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GAS EQUIVALENTS TO GLOW ENGINES?

Old 05-13-2012, 03:04 AM
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Loopman
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Default GAS EQUIVALENTS TO GLOW ENGINES?

Hey Guys,
I have a plane that had a ST2500 on it and I want to go to the gas equivalent of that engine. How do you determine what gas engine would replace a glow engine? The ST2500 was swinging a 20x6 JZ prop, I need to swing that same prop on a gasser and get the same thrust.
Thanks

Loopman
Old 05-13-2012, 03:28 AM
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Default RE: GAS EQUIVALENTS TO GLOW ENGINES?

The formula I use is 1 cubic inch is equal to 17 cubic centimeters plus ten percent. So, if you had a 2.0 glow, it would convert to 2x 17cc, + 10% = appx37.5cc, round off to 40cc. Hope this helps. red
Old 05-13-2012, 05:05 AM
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Default RE: GAS EQUIVALENTS TO GLOW ENGINES?

I believe a 2500 is 25cc , what type of rpms are you getting with the 20x6? Depending on the rpms you need and engine set up ( front or rear carb, exhaust, mount, ect. ) that will tell you the rest. I'm guessing anywhere in the 30-35cc range.

Andy
Old 05-13-2012, 05:35 AM
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Default RE: GAS EQUIVALENTS TO GLOW ENGINES?


ORIGINAL: Loopman

Hey Guys,
I have a plane that had a ST2500 on it and I want to go to the gas equivalent of that engine. How do you determine what gas engine would replace a glow engine? The ST2500 was swinging a 20x6 JZ prop, I need to swing that same prop on a gasser and get the same thrust.
Thanks

Loopman

just for reference my DLE30 swings a 19x6 Xoar Beech wood 8k rpm
Old 05-13-2012, 07:03 AM
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Default RE: GAS EQUIVALENTS TO GLOW ENGINES?

To give you some idea I replaced a 35cc gas engine on a scale biplane with a ST2500 running straight fuel, no nitro and saw a pretty large gain in performance. I would think you need at least a 40cc gasser if not bigger to equal the ST2500. My ST2500's will turn a 18X8 prop ( should be equivalent to a 20X6) at 9,000 rpm. I use a 1.5 multiplier when trying to equate gas to glow, seems close.
Larry
Old 05-13-2012, 10:34 AM
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Default RE: GAS EQUIVALENTS TO GLOW ENGINES?

0.60cui = 10cc

therefore a 25cc or ST2500 is 1.50cui.

power wise you probably looking for a 30cc gasser to do the same thing.
Old 05-13-2012, 12:25 PM
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Default RE: GAS EQUIVALENTS TO GLOW ENGINES?

The st2500 ia a 14.7cc engine. So a 15-20cc gas would be the equivalent. No the gas won't turn the same rpm's but the added torque will turn a bigger prop. I'm running several of the 20cc in 60 size airframe's with larger prop's, 17x8 to 18x8. Love the ease of gas well enough I got rid of all my nitro.
Old 05-13-2012, 12:48 PM
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Default RE: GAS EQUIVALENTS TO GLOW ENGINES?

I'm pretty sure the ST2500 is a 25cc...

Closest displacement equivalent is a Evolution / MVVS 26cc which will also swing 18" to 19" inch props.
But  30cc i snot much bigger physically so it'll swing a 20x6 or 20x8 pretty well
Old 05-13-2012, 01:19 PM
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Default RE: GAS EQUIVALENTS TO GLOW ENGINES?

My bad, pulled up wrong engine.
Old 05-14-2012, 07:46 AM
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Default RE: GAS EQUIVALENTS TO GLOW ENGINES?


ORIGINAL: Loopman

Hey Guys,
I have a plane that had a ST2500 on it and I want to go to the gas equivalent of that engine. How do you determine what gas engine would replace a glow engine? The ST2500 was swinging a 20x6 JZ prop, I need to swing that same prop on a gasser and get the same thrust.
Thanks

Loopman
It depends on the gas engine more than it does on displacement in my experience. The ST2500 was an average performing glow engine. A DLE30, SAP180, MVVS26 and probably a couple others would be at least equal in output. The OS33GT would have considerably more output than any of these....
Old 05-14-2012, 10:33 AM
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Default RE: GAS EQUIVALENTS TO GLOW ENGINES?

prop data / sizes without manufacturer is pretty useless info.
work out the thrust from your prop brand and size and rpm, then look from there.........
Old 05-15-2012, 03:27 AM
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Default RE: GAS EQUIVALENTS TO GLOW ENGINES?

ORIGINAL: Loopman

Hey Guys,
I have a plane that had a ST2500 on it and I want to go to the gas equivalent of that engine. How do you determine what gas engine would replace a glow engine? The ST2500 was swinging a 20x6 JZ prop, I need to swing that same prop on a gasser and get the same thrust.
Thanks

Loopman
The average guy here is not going to be able to give an answer to your same prop question.

Why are you soooooo over proped on the ST2500????? my ST's ran 10500 on an APC 17 x 6 pumped on a Bisson muffler (~16 lbs thrust).
I currently still run a ST3250 on an Evolution 18 x 6 beechwood prop on a bisson muffler (~ 18 lbs thrust).

I can only imagine how low on the performance curve that 20 x 6 prop is on that engine.

OK nuf said, basic question how do you determine what engine to another:
1. Weight.

2. RPM on same prop

3. Mounting considerations.

4. Cost.

Any of the common gas 26's will give better rpm on your JZ 20 x 6 than your current choice. (I might go with a beam mount like the MVVS or EVO).
Old 05-15-2012, 08:21 AM
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Default RE: GAS EQUIVALENTS TO GLOW ENGINES?

You could have the ST converted to gas and not have to change out the engine. There are a couple of places doing this conversion, and I have heard it works pretty well.
http://www.lambertsrc.com/index.html This is one I have heard about.
Old 05-16-2012, 09:47 PM
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Default RE: GAS EQUIVALENTS TO GLOW ENGINES?

The correct Prop for a Super Tigre 2500 is an 18 x 6. The ST 3000's would turn a 18 x 8, and 18 x 10. Running a 20 x 6 prop would certainly be way beyond what a 2500 could pull efficiently, and throttle response would be slow. A moddern 30 cc gas engine would certainly be a fair replacement, and similar weight overall.

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