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Autopilot drag

R

Ron B.

Well Known Member
I have an RV-14A with Dynon autopilot. I also have a friends 14 in my hangar and the controls move much easier than mine. I disconnected my roll autopilot servo ( Dynon SV-32 I do believe, it’s what was recommended in 2016), and most of the drag is in the servo. Power off sitting in the hangar.
My controls are much heavier in flight and that why I started looking for the reason.
The other 14 has a Garmin autopilot. I flew it last week in moderate turbulence and it flew the plane like it was on rails , very impressed.
Now like I posted on here before, my autopilot is set with setting I got from someone else, I not too savvy with electronics. I do believe I have the torque set close to 100% as I am getting slip warnings ( in the pitch servo for sure , maybe not on the roll).
Will the setting in the autopilot ( torque) affect the drag when no power is applied ( ie sitting in the hangar)?
Is this drag I’m feeling when the unit is off normal?
Thanks Ron
 
Ron B. said:
I have an RV-14A with Dynon autopilot. I also have a friends 14 in my hangar and the controls move much easier than mine. I disconnected my roll autopilot servo ( Dynon SV-32 I do believe, it’s what was recommended in 2016), and most of the drag is in the servo. Power off sitting in the hangar.
My controls are much heavier in flight and that why I started looking for the reason.
The other 14 has a Garmin autopilot. I flew it last week in moderate turbulence and it flew the plane like it was on rails , very impressed.
Now like I posted on here before, my autopilot is set with setting I got from someone else, I not too savvy with electronics. I do believe I have the torque set close to 100% as I am getting slip warnings ( in the pitch servo for sure , maybe not on the roll).
Will the setting in the autopilot ( torque) affect the drag when no power is applied ( ie sitting in the hangar)?
Is this drag I’m feeling when the unit is off normal?
Thanks Ron
Click to expand...
The slight servo resistance sitting in the hangar is normal and is not affected by the settings and should not be noticeable in flight.
Is the pitch trim adjusted correctly when getting slippage in flight?
 
Ron B. said:
I have an RV-14A with Dynon autopilot. I also have a friends 14 in my hangar and the controls move much easier than mine. I disconnected my roll autopilot servo ( Dynon SV-32 I do believe, it’s what was recommended in 2016), and most of the drag is in the servo. Power off sitting in the hangar.
My controls are much heavier in flight and that why I started looking for the reason.
The other 14 has a Garmin autopilot. I flew it last week in moderate turbulence and it flew the plane like it was on rails , very impressed.
Now like I posted on here before, my autopilot is set with setting I got from someone else, I not too savvy with electronics. I do believe I have the torque set close to 100% as I am getting slip warnings ( in the pitch servo for sure , maybe not on the roll).
Will the setting in the autopilot ( torque) affect the drag when no power is applied ( ie sitting in the hangar)?
Is this drag I’m feeling when the unit is off normal?
Thanks Ron
Click to expand...
Does your Dynon support Garmin servos? The Garmin servos have an electric clutch that disengages completely when the autopilot is not on.
 
I have the full Dynon setup with servo. Before first flight, another pilot commented my roll was stiffer than RV8 but he didn't have the servo. In flight I didn't notice any stiffness. If you experience heaviness, could it be from the heavy wing?
 
PhatRV said:
I have the full Dynon setup with servo. Before first flight, another pilot commented my roll was stiffer than RV8 but he didn't have the servo. In flight I didn't notice any stiffness. If you experience heaviness, could it be from the heavy wing?
Click to expand...
It trims out with the trim and flies straight. Wouldn’t think it’s a heavy wing issue. Same force required both directions.
Thanks
 
PaulvS said:
The slight servo resistance sitting in the hangar is normal and is not affected by the settings and should not be noticeable in flight.
Is the pitch trim adjusted correctly when getting slippage in flight?
Click to expand...
Probably not, will have to stop putting it off and get someone to look at it.
 
I've got 1300 hours on my -14A with Dynon Skyview and autopilot. On the ground without power on the servos, any control forces from the servos being in the system are very minor. The controls, both pitch and roll, work easily and smoothly from stop to stop.

You may want to temporarily disconnect the controls from the servos for a ground test to see how much drag they exert on the system. In my airplane, it is very little. Or, if you have access to another -14 or -14A with a Dynon autopilot, you can just do a back-and-forth test from one to the other to see if they are substantially the same or different.
 
Sounds like you MAY be addressing separate issues - The SV32 servo's have a gear train inside that you are back driving anytime you move the servo, you can feel this with your hand as you move the servo arm with it disconnected or powered OFF and physically disconnected from control surface linkage. It will not feel like smooth back pressure but will instead have a very slight roughness or pulsing as you move it - that is NORMAL for the SV32. That said, mechanical issues inside the servo can amplify this "drag" to unacceptable levels due to many mechanical causes. If you feel the drag is excessive - then you are in the perfect position to do a 1 to 1 comparison if so inclined. Access & disconnect both the roll servo & pitch servo from the control surface linkages - move each servo by hand & compare... they should both be relatively low drag. The Dynon factory will do a "cross shipment" replacement of the servo - sending you a overhauled/warrantied servo in advance so that you have both the replacement servo & the original in your hands - do another comparison to see what a newly overhauled servo feels like. You could also swap the pitch & roll servo's (remember to re calibrate the EFIS controller) to see if the symptoms follow the serial number. SV32's & Garmin servo's feel totally different due to internal structure differences - SV32's, when properly installed & functional, can be "felt" slightly at the control stick on the ground but almost never in-flight.
2'ndly - sounds like you may have the AP settings overly aggressive which is really the only reason you would be seeing slip warnings... I would recommend your re-evaluating all the AP settings possibly even resetting to factory default settings for in-flight tuning. AP's are not meant to keep a plane rock steady in moderate turbulence, they can be tuned to be overly aggressive which puts untold stresses on the airframe & passengers.
Hope this helps
 
AZSteve053 said:
Sounds like you MAY be addressing separate issues - The SV32 servo's have a gear train inside that you are back driving anytime you move the servo, you can feel this with your hand as you move the servo arm with it disconnected or powered OFF and physically disconnected from control surface linkage. It will not feel like smooth back pressure but will instead have a very slight roughness or pulsing as you move it - that is NORMAL for the SV32. That said, mechanical issues inside the servo can amplify this "drag" to unacceptable levels due to many mechanical causes. If you feel the drag is excessive - then you are in the perfect position to do a 1 to 1 comparison if so inclined. Access & disconnect both the roll servo & pitch servo from the control surface linkages - move each servo by hand & compare... they should both be relatively low drag. The Dynon factory will do a "cross shipment" replacement of the servo - sending you a overhauled/warrantied servo in advance so that you have both the replacement servo & the original in your hands - do another comparison to see what a newly overhauled servo feels like. You could also swap the pitch & roll servo's (remember to re calibrate the EFIS controller) to see if the symptoms follow the serial number. SV32's & Garmin servo's feel totally different due to internal structure differences - SV32's, when properly installed & functional, can be "felt" slightly at the control stick on the ground but almost never in-flight.
2'ndly - sounds like you may have the AP settings overly aggressive which is really the only reason you would be seeing slip warnings... I would recommend your re-evaluating all the AP settings possibly even resetting to factory default settings for in-flight tuning. AP's are not meant to keep a plane rock steady in moderate turbulence, they can be tuned to be overly aggressive which puts untold stresses on the airframe & passengers.
Hope this helps
Click to expand...
Thank you for the detailed review. Settings being to aggressive might be the issue. I will try to address this once I get back flying.
You appear to have experienced with both Dynon and Garmin. Should I expect my autopilot to function as well as my friends 14 with the Garmin autopilot once it’s configured correctly?
Thanks Ton
 
Ron B. said:
Thank you for the detailed review. Settings being to aggressive might be the issue. I will try to address this once I get back flying.
You appear to have experienced with both Dynon and Garmin. Should I expect my autopilot to function as well as my friends 14 with the Garmin autopilot once it’s configured correctly?
Thanks Ton
Click to expand...
Ron,
AP overall performance is based on MANY things which include the basic control laws designed into the system, the tuning of the system to the particular airframe. Control laws for "the inner loops" (basic stability) come from various different devices - some use gyro's, rotating or solid state (some are rate based single gyro's & other use multiple axis individual gyros) - some include pitot-static sensors as well. The systems "outer loops" (following Nav, heading & Altitude commands) are configured to interface to well known devices such as the popular GPS navigators & ADAHR & EFIS screens. The servo's are "the muscle" connecting the AP controller to the plane - they come in different part numbers typically having different torque capabilities (which affects physical size & weight) - the "right servo" for a particular airframe is generally selected by the system manufacture based on airframe parameters such as wing area & control surface areas - weight & balance range - acceptable control surface pressures - Trim tab operating speeds - etc... you do not want to "over-muscle" a plane (hopefully you want to break a servo shear pin or screw long before airframe damage occurs). Same thing for control law coefficients - selected carefully for specific applications or in the case of the Experimental world selected for a good "GENERAL" multi airframe starting point to be "Tuned" by the end system integrator (builder - test pilot, Phase 1 & beyond). I know of no reason why one brand of AP would perform better (or worse) than another if properly configured for the airframe - AP performance IS subjective and unless a full up competitive development is conducted, under controlled conditions - then I feel no conclusions could be drawn.
 
Carl Froehlich said:
Sorry for the flippant response. A hold over from being burned by Garmin’s after the sale service on a GTN-650.
Click to expand...
Perhaps your service experience was also reflection of your flippant attitude when dealing with customer service?
This is also where having a local or established dealer working on your behalf can help immensely.
PS: imo there is no better autopilot than the Garmin.
 
Garmin Rocks!!!!!!!

But it takes some tuning if you are flying experimental, as detailed in their excellent installation manual.
 
Walt said:
PS: imo there is no better autopilot than the Garmin.
Click to expand...
I fly my RV with a Trio Pro (usually controlled by the GRT Hx EFIS). I also routinely give flight reviews, check-outs, etc, in the local flying club’s 182, equipped with a Garmin 500 AP system. IMHO both autopilots are so good that I have nothing to complain about, with either system, with two exceptions:
1. The Trio is, of course, much less expensive (and can still function following a complete efis failure);
2. The Garmin is installed with ‘envelope protection’ on upon boot up, but with no obvious indication. When asked to demonstrate a stall or steep turn (at altitude) the pilot inevitably complains that ‘something is fighting him on the controls’ (even though we briefed on this ‘feature’ less than an hour earlier). I really wish there was a bright ‘envelope protection ON’ light somewhere on the AP control head.
 
BobTurner said:
The Garmin is installed with ‘envelope protection’ on upon boot up, but with no obvious indication.
Click to expand...
Just a reminder that there the PFD does show a clear indication that ESP is armed. You can refer to page 310 of the current G3X Touch pilot's guide (revision Y) for an example.
 
mburch said:
Just a reminder that there the PFD does show a clear indication that ESP is armed. You can refer to page 310 of the current G3X Touch pilot's guide (revision Y) for an example.
Click to expand...
Unfortunately this particular installation uses three GI275’s. If the warning is there, it’s too small for my eyes to see from the right seat!
 
mburch said:
Just a reminder that there the PFD does show a clear indication that ESP is armed. You can refer to page 310 of the current G3X Touch pilot's guide (revision Y) for an example.
Click to expand...
To add a little more to the above, not sure about the default status in the certified version but in the experimental version this feature can be set to defualt on/off at startup or it can be easily turned on/off with a single button push after startup.
 
Walt said:
To add a little more to the above, not sure about the default status in the certified version but in the experimental version this feature can be set to defualt on/off at startup or it can be easily turned on/off with a single button push after startup.
Click to expand...
With the tiny GI275 displays it’s not quite so easy - bring up the menu, scroll to the right to find the button to turn it off. In all honesty, I usually pull the CB instead. My complaint (should have a caution light) was because in the flying club, many members only fly this airplane once or twice a year, and they forget that ESP even exists. I do wonder if any complex autopilot belongs in a club-operated airplane, but of course that was not my call.
 
bertschb said:
Garmin autopilot servos are horrible?
Click to expand...
Well, the ones I’ll be installing under the recent “five-year warranty” program will be my third set. With that said, the autopilot has been working fine for some time now. So although my customer service adventure with them was pretty bad, with the passage of time I’ll give the entire experience a solid “meh.”
 
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