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