summerwind

a few months ago i asked if my detonation sound was from being too lean with one of my new OS91surpassII's. my tuning at that time and running was with 10% fuel, 14x6 TF power point, and after finding peak i backed off about 400rpm. it had a noticeable rattling (slight detonation), and the suggestions here were to back the needle off some more until the engine is completly broken in..........i did, the rattling stopped, as did power.
today with same fuel and prop, and 2 gallons thru it now, i again peaked the needle and backed off 400rpm......the rattling is back................today was also a day of "let's try different props", so i tried a 12x10...........at the same needle setting the engine runs fine. next flight the needle gets peaked again and then backed off 400rpm...........no rattling or detonation...........and of course the plane (GP Big Stik) is a bit faster.
i have another OS91 in a GP Super Skybolt and it runs identical to this one.
the reason i went with a 14x6 was because of a few reviews of the Skybolt where the authors said they used 14x6's.
is the 14x6 too much or too little prop for the OS 91surpassII?

wcmorrison

My Feedback: (2)

Well, I use 14 x 6s on both my Magnum 91 and my Saito 91s, and do not have any detonation problems. They work just fine for me. If the 12 X 10 is doing what you want, then stick with it.

Cheers,

Chip

Harry Lagman

The 14x6 is spot on as far as prop loading is concerned. It should be doing around 10K rpm with that prop.

I suspect if your engine is rattling or otherwise sounding like it's detonating, that there may be a problem with it. The OS Surpass 2 .91 is extremely forgiving with any fuel from 5% to 40% (I've tried them all) and it's very very unusual for for one to detonate, espcially with 10% nitro.

A certain amount of mechanical noise radiating from a wooden prop is normal. Try an APC or MA 14 x 6 on it and compare noise output.

carrellh

My brother and I have 3 OS 91 Surpass IIs and the 14x6 is what we run on all of them (we use APC and Master Airscrew). With 10% nitro they usually turn around 9500 peaked and we back them down to 9000 to fly. With 15% nitro they peak between 10000 and 10200 and we back down by about 500 to fly.

We are at about 500 feet above sea level.

summerwind

thx for the replies.......i guess i'm just getting greedy with the R's from this engine...................when i left the hobby 15 years ago i was strictly a 2 stroke tweaker...........gotta learn me sum more disceeeeeplin ma.
today was also a windy day so flying wasn't as relaxing as i had hoped for...........i'll keep testing.

gunfighterII

I'm using a 15-6 APC on my pumped 91 Surpass II. Perfect match for the 60 size U-Can-Do.

krayzc-RCU

My Feedback: (31)

i use to fly my spacewalker on that motor and a 14 x 6 now that i perfer fun flies for 91 i do a 15 x 4w apc

RVator

My Feedback: (1)

On my OS 91 I found that a MA K series 14x6 was not enough prop but a 14 x6 apc was just right. I am using a 15 x4 w apc on a profile now.

summerwind

hey thanks guys..........sounds like i need to discipline myself with these engines........the Stik wieghs 6.25 lbs, is 1,000 square inches of wing and does seem to go vertical forever.
it may be that the TF prop is not loading it enough, and i'm overevving on the ground.

turbo.gst

My Feedback: (8)

My favorite prop for my Surpass II .91 is the Graupner 13.5 x 8

turbo

CustomPC

I've tried the APC 14x6 on my 91 SurpassII with my Skybolt and I wasn't pleased with the performance in the air.

The graupner 14x7 is noticably better in speed and vertical.

The MA K Series 14x6 belies everything i've read here about MA props. The motor really pulled with this prop and the plane performed great with it.

I just tached a MA Schimitar 15x6 and got 9,760rpm peak. I haven't flown it yet but holding onto the plane with the motor at full revs feels like it has more pull that the 14" props. I can't wait for the weekend to give it a try.

Marcol

I run a Graupner 14 x 7 on mine, in a Goldberg Super Chipmunk.

Fantastic combination

summerwind

i think the problem is that the TF 14x6 is acting like a slipping clutch................i hear a lot of good things about the Graupner.....time to try one...............if it works, then i've got at least a dozen TF epoxy mixing sticks

TCrafty

I run a 15X8 MAS on my Kadet Sr with a 91 OS 4 stroke. Flies great. I probably don't get all the RPM out of it that I could but hey, it's a senior! Pulls it straight up, hovers and just puts around the field at a snail's pace. I like the combination.

submikester

My Feedback: (6)

I've been using 14x6s on my Magnum 91s for a while now. I have one on my Sportsman Corsair though and with 20% I'm getting about 9800 RPM. I think I'm going to try a 15x6 this weekend.