SIG Kadet Mark 1: Reimagined - RC Groups
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Feb 11, 2013, 08:16 PM
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SIG Kadet Mark 1: Reimagined

Hello y'all!

I have always been a fan of balsa-built aircraft, and I have completed many projects using balsa as a primary construction material. I know I am much to young to be nostalgic, but building a balsa plane sure does to have a nostalgic effect!

My grandpa built a Sig kadet mark 2 during the 70's or 80's and flew it for several years before permanently shelving. I can recall many, many times when I snuck into my grandparents' basement closet and stared up at the top shelf, at the plane that sat up there.

When I was 12, my grandpa sold his kadet. Amazingly, he still had the original box, which was full of balsa parts which had been intended to be built into a spare wing. Needless to say, he never got around to it, and he gave the whole box to me. It included wing ribs that he had cut, sheets, squares, and more. And most importantly of all, it contained the manual that he had used to build his plane. I valued that beat-up booklet as pure gold, and I spent many hours reading and re-reading it! I think that I can safely say that it was that book that drew me to r/c flying. Anyways, in the back of the booklet, there was a single-page advertisement for the Kadet junior, the kadet mark 1, and several other SIG aircraft. I particularly liked the picture of the kadet mark 1, or the original kadet.

Last year, with the advent of employment for myself, I decided that I would build the original kadet. I would have loved to build the actual kit, but since the original kadet has been out of production for some time, they are hard to come by. Sig used to sell the original plans (i actually think they still do), but I decided to make my own planes.

So: I knew that the kadet mark 2 and original kadet shared a firewall and cowl, and I knew the exact dimensions of the mark 2 cowl and firewall. So, I printed off several pictures from the net; each picture was of the plans for the kadet mark 1. Using a bunch of mathematical ratio calculations and known measurments (which I won't go into), I was able to produce a full size, to-scale plan for the kadet fuselage and wing. I then made another drawing, this time scaling the entire deal down(I don't remember by what factor)

Then, the fun of building began! The entire airframe was construced following the original kadet instruction manual, using the materials and techniques that it described. 1/8th lite ply and balsa was used for entire construction.


Here is the book(s) that started it all, along with the plan I drew up.
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Feb 11, 2013, 08:19 PM
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Alrighty then!

So, here is a quick shot of the hardware I will be using.
Feb 11, 2013, 08:22 PM
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the fuselage side(s) are cut out of 1/16'' balsa. Stringers were applied in the appropriate spots using titebond. Most stringers were 1/4'' balsa. The nose double was balsa as well (as in the original kadet). It was made from 3/16'' balsa, and then epoxied in place.

In this photo, I had already epoxied two strips of 1/8'' plywood in for the landing gear. I will be mounting the landing gear in the same way as the sig Rascal.
Last edited by Universe; Feb 11, 2013 at 08:34 PM.
Feb 11, 2013, 08:52 PM
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While not pictured, the next step was to stack the two sides together and sand them even. So I did that.

There are only three major plywood parts on the original kadet: the firewall, the former behind the firwall (or F-1, whatever) and the plywood wing joiner. Here, F-1 is cut and sanded, prefitted in a fuse side, and then glued. A 90* triangle was used to keep it square.

I had also cut out "C 1," a balsa part that will be used as a guide for the nose balsa. It was titebonded to F1. Notice the small, circular notch in the bottom corner of the hole in F1. That is going to be used to allow the pushrod for the nosewhell through.

For all of the plywood and high-stress parts, I used Great Planes 30-minute epoxy. I actually had to heat up the resin several times througout building the plane; the epoxy is a few years old, and the resin seems to solidify fairly quickly in its old age.

Feb 11, 2013, 09:54 PM
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The horizontal and vertical stabs are cut from 3/16'' balsa. Bother were cut in two separate pieces, and then glued together with titebond. once the glue was dry, all the necessary edges were sanded smooth, and so one.

Some to think of it, before I glued the stab components together, I slotted out for the hinges. The rudder will be using my two remaining nylon hinges--these were a part of my grandpa's 30+year old parts collection--while the elevator will use a floppy disk for hinges. Over in the scratchbuild foamies forum, I have read of people using the floppy part of the disk for hinges. We'll see how that works!
Feb 12, 2013, 10:11 AM
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Latest blog entry: AIrcraft I've built.
Feb 12, 2013, 01:40 PM
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Originally Posted by mnowell129
Indeed. I am shooting myself in the foot right now. Thank you!

But regardless, I did have a lot of fun drawing up and scaling down the plan by using only was a nice way to put some of my math skills to the test!

Feb 12, 2013, 06:06 PM
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Here are a few more pictures.

Shown is the landing gear. Like the original, the plane will have a trike configuration. All of the gear was bent out of 3/32'' music wire. I hate bending music wire. It was like trying to walk through a brick wall.

As well, here is the servo tray and firewall! I am using an EMax CF2822 motor from HK with an 8x4 eflite prop. As usual, firewall was cut using a coping saw out of 1/8'' liteply. 4-40 blind nuts were installed in the proper locations. For the motor itself, I will be using aluminum standoffs to place the motor at the correct distance from the firewall. The standoffs I used were 1'' long.

As for the sevo tray, it was cut from 3/32'' balsa. I then epoxied 1/64'' plywood strips in the locations where the servo screws would be placed.

Feb 12, 2013, 06:20 PM
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Here is a quick comparison of the original Kadet and my own:
Wingspan: 54''
Length: 42''
Dihedral: 3* per panel
Weight: 5 lbs
Engine size: .35 - .40

My own:
Wingspan: 40''
Length: 30''
Dihedral: 3* per panel
Weight: 1.3 lbs
Engine size: probably .049 or electric equivalent

The wingspan on my Kadet was not scaled down by the same degree as the fuselage; while the actual rib length was scaled down by the same degree, I made the wings slightly longer (hope that makes sense!!)

Feb 12, 2013, 06:26 PM
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...And the last set of pictures for today:

The fusalage sides are glued together using epoxy. The landing gear is all installed; I thought that I had more pictures of the landing gear installation and construction by I don't. The top and bottom of the fuselage has not yet been skinned. I will use 1/8'' balsa sticks to brace the top and bottom of the fuse before I glue balsa sheeting on top.

In the second pic, I had already drilled out 3/16'' hole to accept the dowl that will hold the wing elastics.

Take care!

Feb 13, 2013, 11:29 AM
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Lookin' good. Looks pretty darned close for just eyeballing it.
I always liked the look of the old Kadets
Feb 13, 2013, 06:53 PM
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Thanks! I like the simple yet (somewhat) elegant lines of the kadet as well, even if it is just a trainer!

Here is a quick shot of the inside. You can see the servo tray, and most importantly, the main landing gear. I had bent the gear to shape, then, once the fuselage halves had been glued together, the landing gear was slid into the trough created by the two plywood strips. JBweld (an automotive type epoxy) was used to glue it in.

As you can see, in this pic, the bottom of the fuselage was already sheeted. My Grandma (grandpa's wife) donated the ring of sewing pins, which I use profusely when working with balsa! Titebond was used for all of the sheeting.

Michael Arendt
Feb 13, 2013, 06:58 PM
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Alright, so here is the best picture I could dig up showing the balsa sheeting on the nose. The 1/16'' balsa was dampened with water to make it pliable, then titbonded and pinned in place. 1/8'' balsa stringers beneath the sheeting gives it support.

Above F-1, I used a soft balsa block to carve a nice, rounded shape for the transition from the fuselage to the center of the wing.

Feb 13, 2013, 07:11 PM
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Moving the wing!

Every airplane needs some means of generating lift.

The wing was constructed using the technique outlined in the Kadet manuel. On the original Kadet, on either end of the wing was a smooth plastic "cap." At the time that I was building the wing, I did not yet have a vacuum forming setup, so I carved the caps out of balsa, then hollowed them out until they had an identical weight.

Funny...perousing my files here, it seems I don't have any pictures of the wing construction, even though I seem to remember busting my rear end building the darn thing!
Feb 15, 2013, 10:23 PM
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Vacuum Forming

All right...done school for the week...

While I very well could have, I did not want to fly without a cowl. The original kadet uses the same a.b.s cowl as the Kadet Mark 2; if I were building the full size plane I could simply order a cowl from SIG. But since my version is after all downsized, I had to improvise.

Using 1/2x3'' balsa sheeting, I was able to make a balsa block, and then carve out the rough shape of the cowl from it. I then sanded, carved, and sanded again, then filled any dings or dips with balsa filler. I had originall intended to use this balsa cowl as my cowl.

But then I watched a youtube video on vacuum forming, and I just had to try it!
So, I went to my LHS and bought a pack of .020 and a pack of .040 styrene sheets.

Then I had to build a basic vacuum unit. Essentially, what I did was make a box out of 1/2'' plywood, with dimensions of about 15x14x4'', with a hole in one of the sides. I was lucky enough to have a hole saw of the same diameter as my shopvac hose.

Anyways, all corners/seams of the box were then sealed with generic caulking (something that my dad dug up from the basement). For the top of the box, I used a piece of compressed card board (or something) with holes drilled all over the top, each hole being roughly 3/4'' apart.

Then, a plywood frame was made in the same size as my plastic sheets. A plastic sheet would be stapled to this frame. Then, I would turn my oven up to 400*F, and put 'er in for about 4 minutes, or until it was sagging nicely.

Once the plastic was almost ready, I would place my balsa cowl mold on the vacuum box, and plug the shopvac hose into the hole in the side. The hot plastic and frame would be removed from the oven and immediatly placed on the box, over top of the mold with the vacuum on. I'll admit, it took me 5 tries before I got the cowl that I used.

At first, I used rather thin .020 styrene, and I had a lot of trouble with it pulling free of the staples. It also was subject to webbing, and it would crack easily when I pulled the mold, or plug, out of it. I had better luck with the .040 styrene; it was sucked down nicely, and I was able to massage out most of the webbing while the plastic was still warm.

More to come.


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