Improvements to the SuperTigre G51 for Stunt

I have at last got round to writing up the modifications I have done to my ST G51s to get the good stunt performance that I am getting now

http://www.machineconcepts.co.uk/aeromodelling/st51/st51-1.htm

Nice article! I have two T&L G.51's to try out, both Chinese, a stock one to experiment with, and the modified Italian one I've flown for some years. All your mods make sense to me. I am wondering about these "Master" propellers. Not "Master Airscrew", I assume? Where are they made, and where can they be purchased? Steve

Steve Helmick
Renton, Washington
USA

Mike,

Excellent post...thanks for taking the time to share your work with us. Good job on the web site, as well. I suspect that many of us reading your post, wish that we had your machining facilities and ability.

Couple of questions:

1) I may have overlooked this somewhere, but giving the differences between the Chinese and Italian made versions of the G51, which one are you using, and what differences did you find in the final run conditions?

2) With your superb machining ability, why is the port modification made by hand, with a Dremel grinder?

TIA

Cheers.

Warren Wagner

Hi Warren

The engine I am using is a Chinese built version. I haven't flown the Italian one yet, it is a second hand pre-crashed one donated by a kind friend. I have rebuilt it and straightened the crankshaft and plan to try some back-to-back testing with a standard Chinese version later this year.
I grind the ports in the cylinder as the cylinder is made from hardened steel and it isn't machinable with any of the cutters I have.

Hi Steve
The propellers are Master Airscrew 12x6. I have been told that the design of these has changed in the last couple of years and the earlier ones are better for our use but I don't have an older one to test so it is only hearsay.

Hi Alan

All of the Chinese ones are original CL versions. I am not sure about the Italian one but I would expect that it to is a CL version. I will ask

When Brian Eather modifies port timing, he also does it by hand.

The difference though is that he uses a file, not in and out of the bore but across the port from the outside. He says that this gives him a very fine control over the amount of material he removes without any risk of damaging the bore.

One question that isn't obvious to me is whether this was originally the CL version or the RC version of the ST51.

I haven't taken any measuring tools to the two engines, but I had heard from some of the engine rework guys that the only difference between the two versions of the engines was a gnat's whiskers difference in bore diameter. I bought some rings from Frank Bowman, and he asked me which version I wanted the rings for, as he has different rings for the two engines.
I have been running them stock from the box since 1994, and agree with the tube muffler volume. I didn't go to great lengths with it, but I couldn't get a tung muffler to work very well.
I have flown ST.51's on models that weighed as much as 72 ounces with this basic set up:
1) Tube type muffler (Big Art or Scott Dinger type)
2) Hot Plug. I like Glow Devel R/C longs
3) SIG 10% Champion fuel, I/2 Klotz, 1/2 castor for 20% total oil
4) Props have been 12/5 Top Flite, 12/5 BY&O, and redently been using APC 12.25/3.75. Just started working with a Master Airscrew 3 blade 12/6 cut down to 11" and re-pitched to 3.5". So far so good with that but not getting as much practice time with it as I would like.
5) Two to three head shims, depending on the model.
The APC or similar prop would help you wind up problems in the wind. Take off RPM with that prop is in the 10,500 range, and I think this really helps to get the engine up to the heart of it's power band.
I'm going to read you article over when I have the time to really absorb it all. Some interesting ideas in it.
Good luck with it.
Dan McEntee

Mike, in your description of mods to the G51, you show the reduction in crankshaft bore to 8mm. Could you please explain why you did this?
Thanks,
Charlie

Hi Charlie

There were 2 reasons, neither of them very strong.

Firstly to speed up the gas flow. These engines running at stunt revs don't need the big hole to pass the mixture so I think that narrowing it should speed up the gas flow with no detriment to the power we are looking for. It may be possible to make it even smaller but I would need more time than I have at present to do the testing.
Secondly to make a small improvement in the crankcase compression. The better we can get the pumping efficiency the less the change in fuel head in the tank will affect the running.

Reducing the crank bore makes a bunch of sense, when you're also blocking the boost port. [photo not recovered: sipcof.gif] Steve

Steve Helmick
Renton, Washington
USA

Hi Mike,
Thanks for a very interesting article, everything that you have done makes a lot of sense. With a bit of luck, I shall be flying a Northwind, with a stock Italian ST 51, later in the season.
I have been combing the Stuka Stunt archives for ST51 information. A lot of people people claim that with a particular prop (varies a little from person to person) and the right percentage of all castor lubrication, the ST 51 performs well straight out the box.
Your comments about winding up in the wind are obviously a touch worrying!
I wonder if these claims are prompted by variations in manufacture tolerances or deliberate changes during production. Maybe there is a magic prop and the right flight rpm, or are the people that claim they run straight out the box less critical?
Just curious as to the varying performance that people see in this engine. I have no doubt that Mike has a wind up problem stock, other people claim they don't see it........ Curious, anyone care to comment?

Thanks for sharing your experience,

Andrew Tinsley

Hi Andrew

I purchased 2 new CL versions when Tower had a special offer on. I couldn't get a good stunt run out of either of them and I did try a lot of the suggestions that you will find here. The first break through was when I found out that all of the ones I had seen performing better than mine had been breathed on by an engine guru. The third example - the one that I got the best performance from was obtained from a good stunt competitor who, like me, had been told of the good stunt run possible with these engines. He tried for a while and was getting similar poor results to my original problems and gave up on the engine and gave it to me in exchange for a Merco 61. This is the engine that has the blocked boost port.
I think that the source of the problem is that the engine is not designed to run as slowly as we want it to and it is possible that some of the people using it are running it faster with a finer pitch prop. I did try this route and it was better - OK for a bit of sport flying but hopeless for competition.

Hi Mike,
Thanks for your explanation. You are quite correct in the assumption that "other folk " were going the high speed, low pitch route.
I was going to try this method of running the ST51. I have had such a good time flying a Flitestreak with the BBTU FP 20, that I was hoping for a similar type of performance with the Northwind plus standard ST 51! Looks as though I might be disappointed!
Having said that, the best stunt flying that I ever did was with a Black Ghost and Oliver Tiger, some 40 years ago. Since then I have been trying to get a classic 4-2-4 stunt run with various glow engines. Early Merco 35's and Veco 35's were the best motors that I have used. To be honest I have had enough of trying to get a really repeatable classic stunt run, the Flitestreak and BBTU FP 20 were a revalation, just like a good diesel run!!
What were the problems that you found with the high speed low pitch method using the ST51? Is it simply that you don't like this method of running and prefer the classic run? I would be interested in your comments at my age and health, I don't have too much time to experiment!

Thanks and best wishes,

Andrew

Or,

You could have sent them to Tom Lay and they would have run prefect time after time, after time.

Tom's the expert tuner for Supertigre engines, period!


Jim Pollock