Large Model Association Forum

Just curious, has anyone had any success with any large scale applications of a contra rotating gearbox/ prop assembly?

Thanks in advance

Ben

i think its been done on a westland wyvern, first tested on a large aerobatic model, it was in one of the mags, think the power was a DA 150, through a gearbox but for some strange reason, i have a thought in my mind one of the props was a free wheeler???? anyone seen teh article? was it a true contra rotater, or a simulated one??

Hi Alan, thanks for that! I was mainly asking on behalf of a friend that was considering a shackleton build, who cant see the point in having "freewheeling" propellors!

Cheers

Ben

It was simulated Alan....the front prop was free wheeling.

The model is built by Dave Wigley.

http://www.youtube.com/watch?v=xh7vVt15uq8

I'd suggest the reason it's free wheeling is making a 'functional' operative system at this scale would be prohibitvely complicated & expensive (especially 4 of them!!!!!)

Also............the reason for contra-rotating props on full-size aircraft was to harness the power of some VERY large engines (almost 2,000HP in the case of the Shackleton, and over 3,500HP in the case of the Wyvern) Fit a conventional 3-4 blade prop on an engine of this power and the blades would be so large that, 1) The tips would most likely be supersonic (problem!!), and 2) so large in diameter, ground clearance (in the case of a tail dragger) could be a problem.

Our model engines do not posess this power......most struggle to turn a scale diameter 2 blade prop, let alone a 3 or in your proposed case, a 6 blade contra-rotator.

In order to run a contra-rotating prop, you would need to 1) Fit a MUCH bigger engine than is actually required to fly the model (bringing with it weight propblems as well as 'bits hanging out in the breeze), or 2) fit a reduction gearbox to the engine to allow it to turn larger props at lower rpm.

A gearbox and a contra-rotating unit................Mmmmmmmm.......I wonder whay thats never been done?

Phil

cheers for that phil, very informative post

Id already accepted that 4 identical gearboxes would be needed to make it possible at all, though I hadnt considered that reduction gearboxes might be needed too.

I volunteer on WR963 (the MR2 Shackleton at Coventry) and some of the chaps up there were throwing the idea around of building a large scale "Shack" the contra rotating prop idea was the main barrier they came up against!

Cheers

Ben

Hi Benjamin, your query regarding contra props ran a bell with me so I searched through some old mags....30 years or so old and found what I was looking for. Two 10cc engines mounted so they face each other with each shaft driving a coaxial gear system. The rear engine driving the inner prop driver and the front engine driving the outer shaft. Lovely piece of engineering but not too difficult for a decent engineer. Bet it would be great scaled up for larger engines. If you want pics I could email them to you if give me your email address. Dave Hayfield

Dave that sounds very interesting! if you could email some photographs they would be much appreciated!

My email is

nash966 AT googlemail.com

Many thans

Ben

I remember an old workmate at Bristol Siddeley Coventry, who was into scale control line models built a beautiful Fairey Gannet ( beautiful applies to the model, you couldn't describe the Gannet with that word!).
It was covered all over with aluminium foil, had retacts, arrester hook, flaps etc; best of all it had two engines driving contra-rotating props.
They were mounted on an aluminium tray along with the gear train, lovely piece of engineering.I seem to remember they both faced forwards and were mounted horizontally opposed with one slightly ahead of the other.
Never actually saw it fly, though I believe it did; not sure how he started the engines. Wouldn't quite sound the same as a Double Mamba though!
The model was featured in Aeromodeller way back in the 60's
Dave B

Hello Dave Berry, the Gannet you mention with the contra props is another one that I found whilst searching thro' old Aeromodellers but it looked a bit 'Heath Robinson' compared to the one I mentioned to Benjamin. Have those photo's as well if anyone wants to have a look.

Dave Hayfield wrote:Hello Dave Berry, the Gannet you mention with the contra props is another one that I found whilst searching thro' old Aeromodellers but it looked a bit 'Heath Robinson' compared to the one I mentioned to Benjamin. Have those photo's as well if anyone wants to have a look.

Hi Dave could you post a piccie or two, its a trip down memory lane. The guy was Bruce Randle, I think he won the Nats one year.
For the effort required to make it all work smoothly, the benefits seem marginal at best, especially for four engines.

All is not lost Shackleton wise, the early ones were tail draggers and had Griffon engines. I was stationed at RAF Ballykelly in the 1960s and in the early winter mornings going to the section they were parked up all floodlit and didnt half look like Lancasters from some angles. regards Ken 2854

nope i know WR963 currently residing at coventry airport is the last remaining shackleton in a position to move under her own power she needs a lot of TLC though, we should be repainting her sometime soon

Dave Berry, have tried to get contra prop piccies on this site but too much info for it to accept. If you want I will email complete pages to you from mags, let me know address.

Dave Hayfield wrote:Dave Berry, have tried to get contra prop piccies on this site but too much info for it to accept. If you want I will email complete pages to you from mags, let me know address.

Cheers Dave
Sent you a PM