Sig King Kobra Build
 

Thought I would start a new thread on the Sig King Kobra showing some pictures of my construction. I will update as I go if there is any interest, but be forewarned I am a slow builder!

These pictures show the way that I am constructing my KK, but in no way am I saying that this is the way to do it. If you have any different suggestions please chime in.

I am an old Sig fan and will be building another Kougar, a small Kobra, a Komander with retracts, and a few others down the road. I have owned and built several Kougars in the past, also one Komet, but this KK project is my first attempt at installing retractable landing gear into a foam wing. I have done so in a built up wing and feel that it is much easier and faster in such.

Happy Building,

Mike

RE: Sig King Kobra Build
 

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RE: Sig King Kobra Build
 

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Mike,
What a great build thread with such impressive documentation. I too am a big fan of the older Sig designs. A weekend seldom passes without my Kougar going to the flying field with me. I also have a King Kobra waiting near the end of a vary long build queue. Maybe this will entice me to move it closer to the front.
Take care...
Jim...

RE: Sig King Kobra Build
 

yes indeed, very well done!
Are you going yo use tricycle or just the mains on the wing?
I thought of doing this on my Kougar, but a retract nose gear would be quite difficult from my POV.
A very nice "How TO" for foam wing retracts.
Keep up the good work.
cheers jollyroger

RE: Sig King Kobra Build
 

jollyroger,

I am building my King Kobra as a Trike and have it set up to provide a 1/2" more prop clearance since I fly from a turf runway. I'm going to use the new O.S. 75 AX. I will get pictures on the nose retract installation posted soon.

On this Kobra thread (small Kobra) several have built them as taildraggers, and they look neat: http://www.rcuniverse.com/forum/m_54...mpage_4/tm.htm
It would also be fun to have the little Kobra set up as a taildragger with small retractable main gear.

Jim,

My documentation started out as something personal and then I had some requests from club members for pictures. I started adding text to describe what I was doing, and it sort of got out of hand, but I have continued anyway. After sending out 3 or 4 updates over the last several months I decided that I should contribute to this forum since I have gained a lot of knowledge from it myself. This is my way of contributing to the outlet that has helped me with my modeling projects, both directly and indirectly.

I miss my Kougar and will build another one day soon.

Thanks,
Mike

RE: Sig King Kobra Build
 

I've got one of these to build after a couple of others get finished. Keet it up, looks great! I like the dowel tip for the retract mounts, good idea.
Iv'e got the Kobra now and it is a great little plane.
MikeB

RE: Sig King Kobra Build
 

Outstanding work Mike!
I'll look forward to seeing the finished aircraft fly at our new field. ;)

RE: Sig King Kobra Build
 

Hey Harry,

I look forward to seeing this King Kobra fly at our new field as well. See you there!

More pictures.

RE: Sig King Kobra Build
 

Mike,

Looking great with much progress since I last saw the project. I too hope to see this one finished and flying at the new field. Keep up the good work. Maybe this will inspire me to get back to building my SIG cub again.

SM

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RE: Sig King Kobra Build
 

The first picture is of the epoxy fiberglass layups for the landing gear and servo bay covers, and you will probably notice that I used the top wing skins for the form. This was due to the fact that the bottom skins where not to net shape over the open areas left by the wheel wells and aileron servo bays. The airfoil is symmetrical so I used the smooth upper surface. Due to the taper of the wing the top right covers will be used on the bottom left wing and vice-versa for the other side. I hope this idea works.

I don't know for sure that I will mess with landing gear covers but just in case I went ahead and made them. The layup consists of four layers of 7781 fiberglass cloth, and one layer of #120 fiberglass cloth on top for a smoother finish.

The aileron servo bay covers are three layers of 7781 and one layer of #120 cloth. The aileron servo will be attached to the inside of the cover. If the thickness is not enough to be flush with the wing skins I will add more material to the edges to do so, or skin the outside with 1/16" balsa and sand it down.

I use an epoxy laminating resin that I get locally but is similar to Aeropoxy PR2032/PH3660. Aeropoxy makes some really nice products and you can get your composite materials from Aircraft Spruce and Specialty or Wicks Aircraft Supply.

The second picture shows both covers laying on the wing that they will be used. The landing gear cover is ruff trimmed and laying in position. The aileron cover is in position, but does not sit flush with the outer wing skin. It will need work to bring it up flush. If I had used another two layers of 7781 cloth this cover would have been very close to flush, maybe two or three thousandths under, but close enough.

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Looks great!! I am really enjoying this build thread. Keep em coming!

SM

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Subscribed. Just fantastic photos of your build; I just finished a Kougar myself and have always wanted to build the King Kobra.

RE: Sig King Kobra Build
 

scalemaster90 and submikester, thanks for the positive comments. SM, you had better cycle those batteries and get ready to fly at the new field!

HEY SIG, YOU SHORTED ME 1.5"!! :D

After bonding the wing halves together I noticed that the wing span didn't look like it was up to spec. I figured it was just an illusion since the wing tips had yet to be installed, but I measured and my eyeballs were correct. The literature says the wingspan is supposed to be 58.0", but the wingspan on my KK is only 56.5" with the tips in place. I measured the chord lengths and compared them to the plans and there dead on, so I'm at a loss as to where that 1.5" went!

For your building information, each of the foam wing cores measure 26.75" in span (53.5" total) and the wing tip blocks total another 3.0". Measure your materials before you start for comparison. I did not call Sig about this issue. It is what it is!

In the wing pictures you will notice that I left the wing tips squared off. I built my last Kougar this way and I liked it, so the KK will be the same. The aileron servo wire tube exit and retract air line tube exits are barley visible.

The fuselage pictures show the nose gear retract in place, and notice that it is offset to one side. I did this so the wheel would be on the fuselage centerline while retracted (I believe this is mentioned in the instructions). As set up the coil on the nose gear wire will not be visible from the exterior in the extended position, and the tire will be completely inside the fuselage while retracted. The pictures in the manual show the nose wheel slightly exposed while the gear is retracted.

I originally set up the firewall for two engines: a Saito 91 in the vertical position and a S.T. 61 ABC in a canted position for a Tuned Pipe. I originally started this kit two years ago this month and got side tracked with some other projects thereafter, and in the meantime I decided to use the new O.S. 75 and save the .61 for the next Kougar project. I'll have to see how the .75 is going to fit before I get too far along with the fuselage.

In the picture of the plans you'll see my notes where I raised the top surface of the nose gear retract mounting plate (TF) up to the fuselage centerline. If needed for C.G. purposes this leaves room above TF for batteries and/or the retract air tank. The 16 ounce Hayes fuel tank will be located between fuselage former F2 and F3. Former F3 will be modified and another complete bulkhead installed just behind the fuel tank. I'll get pictures posted of this later, as I'm not that far along yet. There is still plenty of room between former F4 and the fuel tank for the elevator, rudder, and retract servos.

Mike

RE: Sig King Kobra Build
 

Mike,
Great job on the build, and the thread.

See you at the field,
Michael

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Say guys,

What is the best way to replace hinges in the vertical stab? My kougar hinges are tearing and need to be replaced.

Thanks

Mike from Michigan near Greenville.

RE: Sig King Kobra Build
 

Mike from Michigan,

I would suggest separating the rudder from the vertical then run an Exacto blade down each side of the hinge until you can get it loose enough to pull out. You can replace the wood at each location with small pieces of balsa bonded in with Gorilla Glue. Sand this smooth and re-slot each location for a new hinge.

If there ends up being more glue in the slotted area than balsa I would not use CA hinges. Although, I do recall reading on another forum where someone used Gorilla Glue on the CA hinges with no problems. I guess if the hinge is lightly dampened and inserted into the glue filled slot that the Gorilla Glue will wick into the fibrous material on the face of the CA hinge. But, you do have to be careful since Gorilla Glue foams up a bit.

It's your choice, but I would probably go back with Dubro pinned hinges or Robart hinges if the slotted area is more glue than balsa. By the way, I only use CA hinges from Radio South and I have never had a failure since using them, i.e., many, many years.

Maybe someone else will speak up if they have a more simple way of fixing your hinge problem.

Hey Michael, I'll see you at the new field when it's ready. Hopefully that will be this coming weekend. Go make some chips and dust on that Sr. Telemaster!!

Mike

RE: Sig King Kobra Build
 

Watch out for this potential building error!

The fuselage bulkheads are precut but the wing dowel holes are not drilled. You have to use the blueprints to layout the wing dowel locations on F2. In my application the dimensions on the blueprints did not work and the center of the holes did not line up with the centerline of the wing leading edge. The wing sits in the fuselage perfectly so I'm at a loss as to why I have to make a correction here.

Anyway, I will have to plug the holes in F2 and re-drill at the correct location.

Mike

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i have a question about your ailerons if you've got that far yet. of course the trailing edge is square to the wing but the ailerons are not true elongated triangles. they are really a elongated triangle half with a beveled leading edge as best as i can describe them. i don't like the way they droop when laid flush against the wing trailing edge. what is your opinion or intentions? thx, david

RE: Sig King Kobra Build
 

David,

My aileron stock was not usable because the leading edge was not thick enough to match the trailing edge thickness of the wing. I went to the my LHS and found some beveled ailerons that will work, and as a bonus the balsa was a little higher grade (more dense), and were already shaped like the bottom aileron side view in the picture below.

The picture below was taken from page 11 of the instruction manual and the top view is the shape of the aileron as it comes out of the box. The bottom view is what it should look like after it is shaped. Notice that the dimension that you are to mark and sand to is not the same on top and bottom. This is due to the shape of the aileron as Sig provides it. If you mark and sand the aileron just as the instructions show here your aileron will come out with a beveled leading edge that is perpendicular to the chord line.

If you have a stocked hobby shop nearby you could take a piece of your aileron stock down there and find two that are the correct size and already beveled. I believe mine cost $3.00 each.

I've had a long day and I'm tired, so I hope my rambling has not confused you. [sm=tired.gif]

Mike