View Full Version : Lift fan ideas

14-Jun-11, 12:40 AM
I'm putting a pulley reduction on my lift fan to actually get the thing to hover; what's peoples ways of doing the fan shaft?

It's got to be as short as possible as the Robin is pretty long and the fan's getting way too low in the duct or the engine's going to be sticking out a long way, or will remake the duct flatter on the hull.

I was thinking bolt pulley to fan hub, then 2 opposed taper bearings. Shoulder on the shaft pushes on the lower bearing and bolt tapped into the shaft clamps the top bearing against the lift frame.

Main problem at the moment is the fan's limited to 4500rpm so the engine is at 4500rpm also.

What are people's opinions on this? (without buying a new engine!)


14-Jun-11, 05:08 PM
by pulley reduction do you mean you want to go from direct drive to belt/pulley and are you going toothed belt or V belt

you can go 1:1 with the pulleys for 4500 but this will stress the belt as the same teeth or part of the belt take the power stroke every time, also don't go too small with the pulleys - better to have a tooth or so different or slightly different sizes if a V belt

only single taper needed as there is only thrust in one direction, i run single taper thrust end and deep groove roller other end

hope that helps


18-Jun-11, 04:16 PM
Yeah that's right, it's direct drive at the moment so going to 1" toothed belt I think.

I was going to go with 30:48 pulleys, is that a reasonable size? The ratio would let the engine go at 6800rpm, and the fan at 4250rpm. Or would it be better to stick with the 1:1 ratio? I was trying to get the engine spinning a bit faster.

Ok thank you about the bearings!


18-Jun-11, 04:22 PM
go 1:1 and you'll have no teeth left on your belt - even if you go just above or below 1:1 it will be better


18-Jun-11, 05:14 PM
OK thanks :)

Out of interest what's the reasoning for almost 1:1 as opposed to 1:1.6?

18-Jun-11, 09:23 PM
1.6:1 is fine - if it's an exact ratio i.e 1:1 or 2:1 then the same teeth on the belt get the hit every power stroke of the engine reducing it's life

Keith Oakley
19-Jun-11, 09:54 AM
Exact ratios also produce a beat between the engine and fan frequencies which can be a very annoying noise