thrust of OS 91FX
 

Can anyone please give me any idea on the type of performance I could expect from a 2800g (about 6 1/4 pounds) CAP 232, using a standard OS 91FX. And what size prop would be best for hoverig? This project is still in the pipeline but I have everything to do it.
Any feedback greatly appreciated
Greg

Cap ?
 

That setup should be near unlimited. I have a 5.75 lbs. (wet) GP Cap 232 and it just hangs on the prop with an O.S. .70 Surpass II with a 13x6 prop. This represents the minimun setup that I would run in a plane of its size. It can do most maneuvers except for those that require a sustained upline. I can do a 4 point roll on the vertical if I do it quick enough. You will want to keep the diameter of the prop big and the pitch low. Something like a 14X6 15X6 etc. Good luck!

Phil (Mesa, AZ)

thrust of OS 91FX
 

Thanks Phil, a bit of good news like that is always encouraging.
The CAP is a Phoenix ARF 50 size. My brother owns the Extra 300 version of the same brand and size. It flies great, but is a little underpowered for my liking with a Saito FA80GK. I had the 91 in a 2500g fun fly and it didnt realy need wings. I have a 14x6 so I'll try that first.
Thanks again Greg

thrust of OS 91FX
 

how abt an apc 16x4...im going to use this on my OK Models EZ Cap3d...engine is 91fx.

anurag

thrust of OS 91FX
 

I have a 91fx in a 7 pound gp shoestring and vertical is truly unlimited. It used to do a good job in an 8 pound cap. I woud use a 15-6 for 3d, other good props are 14-6 and 14-8. I use a 13-8 in the shoestring for speed. You will have too much power more than likely.

thrust of OS 91FX
 

My calypso weights 6lbs 15ozs. My fully standard 91FX with a 13/10apc will accelerate it out of a hover smartly up to good flight control speed (not a climbing hover). With a 13/8 master 3 blade vertical is still good but braking is better. I put an ultrathrust muffler on it and now the vertical looks like a rocket launch.

thrust of OS 91FX
 

Use this online thrust calculator.
http://pages.sbcglobal.net/limeybob/thrust2.html

On my Saito 91, I spin a 15x6 at 8400 RPM so my thrust was 9.52lbs. Not enough to 3D my 8.1lbs pound pig.

thrust of OS 91FX
 

Thanks for all your feedback guys. I cant wait to try it. I cant fly it for another 2 weeks due to other commitments, bet I'll be hangin out to try by then!!

Greg

OS 91FX
 

Ok, where do you guys live?! Smallfly, thank you for a great answer. An OS 91FX should pull a 6 pound plane out of site at 3/4 throttle. The elevation where I live is only a couple hundred feet, and I use a 14x6 prop on a 6 pound airplane and it climbs vertically at 1/2 throttle, not fast but it does it. On OS 70 should easily over a 5.75 pound plane at my elevation but maybe you live at 5,000? I think those who post these types of threads should state their altitude, temperature, and humidity so those with the same conditions should reply. Other wise some guy who lives at 12,000 feet in Colorado will think that a 46 will hover a 5.5 pound plane. I think the guys who need help will get a more realistic picture of what to expect.

Thanks,
Stephen

thrust of OS 91FX
 

Now for my answer:

If you live at a higher elevation you should be able to use a bigger prop as the prop can cut through the thin air easier. A 14x6 down in Riverside, California will put the heck out of a 6.5 pound airplane. It will turn in the 11,000 range I believe and give you around 13.9 pounds of thrust. Or you could use a 15x4W for 3-D type stuff which will give you more like 15 pounds of thrust. If you live higher up, a 14x8 for speed or a 15x6 for pull would probably do good. If you live higher probably a 14x9, 15x7, 16x4.

thrust of OS 91FX
 

Oh, another thing. I recall reading somewhere to run the 91 at 10,500 or higher as to not overheat it. I imagine running at 10,000 would be fine, but remember, this is not a YS and you can't expect it to turn huge props :-). Though I also recall from the 91's manual that it says a 15x8 would be a good break-in prop! Hmmm, don't try that guys or you'll have to pay to get it all fixed...

thrust of OS 91FX
 

Planeboy P51

The flying field I fly at is only about 200 feet above sea level, and the climate is mediteranian, so I'll try the 14x6 and see if I can get hold of a 15x4w.

Thanks Greg

thrust of OS 91FX
 

Have 91fx in aeroworks 540 edge, weight is just under 8 lb on kitchen food scale,minus fuel,zinger 15x6 prop, sig 15% fuel,os#8 plug,will not hover very long then goes into tailslide, vertical is not unlimited,have tried many different props,next is to change to larger engine,bummer.
Watch your 6, John

thrust of OS 91FX
 

I use a 14x8 on my OS 91FX installed in a GP Cap 231EX (no longer made). Mine weighs in at 6lb 10oz, and is truly unlimited vertical. I can take off in 10 feet and pull vertical immediately, doing inverted snaps on the upline -- wahooo!!!

-Chris

thrust of OS 91FX
 

Dude that sucks :confused: ! Um, zinger props are just a plank of wood... go to an APC. If you didn't, try a 15x4W, YS 20/20 fuel. If you wanna spend a little more money go with one of those in cowl Jett mufflers, I hear lots of guys are going with these for your combo. Your combo should put out over 15 pounds of thrust, that's with an APC. A Zinger won't turn the RPMs of an APC, and it's not nearly as effiecient. But the most thrust you could lose couldn't be more than 1.5 pounds...

thrust of OS 91FX
 

Thanks but I've been down that run, also a bunch of other people ,that prop made it worse,1.08 os is next,thanks but there are other threads on this setup,so will not go any futher on this thread.
Thanks again,John

13 x 8?
 

I am planning on running the 91fx in my 6lb 10oz Adrian Page Gee Bee R2. I was told that a 13 inch prop is the largest prop you should consider due to ground clearance. Would a 13 X 8 be a good choice?

O.S. recommends a 13 X 8 or 13 X 9.. and that's it. But I see that some folks are using 14's!

What gives?

thrust of OS 91FX
 

generally speaking,larger dia. less pitch=more thrust,like first gear in a car,smaller dia. more pitch=more speed,like high gear in a car,BUT some where you need to find a happy medium for your plane and style of flying,one way can over rev the engine and go no where,the other extreme is to over load the engine and burn it up.

thrust of OS 91FX
 

I have a a sig 4 star60 with a 91fx / APC 15-6. It weighs in at 8 lbs. dry. I can hover it at about 1/2 throttle, go to full and accelerate up until I decide the plane is to small. I'm using 15% powermasters and sitting at sea level. Of course a really hot day for me here in Alaska around 75 degrees.

Michael

thrust of OS 91FX
 

More info on .91 performance can be found here:

http://www.rcfaq.com/

thrust of OS 91FX
 

I run a 14 inch prop on my R2. You could run an 18 inch prop if you can turn it.

Adrian

thrust of OS 91FX
 

Also try this program, http://www.bmaps.net/software/thrusthpv20d.zip

You can specify prop diameter, pitch, RPM, even the brand of prop you are using to find the thrust