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Flying coupled approach
I have been practicing approaches with my autopilot and having difficult getting a stabilized approach. I have G3x touch and a Garmin 625 and Garmin 307 autopilot. I have tried flying 100 kts 90 kts, 80 kts. I ave tried all different flap settings. The problem is the autopilot will push the plane below the glide path then pitch?s up to correct above the flight path. I can fly it by hand with no problem. I am sure it is a configuration setting that needs to be adjusted. I was wondering if anyone else has this kind of set up that can recommend configuration settings. This pitching and diving would not be ideal in the soup!
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Should be like it is on a guide wire. Send your log to G3Xpert and they will help you get it sorted.
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Pitch Gain settings
Review the G3x install manual about configuring the autopilot pitch torque and gain settings. I had to adjust mine after some issues and it fixed my problem.
Use the AUTOPILOT SETUP page to adjust the PITCH SERVO gain settings. Steve |
Pitch setting
Additional info about the settings, I had to make my settings higher than the book default settings printed in the examples. Actually quite a bit higher, think each RV is unique and may or may not work with someone else's values.
Fly it, and take your time going through the procedure outlined in the manual top get the correct settings. Steve |
Also, the settings required for the -9 are good bit different than the short wing RV's.
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You likely need to tweak the autopilot settings - my Dynon autopilot will fly the RNAV like it's on rails. ILS will hunt a little above 95 knots, and VOR approaches I just hand fly rather than couple them because the corrections are all over the place.
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Maybe a bit slow?
Tim,
I fly coupled approaches in my 6 a lot. I have a Dynon system. I have found that in the RV6, 90 is a bit slow. To me, when I am trying to maintain 90 knots, the plane is like a boat just about on plane. You are heading down hill and it wants to speed up. You slow the engine and it slows, then too much. So you add power again. You speed goes up and down. I fly the approach at 110 to 120 knots, no flaps. Then as I get down to below 1000 ft or so AGL, I pull power, and then add flaps when I have the runway in sight. With these planes landing a little hot or long is not a problem. I?m still turning off most runways at the mid point. The plane is just so much more stable at 120 knots, it?s one less thing to worry about. Like others have said I had to turn up my gain and sensitivity a lot also. Another thing about RVs and auto pilots. Since the plane has such a broad speed range, setting the autopilot to work right at cruise means it might be sluggish at approach speeds. Setting it for approach speeds means it may be a little twitchy at cruise. I have mine set for approach speeds, 120 knots. And it is a little quick at cruise, but I like it that way. RF |
I agree on the speed comments above. I set my engine at 1450 rpm. Fixed pitch. And no flaps. That stays at 100-105 on the glide slope. I just keep my eyes pegged on the tach and fidget with it to maintain 1450. Once you break out or hit mins, kill the AP and pull up and drop the flaps in.
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i will have the trim set up in level flight at say 130 kts. when i intercept glide slope i will throttle back to maintain 130 kts. trim stays the same. if the plane flys well in level flight it should do well on GS. when i finally start slowing down i know to trim up a bit at the same time. good luck. :)
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Larry |
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When doing low clg approaches, I tend to slow down some time after the FAF (maybe 1000 AGL). Yes, it is more effort to hold the GS at 90 knots than 130, but I don't want the extra effort of slowing down at low altitudes with a limited amount of time. I tend to hand fly most approaches, so not doing the throttle dance necessary on coupled approaches. Larry |
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Not just low ceilings but also low visibility. Remember that if it?s really 1/2 mile vis, then at 200? agl you can?t see the runway - just the approach lights. That?s not a great time for reconfiguring the airplane. |
You all have good points. I personally have higher minimums than published. I am going to try some different configuration settings. I just have to dial the auto pilot in. I would think in today?s software you could set the autopilot settings different on approach then cruise. Let?s face it, if you press the APR button on the autopilot it should be able to say hay we are now going to use approach configuration not cruise. Maybe wishful thinking!
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When you hand fly an approach, you have a feeling for what the plane is doing, and you can decide how much elevator and how much throttle you want to use for corrections. But, with the autopilot flying pitch to track the glideslope, you have to adjust the throttle using only airspeed. This can be really ugly if there are updrafts and downdrafts.
Remember your first instructor telling you not to chase the airspeed indicator? That's what can happen here. |
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Larry |
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That said I was tired one day at the end of a flight and it was quite bumpy. I was glad that I had practiced with the AP a bit more, as I felt better letting George fly the approach that day. As long as you stay active with the throttle, they can fly them pretty well. The key is to keep the throttle changes in harmony with the AP's pitch changes. Larry |
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A properly applied, installed, and tuned Garmin AP system will likely perform equal or better than the typical certified system costing many orders of magnitude more. The RV9 should be easy to tune in due to its increased stability. Have you spoken with TeamX yet? |
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The procedure is stepwise and clear. Be sure you pay attention to your set speeds for auto trim too, if you have it. A little off on the tuning and trim setting mismatch and the trim can lag behind aircraft conditions and overload the servo, it hits the torque limit and BAM . . . suddenly you have a nose down 3000fpm. |
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