Hey guys:

I've setup an OS90 in an Xcell 99SE with 8.18 gear ratio and have been breaking the engine in. I'm still working on optimizing the needles, but, I have noticed that the engine will have a tendance to sound like its kicking or not smooth if the mixture is lean.

I originally had the main needle open 2 turns out, but that was too rich and since then I have been leaning it. The other day I tested more power as I lean it more, and found that at 1.25 turn out the engine was still getting stronger the more I closed the needle. I did leave it richer for another 1/2 gallon, but last night I put it back at 1.25 turns out (didnt test any leaner if there was more power, but certainly the rpms were still going up at full power climbouts as I leaned from 1.33 to 1.25 turns or so).

At 1.25 turns out, it seems to kick sometimes in a hover, so I richened the low end. Last night I richened the low end to what seemed to be the max (screw was vertical from original horizontal position) and it still kicked some as I descended from fff back to a hover.

Now I can richen the high end, but, doing so I know will reduce the top end power at full climbouts though it will probably stop the kicking sound in a hover. Its hard to explain the kicking sound, but, if you heard it you will know what I mean. Also, even though it sounds kicky, the tail is still smooth and its unlike what you see in a gasser with the tail wagging with every kick.

Just want to hear your opinions about it if you can help. As an FYI, its running 700mm blades at 180grams each, and the top end pitch is set to 10 degrees at 1700 rpms, 10.5 degrees at 1600 rpms, and 11 degrees at 1500 rpms. With the needle at 1.25 turns out, it can maintain those rpms at full power climbouts, otherwise it starts losing rpms due to richness.

Open to thoughts and ideas guys...!

-=>Raja.

Sounds like you are running 30% nitro. Drop the nitro down to 15% or add a head shim.

My OS 91 runs great at 1 1/8 turns out on PowerMaster 15%.

Yes I am running 30% as I was with the OS61WC previously. Is it a problem with the 91 to use 30%? I can certainly go to 15% as its definately more cost effective, but, am I also to expect losing power with 15% or do they run just as well or even better with the 15%?

I only ask because I need the engine to lift a 7lb payload and fly aerobatics, and the 61 was bogging down doing so hence the changeover to the 91.

Let me know your thoughts, and thanks!

-=>Raja.

If you must run 30% add a headshim. You are getting predetination. Very common on the 91 with 30% nitro.

rbort,
How's that gasser going? Boy that thing must have done some hours now...

Like you've said, the 91's really get mad if you run them lean, mine seems happiest when it's running rich.

I run 10% and have tonnes of power, I've heard they don't like 30% which is good cause the fuel economy I get on 10% isn't flash so I'd hate to think what it would be on 30%!

Si

Hi Eahapkis:

Thanks for the advice. I will go out and buy a case of 15% coolpower tomorrow to fly with for this engine.

Hi Si:

The gasser is doing just fine thank you! Logged flight #833 just this past weekend at a funfly. This 91 is for the MIT heli project that I am the pilot for, so in essence its for a project and luckily for me they pay for all of it including the fuel. Coming from flying a gasser, just the other day I was shocked when the heli quit 8 minutes into the flight on the stock tank (16oz that holds 20oz when filled to the brim). Come to find out it was bone dry of fuel, but I did have it rich for break in. As I leaned it out, it improved so now a 10 minute flight is possible with very little to spare for a safe landing.

I got spoiled when I went to gas, so going back to nitro for this project has been quite a change with the high cost of fuel, short flight times, and the oily mess everywhere when you come home...

I hope all is going well for you, and nice talking to you again!

-=>Raja.

Yeah, after playing with my 91 powered CS for a bit, I decided to dust off the old Z230 and play with that for a while. I've got a week off work coming up so I fully intend on following through with Bill Meador's setup again and see if I can't get the old tank to start hauling.

There's something cool about being able to pull start the heli while everyone else is dicking around with glow plugs and stuff!

Si