I'm just putting together a SIG LT-40 ARF and I have a choice of a couple of engines..

An Irvine .39 or an OS 46LA. The Irvine is an ounce or two heavier than the OS.

So, how does this plane balance? given that both engines probably have similar power, would the heavier or lighter engine be better?

Reason for asking is, I just finished a Hobbistar 60 mkIII. This needed a whole load of lead on the tail with the OS65LA... Whereas my Superstar 60 balanced perfectly....

You have too many airplanes. Pack half of them up and send UPS to...

Seriously, install one of them temporarily (or just set it on the motor mount rails), see how she balances and go from there.

Tiggerinva,

I fly mine with a TT .46 Pro. I had to add 2 ounces to the nose. No big deal as this plane's wing loading is already so low that you'll never notice the addition.

John

Yup, was thinking of installing everything and leaving the engine till last...

I can UPS you over the Superstar if you like, not in very good shape through after putting it through two trees.....

I think my engine situation is worse, I've also got a K&B .45 and an ASP 52 4 stroke I could use but I thought I'd try and keep the selection to two relatively decent lightweight engines....

John,

Thanks for the input, I'm trying to keep the weight down by adding only 'useful' weight and avoid lead if possible.

I did something similar to my Ripmax Zephyr. For that I used a lightweight battery and HS-81 servos. Then I found that I had to add about 1 1/2 ozs to the nose.

After putting my Superstar through two trees, I put together my Hobbistar. But this is a tad faster, and I've developed a paranoia about the close proximity of the trees to the field....

So when I saw the LT-40 at a decent price, I grabbed it although its basically the same size, I'm hoping that the lighter loading will make it slower and more maneuverable.

BTW Hows the .46 pro for power on the LT-40? Will the Irvine 39 or the 46LA be adequate?

I have an LT 40 and put the OS 46 LA in it, but I still needed a lot of lead in the nose, so I'd go with the heavier engine. I don't know how the plane got so tail heavy, but it took 10 oz to balance at the recommended spot for newbies. It flies just right though. My instructor flew it without any trim on it's maiden voyage.

Kerry

10 ozs with a .46LA?
and 2ozs with a TT pro .46?

Its beginning to sound like this plane is very tail heavy.... I might have to consider using the K&B .45 sportster after all, I was a worried about this engine as I've heard some bad things about it on here...

Its still NIB right now, looks like I'll have to run it up tonight to see if it runs OK.....

either that or buy some more lead

But, you can use the battery pack to change the CG.

I have an OS FX .46 on the LT-40 ARF and didn't add any weights anywhere.

I think you're probably overestimating the problems with CG. As long as its close and you have someone experienced to do the trim flight, you're probably ok.

What did you glue the tail on with? If you reinforced it some way it will take a lot of weight. Battery pack all the way forward under tank , and move motor forward on mounts, a spinner will help. I am running Mag. 52 4st on my trainer Balances on main spar from bottom side!

Thanks, maybe I don't need to bother with the K&B....

Mine is not together yet, If you look at the top post, I was trying to find out how the plane balances. I'm trying to get it finished for this w/end.

The good thing about this plane is that the tank is on a shelf with room unerneath for the battery. That will help if more nose weight is needed. I'm also going to be using a 2" alu spinner.

Hows it fly on the 4 stroke? I've got an ASP .52 I could use....

I had someone do the trim flight on my Hobbistar and that took off straight, just needed a bit of right aileron for level flight. As long as it balances correctly, I might do the maiden myself this time....

I've seen multiple LT-40s built from the kit and all tail heavy. If the ARF balances better, it would be nice but unexpected. Personally, I wouldn't hesitate to use the Sportster or another relatively heavy engine.

Tiggerinva,

The .46 LA will fly the LT-40 just fine. All I was trying to get across is with this plane you really don't have to worry about adding some extra weight. You won't even know it's there.

And you'll have to add some especially with an engine as light as a .46 LA.

Don't worry about it. It will fly fine and you'll have a ball. Our clubs main flight instructor has built 8 of these and flown them with everything from an O.S. 52 4 stroke to a K&B Screaming .48.

The TT.46 powers the LT-40 just fine. With a 11.5 X 4 prop it will just about hang. Looks strange seeing a trainer trying to 3D!!!


John

When you get it together trial fit the motors, I have run a OS46 on it , goes to fast to give instructions on, have built 6 of the Lt40 and had no problems. A guy at the Field built one and it took 2os. in nose.

Well, I've just cleaned up after test running the engines.

The K&B .45 Sportster gave me about 11,500 rpm on an APC 10x6 prop using 15% Byron fuel. However, the engine wouldn't transition back to full throttle after idling.

So, I put my Irvine .39 on the stand and gave it a quick run up. Using the same prop etc I got 13,600rpm out of it.

Even if I do have to add a bit of weight, I think the extra 2000rpm is worth it.

I didn't get a chance to try the OS.46LA, but I know it was in the 11000rpm ballpark with a 11x6. Anyone know what gain I might get if I dropped this to a 10x6?

The Irvine is looking favourite now....

Thanks guys for all the input so far....