telejojo

What is the formula for glow power = gas power?

aussiesteve

As a general Rule, I use

From 2 stroke Glow to Gasser - 1:1
From 4 stroke Glow to Gasser - 1.3:1

as an example, for a plane that flies well on a 1.40 2 stroke Glow - I'd use a 26cc Gasser or a 1.80 4 stroke

DarZeelon

TeleJojo,


This is pretty simple to calculate... See [link=http://www.flyhi.org.il/fuel.htm]this table[/link].
The compiler of this table is none other than RCU's downunder.

Methanol produces less energy per unit of weight than gasoline, much less, in fact.

Gasoline makes 19,000 BTU per lb., while methanol makes 9,970 BTU per lb., but that is only half the story....
Gasoline has an ideal stoichiometric ratio (which means the whole amount of oxygen in a given mass of air, will oxidise the entire mass of fuel) of 14.7:1. For methanol the stoichiometric ratio is about 6.5:1.

This means a given amount of air, at ideal stoichiometric ratios, will oxidise 2.26 times as much methanol, as it does gasoline; eventually producing 22,548 BTU, which is 18.7% more energy than gasoline will produce, with the same mass of air.

At ideal power ratios this will not be the exact, same percentage difference, but I guess you got the general idea.

Put nitromethane into the equation, at its low BTU/lb. of 5,000, but at its ultra-low stoichiometric ratios; and you get roughly 2.5 times more power from nitro, than from the methanol it replaces... This messes up the whole calculation...

ttoks

if you run an engine on nitro, and an identical engine on petrol, you can expect to get about 2.7 times more power (thats if your burning 100% nitro), you get about a quarter the power from nitro per weight, but you can burn about 9.6 time as much of it per unit of air because nitromethane is a good oxydiser, when it burn in a chemical reaction it relieses oxygen allowing more fuel to be burn.

NM2K

My Feedback: (14)

Oh if life were but that simple. <G>


Ed Cregger

aussiesteve

So what was your original question TELEJOJO?
Are you looking for an engine size comparison because you are thinking of changing from a Glow engine to a Gas engine, or are you asking because you are considering converting an engine?

For the fuel comparison equation, there are so many variables, including combustion chamber and ignition design that there is no single, simple straightforward answer.

mtwister

In my humblest opinion, a 26cc gasser wont even come close to the performance of a 1.40 glow. My OS 1.60's have tons more power on the same plane as one with an Evo 26 on it. Tons. I'd say a 40cc gas is about equal to a 1.60 2 stroke glow or 1.80 4 stroke glow.

aussiesteve

I have to admit that the only plane that I have any actual comparative data on is an Ultra Stick 1.20 Lite. In that I've had a 120AX, a Saito 1.80 and a G26. I must admit that I prefer it with the Saito 1.80. the 1.20 was about the basic power source for it IMHO and the G26 was OK but a little boring.

DarZeelon

MTwister,


The Evolution 26 cc (and the real thing, its MVVS source), are designed to be at their best, with a tuned exhaust system.

As such, they tend to suffer more from a restrictive, simple exhaust, but to really impress with a tuned-pipe.


On the #3270 Pitts Muffler, the MVVS 26 cc IFS gas engine, will spin a Mejzlik 18x8 prop at 7,400 RPM.
With the #3266 tuned-pipe (still very light in weight) it will be all the way up to 8,300.

Will your OS1.60FX better this by very much? It should somewhat.

The Zenoah G26 (it was Xenoah...) is a rudimentary weed-whacker conversion in comparison.

telejojo

I have a hanger9 27% cap and was thinking of useing an OS 160,but hanger 9 says use a 180 to 250 or 50cc gas. It prob. won't hover but I'm not that good yet anyway.I have a Dave Patrick Ultimate at about 12lbs. and it will go vert. no problem. The cap will weigh about 15 to 16 lbs.

mtwister

Yes, I'm getting 9500 rpm with the OS 1.60 with a Bisson pitts, and APC 18x6W prop on 15% nitro and a vp pump.

mtwister

I personally have watched that Cap fly with a Moki 2.10 and a DA-50. Both seemed just about right. I'd say the OS 1.60 will fly it very scale like. There's a huge difference between 3 pounds on an airplane with the same engine.