Looking for input on GRT Autopilot Performance

I will be upgrading to a GRT EFIS and am currently inclined to use their integrated AP instead of a TT. I was hoping to get some ideas on how the GRT AP performs, especially in turbulence. Can I expect performance similar to what I would get with a TT or other dedicated AP?

Larry

Work Great..

lr172 said:

I will be upgrading to a GRT EFIS and am currently inclined to use their integrated AP instead of a TT. I was hoping to get some ideas on how the GRT AP performs, especially in turbulence. Can I expect performance similar to what I would get with a TT or other dedicated AP?

Larry

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They perform beautifully, smooth or turb.. it all depends on how you have them set up. I think you are smart moving to the GRT autopilot just in usability. Easy control on the screen.

Mine is tweaked where I can shoot very stable approaches from 90 kts to 140 knots. The setup is what's important, again.

TT are wonderful autopilots. I've just found that from an operational standpoint it is so much easier to control the A/P from the EFIS and never have to worry about punching in any commands on two units.

RV8iator said:

They perform beautifully, smooth or turb.. it all depends on how you have them set up. I think you are smart moving to the GRT autopilot just in usability. Easy control on the screen.

Mine is tweaked where I can shoot very stable approaches from 90 kts to 140 knots. The setup is what's important, again.

TT are wonderful autopilots. I've just found that from an operational standpoint it is so much easier to control the A/P from the EFIS and never have to worry about punching in any commands on two units.

Click to expand...

Thanks for the input. I understand that any AP is going to take adjustment. Just wanted to be sure that you can get there from here.

Larry

I had a TT Digiflight II VSG when I originally built my craft. I flew it for a few years.
It is a beautiful autopilot. The control logic and tuning was excellent for my RV7

It did not have the ability to follow a glideslope (vertical control) although it could be set for particular descent rate.

I decided to change over to the GRT in order to get GPSS steering and vertical path following.
That all works as advertized so I wont go back to the TT........BUT..... The TT feedback controll loops were better and smoother.

Before anybody jumps in and says "you have to adjust the gains", be aware that I have spent a LOT of time on it and I understand negative feedback gain adjustment on PID control systems.

So..my answer is that while the GRT delivers the features, it does not fly as "tightly" or as "smoothly" as the TruTrac.

GRT Autopilot

I have both GRT Sport HS & SX installed in 7A and either (switchable) will do a great job of driving my GRT autopilot. Both good in rough air, but I do have the HS adjusted for a softer ride and the gains set higher on the SX for more precise tracking on approaches with wind shear.

Don't know anything about TT but have had two friends change from Trio to GRT.

My only negative comment about the GRT autopilot performance is that in my installation, when the "missed" button is pressed the pitch up is a bit slow and it will loose about 75 feet altitude (fixed pitch on 0-360), but then how many other autopilots will fly a missed approach?

I believe Mr. Pendergrass' observations may be correct. It appears a software change made to the yaw axis of AHRS that use the digital magnetometer, possibly combined with certain (normal) magnetometer errors, could result in small roll oscillations that are not affected by changing gains. Our website now describes this, a fix has been implemented (software), and is pending a flight test before it is released. I expect to have this improvement available no later than the end of February, 2017.

Mr Pendergrass' observations of not flying as "tightly" or "smoothly" are consistent with this problem.

I apologize for not picking up on this more quickly. Since we had not changed any autopilot software, I had attributed this to other causes. Our autopilot normally performs to such a high level of performance that we routinely are complimented by airline pilots who report it as equal to their Boeing autopilot experience. I personally consider a high-performing autopilot essential to single-pilot flying, especially in RV's and IFR. The fix will restore this level of performance.

During the investigation, attention was also focused on the magnetometer accuracy and calibration. This resulted in a slightly improved factory magnetometer procedure. If you had difficulty achieving accurate magnetic headings after performing fine magnetometer calibration, you are welcome to send us your digital magnetometer and we will re-calibrate it with the new procedure at no charge. This is not likely to affect most installations however.

Greg Toman
President
GRT Avionics

Wow, I really like these kind of honest, thoughtful responses from our avionics suppliers. Thanks Greg. You are generating a lot of customer loyalty here.

Erich

Wow. Thanks Greg. I will take a look at the info you described. I hope it will apply to my installation of the oldest versions of GRT hardware.