O S 91 BRAKE IN ??
 

A 91 is in the mail for the UCD . (My first 4 stroke engine) After break in I want a 16x4 Prop.
My question is, can I use this prop for breaking in the engine?

RE: O S 91 BRAKE IN ??
 

16X4 is too big I think, I run a 16X6 on my 125 saito. You want to run the engine with a light load at low rpm, Make sure to read the manual on the break in and do what it says.

RE: O S 91 BRAKE IN ??
 

I would use something like a 14x7 for break in.

RE: O S 91 BRAKE IN ??
 

You might try a 15x4 for 3d with the 91 four stroke on the UCD. I have used 13x8, 14x6 and 15x4 size props on my 91 four strokes depending on the airplane.

RE: O S 91 BRAKE IN ??
 

O boy ! Here I go again all I need is a 120 Props. Right.

RE: O S 91 BRAKE IN ??
 

I Never dreamed the 900.00 cost of this set up .

RE: O S 91 BRAKE IN ??
 

I have used the 16X4 a few times on my .91s but it depended on the plane. I was using one of my .91s in a 60 size Bridi Kaos and it worked out fine for me but when I tried that prop size {APCs} in an extra I didn't care how the prop/plane/engine combo worked out so I went to the 15X4 and I liked it a lot better. That was flying, for break in your instructions will give you the prop sizes OS thinks you should use, always a pretty good idea to follow the instructions then after break in you can start prop testing. I love my .91s!!!

RE: O S 91 BRAKE IN ??
 

O.S. doesn't specify a special prop for break-in, so basically you should use the prop that you're going to fly with. The 16-4 is smaller than the recommended size for the .91 SII. I'm looking at the owner's manual for the one I just put on my Little Toni and it says that 16-6 is as small as you should go. MinnFlyer is correct (when isn't he?) in recommending the 14-7. That fits into the recommended size range. You have a terrific engine there. I'd hate to see you damage it by over-revving. Since you said that this is your first four-stroke, I feel compeled to suggest that you use a tach to adjust the mixtures. It's extremely difficult, if not impossible, for someone used to the sound of a two-stroke to accurately tune a four by ear. Invariably, we tend to lean them out too much. O.S. claims practical RPM's of up to 12k, but I limited mine to 9500 with a 12-11 APC. I'll let it go up to 10,500 after a few tanks.
People are doing their best to suggest props to you. It's obvious that you took some time considering your engine choice and you had to come off a few C-notes for the .91. Nobody has suggested you buy a bunch of props. Fly with one and see how the plane flies. Then you can make an educated decision on which way to go to reach an optimal prop size. You should be able to optimize for your flying style with just one or two changes.

RE: O S 91 BRAKE IN ??
 

I was using the break in size (14x6) for the magnum 91 as my O S. guide.<div>And added 1" longer  1 less pitch 15x 5       and  1" longer  1 less pitch =  16x4  </div><div>
</div><div> In my other engines this method works very well for keeping somewhat the same R.P.M     </div><div>I am looking to make the  UCD plane fly slow. Even in a power dive I have found a long 4 or 5 pitch has saved my other planes, because of the way the large flat prop becomes a brake .  + shorter runway + great vertical.</div><div>
</div><div>I did order a tach.  and 2 props</div>

RE: O S 91 BRAKE IN ??
 

Good throttle management using a tach to ensure you don't over-rev and you should be good to go. The OS manual still suggests you go up one more in pitch, but that's for an OS and I'm sure you'll be careful, so the 15-5 should work well for you. I guess it's good to have a little room left on the left stick. I know I'm glad to have some throttle to play with when it comes to buddyboxing on a trainer.

RE: O S 91 BRAKE IN ??
 

Working RPM range of the OS .91 FS is 2-12,000 and they call for props from 11X11 to the 16X6. As long as you stay in the working RPM range of the engine you are OK with any prop in the given range. All of my engines are kept around 9800 but I have done a lot of prop testing to find the prop sizes I like to use. I do have a big box of props on hand but when I'm testing I make a day of it so taking out one prop wouldn't cut it for me. I only have OS and YS engines with a few Saitos coming into my life once in a while. I do help out friends when they are testing props on there Magnums but I don't own any myself. Using a smaller prop for break in is the norm but after that comes the fun of finding your magic prop that you fall in love with. As long as it keeps the engine in it's working RPM range it's pilots choice as to what prop you use. No one can pick a prop for you. Just have fun with it and follow the instructions.;)

RE: O S 91 BRAKE IN ??
 

Thank you, Gray Beard  .  I just got my 9c radio like yours.

RE: O S 91 BRAKE IN ??
 

Can't be like mine, mine has the finish lifting and rust in the screw holes. :) Truth though, I got mine when they first came out and have flown in snow storms and in the desert when it was 120 degrees, it really is showing it's age.:D Still in love with it though!!;) If you go to the Futaba web site they have a lot of tips on programs and set up with it. Things that never made it into the instruction book.;)
Gene

RE: O S 91 BRAKE IN ??
 

OK , The OS91 is installed In the UCD.  I am still waiting for a tack and 2 props.  <div> I do have a APC 16x4w  prop.  Should I try my first run in?  Or wait.</div>

RE: O S 91 BRAKE IN ??
 

I have my doubts about it doing any harm but a smaller prop would give you better rpm and put a smaller load on the engine. Better for break in. Don't worry, it will start and run fine, I would wait but I know how it is when you get a new engine.:):D

RE: O S 91 BRAKE IN ??
 

First run in today!  I followed the OS directions to the T . After I burnt  10 Oz . of fuel, I went to a low idle for around 10 sec. and the engine hammered hard . Is this normal ?

RE: O S 91 BRAKE IN ??
 

NO, not unless you are getting the idle too low, about just before it is going to quit on you. After the ring starts to seat you can begin adjusting the needles. My .91s just tick over, idle is said to be about 2000 but they will go a lot lower. You can check the valve adjustment just to make sure they are set then set the high and low end so the engine runs smooth all the way from the low to high. Not real sure what Hammered Hard means but they will run hard if they are running too slow.