Hey guys ,
Need some advice. I have a ucando .60 with an os 91fx. today on my maiden flight I used a MS 16-4 and I had poor performance. It spooled up just fine made alot a noise but flew very slow. Can anyone suggest a good prop for me (probably an apc something, I'm guessing) and if someone can post the link for the ucando 60 thread I'd really appreciate it.
Thanks to all who reply.
Mark

i am flying the same os91fx on this bird and use 13x8 with unlimited vertical. if you want even more (faster) vertical try 13x6. both are apc. the os91fx NEEDS to rev. read tower hobbies teck report on this engine or what the pro's have to say in the engine forums. this engine does not like to be over propped. i think a 14x6 is to much. this is a great engine that needs to be unleashed IMO

do re member that this plane's wings do not like speed so if you use an eight pitch back off the throtle on down hill or even level flight. there is an update on the os engine web page recomending smaller diameter props if i re call correctly. happy flying!

thanks capt1597 I'll give it a whirl!
Kram

Here's a link to the 60 size thread. There's an even bigger one for the 46.
http://www.rcuniverse.com/forum/m_22...tm.htm#8245800

Thanks

Barry

Every body has a certain flying style, some like a quick spool up some don't, some like to fly with a lot of breaking action in the down line, some don't some like the higher torque achieved by using larger Dia. low pitch props,some don't other things that dictate prop selection, weight of the plane, parasitic drag on airframe air foil of the wing etc etc. IMO you can't beat this combo (OS 91 FX and a APC 15X4W) for 3D flying with the U CAN DO 3D. You can talk to 10 different guys and they might all have a different setup. That is what I like, Individualality. Ahh the good old US of A Picture is of an OMP Kit Built 65" Yak 54 OS 91 with a
15X4W APC
jerrysu29 Call Sign Wild Man HAPPY HOLIDYAS TO ALL

First I`m thinking a 91 FX is a bit small for the cando 60 which really is a big bird.
My 91 FX turns APC 14-6 at 11500 rpm and MAS Scimitar 14-6 at 12500 rpm and it pulls REAL hard. APC 13-6 spins 12800 rpm and feels to small. It is now mounted in a Katana 70 profile and fitted with a wood 15-6 to hover at less rpm with less noise. The ting is that the stock muffler really kills the engine. To get more power from your 91 FX remove the baffle inside the muffler and drill the outlet stinger of the muffler to the max, this will wake up the engine quite a bit and noise will still be bearable. I used this configuration for a while and then bought a Tower .75 muffler for 18$. That muffler is 2 oz lighter in weight and releases even more power. My tach reading of the APC 14-6 and APC 13-6 with Tower muffler is actually on par or a little ahead of what the the very expensive jettstream muffler will provide. Check the diagram halfway down this site: http://www.jettengineering.com/

The direct link didn`t work. Just click the "muffler and accessories" to the left and then the "Turbo-Jett In-Cowl Mufflers" second from the top page, and then the diagram will appear about halfway down the page. There`s a comparison between the stock muffler, Jettstream muffler and the Turbo-Jett In-Cowl Muffler fitted on the 91 FX

If you are not happy then wake up that engine instead of fitting a toothpick propeller

At one time had a 10 pound plane (GPSpacewalker) with a OS.91FX that I wanted to learn to hover with. I tried a lot of different props listening to advice from local experts and could not find anything that had the pull to hover.
Then I found a .91FX engine test from Engine guru Clarence Lee who tached this engine w/various props: 13x6 12,500\13x8 10,400\14x6 10,900 \15x6 10,200 \15x8 8,100\16x6 8,300. Using this prop/rpm information, I plugged these numbers into a thrust formula published in a magazine. The clear thrust winner on paper was the 15x6 @ 10,200 so I tried it and I had a winner. It had very little pull out, but enough for up high practice. I also noticed that my fuel usage noticeably decreased.
I then picked up a high volume Ultra-thrust muffler (tuned for lower RPM—I think the tower .75 muffler is lower volume & is tuned for higher RPM). My .91FX was turning the lower 10’s with an APC 15x6 stock muffler, baffle removed. When I put the high volume ultra thrust on, it jumped to the high 11’s!! This was a dramatic increase in thrust; pull from hover was very good—enough so that I felt comfortable hovering on the deck. I can say though, that with the way I was using the left stick, my fuel consumption went way up(I was using HP).
The .91FX with high volume Ultra-thrust is now on a 8.75 pound plane (4*60) and it easily wins a vertical drag race with a 10.5 pound/1.6FX plane .

Thanks to all that replyed, not sure what i'm going to do yet, but now I have some choices to ponder.
Kram

15x4 apc or 14x6....perhaps a 15x6 like suggested above .............. im using a 14x6 top flite wood on a st 90 which is close to the power of 91fx and it was the best prop yet for my 4*60 i tried a 13x6 apc, a 13x9 apc, and a 15x4 apc

I'll throw in another vote for the APC 15x4w. That was my favorite prop when I had a 91FX on a Kat 70, and the same prop worked great on a UCD60 with a ST 90.

One other thing to Ponder. Keep the overall weight of RTF plane to a minamum. All my Profiles over 7lb. I run the OS 120 2cyl.
The OMP kit built Yak54 RTF weight was 7lbs. 2oz( OS 91FX APC 15X4W) The New ARF OMP 65" 55-SP Yak RTF weight came out at 8lbs. 4oz so it received an (OS 120 2cyl. APC 16.5X5W) both sport stock mufflers. IMHO a stock muffler works the best for 3D.The Ultra Thrust mufflers such as the one from jett enginering is designed for racing (TOP END power and do not transition well when hovering) one thing I do not like is a plane that will only hover just under full power. I like a plane I can tail slide in from 20 feet at a good decent and stop the tail slide where and when I want. This requires a very high power to weight ratio of at least (2 to1) another thing I like to do is start at one end of the runway at about 30 feet in knife edge. drop to 2 feet and fly down the center line of the entire length of the runway, high alpha knife edge all the way The main thing is to get out and fly, fly, fly and experiment, experiment experiment OOH YEH remember Altitude is your friend when doing these things. LOL!!! P.S. The Goldberg Extreme 540 Extra 47" pictured here has an OS 91 FX (APC 15X4W) on it, theplane is in take off mode, the other is a 47" MVVS, SU-DO-KHOI with an OS 61 FX (APC 13X4W) Accel Katana Saito FA 72a (Zingar 14X4)

Here is the ultra thrust I am using: http://www.pspec.com/results.asp?category=8 It is the sport muffler & not the racing. I also have a 3/4" spacer & that may help with the lower RPM tune.

The muffler is louder than stock, and works fine for 3D on 8 to 10 pound plane. That being said, I would go for the AX120 on a 8 pound plane and a FX160 on a 10 pound plane. My favorite 3D prop for the .91FX on an 8 pound plane is a SK wood 15x6slightly less thrust, but instant spool.