SIG’s

Kadet LT-40 ARF

Basic ARF Trainer

By Dick Pettit

A long time ago, in a land far, far away (Ed. better known as Massapequa, NY), I knew the cousin of a schoolmate who lived right down the block. At that time I had absolutely no interest in model airplanes, and I don’t think my friend’s cousin did either. (Ed. Note: Actually Dick, I had already designed my first twin jet fighter for CL and had flown a foam P-51 CL airplane. My cousin, Ed Granelli, was into RC then and I am now finishing an airplane he started over 50 years ago.)

We were all in high school, and cars, girls and more cars were tops on our list of things to be interested in. Anyway, a few years ago I read that my friend’s cousin was writing for Model Aviation Magazine, the publication of AMA, and since I had been involved in R/C modeling for a while by that time, I got back in contact with my friend’s cousin.

By the way, my friend’s cousin just happened to be Sport Aviator’s Editor, Frank Granelli.

We met again at the Toledo Expo and made plans to work on several projects together, the first of which is this Product Review of a very popular trainer aircraft, the SIG Kadet LT-40. This airplane has been available for a number of years, but has proven itself to be a capable basic glow engine-powered trainer that can be assembled by a beginner, maybe with a little help from a more experienced modeler, and can be used to introduce that builder into stable, controlled flight of a radio controlled model airplane.

The original LT-40 has been a famous basic trainer from the mid-1960’s when it was known as the SIG Kadet. The wood-kit Kadet was modified in the 1980’s to become the Kadet II. Finally, the ARF version was introduced and became the Kadet LT-40. This airframe has given wings to literally tens of thousands of RC pilots during the last 40 years or more.

Photo 1

Arrangements were made to test a brand new Kadet LT-40 and an appropriate .40 size engine. I could use some servos and radio equipment I had in the workshop gathering dust to complete the airplane. But that’s not the way I wanted to do it. It stands to reason that a modeler with more than 25 years of building and flying experience could probably put an airplane of this type together in a few hours, probably without the help of the instruction manual.

My plan was to enlist the help of a true beginner in our hobby, working closely with him to explain what all the various terms and words meant, and to make sure the airplane was assembled correctly and safely. The beginner would then enlist the help of a trained flight instructor to allow the airplane to be flown safely and to provide flight instruction to the beginner.

So whom do I pick? All of my flying buddies already know how to build and fly a trainer, or at least I hope they do. I have a few neighbors that may want to learn to fly, but I don’t think thy have the time. One or two co-workers have expressed an interest in my hobby, but since RC airplanes do not use a video monitor or a joystick, I’ll have to rule them out as well.

But there is one person that is available all summer, he’s the right age and he always enjoys watching me work on my airplanes in the workshop. That’s my 9 year old grandson Cole Setliff, who lives in Reidsville. NC. I’ll check it out with my daughter and her husband, and I’ll have Grandma pick him up and bring him to the house for a few days of airplane education.

Why did we pick the SIG Kadet LT-40 ARF? Here’s what SIG says:

“America's best R/C trainer aircraft is now available in an Almost Ready to Fly version. This is no unproven, overweight, hard-to-fly airplane. The Kadet LT-40 is used by flying instructors because it is known as "the easiest to fly" trainer throughout the world.”

“The Kadet LT-40 is easy to assemble in only a few hours work. Flying it is a breeze. Its large size makes it easy to see and docile in flight. It behaves perfectly in flight with “Hands Off" stability, unmatched by others. Slow flight tendencies are sure and steady, making those all-important takeoffs and landings nothing to fear.”

“Start off right. Start off with a Kadet.”

In my experience, the SIG Kadet LT-40 ARF is one of the best trainer airplanes for any newcomer to the hobby. It has a large, easy to see wing and fuselage, it has tricycle landing gear, it has ailerons, it can be powered by a moderately priced 2-cycle glow engine and it is easily assembled by a beginner with just a little help from a more experienced modeler. Once it has been flown and trimmed by a more experienced pilot, it is stable, gentle and easy to see in the air. All these attributes make the LT-40 a very good basic trainer airplane.

(Ed Note: I have to agree here. The Kadet, in all its many forms and variations, has proven time after time to be one of the easiest to fly basic trainers ever designed. I have probably flown a dozen versions of OPA (Other People’s Airplanes) Kadets and loved them all.)

I guess that about says it all, so let’s get started assembling the SIG Kadet LT-40 ARF.

Photo 2

The Kadet LT-40 and the AviaStar® engine arrived here at the shop a few days ago and I opened the box to make sure everything arrived OK. You can also that I’m holding an engine box in my hand that contains an Aviastar .46 glow engine. SIG offers this engine as part of a combination package with the Kadet LT-40 ARF for about $180.00, a very decent price for a trainer and engine. I’ll be running the engine on my test stand before mounting it on the Kadet.

Photo 3

I had performed a few assembly steps before my grandson showed up at the house, but here’s my reason. It takes almost an hour to cut out the self stick vinyl stickers and they are applied using a liquid soap such as window cleaner or airplane cleaner to “float” the stickers onto the airplane surfaces (Ed. Note: See Sport Aviator’s Liberty review article for complete details on this decal application method.). The excess liquid is then removed using a squeegee or a piece of thin balsa wood and it is allowed to dry overnight. Since my grandson would only be there for the weekend, I wanted to get any assembly step completed that took more than an hour or so. You can also see that every major component is inside a plastic bag for protection from the elements.

There was a rather ominous hole in the bottom of the kit box that went through to the inside. I opened the box and removed all the parts, finding only a small dent in the underside of one wing panel. I took the time to get out my heat gun and covering iron to shrink the few wrinkles from the AeroKote™ covering including the little dent. This process took a little more than an hour.

Photo 4

I also wanted to make sure that everything that was needed to assemble the LT-40 was inside the box. The assembly manual, with plenty of photos and drawings, was supplemented by the SIG book entitled “The Basics of Radio Control”; a nice addition for the beginning R/C modeler.

Photo 5

The kit box also contained all the hardware and accessory parts needed to complete the assembly process. There are formed metal landing gear legs with a spring type steerable nose wheel, a set of very lightweight foam wheels, a fuel tank with fuel tubing and other plumbing, several wood parts including a heavy dihedral brace, a suitable plastic spinner and all the needed nuts, bolts and screws to put things together as well as an adjustable composite engine mount that I had mounted to my engine test stand and is not seen in this photo.

All the parts on the inventory sheet were in the kit box and I put everything back in their plastic bags, waiting for the weekend when my grandson would show up at the house. He still does not know that he is going to build an R/C airplane with his grandfather’s help.

Photo 6

Photo 7

He arrived at the house Friday afternoon and I told him what we were going to do that weekend. Inside the workshop, I showed him the kit box and he began to perk up a little, after looking a little puzzled when I told him that we were going to build an airplane and fly it all in the same weekend. He opened the box and began looking at what was inside.

Photo 8

I asked him what would be the first thing that we should do when we opened the box and he answered exactly what I had expected. He said “take everything out”, but I added a little to that by mentioning that we should read the instructions first. So, with instructions in hand, we began to inventory all the parts in the SIG LT-40 ARF box.

Photo 9

Photo 10

My 5 year old granddaughter Paige came into the shop at that point and she started helping Cole with the inventory process, despite the fact she had absolutely no idea what she was actually doing. She would pick up a part and ask Cole what it was, and he would tell her as he checked it off the list of parts in the manual.

We checked everything off the list except for 2 parts, the wing bolt plates and the aileron connectors. We looked around and found them already installed on the wing panels. It was time to get down to the assembly process.

Photo 12

Photo 13

We started with hinging the fin to the rudder using the Mylar® hinges provided and thin CAA. The hinge slots are deep enough to allow the hinges to push all the way into the slot so I used a handy modeler’s hint by using straight pins through each hinge at the exact center to keep them from going in too far (Photo 12). Once all the hinges are installed, the other part is lined up with the hinges and pushed all the way onto the hinges. (Photo 13) The pins are then removed and 3 or 4 drops of thin ZAP is applied to each hinge, top and bottom. This process was repeated for the stab and elevator hinges and the wing and aileron hinges.

For complete details about installing these hinges, read the Sport Aviator article “Installing Mylar Hinges” in the Flight Tech Section.

Photo 14

Joining the wing is a process that needs to be completed quickly due to the possible early curing of the epoxy used to keep the wing panels together. Here’s the process as shown in the manual and we followed it to the letter (Photo 14)

Photo 15

Photo 16

Once all the epoxy was applied, both inside the spar slots and on one center rib, and the spar inserted into the slots, I used rubber bands on the aileron control arms (Photo 15) and a small clamp on the front wing mount stubs (Photo 16) to keep things in place while the epoxy cured.