AP Yello Jacket .15
 

Hello All,
I purchased an AP Yellow Jacket .15 engine some time ago for an airplane I bought at the same time; the Aero Princess, by Sportsman Aviation.
My question lies with the engine. Why can I not get this little engine to perform? Following the manufacturers recommendations, I adhered strictly to the break-in procedures, ran the suggested amount of fuel, and followed the correct percentage of nitro content. With all of that said, I can not under any circumstances, get this engine to rev up anywhere close to where they say it should. I propped it with the recommended pitch prop for break-in, but now, almost two months later, it will not even spin a 7x6 prop up! What am I doing wrong? I know it is lean enough, and I know it is not too lean. The engine shows no signs of external wear, overheating discoloration, difficulty starting or anything else. It just will not run up.
Can any of you help me? After I broke in the engine sufficiently (actually more than the manufacturer recommends fuel wise) I put it in that Aero Princess whereupon it crashed because the engine did not have enough power. Since then, I have built another airplane that the engine would not even get off the ground! The last airplane weighed in under two pounds, so weight is not an issue either.
Please, if treating me like an imbicile is what is necessary to help me figure this out, then go right ahead. I have another one new in the box. I am afraid to use it for fear they are just useless engines.
Any help is highly appreciated.


Red

RE: AP Yello Jacket .15
 

Try less pitch. Mine runs up nicely with an old Royal 7X4.5. A Cox 8X4 would be about right for a .15 too.

RE: AP Yello Jacket .15
 

Neo1,

What is the ground altitude you are flying at?
What fuel are you using - nitro% and Oil %
Does the engine hold a good idle now?
Have you run the engine in a test stand, and does it perform differently than in the plane?
Two pounds (32oz)! Is ALOT of weight for a .15 size engnie. A highly aerobatic .15 size plane should come in around 24-28oz.
Frankly in the .25 size and down Norvel engines reign supreme in power to weight ratio and the AP engines are dogs. (sory)
Small engines usualy need nitro %'s in the 20% to 25% range to perform well and be sure you run at least 20% oil.
Also be sure 20 -30% of your oil content is CASATOR not synthetic. THIS IS VERY IMPORTANT!!!!. Small engines generaly run hotter due to there constriction, and the higher nitro used to make them run well. Castor Oil wil not break down and loose it's protection properties at these higher temps like Synthetic oils (Klotz etc.) will. Whatever fuel your using add some pure castor to it to bring the oil content up to at leat 20 %, 22%-24% would be better. I have loads of other variables to dink with. PM me and we'll talk about it

Darren

Also, I would contact the MFG, You followed their recomendations so the motor should be "monster" as adveritised. You broke in the engine per their recomodations, so if the motors a piece of crap EFFEM send it back!

RE: AP Yello Jacket .15
 

Darren,
Thanks for the feedback. My last effort was to try some 30% heli fuel to see if that would do it. Nope. See, that is what got me too. It idles great. It just purrs and purrs at an incredible low idle. It even transitions really nice, up to whatever the RPM's are. The problem is that it never winds out. It never reaches peak RPM's.
I usually run 15% nitro castor. (The pink Omega stuff) That stuff keeps all of my other engines purring and screaming at any throttle setting. So I think that it should be fine, with the exception of the need for some more nitro.
Other than that and from reading other posts in here, I found that AP uses the same carb and exhaust from their .09 engines. I guess to cut mfg. costs. So, what I was going to do is ream the hole out on the exhaust a little and open up the carb too. I am not doing any competitions so rules are not an issue.
Since I am an aircraft mechanic by profession, these little mods are easily accomplished. Anyways, thanks for the reply. If you have any other options before I do the required modifications, just drop me a line.
Thanks again for the help. Any more is still appreciated.


Red

RE: AP Yello Jacket .15
 

Neo, I dont think opening up the venturi is going to help. What it will do is decrease the vacuum at the venturi and decrease the engines ability to draw fuel. You seem like you are familure with engine operation so I'd go back to basics.

1. Completly dissassemble the engine, clean and inspect all your parts. Including your fuel tank and fuel lines. Be sure to reassemble the engine per the exploded view that came with it. I once assembled an engine with the cylinder 180 degrees out of sync thus getting the exhaust and intake ports reversed. Can you believe the engine actually ran like this! But not very well. If you haven't done this you will be suprised at how much garbage comes out of a newley broken in engine and how much better it runs once its maticulesy cleaned.

Some ideas are:

Is the needle valve in good condidion? How about the fuel nipple where the needle valve contacts it?
Do any of your fuel lines(including the ones in the tank) have any pin holes in them?
Is your throttle opening all the way?
Is the glow plug tight?
Try a new glow plug.
Are all your gaskets in good condition especially the case to cylinder, head, and glow plug gaskets?
Are you using exhaust pressure to the tank?

Are you running the engine too lean? Start the engine at FUll throttle, lean the needle untill you get MAX (Screaming 2 strokin) rpm keep leaning the needle a clic or two at a time. When the engine starts to sag and loose RPM it's too lean. At this point give it some adjustment to the rich side to get it back to the "screaming 2 stroke " stage then hold the plane straight up and make sure it keeps running if it doesn't it's too lean. Then back the thing down to idle. If it dies at idle you are on the right track and the engine was probably being run too lean all along (which doesn't bode well for it's longevity especially if you used less than 20% oil and none of it was castor) open up the throttle airbleed enough so that the engine will idle.

I cannot emphasize enough how important at LEAST 20% oil is in the small engines. This may be a big part of your problem. Buy some castor at your LHS and add enough to bring the oil % up to 20% 22%. You will be astounded at the difference it makes in the way the engine performs.

Just a few ideas. If I suggested things you already knew please don't take offence. I'm just going through what I would do to get the thing to run.

Good luck and keep us posted

Darren

RE: AP Yello Jacket .15
 

Any chance this is a sleeved engine with the ports not matched up correctly?

Just something I read, someplace.
Good luck,
Dave Olson

RE: AP Yello Jacket .15
 

i have a ap15 on a wonder and love it try 25% i found out 20 was to little and 30 was to much it would start detonating also the only prop i can get it to spin up is a top flite 8x4 but all and all i love this motor

RE: AP Yello Jacket .15
 

Darren,
Thanks for the tips. I will look over all of this as soon as I get time. I really appreciate all your time on this. Who knows, maybe the manufacturer put the cylinder in backwards! It is not unknown to happen!!!

I will keep fiddleing with it and get back to you with my findings. Thanks again.


Red

RE: AP Yello Jacket .15
 

I'm going to disagree with nearly everything Darren has said. I spend a lot of time running .15 engines in RC combat competition.

You don't need high nitro in these engines. I use 15%, and kick plenty of tail with my .15's.

Too much oil is almost as bad as not enough oil. You don't need more oil than a larger 2-stroke. I run Omega 15%, the same stuff you have now. Other guys run Powermaster or whatever their favorate flavor of fuel is. But you don't need excessive oil. Too much oil will actually reduce RPM and make the engine run hotter.

Now, why is the AP running weak? You actually have it nailed. The AP is known to be underpowered, and isn't very common in RC Combat because other .15 put out a lot more power with less work. But a couple of guys have really made them take off by doing exactly the mods you were talking about, open up the carb and exhaust and you will get a LOT more power out of that engine.

RE: AP Yello Jacket .15
 

Welp , it looks like I stand corrected. I'd go with the advice from the Combat pro. I'm taking my ball and going home:D

Darren Capulet

It is the nature of a Montague to disagree with a Capulet:D

RE: AP Yello Jacket .15
 

It's okay guys, I still like you both! Seeing as how this engine is virtually useless to me right now anyway, I will try both of your ideas. I am not one to take sides, but I am one to take from both! [8D]

Thanks again for all the help. I really appreciate it.


Red

RE: AP Yello Jacket .15
 

OK Kirk, lets take'em 1 at a time and please forgive my ignorance as I don't fly .15 combat compitition "alot".

You disagree with nearly everything I said? Well I said plenty. Other than nitro content and oil content what do you disagree with?

Do you disagree with the disassembly, inspection, cleaning suggestion?

Do you disagree that there might be somthing wrong with the fuel delivery system?

Do you disagree with the possibility that the engine has been too lean all along? If it idles well but won't reach max RPM at WOT isn't this a possibility?

Do you disagree that 2lb(aka 32oz) is a hell of a lot of weight for a .15 size plain bearing engine? What weight are you combat pilots flying your .15 size planes at. And if it's approaching 32oz what's the wing area?

Do you dissagree that the engine could be assembled incorrectly?


Pardon my ignorance, but do you use a throttle in .15 size combat or is it eassentially a WOT application? Opening the venturi is great for high end performance but degrades throttle responce substantialy.

Is the fuel you use in combat regulated in reguards to nitro content? Can the guy's your flying against use different fuel than you ?

You say Yes you are right but not untill you start reaching the 25% range. And it depends on what type of oil it is. Synth starts to burn at higher temps, it turns into a combustable componet, degrades the fuels ability to burn and produce power. Once it starts burning the engine gets hotter, causing a lean out situation, reflected in the RPM loss you noted. And if it burns away what's left to lubricate the engine? CASTOR OIL ! ( if you added it to you fuel) It's still protecting the engine after the synth oil has turned to smoke and out the exhaust. If you don't believe it add a little castor to your fuel and see what you wiping off your plane post flight. It might be a little more of a hassle to clean but that is pure engine protection your cleaning off the plane! Oil that didn't combust and was still lubricating your HOT engine!

And finally, you are probably right about the engine mods up to a piont. keep in mind it's a sport aplication neo1 is talking about. When your combat pals modify there AP's I'm assuming there taking engines that run OK to start with then "tweaking" them for maximum performance. Neo was just trying to get the thing to run.

Darren

Also here's some Tech notes from the MFG
"Fuels used for break-in should have no more than 15% nitromethane
and no less than 20% Oil content (made up of a mixture of castor or
castor/synthetic mix).
NOTE: Do Not Use Fuels Containing Only Synthetic Oil. Fuels with some
or all castor oil for the lubricant allow engines to run cooler"
last longer.

RE: AP Yello Jacket .15
 

HI Neo, I met a guy at the field today that was flying a plane with a AP15 in it today. Man this thing was a rocket, highley aerobatic. between our flights I spoke with him and took a good look at his plane. Here's the scoop. He was flying a 46" stick. All up weight was 29oz. I tached his engine at start up got a reading of 16100 on a MAS 8x4 prop. Fuel used was Wildcat 1/2A 25% nitro with added castor to bring the oil content up to approx 22%. We fly at essentially 6000 ft ground altitude (Denver). So I'm thinking you should get the similar performance with 15%- 20% down there in Fla

Darren

RE: AP Yello Jacket .15
 

Hi
A friend of mine purchased the same motor and it ran like crap almost like you mention.
After close inspection I found the cylinder to be misaligned with the ports, if you looked through the exhaust port only half of the opening was visible. After this it ran perfect.
Good luck.

RE: AP Yello Jacket .15
 

Havn`t run mine yet

is this good or bad then ?

RE: AP Yello Jacket .15
 

Here's the scoop guys, from someone who knows first-handedly how to get this baby to turn up. First off, it is true that the carb and muffler are for AP's .09 engine. Since the displacement of the Yellow Jacket is nearly twice that of the .09, more airflow (carb and exhaust) is going to be needed.

I drilled out the out the carb barrel, the shiney metal thing inside the carb, to the same size as the venturi. In fact, I may have drilled out the venturi some also. Anyway, the venturi and the opening in the carb barrel are now the same size.

Next, I unscrewed the stinger out of the muffler. Then I drilled out the exhaust hole as large as I could. When I got finished with the hole, it was so large that the inner walls of the muffler were right at the edge.

I ran this engine on a combat plane for some time until everyone got tired of the noise. It did run quite well, but it was very loud.

Here recently our club has started up some outlaw .15 pylon. I decided to bring out my AP's. I went to the hardware store an bought some copper tubing that has the same threads as the threads inside the exhaust. I made a Mousse Can muffler out of a small butane bottle, the kind you fill lighters and such with. I attached the copper pipe to the rear of the engine at the exhaust and RTV'd the can onto the pipe. I drilled my exhaust hole about half way down the can. I don't know right off how large I made the hole, but it was at least as large as the hole in the copper pipe, maybe a tad bit larger.

When it was all said and done, the engine would tach at 18.4K on an APC 6.5X5 pylon prop running on 20/20 fuel with about three ounces of added castor to the gallon.

How well does it do in the air? That I can't tell you. The two times I tried to get my plane in the air, the torque from the engine was so strong, it pulled the plane into the ground both times (hand launching a plane that is made entirely out of foam, with no throttle). Let's put it this way. A buddy of mine,who built a plane similar to the one I had,but put an OS .15 FP on it was running somewhere around 80 MPH. Hisengine is turning up somewhere around 17-17.5K. As soon as I can get a plane built that can handle the engine, I look to have mine clocked somewhere around 90 MPH, I hope.

If AP would come out with a new carb and exhaust setup, they'd have the best .15 sized engine on the market.

Good luck with your engine,

John

RE: AP Yello Jacket .15
 

No, but it wouldn't surprise me if it didn't show up anything. The symptoms mentioned, to me, don't necessarily indicate a worn out engine, or one damaged by lean runs. It's actually harder to damage a small ABC engine with lean runs than most people think. (many of the 'old hands' with engines are more used to ringed engines, which are much more easily damaged by lean runs).

It's possible, but he said it has no trouble starting, just won't reach peak power. Fuel system problems usually do more than just reduce peak RPM.

Yes, it's possible that the origional poster was wrong when he said "I know it is lean enough, and I know it is not too lean". Also, based on the other info in the post, it sounded to me like the engine ran fine, but just didn't hit peak RPM. Overly lean engines tend to sag, surge, and/or quit. He mentioned none of that. Doesn't mean it's not happening, I just didn't think it likely.

Actually, SSC combat planes have a MINIMUM weight of 40oz. Many are heavier than that. Most have 500-600sqin though. The A class planes tend to be around 32oz +/- a few, the heaviest are close to the max weight of 40oz. The wings here are in the 300-500sqin range mostly. So, depending on what you expect from the plane, how you prop it, and the wing, 32oz is not at all too much plane for a typical .15

Here I agree with you. However, as I said, from what I've seen, everything the origional poster described could be explained by the carb and muffler. Is the liner or other assembly issue worth looking at? Sure, it should only take a few moments, so why not. But I don't expect it to solve the issue, and I don't expect it to make a stock AP turn up with the more commonly used .15's

Most of the time we do actually run at WOT, however, the throttles on most of the planes out there are functional, and I actually sport fly my combat planes, including use of the throttle, etc. I agree that opening the venturi too much causes fuel draw problems, espeically at idle and in transition. But if you compare the AP's venturi with the LA .15 or the Mag .15, you'll find the AP's is much smaller. Since neither of those engines have problems with idle or transition, I'd suggest that the venturi could be opened with out the idle or trasition suffering.

Nope, no fuel rules. But I run Omega 15% as it is. I do like caster in my fuel, so I use Omega.

RE: AP Yello Jacket .15
 

Just out of interests sake, my 15LA after a few tanks tached an APC 6.5x5.5 'toothpick' prop at 18.7k on 15% nitro, stock. Probably turn a little more now.. I run an APC 7x5 now as I dont want to over-rev this engine as it is only plain bushed.
Also out of interests sake, I once stuffed up the ratio of oil in some fuel I mixed up (had too much oil, I run usually 20% Klotz (with 20% of that 20% castor;) ) and the engine would not run at all. Interesting....

Stefan

RE: AP Yello Jacket .15
 

One thing I forgot to mention in my earlier post, the modern .15 engines do not require high nitro or high oil content to run well. In fact, they seem to run better on more standard oil content than with increased oil. If you want to see what the engine can do, get some Powermaster fuel, and run it, with out messing with it first. The guys at Powermaster know what they are doing.

Higher nitro will increase RPM, but it's not a huge deal like it is with the older small engines, like the old 1/2A engines and so on. Most .15s have more in common with a typical .40 class engine than with a typical 1/2A engine, and if you treat them more like .40's, they will run quite well.

Stefan,
The LA seems like like bigger props at lower RPM, though I've seen them hit 19k turning a MAS 8x3 on 15-20% fuel. But when you go to smaller props, the RPM doesn't seem to go up much. The LA has a longer stroke/smaller bore ratio than many current engines, so the RPM seeming to "top off" isn't that surprising. Fwiw, a plain bearing by itself isn't going to prevent high RPM. The Norvel Big Mig .25 on a mousse can is plenty proof of that.

RE: AP Yello Jacket .15
 

You guys must have a lot better quality air where you're from than down here in Louisiana. I have two LA .15's and neither of them will turn over 17.5K on a 8X3 prop. In fact, that's what everyone around here runs for combat, and nobody here is getting the kind of performance you're speaking of.

RE: AP Yello Jacket .15
 

You're right, a lot depends on the weather. The fuel also matters quite a bit, that's why some guys bring multiple fuel jugs and mix as necessary to get close to the limit. I've personally seen a couple of LA's hit the mid-18's, mostly at events like Havoc, where it's drier, or when we had a cool morning.

Personally, my Mags are usually in the 16.5-17k range on 15% omega in most weather conditions, so I don't bother with the fuel thing.

RE: AP Yello Jacket .15
 

Well, the air here is thick and wet. Most of the summer days consist of 95+ degree temps with the humidity 90% and up. Here lately, the heat index has been around 110-115. That's where the humidity kills us. So, the engines here are fighting thick air (drag) with their props, on top of fighting the heat, which they already generate enough of. Makes sense to me.


John

RE: AP Yello Jacket .15
 

Humidity makes air thin not thick. Props, engines, and planes perform better with thick air not thin.

RE: AP Yello Jacket .15
 

Sport Pilot,

I understand what you're saying, but I tend to disagree a bit. Hot air is more thin than cool air, which is more dense. A plane will perform better in hot air. A prop is more affective in hot air, creating more thrust. An engine will run better, by running cooler, in cold/cool air. Most people tend to think that a plane is faster in cool air, which is incorrect. A plane will glide better, and fly faster in warm air, because it's thinner. A lot of people think just the opposite. They think that a plane is faster in cooler air, thinking about the engine running better in cooler air.

What I was getting at earlier was that an engine is going to produce more RPM in an atmosphere that is less "humid". Yes, humidity makes the air feel more hot during the summer, but humidity doesn't make the air more thin, it makes it more thick. What is humidity? It's water vapor. Water being in the air makes the air more dense, regardless if the outside temp. is hot or cold. Look at it this way. An engine in the 100 degree Arizona desert may turn 15K. That same engine on the same prop/fuel setup brought to Louisiana (100 degrees) and ran will probably only turn 14K. Even though the temps in the two locations are the same, the air in Arizona is less humid, causing the prop to spin more freely, with less drag. The air in La. is less dense heat wise, but more dense by humidity.

You may, or may not, agree. It really doesn't matter either way. But, I do feel that my explaination is correct.


John

RE: AP Yello Jacket .15
 

As I understand it, high humidity leads to less engine performance because the water vapor displaces the needed air to support combustion. The engine can only take in a set volume of whatever gasses come in through the carb. An increase in water content because of humidity is also a decrease in oxygen. As a result, you have to lean the mixture out on humid days to decrease the flow of fuel to match the available oxygen. And, in fact, if you have an engine's mixture set on a very dry day, then run it again with high humidity, you will find the engine is running rich.

High temps also reduce engine peformance. The air is less dense, so the engine has to work harder to pull in enough oxygen. An increase in temperature has exactly the same effect as an increase in elevation, and the engine produces less useable power.

regardless of how it happens, though, it's clear that engine performance goes down as temp goes up and as humidity goes up and as elevation (altitude) goes up.