AP-15 YellowJacket - RC Groups
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Dec 01, 2012, 12:46 AM
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Mini-Review

AP-15 YellowJacket


Ever since these engines came out , I wanted one , but there was something that always stopped me , something that nagged at me .

Cruising HK one day recently , I cam upon the YellowJacket and it was in stock , and the price was such as to overcome my reluctance to buy !
I have some spare time on my hands now , so I stripped the engine , and timed it to see whats what .

Exhaust Timing = 160Deg Duration
Transfer Timing = 140Deg Duration [ 10deg Blow down ]
Shaft opens = 35Deg ABDC [ err thats After Bottom Dead Center ]
Shaft closes = 58Deg ATDC [ After Top Dead Center ]

Now , those are fully RACE Timings on what is clearly a sports engine .

Transfers are cut out of the cylinder , Piston Cylinder is ABC , back plate screws in and has a rubber gasket Oring , and the head is head by 4 bolts ..

Now , this looks like a racy engine , kind of named like a racy engine , but for the love of engines , why did they put in a 1.5cc crank shaft ?

Bore and stroke =

Bore 15.5mm
Stroke 12mm

This engine begs to rev its Jellowjacket off ! it really does , but here is the insanity , the crank is a 10mm job .. A 10mm DIA crank in a 2.5cc engine thats been RACE timed !

I dont know who designed this engine , but the crank should have been a 12mm job , they knew this back in the 1970's , a hot 2.5 must have a 12mm crank .

Now I got this engine for my collection , was cheap etc and everything about it is nice , except the 10mm crank , its a tinny little 1.5cc crank .

Also the outlet for the exhaust is a little small , its not a deal breaker [ easy fix ]

Now I really want HK to stock the 09 Yellowjacket , cos if it has a 10mm crank in it , then we might have a hot little engine ..


2.5cc Glow engine [ RC carb ]
twin ball-raced crabk shaft
Bore 15.5mm
Stroke 12mm
Exhaust 160Deg
Transfer 140Deg
Shaft opens 35Deg ABDC
Shaft closes 58Deg ATDC
Crank 10mm with 6.6mm Gas Passage
ABC p/c

Now , if the manufacturer had lowered the exhaust to say 140Deg , eased up on the shaft timing to say 45/50 or 45/45 , then this engine would make sense . As it is , its a little mind boggling to understand the thought process behind its inception .
Last edited by old4570; Dec 01, 2012 at 06:14 AM.
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Dec 01, 2012, 12:54 AM
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jeffie8696's Avatar
Maybe a tuned pipe will help?
Dec 01, 2012, 02:17 AM
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surfer_kris's Avatar
Thanks for the timing numbers, I have been thinking of getting one too for a long time...
The crank and case etc are common with their .09 engine I believe. That engine is really overweight though with a very thick brass liner. Guess they compromised a bit too much and ended up with two weak engines. Apperently they run fairly ok though, once you put a less restrictive exhaust on it.The bore and stroke also makes it a 2.26cc engine if my calculations are correct...
Dec 01, 2012, 10:10 AM
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earlwb's Avatar
I have a couple of those engines, but I haven't done anything with them yet.
Has anyone run one and get some RPM notes with different propellers yet?
Dec 01, 2012, 10:24 AM
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surfer_kris's Avatar
There are some numbers on RCU (not mine); AP .15
Rather disappointing in stock form...
Dec 01, 2012, 11:51 AM
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Once again it looks like I am responsible. I thought I was the only one that bought one of these motors. The reason the crank is so small is because it is just a rebore of the .09, so the carb and exhaust holes are a bit small, and it really is not quite a .15 either. I made an adaptor to fit a pipe for mine, and also a new stinger for the exhaust to give it more power. It revs to almost 25,000 rpm with a little 6.2-5" F2D combat prop, but the rod bearing wears too fast so I would keep the revs to under 20,000. The .09 cyl is similar to the .15 but the bypass flutes don't go right through to the piston. I will try again to get these pics on. The .09 compares well to the TD .09 and OS .10 power, and the .15 is about the same as most other .15's as well if the stinger is opened up, or the stinger just unscrewed. as on the first pic. The middle pic is a control line carb and needle valve I made up that goes a bit better than the rc carb. I flew the kind of crude FAI combat with it and it got me dizzy. The last pic, it is the one with the black head.
Last edited by aspeed; Dec 01, 2012 at 11:56 AM.
Dec 01, 2012, 04:10 PM
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earlwb's Avatar
I have a small P-38 twin engine plane I am planning on using the two AP .09 or .15 engines on. It doesn't really need lots of power or speed per se. But the .15 engines are more light in weight as compared to other .15's and the exhaust is more hidden being in the rear. Plus the plane would tend to come out more nose heavy with heavier engines. So I figured it might be a good match for the plane then. I just have to get around to putting it all together and test run the engines to make sure they are working OK for me too. I'll likely run 7x6 props on the engines, or maybe 8x3's or 8x4's.
Dec 01, 2012, 06:45 PM
Registered User
8-3" or 7-5" for a bit more speed are my choices for sport .15's
Dec 01, 2012, 10:30 PM
Hutch
hutchinstuff's Avatar
Quote:
Originally Posted by earlwb
I have a small P-38 twin engine plane I am planning on using the two AP .09 or .15 engines on. It doesn't really need lots of power or speed per se. But the .15 engines are more light in weight as compared to other .15's and the exhaust is more hidden being in the rear. Plus the plane would tend to come out more nose heavy with heavier engines. So I figured it might be a good match for the plane then. I just have to get around to putting it all together and test run the engines to make sure they are working OK for me too. I'll likely run 7x6 props on the engines, or maybe 8x3's or 8x4's.
Earl, if you want, I've got an AP .15, could send it to you for testing, unless you have them already.....or I can try to find my tach and see what it does. I know it doesn't put out as much juice as the Magnum XL .15, but it does sound pretty darn awesome....
Dec 01, 2012, 10:52 PM
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earlwb's Avatar
Thank you very much for the offer, but I already have two new ones and one used one I can run. So I am pretty much all set. I just need to get going on test running the engines and setting up the P38 to use them. I don't think the plane needs a lot of power to fly as a twin. The better and much larger .15's are too big and heavy for the plane. A couple of the old style bushed crank engines would work well such as the Enya .15's for example. But I sorta like the rear exhaust setup on the AP 15's as there is much less cowl cutting to get the engines to fit.
Dec 01, 2012, 11:54 PM
Hutch
hutchinstuff's Avatar
Cool, I just sold my Magnum and kept the AP! I'm excited about finding a project for it one of these days, may be an old timer when I come across one again....


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