mrcumming

Be Nice Guys

I have just bought a Richmodels Keecat 65 and will be fitting an OS91 FX engine.

What is stopping me hooking an OS91 FX up to a fan unit?

If it would run a fan unit would it out perform a prop.

I will now open the can of worms!

If this is a complete non starter what engine and fan would you suggest.

Your help and suggestions would be much appreciated guys

Many Thanks
Lex

jason

My Feedback: (1)

Hi

It won't rev enough if its not a DF or marine engine.

Jason

LGM Graphix

My Feedback: (22)

As Jason said, nowhere near enough RPM, and you'd have a heck of a time mounting it with the front intake and side exhaust.
If you want to use a ducted fan get an OS90VRDF but the pipe mounting will be a bit of a trick.

Ram-bro

My Feedback: (101)

what they said.....

Jet Doctor

Hi Lex

As the others have said - too low RPM. Most of the fan units that actually worked ran the OS 91 VRDF motor. These would give you in the region of 25 - 30000 rpm. The fan unit that worked best with that was the Ramtek unit. The other key to reliable performance was the BVM tuned pipe and BVM in flight mixture control. Fuel needed to be around 10% nitro and 23% oil, 18 castor and 5 synthetic.
BVM also produced a .91 which became a .96 with BV's own fan unit. You would probably be better off looking around for one of those combo's. I am sure there are plenty lying around with the move to turbines. Motors we could not get to work here (6000ft asl) were the Rossi's and K&B ducted fan motors.

mrcumming

Thanks for all that guys. My next question is where you can buy these fans in the UK especially. Is the gdf becoming out dated or is it just a bit specialised. And finally before i invest my hard earned in a fan kit what really is the advantage. I had originally decided on an OS 91FX and a 14 x 6 pusher prop. Will an OS 91 VRDF motor and fan out perform it or will it just sound nice. I am a heli flyer and am quiet used to the unnecessary expensive upgrade stuff. Pros and cons please.

mugenkidd

My Feedback: (94)

IMHO the 91fx is just the wrong engine for this plane. The .91 fx is a torque monster and when wanting speed from a .60-90 size pusher you really need to look into something that can get you RPM's with the props that will fit you plane. youget speed from pitch and RPM, with a 14x6 prop you'll probally be getting about 12000rpm on a 6in pitch prop so you'll have around a 70mph jet [:'(] Look for something that can turn an 11x7 or 10x8 pusher prop somewhere around 15000rpm +, something like a rossi or dubb jett engine....or if you want something cheap try a tower .76 or a gms .76 with a 10x8 pusher... may not last really long but you will have flights over 100mph , I had a GMS setup (10x8 apc pusher prop at about 14,700rpm on the ground) on the bobcat 50 with over 20 reliable flights before a sold it.

As far as your last question the only thing the .91fx and .91VRDF have in common is the ".91" totally different engines, the 91VRDF makes about 5hp at 20K+ rpm while the fx makes around 2.7hp at 15000rpm. One thing that you could do is use a .91 vrdf with a byron impellor without the shoud, but my suggestion would be to look in the "extreme speed prop planes" section of RCU a lot of good information over there.