It's time to build a new LT-40 club trainer this winter. I like this plane a lot, but it's a bit too much of a floater, which makes it hard for some students to land. My question is, how much to clip the wings. Would taking out two bays on each side be too much? I'd like to hear from someone who has done this.

If it matters, I use an O.S. .46 engine and a Fults dual strut nose gear: otherwise no modifications.

Raise each aileron 2-3 degrees, it will stop floating.

I know that I can make a Hangar 9 Alpha 40 63" wing fit a Kadet MK II 57-1/4". You might see if someone in your area hasa wing from each planethey would loan you for testing. That wing is longer than the Kadet MK II, so it flew like a kite. The Sig 1/4 scaleclipped wing cub has a 86" span while the regular 1/4 cub has a 105". That's about a 82% of normal span, which would leave the LT-40 that has a 70" span with about a 57.4" span. That's about the same size as a Kadet Mk II.

Joe

Just currious, I've been teaching wiith the LT 40 for nearly 15 years now, in Oklahoma winds up to 16 MPH.

I think it is just about the perfect trainer, esp. from the stand point of teaching how to build a kit. And I have flown a wide varity of various kit and ARF trainers.

The ONLY time I've ever seen a KADET "float" is after the student is diving at the runway, instead of flying a proper approach. There have been other factors, too nose heavy, not enough elevator throw, idle set too high. But when it is set up properly one can usually set it down full stall on the mains with no float at all.

How is yours behaving so that you believe it is a floater?

If you are questioning me about the Kadet MK II being a floater, I don't have that problem anymore.At the recommendaton of a friend I puta 1/4" wedgeunder the TE of the wing and itflies fine. It has a Super Tigre 40 motor that idles just fine. This was an old garage sale find that needed to have some bugs worked out.

My LT-40 has minimal elevator authority - definitely needs more (more, more - an echo) ...

Winds up to 16 mph are no problem; I've taught people in higher winds than that. A good headwind reduces your ground speed and makes it easy to land. But when it's calm, it takes quite a while for it to come down, even at a nice slightly nose-up attitude. We have a fairly short runway. And if you slow it up too much, the ailerons become ineffective, which doesn't bother me, but it's hard on beginners.

Most Sig planes I've flown have a very low wing loading. I built a Mid-Star 40 last winter with one bay taken out of each wing and the wing tips squared off (which takes away almost another one bay's worth on each side), and it's a real pleasure to land. It's not that it comes down really fast, but it doesn't stop sinking the minute it hits ground effect, the way my 4-stars used to do. (I have a Kadet Senior (with ailerons added) too, and that one lands beautifully: just the way I'd like to get the LT-40 to land.)

There is another solution to clipping the tips.

Bolt a pound of lead on the CG on the bottom of the fuselage. Keep adding weight till it flys like you want it too.

Clipping the wings is easier and cheaper, and the wing won't take up as much room in my car.

I think I'd use two aileron servos and do a (mild) spoileron mix before altering the airframe.

Well, I've never used spoilerons. I'm reluctant to make my first attempt on a plane that already has somewhat ineffective ailerons at low speed.

I like the LT-40 a lot, but it, like a lot of other trainers, dates from pre-buddy-box days, when the main goal in designing a trainer was stability. The idea seems to have been, if the student gets in trouble he can take his hands off the controls and hand the transmitter to the instructor. For that, you want a plane that doesn't do much of anything when you take your hands off the sticks (and a student who doesn't get into trouble near the ground). Now that we have trainer cords, a more-responsive plane seems to me to make more sense as a trainer. Clipping the wings should make it easier to land and improve the LT-40's very low roll rate, too. Experience with other planes convinces me that some shortening of the wings will be good; the only question is, how much? If I don't hear from someone who has tried it, I think I'll start with one bay on each side. If that doesn't change much, I have a band saw.

I clipped a single bay off each panel on an LT-40 after an accident damaged a wing tip. I didn't like the way it flew afterward, much to my surprise. While it did make it easier to land, it lost the effortlessness of flight in simple acrobatics. Where the stock version could easily do outside loops, it struggled with less wing area.

My suggestion is to move the CG to the back of the position shown on the plans, crank up the throws, and put on a large diameter low pitch prop. You can also decrease the decalage (wing incidence and down thrust), but re-balancing it gains the most bang for the effort.

Thanks for the input. I already have the CG pretty far back: another oddity of Sig kits is that their recommended CG positions tend to be too far forward. I do have a damaged but fixable extra wing. Maybe I'll mess around with that first.

I'm looking forward to your efforts. I have a LT-40 to build one of these days. Iwould try different length wings borrowed from other trainers before you cut one of yours up. Theyprettymuchall have the same wing chord and dihedral.

Joe

Hi Top_Gunn, I am also a really big fan of the LT-40. I have flown/instructed on at least 10 different ones, both ARF and kit built. Ihave always thought that they landed better than most trainers, nice and smooth. I also have never really had any issues with float at all...unless your approach is too fast.

Let me explain something I have noticed/learned in 16+ years of flying, and at least 12 years of instructing. Most people have troubles with landing because they are afraid to slow the airplane down. Many guys are deathly afraid of stalls, because they do not want the dreaded "tip stall" and crash, so they approach at too high of a speed and then try and force the plane on. This of course results in either porpoising down the runway, or floating into the tall grass at the end. Stalls are nothing to be afraid of, I practice them all the time, and I get my students to practice them as well. Get used to the feel of the airplane at slow speed, and to recognize an impending stall, and know what to do about it. This enables you to comfortably approach a bit slower and have better landings.

Another thing, and this is a "problem" with the Kadet LT-40, Senior, and Seniorita series of airplanes. They have a lower wing loading and do like to fly slower than most other trainers. Guys who are used to flying/instructing using faster airplanes such as the Eagle 2, Tiger Trainers, Nextars, etc will naturally fly the Kadets the same, not even realizing it. This again causes them to approach too fast and float too much. It really is simply a matter of learning the different flight characteristics in this case.

The other problem that I have seen that causes most guys to float too much on landing is the prop size. Typically, when you go into a hobby store and buy a .40, you will get a 10X6 prop to go with it. This maybe is fine for a faster sport model, but for a slow flying trainer, it is too much pitch. That extra pitch might be just enough that it will not let you slow down, couple that with a slightly high idle, and you have an airplane that doesn't want to come down. Remember, pitch gives you speed, and diameter gives you thrust. On a slow flying trainer type aircraft, there is a "top speed" that the airplane will fly. Sure you can always put bigger engines and steeper props, but the speed will hit a point that it no longer wants to go faster. So, why not prop accordingly. For example, on a few of the LT-40's I have flown, they were powered with .40 engines, so I had them use either an 11X5 or a 12X4. Contrary to popular belief, even 4" of pitch is enough to hit that "top speed" with an LT-40. The other advantage of a larger prop diameter is more drag when the throttle is at idle. This will also help reduce the float. For an OS .46, I would use a 12X4 or 5 as long as you have the prop clearance.

As far as clipping the wings, there is no way Iwould do that. You would eliminate what makes the LT-40 so nice of a trainer, the slow flight, and stability. Personally I would not use any spolieron mixing either, just one more thing to be trying to fiddle with at the most critical point in the flight. The less stuff you have to mess with on short final, the better. As my full size instructor used to say.......first priority is to FLYTHEPLANE, everything else can wait.

The main goal in any trainer is stability, buddy box or not. More responsive airplanes for the most part make it harder to learn, because things just happen too fast. A student will get themselves into trouble so quickly that they don't even know what they did to get it there, and they have no time or ability to react properly. They will get stressed and try and right it themselves and overcontrol, making the situation much worse. Even with a buddy box, by the time the instructor has it, it may be too late. A good trainer should be slow, stable, and yes, nice and docile. Less responsive is better, it gives the student more time to react, correct, and fly. Less takeovers by the instructor also will help boost the confidence of the student.

Hi Seamus, can I make a quick suggestion. Try moving the CG back a bit at a time until it flies the way you like it. If you are comfortable flying on your own this should not be an issue.

rhall - you make excellent points. My LT is laid up waiting for some post off runway acrobatics. Just after getting airborne - dead stick. We have plenty of prairie dog holes and the LT found one.

I mis-typed - thinking ailerons I typed elevator. It has plenty of rudder and elevator but rolls - well you start today and end tomorrow. After the snow melts ....

Ahh yes, my brother-in-law had a GMS .47 on his LT-40 and we could not keep that one running for anything. We got lots of deadstick practice with that airplane. But we were actually flying off a private strip for full size airplanes so we had 2500 feet of smooth grass to play on

You know, moving the CG back might help a wee bit with the roll rate as well, plus, yo could increase the aileron throws a bit. Another trick that I like to use the mostthough, when you are doing your roll, use a bit of rudder to help it around. NOTE: this will only work if you have stock dihedral. If you have flattened the wing at all, the rudder will not help it roll. By the way, a stock LT-40 CAN be made to roll using ONLY the rudder

But all that being said, the LT-40 is a trainer, it is not meant to be super aerobatic. Look at it this way, when you go to get your pilots license for full size airplanes, you do not start in a Pitts Special or Extra 300. You start in something like a Cessna 150 or 172. Why not give your R/C beginner the same treatment, start with docile, slow, and easy to fly.

If I want real roll rate I'll put my SSE on high rates and laugh my way across the sky - quickly losing count

I'm just thinking in terms of a decent roll rate for a trainer - likely with (impatient)someone on a buddy box.

Ahh, I see. I guess I have never thought that to be a concern as I have already explained my thoughts on trainers.

An instructor is kinda like a reserve parachute when your main has failed. Most times it works, but sometimes it don't. A forgiving design responds predictably 100% of the time barring mechanical failures.

When the learner bounces the lt40 off the ground on landing and flys it at practically zero air speed 5 feet off the ground then you will be glad off the large wing, I know.Still have mine, was my first kitand plane and now has over 150 flights for sure.

Its NEVER going to be a nimble plane and does what it is designed for, it is easier to fly than just about any arf trainer you can buy so great for that student that is as rough on the sticks.