Fuel economy, ST 60, oxymoron?

Stuka Stunt Main Forum · 8 of 8 known posts recovered

EricV · May 15, 2001 07:19 AM

Hi Y'all,

Here's one for you...

SV-11, ST 60, perri ported version, 312 Delrin venturi, Smith Aerotiger NVA through the middle, stub muffler, waiting on a Tube one from Big Art, 5% Sig all castor. 5.2 laps, 63Ft lines, (Eyelet to eyelet)6.0 Oz Smith tank, 12x6 Master Airscrew with wood with the yellow tips, ( I've swept them back like a Bolly). I'm making it to the overhead 8's, if I leave out 4 inverted laps. No time for the four leaf.
Plenty of power (and I mean plenty) Where do it adjust?? Venturi size? Type of fuel? More fuel? I have room for a 6 1/2 oz tank, but I'm Sooooo close, you know what I mean?

Only got about a dozen flights on this new bird so far, it may just "break in" to longer flights? I've had'em do it. This thing rides the parking brake on the down leg of the outside square, I'd hate to do anything that would change that!!!

Suggestions would be appreciated!
Thanks in advance,
Eric

Paul Walker · May 15, 2001 02:13 PM

#1 source

When I ran ST 60's, I used a 0.285 dia venturi. This still provided plenty of power (the setup I used at the '87 NATS). In light airplanes (~55 oz.) I could get by with 6 ounces of fuel. In heavier planes (65+), even with a 0.285 dia venturi, still used 8 ounces of fuel.

For your problem I would start with a smaller venturi. Good luck.

Nils · May 15, 2001 08:51 PM

#3 source

I have a T&L ST.60 in my Shark 45. I don't know what size venturi Tom put in it, (but Paul probably does). It only has 29 runs on it since I got it back from Tom, so it's fairly fresh too. I've been flying it on 66' eye to eye lines with a 13" zinger repitched to 5.0 with 5.25 tips. I have a 6.5 oz tank & have to pull fuel out to avoid an over run. With only 22 flights on this airplane I am still sorting out the fuel load so I have been paying attention to fuel consumption. (Side note: The weather here has been crappy & I started a new job 20 miles from my circle. Both of these factors have cut into my flying time considerably! Jobs are such a nuisance.) Anyway, in Portland at the Jim Walker Memorial a few weeks ago I had to take out two cranks (on my fuel pump) of Sig 10-25 all castor, & I think I should/could take out more, but I didn't have any more time to experiment. It likes to be launched at 8,600-8,700 with this prop. You might try longer lines & lean out the needle a little to keep your lap times. The ST should be able to pull another three feet of line length easily.
Nils

Bill Hummel · May 15, 2001 07:53 PM

#2 source

Hi, Eric,
The ST 60, all versions, responds well to adding a .010 to .016 head shim to gain a little fuel economy. This will not kill off "power" as much as you might think. Also, adding the Bru-line air filters gives much the same effect, and is helpful in fuel tuning, as well as killing off some of the 2-cycle surge.
I've not found different styles of mufflers to vary much in fuel use. Try the head shims, I believe you will be happy with the results!

EricV · May 16, 2001 09:33 PM

#4 source

Thanks everyone... I have a question regarding adding the head shim.... Since this is a late model ST 60 with the small chamber head, wouldn't I do as well to put on an older style Hemi head, which would also increase volume/decrease compression much the same, with the benefits added of the Hemi? For the venturi, my next size cutting tool for downsizing would temp me to try a .292, before I go down lower. Thoughts?
Eric

Steve Helmick · May 16, 2001 10:09 PM

#5 source

LAST EDITED ON May-16-01 AT 10:18 PM (EST)

Lower compression and smaller venturi should help, older head may or may not, but worth a try if it clears the piston ok. Longer lines will increase your fuel consumption (making it go further and produce more power for more miles), tho I also thought your lines were too short. The engine should improve fuel economy with break-in, but I wonder if there is not enough ring end-gap? I am not a fan of nor expert with ringed engines, but know a lot of them are set wrong at the factory. If I remember right, you can tell if the gap is too little by seeing if the ends of the ring are shiny. Finally, Derek Pickard reported in SN 3 or 4 years ago on an example of the ST .60 PDP, and the most memorable detail was that the fuel economy of the PDP was much better than other versions, so there's hope in there somewhere. Steve

LNeumann · May 16, 2001 10:14 PM

#6 source

Eric, anything under .300 is already overly conservative. Since you are "so" close, maybe just dropping to .302 would help you. You do have a samll prop for that engine, however, so it is possible to go smaller.

One other thing you could try is the longer lines. Actually that would cause you to set the engine leaner to keep you lap times and should improve fuel economy.

And, of course, there is nothing wrong with going to a 6 1/2 ounce tank if that is all that is needed. If you like everything else about the way the plane is running, why not?

Leonard Neumann

Randy · May 17, 2001 12:29 AM

#7 source

I used an ST.60 (Big Jim and Stock) for a number of years. Because I flew at 4500 feet elevation, I usually used a .320 to .330 venturi. Regularly used 7 to 8oz of fuel. Made it interesting when we came to contests at sea level.

Randy