stunthanger.com
Engine basics => Engine set up tips => Topic started by: Duke.Johnson on February 18, 2013, 02:08:51 PM
-
Guys
My son is replacing the engine in his Brodak P-51. He has a old O.S Max .25 to put in it and we didn't know what size prop to use for sure. Any ideas? He flies it on 52' lines. And he's just learning the pattern so it doesn't need to scream, just pull through the pattern.
Thanks
-
How old?
If it's an OS 25S baffle-piston, then the paperwork that came with the engine recommends a 10-4 or 9-5.
If it's an OS 25FP Schnuerle or an OS 25LA, then you probably want a 10-4 -- and possibly longer lines.
-
I'm not sure can you tell by the picture?
-
Wow, you shrunk that down!
It looks like a 25S. Is it the 48-inch span P-51B? If so, then even on 52 foot lines that's not going to be much engine for it -- certainly not enough to do much stunting.
-
320sq.in. +/- and 39" WS
-
It might fly OK on that, on those length lines.
-
It might fly OK on that, on those length lines.
So an 10x4 or 9x5.
-
The photo of that engine shows that it is definitely the OS 25 Max. It is a non-schneurle engine like a little brother to the OS 35S from that same era. It does not have the power of the OS 25 FP, but it is an ounce lighter. I used one on the two Pagan's I built several years ago for OTS. Those models had a 46" span, 364 sq in of area, and weighed about 24 oz. For OTS, it was like driving a little sports car. In the air, it acted like all it wanted to do was what I wanted it to do. Flew on about 0.012 solid 58' lines, eye to eye. Placed at a number of contests, including the Nats and VSC. I ran it without a muffler, though OS had a muffler for this engine. I did get a few complaints about noise.
The best prop I had on it was a narrow blade APC 9.5 x 4.5. Unfortunately, that prop is no longer available and the current APC 9.5 x 4.5 is really thick and heavy and does not work nearly as well. The next best thing may be a Rev-Up 9 x 5 or 9 x 6. Maybe a Zinger in one of those sizes would work but thin the blades a bit. I had a carbon 9.5 x 4.5 Bolly from Randy Smith that worked and probably would be better than the Rev Ups of Zingers.
Keith
-
The photo of that engine shows that it is definitely the OS 25 Max. It is a non-schneurle engine like a little brother to the OS 35S from that same era. It does not have the power of the OS 25 FP, but it is an ounce lighter. I used one on the two Pagan's I built several years ago for OTS. Those models had a 46" span, 364 sq in of area, and weighed about 24 oz. For OTS, it was like driving a little sports car. In the air, it acted like all it wanted to do was what I wanted it to do. Flew on about 0.012 solid 58' lines, eye to eye. Placed at a number of contests, including the Nats and VSC. I ran it without a muffler, though OS had a muffler for this engine. I did get a few complaints about noise.
The best prop I had on it was a narrow blade APC 9.5 x 4.5. Unfortunately, that prop is no longer available and the current APC 9.5 x 4.5 is really thick and heavy and does not work nearly as well. The next best thing may be a Rev-Up 9 x 5 or 9 x 6. Maybe a Zinger in one of those sizes would work but thin the blades a bit. I had a carbon 9.5 x 4.5 Bolly from Randy Smith that worked and probably would be better than the Rev Ups of Zingers.
Keith
Keith thanks. That's what I was hoping to hear.
-
I'm not sure can you tell by the picture?
That appears to be the baffle piston motor. On a 39 in. plane a 9/4 wood prop will be enough. That is not a big plane or a big motor. Also, if it is profile mounted watch out for the Fox burp. A friend has the 20 version which has a dreadful burp. Sounds like it's going to quit(and half the time does) in the first half of an outside loop. He unfortunately hasn't take the time to try any of the Fox cures so he's gotten lots of practice in making very smooth outside turn well-place for the wind to blow the airplane out if the motor quits.