E720 tail (build/design issue?)

[rotormonkey]

I'm most of the way through the build on a new E720, and I'm a little perturbed with the tail.

All the bearings and shims are installed according to the manual, but the whole grip on one side floats back and forth. The issue is this:

Most grips are designed so that one radial bearing is installed from the hub side of the grip, then you put the rest of the stuff inside (the other side of) the grip and it's all captured and holding itself together.

The E720 grips - everything goes on the inside. There seems to be a tolerance issue where the bearings fit loosely in one grip (actually both, but one is real bad). As a result the entire grip can be slid back until it hits the center of the hub. You can see all the bearings are captured where they're supposed to be - they don't move.. But the grip itself slides back a bit and the bearings punch out the other side.

Does this all make sense? Not sure I'm explaining it well.

Have I done something wrong here? Or is this just a tolerance issue? If the bearings fit tightly this probably wouldn't be an issue. I tried slathering in some bearing retaining loctite, but it's too loose for even that to work.

[borntofly]

That is normal. It is designed that way. In flight the grips pull outwards. They grips need to slide back and forth smoothly on the bearings.

Do not put retainer in there!!

[rotormonkey]

I kinda figured centrifugal force would pull them out anyhow.. Just on the off chance there's a side load that makes it snag a bit I figured I'd be in for some vibes if it didn't pull out..

What an odd design. What advantage can "floating" grips have?

Ahh well.. Guess I'll pull 'em apart, clean 'em up and put some grease in there instead of retaining compound :)

[borntofly]

Not to sure what benifits that design has. I am sure there are some though. The do work really well. Blades track perfectly and i have very little slop in the grips after quite a few flights.


We actually did some calculations the other day. Mainly with main blades and the forces on spindle bolts and blade bolts. On a 90 with 710's at around 185grams a blade, Spinning at 2250 there is around 550kg of force on those bolts, each!!. Over half a tonne!!!



And we did some quick calcs on the tail too. 105mm blade weighing 7 grams, when spining at 10,000rpm the weight of the blades is equivelent to around 85kg!! Scary stuff lol. So yes centrifugal force would definitly see those grips pulled all the way out :)