I find my Tower Trainer flying in a similar "jerky" fashion where the .46 FX engine is pulling the airframe around behind it rather than the plane flying on the wing like a trainer should.
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One thing a lot of people forget to use is that amazing thing called the THROTTLE - WOW you pull it back a little and that thing will slow down. Amazing. We have one in a Eagle 2 & at 1/2 to 3/4 throttle it will fly on the wing like a trainer.

I knew I should have bought a radio with two sticks instead of one! I'm just used to flying control line and I soldered my throttle wide open.

It's hard to beat the Supertigre 40! Only $50.00 and runs great, probably 50% more power than an OS LA 40 and less than 1/2 the price of a OS 46AX. Why risk a high dollar engine on a trainer?

I agree with ChuckW, I also have two O.S. 46AX engines. I had one in a GP Trainer 40 which is the same as the Tower Trainer 40. I had no problem with the plane being nose heavy. You just have to configure the plane correctly. Obviously bigedmustafa has a problem with the weight of the 46 AX as he has repaeted it several times in this post. As for putting a smaller engine in keep in mind where you will be fying. If flying off grass you will need more power than flying off pavement or any other like surface. Nice thing about the 46 AX when you outgrow your trainer by the end of the summer you can put in something nicer. A cheaper engine like the 46 LA will not have as much power and will not last as long.

"I had no problem with the plane being nose heavy. You just have to configure the plane correctly."

Yeah, by adding weight to it. Once you've moved your receiver and battery as far to the rear as is physically possible, that's pretty much the only option you have left.

The .46 LA would actually be a better choice for the Tower Trainer .40 than the .46 AX. It's much lighter weight (12.4 oz w/muffler versus 17.2 oz for the .46 AX) and it still has plenty of power for a trainer that is this light weight. There is no reason why a .46 LA should not last as long as a .46 AX either, as long as the recommended fuel is used. Bushings love castor oil.

I just built a Tower Trainer .40 MkII and I own 3 O.S. .46 FX/FXi engines. I think the O.S. .46 AX is a wonder engine, it's just too heavy for the application being discussed. The Tower Trainer .40 MkII is a light airframe compared to most .40-sized trainers with a similar wingspan, and it seems to balance best with a 12 oz or 13 oz engine.

There's no reason why you can't build a Tower Trainer .40 Mk II with a .46 AX. You'll either need to buy a 1200mah receiver pack for the plane or simply fly it nose heavy. I just think the plane would fly better if the weight/wing loading were kept down and it balanced out at the recommended CG point.

If you think you can build the Tower Trainer .40 MkII ARF with a .46 AX and balance it simply by moving a 600Mah receiver pack to the rear, you're going to be disappointed.

It doesn't take that much ingenuity or modeling skill to re-position the wing an inch forward on the fuselage of your typical rubberband and dowels trainer. This way, you'll be able to mount the .45-.50 engine and fall into the CG range. These planes are like pack mules, so an extra 1/4 pound isn't that big of a deal. The sport planes that are available for aerobatics favor the .45 engines, so if you can get through this hobby without ever owning a .40, you will be money ahead. The fewer engines a guy has to own, the better. The Rossi .45 with the factory tuned performance muffler is an awesome engine, but it might as well be considered a .60 as far as weight goes. The Webra .50 -.55 is also a fine engine, one of the best power to weight ratios of any model engine ever built, period. The mainstream flyer wants to stay with airframes that perform best with 11 inch props, that is the reason why .45-.50 sized engines were put on this earth was because your good old .40s weren't getting the job done as well for the dollar and those .45s will fit [sometimes with a little bit of work] anywhere a .40 will.

"The mainstream flyer wants to stay with airframes that perform best with 11 inch props, that is the reason why .45-.50 sized engines were put on this earth was because your good old .40s weren't getting the job done as well for the dollar and those .45s will fit [sometimes with a little bit of work] anywhere a .40 will."

If an entire pylon racing series can be based around flying a factory standard Thunder Tiger Pro .40 engine, I pretty sure that a good old fashioned .40 can still get the job done. I haven't done any pylon racing myself, but I imagine that it is at least as demanding on engines as primary flight training.

What's funny is, as the .52 and .55 2-strokes continue to gain popularity, folks will probably make the same claims about .46 ball-bearing motors 5 years from now (assuming we haven't given up on glow engines all together in favor of brushless siderunner motors and Lithium Parchisium batteries or whatever). Why run a tired old .46 ball-bearing engine when you can get a .52 or .55 2-stroke for practically the same price? Sport flyers would rather spin a 12" prop anyway.

I had no idea that advocating a lightweight engine that would provide plenty of power and balance the plane properly would be such a controversial opinion. Conventional wisdom instead dictates that the best engine for a trainer is the engine you'll want for your second plane after you've destroyed or abandoned the trainer. Why not just build and fly and enjoy the trainer?

A 2.5 HP, .40 size pylon engine is scary enough as it is, the AMA racers have no desire to move up in size. Even the entry level TT.40 class is scary enough. But we are talking about flying planes that use 8 or 9 inch props, so you are mixing apples with oranges. If anything, pylon engines might have to go down in size someday if the sport gets too dangerous.
To get back on topic, a $60 LA .40 will get the job done for your trainer, obviously.
Nothing wrong with going that route, slap your modular ARF together, drop your .40 down into the factory pre drilled holes and then go have yourself a BigMac to celebrate your instant success.

I believe that most of the engines manufactured today are good engines. The key , is learning to dial each different one in. Much like a woman.
Im believe also , that a key factor to this hobby is having the skill to set up and fly the plane with what you have to it`s most potential.
Engines are like women. Some are high maintenance , but it`s the reliable one you`ll marry/

Stick with OS or Thunder Tiger. You'll be glad you did.

thanks everyone, now i have some good options

i also vouch for the 46AX as the best engine for a beginner in that range.

if you must have something lighter, however, you can opt for the 32SX. i'm sure it'll have no problems flying your trainer. i had it on a TT Lazy P-51 and was a lot of fun to fly. but it aint cheap neither.

good luck!

I would just like to add that the O.S. engines are the most reliable I have ever ran. I've run a ROSSI, ABC Super Custom and the newest O.S. LA 65 and this engine is the tops. Good startup, great acceleration, and awesome cooling give O.S. engines a real step up from the rest. They are a hare more expensive, but you will have that engine running great for years with minor upkeep along with your trainer. However, I must note that if you are going to be flying in sport/competition, ignore my advice. All my experience is backyard, dirt, unimproved surface and concrete runways with trainers...nothing more. I have heard that other brand engines run better(more $$ for the engine purchase and fuel) when in competition; however for weekend flying try to stick with O.S. engines.. Also, If you are a beginnner or don't consider yourself intermediate just yet, keep the stock SIZE(brand can be changed depending on dry engine weight difference) that your aircraft is expecting... a 40 size engine for a 40 size aircraft(60 for 60 etc..). When you do this, and ideal balance(stock location of C/G or C/B), the aircraft will better handle a little extra weight for accessories(night lighting, cameras, and my favorite the candy bomb bay etc). Now, Take Off!
Safety: First, Last, Always.