stunthanger.com
Engine basics => Engine set up tips => Topic started by: Bob Reeves on September 20, 2007, 07:04:49 PM
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For the last several weeks I have been soliciting and reading all the info I could find on the ST 51. I have read or heard very conflicting setups that the pilot is happy with. For instance some say use a low pitch prop (4). others say use a 5 or 6 pitch prop, Some say lower oil (20%) some say higher (25%), 0% nitro to 15% nitro..
It must be assumed that everyone running a ST 51 and offering a recommendation must be satisfied with the engine runs they are getting. Now I can't believe one engine will do it's best under all the different setups I have seen. I know the Brodak 40 comes close but even it has a range much less than what has been reported for the ST. The trick question is which one comes closest to the optimum for the ST and the average stunt ship. Wished I knew the answer???
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Hi Bob,
My ST 51 is in a 64 oz. plane and I like the way it flys. Send your address and I will pull it out and you can try it and see if it is any different in your ship. I have another I'd like to break in anyway plus it'll give me a chance to return a favor. Grins
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Hi Bob,
Interesting question. I know you have been chasing that ST 51 in your Skylark, a set up that I would think would be perfect.
I think all the factors involved relate to which set up to use. The personal preference of a high rpm/flat pitch vis a vis a 4-2 run. Also altitude denisty, etc., etc,. plus whether it is a stock, T&L, Smith, Dixon, Barker, or....... set-up.
I have run the T&L for several years in competition. I found it to work best with a surplus Rev-Up 12-5, 5% nitro in a 64 oz. SV 11, and an Eather 11 1/2-4 3/4, 3 blade flat back in a 54 oz. USA-1.
Props were different depending on the plane with the stock one I had, but it like 11 1/2"-12" and around 4.75 to 5 pitch, and the Rev Up surplus was the usual culprit. Uniflow, no pressure, tongue muffler from Windy. Don't know the launch rpm, but propbably in the 9000 range. Just in a hard "cackle". Break from 10 to 2 o'clock and sometimes just at the top. Don't know the venturi size, got the ones for the stock one from Randy. Always 5% nitro, very seldom needed 10%. 5 1/4 to 5 1/2 oz.
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After a great deal of experimenting (trying to cure an uncontrollable runaway into a very fast 2 stroke) I finally ended up box stock standard apart from a Bolly CF Supermuffler and using 25% all castor with zero nitro. That gave me my preference of a rock solid 4 stroke through the entire flight. The extra oil (up from 20%) eliminated the overheating that was causing the runaway and I suspect a little playing with slightly lower oil content might allow some fine tuning of a 4-2 break if that's what was needed. Prop used was a Zinger 12x5 wood, clunk tank on Uniflow and muffler pressure.
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Hi Bob,
My ST 51 is in a 64 oz. plane and I like the way it flys. Send your address and I will pull it out and you can try it and see if it is any different in your ship. I have another I'd like to break in anyway plus it'll give me a chance to return a favor. Grins
Appreciate the offer but I already have two ST 51's and both have been in the Skylark. One stock and the one in it now that has been through Bowman. I started this thread a little sooner than I should have because I need to get the Tulsa contest over before I can really get back on the Skylark and play.
Bill, the first prop I tried was a surplus Rev-Up 12-5 and didn't like it at all, sad because I think I have a couple dozen of the silly things. The best so far was an APC but I can't make the Dubro spinner I need to use fit it, even the APC wasn't that great. Personally I don't care if it runs in a rich two or a 4-2-4 I just want it to pull the airplane over the top without slowing down.
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Mine is a Bryon Barker ST51
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I just want it to pull the airplane over the top without slowing down.
Hi Bob,
Is it the engine or the airplane that is slowing down? I mean is the engine still running at the rpm and the airplane is slowing? Or is the engine actually dropping rpm?
Bill <><
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Well the airplane is slowing down because the engine doesn't produce the thrust to keep it from slowing down. The problem I am having is I have been spoiled by flying 4 strokes all summer.. Neither my 40 or 56 slow down (or speed up) one bit and both are in overweight airframes.
As I have said before people are flying 60 ounce stunters with ST 51's and are perfectly content, I'm thinking I am being too picky. The airplane with a stock ST 51 did win Advanced Classic at Brodaks and I'm still not happy.. Good grief Charlie brown ~^