I just finished my LT-40 kit. SIG's website suggests a flying weight of 5.5 to 6 lbs. Mine came in at 6.5 lbs with an OS 46 LA for power w/ MAwood prop. Only other replacements from OEMare Dubro plastic spinner and Sullivan Gold-n-rod (yellow/blue) pushrods for the elevator and rudder. I'm using a Spektrum 1500 mAh NiMH (3.7 oz)battery, AR6100 Rx, Hitec servos. Covering is Ultracote.

And, it's gonna get heavier because as it sits (only things to do are balance fore-n-aft and set the throws) it rests squarly on its butt! Too bad it's not a taildragger - thought about it but it's gonna do club training gigs.

In the upright pics the tail is supported by a foam-covered 4x4. Em, might make a good anchor ...

Comments?

<><><> Just tossed a bit of weight at the firewall to get it a bit nose-down with CGat center of the main spar - 14.5 oz. Hey, why not back it an even 1 lb.? Is this reasonable? Where did the build go the wrong way? The tank is as far foward as 1/2" foam between tank and firewall will permit. The battery / foam pack is hard up against the firewall. The servo tray is 1" behind former F-2 (instructions suggest 1 7/8" behind F-2). Titebond IIand CA was used with exception of firewall-to-fuse bond. The CA hinge lines (elev, rudd &aile) were all sealed with covering on both sides per RCKen's Pay It Forward LT-40 build thread. Lite ply was used to add pushrod supports in 2 rear formers. Yea, I did think that the balsa that SIGprovided for the tail (fin &stab) was rock hard (aka heavy) but thought that it was their "it's a trainer - need to be strong" approach.

Geez - 14.5 OZ? Where's the helium?

If You can try and move the battery to get Your balance right. It is real easy to get them tail heavy. Your plane looks real good.

Hey jship - Me thinks I'd have to build a fishing pool cantilever contraption to mount the battery pack about a foot and half in front of the prop

Em, I do have an OS91 FXon the bench. Wonder if it would cure the CGissue?

I had the same problem and had to put 5oz of lead in the nose to get the plane to balance. It flew like a dog with the 46LA. I swapped it out for a 46AX, pulled out the lead, and it was a totally different airplane.

The 46AX should be the minimum for the LT 40, in my opinion.

cvause - Makes sense because the LA weighs 12 oz and the AX weighs 17.4 oz.

If my LT-40 needs to weigh in at darn near 7.5 lb I should go for the 55 AX which weighs in at 18.4 oz. Better yet, Ihave a Saito 82 that weighs 17.6 oz. Still needs 8 - 9 oz of lead.

Geez (am I repeating myself?) [:'(]

There are days that the brain's in neutral. I have an Evolution 52 NX on the bench that weighs in at 17.7 oz. Gives me an extra 5.7 oz and some decent power. Seems that I should spend a bit of time swapping motors.

Where are you checking your CG. it shows 3 1/2 to 4 1/8 from leading edge of wing. Great Job on the plane I just can't see where you put all the weight. The 82 will work and with the battery under the fuel tank next to the fire wall All you should need is 2 oz.s maybe a little more it will still fly great in the 6lbs area.
Larry K

LW - the current CG is approx. 5 3/8" from the LE. It is so tail heavy that it rests on the main wheels and the tail. With 14.5 oz at the firewall the CG is at 3 5/8" behind the LE. Which is fairly close to the "beginner" location. Since this is going to be used with novices on a buddy box that is my goal.

Hope this makes sence to you. but the forward CG is for sport flying and rear is for trainer. With the other choices of engines you should be able to balance it . With the extra weight , wing loading will change so you will have to watch how you fly it, no fast rols and no high G loops[:@]

It's a 3:1 ratio on the fuselage. 1 part in front of the CG and 3 parts behind the CG. So 1oz of tail weight costs you 3oz on the nose, sometimes more. Why not quit thinking of ways to make the nose HEAVIER and start thinking about ways to make the tail LIGHTER? An added benefit to getting the CG correct is an overall lighter airframe. Win/Win...... instead of a heavy compromise.

Cut the covering off the fuselage and get out your dremel. Concentrate on the area behind the wing saddle. You can easily dremel out 1oz or 2oz with a rough grit sanding drum. 2oz out of the tail will save you 6oz or more in the nose. Remember it's a 3:1 ratio. Can you get 3oz out of the tail? How about 4oz?

I know you do a nice job with covering, Jim. And I know it's time consuming and expensive. But tossing a little covering in the trash now will yield a better flying plane in the long run.

Tip for the next build:
Frame it all up and do a complete assembly on the bench, but without the covering. Mount your servos, linkages, engine, battery, switch. Mock the whole plane up on the bench. Check the balance. Adjust until it's noticeably nose heavy. Now cover it and glue in your hinges. You'd be amazed how heavy monokote and hinge glue is. Set it up just a little more nose heavy than you think, when you're mocking it up on the bench for the first time.

Rc
With the workmanship he has on the plane I can see why he is trying to keep from redoing any thing on the plane.. A person can move the servo's in the plane as far forward as he can and save the structure. I bet he has read many posts on how weak the tail section is an Epoxied the heck out of it. I have had serveral of these Lt 40's and they all took a little weight in the nose depending on the Engine used.
Larry K

Things that I have learned ...
LT-40 is actually a 60-sized plane
LT-40's are notoriously tail heavy
LT-40 ARF will balance pretty nicely with an OS61FX (that's 13.6 oz heavier than an OS46LA) - em, I'm off by 14.5 oz)
Some people assume that the author of a thread has used a 5 lb sledge hammer when a tack hammer was needed
SIG tech support doesn't share much info

What will I do to proceed to "maiden" flight status?
Replace the engine with an Evo 52
Install a new longer mount
Replace 4-40 mounting bolts / blind nuts with 6-32
Replace 8 oz tank with larger tank
Most importantly - add a partridge in a pear tree (with lead weights as needed).

Btw, RC suggested doing a "precovering" assembly. I did just that. Everything (including Spektrum Tx, Rx programming) was installed & tested. What I didn't do was to ensure that this turkey was extremely "nose heavy" before covering. Not sure my "to-do" list would be any different because the plane's structure had been established.

Also, I don't subscribe to the "if a little glue is good, a whole lotta gobbed on glue is better" theory. If there is a known weakness, I try to figure out how to reinforce the structure before any glue flies. Just ask RC, sometimes what I come up with doesn't work the first time and he has to fix it. Yea, we have plenty of club members who subscribe to the "Gorilla glue it until you run out of glue" theory. I'm not one of them.

Well, it's off to the store ...

I'll bet you're wrong. Jim is an accomplished builder. He's not sloppy with the glue and he doesn't use epoxy as a filler for bad glue joints.

Please read the reply
Sorry to intrude
Larry K

I wouldn't go too much larger with the fuel tank. You can end up with a tank so large that your carb settings won't cover the range of head pressure adequately.

What you need is an Enya 60 or 80-4C four-stroke engine in the nose. Both swing a 13x6 briskly and both are a bit weighty. Other good engine choices would be an OS/Magnum .70/.91 four-stroke engine. Weighty and powerful enough.

I saw an LT-40 ARF fly at our field that was using an ST GS-40 engine. It was making the rounds quite briskly. I can't see where any more power was needed for training purposes.

Oh, one more thing. Someone said that the forward CG was for sport flying and the rearward CG was for training. This is just backwards from the way it really is. Rearward CG's make an airplane more maneuverable, but less stable. Stability is what is needed in a trainer.


Ed Cregger

Em, RC, actually I do use epoxy as a filler. Here's how. I mix up a batch of finishing resin (2 part epoxy) and then triple (or more) its volume with micro-balloons. Makes for a very stable and sandable filler. I used it to: fill the nooks where the stab butts against the fuse; ensure that the wing saddle mirrors the bottom of the wing (the right saddle needed a 1/32" shim to square the wing with the fuse); and fill around the rudder control rod tube where it exists the top of the fuse. Just enough to fill the gaps to help out the covering around stab & rudder controls.

Here's the laundry list:
<ul>[*].4 oz - 12 oz tank (replacing 8 oz tank)[*].7 oz - replace 3" engine mount with 3.5" SIG mount[*]6.0 oz - replace OS46LA w/ Evo 52 NX (center of mass 1/2" farther away from firewall) [*]2.5 oz - replace spinner w/ Higley heavy hub[*].9 oz - replace wood prop w/ APC prop[*].5 oz - replace 1500 mAh NiMH 4.8 w/ 1100 mAh NiCd 4.8 (or 1400 mAh NiMH 6.0 or 2300 mAh NiMH 4.8)[/list]Total is 11 oz - most in front of the firewall. If the engine center of mass is far enough forward (additional 9.4 oz) might bring it close. Good news, all of this stuff is "on the bench" - biggest pain will be relocating the blind nuts for the new engine mount.<br type="_moz"/>

Thx Ed -

I get the comment on the CG - the closer my fingers (holding up the wing) are to the LE the more docile, the farther back the more the fun. Dean Pappas wrote / published some pretty thorough trimming stuff that includes the CG issues. Good read.

I'm cheap and want to keep this "club trainer" cheap so I'm trying to keep the upgrades "from the bench" so to speak. My engines include the Evo, Saito 82, Super Tiger 90, OS 91 FX, Saito 91, Saito 100. I used the Evo 52 on my Avistar and it's speed was too much for a club trainer. Gonna have to mess with props and maybe radio throttle limits to keep the top speed down for the "throttle to the wall" novice. The 82 is slated for my ShowTime 50, the OS 91 for my Kadet Sr, the Saito 91 for my 4Star60 and the Saito 100 for my Hog Bipe. There is also an OS 61 FX waiting for me to finish my Bridi Killer Chaos 60. As you can see, the Evo ain't got a home

I've flown the Evo 52 and a Dubro 12 oz tank in the Avistar &amp; Tiger 2 (RIP) and carburation &amp; flight time is fine.

Back to the dungeon ...

SeamusG, I'm offering the setup on my LT40 ARF as a reference.

Engine: OS 46AX.
Weight: 6.0 lbs. (digital scale)
No weight/lead added.
Battery crammed up as far as it'll go, stock ARF servo locations.
CG: 3 11/16", which is very close to your 3 5/8" goal.

WCF - ARF vs. Kit

I'm using a digital scale as well. The AX weighs in at 17.4. That means the ARF all-up weight excluding engine is 4 lb 14 oz. My kit all-up weight excluding engine is 5 lb 12 oz. That's darn near a pound difference (no shots from our Brit friends please).

I'm at a total loss trying to explain the nearly 20% greater weight of the kit - 14 oz. Ultracote doesn't weigh THAT much.

Hey, I'm gonna run down to check the box. Maybe the name is LT-60 [:@]

I agree with the suggestions to dump the .46LA. I bought one on an impulse and it is indeed a dog. I put it in a SIG MidStar and getting it off the ground generally required a brisk head wind and a generous bump in the runway. On the other hand, the .46 AX is everything the .46 LA isn't. I have a couple of them and put one in a SIG LT-40 which I use to train new members. Plenty of power, wonderful range. Worth every penny. By the way, the LT-40 is one wonderful airplane. Many members of our club have learned to fly with one, and and in addition to flying well, it builds well too.

Good luck to you.

I have a 46 AX on my SSE with a Macs 1-piece exhaust. Sweet performer. I've found that the Evo 52 NX is very comparable to the 46 AX.

I guarantee that there will be no more 46LAs anywhere near me. The one that was mounted in the LT-40 has since been (permanently) decommissioned.

The first two LT-40's in our club were flown witrh OS 46s and woukd just barely fly. Every other one built-ARF's or kits- were powered with OS 46 FX or AX. All flew like new planes. I flew mine on floats as well, and it weighed 7 and a half pounds with the floats on.
The LA is just not powerful enough nor weighs enough for this plane.

I flew one for years on a Magnum 40. (kit Built)
Mine balanced with no weight added, the batteries were located under the fuel tank and the servo's were as far forward as possible. You could put this plane into a slight breeze at 1/4 throttle and it would almost hover there. I can't see flying this plane with anything over a .46
I sold the plane to a buddy and taught him how to fly on it and he finally destroyed the plane after a couple of years and throwing it around like a sport plane.
Anthony

My head is really really really hurting! How can my kit built LT be so exceedingly tail-heavy? Time to get out a hammer and put the piece to rest.

I have one of those planes, OS55, complete and ready to go, 5.77 lbs., dry. Now my pattern ships come in at 7.5 - 8.2 lbs. How did you get an LT-40 to that weight ?

Crank