It says it has 0.9 horsepower which is very close to the one horse 40LA currently in the plane. And burn 40% less fuel.

Another question: What happened to the 40LA? I can't find any replacements.

I would not take a chance. The Avistar was designed for .40 minimum. Anything less would be risky, personally I would spring for the OS46AX or similar .46 from Evolution, Thunder Tiger etc.

Originally Posted by rmsingh

Anything less would be risky

The 25AX in a 40plane is "risky" as in dangerous to me or other spectators? :-o

It's a shame O.S. discontinued those blue LA engines. So what's the difference from FX to AX? The AX appear to spin slower/have less power but I don't know why. Another gentleman said he tried 46AX is an Avistar but didn't like it... too much weight. He went back to the LA.

Originally Posted by theaveng

The 25AX in a 40plane is "risky" as in dangerous to me or other spectators? :-o

It's a shame O.S. discontinued those blue LA engines. So what's the difference from FX to AX? The AX appear to spin slower/have less power but I don't know why. Another gentleman said he tried 46AX is an Avistar but didn't like it... too much weight. He went back to the LA.

The LA engines are not discontinued. The color was changed from blue to natural.

The color wasn't changed. O.S. 40LA engines have always been available in two colors: Blue or natural. I have two of each dating back to 2005. But the blue was discontinued.

I agree, 40 sized trainers do way better with a 46 of your choice.

It would very anemic at best or might simply not get off the ground.

I use a 46FX on mine and it goes real good with that.

It will fly, but it will take a long time to get off the ground and it won't do much more than circuits. The Hp might be similar to a .40, but the amount of torque it produces will be much less, resulting in requiring a smaller prop and producing less thrust. To illustrate, the .25AX will be happy on a 9x6 prop, whereas the .40LA will be happy swinging an 11x5 prop.

Originally Posted by theaveng

The 25AX in a 40plane is "risky" as in dangerous to me or other spectators? :-o

It's a shame O.S. discontinued those blue LA engines. So what's the difference from FX to AX? The AX appear to spin slower/have less power but I don't know why. Another gentleman said he tried 46AX is an Avistar but didn't like it... too much weight. He went back to the LA.

The AX are probably evaluated differently than the FX, they are mechanically very similar and should, in the real world perform just as well. In any event, the FX/AX engines certainly have a lot more power than an LA engine.

Originally Posted by ChillPhatCat

the amount of torque it produces will be much less, resulting in requiring a smaller prop and producing less thrust. To illustrate, the .25AX will be happy on a 9x6 prop, whereas the .40LA will be happy swinging an 11x5 prop.

That clarifies things. Thanks. Would be nice if O.S. published torque ratings too.

Originally Posted by theaveng

That clarifies things. Thanks. Would be nice if O.S. published torque ratings too.

Well, they do publish propeller ranges which can give you an idea of what kind of thrust you can expect. Generally planes are designed around a certain sized engine, not based on horsepower, but the minimum thrust that you need and the engines that can swing a prop to give you that thrust. Engines of similar size tend to have similar torque, regardless of power output.

1) stop looking at horsepower figures. they are meaningless.
2) yes, in fact you can fly most .40 sized trainers on a .10-15 if you know what you are doing. i've done it...

keep in mind you could strap an average sized brick on the wing saddle of a .40 sized trainer with a .40 engine and it would still fly...

a hot .25/28 will fly a .40 sized trainer adequately. provided you realize that you will not be climbing out at 45* 30-35*. the difference is that youll likely settle on a 9*5 prop and trying to turn it about 15k. where the engines this class of plane were originally designed around were turning 10*6's about 12-13k.
youll want more power, and very likely need nose weight, but yes. it will fly.



also, where you get into trouble is crappy ARF trainers like the avistar and alpha are f'ing pigs. kit built trainers that size/type can come out at four 1/2 pounds (without using micro electronics mind you), where its not uncommong for those arf trainers to be at six pounds or more. so you really may want to weigh that airframe considering you can just go buy a used .40-46 on ebay for cheap & clean that up.

Or get one that is already clean from me at a bargin price: http://www.rcgroups.com/forums/showthread.php?t=1688060

Originally Posted by ChillPhatCat

Well, they do publish propeller ranges which can give you an idea of what kind of thrust you can expect.

Okay. That means a 25AX which recommends 10x6 prop is about the same torque as the 40LA (also recommends 10x6). Could be an interesting experiment but I think I'll pass.

Originally Posted by theaveng

Okay. That means a 25AX which recommends 10x6 prop is about the same torque as the 40LA (also recommends 10x6). Could be an interesting experiment but I think I'll pass.

It's really just engine size that you can compare when it comes to torque. The 25 has a lot less torque than the 40 and it will turn the 10x6 a lot slower than the 40 will (read less thrust), this is a guarantee. Generally, the props that are the biggest recommended will not perform well. I would guess that you would get about 80% of the thrust from a hot 25 versus a 40LA.