Confused About Engine Sizes
12-08-2013 | 01:56 PM
#1
Thread Starter
Junior Member
Joined: Nov 2009
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
From: Atlanta,
GA
Confused About Engine Sizes
Building Balsa USA P-51 Plans call for 1.08 -1.5 two stroke engine. Horizon Hobby tech support advised Evolution 20 was the comparable size but it certainly looks awfully small. Finished weight will be around 13.5 lbs. Built a Waco...same weight...used DLE 30. So is Evolution 20 comparable to 1.08 - 1.5 and DLE 30? Any thoughts greatly appreciated. Happy Holidays to all.
12-08-2013 | 03:11 PM
#4
Senior Member
My Feedback: (48)
Joined: Dec 2003
Posts: 990
Likes: 0
Received 0 Likes
on
0 Posts
From: Millington,
MI
Building Balsa USA P-51 Plans call for 1.08 -1.5 two stroke engine. Horizon Hobby tech support advised Evolution 20 was the comparable size but it certainly looks awfully small. Finished weight will be around 13.5 lbs. Built a Waco...same weight...used DLE 30. So is Evolution 20 comparable to 1.08 - 1.5 and DLE 30? Any thoughts greatly appreciated. Happy Holidays to all.
Last edited by tande; 12-08-2013 at 03:18 PM. Reason: spelling
12-09-2013 | 06:53 AM
#13
While indeed a 20cc gas is roughly equivalent to a 1.2ci fuel, I believe the fuel equivalent is a 4 stroke not a 2 stroke. If that is true then the 20CC gas is, power wise, equivalent to a .90ci 2 stroke.
I'm sure someone will correct me if I am wrong,
I'm sure someone will correct me if I am wrong,
12-09-2013 | 12:01 PM
#15
My Feedback: (7)
Joined: Feb 2002
Posts: 2,051
Likes: 0
Received 0 Likes
on
0 Posts
From: Keller, TX
20cc = 1.22 ci. My .91 Magnum 2 stroke turns a 15X6 prop at around 8600 rpm. My 20cc DLE turns a 17X6 at around 8500 rpm, as does my Zenoah G20. These are static rpm, don't know what the unloaded rpms may be.
12-09-2013 | 01:43 PM
#16
My Feedback: (7)
When trying to go from cc (cubic centimeters) to ci (cubic inches) you take the cc size in this case 20 and you then multiply .061, so you will take 20 x .061 and that equals 1.22 ci.
The idea of going with the larger displacement engine of the engine spectrum is the best way to go, just do your homework and pick what is best for your model and enjoy.
The idea of going with the larger displacement engine of the engine spectrum is the best way to go, just do your homework and pick what is best for your model and enjoy.
Last edited by rglgatortail; 12-09-2013 at 02:31 PM.
12-09-2013 | 01:54 PM
#17
My Feedback: (6)
Uh oh.... here we go...
Gasoline has a much higher BTU rating than glow fuel, not lower. Gasoline has approximately 114,000 BTU's per gallon. Methanol, the burning ingredient in glow fuel, has about 57,000 BTU's per gallon.
The reason an engine makes more power running on methanol is because an engine uses TWICE as much of it, thus releasing more BTU's. Further, methanol has a cooling effect on the intake charge which helps power, and has a higher octane than gasoline so engines designed to run on it can be made with a higher compression ratio, which once again, provides more power. Further, most glow fuel has a percentage of nitromethane in it, which increases power even more.
As mentioned though, the difference is not as great as it might seem, because gasoline engines are able to turn larger, more efficient props and that must be factored into any glow versus gas considerations.
AV8TOR
Reference: http://en.wikipedia.org/wiki/Gasoline_gallon_equivalent
Gasoline has a much higher BTU rating than glow fuel, not lower. Gasoline has approximately 114,000 BTU's per gallon. Methanol, the burning ingredient in glow fuel, has about 57,000 BTU's per gallon.
The reason an engine makes more power running on methanol is because an engine uses TWICE as much of it, thus releasing more BTU's. Further, methanol has a cooling effect on the intake charge which helps power, and has a higher octane than gasoline so engines designed to run on it can be made with a higher compression ratio, which once again, provides more power. Further, most glow fuel has a percentage of nitromethane in it, which increases power even more.
As mentioned though, the difference is not as great as it might seem, because gasoline engines are able to turn larger, more efficient props and that must be factored into any glow versus gas considerations.
AV8TOR
Reference: http://en.wikipedia.org/wiki/Gasoline_gallon_equivalent
Last edited by av8tor1977; 12-09-2013 at 01:59 PM.
12-09-2013 | 02:39 PM
#21
Joined: Feb 2006
Posts: 1,133
Likes: 0
Received 0 Likes
on
0 Posts
From: camden, SC
12-09-2013 | 02:54 PM
#22
My Feedback: (6)
Your answers are right here in your chart. Look at the energy content of gasoline versus methanol. Then look at the Stoichiometric fuel/air ratios. It takes much more of the lower energy content fuels to run the engine, and that is where the extra energy comes from; not the fuel itself. In the case of nitromethane is not so simple, but similar. Nitromethane "carries it's own oxygen", which adds to the power as well.
AV8TOR
AV8TOR
Well you seem to miss several ingredients of glow fuel, Methanol is not the power source of glow fuel but is the reason of the catalytic reaction for the glow plug to work, no the power of glow engine comes from the Nitromethane that is added to the methanol to increase power and to make the engine easier to tune so glow fuel has in rights more BTU I cant find the exact number but if you was to take a gas engine say how about a Zenoah 38 cc engine turning a 20 inch prop and make it run on gas and record its high rpm numbers, now take the same engine and make the few mods to the carburetor that it will need and then install a glow plug in place of the spark plug and record the high rpm numbers again you will find that the same engine will in fact turn almost 3000 rpm faster with the same prop because the nitro and methanol in glow fuel. I have done this exact mod to this exact engine to get more power because you just wont get power from a gas engine as compared to a equal size glow engine and that's a fact. Its too bad that Clarence Lee don't visit this forum because he is the guru of model engines and facts of all of this, I do however am relying on old information that I use to read from the now defunct magazine RC modeler magazine. A lot of what I know and what I learned is from what and when Clarence wrote in his articles and im trying to recall what Clarence wrote so im not in total fault here just my memory is not all that what it use to be.
[TABLE]
[TR]
[TD]Fuel[/TD]
[TD]Engine Air Flow (cfm)[/TD]
[TD]lbs of air (lbs)[/TD]
[TD]A/F Ratio[/TD]
[TD]Pounds of Fuel (lbs)[/TD]
[TD]Energy Content of Fuel (BTU/lb)[/TD]
[TD]Total Thermal Energy (BTU)[/TD]
[/TR]
[TR]
[TD]Gasoline[/TD]
[TD]567.53[/TD]
[TD]42.64[/TD]
[TD]12.8:1[/TD]
[TD]2.89[/TD]
[TD]18,500[/TD]
[TD]53,176[/TD]
[/TR]
[TR]
[TD]Methanol[/TD]
[TD]567.53[/TD]
[TD]42.64[/TD]
[TD]6.0:1[/TD]
[TD]7.11[/TD]
[TD]9,500[/TD]
[TD]67,545[/TD]
[/TR]
[TR]
[TD]Nitromethane[/TD]
[TD]567.53[/TD]
[TD]42.64[/TD]
[TD]1.7:1[/TD]
[TD]25.08[/TD]
[TD]5,000[/TD]
[TD]125,412[/TD]
[/TR]
[/TABLE]
http://www.klotznitromethane.com/
[TABLE]
[TR]
[TD]Fuel[/TD]
[TD]Engine Air Flow (cfm)[/TD]
[TD]lbs of air (lbs)[/TD]
[TD]A/F Ratio[/TD]
[TD]Pounds of Fuel (lbs)[/TD]
[TD]Energy Content of Fuel (BTU/lb)[/TD]
[TD]Total Thermal Energy (BTU)[/TD]
[/TR]
[TR]
[TD]Gasoline[/TD]
[TD]567.53[/TD]
[TD]42.64[/TD]
[TD]12.8:1[/TD]
[TD]2.89[/TD]
[TD]18,500[/TD]
[TD]53,176[/TD]
[/TR]
[TR]
[TD]Methanol[/TD]
[TD]567.53[/TD]
[TD]42.64[/TD]
[TD]6.0:1[/TD]
[TD]7.11[/TD]
[TD]9,500[/TD]
[TD]67,545[/TD]
[/TR]
[TR]
[TD]Nitromethane[/TD]
[TD]567.53[/TD]
[TD]42.64[/TD]
[TD]1.7:1[/TD]
[TD]25.08[/TD]
[TD]5,000[/TD]
[TD]125,412[/TD]
[/TR]
[/TABLE]
http://www.klotznitromethane.com/
12-09-2013 | 05:08 PM
#25
My Feedback: (19)
Certainly this is an oversimplification! But for my money these days, I'll stick with the lower RPM purr of the gasser over the high RPM whine of the glo engine. Being an old pylon racer, I live the sound of a high RPM racing engine but not when there is work to be done.
