[maus92]

I performed the first vibration test on my installation yesterday, and alas, it failed. The GMU25 is mounted on the port (left) longeron under the floor aft of the aileron push tube and forward of the roll trim servo. I *thought* that the area would be a solid location, but I guess not. I spoke with the G3X peeps, and described how the airplane reacts on the ground at full power (the airplane really rocks and rolls when brought up to full power,) and they said that would likely cause a failure. One suggestion was to ratchet strap the plane at a tie down spot and do the run up, which I will do today (I will still use the brakes ) If that doesn't work, another suggestion is to fabricate a doubler / stiffener to apply to the longeron beam. If that doesn't work....

Anyway, I'm curious where other RV-8s have mounted their GMU25s?

I'm wondering if the -8A moves around a bit more on run-up than the conventional gear -8?

CA

UPDATE:

The ADAHRS vibration test passed after ratchet-strapping the aircraft during run-up, so no need to relocate the GMU25 or install a stiffener plate.

I'm still curious where other RV-8 builders are locating their units.

 

[Robert Anglin]

Try a few spots.

We looked at a few spots, but found the back of the GDU-460 was as good a spot as could be had. We also have an 8A and with a very strong engine and very lite prop, that will start to drag things around if you don't tie down. That the mount pad made onto the back of the GDU works fine. I don't remember the figures, but I think we got less than 25% on the test run-ups.
You may need to mount yours some other place and I have seen others that wished to place theirs at other locations. I think you can try different spots as you like and fine one that way. One guy I know went through three locations till he found one that worked for him.
Don't know if this will help, but it is what we have seen in the field.
Yours, R.E.A. III #80888