will not stall even if you run out of power/climb, you will do just like gliders
If you set AP PIT = 20 deg in any GA aircraft, except Extra300, you will stall
