twn

Well I’m still out of work and I’m going out of my head with little to do.

Through long thoughts and serious temptation to build my Goldberg Extra 300 (seriously I [sm=tongue_smile.gif]REALLY[sm=tongue_smile.gif] wanted to build it, drooling even!!) I decided to build my Sig King Kobra. If I don’t do it now I might never once I make the jump to 35%. I originally bought this kit 3 years ago to be one of my transition planes. I was going to go from the kadet to the midstar to the king kobra and on and on but I got side tracked to a sig somethin extra (BTW a great little fun fly plane but it creates a lot of bad habits in flying.) Then I jumped to a 60 size gp extra 300 and then to large gas, 50cc extra 260 and a 50cc ultimate. Along with many other planes including a recent goldberg ultimate (to which I seriously enjoy)

When I bought the King Kobra I had no knowledge of pattern flying or even aerobatic flying. I was told that it was a nice flying aircraft and a good 3rd plane for somebody with intermediate to advance flying skills and I figured that I would be able to handle it after 2 planes… But it got shelved. When I met my imac buddy, Stacy and his dad, Alec I learned a lot about precision flying. Alec was a pattern champion back in the day and is still an awesome pilot. Watching Stacy fly is unbelievable! Anyhow prior to meeting Stacy and Alec I was one of those flyers who wanted to go straight to 3d flying. When I started flying my Kadet 3 years a go I watched my buddy Rory, a great guy who has helped me out a lot do some fantastically crazy stuff with his ultimate. I was hooked and desparetely wanted to do that kind of flying fast.

When I met Alec he slapped me hard with the proverbial pattern stick. His advice was to stop the 3d and start learning pattern then advance to imac and then move into 3d or I will be one of those guys who can only hover and flat spin… After flying with Stacy for a year I knew he was right and I learned a lot in that year. Not many clubs have guys with as much skill as pilots like Stacy. We are blessed and VERY grateful to have him as a regular here. I spent a lot of time standing beside him and focusing on the sticks and the plane. It was more important to me to watch what he was doing rather than gaze on the incredible flying, which was very easy to do… lol It was incredible it didn’t matter what maneuver I asked him to do, he did it without hesitation. About 4 months ago I started doing rolling circles and some sequences and I'm very excited about it. LOL It helps to have talent around because any time I do a dead pass I get swatted!

By trying to dive right into 3d from sub-intermediate, precision was thrown right out the window and I had no idea the negative impact it could have on my flying. After learning that Stacy flew pattern for years on old school pattern ships with strong older engines like Rossi I have been tossing the idea of building the King Kobra, an old school pattern flier and power it with either a 60 or 75. I will ask Stacy what his favorite choice of old school pattern plane and engine was and post it here.

Anyway enough of memory lane. On with the build. This will be my first foam core and I intend to use the polyurethane glue to skin the wings. I will cover the plane with ultracote to keep the weight down (no glassing.) I am not going to use retracts as I have to keep the cost down on this plane with x-mas and all. The other half would be none to happy to find that I was spending money this month or next month as January is always a broke month trying to catch up to the grotesque money we spend at Christmas… But my other half loves Christmas and it gives her something to look forward to every year. For her Christmas starts in early November!

I will be using the King Kobra for nothing but pattern and prescision.

I have most of what I need to build the plane. I would like some input on servos and engines. I have some 475 kicking around in good shape and 1, 635. I wonder if the 475 will be strong/fast enough for this kind of plane with either a 60 or 75 in it. I have never flown a prop jet. I see that the control surfaces are small so do they need strong servos? Does it need fast servos? 475 @ 4.8v is like about .24 for speed which is incredible slow. At 6v they are .20 a bit better but I have no idea as to the preferred servo when it comes to this kind of plane.

I have a supertigre g61 and perry pump doing nothing. If I go with a 75 (os 75ax) I will have to buy it probably in February.

I would love input about anything to do with this plane. Also any suggested mods?

twn

I am curios, the stock landing gear blocks, they way the instructions say to install, will the block eventually become wiggly from loads of landins or hard landings? Is there a good way to re-enforce? Again I have never worked with foam wing cores...

iflyg450

The 475 is plenty of servo, don't forget when the king kobra came out very few servos had the torque and speed of the 475. As for the lading gear blocks getting loose? I have flown my king for sometime on rough field and they are still tight. The only change I made was for the aileron set up. Insted of using one servo. I went with 2 HS 225MG side by side in the same location, this way I could run flaperons.

Look in my profile for my King Kobra.

hattend

My Feedback: (20)

I agree with IFlyQ450... go with separate servos instead of a single in the center. If you feel like digging a 1/4" wide trench in the foam wing, put each servo about 12 inches out in the wing. That'll help balance the aileron load alleviating any chance of flutter. After you put in the servo extension, cover the trench with a 1/4"X 1/8" inch balsa and then sand it down to the foam.

Don't worry about the blocks coming loose. Epoxy them into the wing and then when you cover the whole wing with the balsa sheet, that helps lock the whole thing in. Then use either previous measurement or a straight pin to find the LG slot and cut it open..

You're going to love the KK. I don't have any pics of my KK but I have some pics of mounting the servos outboard in a foam wing at this thread starting at about post #19.

http://www.rcuniverse.com/forum/m_15...tm.htm#1538947

Don

dhal22

when you polyurethane the wingskins be sure and roll the glue to just a sheen (on the foam) and then lightly mist the balsa skins. i also recommend placing the cores and skins between the shucks and clamping between 3/4" pieces of MDF. (or vacuum bagging) you won't believe how far the glue expands into the foam.

are you considering retracts? i painted mine (almost finished).

doxilia

My Feedback: (3)

Tom,

you'll want to consult the de facto reference RCU KK build:

http://www.rcuniverse.com/forum/m_64..._1/key_/tm.htm

It will tell you how to do just about everything KK related. Also, David (dhal22) has built one and will have good suggestions.

Off the top of my head, I'd recommend that you locate the HW torque dowel (assuming there is one) for the landing gear, cut the core out for that as well as for the support block, assemble the blocks beforehand and mount the LG to them. Then, you an insert the assemblies into the core and check for a matching setup in each core.

Also, although not necessary, you might want to add some CF mat to your cores (one strip top and bottom) along and above the LG location (top of wing). Once sheeted, this will give you a rock solid wing.

Another technique for the servo leads: you can also bore the core out from the root with sharpened brass tubing. Usually 1/2" is more than enough. Maybe 3/8" is enough (depends on your connectors). Make your wood pockets for the servos first (easier), draw their locations on the cores and then run a straight line to the root where the lead will run along. You the bore along this line a little at a time.

When building foam wings, the trick is to have patience working with the cores. Try to do as much prep as possible on the cores before you sheet them so that once that is done, you simply have to sand them smooth, cut out your recesses (servo bays, LG grooves) and they are ready to assemble. I'm not sure what technique is used for the bolt dowels in the rear of the wing but using 1/2" HW dowel epoxied into the core/skin sandwich makes for a solid mount point. Be sure to drill them out (straight) with 1/4" holes to pass the bolts.

There is some info on building up wings from cores on my little Deception thread here:

http://www.rcuniverse.com/forum/m_8196707/tm.htm

It might be of help too (I did things a little differently from Mike in his KK build.

David.

dhal22

tom, my KK was constructed with spring air retracts, ailerons servos in the wing, flaps (for the heck of it). i buried the rudder control in the fuse so it's not visible and even extended the fuse to cover the elevator control connection point. it is glassed and painted. a very nice plane to build imo.

FastnLow

Very kind words about dad and I Tom, thank you. My favourite old timer pattern planes were Curares and Tiporare. Just love that antihedral tail and they groove like a jet. I still have a Tip flying with a Rossi 5 port on a pipe, and spring air retracts. Can't wait to get out with you this spring bud!

twn

Hey guys! Thanks for the awesome responses! I'm contemplating a few things. First is it really necessary to put a tube in for the servo wire like experimentaviator did? Or is just a balsa cap fine? I'm assuming the tube is to ease the installation of the wire so the connector doesn't get hung up on the foam as it is pushed through? We don’t have paper/cardboard tubes here that are that small. I suppose I could make my own paper tubing with a mold if necessary… I noticed at 7-11 they had these giant slurpee straws. Perfect size to allow a servo connector through, grabbed a few and might use them they are plastic and very light. I don’t know if the gorilla glue will grab it. Probably if I sand it.

The carbon sounds like a good idea. How firm is the wing built as per instruction? I don’t have any more carbon tape at the moment. I used it up on my GB Ultimate. Has any one ever had wing failure that would have been preventable with the carbon? I do have 1 square yard of 1.5 oz cloth. I could run some 1-2” wide strips on the top and bottom of the wing sandwiched between the skin and foam. The 1.5 oz cloth is very thin. Same results in strength as the carbon I would think.

twn

Retracts, maybe the mechanical ones. We will see. All monies coming into the house between December and Jan (and sometimes Feb) I don't even bother to ask for, lol Learned my lesson! Once February comes I can indulge with little to no friction from the other half. Kind of an understanding she and I have. She is great too cause man wow I have blown some [X(]serious[X(] money!!

For now I'm going with no to retracts on this bird. I'm looking into some mechanical retracts if my hobby guy can find some affordable ones with a steerable nose. I'm pretty sure I won't tho.

My work bench is topped with 3/4" MDF. I have some extra 3/4" MDF. However it is a 8 foot by 2 foot slab that was left standing up against a wall for a few months. Now it has a nice minor bow to it. DOH! So I cut a useful chunk off for the foam shuck and put it into a jig to bend it backwards. I took it out of the jig and it looks good now against a straight end and to the top of my bench, which is plum. A couple of car batteries should hold it down firmly to the foam cores when bonding the skins.

twn

I think this might be what I was thinking of with the landing gear. I'm pretty sure there is just a small block to be glued to the end of the LG block that gets recessed a bit further into the foam. No mention of a torque dowel. Can you explain a better picture of this to me? Some thing similar to the crude picture I did below?

doxilia

My Feedback: (3)

Tom,

your drawing is fine. There is no small chord wise dowel though. Sometimes, instead of a vertical block insert into the core, a 3/4" drilled out dowel is used instead and inserted vertically but use what's in the kit.

However..., you will be sorry to have the legs sticking out of a bird like this. It ain't an Ultimate or an Extra. These are sleek sport pattern birds and at this scale deserve retracts. Mechanical are relatively cheap in the grand scheme of the build cost. Most of the extra cash is spent on servos (2) preferably. A set of 60 size GP or Hobbico retracts should do you fine if you want to save some cash.

On the other hand, it is probably the trickiest part of the build but if you like a challenge...!

Regarding the CF, if you don't have any you can use light glass cloth in between the core and skin. Only a couple of "spar like" strips with one along the thick point of the airfoil and another behind the LG. Dave Brown CF (or other mat) is the way to go though. I would do this if the wing was to be covered in film. Otherwise, if it is to be glassed and painted I wouldn't bother. They are just little touches that make a more durable wing but few people that I know of have reported failures due to wing snapping in flight.

On landing though, that's another story... The CF makes for a rock solid wing across the root.

David.

P.S. Since your mentors Alec and Stacy appear to have posted (go B.C.!) and they have fond memories of Tiporare's, I thought I'd post a coupla' pics of my 40" span scratch built Tipo - named the Picorare . I'm building a pair of the large brothers at the moment. Next this winter will be a 77% 50" span UFO for a piped 25.

Hope this doesn't contaminate your KK thread too early on!

twn

R u kidding? This is great! I hope others post pics of their favorite pattern planes here! In fact I would like to know links of manufacturers and or retailers who are still selling old school pattern planes! I saw some here on RCU that had a dude holding a plane across his chest, looks like the pic was taken in the 70's the plane was black and I think silver and the dude had that seventies look but the plane was awesome! I have never ran across it since. I really wish I had paid more attention to the name of the aircraft. I saw it about 3 months ago or so. It was another thing that got me thinkin about the King Kobra I had on my shelf.

btw, very nice Tiporare! Interesting tail, anti-dihedral. I take it they are not in any kind of production anymore? Plans still available? I see there is a new post of a kit on ebay, a 60 size. I bet the final bid will be waay up there!

twn

Hey Stacy!! How’s it going? You guys as cold in Trail as we are in Revelstuck!! (Minus 16 without wind chill, YIKES) I took my gb ultimate out a few days ago and man talk about chilly! I froze my butt off! But it was soooooo worth it! I had no feeling in my ears because I left my toque at home, DOH! Hey did you get that stuff sorted out over the damaged Krill Yak? Please tell me yer still getting the plane? Please please!!

dhal22

If.....you decide to think the retracts situation over some more, i have a set of hobbico mains that you could just have. but spring air's are a lot simpler and you can activate them with a mini servo. i could provide you with the measurements needed and you could mount retracts later. my retracts are 2 yrs old and still not permanently mounted.

twn

Thanks dhal22. I appreciate the offer but my hobby guy (Lester’s Hobbies, who I called today about this) can get the these ( http://www.hobbico.com/accys/hcap4000.html ) to me for $25can (yes mains and nose together for that price) which is screamin cheap and I’m sure I can cover it without too much grief.

I have a few concerns about nylon mechanical retracts. First I am sure I will need to run 2 servos for a trike. Is there enough room to place the extra retract servo in the fuse and is there a decent line of sight from the retract linkage to the retract servo? Looking at the plans it seems that the wing may obstruct it. The servo for the mains in the wing is not an issue…

With it being a trike system I am sure that front retract is going to go through hell, most likely break and rip out on our grass runway. Also there is a good chance I will throw some skis (or floats…) on the plane and fly in the snow. I guess I could convert to a tail dragger but the king kobra looks so natural as a trike, even though I HATE [:@]trikes![:@]

I think rather than putting in the lesser value retract I should do the plane up with a standard LG setup and if I like it then invest in some spring air later. A wing kit (or just the core) is easy to obtain if needed… After mods don’t scare me! I suppose I could even install the retract mounting rails in the wing for future use.

Has any one used mechanical nylon filled retracts in a trike system with this plane (or similar) what was your experience like? Worth the hassle to use the cheaper retracts?

dhal22

i need to look and see if a mini servo would fit in the nose wheel bay on my KK. it's an idea i've seen on warbirds. you have a pretty big bay in that area.

twn

Retracts ordered. Picture below. I hope they don't break! Total cost with linkage and 3 retracts was $33CAN I will have them next Friday. I like my hobby guy, he brings my stuff right to my door! (Actually to A&W across the road!) He has a circuit that generally takes him from Nakusp to Revelstoke, Sicamouse, Salmon Arm, Kamloops, Vernon, Kelowna and even Penticton. He sells at the events, indoor and outdoor...

Retract part number HCAP4000 (this is the hobbico #. I think he is getting them from Great Planes, same part different number...)

So I guess I have to find something else to build in the kit before the main wing! Perhaps Stab and fin assy.

doxilia

My Feedback: (3)

Tom,

those retracts should be fine on your KK. Make sure your support blocks are strong (1/4" ply with 6 pegs into the core)! Likewise up front. Use 4-40 bolts. The key thing with flying on grass will be the wheel size. On a KK you should be able to install 2-1/4" on mains and maybe also on nose. If not, a 2" on nose.

Make sure the lawn is mowed...

If you haven't built foam core surfaces before, I recommend you start with the stab. Before you do anything else, take a piece of paper and trace the root and tip airfoils. Then draw up the wing planform from the shuck. It doesn't have to be to scale so long as the measurements and angles are correct.

Then you are ready. Thin felt tip pen, long straight edge. Mark everything ad nauseum - root, tip, LE & TE C/L, gear C/L from root to tip. Double check. Then mark the core bottoms for the location of the gear plates being sure you are symmetric about the C/L. Cut the foam out for the plates first, install them, pin them and mount the gear bodies. Make sure all looks good. The thing with foam, unlike built up wings, is that once they are sheeted you don't want to go back in and mess with them. The continuity of the sheeting is what gives the wing strength.

I'd recommend you lay down a spar of C/F veil on either side of the core under the sheeting. Make sure it is as thin as possible so it doesn't distort the airfoil. It's alot of work until you get it sheeted but once your cores are sheeted, the rest seems to go nice and smooth.

Unlike built up wings, foam core wings look worthy of desert! Smooth and round...

David.

dhal22

the KK stabs are built up. but you can still practice with any random piece of foam and some extra balsa.

twn

dhal22, doxilia, thanks again for all the advice so far! I really appreciated it! You guys are GREAT!!



I'm guessing that the peg (dowel) size is not really a concern? Lighter 1/8-3/32 or 3/16-1/4, or bigger? Epoxy to glue in place or gorilla?

I had my hobby guy order me some dave brown treaded lite flight wheels. 1 set of 2 3/4" (mains) and 1 set of 2 1/2" (front) I always use these wheels, light and really durable. I went with these sizes as the plans show them like this. I hope this will work. I'm sure they will...

doxilia

My Feedback: (3)

Tom,

1/4" dowels through the 1/4" ply plate should be fine. Drill the plate before installing - 6 holes. once installed, use a 1/4" brass tube to extract the foam from the dowel holes. GG is nice here as it will expand to fill any gap between the dowel and the foam.

The DB wheels are nice. I use them too. However, they are soft. I'd be cautious to use a very soft wheel on the nose gear - you don't want your prop to hit the ground! The wheel size sounds pretty large for an old 60 size design. On the wing there'll be no problem. The issue will be to make sure you can get a 2.5" nose wheel to retract. Of course you shorten the strut but still, that's a large wheel for what the KK looks like. 2 or 2.25" is typical on these birds. If you can sort everything out and level the plane with this wheel size, more power to you - it will help on grass.

David.

twn

Some progress, YAAA!!

The 240ml bottle of gorilla was $30 here. I chose the Elmer’s Ultimate @ $12 a 240ml bottle (I believe this product is called Nano now) Apparently this stuff foams like gorilla but this stuff is WAY more runny, like syrup. Should be easy to roll out on the wings. I hope it has a decent working time or I’ll be doing one side per night! DOH!

Stab construction is straight forward, simple. Following the directions… I added some super light ¼ balsa to the hinge areas. This is because I will be using the dubro pinned hinges I think. I might use the included ca hinges. I find that the sig ca hinge doesn’t last long even if done right I’m moving the inner hinges out ½” each and putting an extra hinge in the center. I always like to have a hinge near a control horn. The kit only has us putting in 4 hinges. I grouped the equal ribs together for an initial sanding. Very little sanded just enough to make them the same. I drilled out the 3 center ribs to remove some weight because the balsa that sig gave me was hard and ridiculously heavy, brittle so I only did the 3 ribs (actually 4 because the center is 2 ribs laminated together. I used my forcner bits to cut the holes. It worked well but there was some minor tearing on the smaller ribs so I stopped with just the 3 ribs. I didn’t think to check the weight but there was a noticeable difference in my hand. There was a minor warp in the TE ¼” stock so I steamed it out just prior to sheeting. The sheeting was easy. I used thick ca and thin ca to attach the 3/32 balsa. When I was gluing the first 2 pieces of sheet (LMAO because I just noticed what I typed) They lock the TE down. One sheet on the top and one on the bottom. I first marked off on the framing where the sheet sat so I wouldn’t put too much thick ca on. I used a long straight edge to hold the assembly down perfectly straight on the TE while the ca kicked. This took about 5 minutes per side. I should add that I wet down the outer tips of each sheet, this put a natural curl in that contoured the surface nicely. I did this with the rest of the sheeting too.

For the next of the sheeting I marked off the framing again and applied more thick ca. With the third and forth pieces of sheet (lol) I held them tightly (one at a time of course) on edge against the glued sheet and used very small amounts of thin ca to attach to the previous sheet. This allowed me to align the sheets so there were no ridges to have to sand. I started in the center and worked out ward a little at a time. I used VERY little thin ca and a piece of toilet paper to soak up the little ca left on the sheeting join as I went. This has to be done with thin ca. Aliphatic resin won’t kick fast enough to work. Do it like your stitching, tiny droplet of thin ca. Too much thin ca will wick way out and make it grab in unwanted areas so go slow, little by little.

The last triangular pieces at the front the stab are a bit tricky. A bit of water sprayed and some forcing and kicker applied (not sprayed just “droplets”) sparingly and carefully.
Worked great!

This stab btw is REALLY solid. I can’t twist it.

I glued the outer tip blocks on with aliphatic resin (I hollowed them out with the dremel first)

For the most part I’m following the instructions. I’ll add some completed photos tomorrow.

Final weight before sanding the tips is 3 ounces. A bit more than I would have liked but still acceptable.

twn

I wonder if this plane is capable of anything imac?

Also I need a float plane for the bc float flys. I wonder what the King Kobra would be like on floats?

Revy

My Feedback: (1)

Post #23 was pretty sheety, roflol!

Looking good as always, Tom.