LT-40 Mods

dave

had one traded it to a friend and still in use great trainer the only problem was the landing gear too springie also very narrow replaced with alum. about 3"inchs wider will keep it from tipping over on cross winds and turning around

EARL

I'm currently training my son with one. I agree with Earl that the landing gear is way too springy and narrow in comparison with the size of plane. On a hard surface runway it causes lots of broken props due to bouncing which is very unusual for a trike geared A/C. I'd replace the nose gear as well with a stiffer spring as well. Mine is bent towards the rear of the plane and allows the nose to drop too much on landing.

I havn't had any problems with the vertical stab being weak at all. Just make sure you use enough adhesive to hold it well. I used 30 min epoxy. Have had no probs with the aft part of the fuse either though the covering is a little worn from ground contact. However, with less springy gear that problem should be solved.

Hope this helps.

Make sure you get plenty of epoxy in the vertical fin socket. Had a friend whose LT-40 shed the fin/rudder and did a flat spin to the ground, luckily with only minor damage. He glued it back in and put

1/4" triangle stock >Hello All,

I wouldn't worry about beefing it up, but I would use plenty of glue. Do not use 5-min. or 15-min. epoxy. They will not soak in, creating only a surface bond. I agree with everyone else that it needs stiffer landing gear.

Good luck and let us know how it flies.

Dr.1 Driver "There's a Hun in the sun!"

Lots of Kadets at the field many days - often in the hands of experienced pilots who just want to relax...

Concur that the wire main gear is a bit wimpy. Replacement would be a good step. The fin mount is OK as designed - with enough glue it'll stay on as needed.

A couple of mods to ponder --

1. It wouldn't hurt to reduce the dihedral to 1/2 of the amount called for in the plans. The plane is WAYYY stable even with the reduced dihedral.
2. I experienced considerable slop in the aileron linkage after a bunch of (a couple hundred) flights -- the cause was a lack of a bearing on the aileron torque rod. (Just finished doing this mod to mine with the ailerons in place - much easier to do when assembling in the first place....) It's easy to make up a set of torque rods from two 4-40 threaded-end rods - available from any hobbyshop. When you're bending them up before making the final bend, slip on a short section of brass or aluminum tubing that will glue into the wing trailing edge block-- the area of the wing root inboard of the aileron. End of aileron slop - more precise control.
3. - Slightly more 'radical' (for a Kadet) setup -- The plane will still work fine as a primary trainer --if you: a. build it with 1/4 of the indicated dihedral -- or even none at all (though that looks silly on the ground, it flies much better than stock that way). b. (thsi can be done while building or added later) -- reduce the wing incidence by raising the trailing edge of the wing -- adding a 1/4" - 3/8" shim under the trailing edge of the wing. (a nice wedge of balsa built onto each side of the fuse and covered w/ Ultracote / Oracover is hard to even notice) and again the plane will penetrate better and generally behave more nicely - while still retaining good 'trainer' characteristics.

It's a great trainer and an outstanding intro to the hobby/ sport- enjoy!

You've chosen the ideal trainer. Treat it like a trainer and leave the mods for when they'll match your skills. The LT-40 is perfect for its

*intended role* just as per the instruction manual & plan. The LT-40 was never intended to be other than a primary flight trainer.

Modding the Gear

---------------- The springy wire gear isn't just used instead of a sexier looking aluminium because its cheaper, though that is an additional benefit. It is far more forgiving of bad landings. You only need do rudimentary research to figure this out. If you want to be repairing the airframe regularly, use an aluminium one piece unit. If you want to be flying immediately after a less than perfect touchdown, use what SIG supply. Once you're an ace, you can use what you want. But once you're that competent that landings aren't an issue, you'll quickly tire of the LT-40. Not to impune the design as I think it's the arguably best primary flight trainer available in the marketplace today, but why anyone would want to fly an LT-40 unless they were either instructing or receiving instruction is beyond me!

Fin mod

------- The LT-40's vertical fin also doesn't need "beefing up". That sort of thinking belongs with those who still think in terms of the "Titanic" as unsinkable and of battleships as 'ruling the seas'. Follow SIG's instructions and glue the fin to the fuselage as a butt joint using sufficient but not an excess of epoxy. More is not better or stronger. More is simply heavier. As such the joint will not fail under normal operation. It may fail if you prang on landing and strike the fin, and that's what you want it to do. ie: To fail neatly along a designed structural failure point which can be easily and quickly repaired rather than shatter and fragment about the area you've built up with triangular stock and epoxy. *I know which I'd rather repair!* And don't kid yourself, both will fail if subjected to significant impact beyond the elastic limit of the joint or structure. Neither will fail under ordinary operation of the LT's flight envelope.

As for the tail skid. It's not only unnecessary, but it and the epoxy you use to glue it with will add weight at an extreme arm to the CofG. The LT-40 usually turns out tail heavy, and you don't require a lot of weight at that arm to effect a large moment requiring stacks of ballast up front to statically balance. Cumulative with the extra epoxy and weight of the equally unnecessary triangular stock reinforcement, you'll almost certainly end up with a significantly heavier model by the time you ballast and balance it. Even with that massive wing area, within the structurally deficient extreme, lighter is always better when it comes to model performance. A bigger engine is not a solution, it's a kludge.

Other potential mods

--------------------

Elevator Hinges

--------------- If anything at all requires substitution or modification on the LT-40, I'd argue that it's the type of elevator hinge used. The combination of load on that surface *of this model in particular* in conjunction with the workout they get wears out Easy Hinges pronto. Do a bit of research and you'll discover that with heavy use, they have a propensity to fail *on the LT-40's elevator*. That was also my experience many years ago. They are simply not up to this job *long term*. Of course you can expect to hear Peter Perfect pipe up in defense of Easy Hinges and their flown once every three months LT-40 exception now. Believe me, Easy Hinges will start to fail on *that* LT elevator if you fly the arse off the LT. So if you use 'em, keep an eye on 'em during every pre-flight as you start to notch up significant hours on the airframe. If you know what a pre-flight is and don't mind replacing Easy Hinges sometime during the LT's operational life, Easy Hinges will work well until they fail.

Nyrods

------ SIG's nyrods are ordinary compared to DuBro's and Sullivan's, though they do do the job. Given how inexpensive DuBro hardware is in the US, I'd substitute this part as there is a benefit without a contra (except cost) in doing so.

Caveat

----- My own experience was with the LT-40 kit/s rather than the ARF. So you'll have to interpolate variations between the two relevant to the above for yourself.

Just build it straight and true as per plan without unnecessary mods, get good instruction and fly the arse off it. Nice choice.

You had me until that sentence. I've used CA-type hinges for 20 years on planes ranging from pylon racers to unlimited competition class fun fly to a giant Stinger, with no problems. I've used Sig, Great Planes, and Radio South. I've only seen two hinge failures: one due to catastrophic flutter (that destroyed the wing), and the other due to improper installation (the builder doubled the hinges and used thick CA).

Properly installed, the hinges will outlast the plane. Here's how:

CA Hinge Installation

There are several rules to follow for an easy, correct CA hinge installation. These rules are good for hinges from different manufacturers, including Great Planes and Radio South. I?ve used them on many planes from pylon racers to Unlimited class Fun Fly planes to even a giant scale Stinger (the 1/4 scale size hinges). I have never seen an in-flight failure using this procedure.

Here we go:

Use a #11 blade to cut the slots. Cut only once per side/per hinge. Use only thin CA. Do not double the hinges. Do not use ?kicker?. Install after covering.

1. Slot the wood pieces, install the hinges, and mount the control surface. Gently push the pieces together.
2. Flex the control surface both ways for the maximum amount of travel you expect to use. This will automatically create the proper hinge line gap.
3. Slowly drop 2-3 drops of CA on each hinge at the hinge line on one side only. If any CA puddles in the hinge line, blot it with a paper towel.
4. When that is dry, apply 2-3 drops of CA to the other side of each hinge.
5. When both sides are dry, flex the control surface both ways.

That?s it! The wood will pull out before the hinge will let go. The surface will tend to stay centered and will not flop around. Both will help prevent flutter. Dr.1 Driver "There's a Hun in the sun!"

After 10+ years of R/C flying and getting ready to go out to the field with my old and very repaired( make that VERY old, it has been the test plane for no fewer than 6 different engines) LT40 I can tell you why. It's a pleasure to take out for a very relaxing day. It just flies nicely, especially on a day after the holidays when you just want some easy flying. Also, after the holiday, a number of newbies show up with tteir trainers. Sometimes I find it easier to let them a turn at the sticks on mime as a 'guest plane'. Take yours out again...it is fun. Happy and safe flying and New Years to you. Andy

We can make a box of wood.....FLY!!

Aha! If that's the case, I'd swap'em out for another brand. Dr.1 Driver "There's a Hun in the sun!"

Well, this one won't being going out again. Glitch hit with a strong down, wouldn't come out after I released the trainer button. Got one side of the plane back to kit form..lol. It was fun, now passed along to my student to learn rebuilding skills - hey it is a trainer after all. Andy

We can make a box of wood.....FLY!!

Hi 'triguy'. The problem mentioned more than probably does *to some extent* lie with the "properly installed" clause. Of course therein lies the conundrum. :?

On balance of probability, most LT-40 builders/assemblers will be constructing their first R/C model. As I suspect you'll agree, just like covering with 'Choose-a-cote', properly installing Easy Hinges is not only an acquired skill requiring practice as well as an awareness of technique, but due to the nature of CA you only get one go. The inability of (thin) CA to follow "only flow there" instructions any better than the assembler doesn't help. ;) As can be seen by the "more is always better belief" frequently displayed with in everything from epoxying tailfeathers to engining the airframe, over generous application of CA doesn't assist the situation either - as you have already pointed out.

Thus at the end of the day, it doesn't matter what one *should have done*. The consequence is that most novice builders will not install Easy Hinges in accord with the ideal, or the instructions. For that matter, nor do many flyers with quite a few ARF assemblies under their proverbial belt. I say flyers, as most experienced builders of many years will figure it out with a little practice, although I can vouch for a less than satisfactory result on my own first attempts with Easy Hinges, and probably like you, I've been aeromodelling quite a while - since the 60's.

In conjunction with this, I suspect that because of the size, thinness and span of the LT's horizontal stab, some flutter, minor harmonic vibration or torsional stress on those hinges is easily induced and occurring. Given this and the aerodynamic load on that huge span elevator borne by few hinges, it has been both my experience and observation from the anecdotal reports of others, that the LT-40 bears an idiosyncratic tendency for Easy Hinges to prematurely fail - specifically on the elevator.

To reiterate I suspect it a combination of factors elaborated upon above. I'm not suggesting for a moment in general that Easy Hinges are rubbish. I would suggest that much like painting vs 'Choose-a-coting', once the application technique is acquired, they are easier to install, but do present a more difficult task to do so neatly initially.

I think you'll agree that the first time any of us attempted to install them using the recommended technique with just a couple of drops of 'sh*t I didn't intend it to go there!' thin CA per side, not only was it an 'improve as you go' technique, it didn't instill confidence that the hinge would hold under load and it WAS difficult to resist wanting to either pin it or flood the hinge with CA "just to make sure". Of course, experience and hindsight has shown *us* otherwise, but looking from the novice builder's viewpoint one can easily view that same "that's not enough, I'll just make sure" perspective. :]

BTW, I do use Easy Hinges all the time and concur, that proper installation does extend their life and increase efficiency.

cheers

p

Actually Roger, though I'm possibly at fault here, I suspect you are mistaken.

I was specifically referring to the Easy Hinges product SIG supply with their LT-40 kit and others. eg: Four Star 40. In calling them Easy Hinges though, I *was* simultaneously also referring to generic similar style of CA hinges known under their respective proprietary brand labels. Here's a SIG reference for Easy Hinges. Apologies for the long URL. If it wraps, you'll have to cut and past rather than just click.

DR1driver was certainly referring to the product to which I intended to refer.

Could you be confusing them with another polyplastic product I vaguely recall seeing distributed as EZ or Ezy (sic) Hinges? Hence the confusion. I concur that those poly plastic type hinges are utter crap.

cheers

p

Andy I think the LT is a superb trainer for both the giving and receiving of instruction, *and* if I might take the liberty of elaborating further as I should perhaps have in my earlier sentence, initial post instruction accumulation of confidence and skills. It is also a superbly stable general model for the encumbered R/C pilot, whether that encumbrance be one of age inflicted deteriorating eyesight & reflex or simply one of lacking confidence and/or outright ability.

If someone enjoys flying an LT ad infinitum, so be it and I'd neither criticise nor ridicule. But for most of us who've progressed any degree post initio, it is pretty tame and there are more flexible choices which are sufficiently stable and almost as easy to fly and see, but aren't quite as restrictive as the LT-40 (eg: TWM Mfg. Super Stunts 40) - without going to extremes 3D or a pattern ship. Hence the gist of my earlier statement.

I'm sure you understood what I meant, and it wasn't too insult either LT-40 drivers or the model. I loved one myself as my first R/C model and appreciate its worth in the additional roles you have mentioned. For the purpose you illustrate above, I would suggest that the World Models Mfg. Super Stunts 40 on low rates an alternative and preferable choice - not to be misinterpreted as my choice is superior to yours.

cheers p

Excellent reply. I agree completely, which is why I included proven instructions for CA-hinge installation in my post. Like "Choose-a-cote" application, hinge installation DOES require practice. This being said, I still think CA hinges are the "least of the evils" for the novice flyer.

You've also differentiated between ARF flyers and scratch/kit builders very well. ARF models require assembly. Kits and scratch-building require construction.

It's a shame that, with the flood of ARFs and RTFs on the market, building/modeling skills are a lost art.

You correctly assume that I also have been in RC, both flying and building, a long time (25+ years).

Thanks again for the great comments.

Dr.1 Driver "There's a Hun in the sun!"

If the plastic doesn't have a steel pin, toss it. Goldberg supplied both the crappy milk carton hinges at one time (old kits) and the much superior Klett brand.

Don

The latest veersion of the ARF has what I think is the most important mod I would suggetst doing and that is wing bolts rather than those *&!2$$@#*!!! Rubber bands. My experience with the bands was that the instructors at the field had me putting so many of them on that the dern thing wounldn't pop off (as advertised) unless the crash was significant enough to break it anyway. :-) I agree with the springy landing gear theory withthe caveat that you shoudl wait until you are pretty good at landing consistently before you beef it up. Lastly, I gussett the Vertical stab on all my LT's (I always have one n the hanger. I love them as flyers and have even taught mine a few tricks. see my other post). the 30 min epoxy might take care of it, but it can't hurt to make it stronger. I also put gussetts of triangle stock under the horizontal stab another one of those "later" mods is to make it into a tail dragger (Convenntional) plane. the original Kadets were and the LT-25 is still primarily a tail dragger.

Great plane! Love it, Fly it! ENJOY! Mark

My experience with wing bolts on trainers flown by newbies is that a cartwheel rips the top of the fuselage off with the wing. I've only had one plane, a GP Easy Sport, that survived a mishap relatively undamaged because its single wing bolt sheared off on impact. (Combination of dumb thumbs and a stiff crosswind caused the wingtip to hit a fence post while landing.) The main thing to remember with wing bolts is that they're supposed to be strong enough to hold the wing on, but weak enough to shear off in a crash.