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Post  batjac Thu May 13, 2021 5:27 am

A couple of weeks ago a club member said, “You do Cox planes, don’t you?”  I agreed, of course.  “Do you have any Viper parts?”  You mean a Hyper Viper?  “Yes.  A Hyper Viper.  Do you have any spare parts for a Hyper Viper?”  I said I have one NIB, but I don’t have any spare parts.  “Ron gave me a Hyper Viper that he picked up somewhere because he knows I do 1/2A engines.  I think it has a broken wing, but it’s mostly there.  Would you like it?” Ummmm. Of course!

Well, I picked it up, and the wing is not broken.  Unfortunately, the fuselage is.  It’s been repaired a couple of times, and it’s beyond reasonable repair.  Seems that when Cox tried to make these light weight, they also made them somewhat fragile.

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My options are to try to fix the fuse (not even gonna try), build a replacement fuselage, or tweak the wing and make a profile fuselage.  I could try to make a full fuselage out of 3/32 balsa and maybe reuse the current tail surfaces.  Seems like more trouble than it’s worth.  I’m thinking I’ll do the profile fuselage with a TD on bladder.  What do Y’all think?

The Crazy Asp Mark
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Post  Coxfledgling Thu May 13, 2021 5:38 am

A good clean, modern glued and some reinforcement that would repair I feel, what have you to loose...

3d printing these days...
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Post  getback Thu May 13, 2021 6:16 am

I agree there are some really good glues out there that will scab it back together with some maybe glassing reinforcement , just my Two Cents RC Plane Popcorn
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Post  aspeed Thu May 13, 2021 10:45 am

Maybe make a male plug of the two fuselage parts. Then shrink a Coke bottle over it. You could make some extras for friends. It may be thinner than what Cox used, and the fuselage formers may need removal or whatever. Just thinking out loud. A fiberglass mold may work for a fiberglass fuselage too, but Coke bottles are quick cheap and dirty.
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Post  Marleysky Thu May 13, 2021 11:55 am

Rusty was working on a Balsa kit. This thread shows what he did with a kit made by Southridge. Maybe you can use the foam wing and build the balsa fuse??

https://www.coxengineforum.com/t12749-my-southridge-cnc-hyper-viper-build?highlight=Hyper
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Post  rsv1cox Thu May 13, 2021 12:09 pm

Do both Mark, repair the original and build a profile.  

You know me, I would do my darndest to repair the original from the inside out.  Been there more than once.  Ya, what do you have to lose.....I used to pay big bucks on ebay for those relics.
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Post  Cribbs74 Fri May 14, 2021 3:55 am

The castor pickled insects are a nice bonus. Keeping the wing and building the Southridge fuse would be my plan. Either way nice find.
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Post  batjac Fri May 14, 2021 6:01 am

Okay.  I'll give it a shot.  I'll need to pull my NIB plane out of the closet to see what parts I need to fabricate for the front end.  I'll soak the fuselage in some Dawn detergent to try and get some of the fuel residue out of the cracks.  I'm thinking Testors plastic model glue to try and repair the fuselage, with some carbon fiber tow to strengthen the broken side.  Not sure how I'm going to fix this part.  The crack goes all the way across the bottom of the fuse pretty much.  I have some carbon fiber mat, so maybe rough up the bottom and lay the mat across the bottom.  Ugly, but possibly effective.  To tell the truth, I don’t see putting a lot of effort into making look nice.  Just flyable.  I’m still leaning towards a TD with bladder.  Even with the thin plastic, this is still heavier than I’m used to.

The Mechanic Mark
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Post  rsv1cox Fri May 14, 2021 6:11 am

I have had excellent results with Testor's red tube, not so much blue tube.  Use a compatible thin plastic sheet for the inside cut to shape and cover both mating surfaces completely clamp and let dry over night (very important.)  

Ron has one of my lesser creations, a Cox PT-19 that I tacked together just to fly.  I think I used butter cup top plastics as reinforcements.  Not wonderful but it held.

I pieced this one back together from a crushed original (Thank you USPS distribution center Washington DC) wing, fuselage, struts. But there was no castor damage.

What a friend gave me. P1010984


Good luck, and I would love to see the outcome.

Bob
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Post  modelbuilder49 Fri May 14, 2021 1:33 pm

@Coxfledgling wrote:A good clean, modern glued and some reinforcement that would repair I feel, what have you to loose...

3d printing these days...
Hi! Love your suggestion but just out of curiosity ... what would it take to 3-D print something like this? How could it be done? How long would it take? How much would something like this cost?

Jim
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Post  batjac Fri May 14, 2021 4:19 pm

Okay, I started by doing a scrub with a toothbrush in Dawn detergent (Shhh!!! Don’t tell my wife I’m using her casserole dish to clean castor gunk!)

What a friend gave me. DSCN7725


I glued the break in the upper section together.  Then I used some carbon tissue across the break.  I laid up two layers of tissue inside an out.  Then I cut a piece of 1/16” ply and glued it in place across the wing saddle.  This was sanded and two layers of carbon fiber tissue laid up over it.  This resulted in a much stronger and stiffer fuselage than I expected.

What a friend gave me. DSCN7729
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Next I attended to the fuselage bottom after ensuring it had dried completely.  I figured that since it was so damaged, the best way to do it was to have it in the flying position when glued up.  I put two layers of plastic wrap over the foam wing, and then taped the two fuselage halves together over the wing in the assembled position.  A thin layer of glue across the crack to hold it together was first, then I started laying up the tissue.  I just put strips across the cracks, and then one large strip across all of it.  As I said earlier, I wasn’t worried about being pretty, just strong.

What a friend gave me. DSCN7732
What a friend gave me. DSCN7748


Then I flipped it over and did the inside.  With this done, the lower fuselage was very stiff.

What a friend gave me. DSCN7750
What a friend gave me. DSCN7755


Now I just need to figure out how to replace the broken plastic standoffs inside the upper fuselage that the screws go into.  I’m thinking the easiest and quickest way would to be just to use some wooden dowel that has been center drilled, glued in, and then finished with JB Weld.

I think this will be a good use for my Kamtechnik TD/Medallion radial mount backplate for a TD.

The Stripper Mark
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Post  rsv1cox Fri May 14, 2021 5:08 pm

A++++++++++++ Mark!

Curious about the glue you used and the carbon fiber tissue? I'm thinking perhaps resin/mek brushed lightly on the CF would work miracles without being to heavy. Got a source for that tissue?

Those cracked/hogged out pylons. Yours is the better way, but I have had good luck with just Testors red tube liberally applied then wrapped with waxed paper and clamped followed by a long cure period then drilled out for the self-tappers. Not much stress there and you retain the original components without worrying about alignment. Whole different story if the pylon(s) are missing completely.

The curious, questioning, and probably unhelpful - Bob Smile
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Post  NEW222 Sat May 15, 2021 1:59 am

Well, I have been out and busy and just sat down to see this thread. You are doing a fantastic job on fixing up the Hyper Viper.
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Post  NEW222 Sat May 15, 2021 2:05 am

@modelbuilder49 wrote:Hi!  Love your suggestion but just out of curiosity ... what would it take to 3-D print something like this?  How could it be done?  How long would it take?  How much would something like this cost?

Jim

I wish I could give you a better answer, but here is what I can say. As I am still 'green' to 3D printing, it is possible to print it out in pieces once the complete model is 'sliced' into smaller pieces then glued together to make it complete. Just going to throw out a guess as to time, but would expect 24 hours to be in the ballpark, and cost, I do not have a clue as to how much material would be used. I only know how much material I will use when I 'slice' a file to print as it then tells me how much it uses. Hope this helps answer your question some. But take my time also with a grain of salt....
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Post  coxaddict Sat May 15, 2021 4:45 am

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Post  getback Sat May 15, 2021 7:52 am

Here's the link i was looking for https://stunthanger.com/smf/southridge-cnc/hyper-viper/ Wonder if he got the Spook done ? I know its not CNC but he has a machine and the pattern . Smile
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Post  batjac Sat May 15, 2021 9:47 pm

@getback wrote:Here's the link i was looking for https://stunthanger.com/smf/southridge-cnc/hyper-viper/  Wonder if he got the Spook done ? I know its not CNC but he has a machine and the pattern . Smile

Eric, I do have one of these. But it is on the back burner. I was waiting to see a couple of them flying before I spent time building. Seems like it will be very nose heavy.

The Lurking Menace Mark
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Post  batjac Sat May 15, 2021 11:16 pm

Bob,

I was going to try styrene glue, but I didn’t have any.  I was going to try to disassemble the fuselage to clean it, but the previous owner used CA on the cracks, and it seeped into all the joints.  The CA is holding extremely well, so I just decided to CA the carbon fiber tissue in place.  The carbon fiber tissue is sold by DeLuxe Materials.  Should be able to get it just about anywhere.

What a friend gave me. DSCN7759


Not sure how to fix the standoffs, I went to the local hobby shop to look around and see what there was.  I found these styrene tubes in the model train section.  I picked the ¼ inch tubes because they matched the OD of the existing standoffs.  The 3/16 nests inside and the hole is the right diameter for the screw threads to stick through.  I made an insert for the left rear screw well of the lower fuselage.  Then I trimmed it flush with the outside of the fuse.

What a friend gave me. DSCN7757
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Then I glued a couple of ¼” tubes over the broken rear standoffs, and I split a tube to slide over the front broken off standoff.  I figure I’ll fill the tubes with JB Weld, trim to size, and then drill them out for the screws.  Unfortunately, I don’t have any more JB Weld.  I used the last I had on my computer chair.  I went to the local Fred Meyer this afternoon for more, but they don’t carry it anymore.  I’ll have to find some somewhere else.

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Next is the firewall.  I’m not sure what to do about that.  The plastic firewall is all cracks.  I don’t know how well it’s going to stand up, even with the carbon tissue.

The Tubular Mark
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Post  getback Sun May 16, 2021 5:20 am

Well Tubular Mark that there is sure enough a mess LOL Huh... did the CA melt the plastic were you put the tube in or was it like that? If not i think i would make a plywood insert for the mount and glue to the plastic mount put some wood nuts in there to attach ?!?!? Very Happy Looking good so far This Site Rocks!
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Post  rsv1cox Sun May 16, 2021 7:13 am

I'm lovin' it Mark, becomes a contest between man and material.

I'm a glue-acholic trying most anything. A small sample I keep in the basement. Others in the loft and garage.

What a friend gave me. P1010990

But my son, another Mark swears by this stuff for plastics which I haven't tried yet.

What a friend gave me. P1010991

I'm picking up some of that CF. Thanks for the clue. Smile
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Post  Ken Cook Sun May 16, 2021 7:22 am

I've never successfully repaired a flying Cox model. I mean that yes, it can be repaired but it will break fore or aft of the repair later. The posts break again as it can't endure the shock of landings and stresses from flying especially in the gear area. In addition, the firewall mount which was a huge problem with the Hyper Viper when new and seeing it now looks like it's really compromised. The engine would rattle around in the mount due to it not fitting tight enough. This  probably assisted much of the spider webbed cracks you see. I'm certain a ground hit didn't help it much. The plane was underpowered but as Mark mentions, he's changing that. The plane was also quite heavy for various reasons. I hope it works out and offers the satisfaction when completed. If you have the Southridge Viper, we all would love to see that completed and flying. He did a beautiful job on that model and it just looks too cool to not have it completed.
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Post  rdw777 Sun May 16, 2021 5:03 pm

Nice to watch the rescue of one of these old models rather than sitting in a box o parts.... Even if it only flies a few times I would call it successful.....

Sparks a memory of when I was a kid my friend down the street got a Cox P-51 for his birthday ....It was the green one with raised rear deck.... We were about 10 so dad was the pilot.... He flew it a lot and whenever we heard the unmistakable sound of it burning circles all the kids in the neighborhood would run over to watch it fly.... I think his dad had some previous experience.... He did break the the outboard wing off one time but glued it back on with who knows what and it flew a lot after that....

Good luck with your repair/rebuild!
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Post  batjac Sun May 16, 2021 9:08 pm

Well, the wife went to Walmart today and tried to get me JB Weld. But there were so many options that she just gave up.  She tried calling me, but I'm at work and it was too noisy to hear the phone ring.  I'll probably head over to Walmart or Ace on Thursday to get some.  I'll do the normal JB Weld for filling the tubes to drill for the screws.  I'll also pick up the PlasticWeld to try and fix up the firewall.  I have a couple of ideas to clean up and prep the firewall.

I've also been rethinking my engine plan.  I'm still partial to the TD, but I'm now thinking Killer Bee clone.  There's actually lots of room in the nose for a bladder after I put in a tube to protect the bladder.  So a Killer Bee with a fine needle spinning an APC 5.7x3 or 6x3 sounds tempting.  

I have a couple of new Killer Bee backplates from Bernie, and couple of rebuild kits for the gasket, reed, retainer, and screws.  I have a couple of fine needle assemblies I got a while back.  I know I have at least one KB crank.  I'm not sure about the zero drag driveplate, but I'm sure I've got a new one somewhere along with the zero drag spring.  Plenty of new crankcases (Darn you Bernie, and your oh, so easy to order from website!).  I'm just not sure about the cylinder.  I don't have any new TD piston/cylinder sets, and if I order one from Bernie it will turn into a $120 order, as usual.  I'll see what I have for uncommitted #4 cylinders on TDs in the rebuilt engines box.  Maybe I can "borrow" one for a little while.  I also have that nice, new Kamtechnik turbo head I got a couple of weeks ago.  Maybe that and a #5 plug?  I guess I can try a high compression Cox head and the turbo head and see what difference there is.

Then again, I'm pretty sure I have a "Black Lynx" I got from Matt a few years ago that I never ran.  Maybe I'll pull it out of the model its in and fire it up on the test stand.

The "We Don't Need No Stinking Badges" Mark
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Post  batjac Sun May 16, 2021 9:22 pm

@getback wrote:Well Tubular Mark that there is sure enough a mess LOL Huh... did the CA melt the plastic were you put the tube in or was it like that? If not i think i would make a plywood insert for the mount and glue to the plastic mount put some wood nuts in there to attach ?!?!? Very Happy Looking good so far This Site Rocks!

The CA seemed surprisingly compatible with the plastic.  No "melting", just joining.  I've thought about a thin ply surfacing of the plastic firewall.  I've considered cutting out the plastic firewall and gluing in a 1/8" ply firewall.  I've pondered roughing out the surfaces and using the above PlasticWeld.  I think I'll end up using a combination thereof.  

The Thinker Mark
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Post  batjac Sun May 16, 2021 9:36 pm

@Ken Cook wrote:I've never successfully repaired a flying Cox model. I mean that yes, it can be repaired but it will break fore or aft of the repair later. The posts break again as it can't endure the shock of landings and stresses from flying especially in the gear area. In addition, the firewall mount which was a huge problem with the Hyper Viper when new and seeing it now looks like it's really compromised.

I'm not sure how much I'll fly this, or how long it will really last.  I'm leaning towards not putting the landing gear back on and just flying this over grass.  I still have the profile fuselage option for later if the fuse just doesn't hold together long.  Also, after I get the standoffs fixed, I'm going to do belt and suspenders by doubling up a couple of rubber bands and wrapping them around the fuse to hold the two halves together in addition to the fuselage screws. Heck, if the standoffs do break again, I can just do the field expedient fix of just taking electrical tape and taping the two halves together to keep it flying.

The Backup Plan Mark
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