Author Topic: ST 51 run issues (Read 2909 times)

Bob Reeves · « **on:** June 02, 2011, 07:57:00 AM »

Have a ST 51 new version in a Skylark.. What it does is burp rich on insides and doesn't come out of the break soon enough. It will break going up hill but stay in a two stroke (on the downhill side) till its back in level flight.

Running a ST46 size venturi as I had all kinds of different run issues with a larger intake. Prop is a TT 12.5 X 5.5, have tried several including the Rev-Up 12-5 that everyone says works so well. Fuel is 10-20 all synthetic, it won't hardly run on 10-22, tries to quit on the take-off roll. Running a tongue muffler with two holes plugged, it doesn't like tube mufflers at all, same kinda results as I got running 10-22, tries to quit on the take-off roll. Have tried all kinds of plugs, today I was running one of the new Fox plugs and it wasn't any different than a Thunderbolt or anything else I've tried.

I have two engines both with Bowman rings that he installed. Both engines do exactily the same thing.. Of course I am running the same intake muffler and prop. Could the intake still be too large?

Any Ideas on what I can do in the next week to help it? Will be heading for Brodaks next Thursday and really would like to do something to try and fix it before I leave.

Thanks..

Peter Nevai · « **Reply #1 on:** June 02, 2011, 12:22:38 PM »

Hmmm. Higher oil content carries away more heat, cools the engine, Tube Mufflers run cooler. Less oil carries away mess heat, Tounge mufflers retain more exhaust heat. Ring sealing, end gap problem? Not enough run time? Right now with your description, the common thread between muffler and oil content is heat. As you have two engines given the same treatment, hoping the other alternative is that who ever did the mod work did not hose both engines. Anyone else?

phil c · « **Reply #2 on:** June 02, 2011, 02:12:51 PM »

Sagging on takeoff usually indicates too large an intake. Or the position of the uniflow vent is too far back.
Sagging is also a sign of too much heat in the engine. The takeoff acceleration leans the mixture causing the engine to overheat briefly. Once it's in the air everything settles down after a lap or so.

Leaning too much in maneuver is also a sign of too big an intake. What does it do on outsides? Could be the tank height is off, maybe too low.

RandySmith · « **Reply #3 on:** June 02, 2011, 02:24:21 PM »

Quote from: Bob Reeves on June 02, 2011, 07:57:00 AM

Have a ST 51 new version in a Skylark.. What it does is burp rich on insides and doesn't come out of the break soon enough. It will break going up hill but stay in a two stroke (on the downhill side) till its back in level flight.

Running a ST46 size venturi as I had all kinds of different run issues with a larger intake. Prop is a TT 12.5 X 5.5, have tried several including the Rev-Up 12-5 that everyone says works so well. Fuel is 10-20 all synthetic, it won't hardly run on 10-22, tries to quit on the take-off roll. Running a tongue muffler with two holes plugged, it doesn't like tube mufflers at all, same kinda results as I got running 10-22, tries to quit on the take-off roll. Have tried all kinds of plugs, today I was running one of the new Fox plugs and it wasn't any different than a Thunderbolt or anything else I've tried.

I have two engines both with Bowman rings that he installed. Both engines do exactily the same thing.. Of course I am running the same intake muffler and prop. Could the intake still be too large?

Any Ideas on what I can do in the next week to help it? Will be heading for Brodaks next Thursday and really would like to do something to try and fix it before I leave.

Thanks..

What type of intake is it? (true venturie or restrictor)
What size intake?
Where is the spraybar mounted?
Are the rings run in?
I have done 100s of these.. never saw one that didn't run better on a tube than a tongue..both work
They run well on 23 to 24% oil 1/2 castor

Randy

Bob Reeves · « **Reply #4 on:** June 02, 2011, 03:25:01 PM »

Quote from: RandySmith on June 02, 2011, 02:24:21 PM

What type of intake is it? (true venturie or restrictor)
What size intake?
Where is the spraybar mounted?
Are the rings run in?
I have done 100s of these.. never saw one that didn't run better on a tube than a tongue..both work
They run well on 23 to 24% oil 1/2 castor

Randy

The intake is a spigot/sprinkler per what Brett Buck was running in ST 46's. Using a small SIG rivet in a .177 hole. Tried a .185 when I first started messing with it and the .177 ran much better. I replaced a ST 46 and the needle needs to be at the sprinkler location rather than through the intake. The needle I'm using is a PA needle assy. Acording to my calculations the stock CL intake is .0196 sq/in and mine is .0189

Both engines are well broken in have been putting up with this for several years, trying different stuff.

It doesn't seem to be starving, when it flames out with 10-22 or a tube muffler it quits rich. Tank is conventional wedge uniflow and upright/inverted lap times are good. Actually it runs great except for the inside burp and not switching back soon enough.

Brett Buck intake from an old thread on Stuka Stunt...

Peter Nevai · « **Reply #5 on:** June 02, 2011, 04:04:42 PM »

Really, weird, likes more exhaust back pressure, and or less oil, seems unresponsive to other changes, would of thought a too cold glow plug, but no improvement with plug change. Heck change the tank, if there is no change then it has to be the motor.

Steve Helmick · « **Reply #6 on:** June 02, 2011, 04:19:11 PM »

I saw Pat Johnston flying his Mustang this weekend, and it did some odd burps and belches. Questioned about it, he said it now has a G.51, that it was set too rich, and added that it seems to be a cold blooded engine...maybe from too much head fin area? If you have two engines, you might take one head and cut about half the fins off, and see if it makes a difference. With all the cooling fins, you might try a 4 cycle plug...bet you have some of those around!

I've only run one G.51 (but with two different cylinders) and always used 10-22 and always with a tube muffler...one being a Big Art, the other a Randy Aero CNC. It always ran well. I would say that the full 12.5 x 5.5 TT Cyclone is a lot of prop for a G.51. I would suggest an RSM 12-5/6, but I haven't run one of them. The 12-5 APC is a good choice, and the 12.25 x 3.75 APC works surprisingly well.

Steve

Bob Reeves · « **Reply #7 on:** June 02, 2011, 04:24:47 PM »

Quote from: Peter Nevai on June 02, 2011, 04:04:42 PM

Really, weird, likes more exhaust back pressure, and or less oil, seems unresponsive to other changes, would of thought a too cold glow plug, but no improvement with plug change. Heck change the tank, if there is no change then it has to be the motor.

Thanks for trying but tank isn't easy to change, this is an early RSM kit, wasn't paying attention when I built it and didn't discover the fuselage formers were cut too narrow till I tried to install the tank. It isn't 2 inches wide on the inside. I had to make a special tank but that isn't rocket science. It's pretty standard and plumbed just like every other tank that works just fine. A Brodak narrow wedge that holds enough fuel ends up being too long to fit.

Bob Reeves · « **Reply #8 on:** June 02, 2011, 04:33:41 PM »

Quote from: Steve Helmick on June 02, 2011, 04:19:11 PM

I saw Pat Johnston flying his Mustang this weekend, and it did some odd burps and belches. Questioned about it, he said it now has a G.51, that it was set too rich, and added that it seems to be a cold blooded engine...maybe from too much head fin area? If you have two engines, you might take one head and cut about half the fins off, and see if it makes a difference. With all the cooling fins, you might try a 4 cycle plug...bet you have some of those around!

I've only run one G.51 (but with two different cylinders) and always used 10-22 and always with a tube muffler...one being a Big Art, the other a Randy Aero CNC. It always ran well. I would say that the full 12.5 x 5.5 TT Cyclone is a lot of prop for a G.51. I would suggest an RSM 12-5/6, but I haven't run one of them. The 12-5 APC is a good choice, and the 12.25 x 3.75 APC works surprisingly well. Steve

Ya if it was a Saito I would know what to do

I've been messing with this thing on and off for 4 years, think I've tried about every prop I could imagine and then some.. I spent a full day at Brodaks last year trying every plug I could beg borrow or steal. What I have now is the best it's ever ran and I'm still not happy.. Been planning on sending one of the engines to Randy but never got around to it and now I don't have enough time before Brodaks..

Chris Wilson · « **Reply #9 on:** June 02, 2011, 06:08:50 PM »

Quote from: Steve Helmick on June 02, 2011, 04:19:11 PM

I saw Pat Johnston flying his Mustang this weekend, and it did some odd burps and belches. Questioned about it, he said it now has a G.51, that it was set too rich, and added that it seems to be a cold blooded engine...maybe from too much head fin area? If you have two engines, you might take one head and cut about half the fins off, and see if it makes a difference. With all the cooling fins, you might try a 4 cycle plug...bet you have some of those around!

Rather than doing irreversible machining to the engine just try rolling down over the cylinder fins some large O rings to keep some heat in.

The number and position of the rings is eminently tunable and very cheap to do, and the same principle can be applied to the finned head - just jam some sliced rubber ring between the fins and pick it out after wards if its not needed.

M Spencer · « **Reply #10 on:** June 03, 2011, 06:15:34 AM »

If youve a Tornado 10 x 6 3 blade , youre saved !

Though there still a bit overpitched .

General theory in Aus is 1 gasket per 5 % Nitro , extra.
So youd have THREE .

If there well bedded in , Hours worth of running , youll have
a big ' T ' stain or better on the piston crown , or they arnt.

Looking at threads , one consistant line , is 18 % oil is fine .

Ive had mine tractoring 2 kilo planes arond on 12 x 6s ,
and a 1.45 kilo one , but running steady speed , and slow .
For that motor , if it is stock internally .

A Double Zinger 11 x 5 is the other best prop ive had, on the heavy plane.
Hopeing to make a 11 x 5 3 blade . glass one .The black Tornados are ideal.

Ive used the supplied plug or a Enya 3 or 4 , probly the 4 is better .
Chrunched the Fireballs prematurely .

A 12 x 5 Zinger cut to 11 1/2 is O.K. ,
If youve an old Tornado or Topflite Nylon 11 x 6 , chuck it on and youll see how the motor likes to run.
One of mine with gallons through its got the piston marked as ive said, ands settled in. Others clean
despite a gallon or two so far, and ones still in the box.

Got a 12 x 5 Tornado , yellow now.Apart from being to heavy is probly pretty close to good,
or a 12 x 5 Top Flite Wood , if you have one .

From this you can see im still in the eigthenth century.

Best ive found no nitro . Prime it with 10 % fuel, as in ' wet ' it and turn it through, if the weathers real cool
for instant starts. She should snarl around up there , Switching / changeing tone , with the load .

Best its done it ons that Three Blade 10 x 6 , hauling the Two Kilo truck ( Spitfire ) in the wind , like a sunday drive .
Kicking into a snarl in the tops of both loops in the V 8 ,moreso in the top one, she'll only need 100 cc fuel 19/82 .

Brett Buck · « **Reply #11 on:** June 03, 2011, 10:51:47 AM »

Quote from: Bob Reeves on June 02, 2011, 03:25:01 PM

The intake is a spigot/sprinkler per what Brett Buck was running in ST 46's. Using a small SIG rivet in a .177 hole. Tried a .185 when I first started messing with it and the .177 ran much better.

In the spirit of full disclosure, my take on it was strictly notional, I never ran a spigot venturi on a ST46. The original picture is below (the one you attached was for the PA, although the basic idea is the same). I *did* have the extra o-ring below the annular fuel manifold and that made a big difference.

Brett

M Spencer · « **Reply #12 on:** June 04, 2011, 05:32:59 AM »

Very Sensible Brett .

One other thing , I dont have a Tacho , ( or phone or TV or . . . ) Um . . .

NEEDLE , winding in , to high 4 stroke , starting break , on ground can be missleading .You can still be a full tun rich , on the Std. intake .
What I ended up with , to find setting , was wind it in , to STEADY 2 stroke ( in ; break , not switching ) thisll get the heat up , THEN
open it out so as its starting to fall into 4 stroke , thereabouts . As I said , just going up , you can be a turn rich and still think your
' just ' below a clean 2 stroke .

On an aeroplane that it doesnt ruin , the ' silent muffler ' works very well . could save 3 1/2 Oz of noseweight .

The extra tip Wt
to offset it could ruin your day though , and the Drag on inboard side . Nevetheless , ive flow a few planes with it .

The big Spitfire sounded like a big U.F.O. in the mist in the valley one winters morning. Tissue over silk , so a ' resonance ' unlike the
usual ' bark ' , when its doing some work, remember its RATED at 1.1 Hp, detuned from 1.6 Hp. A .46 ST rate at maybe .75 Hp .

Alan Buck · « **Reply #13 on:** June 04, 2011, 07:39:25 AM »

Hi Bob I a have st51 on a profile that is stock out of the box with a tube muffler that run fine my set up is a 12/5 zinger and or a 12/6 master airscrew 3/blade uniflow tank on pressure rpm set 8800/9000 plane weights 64ozs. no problems have 5/6gallons of fuel on it

jim welch · « **Reply #14 on:** June 04, 2011, 06:24:48 PM »

Wipe it off A....... it might fly better! ( quote...I have 5/6 gallons of fuel on it)...he he he Jimmy

Bob Reeves · « **Reply #15 on:** June 16, 2011, 02:44:35 PM »

Hi Gang,

Sitting in John Brodak's shop relaxing after a hard day at the flying field.

Thought I would bring everyone up to date on the ST51 madness. Tom Dixon sold me a couple Double Star head shims that happens to fit the ST51 just perfect. When I first arrived in PA I stuck one in and flew it on my standard 10% fuel. It was a little better but still didn't come back from the break soon enough. Went ahead and added the second, now we were getting someplace, engine ran great but was down a little on power. Tom D suggested increasing the nitro so I mixed 10% and the 20% I run in my 4 strokes 50/50 for 15%, a little better but still a little down in power. Decided to run straight 20% nitro and see what happens..

Best the engine has ever ran, if you saw the Advanced Classic score board photo in the general section you will see the final result. I'm a happy camper and usually have 20-20 with me anyway. Just another way to run a stock 51 if you can stand feeding it 20% nitro...

Author Topic: ST 51 run issues (Read 2909 times)

Bob Reeves

ST 51 run issues

Peter Nevai

Re: ST 51 run issues

phil c

Re: ST 51 run issues

RandySmith

Re: ST 51 run issues

Bob Reeves

Re: ST 51 run issues

Peter Nevai

Re: ST 51 run issues

Steve Helmick

Re: ST 51 run issues

Bob Reeves

Re: ST 51 run issues

Bob Reeves

Re: ST 51 run issues

Chris Wilson

Re: ST 51 run issues

M Spencer

Re: ST 51 run issues

Brett Buck

Re: ST 51 run issues

M Spencer

Re: ST 51 run issues

Alan Buck

Re: ST 51 run issues

jim welch

Re: ST 51 run issues

Bob Reeves

Re: ST 51 run issues