Hello,

I have been flying for three years now, I'm considering to step in to large scale models(mainly for pattern and 3D)

I'm thinking of a Yak 54 or Cap or something similar.

I wonder, what source of power would be best for 3D manuvers is it Nitro or Gasoline?

which one givesbetter power-to-weight ratio?

I know that Gasoline are lower in RPM, but hight in tourqe but again heavier in weight. Will that be a disadvantage??

I also know that when it comes to giant models ther only source of power available would be Gasoline, but what about the large scales that accepts both, which one would be best for 3D flying?


Fly Hard,
Model_Aviator

Model_Aviator,

Boy, that's a tough one. You'll get a lot of opinions and most will be based on personal preference including mine I guess. It all depends on how big you go, how you want to fly, and if the price of glow fuel matters? Gas engines are really coming on in the market as far as power and weight compared to glow. Some gas engines are about the same weight as big 4 stroke. For example, the new line of DLE engines. They are light weight and produce a lot of power for their size. Big glow engines produce a lot of power but like you said, only up to a certain size plane. The YS 1.40 and 1.70 is a popular power plant for big Pattern planes so compare those engines to what size plane you want to fly and what gas engine you want to run. For 3D, glow will propably be better suited but that's just my opinion. The choices for what combo you want to run are almost unlimited and it will take a lot of research and trail and error to find what you really want. To find that perfect combo takes a little doing.

Something that a lot of people don't take into consideration is that gasoline is MUCH more volatile that methanol, so in equally sized engines, the gas engine will produce much more power.

Personally, 120 is the cutoff size for me. At that size and above, I go gas.

Gasoline has a much different air:fuel ratio than glow fuel. Gas engines have about a 17:1 ratio, while glow is closer to 4:1. Therefore in equally sized engines you burn roughly 4 times more glow fuel than gasoline. OS rates their 1.60 (26cc) engine at 3.7bhp, while Fuji rates their 1.40 (24cc) at 2.2bhp.

Glow engines have a much better power to weigh ratio which is why you don't see gas engines on small planes.

Hi!
Yes ! gaRCfield is right!
Glow engines are much more powerful than comparable size gas engines.

The alcohol burning engine will make more power for a given displacement but it will also burn much more fuel doing it.

I think that the original question really depends on a few factors...

- How is the availability of glow fuel in your area? If it is hard to obtain or outrageously expensive then gasoline is the better option.
- What size plane are you talking about? Up to roughly 1/4 scale either is viable but once you start getting bigger, gas is about the only option that makes sense.
- Do you like glow engines? Some people hate them and prefer gasoline. I kinda like glow engines myself but I also like gas engines. Come to think of it, I like all engines.

Gasoline engines have really come down in price and many of them are extremely good for the money. They will also burn less of a lower cost fuel so you can definitely make the argument that they are more economical.

Things like electronically controlled spark ignition also make them very reliable. I have never had a dead stick with a gasoline engine unless I ran it out of fuel.

Bottom line is pick what you personally like. Sometimes you don't know what that is until you try it all though.

The stoichiometric (ideal) A/F ratio for gasoline is 14.7:1 at sea level. Pure methanol is around 6:1. Glow fuel also has nitromethane in the mix so that changes obviously.

Gasoline has roughly twice the BTU per gallon than pure methanol. Nitromethane has even fewer BTU per gallon than methanol. So why do high performance engines burn methanol, nitro or both? Even though they they contain fewer BTU per given volume you can oxidize much more of the fuel per specific volume of air than you can with gasoline. The result is a higher overall power output because you are burning a lot more fuel.

When it comes to producing the most power while burning the least amount of fuel, gasoline wins hands down. Diesel is even better.

That's one of the reasons behind the failure of this whole ethanol thing. Ethanol falls just above methanol when it comes to BTU per pound. This stuff was supposed to revolutionize transportation and ethanol plants popped up everywhere. Nobody bothered to mention the fact that it takes as much energy to produce the stuff as you get out of it and that you have to burn almost twice as much to get the equivalent power of gasoline. Not only that, the stuff was made from corn which put a dent in the supply and raises food prices. As a result, these plants are folding left and right (at least here on the west coast).

Gasoline is still the most bang for the buck.

As you can see, it's pretty hard to come to a conclusion without more specifics. Much depends on the specific airframe you want to use. Pick that out, and then do some research on what type of power has proven most successful for it.

My cut off point is also 1.20, however if someone was to give me another YS 1.40 I would be jumping for joy!!!!!! Smallest gas engine I have is the RC Showcase 1.40 22cc. Outstanding engine but I don't care for the rear induction carb, the needles are dead center to the fire wall. With some of the new gassers out of China the weight difference is no longer a big deal. The plane itself has a bunch to do with my choice of engine. I like both gas and glow but find less problems with gas, they are more tune and forget.