Which engine should I buy if I wnat to turn a 3 bladed prop? Gas or glo. And does anyone have a conversion chart to convert CC's to inches? Or maybe you can tell me, if my plane calls for an engine between .90-1.8 cu in glo what that translates to in gas engine size. CC's or inches.
Thanks.

Any engine will turn a three-bladed prop. Just drop 2" off the diameter of the recommended two-blade and keep the same pitch.

It is not a direct cc to inch conversion for what a model can fly when hopping from glow to gas. .91ci converts to 14.9cc and 1.2ci converts to 19.66cc. But I know folks who insist a 40cc or even 50cc is needed for a 1.2 2-stroke glow size model; which is insane but so are they. Gas engines have "baggage" of either a magneto or a flight battery for EI that glow gets away without so you need to "boost" the gas size in the swap . . . and usually reinforce the landing gear also. A model that calls for a 1.8c.i. glow will probably enjoy a 30cc or larger gas engine. I fly a 43cc Fuji EI in a model designated for a 1.8ci glow and it is a good marriage. For your 1.2ci example a 26cc should be good, 32cc for some real power.

Gas engines make less horsepower per displacement and weight than glow engines do, so you do have to go bigger when changing over to gas from glow. Choose the engine that has the power and weight you need for the plane, then pick your prop. Just understand that if you go gas you will be adding some weight onto the nose for the same horsepower which also means adding some weight to the tail to balance it. If the plane you are working on is marginal on wing loading, you may not like the result.

I don't disagree with you but I think there are some errors or generalisationshere.

"Gas engines make less horsepower per displacement"

Perhapsbut at what RPM? A gas engine has oodles more torque and much better midrange performance (where most people fly) than a glow engine. It also does not have transition issues.

Gasoline has nearly twice the heating value of Methanol so unless you have a poor gasoline engine, theoretically it should be at least on par in terms of power. Methanol has the advantage of higher flame speed which means you can get higher rpm to make up for the lower torque.

You have to look at the problem from an engine by engine basis and consider the application heavily. For a large aerobatic aircraft than superior midrange torque and reliable ignition is favoured over a glows iffy transition and more sensitive throttle management requirement.

Conversion from Cubic inches to Cubic centimetres? 1cu.inch = 16.387 cc

S0 .46ci = 7.53cc

1.2ci = 19.66cc or classed a 20cc unit
1.6ci = 26.23cc or classed a 26cc unit etc etc etc

Of course you need to use actual bore and stroke measurements to get the exact displacement because the indicated cubic capacity is seldom exactly the actual.

Is a Gasoline engine heavier? Well it can be and in some cases not.
Yes there is additional equipment on board like an ignition coil, bigger battery to power the plug some electronics to control it but these are usually ringed engines which means a lighter piston.
Also the engine blocks can be moreheavily finned because the gasoline generates more heat during combustion and that needs to be dissipated.

The onlysize where thay can be compared side byside is the 1.6 glow / 26 gasoline.

Then the one bigy that being forgotten is the fuel.
Methanol fuel is not signifacantlyless dense compared to gasoline but because of the gasoline higher energy content you can carry less of it on board at take off. So that saving largely negates the additional equipment weight.

So the answer is not as simple as it first appears. Deciding which engine to use depends larlgey on how you want to use it. However at that sort of size, I'll opt for gasoline everytime simply because of the lower consumption and better midrange performance.
Oh yeah, they'rea lot cleaner too. No castor/syn oil all over the airframe to soak up your costly detergents.

If gasoline makes it down to .46 size I'll switch over. Closest I can get right now is a 4S engine.

PS: One aspect thats being forgotten about is the fuel volume and consumption. Gasoline will fly longer on the same volume of fuel hence you can take off with less, negating any slight weight advantage a glow engine may have.

Have not worked out if this translates to <26cc engines yet. will have to do the math.

Sounds like the old bike argument, which is better, more low end torque of the V-twin or the high end speed of the inline 4 engine. I liked the quarter mile track myself. Since this is my first build maybe I should rely on the old KISS method and find the engine recommended for the plane. Platt shows a ST2500 glo. And there's the cost thing, seems from shopping around that it'll save me money for the radial I'd like to get for the Meister Zero I have as a second project.

If I go with the glo engine, how much like a 2 stroke dirt bike will it sound? Engine pitch is part of the appeal of a warbird afterall.

This is RCU so you will get debates like that all the time. Planes state the size range you can use. The smaller choice will fly the plane OK but it's usually decided to go with the bigger engines in the planes range. Usually a little larger. A lot of us start using gas engines after about the 1.20 glow for a lot of reasons, one of them is cost of fuel and ease of operation. Dependability is another big factor, gas is a better choice after 1.20. Right now the DLE gas engines are the fair haird child, not a lot of money and cheap to operate, very dependable and these new engines from China are very light for there power. I have one of the ST 2300s and I pulled it from the plane and used one of my small gassers. It isn't all that great of an engine and it never met a fuel can it didn't fall inlove with. Take a look at the gas engine forum and see what people are talking about. There are some very good choices out there right now. CRRC and DLE are very good choices. All engines will throw a three blade, there is more trouble finding them and the spinners unless you mail order though.

A 2 stroke glow engine will sound like a weed eater. A 2 stroke gasser will sound like a big weed eater. If you want the rumbly warbird sound, you have to go 4 stroke. That's more money, but you do get more torque and better fuel economy with a 4 stroke engine.
A good point was made above about fuel cost. There's a reason that big glow engines aren't all that common, and that's the $18 a gallon fuel that they like. It doesn't take long for a gas engine to pay for itself.

idk if you guys have seen this yet but
http://www.hobbypeople.net/gallery/210550.asp
its a .52 c.i (meaning 40 sized) gasoline engine, aparently it has the power of a .70 4 stroke (similer powerband, turns 13's in the 900- range is what they are saying)
but if it runs well the end of the glow age could be comming, and if gas makes it down to .40 sized and is comparable to glow i doubt electrics will make a big impact since gas will be way cheaper then electric or glow.
that being said a .52 gas engine at $200 is a bit much for me, the magnum .52 methanol version runs at about 70 bucks.....130 bucks will buy you quite a bit of glow fuel.....im mixing my own for 6.75 a gallon so 130/6.75=19.26 gallons before it would catch up in price...thats a lot of flying
also the .52 methanol is much more powerful and 5+ oz lighter not counting the ei batt....another 3+ oz.

that being said if i didnt already have glow engines i would buy the small gas one and just stick with them, in the long run it may be cheaper.

imo the biggest breakthrough that the small gas engine market could ever hope for is a very light ignition/spark setup, maybe 1-2 oz w/ battery or magneto, granted this wont be easy but if it could be done the glow engine age would be over.

The end of the Glow engine is nigh.

You can purchase a conversion kit from Just Engines in the UK that will convert a glow down to 0.46 size to gasoline/petrol/benzin.

The electronics is not a limting factor anymore. Conversion kits weigh around 123gr or 5oz(?) which really helps to balance the aircraft anyways since most need balance either fore or aft and these units can be placed anywhere. The JE conversion kit will run off your Rx battery so a min 1200mA.hr is required.

I don;t think electric will take over in the near term. Batteries are not cheap and they are easily damaged. The A123 cells will open the doors but total weight and out right performance will always be a problem on larger motors.

As mentioned, any 2stroke will sound like a weedeater, the OS MAx AX range with power box seem to sound  better than the other brands ( I fly mostly GMS2000) but 4 stroke is where the real scale sound lies.


One last thing on the power to weight of gassers s glow.

Gasser design is maturing all the time and the weight is coming down so the power to weight is leveling.

But that means nothing since we are interested in THRUST to weight ratio and here the picture is leaning heavily toward gassers.

Four stroke gasoline engines are a little pricey compared to their two stroke  brothers but the 2 stroke still sound better than the 2S glow; sort of like a weedeater with a deeper voice...

IMO, 4 stroke is where the exciting stuff is. I would strongly consider 4stroke gasoline for better midrange, throttle response, sound, fuel cost, reliability. To me they just seem BETTER.

Are the 4 strokes wet sump or dry? If dry I would imagine that oil tanks are available.

I noticed Saito has smaller ones at a price range on par with the glo's.

OK, will this engine [link]http://www.horizonhobby.com/Products/Default.aspx?ProdID=SAIE125A#quickSpecs[/link] pull this a/c [link]http://www.daveplattmodels.com/Short%20Kits/index.htm[/link] around?

As to my previous question about the oil sump, I'm beginning to think the fuel type contains the cooling/lubicating element.

To my knowledge all model-sized aircraft engines - gas/glow/2-stroke/4-stroke - require oil mix in the fuel. Whether castor, synthetic or 2-cycle chainsaw oil. A sump & splash system won't work in an aircraft and a oil pump system would be heavy and expensive.

PS - your link to Dave Platt is to the index of all models. Not a apecific one. At least for me. HEY! I'm one of the "one or two" among hundreds of visitors that cannot see the menu selections at his website per his help link.

When I am comparing engines, I look at the manufacturers spec data for the various engine sizes and try to match these as closely as possible. There are many specs and not all specs and not all mfg's publish the same info, so I work with what I have and generally be conservative. I first try to match the horsepower ratings since this is an indication of how much power would be required to propel the plane. Torque and rpm come in next and then recommended prop sizes.