Which prop for os35s

[phil myers]

I've increased the castor content to stop the OS35s from leaning out too much on my Ringmaster S1 using a APC 10x4 but the lap times are still in the low 4sec. Should I be using a bigger prop ie 11x6 or a smaller one to slow things down. I want to bring the lap times down to around 4.8. I'm using 60ft lines.
Thanks for any advice
Phil

[Dick Pacini]

I always ran 10X6 on my OS35s.  Of course, that's what most everybody ran on a 35.

[Balsa Butcher]

If you have any, Top Flite 10x5 or 10x6. An RSM 10x6 is may also work. 10x4, not enough pitch. 11x6 too big. Don't look for much of a break, my best ones run a a fast 4 stroke, a little like a Brodak 40 but less power. 

[phil myers]

Pete, are you saying the 6" pitch will slow the plane?
Thanks Phil

[Balsa Butcher]

I think you may need to slow the engine down a bit. These aren't like FP's or LA 40's. They are quite happy at lower RPMs, (high 8000s) and will put out plenty of power there. The Top Flite 10x5 imay be your best bet. Get the engine running well then increase line length to get the lap times down to where you are comfortable.

Going down on Nitro is always an option as well.  They were the engine of choice at my previous flying field and 10x5's or even the cheap black master airscrew props all worked well. In my Smoothie I liked 10x6. The fuel of choice was 10% nitro, 25% castor, 3% synthetic. As you correctly noted, they do like castor. While I like APC props and find them the best on some engines, on others they may not be the best choice. 

[Randy Powell]

Hmm a 9x5 Grish Tornado 3 blade?

[Steve Helmick]

Try a 10 x 5.5 Thunder Tiger Cyclone. Tower has them, as does Randy Smith. They're inexpensive and an excellent propeller. Balance is very close, right out of the bag. You need to back off on the needle to get a 4-2-4 run and slow the lap time. Set it so it's 4 cycling when "on the wheels" and breaks into a 2 cycle when you tilt the nose up 45 degrees. You'll need a hot glowplug, like an idle bar K&B 1L, Zinger or Thunderbolt R/C. I am not a fan of  Fox glowplugs, and OS has shortened their glowplugs to a "medium" (metric) length, that I think could be a problem. A short glowplug in an engine that needs a long glowplug is the PITS, so a "medium" length can't be a good thing, can it?  Steve

[M Spencer]

9 x 6 & 10 x 4 3 blade Grish are both o.k. ,on the stock intake .
Seeing its an ancient engine you could whittle scrape and thin obsolete  timber props , to keep with the theme

Starting with around a 11 x 5 . Theres a few 10 x 6 EW top Flites about too .

[Will Davis]

If the engine is running away, I would try restricting the venturi size too, I Fly a OS 35 S on a Classic plane , .255 venturi size, no Air Cleaner  10 1/2 to 11 inch prop   5.5  pitch prop ... 10 /22 1/2 syn 1/2 castor

[Garf]

I am running an OS 35S on an ARF Nobler. Today I tried an XOAR 11-4 prop. It is the best yet.

[Steve Thomas]

It's a bit surprising that it's running away - I've found that with a 10x6 (I use a RAM or RSM) and 5% nitro/25% castor, you can't really go wrong with these things. Could there be an issue with the venturi size or tank? 

[Steve Helmick]

What (the heck!) is a RAM prop? Where are they made, and where can they be obtained? The Thunder Tigers are really good (if they have the right size...and I would try the 11 x 4.5 as well as the 10 x 5.5), AND very inexpensive. I admit to having a propeller fetish.  Steve

[Steve Thomas]

What (the heck!) is a RAM prop? Where are they made, and where can they be obtained?

Hi Steve

RAM = "Radio Active Manufacturing" .  They're made in the UK, and I've found a couple of stores out here that stock them.   Here's a link: http://www.radioactivemfg.com/propellers.htm

I've been using them in 8x6 (for .15 diesels), 9x6 (for all sorts of things), 10x6 (for glow .35s) and 12x6 (for a .35 diesel), and really like them.  For some reason I get a more pronounced 4/2 break on a MAX-S 35 with the RAM than with the RSM wood prop - no idea why. 

I've heard that there may be structural issues with them at high rpm in racing motors, but for sport/stunt use they're just fine (and not expensive).

Cheers
Steve

[phil myers]

Many Thanks to all, I've just ordered some 10x6 RAM props off Ebay, (no luck with the TT Cyclone, not sure they're available in UK, and the postage costs from the U.S. are pricey... £7+ per prop). The venturi size i'm using may be an issue; I'm using .28 ID from Leonard @ Stuka Stunt. (I've given up trying to order stuff again from Leonnard, my emails are always returned undelivered) Who else sells .25 ID venturis?  I'll also try and get a couple of black Master Airscrew props (11x5/6) @ MLHS. Posted photo of my engine setup with forward facing vents top and bottom. The tank is a Brodak 3.5oz cut down a little coz space was tight. There are no leaks. I've tested it several times. Phil

[john e. holliday]

Contact Jim Lee at Lee's Machine Shop.   Well worth the money and he has a variety.  Look in Vendors Corner.

[phil myers]

Thanks Doc, Have sent email to Jim..
Phil

[Balsa Butcher]

Just a few thought: Make it the black master airscrew 10x5 rather than 11x5 ifn you want to slow down. The stock muffler on OS-35s is very restrictive and can lead to heat build-up. Might try drilling enlarging the outlet. I know the tube is thin already but still can be enlarged a bit. Some have just drilled a few holes in the back of the "can" above the outlet. Might check with Randy Smith who can supply you with a less restricritive muffler and tell you how fashion a strap to secure it with.

I have never had good luck with those type of tanks. They are not uniflow so the engine will speed toward the end of a run regardless of what you do. Try a Brodak or RSM tank uniflow tank even if you can only fit a 3 ounce one in the space. These engines are very thrifty on fuel and that amount should get you a good flight. If you decide to retain that tank go to Heman Lee's "Aeromaniacs"  web site. Under tips you will find an alternative tank set-up called the "Isobaric Bush-alator". Try that and let us know if it works for you. 

[Ed Keller]

I picked up several of these older OS 35's a few years ago, & am just now getting around to setting up a couple of profiles to use these engines. Question: these engines are not all alike, there are some slight differences in the case, plus some have cast fins, while some are black steel. Is one model better than some others? Ed

[Bill Little]

I picked up several of these older OS 35's a few years ago, & am just now getting around to setting up a couple of profiles to use these engines. Question: these engines are not all alike, there are some slight differences in the case, plus some have cast fins, while some are black steel. Is one model better than some others? Ed

HI Ed,

Sounds like you have some MAX III .35s (black steel liner fins) as well as the .35S.  The earlier, "III" is more of a "performance" .35 and likes higher revs (plus a touch heavier).  The "III" just doesn't 4-2 as easily as the .35S.

I love the way the .35S "runs" in a stunt plane.  I set mine in a "cackle" (popping between a 4 and a 2) on the ground where it will break into a clean 2 stroke when the nose goes up.  I have used mostly 10-5 props (Rev Up 10-5W and EW).  5% nitro has always been plenty except on the hottest days.  We did, however use to mix 5% and 10% to get 7 1/2% lots of times which also worked real well.  10% works well if the plane is a bit "porky".

Big Bear

[Peter Nevai]

The OS 35's

[Bill Little]

Thanks for the pictures, Peter!

Big Bear

[phil myers]

Pete, the Hemen Lee uniflo version looks very interesting. I will try that next time I'm out and report back.
Phil