Break in Prop?

I'm just about to start breaking in a batch of engines, including aome L&S Fox .35's.

I've just about finished the breakin stand.

What is the philosophy on a prop for break-in?

If a strong engine is presumed to use a Top Flite 10/6, (let's say) do I want to break the engine in using less pitch to allow the engine to turn easier during break-in, or more to load it up, or just the same as I expect to fly?

Do most folks keep an engine log these days? (I sure didn't back in High School.)

Cy

I would use an APC 11 x 5 for the first start, just to get the needle about right, one 10 sec run. Then switch to a Master Airscrew 9 x 4, and let it wind. The idea being to let the engine turn at 10-11K whilst quite rich. Do the recommended short runs, cool-down, etc.

For a Fox .35 stunt break-in prop you want a wide blade wooden prop that will let the engine rev to 10,000 rpm and, still be in a 4 stroke. You want the prop light so you don't beat up the pins and, the wide paddle blade will provide better cooling. The best thing I've found for this is the Top Flight 9-6 wood Power Prop cut down to 7.5" diameter. Round the tips a little so the wood doesn't split. As soon as the engine will hold the richest 2 stroke without seizing, put it in the airplane and finish the break-in in the air.

Hope that helps,
Giffy;)

Wow.

A 7.5/6 Prop sounds like not very much prop at all for a .35.

So I guess the philosophy is to let the engine wind up as much as it can while running as rich as possible, so that the piston and cylinder hone each other with lots of castor as lubricant flushing through the system.

I'm running 25% pure castor, 5% nitro fuel.

Am figuring lots of very short runs, just to get the engine up to temp and back down again.

Cy.

LAST EDITED ON Jul-01-03 AT 03:04 PM (CDT)
 
>For a Fox .35 stunt break-in prop you want a wide blade wooden prop
>that will let the engine rev to 10,000 rpm and, still be in a four
>stroke. You want the prop light so you don't beat up the pins and,
>the wide paddle blade will provide better cooling. The best thing
>I've found for this is the Top Flight 9-6 wood Power Prop cut down
>to 7.5" diameter.

Actually, and this is something that George A. and I were both doing, but I can't recall him suggesting it to me, we used LOW pitch wide blade props, BIG props, cut to small diameters -- cut an 11-4 down to an 8-4 size. That gets the "load" down, but still offers some good flywheel effect for starting. And Giffy is correct, let the engine rev some with a low load, in a rich 4-cycle, but I just don't believe that it will reach quite as many r's as 10,000 rpm until it's already broken in.

>Round the tips a little so the wood doesn't split. As soon as the
>engine will hold the richest 2 stroke without seizing, put it in
>the airplane and finish the break-in in the air.
>
I never found a need to do anything special with the paddle ends, just sanded them to remove any splinters or sharp edges. I did use less oil than George always harped on for a Fox 35 Stunt. He was certain that nothing less than 29%, and no synthetic in that oil, was pretty much what was needed.

The only time I've used more than 25% in total has been for break-in, but I stopped using all-castor mixes when I stopped buying K&B 100, which was before I had really thought much about how much oil of what kind was right for what engine (1972 or so). But I'd been using "too little" oil in Foxes and OS Max-S's for a long time (the K&B fuel) -- without much of a penalty in the form of toasted engines.

.
Kiwi

Cyber,

Get well away from neighbors. It is hard to convince cops you aren't home with the racket coming from the back yard. Use a short prop to minimize load on the new engine. Wide blade to move maximum air over the engine. Reduce the load until the engine will run ia a solid 4 stroke at about 10,000 rpm. Use extra oil or an oil rich fuel. A number of short runs is best, but I usually just hook it up to a gallon of fuel and run 3 hours adding fuel as necessary. I may occasionally squeeze the fuel line to bump it up into a 2 cycle song, but I'm not sure it helps or hurts. It ain't optimum, but it gets the job done.

>Cyber,
>
>Get well away from neighbors. It is hard to convince cops
>you aren't home with the racket coming from the back yard.

Thanks, Al!

Is it a plus or a minus to put a tongue muffler on an engine while breaking it in?

I figure short bursts of a couple of minutes each during the day won't be to objectionable.

Cy.

Cyber,

Any restriction of the exhaust causes back pressure and more heat. I'd leave the muffler off until the engine goes into the airplane where it will have flying speed to help with the cooling. If neighbors are a problem, maybe I'd use a muffler, but I wouldn't like it. Short runs means screwing with the engine all day nearly to the exclusion of anything else. I simply run for three hours and maintain an awareness of the engine sound. If it changes, I adjust the needle and maybe check with a tach. Most engines sound "happier" after about an hour.

LAST EDITED ON Jul-01-03 AT 10:20 PM (CDT)
 
You can cut the noise considerably without resorting to a muffler. Get a large cardboard box (apple box size +), fold the lid flaps in, and if you can, stick some of the cardboard or foam eggcrate stuff in the bottom, or at least a couple layers of plain wrinkly cardboard. This face will be presented to the engine, and will considerably reduce the noise spread around the neighborhood. The closer you can park it to the engine, the better it will work. Put a brick or two in the box to keep it from blowing around. Not a bad idea to put a Bruline air filter on the intake, either. Steve