I'm seriously considering getting one of these kits to build but am in a quandry over what size engine to put in it. After browsing a lot of posts on this board it looks like a .40-.46 might be just the ticket but I don't want to add unnesary weight either and have considered a Thunder Tiger .36 for it, which according to the plane specs, should be plenty. Let me know your opinions!

A .46 will be way to much engine for this plane. I fly the LT-40 with a OS .46FX and it hauls!!! I would look at a OS .25FP or if you want a bit more power try a OS .32 but not a .46 on the a .25 size plane.

After the demise of my LT-40 I put it's OS LA40 on an LT-25. Great combination! My thumbs killed it but I'm building another one just like it this winter. Took out most of the di-hedral and used seperate aileron servos. This engine is light enough that it balanced perfectly without weight.

I have a TT25 on my LT25. It's a nice combination for relaxing and fun flying. Have even flown it it 20MPH winds, more like hovering though!
If I were to change engines I would go with a 30 size but not a 40+.
I fly mostly my larger planes but really have a lot of fun with this setup.

So far we have two votes for a sub .40 size and one vote for a .40. What do the rest of you think?

The OS LA .40 is roughly the same power as many .32 class engines and some hot .25s out there. The LA is a tad heavier though (I think). A lot depends on what you're doing with the plane, of course. An OS .32 would pull that plane vertically out of sight easily. More power than you need for traning. Any of the BB .25-.32 engines will give you plenty of power with out a lot of weight.

Oh, be careful when shopping in the .30range. Some .32-.36 engines are basically overbored .25 engines. This makes a light-weight powerhouse, and is a good thing. The OS .32F is like this. Mounts and weighs the same as most .25s, but way more power. But some .36 engines I've seen are closer to under-bored .40 size engines, making them noticeably heavier than most .25s out there. Look up the weight of a couple of .25 engines.

Anything with a weight close to that would be fine.

I'd expect eventual structural failure with a .46 unless some serious reinforcing went on. And the added weight of the bigger engine and extra structure would likely change the way it flys enough to make it not a very good trainer.

(btw, I keep references the OS .32F because I happen to have 2 of them. I've done engine swaps between the OS .32F, the OS .25FX, and Magnum .25XL and 28XL as they share the same mounting bolt dimensions. The .32 out pulls them all easily. The OS .25 and Mag .28 are about even, the Mag .25 is slightly weaker and slightly heavier) (The Mag .28 is exactly the same as the .25 except for the piston and liner)

Mine has a .40 FP on it. Don't use the LA, they're junk. Howabout a Webra 32??

My LT-25 has a fox .40 on it, and for my experience level and amount of flight time on this plane, it has FAR mor power than it need s. On 3/4 throttle, it will climb almost vertically. As said before, it all depends on what you want the plane to do. For a trainer, IMHO, the .25 to .32 engines will be fine.

Mine would take off from grass at 2/3 throttle with a 25LA. I don't think I would go bigger than a 32. A 40 or 46 might be a bit much. It's a fun plane; you'll like it.

Larry

i have twin sons with lt25's one with a 25fx and one with an irvine 25 . both fly with authority . if you want a powerhouse get the irvine 39 it is truly in the 25 case and is a little tourque monster.

A saito fa-30s would be perfect for this plane.
A member at our club has one on his LT-25
and its nice. But most people will go the cheaper
route. Little do they know the saito engines
will out live other engines 3 to 1 .

i got a os .25 on the front of mine. the engine was easy to run (when i first started flying) no problems tuning engineample power for that plane. its built light and strong like all the sigs ive built. however with the slightly more aerobatic plane you say your building a 32 might be better but i wouldent go higher than that. you will tear the fus apart. its strong, but is not designed for that.

Just took my LT-25 out today for its annual flight
GOod little airplane.

LA? FP? put on a blind fold, and unless you are holding them both, you can't tell the difference.

My vote is for the .25 engine on the .25 sized plane, it will still have too much power!

Jetts

What your looking for is power to weight. I put a Norvel BigMig 25 (total weight with muffler 8oz) as was able to hover my LT25.

I had good luck with an old FP20 not over powered but was capable of 30 min flights.

the .32 (asp and os) worked great but the weight penality wasn't worht the extra power.

any thing from .20 to .32 is very good, a plain bearing 40 (LA FP) is about the same as a normal .25 for power with a little more weight.

Don't worry with this plane you can't go wrong.

Tom

Thanks all for the advice! I guess I'm leaning towards a GP 42 due to it being light and the price being right for an engine that will probably take some abuse. The other option is a .25 but it's not a whole lot lighter and really lacks in horsepower. A .32 for around 60 would be an option for me. I have an OS .15 with under 2 hours on it but it's to small for much of anything. I've got a radio now! My dad gave me back a 4 channel Airtronics with low hours, but it's probably from 1997, that I used to have. Thinking of getting a new battery pack but he says it still works fine. Feel free to add more comments!

Blindfold me and I will be able to tell the difference.