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SkyView Servo

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stevengrasley

Member
A few weeks ago I was tinkering on my RV-7A in the hangar and found my ailerons "stuck". I could not figure it out. Suffice it to say that the roll servo was locked up and the shear pin let go in my process of figuring it out. However, the servo seemed to operate just fine.

Contacted the always great guys at Dynon and got an RMA to ship it back. It has been in service for 2.5 years and about 500 flight hours. (Yup! That's 5 followed by two zeros and no decimal. Not a typo.) Anyway, shipped it back.

A few days ago I get an email that says I better buy a new servo as this one is beyond repair. Well, I bought one about a day after the lock up because I could not imagine the 6 hour cross country I had planned without my trusty autopilot. But I thought I was going to have the repair back for a spare. Not to be.

Here's a couple pics that Dynon sent back to me. Whiskey Tango Foxtrot?! This is installed in the standard location in the right wing. Has anyone ever seen or heard of such a thing? Seems to me there had to have been a seal problem or something. The inside of the wing looks like it did 2.5 years ago when I built it. No signs of this kind of crud anywhere. Did a get a bum unit from Spruce when I first bought it? I think it was a fresh box.

Any insight would be appreciated.

Well...sorry about that. I have to learn how to post a pic first. I'll do that in a few minutes. Next post should have the pic.
 
Pics to go along with the thread

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Here are the two pics that go along with my opening thread. Hope this works.
 
I've seen a similar issue on an RV10. Nowhere near salt water and always hangared. I agree that something is amiss on Dynon's part. These are not the only ones.
 
jabarr said:
I've seen a similar issue on an RV10. Nowhere near salt water and always hangared. I agree that something is amiss on Dynon's part. These are not the only ones.
Click to expand...

That is very interesting. The Dynon servo is not mechanically dramatically different from others. The difference is in the electronic connection. If I would have known the unit was dead I would have kept it to tear it apart myself and see what I could learn. But notice how the "moisture" was clearly only in the top of the rotor. How did it get there? Seems that a shaft seal or a case seal is not right. Flowing down from above it seems. There must be a clue here.
 
We have seen a few of these over the years, but in the neighborhood of 0.05% of all servos we've sold, and we've been selling servos for 10 years.

The motor is not actively sealed, so this doesn't represent the failure of a seal. The only commonality we've been able to identify is most of them are from Florida. In some cases the owner was aware they actively got exposed to water and those ones look the same as the unknown ones.

Only the AN trolls really know what goes on inside a wing when nobody is looking ;)

--Ian @ Dynon
 
dynonsupport said:
We have seen a few of these over the years, but in the neighborhood of 0.05% of all servos we've sold, and we've been selling servos for 10 years.

The motor is not actively sealed, so this doesn't represent the failure of a seal. The only commonality we've been able to identify is most of them are from Florida. In some cases the owner was aware they actively got exposed to water and those ones look the same as the unknown ones.

Only the AN trolls really know what goes on inside a wing when nobody is looking ;)

--Ian @ Dynon
Click to expand...

Well...guilty about being from Florida. And I do fly IFR regularly and have flown in steady rain on several occasions. But not sure how this would be a factor when there are lots of RV's flown in rain. Are there any recommendations for preventative maintenance or perhaps a mod that could prevent this failure mode? Is there a shield that could protect the servo from getting wet in rainy conditions?
 
Steven,
Given how rarely this has happened, we don't have any good input on how to protect the servo in the future.
 
I think I'm going to try bagging it somehow to keep it from getting wet when I fly in rain. I am certain the inside of the wing gets wet during flight in rain. I'm just not sure how bad the conditions can get in there. Thought about flying with a Go-Pro in the wing during some rain as a test but that is not an easy situation to arrange. So, in the mean time I'm going to experiment (what a concept) with some approaches at plastic bagging the servo to protect it.

Anyone with any insight into this approach?
 
Steven,
The servo creates a fair amount of heat when in operation, and is designed to dissipate that via convection. I don't believe it's a good idea to seal off the air to the servo via a bag around it unless you can create some airflow inside that volume or give the heat a mechanical path.
 
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