GRT Roll Servo In Wing - Installation Questions

[jackking123]

I have a few questions, and request for pictures.

Questions concern:

• Where to drill hole in bell-crank to attach servo actuator rod? Comments?
• Bolt head clearance between lever and servo body. I would like more. Move lever out? Lower profile bolt head (AN3 is already 1/8")? Comments?
• Not a fan of cantilevered bolts with spacers, but that seems to be the standard. Thinking of riveting on spacer to bell crank, to reduce bolt bending. Comments?
• Bracket is cantilever off existing bolts, sure it's OK; Any one consider a chicken fastener to stiffen it up. (AN3) hole in web nil effect on spar. Comments?
• BONUS Question - The Control Rod Hemi Bearing is stiff as all heck. May be due to kit sitting for years. Comments?

 

[rv8ch]

I used the Dynon guide - it has a lot of good information.

https://dynonavionics.com/includes/guides/RV7-8-10_Roll_Kit_Instructions_Rev_H.pdf

in case this link changes over time, just search for "dynon autopilot installation manual"

 

[Ralph Inkster]

No GRT instructions included with package? They should be the source for dimensions.
Mounting bracket (black in picture) looks very similar to Garmin, Dynon, TruTrak so should be plenty strong without adding bolts through the spar.
If I remember correctly installing other brand servos, bolts & spacers etc were included in packages & not requiring additional spacer blocks being fabricated. Forces from the servo aren’t anywhere strong enough to bent bolts.
If the end bearing is stiff-replace it.

 

[jackking123]

No GRT instructions included with package? They should be the source for dimensions.
Mounting bracket (black in picture) looks very similar to Garmin, Dynon, TruTrak so should be plenty strong without adding bolts through the spar.
If I remember correctly installing other brand servos, bolts & spacers etc were included in packages & not requiring additional spacer blocks being fabricated. Forces from the servo aren’t anywhere strong enough to bent bolts.
If the end bearing is stiff-replace it.

Thank you. I'd like that. So show me please? I am fully capable of missing skipping over instructions. I have all the PDF instructions... I did not see exact number. There is a disclaimer that every installation is different... etc. RV-7/8 installation kit has all (almost) all the parts, parts list and PDF instructions, shows the picture above. Good enough... I guess. From picture servo is at 12 O'Clock last hole level with servo and attaches to bell-crank. Looks like it is half way. This is LIGHT YEARS better than the NavAid I put in my first build, a RV-4. The servo was crude analog. It worked, wing level, track...

Instructions talk of servo actuator has three holes, explains throw vs torque. The BIG CAUTION, is NEVER go past 60 degrees, plus/minus from over center. Got it.

I believe the servo is electronically calibrated from EFIS. It will a bit of hold thumb out one eye closed engineering (really measuring required throw and clearances doing some basic trigonometry calcs, measuring with a microscope and cutting with Ax, ha ha).

Ideal you don't want to get too close to the 60 degree point, have the nominal pretty much at 0 degrees from over center (actuator 90 to servo arm).

I agree extra bolt is overkill but it would slightly reduce deflections. Strength not an issue. Any play or "springs" in a control system can cause the system to perform less than ideal (or make no difference). I just get WEIRD with controls. This is the thing that can kill you. Bad rivet...no. Control lock up, bad bad bad thing. Not that the stock design, sans extra bolt, would lead to control lock up.

Bearing stiffness... I agree I am going to buy new ones... The good ones are loose, free and sold. How they got bound up not sure? I will try and move them around and get play. Lubrication should not be needed or used to get smooth operation as these are plastic (Teflon I think) lined. In fact lube might hurt it. I don't recall lubing the bearing. I may get the out and try and work them, may be they took a set and just need exercise. Hemi ball bearings tend to be very long lived.

 

[rv8ch]

I am fully capable of missing skipping over instructions. I have all the PDF instructions... I did not see exact number.

I believe you. I recommend downloading the Dynon instructions - the information you are looking for is in there - not sure if you have had a chance to look at those, but I really recommend it. This is not an area for experimentation or invention - the Dynon guys have figured this out, and it's working well in 100s or perhaps even 1000s of aircraft.

At the risk of being put in jail for sharing Dynon's IP, here is just one of several drawings from the PDF that answers one of your questions:



As you can see, the clarity and quality of the work they have done is impressive, and the rest of the document is also easy to understand.

 

[jclark]

No GRT instructions included with package? They should be the source for dimensions.
Mounting bracket (black in picture) looks very similar to Garmin, Dynon, TruTrak so should be plenty strong without adding bolts through the spar.
If I remember correctly installing other brand servos, bolts & spacers etc were included in packages & not requiring additional spacer blocks being fabricated. Forces from the servo aren’t anywhere strong enough to bent bolts.
If the end bearing is stiff-replace it.

There are 36 pages, I believe, of GRT instructions, pictures, and dimensions on this. As I recall, the original "instructions" were of the Trutrak servo installations (20 years ago?????). So, servos like these have been successfully installed for years. Then GRT and Dynon (CORRECTLY in my opinion) used the same "form factor". So if you had an installation of Trutrak or knew how to do those, you could do the Dynon or GRT based on that, for the most part. Over time, the quality of the instructions improved, and Dynon set the high bar.

I mention this "background" so that new people just getting to this point in their build won't feel like they are plowing new, unsafe ground.
Critical to be done correctly, but "no new invention required".

Best of luck on your installation!

 

[jackking123]

Thanks Gents, everyone.... Yep Dynon has a pretty close to what I got last night playing with the geometry. If just eye balling it, assuming 3" total arm, instead of 2" I came up with approx 1.75" from pivot.

I noticed Dynon has the Rod on the outside of the Servo arm. That is fine but that makes the off set at bell crank even more. As it is now it is almost 3/4". This does assure better clearance to servo and actuator rod and it's hardware.

You need to be able to move aileron full up and down, while getting anywhere near 30 degree servo lockout (over center). Middle of servo travel is middle of bell crank travel is a good goal, except for next Par. (Aileron deflection down / wing goes up) is less than Aileron deflection up / wing goes down, I recall.)

There is also a compromise between total travel and force. Less load (servo torque) the more servo actuator needs to deflection (rotate).

Dynon I am sure figured all this out. I will gladly steal the info.

Thank you.