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  • December 12, 2018, 07:57:49 PM

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Author Topic: Stalker engine run  (Read 749 times)

Offline Glen_Alison

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Stalker engine run
« on: October 11, 2018, 02:35:48 AM »
Hello I need some advice please. I have a Stalker 76 mounted inverted in a conventional model and using a normal proven tank. The problem is that it behaves ok in consecutive loops and outsides. However, when you do a horizontal eight the first loop and bunt are ok but it then seems to flood rich at the transition from outside to inside losing a lot of power. ( applies to round and square eights) Almost as if there is a build up of fuel in the crankcase when the cylinder is on the inside of the manoeuvre (outside loop) but then gets transferred to the head at the changeover to being on the outside for the inside loop. Help please! I am running on the recommended staight fuel and on a large prop.
Thanks, Glen Alison


Offline Brian Gardner

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Re: Stalker engine run
« Reply #1 on: October 11, 2018, 03:53:31 AM »
What oil content are you running? They don't like more than 18% and will do what you describe if running 20%

Online Gary Dowler

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Re: Stalker engine run
« Reply #2 on: October 11, 2018, 05:36:03 AM »
What is a "normal" tank??   Are you using a uniflow tank?  It sounds like it isn't such a tank, and just has standard plumbing.

Gary
Profanity is the crutch of the illiterate mind

Online Brett Buck

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Re: Stalker engine run
« Reply #3 on: October 11, 2018, 09:34:38 AM »
Hello I need some advice please. I have a Stalker 76 mounted inverted in a conventional model and using a normal proven tank. The problem is that it behaves ok in consecutive loops and outsides. However, when you do a horizontal eight the first loop and bunt are ok but it then seems to flood rich at the transition from outside to inside losing a lot of power. ( applies to round and square eights) Almost as if there is a build up of fuel in the crankcase when the cylinder is on the inside of the manoeuvre (outside loop) but then gets transferred to the head at the changeover to being on the outside for the inside loop. Help please! I am running on the recommended staight fuel and on a large prop.
Thanks, Glen Alison

       It could be any number of things, including your theory. Stuff like this (on schneurle engines) is why we stopped attempting to run them at low revs. Frank Williams discovered something similar with the ST60 when run at low revs, the solution in that case to run the engine with the cylinder on the inside.  Given that there is very little database on running these gigantic old-tech engines, I would hesitate to make any guesses as to the specific issue. But bearing in mind that you are running a HUGE engine at a tiny fraction of its capability, and at presumably very low revs, running faster/leaner would generally help. The problem, with presumably no pipe regulation, is that if you do that, you will have far more power than you can possibly control.

   By "straight" fuel, I presume you mean "FAI" fuel, that is, no nitro. Usually, standardizing on that is a big mistake because even if you get it to work, it's hair-trigger with respect to adjust and particularly, the required compression ratio is very high meaning even slight changes make a *huge* difference. However, adding clearance and also nitro probably makes the problem above worse, you will run even richer. Just for experiement's sake, I would try a *tiny* change in the compression, lower, by maybe .001-.002" (that is, add this microscopic thin fragile head shim), or even just put in a second glow plug gasket, and see if it changes anything.

A giant engine with a giant prop on a regular-sized airplane and nothing to regulate will make it very touchy, much more touchy than something like a PA75/pipe.

   With no other information and very little experience with this sort of engine by the more experienced modelers I talk to, I would guess you are probably right, it's probably some sort of internal ballistics issue, which just seems to get worse and worse the larger the engine gets (since the capability of the engine gets bigger and the power required stay the same (or even goes down with giant high-pitch props)). If it was me, I would look into an inboard cylinder, since that seem to give you the best chance of success.  ( I like Brian's idea better and it won't require a new airplane BWB )

   Brett

Online Brett Buck

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Re: Stalker engine run
« Reply #4 on: October 11, 2018, 09:38:38 AM »
What oil content are you running? They don't like more than 18% and will do what you describe if running 20%

   That's very interesting, I have the same issue on my engine with excess castor content. 22% with 5% castor/17% is A-OK, 22% with 11% castor and 11% synthetic loads up on insides. 18% 50/50 is fine, straight synthetic up to 25% is fine.

     Brett

Offline Lauri Malila

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Re: Stalker engine run
« Reply #5 on: October 11, 2018, 10:39:06 AM »
Hi Glen,

There is only one really efficient solution, you need to tilt the cylinder position to about 45 degrees from vertical. But I guess you don't want to do that to your nice new model :)
To make the problem smaller, you should try the following things (not in any particular order):
-Lighter prop load.
-Hotter plug. I have very good experience with Merlin #2004, it gives a better running symmetry than Enya #3 for example.
-Lower oil persentage (20%>17) may help, but I would especially look for oil with lower viscosity. The good old AeroSynth 3 seems to be un-obtainium at the moment, but Klotz HeliGlow #189 is good and easily available (at least via Sweden:). No need to believe what people say about nitro, it is not necessary with these engines and it won't help your problem.
-Make sure that you use high enough compression ratio. I have no personal experience with your Stalker but I think you should look at something like 1,45..1,55ml head volume when piston at tdc. It's easy to measure with a 2ml syringe & needle, from plug hole.

Cheers, Lauri

Offline David Campbell

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Re: Stalker engine run
« Reply #6 on: October 12, 2018, 01:39:53 AM »
Hi Glen
I have 2 stalker 76 re engines and both of them run the same. No problems with the motors sagging when going inverted . I use 20% oil, 5% castor and 15% klotz 200.The props i use are 14x6 stalker or DS or 14x5.5 Brian Eather carbon fibre .The motors are set inverted with a uniflow tank and i set the revs at 7000 or just under . Fuel for flight is about 126 mls. Great motors. I use idle bar plugs Sig, Glo Devi or Thunderbolt.
David

Offline Glen_Alison

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Re: Stalker engine run
« Reply #7 on: October 14, 2018, 10:31:06 AM »
Thanks for all the helpful replies. The engine is rear exhaust. The tank is a uniflow (metal) and I have no reason to suspect it. The fuel is  Formula Irvine from Technics with another 5% castor added which would make the oil content 22%. I am using the 14" wooden prop at about 6500 rpm. So maybe I will try a smaller prop to get the revs up to maybe 7500 and try the lower oil content as a first attempt. I would emphasise that it is fine when doing normal consecutive loops or bunts, The problem only occurs at the changeover when the cylinder suddenly becomes on the 'outside' of the manoevre. It would appear that fuel in the crankcase gets thrown up the transfer to put the plug into a rich condition. It does not stop the engine but cuts the power dramatically.
Glen

Offline Brian Gardner

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Re: Stalker engine run
« Reply #8 on: October 14, 2018, 09:00:12 PM »
too much oil, and pretty low on rpm, it's running too cold.

Thanks for all the helpful replies. The engine is rear exhaust. The tank is a uniflow (metal) and I have no reason to suspect it. The fuel is  Formula Irvine from Technics with another 5% castor added which would make the oil content 22%. I am using the 14" wooden prop at about 6500 rpm. So maybe I will try a smaller prop to get the revs up to maybe 7500 and try the lower oil content as a first attempt. I would emphasise that it is fine when doing normal consecutive loops or bunts, The problem only occurs at the changeover when the cylinder suddenly becomes on the 'outside' of the manoevre. It would appear that fuel in the crankcase gets thrown up the transfer to put the plug into a rich condition. It does not stop the engine but cuts the power dramatically.
Glen

Offline Mike Greb

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Re: Stalker engine run
« Reply #9 on: October 16, 2018, 08:02:20 AM »
Sounds a bit like the Fox 35 outside burp.


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