Hey friends, I was hoping you could inform me if my ducted fan 91 would work as a prop puller. It spins at 24k will props agree with that? Thanks for your support. -Dann

I have seen threads about it.... I think you can get a 10x10 around 17K (Guessing) Try a search---

Hi,
Yes it works for a speedplane. If you use a DF-pipe then you should use a header of atleast 6" long to begin with. Start cuting the header 1/2" each time until you reach the maximum rpm for the propp you wish to use. My rossi 105 turns a APC 10x10 about 17000 and gives good speed, about 120mph, for my airplane 80"wingspann and 11LBS. I also have a CF-propp 9x10,5 from Mr der Steuermann that I am gonna try very soon. My rossi turn everything from 10x10-12x12 without showing too much signs of overheating and the plugs lasts. I could probably shorten my header 1-2" and gain more rpms on the 10x10, but it is already kind of on/off and peaky, so I dont want more boost in my system for now. OS carburetor has always been among the best so you should get good success with your engine.
Thanks, Amir

Yes and does it work! I finally put my new OS vrdf .91 on the front of my old EZ Dago Red (55") with the belly scoop and stock cowl changed to a Stiletto Configuration. With 15% and an 11-8 apc I did have my hands full. At a slightly rich setting using a 13.5 cc pipe, it was moving faster than with my .65 vrdf and stayed even with the .77 which has been clocked at 180 mph. Static it was turning 22k plus and VERY LOUD. I will lean it out this weekend. This is one fast bird which is rock stable. Even the tendency for a 'fall-out' in a pylon turn went away with the .91........ any ideas???

rc guy

Your 11" prop at 22K rpm on a plane doing 180 mph is having supersonic tip speeds... that's probably where the noise comes from... and it's not very efficient either... which means you're wasting energy... which means you could probably go faster with the right prop (APC's weren't meant to go supersonic)...

Obviously prop choice can be a bit tricky on these engines.

So as a reply to the original question here: yes the 91 will work with props... but it won't be as simple as slapping a 10x6 on a .40...
If you want your .91 to spin up to 24K you better start thinking about carbon props too.

I have read similar threads like this where the prop blades came flying off, luckily no one got hurt, choose your prop wisely

If you want to go fast using a .91 DF you might want to try control line speed props.
Go to www.clspeed.com parts finder page.I am currently working with a 8x10.5 CF
prop from John Newton that I will be using on a Jett FIRE BSE 65 in a modified Diamond
Dust. There are several people on this web site that sell props, so you will have to make
a few phone calls. Generaly you will want to use props for D speed which are used on
.65 and larger engines. By the way these props are not cheap! The one I got from John
was $14.00, and still needs to be finished,but this is one serious prop! Hope this info is
helpful, and please be careful because it's hard to fly without fingers!!!!
Sincerly, Scott Romine

r-c-guy,
My Rossi 105 DF-engine turned APC 11x8 at only 16800 rpm with a muffled pipe, and I got afraid the prop will explode any time. APC at 11" diameter should never be turned faster than 17300rpm static. The APCs are rpm limited to 190000/diameter. So if your engine is so powerfull then you should only use CF props.
Thanks, Amir