How hard do you tighten yours?

[Adrian Smith 1]

In a more whimsical moment I was wondering about tightening the four propellor bolts on my OS petrol engines and when to stop. Given that the wood hub is easily compressed by tightening bolts, one can quite easily tighten the bolts indefinitely until the hub eventually splits, or at least over period of time splits as the hub weakens due to compression from the prop plate. Any ideas?

[Phil 9]

if only there was a tool that can tell you how tight a bolt is?

[Denis Watkins]

Adrian, Phil says buy a Torque Wrench.

[Ultymate]

There is it's called a torque wrench

[Adrian Smith 1]

I have a torque wrench guys which fine for hard materials (metal) , but with wood it is difficult to get the correct tightness (what ever that is) without over compressing the hub. I have seen no guidance on this anywhere. I know for M5 bolts the recommended tightness is 5 to 6 on the scale, but that's not for wood because that just mashes the hub (don't ask me how I know!).

[Flyer]

Use a washer too on the hub? It will distribute the load across the hub, thus reducing excess compression.

[Shaunie]

Surely, if I the hub is excessively crushed before the bolt reaches the correct torque then there is insufficient load spreading under the head of the bolt. Either you need bigger washers or a boss plate the size of the prop boss with the same bolt pattern as the prop is drilled. This should be of sufficiently thick material not to deform as the bolts are tightened.

Shaunie.

[Adrian Smith 1]

I am using the boss plate supplied with the engine pre-drilled, Shaunie. I am not sure how adding washers too makes that much difference, flyer. Probably the boss plate is undersized, but I am using props recommended for this engine so you would have thought OS would provide the right size boss plate.

[cymaz]

After flying I release the prop bolts so that there is some slack on the boss. This means the wooden prop will not shrink under pressure and go loose without me noticing.

Edited By cymaz on 01/07/2016 06:19:15

[Rich too]

I'm with Adrian on this. Just fitted a wooden prop on my first multi bolt hub, and had exactly the same thoughts - the bolts don't seem to tighten and bite, they just squash the hub more and more! And no torque settings are available? Mine is a DLE 30..

[Matt Jones]

There's some data in this thread including, allegedly, some supplied by DA.

http://www.flyinggiants.com/forums/showthread.php?t=48054

[Rich too]

DLE manual is very useful

9. Mount the propeller to the engine using the 4x35mm SHCS with

4mm lock washers and flat washers. Be sure to use threadlocker.

[Adrian Smith 1]

That is useful Rich. So two different types of washers per bolt. I don't use thread locker on props as at the end of a flying session the spinner and prop are removed and stored. Mainly because I protect the prop from the humidity in the air in my work shop. After 3 or 4 eight minute flights, during a session, I usually check the bolts for security and thus far I haven't had a problem with the prop becoming loose.

Thanks Matt I will give it a read.