Hi Just tried to fly my new HOR yesterday with an AP .15 Yellowjacket engine. I wasn't impressed too much with the power. Anyone out there running this engine, and what tach readings arwe you getting with the SSC standard, Master Airscrew 8x3 prop. Thanks for the info

Same bad experience here. Last weekend I had an antique .19 veco boat motor on my HOR and it rocked. Yesterday with the AP I couldn't get it in the air. Didn't tach it yet. I wonder if I run it on the bench some more if it will gain some revs.

rrh

Yeah I listened to someone who said he had a good experience with the AP engines, looks like I listened to the wrong guy. That's why I want to see what some others have been taching with this engine. I hope to get a little more power as it breaks in, but I really don't think it is going to be enough. So if anyone else out there has one of these engines, let me know what you are taching with an 8x3.

Buggerus, I was looking at the SSC rules and looking at my HOR. I'm 5oz overweight plus the wing is 128 sq in over the minimum. I was using an 8x4 prop. So if I get some more revs with the right prop and some more breakin and go on a weight loss program, it's going to get in the air probably to be easy pickins by those magnums. Is it worth it?

rrh

I don't know about whether it's worth it or not yet. I tried to fly it, really windy day though. I am going to wait for the weather to cooperate, and try it again. I want to see how it performs once it's broken in. If no performance increase, I will probably buy an OS LA .15. Oh well I guess we'll see.

Everyone I've heard talk about the AP had said the same thing:

It runs well, is easy to get working right, and so on.

But it's under-powered and not competitive, even in SSC. Sorry.

There seem to be 2 tried and tested SSC engines, and a 3rd that apparently has promise.

The OS .15LA and the Mag .15 seem to be about equal in SSC. (The Mag is more powerful in A class, with a different prop though)

The Megatech .15 may have potential, but it's too soon to tell.

Yeah unfortunately that is what I expected to here. Oh well I guess I had better get an OS LA.

Thought I would give the AP one more shot, so I dumped some 30% nitro I had into it, and it only brought the RPMs up 15,000. Still a far cry away from the 17,000 that the guys with the OS engines are running. Oh well called Starfleet Hobbies, they have an OS .15 in stock, I am picking one up tomorrow. Anyone want to buy a hardly used AP .15 Yellowjacket?

So if I bought yours and put it with mine they would maybe equal the antique .19 Veco boat motor...live and learn the hard way...

rrh

Yup and your name says it all, rrrrrrrrrh bad AP, bad engine!

I've heard the exhaust is very restrictive on the Hornet. You could try boring out the muffler exit a bit. if you go to far you will lose tank pressure though. This is currently against the rules but if you don't exceed 17,500 I don't think anyone would care. I think the named engine part of the rules might eventualy be dropped as the RPM limit takes care of it.

The whole exhaust system seems kind of goofy, more like a pocket watch than a muffler, it would be out of sight in a cowel, though. I have been thinking about making a tuned pipe for it but then there are the rules. The outlet is mighty small, enlarging it would be worth a try.

rrh

I guess I could try boring out the exhaust a little. Maybe this would help. I will let everyone know the results. I still think I am going to get the OS LA .15.

Could you test run it on the ground with out the muffler attached at all, and see what the RPM is? If it's not much better, then you'll know not to bother boreing out the muffler. Just a thought.

Actually I thought that some back pressure is necessary for proper running of the engine. I think that fuel feed would be a problem for one thing. no muffler, no tank pressure. I am not planning on running the engine anyway, so I might as well bore out the muffler. We'll see what that does, who knows it might unleash a screamer, although based on current performance, I doubt it.

I went ahead and ran an 11/64 bit down the stinger. It wasn't much of a bore out, but I didn't want to actually remove the stinger. This bit allows the stinger to stay on the muffler, as for performance, I will let you know tomorrow. If the weather cooperates, I will take her out.

2-stroke engines run fine with out a muffler, in fact that was the way most of them used to be run.

It's true that a good muffler will increase power though tuning effect, though most stock mufflers actually reduce power by a few hundered RPM.

Fuel draw in the air in various attitudes is usually much better with pressure to the tank. But I wasn't talking about flying it that way, just a quick run up on the ground to check the RPM. Basically a test bench run. Fuel draw shouldn't be a problem if you locate the tank high enough. You could even use an external tank.

Either way, it's not a big deal. I suspect you will find exactly what you said you expect to find, that the engine is just plain old underpowered. Thanks for bothering to test it though, I'm sure curious to see what the result is.

Well it looks as iff it might rain here in wonderful cincinnati. If it doesn't I will take it out. As for running w/o the muffler, I don't think that is going to be possible today. The way the engine is mounted, I cannot remove the muffler without removing the engine from the mount. I am going to fly it as much as possible tonight, checking the tach before my first run and after my last run to see if a little break in helps. This will all be done using 30% nitro. Well not quite 30%, cause I dumped in a little extra castor, but close enough. If by the end of the day it starts turning 16k+ I'll probably keep it as a back-up, cause lord knows you need a back up when flying combat. If it still is only turning 15k or so, it is destined for E-bay or the classifieds here.

Maybe a bit off topic...but I was looking for a .15 on Tower's website so I'd have something to tow streamers in Open A for Montague at the end of the month. I looked at the AP .15 but noticed that it's actual displacement was .17293 cubic inches. Would this be a legal engine for Open A and SSC anyway???

After reading this thread, I'm glad I spent 5 bucks more for the LA...it screams!

John C
AKA Cuda

Well the results are in. Even after boring out the exhaust, which did get me about 300-400 more RPM, the engine is still a dog. It could barley pull my HOR around. It ended up doing a nasty snap roll and buried inself in the dirt. This probably was do to the construction of the airplane, but either way the AP was grosly under-powered. So anyway, I'll be repairing the old HOR, and installing the OS LA .15. Hopefully I will get decent performance from this setup without having to result to 30% nitro. From the looks of the other Hor's at the field this won't be a problem. So I'll say it again, anyone want a slightly used (and abused) AP .15 Yellowjacket? $30 or highest bidder.

The carb barrel is for their .09 motor. This severly castrates the potential power of this engine. They should have bored the barrel for the common .15 sized motor. They are obviously cutting cost with this an the intake is WAY TOO SMALL! You can bore the exaust as much as you want and it will make little difference because the bottleneck is in the carb. I bored out the barrel as big as the carb intake so that they are flush when wide open. I also used a 1/4 inch circumference and 1 inch long exaust tube in place of the old exaust which is also for the .09 and very restrictive. I bored out the exaust on the can muffler and JB welded the new 1/4 inch tube to it (got it from home depot). I also didn't like the vent tube coming off the side because of the added length of tubing it took to get it to the tank. The longer the tubing the more resistance the pressure to the tank. I learned this the hard way with a JKA mustang when I put the tank too far back in the foam fuse and fuel draw became an issue. Anyway, I tapped a new vent tube coming out the back of the muffler and ran a fuel line directly from muffler in a straight line to the great planes 4 oz tank. (I also plugged the side hole with JB weld). The top end is great but the low end is now very touchy to tune. This is combat so I don't do much idling anyway so I don't mess with it much. You can see picture of it on my SPAD defender at http://www.nearc.rcclubs.com/photo2.html
It't the yellow and red one. It has been dirt napped alot as you can see in the bottom photo. I dirt napped it again today and broke the connecting rod I think. The prop is now freewheeling so I guess thats what happend. Anyway I was just looking at the replacement parts on Global Hobbies and they were pretty cheap. The barrel is only 5$ so if you don't like the bored out verson then buy another (also debur the barrrel with fine grit sandpaper around where the bit ran through so you don't sctratch up the carb housing when you put it in and work it). The connecting rod is only 8$ so I'll have it back in the air in no time. Being a rear exaust, I just bought a kyosho ducted fan for 11$ and will mount it in a duck tape tube and circular wooden motor mount. I have a 95 cent 2 oz fragrence can (like a miniature mousse can) to use to up the performance. I figure if I'm getting 18k with a goofy muffler and 8X3 prop, a mousse can with ducted fan should get me over 20k which would fly the flying wing configuration that Ive been designing in my head for the past several weeks. Anyway, try boring out that carb as far as it will go and see the performance difference. If you don't like it your out 5$. If you do, then you won't be giveing me such a good deal on that engine!

I know this isn't the classifieds, but if you want the engine I will gladly sell it to you for $30. I already bought the OS LA 15, so I am going to go with that. The AP did take a dirt nap as well. As far as I can tell it isn't hurt, but I haven't tried to run it since then. I don't see the point as I am going with the OS. So if you want another AP to expierment on, or the spare parts, let me know, I will even pick up the shipping in the lower 48.

Roger,

Thanks for the input, I was thinking about starting to do some enlargements and you have given me some places to start.

rrh

I just looked at the rules for SSC, no carburator mods allowed. Stock muffler must be used, the only modificatio to the stock muffler that is allowable is to remove a baffle, if the baffle is considered removeable. No material may be removed or added to the muffler. So it looks as if the AP is useless for SSC anyway.

I bet if you used the stock muffler with the carb bored to the standard ventury size no one could tell or would be concerned if it didn't turn over 17.5k How much did you bore out the exaust tube? Is it noticable? I like this motors configuration for SSC because it's harder to tear up in combat. It's muffler is behind the piston so it's less likely to get banged up in a midair. You can deflect the exaust downward so that its blows out the bottom of plane while keeping the engine upright (easier starting) and the needle valve is less suseptable to breaking off because it is angled back. If AP engines did thier homework and put a standard carb barrel on there this would be a very competative engine in SSC and some of the big boys would be using it. It's got duel bearings and the ports on the sleave are huge so it can pass a lot of fuel mixture through the engine. I will never go to the national events as My wife won't let me get too far (she holds our two small children over my head), but our club does a lot of SSC and we are not concerned with the specifics of motor modification as most planes are fairly equal in performance (mine included). If I only bore your carb to the standard .15 size it should be 17.5k (mine is a little bigger than the magnums and LA's) and probably no one would care (heck they don't care now!).
Anyway I live in the northeast part of Louisiana so I'll take you up on your offer. Email me your email and we'll exchange money and motor.
[email protected]