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  #31  
Old 05-07-2014, 09:27 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by BillL View Post
Hey Bill,
Can the bolt with spacer be extended through to the second parallel plate to avoid having a bending load on a relatively thin plate?
...

Just a thought.
Good thought but it won't work because there is a lightening hole directly above the bolt.

BTW, this looks to be unique to the -9 and maybe the -4, if the roll servo is mounted in the wing. The reason is the -9 uses RV-4 bell cranks.
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  #32  
Old 05-07-2014, 09:35 PM
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RV-7 Flier,

You read that right. Yes, the servo generated enough torque to bend the attachment tab.

Also read my post directly above this one. The -7 and -9 have different attach points for the push rod. In addition, the -9 uses a larger roll servo (SV42) than the short wing RV's due to its longer wing. During testing I found the smaller servo didn't have enough strength to manage the roll forces in the -9.
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  #33  
Old 05-07-2014, 09:44 PM
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RV7A Flyer RV7A Flyer is offline
 
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So what "test" were you doing on the ground? The sort of standard "engage autopilot and verify roll commanding left and right/verify pilot can overcome servos" sort of test? And if so, you let it run all the way to the stop?

I have to admit, back when flying Pipers and Cessnas, we just did a quick check...engage it, turn the knob left/verify left yoke, turn right, overcome control forces, turn A/P off. Never let if go all the way, as far as I can remember.

And on the -7, with the Dynon SV A/P, it's inconvenient to set up and engage/test the A/P during run-up, so I don't do usually do it...hmmmm...maybe I'll start!

Put those servo limiters in, though...glad I did!
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  #34  
Old 05-07-2014, 09:54 PM
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BTW, I'd submit that if the servo is not slipping when the aileron *hits the stop* (a force against the servo much higher than any it would see in flight, no?), that the slip torque value is set WAY too high.
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  #35  
Old 05-07-2014, 10:03 PM
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N941WR N941WR is offline
 
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Originally Posted by RV7A Flyer View Post
BTW, I'd submit that if the servo is not slipping when the aileron *hits the stop* (a force against the servo much higher than any it would see in flight, no?), that the slip torque value is set WAY too high.
All I have to say is, you don't fly a -9 and I'm 100% certain you haven't tested the AP as extensively as I have. The settings I am using are where they need to be in flight and yes, they do slip from time to time.
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  #36  
Old 05-08-2014, 04:54 AM
TThurston TThurston is offline
 
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Question For the rest of us...

If there are problems in the autopilot installation for a significant beta tester, what issues do the rest us need to worry about? This thread makes it seem as though it's easy to inadvertently install things in a way that's unsafe.
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  #37  
Old 05-08-2014, 06:39 AM
krw5927 krw5927 is offline
 
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Quote:
Originally Posted by N941WR View Post
In addition, the -9 uses a larger roll servo (SV42) than the short wing RV's due to its longer wing. During testing I found the smaller servo didn't have enough strength to manage the roll forces in the -9.
This is significant, and may even be a cause of the bent steel. I have the SV32 on my 9A for both roll and pitch, and while I'm still in Phase I with not nearly as many hours as the OP, I've not had any slip problems in some very gusty conditions. In fact, Dynon recommends the SV32 for RV9 roll and pitch in its servo application guide:

http://wiki.dynonavionics.com/Servo_...ion_Guide#RV-9

Could it be that the bellcrank bracket simply isn't strong enough to withstand the forces that the stronger SV42 is capable of imparting?
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  #38  
Old 05-08-2014, 06:55 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by N941WR View Post
...Only one problem, the idea of washers to raise the servo won't work because the critical dimension is between the top of the servo arm and the bottom of the servo body. No joy...
I'm not quite following here Bill. Are you suggesting the airplane structure located between the servo body and the output arm is so close to the arm that the servo can't be spaced at all? I'm only suggesting a spacer here as an incremental step. Any space you gain here can be removed from that "final" spacer, which is the main goal.

As for running out of space for a bolt head if you flip the rod end- you might try using a Hi-Loc pin as a bolt. Plenty of strength with a Hi-Loc, so no worries there, but they have a very low profile head. I have a bunch of them around and use them in cases like this. If you think that may work and can't find one, provide me the set up (grip length) dimension and I'll see if I have one. If I do I'll throw a couple in the mail to you.
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  #39  
Old 05-08-2014, 07:09 AM
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Originally Posted by krw5927 View Post
...Could it be that the bellcrank bracket simply isn't strong enough to withstand the forces that the stronger SV42 is capable of imparting...?
Maybe. This looks like a case where little details can bite you. Just eyeballing this setup, I don't like to see the total length of that attaching arm... There is a lot of force involved and an arm that long provides a bunch of leverage. That said, the main factor IMHO is the small diameter of the spacers involved, particularly that last one. Evidence supporting this conclusion is the fact that the metal bent right at the edge of the spacer. While still far from ideal, I'd suspect that simply increasing the diameter of the spacers will increase the stiffness of the system enough to prevent the servo from bending the metal.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

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  #40  
Old 05-08-2014, 08:20 AM
krw5927 krw5927 is offline
 
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Quote:
Originally Posted by Toobuilder View Post
Maybe. This looks like a case where little details can bite you. Just eyeballing this setup, I don't like to see the total length of that attaching arm... There is a lot of force involved and an arm that long provides a bunch of leverage. That said, the main factor IMHO is the small diameter of the spacers involved, particularly that last one. Evidence supporting this conclusion is the fact that the metal bent right at the edge of the spacer. While still far from ideal, I'd suspect that simply increasing the diameter of the spacers will increase the stiffness of the system enough to prevent the servo from bending the metal.
I agree with you. However there may be hundreds of -9's flying with this installation per the Dynon instructions. We seem to be on a path of suggesting that the manufacturer's installation instructions and parts are inadequate, which may not be the case. The OP has a non-standard installation that will produce more than a 50% increase in force over the standard installation, using the same hole in the servo arm. Given the same geometry and test routine, would the SV32 have been capable of damaging the steel brackets? Who knows. But thankfully this is the first case we've heard of.
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