The mysterious outside "charge"

Hi Guys,

Here's an engine run question for you all. Running a Stalker .51 on my Gladiator. I get good smooth powerful runs, great 4-2-4 and lap times within .1 seconds begining to end of flight. Here's the thing, on outsides the engine charges, I mean it really screams. Inverted is fine, its most evident in the outside loops, but still there even in outside corners. I tryed lowering the tank 1/16" and the run went to pot.

What now?

Thanks,

THIS IS HONESTLY A TOUGH ONE. You may get a lot of varied advice for this one.

Your lap times do not need to be equal. Slower inverted lap times, to control the surge in the outside maneuvers, are acceptable and sometimes necessary.

The following may cause the phenomenon you described.
1. Too cool a plug.
2. Too much nitro.
3. Too much oil.
4. Too much load from the prop.

If all else fails get a new motor…HA HA! (just keeping it light).

>Hi Guys,
>
>Here's an engine run question for
>you all. Running a Stalker
>.51 on my Gladiator. I
>get good smooth powerful runs,
>great 4-2-4 and lap times
>within .1 seconds begining to
>end of flight. Here's the
>thing, on outsides the engine
>charges, I mean it really
>screams. Inverted is fine, its
>most evident in the outside
>loops, but still there even
>in outside corners. I tryed
>lowering the tank 1/16" and
>the run went to pot.

I thought the Stalker was a baffle-piston engine, but this is classic schneurle behavior. The only thing I've ever been able to do to reduce it is to run more rpm, to get the gas flow velocity up, which hypothetically will make it less prone to scavenging differences between inside and outside.

I don't know how to solve it, most things suggested like hotter plugs just reduce it. Shimming the tank, as you found, just messes up other things, and I don't find this an acceptable situation.

If you are running any nitro you will need to install some additional head shims over the stock setup. I've had a lot of experience with the 61's and a few 51's.

For example: if you run 5% add 2 additional shims, 10% add 3, 15% add 4. You will find this to make it amongst other things more tolerant to needle settings and tank height.

Don't concern yourself too much with lap times. Get it close to equal flying round horizontal eights, personally I prefer very faintly leaner on outsides, it will help with the verticals and hourglass.

>If you are running any nitro
>you will need to install
>some additional head shims over
>the stock setup. I've had
>a lot of experience with
>the 61's and a few
>51's.
>
>For example: if you run 5%
>add 2 additional shims, 10%
>add 3, 15% add 4.
>You will find this to
>make it amongst other things
>more tolerant to needle settings
>and tank height.

I have a friend who has a new Stalker 61. Doug Moon has been trying to get it to run with no luck. The motor suggests a tremendous amount of break-in. I suggested that the compression ratio may be set-up for 0% nitro. If you shim the head for nitro, what is the thickness of the shims?

Can you provide any tips to help get us off the ground? I understand you have run several of these engines.

I ran that stalker 61 with FAI fuel and it was not very happy. The motor would run sloppy rich in level flight and the break it would go like a rocket. I started in on upping the nitro to help bring up compression. 5% was a better run but still rocket. 10% is unflyable when there is a break. 5% was the fuel of choice. Then onto an aray of props and sizes. BY&O 13X5 was working ok I guess. I could fly some of the manuvers. The motor really needed alot more bench time. Then the local engine guru Glenn Reasor looked at it and noticed alot more play in crankshaft than there should be. He was lightly pulling on it and it would move in and out a noticable amount. I thought it was just cold and would tighten up afetr it runs and gets hot. Not so it was actually looser after the run. He has it now and is checking out in his shop. He has all those cool tools to do that stuff.

Doug Moon

This is a tank problem that has fuc%staited alot of flyers. My McCoy's did this. How far is the tank to the engine? You might have to move it foward. AND go to larger fuel tubing!!! It worked for my McCoy, ST-51, And the JETT-50. Can only give it a try...

Hello.

I get the same type of behaviour from my Stalker 61 SE.
I had also problems with the ST51 going blubbery in insides.

I was not able to completely get rid of either problem.

That's why my actual ship is using a sidewinder configuration
with a Stalker 61 Rear exhaust: Complete symmetry between insides and outsides and lots of power.

I have not noticed any disadvantage using this configuration, except from a more complex nose construction.

Regards,
Paul

Boy I would sure like to hear more about problems and solutions with the Stalker's.. I have one each side exhaust and rear exhaust .61 acquired in a multi engine buy and someday was hoping to build something for one or both.

Second that-

I was re-looking at the 51 as a possible for a Bucanneer 746 project after getting other comments here.

Randy Powell Has the best set up out there. Hope he posts on what he's done. More power then most PA-61's

Guys,

On the stalker 61.

For 5% nitro add .008" head shim.

For 10% nitro add .012"

For 15% nitro add .016". They will tolerate up to .020" if you want to soften it more.

Use Thunderbolt I/B, McCoy I/B or Fireball idle bar plugs.

The symptoms with these needing more shims are a rough raggy 4 cycle and hard switching, sensitive needle settings, and you might think it needs more running in.

They typically don't need a very long break in unless you get a particularly tight one.

Shaft end play, I have come across this once back in the early days of these. The bearing shoulder dimension in the case was less than that of the shaft. After measuring it was cured with a shim behind the outer race of the front bearing. I'd suggest you look in this area.

Props, the love the Eather 12 x 5.75 round tip 3 blade. The Bolly 12 x 6.5 would work well also with the tips set to 5.5". You'll need 10 to 15% nitro to spin these properly depending on your model weight and location. A zinger 13x6 with the tip pitch increased to 5.5 will work well also. They come with tip pitch between 4.5 and 5". You'll loose a bit of leading edge in the process, just make the tip elliptical and re-shape the airfoil.

I think somebody mentioned ST51's. Yes they tend to get a rich surge on hard insides, even when you have them even for inside and outside rounds. Fill the boost port and keep the revs up and again run something like a Thunderbolt or McCoy idle bar plug. If running nitro they usually like .010" extra under the head from stock. Its all about gas velocities!!!!

Hope I've helped out here.

Another thing worth mentioning. They love muffler pressure. VERY carefully tap a nipple into the front face of the muffler chamber. When you screw it in use high temp loctite or JB weld.

Thanks Guys,

I forgot to mention that I am running muffler (rear exhaust)pressure which brought the engine to a very consistant run.

I have to restate that it is performing beautifully except for the outside surge. The tighter the loop, the harder it runs. Maybe this is good, it forces me to keep them out where they belong.

I'm running Powermaster 5% nitro and synthetic/castor blend. The castor solved the overheating problem I was having. Anyone that's watched this airplane fly comments on how nicely the Stalker does with it. 720 Sqs at 60 oz, the .51 seems made to order. I'm very happy with this engine with the only exception being this minor vice. Might try some shimming, but I'm not confident that that's where its at.

Thanks again,

I run a Stalker 51 RE and fully endorse everything Bri has said. The shimming is the key and Bri's numbers agree with my experience. My 51 gives a powerful, dead steady run from start to finish with a nice break into a two stroke under load. Excellent run. I also run the Eather three blader, but use Fox plugs. Stalker themselves recommend against using any Castor. Personally (being a wimp), I run 5% castor and 15% Cool Power along with 10% nitro. If you are running all castor, perhaps that is mucking something up.

'cause, it could just be that it prefers the Aussie accent to your American one, or perhaps we use better swear words..**grin**