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Sterling P-63 King Cobra restoration

Old 10-16-2008, 01:17 AM
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stuntflyr
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Default Sterling P-63 King Cobra restoration

Here are some pics of the Maxey Hester designed Sterling P-63 King Cobra. It is a cool looking Semi-Scale Pattern ship kitted about 1962. I received it from a friend already built though it had never been flown (by the looks of some of the construction features it is a good thing it did not!).

I mocked it up with a Super Tigre G21 40 R/C complete with exhaust baffle, a Veco prop extension, Froom spinner and Top Flite 11x8 R/C prop just for the pictures as it came with a Magnum 75 2 stroke. The plans show a K&B Torpedo 45.

It's a pretty neat model. The plans show a diamond airfoil section on the stab, this one has a flat sheet stab. The ailerons are interesting as they have a hinge point about 25 percent of the chord and a slot formed between the leading edge of the aileron and the trailing edge of the aileron cove of the wing.

It has longish gear, so I'm going to have plenty of room for a 14 inch prop on the Magnum 91 4 stroke.

I'll update this as the resto moves along. I plan on spending a few hours a week on it and have it flying in a new scheme and with some cool old style features sometime in the spring. Hope you find it interesting.

Chris...
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Old 10-16-2008, 01:58 AM
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Default RE: Sterling P-63 King Cobra restoration

Chris,

Interesting your King Cobra. Very nice plane.
I read also about the ailerons.
In 1962, the period of my Orion (1960) I think "Frise" ailerons were popular.
Let us check of these are "Frise" ailerons because you have to know how they work.
I use them on my Orion.

Succes with this plane, I will follow your thread.

I show you two pictures of the Orion, first one is bottom of the wing, second is the top.


Cees
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Old 10-16-2008, 06:36 AM
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Default RE: Sterling P-63 King Cobra restoration

Nice project Chris. Back in the early sixties when this model was produced, radios weighed close to 2 lbs. and the biggest engine around was the K&B Torpedo .45. I picked up a Sterling F-51 in similar condition that had also never flown. I stripped the covering off and recovered it with tissue on the fuselage and silk on the wings and tail. I fitted a Veco .45 and installed a Kraft radio but when I hefted the thing, I felt that the .45 may not be enough so I plan to fit a ST. 56 or .60. It's sidelined for now. You may want to peel off the Moneycoat and recover it with your faovrite covering material. This will give you a chance to look at all the internals. Glad I did it on the Mustang as I found a lot of sins! Good luck with your project and keep us posted on your progress.
Old 10-16-2008, 09:04 AM
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Default RE: Sterling P-63 King Cobra restoration

Interesting project, Chris. Do you have any idea about when it was built? If it is super-old, it may be built with Ambroid glue or the like. If the joints fit well, wicking in some thin CA should give the airframe much greater integrity. The suggestion to peel the covering and check is a good idea.

Have fun,
Robert
Old 10-16-2008, 03:20 PM
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Default RE: Sterling P-63 King Cobra restoration

It looks just like my Jemco P39 Aircobra but with bigger fin.
Flew like a trainer, I still got it in the attic somewhere.
Old 10-17-2008, 02:47 AM
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Default RE: Sterling P-63 King Cobra restoration

Cees, Thanks for the pics. I'll see what the original plans versus construction of this model is to find a direction to go on this aileron design.
Waco Michael and Robert, I agree on removing the covering. I am not into military finishes anyway. This model was built in the mid-nineties and so epoxy and CA was used to build it. Mostly kit wood so it has plenty of ballast to keep it from being too light and flimsy! There are some incomplete components that need adressing and some nose redesign and beef-up required for the Magnum to stay in the model too.

It's crazy how I remember the Veco 45 and Torp 45 being so big and powerful when I was a 8 to 10 year old. I recall the flight of so many of these old designs when I would get bored of watching Dad and his buddies flying Stunt and wander over to the R/C field at Sepulveda in the sixties. Now there are so many choices of powerful and too powerful engines for our models. It boggles the mind...

Martensen, I'm not familiar with the Jemco kit but I know how the Cobra's look similar. A couple people have said this model flies like a trainer too. They say it'll be way more forgiving than the Kaos.

I'm glad for all of your remarks.
Chris...
Old 10-18-2008, 11:36 AM
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Default RE: Sterling P-63 King Cobra restoration

I just went and logged in so I could reply. I have one of these kits new in the box upstairs. I bought it at a hobby shop noted for having different stuff in the basement goody bin. I thought it was a scale bird. Picked it up for peanuts. Nice to know it's actuallt an SPA type ship. I'll build it some day. Glad to see one here. I wish you the best with the restore job.

Mark Shuman
Old 10-27-2008, 01:27 AM
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Default RE: Sterling P-63 King Cobra restoration

Hi Mark,
Thanks for the encouragement. Maxey did fly it in Scale and Pattern. Either one is appropriate for this design, I guess. I actually intend a scale finish for this model.

I spoke to Tony Nacarrato last week about some details of R/C construction and he told me his parents flew more than one each of the P-63's in the Pattern event in the 60's.
The design apparently needs a bit more washout than it has drawn in (none as far as I can tell). I intend to induce some through re-profiling the outer section a bit by shaping by sanding. Whatta you guys think on this?
He also told me that the design has positive incidence in the wing and horizontal stab so the fuselage looks like it is nose low, an attempt to lend the appearance of speed. I think I may remove the incidence and zero the thrustline, wing and stab for trimming simplicity.
I asked specifically about the diamond stab airfoil and Tony believes it's a good design. Since it lends more nostalgia to the model, I am going to build a new one to the plans.

I found out an interesting and fortuitous thing. The Magnum 75 2 stroke that the model was built around has the same mounting holes as the Magnum 91 4 stroke! I just returned from the garage where the firewall and noseblocks were relieved to accept the 91 and the old throttle pushrod was removed. The firewall and motormounts aren't too badly assembled, there are a few voids where the builder wasn't so careful as to get accurate fits. The former at the wing leading edge at the top where the tank passes through looks as if it was trimmed by biting. I'll repair the former and address the voids with some balsa scraps and seal it all up with epoxy and microballoons forced into any corners. I want to be sure that all voids are closed so the 4 stroke's pounding won't damage the structure.

I'll post some pics tomorrow.

Chris...
Old 10-27-2008, 11:34 AM
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Default RE: Sterling P-63 King Cobra restoration

Leave the angles as they are, a P63 flying around dragging its ass would not look right, you wouldn't be happy with it at all. The 'nose down' look is only apparent, and is probably the fuselages lowest drag angle anyway. And it give a bit of downthrust, which it probably needs, without bashing the front any more.
Evan.
Old 10-27-2008, 11:44 PM
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Default RE: Sterling P-63 King Cobra restoration

Thanks for the comment, Evan. My thought is that the airplane will be easier to trim if it's zeroed like a modern model. The decalage thing always makes an airplane trimmed for only one airspeed. With the Magnum 91 speed should be pretty high if necessary, at least those are my thoughts on the matter.

The pictures show the engine installed in the same mounting holes as the Magnum 75 2 stroke installed when it was built. It fits the model size well, not as big as I thought it might look.

The F2 former is all ragged out from using some instrument other than a saw or knife, but over all the construction looks OK. A little repair and reconstruction needed here and there.

I had to lower the left side F1 former for the needle valve and relieve it in the center for the carb and choke.

The engine prop drive washer sets out beyond the original nose ring and because of the size of the engine it has to, as built. I'm going to add some balsa to the nose and add a ply nose ring to match up with the spinner. The front of the model is full of dimensional inconsistencies, but it looks as if the kit had the parts cut to arrive with right and down thrust.

Do most late eighties/nineties pattern ships have right and down thrust? I know the carry over from full-sized and free flight ships to these early jobs but I would like to modernize a little bit.

I'll build up the fuse noses sides and then pick an elevation and make a cut to install a removable cowling around the engine. Then it'll look pretty finished off rather than open as it is now.

Here are the pics. Any suggestions are welcome.

Chris...



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Old 10-28-2008, 06:53 AM
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Default RE: Sterling P-63 King Cobra restoration

Check out this Cobra. http://www.vintagercsociety.org/muncie2007pics.html
Old 10-28-2008, 08:57 AM
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Default RE: Sterling P-63 King Cobra restoration

Chris - like Evan says, leave the wing and tail angles as designed. If they are both the same you have 0-0 anyway plus the advantage of a little built in downthrust. This was a favourite design trick of Hal deBolt which he used on lots of his pattern ships and, as Evan puts it, avoids that awful "draggin its ass" sit in the air and probably puts the fuselage at it's minimum drag angle.

By the way, just to be fussy - this difference in wing and tail angles is called longitudinal dihedral. Decalage is the angular difference between the top and bottom wings of a biplane.

Good luck with the P-63. Beautiful aeroplane.

Ray
Old 10-29-2008, 11:24 PM
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Default RE: Sterling P-63 King Cobra restoration

This is real interesting and well I bet it will take to the air real well,having less wing loading and WAY more control with the present R/C systems available today.
Old 10-30-2008, 03:54 AM
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Default RE: Sterling P-63 King Cobra restoration


ORIGINAL: RFJ
By the way, just to be fussy - this difference in wing and tail angles is called longitudinal dihedral. Decalage is the angular difference between the top and bottom wings of a biplane.
Not that I'd disagree with anything said here, on the contrary, I totally agree. Just to thank you, Ray, for illuminating a word I was musing about for a long time: decalage.

I adopted its meaning from a trustworthy source but was still in doubt. Now I remembered having a glossary of aeronautical definitions, and there's your definition of decalage. Nevertheless, American sources define decalage as "the difference in zero lift angles" (or chord lines, for that matter) "between the wing and horizontal stabilizer". So does [link=http://en.wikipedia.org/wiki/Decalage]Wikipedia[/link].

Now I searched in the glossary for a translation of our German term Einstellwinkeldifferenz (abbreviated EWD), which means the difference of chord line (incidence) angles of wing and stab. The glossary translates it to "tail-setting angle", referring to British Standard 185, Sect. 5, No. 5211. The whole book is based on BS. Maybe our American friends really call that thing decalage while we in old Europe are a bit out of style.

This is all quite off-topic but nevertheless interesting, at least for me. Thanks again...
Old 10-30-2008, 05:19 AM
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Default RE: Sterling P-63 King Cobra restoration


ORIGINAL: stuntflyr

(snip)
I spoke to Tony Nacarrato last week about some details of R/C construction and he told me his parents flew more than one each of the P-63's in the Pattern event in the 60's.
The design apparently needs a bit more washout than it has drawn in (none as far as I can tell). I intend to induce some through re-profiling the outer section a bit by shaping by sanding. Whatta you guys think on this?
(snip)

Chris...


************


The problem with washout is that it becomes washin when inverted. An aerobatic model spends almost half of its flying time flying inverted.


Ed Cregger
Old 10-30-2008, 05:58 AM
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Default RE: Sterling P-63 King Cobra restoration

Hello Ed,

With a lot of washout, maybe in that period the plane was better controllable in low speed condition during landing. The amount of washout has to do with the speed you want your profit.

I think it is important that we do not forget the plane was used in the 60’s.
The program that was used to fly also was very different with later programs I think.

That’s also the reason we see the Frise ailerons on (the Orion and probably on) the Bell King Cobra also.
Frise ailerons also behave contra in inverted flight.

For one thing I do not have an answer yet, why this Cobra LOOKS like it has the wing setting of a taildragger, while the original is a tricycle! Because this is the reason you generate drag in normal and inverted flight (I think!).


Cees
Old 10-30-2008, 09:17 AM
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Default RE: Sterling P-63 King Cobra restoration

Chris, what is the winspan of your King Cobra? I think Wing manufacturing has a smaller kit available, around 53" if I remember. Canopies are separately available if anyone wants to scratch one. You've got a great restoration going. Thanks for sharing.

Here is some other sorta related historical stuff. The first, bad, scan is Maxie Hesters 1964 nats scale winning "Pin Ball" from the cover of RCM 10/64. It looks like a P-39 to me. The magazine said he flew something else, a twin rudder Straturs, in pattern.

The next scans are from RCM 12/69. They show a just a hint of King Cobra in the Beatnik. Apparently, the plane had been around a few years (5 at least) before the plans were published. The plans are white and black and are hard to read. But they indicate the canopy on the original is from a Sterling P-63. The ailerons are inset and are top hinged. The stab is flat. The airfoil is semi-symmetrical. Power was a Super Tigre 60.

Jim
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Old 10-30-2008, 09:43 AM
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Default RE: Sterling P-63 King Cobra restoration

I really like the looks of the Beatnik. He flies a great brand of radio too. I've had several of the black boxes in my day.


Ed Cregger
Old 10-30-2008, 02:02 PM
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Default RE: Sterling P-63 King Cobra restoration

Hi Michael,
Thanks for the link to the King Cobra flying nowadays.

Ray,
I have thought a lot about it and think I am going nearly inline so as to not drag it's "butt" inverted. I am cheating the fuse and fin shape more towards scale as well as the aft fuse outline is too tall and pot bellied and lends nothing to the looks. The "decalage" term is one used throughout my life in working on making racing planes go faster; Like P-51's, and Pitts Specials. They all need the leading edger aised as they are set-up to make nice three point landings.
I am sure in some pure definitions you are correct, we also used it when truing the rigging of the wings top and bottom on bipes. Thanks for the input.

UStik,
Thanks for the research. It kinda folowed my thinking but I really just picked it up through the years working in aviation and was sure I could be wrong!

Hi Ed,
I was wondering about that all the way home after speaking with Tony. His comments were that it had a thin and unforgiving airfoil in his recollection and it would snap during certain maneuvers.
I wonder if the problem was high wing loading and slow control response of the 60's model and radios?
Or lack of ability to use differential on the down aileron travel?
Or that the positive incidence made the stalling problem worse?
I feel that mounting the wing with just enough positive incidence so that it isn't negative and matching the stab to it will be sufficiently safe. Then rigging the ailerons for a lot of differential and to hinge them on the top surface and build a seal for the aileron coves to close up the "drag buckets" underneath.
Thanks for your comments, I read a lot of your stuff!

Hi Cees,
I think I follow your thinking and I am just trying to make it fly reasonably well and make sure it carries the flavor of the old models without having all of the inherent problems of;
1) the large incidence angles,
2) "low stick load" boosted aileron design.
I figure most of this stuff are attempts to get a quicker reaction from low powered servos of the time and they used known full size airplane techniques to help those problems.
The airplane might look good with that high positive incidence upright, but it'll look way bad inverted. I'm trimming a lot of side area off of the bottom by making a (scale) straight line from the trailing edge of the wing to the bottom of the rudder. This will improve it's "butt dragging" profile I hope.

Hi Jim,
This model has a 70 inch span. Thanks for the scoop on the canopies. Your welcome, I love reading guy's build and rebuild threads...
The Pin Ball was a King Cobra, totally different than the Airacobra. The King Cobra was an evolution of the Airacobra design, but totally new, bigger, and had the P-51 style laminar flow wing and aux supercharger for high altitude performance. The Bell fighters are one of my favorites, several of my Dad's friends raced them through the years. Pretty rare now. The Pin Ball was a scheme to train bomber gunners in live fire training. The Pin Ball airplanes were built of thicker skins and armour protection for the engine, radiators, pilots, etc. Hence the metal covered rear canopy area.
Maxey flew that model in a couple, or three paint schemes. Thanks a lot for that picture as it shows the revised shaping which makes my mods legit for the early period! (I guess dropping the Magnum in there inverted would be cool!)
The Beatnik was a cool model, I remember them when I dreamed of flying R/C as a small kid. The canopy is absolutely the Sterling kit part. Thank you for the great post, helps a lot.

Ed again,
You bet, neat looker.

Thanks all, you help me more than you know!
Chris...
Old 10-30-2008, 02:44 PM
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Default RE: Sterling P-63 King Cobra restoration


ORIGINAL: Taurus Flyer

Hello Ed,

With a lot of washout, maybe in that period the plane was better controllable in low speed condition during landing. The amount of washout has to do with the speed you want your profit.

I think it is important that we do not forget the plane was used in the 60’s.
The program that was used to fly also was very different with later programs I think.

That’s also the reason we see the Frise ailerons on (the Orion and probably on) the Bell King Cobra also.
Frise ailerons also behave contra in inverted flight.

For one thing I do not have an answer yet, why this Cobra LOOKS like it has the wing setting of a taildragger, while the original is a tricycle! Because this is the reason you generate drag in normal and inverted flight (I think!).


Cees


************


I can understand why the designer utilized washout in the original design. The radio and the huge battery load was really weighty. Combine that with a silk and dope finish and you have a model that is prone to snap rolling. I just don't know if I would bother to include the washout were I building the model with today's radio systems and light weight components. We're just talking here. <G>


Ed Cregger
Old 10-30-2008, 03:25 PM
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Default RE: Sterling P-63 King Cobra restoration

Hi Ed,
Thanks for the reply.
To make it clearer than I have before, the design does not indicate any wash out on the kit plans. I have not printed out the magazine plans yet, but they look exactly the same.
Tony Nacaratto suggested it might be of help after I suggested it actually, but we were speaking between customers at the hobby shop so he may well have advised me differently after a few minutes of thought about it.
Maxey's first one weighed about 9 lbs, I think this was the one with the ton of paint. He lost a pound in the refinish. I think I can make this one weigh 6.5. Plus he had a Torp 45 and I have a 91! I plan on painting the fuse and Monocoting the wing and tail.
Thanks,
Chris...
Old 10-30-2008, 04:31 PM
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Default RE: Sterling P-63 King Cobra restoration

Chris,

Two ads to my post,

The wingsetting I did mean I later saw in the post of jjscott, drawing of the Beatnik, see and compare.
The Beatnik has the right incidences for the tricycle.
So the difference in the wing and stab angles is the same only the mounting angles in the fuse is different. I did redraw your picture to explain


Second point is the frise ailerons are to compensate the adverse yaw effect, not boostering or I do not understand "low stick load boosted aileron design" right.

Only to complete my message, not to discus about, succes Cees
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Old 10-30-2008, 04:49 PM
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Default RE: Sterling P-63 King Cobra restoration

Chris, your nice model should not be vicious, at least neither by airfoil nor by weight. Only the wing taper could make for a tip stall, maybe (hard to see from the pictures). Some taper is often used for better flick/snap ability. Below is a drawing from an old book about aerobatics. It compares a classical aerobatic plane (Zlin Z-526AFS) to a somewhat newer special design with symmetrical airfoil and zero incidence and decalage (in fact, the Akrostar had a mechanism for automatic decalage upright/inverted).

The Zlin has semi-symmetrical airfoils (NACA 2418 at root to NACA 4412 at tip) and even 3 degrees washout. This is all but a vicious design, but snapping is achieved by the wing taper. The decalage is about 0.5 degrees. This is an asymmetric design regarding the longitudinal balance. At aerobatic speed, you have to push elevator both in upright and inverted flight if the decalage is big and the c/g is in a stable position. If the decalage is small and c/g is more aft (40% of chord) as not unusual for an aerobatic plane, virtually no elevator is needed both upright and inverted despite the "asymmetric" configuration.

That's how the classic aerobats were able to fly all patterns, even if quite a bit of stick work is required. And that's why it's called Kunstflug in German - artistic flying. The benefit of a symmetric design including symmetric airfoil is freedom of airfoil pitching moment and neutral behavior over a whole speed range. The pilot's workload is lower so he can fly more complicated patterns and more negative g-load is possible.

I think you should fly your model as it was intended. Just depending on the given decalage, you'll have to set a more forward/stable or more rearward/neutral c/g and use more or less elevator. In any case, a more forward c/g makes for higher speed balance.
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Old 10-31-2008, 02:26 PM
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Default RE: Sterling P-63 King Cobra restoration


ORIGINAL: Taurus Flyer

Chris,

Two ads to my post,

The wingsetting I did mean I later saw in the post of jjscott, drawing of the Beatnik, see and compare.
The Beatnik has the right incidences for the tricycle.
So the difference in the wing and stab angles is the same only the mounting angles in the fuse is different. I did redraw your picture to explain


Second point is the frise ailerons are to compensate the adverse yaw effect, not boostering or I do not understand "low stick load boosted aileron design" right.

Only to complete my message, not to discus about, succes Cees

I see, Cees.

The model has the nose strut mounted lower in the fuse than the plans call for, but that is good for my engine installation. The wheels are all the same size, too. This gets the nose up a little higher than it should be. I will buy new wheels for this model and get the main gear effectively longer by larger diameter wheels.

I use the term "attitude". It's the airplane's relationship to the horizon. In this case, nose high attitude. Incidence is typically used when referring to a comparison of thrust line to wing and tail angles.

I'll pm you about the ailerons some time. I have a long way to go before I get to working on the wing.

Thanks for the coments,
Chris...

Old 10-31-2008, 02:31 PM
  #25  
stuntflyr
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Default RE: Sterling P-63 King Cobra restoration

Neil Williams, "Aerobatics".

What a man in the aerobatic world. My Dad's friend Bob Herendeen witnessed his fantastic save of the Zlin at Hullavington in 1970 and I was there when Bob told the story. What a thrill!

Interesting observations about aft cg airplanes and relative stick movement. I had an S-1C and an S-1D, 160 and 180 respectively and they both flew with little stick forward inverted even with their "flat bottom" airfoils. Being around 195 pounds I was always around 30-35% MAC, easy!

I loved the fact the akrostar had flaps like a Ultimate. I flew C/L Stunt at the time and thought that wa just great!

Thanks for the trip down memory lane, and the thoughts,
Chris...

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