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New Trutrak screw retainer interference

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pauldan181

Well Known Member
Has anybody tried to install the latest fix on their RV-8 pitch servo? The gap between my elevator crank supports is per the plans, 3/4 inch and the width of the new servo arm screw retainer is 13/16. Here's a lousy phone photo of the problem.

servoclip.jpg


It's too hot to mess with it anymore today. :mad:

Paul Danclovic
Jamestown NC
RV-8A N181SB
 
Hard to tell the exact problem from this photo, but from your description, I wonder if you could just make a spacer to go between the servo and its mount, (from some sheet stock), and move the servo out a bit, equal to the thickness of the new retainer??
 
Mike S said:
Hard to tell the exact problem from this photo, but from your description, I wonder if you could just make a spacer to go between the servo and its mount, (from some sheet stock), and move the servo out a bit, equal to the thickness of the new retainer??
Click to expand...

Yeah, I didn't describe this very well. The servo arm must be vertical ( parallel with the crank). This means the new retainer will hang down between the crank and servo mount angles. The retainer is wider than the space between the angles.

Paul Danclovic
Jamestown NC
RV-8A N181SB
 
adding a spacer between the servo body and the outside of the 1/8" angle will only work if there is enough clearance between the servo arm body to the inside of the 1/8" angle.
 
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This particular installation was going to be my Sunday afternoon project tomorrow. Now I guess I'll be putting that one off a bit... Thanks for the heads-up, Paul.

This is a head-scratcher, because it looks like there's not really much room between the servo-arm screw head and the servo attach angle for ANY kind of reinforcement like the TruTrak-supplied part.

Have you notified Lucas at TruTrak of the issue?

(I guess this thread just did, actually...)
 
Timely Post

Yep. Having the same problem. Tried to PM Lucas and it said his in box is too full (on this PM, not the TT one). Dave
 
Thanks for the head's up on this one - I got four of the retainers (two for each of our airplanes) in the mail this past week, but they haven't made it any farther than the kitchen counter so far. When we discovered the backed-off screws on the RV-6 a couple of months ago, we built safety brackets for it, and are comfortable with them until we open things up again. The -8, I inspected at that time, and the screws were tight. So I figured I'd install the new brackets the next time we're opened up. Y'all come up with a fix before then, OK?

Seriously, my first thought was carving away the offending part of the angles that form the bracket, but looking at the picture in the first post, that looks like it would be too much material. More head scratching.....

Paul
 
That entered my mind too

It entered my mind to carve off some of the L bracket, but reality set in (like with you Paul) and that's not the appropriate way in my opinion. I think if they used a thinner material (like stainless steel) and had a joggle to curve down the arm, then another joggle to go down the servo, that might work?

I don't know if that would work because there still might be a clearance issue -- it's all pretty tight quarters right there. Dave
 
We were aware that it probably wouldn't fit every installation. Having access to only a few models to actually test, we weren't able to pinpoint which ones that would be. Anyone that has an RV-8 can send in their pitch servo to be retrofitted. Please contact us to obtain an RMA number before sending the servo. I am out of the office today, but should be back tomorrow. Thanks!
 
This is great news, Thank you Lucas.

Is there a chance to get a servo turned around before OshKosh? I certainly don't need my pitch servo for 90 Knots down a RR track practice, but it sure would be nice for the trip up.

Paul Danclovic
Jamestown NC
RV-8A N181SB
 
I wonder if....

Could the bottom be cut off and then a second hole drilled through the servo harm at the location of the inter-most hold of the retainer clip. A second screw would secure the clip to the servo arm and the end of the clip still set over the servo screw?

The current design worked out well on my RV9A installation.

Kent
 
Lucas

Lucas,

You say to send in the servo for the retrofit. I'm curious what are you going to do retrofitting the servo, in the RV8 application, to fix the problem. It appears to be a clearance issue with the mount.

Ted
 
I wonder if...

Yes. In answer to KentB's question, I did cut off the end of the clip and secured the clip to the servo arm with an additional screw and nut. This avoided changing the geometry of my existing installation. (this was in a 6A with an underseat mount, with a longer than standard servo arm).

Eric
 
Eric Petersen said:
Yes. In answer to KentB's question, I did cut off the end of the clip and secured the clip to the servo arm with an additional screw and nut. This avoided changing the geometry of my existing installation. (this was in a 6A with an underseat mount, with a longer than standard servo arm).

Eric
Click to expand...

Maybe I need to see a picture, so I might be mis-understanding you...but the "bottom of the clip" (the part that wraps around the end and under the capstan) is what it going to actually retain the arm on the capstan if the screw comes out, while still allowing the shear screw to do it's job. If you secure the clip to the arm, that's doesn't keep the arm on the capstan if the main screw backs out.

Paul
 
Ironflight said:
Maybe I need to see a picture, so I might be mis-understanding you...but the "bottom of the clip" (the part that wraps around the end and under the capstan) is what it going to actually retain the arm on the capstan if the screw comes out, while still allowing the shear screw to do it's job. If you secure the clip to the arm, that's doesn't keep the arm on the capstan if the main screw backs out.

Paul
Click to expand...

I think Eric did the same as I did with the roll servo. I didn't care for the way the retainer would move the pushrod aft (the thickness of the retainer) and that much closer to the floor stiffner angle. I cut off the top two holes and fastened the retainer with a short screw in the third hole. This allowed the pushrod attach hardware and alignment to remain the same and the "clip" part of the retainer is still there.

Paul Danclovic
Jamestown NC
RV-8A N181SB
 
Still speculating here...

Ironflight said:
Maybe I need to see a picture, so I might be mis-understanding you...but the "bottom of the clip" (the part that wraps around the end and under the capstan) is what it going to actually retain the arm on the capstan if the screw comes out, while still allowing the shear screw to do it's job. If you secure the clip to the arm, that's doesn't keep the arm on the capstan if the main screw backs out.

Paul
Click to expand...

I believe that the bracket only keeps the screw from backing out. The wrap around gives the bracket two points to keep the retaining hole over the screw. If you use two bolts/screws on the bracket, you should have the save effect.

I think that if the screw would shear (I don't know how that would happen) the part that wraps around the bottom of the arm would not keep the arm from sliding off.

Kent
 
kentb said:
I think that if the screw would shear (I don't know how that would happen) the part that wraps around the bottom of the arm would not keep the arm from sliding off.

Kent
Click to expand...

That's what I am talking about - you don't want to cut off the part that wraps around - it is what is retaining the arm.
 
"what we have here is a failure to communicate"

Ironflight said:
That's what I am talking about - you don't want to cut off the part that wraps around - it is what is retaining the arm.
Click to expand...

Please remember that I am not a mechanical engineer and am just speculating an idea, and not very well.:D

So there is my 1000 words:




The lower left is the current SB. The two arrows show the points that are helping retain the screw. If the screw looses ability to hold, IE stripped or broke and the pin in the arm breaks the assembly can slide off the servo shaft and flop about (BAD).

The upper (bigger) picture is what I was wondering about. The upper bolt is the first point and the second screw/bolt (represented by the orange line) is the second point. The screw can't back out. Again you could have the same failure mode as above, but the screw can't back out.

The second screw would need to be sized so that it wouldn't interfere with the motion of the linkage.

I hope that I am clear with my idea.

Please remember that I am not arguing that this is a good fix. I am just asking of those that are more mechanical if this wouldn't work?

Kent
 
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Retainer

I agree with Paul and would not cut off the wrap-around end. Without it the purpose of the bracket is undone.
 
kentb said:
The screw can't back out. Again you could have the same failure mode as above, but the screw can't back out.
Click to expand...

Kent, I think the problem is that with the bottom wraparound gone, the screw can still back out of the shaft. The arm will 'back out' with it. In fact there's nothing to prevent the arm/screw assembly to back completely off the shaft, so the linkage binding problem can still happen.

--Paul
 
Sorry for the confusion...

I modified the clip as both Paul and Kent described. Removing the extra mounting holes (NOT the wraparound), and securing it with an additional screw (pan head) and nut. This allows the clip to perform the function intended by TruTrak, without having it affect any of the previously installed pushrod geometry.

Eric
 
Eric Petersen said:
I modified the clip as both Paul and Kent described. Removing the extra mounting holes (NOT the wraparound), and securing it with an additional screw (pan head) and nut. This allows the clip to perform the function intended by TruTrak, without having it affect any of the previously installed pushrod geometry.

Eric
Click to expand...

Just did my 6 roll servo the same way. If the clip was simply a bit longer it would have been a non issue. Cut the top hole off to avoid any possible binding. Drilled a #6 hole through the long servo arm and bolted clip through that after wrapping it around bottom.
 
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