How to break in an OS91 DF?
 

The instructions say to use a 12" prop but don't specify the pitch. Is this the best way to break in an OS91? The last one I had, I just put the Fan on and blew cold air on the head with an air compressor as it was running.

Also, how long should it run before it will be reliable in the air?

OS.91 break in
 

W0mbat,
try a 12/6 prop-you want this engine to be able to rev up as it breaks in-also you can just put it in the fan and run it on a test stand-either way is good.


Jackjet

Engine Breakin
 

In my opinion, breaking in engines on test stands simply converts perfectly good fuel to noise!! :) So I install them in my airplane, tune them, and go off slightly rich on the first few flights. This assumes that you have enough experience to set the engine correctly at the top and bottom.

A couple of suggestions for setting for the motor:
1) Be sure you have a quality idle, since top end is predicated on the low end setting.
2) Be sure the engine transitions cleanly out of idle to full throttle
3) Check to see that the needle valve richens and leans the engine at full throttle
4) Do the pinch test at both idle and full throttle. At idle, if your engine gurgles when you throttle up, it's too rich; if it struggles, it's too lean. This is where the pinch test is helpful. At idle, pinch and hold the line to the carburetor. You are looking for a slight rise in rpm before it tries to quit. Once you have adjusted the bottom end so you have a clean transition, open the throttle all the way and pinch the line to the carburetor abruptly, then release it before the engine quits. Again, you're looking for a small jump in rpm. For first flights set the top end slightly rich--then go fly!

I've also found that adding one generous ounce of turbine engine oil (Exxon 2380 or equivalent) to each new gallon of sport fuel (I use 15% sport in all my D/Fs) prolongs the life of the engines by acting as a true lubricant. Turbine engine oil won't burn off at model engine operating temperatures. Even if you run the engine lean, it still lubricates the engine because it won't burn like castor or synthetic oils. Actually, I use this additive in all 2-cycle and 4-cycle motors--and you can put it in your lawnmower if you want to!

This may be more than you want to know, but perhaps it will be useful to you or others.

Best regards,
Larry Wolfe
[email protected]

How to break in an OS91 DF?
 

I quit doing the PINCH test at full throttle when I blew the engine at Heart of Ohio two Years ago! :( (Dynamax Fan tho, probably no problem with Byron)

Had to come back to the Fort to get my Spare OS .91. Before I could fly # 5 Interceptor.

OS.91 break in
 

Terry,
I still do the pinch test on my F-4 before each flight- I just dont pinch too hard or too long...............



Jackjet

Nitro/Oil Content
 

Don't forget ... the OS91 VRDF is most happy with no more than 5% nitro and around 22% oil. Wildcat 5% d/f fuel is the choice of many. If you're not totally familiar with the engine I think it's a good idea to bench run with a Zinger 12x5 and run a couple of tanks of fuel through it then go a tad rich for the first few flights. You might "waste" some fuel bench running to make sure it's close but you'll likely save an airplane: Dead stick landing are a bad thing.

Mike

Re: Nitro/Oil Content
 

Not to say also a piston and sleeve....................fuel is a LOT less expensive than a new piston and sleeve................




Jackjet

In the Plane!
 

Breaking in a DF engine on a bench with a prop is dangerous and unnecessary. It's always best to break in an engine under conditions similar to those that it will experience in use (rpm, load, temperature). I always run them in the plane pretty much following the instructions that come with an OS engine, except I do vary the rpm a bit.

Run WOT rich, short of 4 cycling and every half minute or so lean it out to just rich of peak for about 10 seconds, then back to just short of 4 cycling. Gradually increase the time at the leaner setting.

After two tanks you should be able to maintain a good idle. The acid test is to be able to idle for about a minute then smoothly and rapidly increase the throttle without any stumble or hesitation. Then you are ready to fly.

Keep it rich for the first couple flights, then gradually lean out each sucessive flight until you are at at normal few hundred rpm on the rich side by flight #10.

Good luck,
Joe