It must be a dependency of any IAS mode.
Not a problem, so long as a) you are aware and b) nothing else is lost.
What an IAS mode does is that it lets you do climbs and descents on a particular airspeed rather than VS which can let the AP fly you into a stall
Like I said, the PIT mode will do the same. I could take off, trim for say 100kt, engage PIT at 100ft, and climb to FL200 (plus or minus ISA deviations; the TB20 won’t do FL200 with ISA+15) with no other pilot input other than progressive leaning to maintain 1330F on some chosen cylinder.
That also works with a King AP.
Funnily enough, it depends. My KFC225 treats VS as “what you want, but I will add or subtract 100ft randomly”. It works for descents, and for climbs with enough reserve power (basically anything below about FL150).
I know I am often alone here advocating fixing older kit but everywhere I look I see pilots who are grounded for months for various reasons, and what do they do when they can’t fly? They spend 30-50k on avionics 
Then they get the plane back, engine probably corroded due to months of sitting somewhere, and they find various gotchas… The biggest avionics spenders are consistently the pilots doing the fewest trips. And some don’t fly at all.
Darkfixer wrote:
How does the GMC 507 work?
It has same panel as GFC 500 ??
@Darkfixer, GMC507 is the control panel of the GFC 500.
AFAIK this autopilot consists of:
GMC 507 – control panel
NxGSA 28(?) – servos (few of those, where N depends on how many axis you want)
A Garmin EFIS – one of: G5, G3X, GI275
The actual logic (computer) is inside the EFIS, that’s why it is not going to work with just some another EFIS.
You could start with G5+GFC500, or to be more precise, with G5+GMC507+NxGSU28.
After that you could either keep it as is OR replace Aspen with G3X (you’ll lose all DME/ADF/… integration) OR replace Aspen with G500TXi (in that case you could go for engine monitoring and better integrated cockpit).
G5+GFC allows you to use all the nice features of GTN (including Enroute VNAV etc), IAS hold, Alt preselect, etc…
I am getting interested in the functionality here.
While it is clear that the GFC500 needs the G5, can it take any inputs from the Aspen at all? Such as the HDG bug? Or would the HDG selected on the G500 via the G5 be fed back in some way to the Aspen?
Or in general, those who prefer Aspen over the Garmin EFIS offerings and want it integrated are more or less restricted to the STEC55 or, where STC available 3100 or DFC90?
Peter wrote:
It must be a dependency of any IAS mode.
Of course, if you loose air data, you can’t use the IAS mode. But most probably you also will have a problem with Alt Hold and VS unless they take their feeds from separate sensors AND a separate static port.
What got fixed is that in the original Aspen, if you loose air data you loose practically the whole instrument, Attitude, the works, are crossed out. In the Max, if you loose air data, the display becomes “degraded” but attitude and heading e.t.c. still work as before, the speed and altitude bands get x-ed out.
Peter wrote:
Like I said, the PIT mode will do the same. I could take off, trim for say 100kt, engage PIT at 100ft, and climb to FL200 (plus or minus ISA deviations; the TB20 won’t do FL200 with ISA+15) with no other pilot input other than progressive leaning to maintain 1330F on some chosen cylinder.
What is the PIT mode based on? Holding a particular pitch angle? I don’t know this mode and can not recall it from my KFC150 days.
Peter wrote:
Funnily enough, it depends. My KFC225 treats VS as “what you want, but I will add or subtract 100ft randomly”. It works for descents, and for climbs with enough reserve power (basically anything below about FL150).
Really? Wow. I have to say the 55x does VS pretty well. The important thing with VS mode simply is that you either have to adjusting VS to IAS all the time or, as you say, use a VS which works up to a particular altitude in most cases and then adjust it. In my set up, we have chosen 500 fpm below FL100 and 300 above, but while this is a workable solution, it is far from optimal. Rate of climb in a normal single would go from approx 1000 fpm at SL to gradually 200 fpm at service ceiling. This however means you are almost always flying faster than the optimum climb speed and you do not climb at the optimal profile.
So in IAS or FLCH mode what happens is that pitch is steered to maintain a constant speed against the power setting you apply. That way, VS is variable. It can range from positive to negative, but it will never stall the airplane or slow it down below the IAS you select. In most airliners, IAS is set to 250 kt below FL100 and then to a pre-defined climb IAS and, once it becomes applicable, Mach number. I’ve seen quite a few of those climbs turn into momentary descents i.e. in the event of an inversion. But it will never stall the plane.
For descents in our piston airplanes, VS is just as fine as IAS or FLCHG and probably more constant, as we can’t simply pull our engines to idle. The big advantage of IAS vs VS is definitly in climb.
Peter wrote:
I know I am often alone here advocating fixing older kit but everywhere I look I see pilots who are grounded for months for various reasons, and what do they do when they can’t fly? They spend 30-50k on avionics
I am all the way with you to fix older kit as long as it is a) economically fixable and b) still is adequate for the job.
Autopilots are almost always more economical to fix or to upgrade existing installations (i.e. with a pitch channel) than to replace totally. I’ve flown airplanes which still had the old Piper setups which worked beautifully (and in some cases better than the S-tecs) such as the Altimatic IIIB and similar and also some Autocontrol AP’s which were upgraded with an STEC 60PSS. If they work and are fine, I’d never dream pulling them out.
The discussion here however is a very different issue: If you install from scratch, I think you should go for the best there is for the budget you have. And being recent means longer support as well.
And with IAS mode you get a drawback: you get an AF447-type dependency on the airspeed. Depending on the navigator/PFD design, you can lose a large chunk of your panel if airdata is lost.
Is AF447 really applicable to this discussion?
Older rate based autopilots simply trimmed up to keep climbing in VS mode, which caused plenty of upsets. IAS mode prevents this, a very useful mode, not a drawback.
Regarding losing ATT + Airdata with blocked pitot: That happened in an Aspen system, right? Nevertheless I don’t see the connection to the AP topic.
PIT mode holds the pitch angle. I think generally this comes from whatever the pitch/roll reference is, which could be a KI256 in the older systems.
VS mode uses just the static input, which is relatively unlikely to fail. IAS mode uses the pitot+static data, and the pitot portion is relatively likely to fail.
“AF447” was tongue in cheek but their whole problem was loss of pitot data + muppet pilots.
For a completely new installation, by all means go for the latest.
Mooney_Driver wrote:
While it is clear that the GFC500 needs the G5, can it take any inputs from the Aspen at all? Such as the HDG bug? Or would the HDG selected on the G500 via the G5 be fed back in some way to the Aspen?
@Mooney_Driver, I think it would not be possible – to my knowledge, both G5 & the servos are CAN BUS devices, while Aspen is not.
@Peter might say something here as electronics specialist, but I think if the devices are unable talk to each othert electrically without some extra devices (completely different interfaces), I don’t think they are compatible at all.
arj1 wrote:
I don’t think they are compatible at all.
Right.
So basically this means that Garmin is in it’s own world and excludes everyone else.
In which case, the venable Stec 55x may well stay the only real alternative for anyone having put their $$$ on the Aspen-Horse.
PIT mode holds the pitch angle. I think generally this comes from whatever the pitch/roll reference is, which could be a KI256 in the older systems.
Makes sense.
VS mode uses just the static input, which is relatively unlikely to fail. IAS mode uses the pitot+static data, and the pitot portion is relatively likely to fail.
Relatively likely to fail? In any case, simply push IAS a second time and it will select pitch mode.
For a completely new installation, by all means go for the latest.
Only Garmin takes care of the market. Why no DFC90 for Pa28 etc..
Snoopy wrote:
Why no DFC90 for Pa28 etc..
I don’t know why no DFC90. Again, it sounds totally stupid that it’s not available as I would most definitly have upgraded mine and so would several thousands of folks who have 55x’s installed. It was a big sales pitch for Cirrus owners and I hear that also other types which are certified.
I do recall however, how Genesys tried to find people to supply their planes for installations for the 3100 to develop the STC. They failed miserably, as nobody wanted to do that. The only “prize” was that you would get the installation for free but still fully had to pay for the system, which you did not know would be certified or not…
So last time I checked it is certified for e.g. the PA24 but not the PA28. Which is totally stupid, as there are a factor of multitude of PA28’s available which are potential customers. But the concept of Beta Test by end users is always one which carries a lot of risks.
