I fly a lot of .15 powered planes in combat, and there are a lot of .15 engines out there in various price ranges with various strengths and weaknesses.

All of these engines put out more power than a stock AP Yellow jacket.

OS makes two .15's, the CV-A and the LA. The LA is ok. It acutally turns an 8x3 prop with some surprising power, it's a low rpm, high torque motor, so don't put a small prop on it. Oh, it's a "MUST" to take the baffle out of the muffler, or at least drill it out. Makes a HUGE difference. It also has problems with the plastic backplate and the all the screws on it are cross point, not hex, and pretty cheap. In the combat community, guys often replace all the screws and some guys get metal backplates (the old OS .15FP backplate fits). If your OS LA starts running funny all of a sudden, it's most common that the backplate is leaking or cracked.

The CV-A is high dollar, but very high quality, with solid power. If you can afford it, get it, there are no downsides to this engine. (it's not legal in SSC class combat though, not that you need to worry about that)

The Magnum .15 is a pretty good running .15, but the carb needs attention. If you go with the Magnum, you should take a quick look at the "Magnum Notes" on my website at www.MidAtlanticCombat.com. If you don't take care of the carb, the engine will run fine at first, then go to hell, mostly because of the O-rings on the high and low speed needles. I have 4 Mags, and they all run just fine. Some folks have had problems with the front bearing getting dirt in it. I haven't had to do a bearing change yet, but the bearings aren't shielded as well as some other motors. Bonus: global hobbies does a great job supporting these, and spare parts are cheap and easily available.

Megatech .15, this is a clone of the CV-A. Great power, maybe best bang for the buck out there. Not well known, sometimes hard to find, and who knows abott spare parts. I did see one blow up a bearing in flight once, but that engine was turning some serious RPM, so I don't think it was normal.

Norvel makes two .15's a ball bearing and a bushed .15. Both are screamers, but both are kinda odd. You need to get a special head wrench to work on them, and if you don't have the wrench, the head will losen up on you. The carbs have iffy quality control on them, and the muffler attachment method sucks (spring clip, not screws). But they SCREAM for the guys who know how to get them running right.

Thunder Tiger makes a .15. I haven't seen much about it, but it appears to be reliable enough, though not as powerful as the OS LA and the others above.

Fox and Enya make .15's. Both have good reputations, but I haven't seen them in competition, so I can't really say for sure how they stack up, and if they have any problems.

There are also a collection of high dollar .15's used in FAI competition, but they are pretty ignoreable for this forum.