Belt or shaft?

[BABY HUEY]

An open Question to all,
Can someone explain to me how a shaft drive is supposed to be more efficent than a belt? The modern timing belt that we use on our helis is light, can't slip, minimizes gears and bearings and doesn't get hot so where does the "wasted energy" go?
Go ahead guys, Give me hell.

[Aztek1701]

Hi mate,

I wondered that myself so I googled it. I found what might be the answer on an RC car site.. Looks like there are 2 reasons why a belt looses energy... Harmonic vibration and stretching.

"there is only one factor that causes inefficiency. That factor being the belts! As speed increases a few things happen, firstly the belts will find their natural frequency and start resonating (vibrating up and down), thus expending power that could be at the wheels. As speed increases further, the belt tension increases and the growing rotational (centrifugal) forces try to pull the belt away from the pulleys which reduces the contact patch between the two and more power is lost. This is why belts stretch!"

Im guessing with the speed and length involved in a 600 size tailbelt, those two will be quite significant and this is where a shaft drive will better the belt. Probably not by much though.

Does this make any sense?... Azzy

[BABY HUEY]

That could be it although the energy has to go somewhere as heat or motion. The vibration could cause loss through heating but the contact patch won't matter until the belt actually slips. Meanwhile a shaft needs bearing support and bearings always rob power.
Thanks for the info.
Huey

[DaveC]

I think the advantages of shafts over belts is more theoretical than practical – shaft drives do tend to be more delicate – that’s why such models as the zoom 400 were soon converted to belt drive – However shafts do have one definite advantage - no static discharges.

Regards David

[BABY HUEY]

That's one thing that I hadn't considered, Static generation could consume energy from the belt and then cause problems in the electrical system. Just like a VanDegraf generator.
I bet that CF booms are very bad for that.
Wild!

[DaveC]

Yes in many of the metal framed models it can be quite bad and cause severe tail kicking, lot of people mistake it for radio glitching.

[uneverno]

The big downside of shaft drive is that on a boom strike, the crown gear tends to strip which means to repair, you have to remove the main head shaft whether anything else is damaged or not.

Shaft also tends to be noisier, if that's an issue.

A new belt will loosen over time. Checking tension should be a part of your pre-flight checklist. Once they get broken in - 40-50 flights - they don't stretch as quickly or as much.

I have read on some sites that if you spray a little WD-40 on the belt, it reduces the possibility of static build up. I've read you shouldn't do that on other sites, but no reason given as to why. Can anyone confirm or deny?

[DaveC]

I would Stay away from WD40 by its very nature it dammages the belt - silicone is much better - but both attract dust.

Completely agree with what you say about shaft driven being more delicate though.

Regards David