Taming a ST G21 35

Has anyone here ever tried to set up this engine for a stunt plane? I used to use them for slow combat 30 years ago and did pretty well with them. I still have a half dozen or so of them that run decently and don't plan on using them for slow combat as I dont like the event anymore since a kill doesn't count as any more than a cut. I suppose I could use them as a sport flyer but they don't seem to run a particularly good 4 cycle.

I have one of those as well. Got mines in a trade. Not sure what plane it would be good for. I would like to know as well what it would need to be a good stunt motor.

Run it like a Schneurle engine, high rpm, low pitch. You can also experiment with lowering the compression. Since it is timed for 18,000 rpm on an 8 inch prop it may need lower compression to run reliably on a 10 or 11 in. at 10K.

I believe Bob Baron ran this kind of setup for a couple years. He published a design for it.

Phil,
I have one of these on a Core-House wing, and a fuse built up like a slightly oversized Flite Streak. And I'm not getting the performance I had hoped for from it. It only has about an hours run time on it... What prop, nitro content, venturi size should I be using? (APPROX.) I now have a 9 X 6 APC, 10% nitro/23% oil, and a true venturi of unknown size.

Thanks,

This sort of talk brings a tear to my eye. It's sorta like seeing a Kentucky Derby winner pulling a plow in his later years. I guess you can't put old combat engines out to stud. Old combat flyers is a different matter. Hmm, I think I'll work on this metaphor.

When I used them in slow combat I used 25%nitro 20% oil. With a 9-6 they screamed. The problem is they get real cranky as far as the needle setting goes and are hard to start. I guess I wanted to know if anyone ever stuffed the schnerl passages.

A stock G-21 with the stock suction venturi should still be a nice sport engine although it tends to run fast. Up until very late in the production the sleeves were built with the exhaust and bypass timing the same. Both ports opened simultaneously. A lot of combat guys(Howard) raised the exhaust and later the factory did too. With the raised exhaust it will be very difficult to get it to run decently on a prop larger than 9 in.

The stock suction venturi was a sprinkler type with about a 5/32 diam. hole. A lot of combat flyers opened this up to 3/16 or more.

Check the head clearance. It should be at least .015 in. for sport flying.

Run it on 5-10% nitro and 25 % oil, at least half castor, like any iron piston engine.

Take a good look at the piston through the exhaust port. The piston should have a smooth satin appearance. Shiny spots mean it has not been broken in enough, so run it some more on a cut down 10/4 fast and rich. They can take a long time to break in- at least a gallon of fuel.

Try running a 10-4 or a 10-3 and let it scream. I've done that with a Fox 36X and it worked OK for fun flying.

Howard: Dept of Useless Info, Currell Pattie, Proprietor...

I still recall this article in the Washington Post, maybe 40 or 45 years ago. The Mounted Cops in DC, that worked Rock Creek Park, or the National Zoo, or something, used a horse that had come in 11th out of 13 in, I think, the 1949 Kentucky Derby. Better that than the Ambroid Factory. Ok, he didn't win the Derby...

Anyway, yes, run it as if it were an ABC Schneurle. You could play with head gaskets, and make certain the venturi isn't too wide open. On a similar note, I have found that Fox 35Xs make a decent sport or stunt motor, despite their more aggressive timing.

Mine ran nicely using an APC 11X3 running 5% fuel with 25% all castor. Is this the plain bearing or ball bearing? Do you have the small venturi or the large combat venturi? The small one has excellent draw while the larger one must have pressure.

>Mine ran nicely using an APC 11X3 running 5% fuel with 25%
>all castor. Is this the plain bearing or ball bearing? Do
>you have the small venturi or the large combat venturi? The
>small one has excellent draw while the larger one must have
>pressure.

I ran them in slow combat with the small venturi and non pressured. Used a 9-6 prop. They are the ball bearing model. I have one with the non BB I think it also is a baffle. I have several ST baffle 40's that will probably work fine for stunt, but not on a smaller size profile stunter.

>Has anyone here ever tried to set up this engine for a stunt
>plane? I used to use them for slow combat 30 years ago and
>did pretty well with them. I still have a half dozen or so
>of them that run decently and don't plan on using them for
>slow combat as I dont like the event anymore since a kill
>doesn't count as any more than a cut. I suppose I could use
>them as a sport flyer but they don't seem to run a
>particularly good 4 cycle.

I had pretty good luck with mine. I ran either a 11-5 or 11-6, and it really had no problem at all staying under control.

Of course, there's a lot of different versions of the 35 (just like all the others). Mine had a flat-topped piston, with interesting-shaped ports.

My ST 35 runs a real solid stong 4 stroke with a soft break. Talked with George Aldrich and he said to add gaskets until it started to break. Been running it that way for a couple of years now. Running a 10-6 BY&O on 64 Ft. lines. I like it. I'm using a venturi from a ST 46 which is a little larger. 5%nitro, 22% oil 1/2 and 1/2

>My ST 35 runs a real solid stong 4 stroke with a soft break.
>Talked with George Aldrich and he said to add gaskets until
>it started to break. Been running it that way for a couple
>of years now. Running a 10-6 BY&O on 64 Ft. lines. I like
>it. I'm using a venturi from a ST 46 which is a little
>larger. 5%nitro, 22% oil 1/2 and 1/2

Mine was pretty much straight out-of-box. It was way more powerful than the Fox I had used previously. It had no problem at all pulling around my 615 square inch, 50 oz. 7:1 aspect ratio plane. I eventually wore it out. At no time did I find it particularly jumpy or uncontrollable. At the time, I was not particularly discerning, but I could have told if it was not at least close to right.

I wouldn't necessarily recommend it as an engine to seek out, given that there are much better engines available for $65 and a 30 second internet transaction, but if you have one, it will probably be fine.

I've sold 4 used ST G21 35s on Ebay for $75.00-$90.00 & 2 new ones for well over $100.00. I would keep your best one for your collection & sell the rest. You will have a hunk of money to buy nice stunt engines with.
I used to fly alot of combat.

I've also sold the engines and got over 100 dollars for NIB and never used engines. I thought about selling some of the used ones and wondered if it is worth the aggravation. I have enough of the engines to not worry if I screw one up by experimenting, hence my post here. I also have plenty of extra cyl. pistons gaskets etc. I have never competed in a stunt event nor have I ever flown a complete pattern. I haven't flown at all since 1974 so I won't be buying any new engines 'til I get back into it and see If I can still fly. I just finished a 440 square inch flapped profile stunter of my own design and equipped it with a fox 35 stunt. As I mentioned in one of my other posts, I don't like slow combat since they changed the rules back in the 70's so I will make an attempt to fly some stunt. Do they allow a 60 year old man in beginner stunt?

I must have a total of 200 or so engines from .020 to .60 mostly .25- .40 in size so I have plenty to experiment with. The local club is mostly stunt oriented, so I'll give it a go.

I have a couple of OS .40 RC engines I used in carrier back in the early 70's so maybe they can be converted to a good stunt engine when I build a full body stunter.

Thanks all for the comments and suggestions.