Hog Head

Hello. Just got an LT-40 kit today for my wife and after going through the construction manual I have a few questions. This is not my first build, kit or ARF, and I noticed that the construction manual does not use epoxy in the usual places. It says to use thin CA for the dihedral braces and when joining the two wing halves together, medium CA for installing the firewall and slow CA for the horizontal stabilizer and fin. Unless my memory has gone south, I remember all these areas being high stress areas and requiring epoxy on the planes I have built in the past. Are the adhesive methods for the LT-40 strong enough and safe? Thanks for the help, Gene

Test005

Go with your instinct.
Epoxy the high stress areas such wing joiner, tails areas, firewall & landing gear plate.

....Most important of all, have fun!

SoonerAce

My Feedback: (1)

Also, don't forget to add a piece of triangle stock balsa along the meeting point between the Rudder and Stab. on both sides of Rudder. another weakpoint.

chris_in_montreal

My Feedback: (1)

I agree, i used epoxy in all these areas on the LT-40 kit i built last year. For the rudder and stab try and get as close a fit as possible. Mine ended up really tail heavy after using triangle stock.

Test005

The triangle stock reinforment mentioned, looks something like this: (This is not the LT-40, but same idea) Fin goes in the empty slot.

Mindwarp

If I remember rightly (I built my LT-40 over three years ago) the instructions say something about fitting the wing halves together via the dihedral brace, using tape to seal off most of the join gap, then pouring thin CA into the gap and let it set. Once that's done you remove the tape and 'glass the joint. For what it's worth, if I were building it today I'd use epoxy just because it's stronger and quite frankly easier than joining with thin CA in that manner Having said that, I built my LT-40 using the thin CA method and three years down the line there's no sign of the wing root joint giving way (and trust me, with some of my landings if it was going to give way it would have by now [8D])

I'd second (third?) the comment about using triangle stock to reinforce the fin/stabiliser joint though. Without the triangle stock there's really not much contact area between the two. I feel far safer knowing that I've got an extra 1/2" of wood-wood adhesive contact along the length of it.

Hope you enjoy your LT-40. It's a real floater and a delight to train on. It's also a lot of fun to take up on windy days when you have more experience under your belt

Hog Head

Thanks Mindwarp and everyone else of course. Your memory is correct about taping the bottom and then flooding the joint with thin ca. It just didn't sound like it would be as strong as epoxy. But you say that yours is three years running and no problems? The ca would definitely be lighter and I am planning on glassing the center. Hmmm, what to do, what to do! I am almost done laying up the left panel, so I have a little time left.

Definitely had already decided to use triangle stock on the tail feathers before I had ordered the plane as I had bookmarked all of the LT-40 threads. Do you think I should do the top and bottom or do you think the top would be enough?

Thank, Gene

tschuy

My Feedback: (1)

Epoxy is probably the best way to go. Holding power of both glues is about the same but the big difference is that Epoxy has some flex in its holding power where as CA is brittle. A good test is to take two pieces of hardwood and glue them together with an overlapping joint using CA. let it dry and then take a hammer and hit it with a solid blow. The joint will most likely "pop" apart. Now do the same test with epoxy. You find that it'll hold better.

My 2 cents worth.

Mindwarp

There is only the top with the LT-40 fin. The stabiliser sits flat on the top of the fuselage and the fin glues directly onto it if I remember right. There IS an angled part of the fin that lays along the fuselage rather than the stabiliser though, if that's what you're talking about. With mine I just added the triangle stock to the part of the fin that glued onto the stabilizer.

Good luck,
Neil.

P.S. I'd use epoxy on the wing joining. It'll be a lot easier and trust me, you don't need to worry about the added weight on this bird! The thing practically floats like a Helium balloon as it is! There'll be days where you'll be begging for more weight to help get it down on the ground again

Hog Head

I'm going to to ahead with the epoxy which is what I would have used had I not read the instructions. On the subject of the tail-feathers, I was talking about where the horizontal stabilizer meets the fuselage on the bottom of the stab not the fin. Going to be mounting a .46AX on the plane. Is this going to be a good combo? Hope so. I already bought the engine.

Gene

Mindwarp

I wouldn't worry about triangle stock between the fuselage and the underside of the stabiliser. There's plenty of surface area to attach those two together with.

Cheers,
Neil.

tschuy

My Feedback: (1)

The combo should perform very nicely for you. I have the LT-40 with a GMS 40 engine on it for our clubs training platform and it does very nicely. Plenty of power and with our student pilots we end up flying at slightly less than half throttle. One of the easiest airplanes to land. You might do yourself a favor and toss the POS fuel tank that comes with the kit and get a better quality Dubro or Sullivan. The one we have popped its top and leaked all over the inside of the fuel bay. Replaced it with a Dubro and it hasn't been a problem since.

Cheers,

Hog Head

Figured the 46 would be a good choice. It also gives me a good engine for something else when the plane has served its purpose. The LT-40 kit came with a 8oz Dubro tank as advertised. However it did not come with the Dubro tires that it said it would come with. The kit contained a brand called Kavan and they are hard, hollow plastic. Pretty cheesy in my HOB.

Thanks, Gene

Al Stein

Haven't seen it mentioned so far -- LT-40s around here have tended to build tail heavy, so feel free to get excited about sanding the fuselage rear, rounding over the edges, etc.

Test005

� power my LT with a OS52 fourstroke, it's a beautiful combo, I love it!
Also converted to taildragger, recommended, it's nicer than trike gear imho.

Mindwarp

Yup - that happened with mine too. Powered with an O.S. 46 LA my LT-40 has a weighted prop hub on it and even then needed a couple more ounces of Lead epoxied into the engine compartment. Don't be afraid of losing weight from the tail (or you can take the alternative approach and just stick a bigger engine in [8D])

Test005

I'd say that the AX46 is plenty of power for this airframe and you'll go 40%-50% throttle most of the time, using a bigger engine won't do any good.
Go ahead and install the AX, mount it as far forward as possible and use a weighted prop nut if needed.
This engine will also be great later on in a .40 size low wing sport plane.

chris_in_montreal

My Feedback: (1)

Yup, I have the AX on mine with an 11x6 prop. Plenty of power, cruising between 1/4 and 1/2 throttle, in the hands of my instructor i've seen it do loops, rolls, inverted flight, stall turns and some other stuff i don't even know the names of!! All the comments on it building tail heavy are consistent with my experience. I'd check out the balance before covering with the engine mounted and radio gear in. I ended up needing a 3oz prop hub plus an extra 4 ounces in the nose cheeks to balance on the main spar.

Test005

On the other hand weight might not be only a disadvantage here.
I find the LT to be so light it's hard to get it to land when my .52 was new and had a higher idle.
A heavier pplane also penetrates wind better and doesn't 'bounce' around as much in the wind.

The LT can sure take some extra led and still be a top-notch, low wingload flier.

fledermaus

Re: Tri-stock for the fin on LT-40.

I also noted that the butt joint between the fin and stab was a weak spot when I built my LT-40, but I did not want to put tri-stock on the outside. So, when I built the fin, I made the stern post longer than the plan said. I then carefully cut rectangular holes in the solid slab centre portion of the stab, and also through the plywood support in the fuselage. The alignment required a bit of care, but when the tail feathers were assembled, the extended stern post of the fin went right through the stab and the ply, and projected about 1/8 inch beyond into the fuselage. The whole thing was glued with slow CA, but I must say that in retrospect I would have used epoxy.

Anyhow, this arrangement gives a very clean line, and a very firm mount for the fin.

Re: Engine for the LT-40.

I have a Leo 46 in mine, and I use an 11 x 6 prop. I found that the "recommended" 10 x 7 prop gave really "soggy" flying, but the bigger and lower pitch prop pulls very smoothly.

Re: Tail Heavy.

My LT-40 balanced precisely on spec as built with no additional weight required. Maybe all that sanding paid off .

Final comment - put your LT-40 on Floats! It really flies nicely with floats, very scale-like performance and a whole lotta fun.

onlyb

When I built my LT-40 (over 5 years ago) I went with the instructions. CA'd the tail too. Was doing some taxi training and had the plane flip over in a high wind. Snapped the tail right off. Took it home and epoxied it back on. Haven't had any problems since. Haven't had any problems with the other areas I used CA on. If I remember right, the only thing I did epoxy was the firewall.

For an engine, I used an .40LA. Had plenty of power and flew great.

I did have to add a lot of weight to the nose to balance it too.

Hog Head

Well all the major construction is done! I am going to install Dubro Super Strength Landing Gear in place of the stock wire mains which will raise the mains an inch so I also had to order new nose gear (Dubro also). I read on a couple of threads that there were problems with the elevator and rudder push-rods with flex and distortion due to heat, so I added braces to F-4 and F-5 which took out all play in the push-rods between F-3 and F-6 which was where the only support for the rods were. I epoxied the firewall in along with the triangle support and I am also going to use epoxy and triangle material on the tail-feathers. I decided to stay with the rubber bands instead of bolts, as my wife will be learning on the plane. Here is a link to the Dubro gear at the Dubro and Tower Hobbies web sites, [link=http://www.shopatron.com/product/product_id=DUB789/101.0.5161.5171.0.0.0]Dubro[/link] and here is another view at [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXNM65&P=0]Tower Hobbies[/link]. If anyone has had any experience with it, good or bad, please tell me about it. I have decided on white and transparent blue for the color scheme so it won't look like everyone else's LT-40 ARF's at our field. If anyone can think of anything that I might of missed, I would definitely appreciate the help. I would post some pics but our digital camera isn't here yet as I just ordered it yesterday.

Thanks. Gene

flmlm

Gene,

Was just wondering how it's going with the LT 40. Currently I've got one on the bench, the wing is done and I'm starting the construction of the fuselage. I agree with you the kit supplied wheels look and feel really cheezy, I'll probably end up replacing mine as well. Also, did you use the supplied push rods or did you swap them out with an alternative? Good luck and happy flying.

Regards
Mike

Hog Head

Hello Mike,

Everything except the wing is covered. I emailed SIG and it seems that they merged with Kavan; thats why the difference in hardware. They did say that they would send me the Dubro hardware, although I haven't seen it yet. Did a little research on the Kavan wheels and they are $2 - $3 more than the Dubro. I will give them a try and if I don't like the way they handle, I will swap them out.

We don't get the heat here in Oregon like you get in Florida and other parts of the country, so I stayed with the supplied push rods and I will just keep an eye on my trim settings. I supported them at F-4 & F-5 in the same way that they are supported at F-3. I glued them well at F-3, then pulled them tight and glued at F-6/top deck. After gluing in the added supports, there is little to no play in the control rods.

I changed out the nose gear with a Fults strut set and the mains with Dubro's Super Strength Gear and 5/32 x 1 1/4 axles.

I received the rest of the items to finish the plane yesterday. If work doesn't interfere too much, I should be able to complete her pretty quick (I just got called to go to work, LOL).

I will post more when I can. Good luck with your LT-40.
Gene

MJFinegan

My Feedback: (2)

Count me among the advocates of triangle stock, lead in the nose and ultimately a Magnum.46.
Flies like a dream especially w/ the larger engine. I originally had a .40LA. Ran nice, just a little too little engine for too much airplane. I built mine per the manual with regard to joining the wing halves. In retrospect, I probably would have gone with epoxy. Strong, comparatively inexpensive less irritating etc. etc. etc. What ever you do. Have Fun. You've got a sweet building kit and a real gem of a trainer.

Mike