prop size for 15 OS FP
 

Put together a spad for combat, have an OS Max 15 FP- What prop should I use????

RE: prop size for 15 OS FP
 

Are you flying in an organized event using SSC rules, or some club combat? The SSC rules require a Master Airscrew 8x3. If you aren't flying with those rules, you might try a MAS 7x4

RE: prop size for 15 OS FP
 

I always liked a 8-4 on mine. I was never using it in competition though. I think I would try a 7-4, 7-5, 8-4, and stick with what works best with your plane. It should be one of those 3.

RE: prop size for 15 OS FP
 

Many people say the APC 8x4 Sport is the best performing propeller for this particular engine. The problem with APC propellers and combat flying is that you very easily break the blades on landing, other brands are much tougher to break.

RE: prop size for 15 OS FP
 

If you mount the prop so that the blades stop horizontally, and you're careful with your landing, you won't have much problem with breaking the prop. I use some APC props on some of my combat planes, mostly in the .25 size classes, and it's rare that I break them on landing.

RE: prop size for 15 OS FP
 

Sorry it took so long to get back-A friend is going to give me a couple 8x4 MAS props. This is just local club fun. I will try the 7x4 also. I don't know what this old FP will do, I don't believe it's been run much, picked it up at an auction (box full of engines) and two were new. An enya 9 and an OS 40 FP. Thanks for your help, SAT. AM I'm going to fire it up.

RE: prop size for 15 OS FP
 

Well I fired up the OS 15 FP, smallest engine I've run and it doesn't seem to have much. The spad I'm building is from the Web site Spad to the bone, called Hell on Rails. Finished it tonight and seems heavy for that little engine. Ran an 8X4 MAS and peaked it 13400. Richened it up a bit to run at 13100. Is this about normal for a OS 15???????????

RE: prop size for 15 OS FP
 

i would really give a 8 x 3 a try it will allow it to come up into the powerband more, i am running a la 15 on a combat plane which hits 17300 on 15% wildcat fuel

RE: prop size for 15 OS FP
 

My .15 FP does something like 12600rpm on 8x4, on 15% nitro, and way over 15000rpm on 7x5 (Master Airscrew). I guess the .15 LA is way more powerful than FP. I also have OS .15 R/C (the ancestor of FP), and that's also somewhat more powerful, and also awfully noisy.

Montague, I mount my propellers that way too. The problem is that I'm not quite happy with the throttle cut switch ergonomics on Hitec Eclipse, usually I'm way too busy landing a WWII scale combat plane to find the throttle cut button. I've tried a throttle setting where min throttle will stop the engine (instead of running at idle), but that takes some learning too. Especially if you mostly fly something else than combat.

RE: prop size for 15 OS FP
 

I'll buy one of both the 8x3 and 7x4. First time out doing combat with a spad-First spad? I don't know if this thing will even fly, i'm used to so much more thrust-oh well as they say with the spad "nothing lost" should be really fun, just hope this little OS keeps up with the Magnums out their.

RE: prop size for 15 OS FP
 

The 8x3 will give you the most thrust. A strong running .15 will turn the 8x3 over 17.5krpm in good weather, assuming you aren't in Denver or something like that. The FP is a little older, so you will probably get a little less power.

When you go to launch it, give it a good hard shove into level flight, don't throw it upwards, and be sure to throw it into the wind. The newer SSC planes fly great, and can be hand lauched downwind, crosswind or whatever, but most of the SPAD designs don't have much wing area, and can get into a stall pretty easily.

With the engine you're using, you aren't going to be able to power out of a problem. SSC planes can't climb vertically out of sight, they aren't designed to, and if you get the nose up and the airspeed down, the engine will not pull you out of it, you'll have to push the nose down.

RE: prop size for 15 OS FP
 

If this engine don't cut it, I'll sneak a 25 on it, guys in the club won't know what hit them. Thanks for the advice-should be flying soon, wisconsin weather starting to break.

RE: prop size for 15 OS FP
 

there are two MAS 8x4 props. there's an older version with very wide blades, and a newer (but still out for the last several years....) version with thinner blades. I'm not talking about a new GF3-version (I'm not sure if MA redid the 8x4 for the GF3 series- the 8x3, for example, has not been redone). If you have one of the wide blade versions, it won't rev up as much, at least 1k down from the narrow blade version. the 8x3MA is kind of a "magic" prop for relatively heavy, draggy planes like SPADs and other combat planes. On a light, clean plane like a SIg Wonder or a Lanier Shrike, the 7x4 or 7x5 might be better, but I think the 8x3 is a good starting point for a SPAD. The 15FP should turn that prop about 17k. Some will exceed 18k. It depends on the engine. Things to do to improve performance: If you have the longer muffler with a center baffle section, remove that section or enlarge/remove the baffle hole. Make sure there is no casting flash at the joint of the muffler header to the main body portion, and also none in the stinger hole. Loosen the jam nut that holds the NVA to the carb (usually a 7mm hex) and back the spray bar out until the tip is just peeking into the side of the carb. This will really reduce the intake restriction. Finally, you can try removing the head gasket. It's pretty thick, like .017" or so. Some engines don't run better with the head gasket out, but most do, at least on 10-15% nitro. When resintalling the head, be sure to carefully tighten the head bolts so the head is on square to the cylinder. The 15LA seems to have more power than the FP, and other than removing the muffler baffle, it should turn 17.5k to 18k out of the box with no mods, on 15%. But a 15FP should be perfectly adequate for a SPAD or other combat plane up to about 3 pounds weight, over that, the performance will suffer. If you can keep it to 2.5 pounds, even better, a few ounces make a big difference on the .15 planes.

RE: prop size for 15 OS FP
 

Thanks so much for your tips and insite-Like I said I'm only getting 13400 from the engine with a 8x4 prop. FAR from 16K or 17K. I will try a few things you mentioned. The Spad came out to 2-3/4lbs. If I build another-which may happen shortly after I chuck the first one in the air, I know were I can lighten it. Thanks