Rich engine run in inside manouvres

I guess everyone knows this symptom of having richer engine runs in inside loopings our inside manouvres. Many reverse it and say my engine accelerates in outside manouvres. Well, for me the outside power is just fine (ST-51 with expansion chamber muffler and 12x5 U/C Eather prop)but the inside power goes down especially in consecutive manouvres making it difficult to fly geometrically correct.

I fly with the cylinder hanging in the fuselage and would like to know what in fact causes the rich runs. Gas speeds inside the engine might be to high as if g-forces from ouitside could have an effect.

Many say that a side mounted engine has just the opposite problem (we are still talking of side exhaust engines) and that a 45°position should be the solution to the problem.

Since I know there are many experts for engines out there I would really appreciate any idea on that topic. Both is welcomed: Solutions that work as well as highly sofisticated theories why it is that way and what is the solution.

Thanks to all!!

Christoph Holtermann, Germany

When the engine is inverted (piston down) then fuel flow is quicker and easier doing inside loops and harder and slower doing outside loops. Yes, you can cant the engine some and perhaps overcome the problem. The simplest solution, assuming you have no major problems with the engine, is stimply to shim the tank slightly to make inside and outside loops even. Lap speeds may become slightly different, but that becomes immaterial when the maneuver speeds remain the same.

>>>The simplest solution, assuming you have no major problems with the engine, is stimply to shim the tank slightly to make inside and outside loops even.<<<

Christoph,

Lens suggestion typically does not solve the asymetry, but if you say the CONSECUTIVE loops are different also, you have to really shim the tank. Then the asymetry will remain only in intersections of round maneuvers - like different sound for a quarter loop between inside and outside loop in round eights.

I think the reason is that fuel or oil from fuel collects under G force somewhere in crank case of engine and under opposite force after intersection flushes quicly out. I saw several solutions for that including glow going deep to combustion chamber (OS F) or R/C iddle bar or even fixed "umbrella" over glow like in Retro engines, but also minimized volume of crank case or filled transfer ports or small ventury. The most effective way is in my eyes opened muffler as much as possible.

But you know - I vote for 45 deg position - that works well ... at least on OS LAs.

Hi Christoph,

We are all jealous about the way you make your ST51 engines run!!

But perhaps you would still like to checkout this thread:

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=3650&forum=DCForumID1

Kind regards.
Paul

See you in Verviers?

Thank you Paul for advising me that this was already a topic for discussion. I'm relatively new in the Forum and see that there exists already a huge amount of know-how allowing to avoid the re-invention of the wheel.

I learned so far that if one wants to continue using Schnürle-engines and continue to have the nice looks of an inverted mounted engine the only solution is to minimize the effects of the rich blurps in inside manouvres.

Years ago when I was testing and using the hemi head in my ST-51's I realized that for adjusting the engine to same speed in inside and outside manouvres I had to shift the tank less than with the stock head. I was opting for the stock head again because it was making more overhead 2-cycle power. The hemi head ran so smooth and had so little overhead power that it only worked well in calm conditions.

Yes, I will come to the competition in Verviers and we can continue discussing it. Igor will also be in Germany for a two week trip and perhaps he will come as well.

Christoph

I am in Germany till 13.8. I think Verviers is that weekend after - is it so? That is weekend when we have contest In Bratislava, I afffraid I will go home. It depends if I go by car or by plane (menas if I can tak model or not) and if I will have chance to go home in real time (it is 10 hours to drive ... and to fly afterwards). I will see.

Hi Christoph. Super article by Randy Smith in May'June SN p71. Covers your query. Regards,