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Corroplast Kraken

#1
So I've been enjoying flying wings since 1999 when I had one shipped to my hotel at a trade show in Vegas. Im not a gambler and a week in a hotel for me isn't about the town or even the theatres, but what to build on that second bed! I built a Zagi 400 and Chip Hyde even flew/signed it at the TOC the following weekend. It paid to plan my show attendance dates accordingly.

So my FT wing experiences have been great too. My son and I enjoy our Mini Arrows, but only a few plops in our less than groomed high grass and the noses collapsed far too easy. For us the whole fun of wings is fly where you are.

To some extent, the nose crush problems on all Dollar Treem Foam fliers could be minimized with what I term "an ejecto-chute" a block of EPP under the battery with a 45 angling cut in front of the battery attached ONLY with flat velcro-no strap. in the event of an abrupt stop, the velcro releases. There is a science to this..less velcro can be more..and the mass of the battery contributes less...to the shattering of the foam nose. In truth, my EPP Zagi nose is still intact on retape # infinity... Note that experience taught me to tether my ESC wires back with zip ties so the shock of separation doesn't rip the wires out of the ESC. Castle Creations stock investment- a good idea..

So I started recently to think about how to improved mini arrow/Kraken durability.

About a year ago I visited a sign shop and walked out with a 4x8 sheet of 2mm Coroplast fluted vinyl sign sheeting. "$20 left over, you bet I'll buy it"....Then, It languished in a corner, my wife even used it as a blotter when staining a table...But with the cold blast in the midwest this past week I broke out my Kraken plans. With the landing gear the Kraken isn't so vulnerable, but I've had sooo many small wings, Zagi Razor, Arrows etc, and hey, I have enough material for a Kraken right? Weight savings is not a big priority with this design. I slope soar too, the Big M hill in Platteville WI is visible from my yard-so a huge "mother ship" for sloping has always been on my short wish list, not to be confused with my tall wish list. I'm short so that's nonexistent.

A few build details:

The corroplast to foamboard bond on the spar box is fiercely strong. I wiped the corro with laquer thinner to clean off release agents etc.

I added a couple lengther of carbon fiber. a ridgid tube on the leading edge to add vertical dimension to the leading edge of the air foil, and some added but seemingly unnecessary rigidity.

I plan to slope with this so I added a square carbon fiber tube that spans and ties to the foam core box spar. I didn't want to discover after folding that the corroplast would permit a flexy spine. This triangulating spar did the trick.

Servos. Kudos to Bixler, but 9gram servos even metal gear versions just aren't my speed..literally. All my other wings struggle to get the C/G forward, but with the tractor motors that's just not going to be an issue here. I opted for standard sized MG servos installed on their sides.

So that's my build progress report. My wiring harness is done...Man buy that $9 power harness from FT my soldering iron got a major work out heating 13g wires. Honk on those connections to be sure they are not "cold soldered

For sloping it occurs to me I can remove the swappable pods...it might be worth the extra effort to attach my landing gear with brackets just so I can plop this one in the grass to prove my point about having built a more durable nose.

Cheers!

PS Flite Fest 2018 was a highlight of my family's year. We spent a week at Air Venture, I earned my PP in 2018, but Flite Fest in OH despite the heat was a great memory. Thanks all.
 

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Bricks

Well-known member
#4
RcGreaves you need to come down to Comros RC spring fly in out side of Durand, it is 3 days only cost is a donation of either food or money for the food pantry, and they give free rides in there Beaver plane with floats. Friday night is free beer, soda and pizza for all pilots it is just plain fun. All the pilots that want to put on an airshow for the spectators.

I see you have PP if you want you can fly down and land on there grass airstrip there have been an amazing amount of full size aircraft fly in. Two years ago we had a P51 and F4U Corsair come in.
 
#5
RcGreaves you need to come down to Comros RC spring fly in out side of Durand, it is 3 days only cost is a donation of either food or money for the food pantry, and they give free rides in there Beaver plane with floats. Friday night is free beer, soda and pizza for all pilots it is just plain fun. All the pilots that want to put on an airshow for the spectators.

I see you have PP if you want you can fly down and land on there grass airstrip there have been an amazing amount of full size aircraft fly in. Two years ago we had a P51 and F4U Corsair come in.
Thanks bricks except several Google searches didn't show any event. Im not certain if you mean Durand Wisconsin or someplace preferrably warmer today!
 
#6
RCGreaves:
Have you considered 3D printing a reinforced nose overlay for greater strength? My college age sons and I are in early stages of designing craft(s) for 2019 OHFF combat. We are looking for means by which we can increase structural integrity. Survive impacts in the air and ground. Your coroplast might be the ticket over DTFB.
 
#7
RCGreaves:
Have you considered 3D printing a reinforced nose overlay for greater strength? My college age sons and I are in early stages of designing craft(s) for 2019 OHFF combat. We are looking for means by which we can increase structural integrity. Survive impacts in the air and ground. Your coroplast might be the ticket over DTFB.
I recall doing slope combat with Zagi EPP ships 20 years ago and plowing full speed into thew "granite cumulous" side of the hill when up ended and pointed there..BOOM!! Under the taped skin was EPP popcorn. repairable, similar to dumping your intestines into your gut when hit with mortar fire...

Mating something really tough to something really not will always result in the not tough shattering first. So covering foamboard with a tough shell helps survivability but only to a point, right?

Getting the battery up and away is a big part of it. "less mass to crash"..

Trick R/c in CA did some innovative things with EPP, like they bonded a leading edge band of EPP to a wing in EPS for the THL ZAGI to get lightest weight. Still have mine thousands of flights later..

For combat weight is less critical. I was always amazed that Uline/mailing tape would take a compression impact and hold back the rebound back sort of like the exoskeleton on a bug gives it form from the outside skin... A taped wing might help.

A wire cut EPP V around the front 2 or 3" with the airfoil shape then bonded to a wing like the mini arrow would work better, but corro or all epp is probably best. THere may be a new product in this idea BTW..

There are free plans decades old for a corroplast wing called the Pibros that may speak to you. All corroplast and so very simple to fold and fly. Foam board is great for all the known reasons FT is successful, and it gets my kid carving. But,your application definitely demands a glove or something covering the nose like a steel toe protects your foot right? So, To answer your question, I think a tough cap on the nose that ALSO ties in the battery tray, my "ejecto" idea has potential.

Teach me more. 3d printing is still new to me.

Cheers!
 
#8
I guess the real news Not mentioned from my experiment is that the thinner 2mm coroplast fluted material rolls around the spar box with next to no distortion of the shape. Typical 4mm would never work...if would distort etc.

Also, I chose to orient the flutes on my "Corro Kraken" - Huh, huh..that's got a ring to it!! --the flutes are at a 45 degree to the spar. Worst case I figured I'd need to turn them parallel to the spar but no...It rolled fine and probably gives greater strengthening with that orientation. The wing probably doesn't need the extra spars I added but after a few combat plants to terra firma, I'm guessing the Corro might fold in the middle of the wing and flap requiring rebuild or dumpstering. What I have here appears to be very tough.

Another older Corroplast technique I forgot to mention is they fashioned spars from paint sticks and wooden yardsticks. I would have except that the foam core box spar to BOTTOM ONLY Corro bond could be flapped in the wind so to speak without releasing at that joint. So I didnt bother with that option. Wood does bond very well to cleaned Corroplast BTW but maybe not as aggressively as foam core..once formed the box spar joints on my " Corro Kraken TM..there I said it again.. they are solid. I worried they would release, not so far.
 
#9
BTW this discussion inspires me to fashion an EPP Battery bay internal to the wing with ejecto shoot. Less drag than a battery dangling from the bottom.
 
#11
So another ice storm tonight has me busy in the shop. Captain Video's comments about combat durability got me thinking about past combat ships so I added a nose cone for your entertainment pleasure. I figure once the pods come off and I slope this monster that extra layer of corro will make it less likely to collapse in a nose in crash.

Another combat trick I like is Tyvek. Instead of foam board elevons, I laminated 1/8" hard balsa then sheeted that with Tyvek and 3m77 adhesive. Then an outer skin of mailing tape, hinging top and bottom, and perimeter tape is Extreme packing tape. AWESOME STUFF! My spanwise Carbon spar was nicely placed to reinforce my servo install. I cut off the mount tab on one side, scuffed the case with sandpaper and added a 4mm coroplast bulkhead behind the servo. This keeps the servo mount rigid and adds an axis of attachment for the servo.

tomorrow I'll finish the landing gear install, elevon control rods, battery bay and finally the wing tip plates.
 

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kilroy07

Well-known member
#12
The way you oriented the elevons.... is there a reason you’ve done it opposite the design?
Just curious, I really like mine and have been using it as a test bed for all sorts of crazy ideas.

Love the Tyvek trick (and your source ;))
 
#13
Kilroy07,

"wow- that is different than the plan"...

Candidly sir, when I cut up my plans months back the elevon drawing got "dropped in the bin" as the Brits say. So I thought on and off over a week as to what I wanted to accomplish with this build and I simply eyeballed from the build video and from memory. That is to say, I took some measurements and drew the shape on my bench. (I took a quick pic below) IMG_1848.JPG IMG_1571.JPG IMG_2491.JPG . Now the memory part:


So Flite Test is half about the memories made, Right? Some of my best family modeling memories have been with combat wings back in the1990s when my boys were tiny tikes. No more. Some hard-won lessons from smackdowns on the slope are in my mods to the Koro Kraken TM patent pending.

So Bixler makes the elevon wider inboard to leverage the prop thrust over the control surface right? And with a rather flexible Foam Board elevon where will you get the most throw under load? Right, at the control horn-yes? Makes sense, but a good part of my mission is slope soaring where the requirements are different. I think it's a good exercise to answer why and explain why.

So if you look at my images, besides my memory lane trip with my boys.. Combat wings generally have wider elevons outboard than inboard. Plus it just looks cool! Also, the elevon stick must be rigid to transfer that twisting load solidly to the outer elevon tip. So for sloping, stiffness is important, and crash survivability critical especially for combat. I've shattered and rebuilt a lot of elevons so the extra time and effort to make a tough part is easily justified knowing I plan to chuck this off a slope and do carnage. Carbon fiber I shaped sticks on the trailing edge "Shock Flier style" with a taped skin does the trick. For furball action, I've been known to show up with elevons laminated in 1/2 ounce fiberglass. Now Tyvek and Extreme packing tape get that same job done with less mess.

So the landing gear arrangement on my Kraken is amazingly tough, Kudos to the FT design team (though my landing gear legs will go behind the barbeque skewer so the skewer and hole don't shatter in a crash or bad pancake landing.

Finally, the lever moment at the tip of the elevon is more powerful than the inboard position so I would argue that, overall, wide at the tip is the way to go. For slope gliding, I opted for that knowing that either way would work with the twin powered set up. On the slope without motor thrust, the original FT design would be a disadvantage.

You make me want to experiment with an added panel right behind the motors for comparison. I am curious whether I overlooked any other rationale for the shape he used. But that's half the fun right? Think building is a beautiful thing indeed.

The Zagi shape is edgy, the Kraken more rounded. I may reshape the tip plates so they are more triangular to make it even more distinctive.

Thanks for the memories. Cheers.
 

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kilroy07

Well-known member
#14
I've only been the hobby for a short time (about a year and a half) I the reason I questioned is I'm always learning something new.

As I understand it, since your setup is changing more of the chord of the wing at the wingtip (which would provide the most leverage) I was just a little concerned it would lead to twitchiness, but at the gain of much more effective control response. Which would seem to be your goal.

I built my first (won't be my last) Kraken last year and it was such a fun plane to fly.
After stalling her out FPV and seeing nothing but trees, I nosed her in (Dang trees have claimed WAY too many of my airframes!) I decided to rebuild her as a pusher and lost the ability to loop. So I think there was some nose authority lost without the propwash...
https://forum.flitetest.com/index.php?threads/pusher-kraken-mod-lost-some-elevator-authority.56830/

My next "update" will be to split the wings and add a center pod arrangement with removable wings (the thing sticks out the back of my truck unless I put the seats down!) :LOL:

So when I saw how you have your elevons arranged, I thought... "Hummm... I wonder..." :unsure:
Thanks for the information. (y)(y)
 
#15
So your comment about twitchiness is a good one. I probably only made them that wide to be similar to the original, backward or not! I could hack off the trailing edge of my elevons an area similar to the width of a yardstick and the thing would probably fly the same but with less twitchiness knowing that the elevons are stiff. There may be some Bixler magic in having the wider section inboard but I always equated that with the foamboard being so flexy. Looking at my elevons today, I'm not too sure I didn't go overboard with the outboard width of the elevons. Lots of wings use a simple rectangular balsa strip elevon. "Note to self, max out expo on Kraken".

Pusher is worth trying if you haven't, but bear in mind the real genius of the Kraken.

All pushers are required to put the battery all the way forward to achieve CG. With narcelles and motors out front, the Karken battery can sit on or near the CG and be a whole lot less vulnerable to damage. As the span of a delta grows, this aft of CG moment for the motor grows longer and this aft (backward) ballast harder to balance. So overall the tractor set up can be lightest.

Trick RC ( the Zagi maker) did a twin pusher with tiny motors that worked. it flew very well, sounded awesome but didn't hold my attention like the Kraken. It has sort of a Dehavilland Mosquito feel I like.

Anyway, if you pick your outrunner well a pusher has some advantages. Great to hand launch by grasping the nose and chucking overhead. No landing gear required. Prop is away from the view of an FPV camera forward and the camera gear helps with adding nose weight.

A plug-in wing is a great solution for this mother ship. And the center blunt nose pod section idea allows you to move the pusher motor quite far forward if you went that route. I may have to give that a go myself.

It occurs to me that I only did one other powered wing with tractor power. It was a Cox .049 velcroed to the nose attached to a U shaped ply motor mount. it needed a foot long length of music wire hanging aft with a couple ounces of lead to get it balanced. Reminded me of some prehistoric bird. When the motor ran, it flew great.
 
#16
Kilroy07: I really appreciate you calling my attention to my having installed my elevons "Zagi style" from memory vs the plans build from FT. After sitting on it a couple snowy weeks here in Wisconsin I think Im ready to wrap this thing up and do a maiden. I have decided to take the time to refit my nicely hinged elevons, reversing them and may even take an inch or so off the trailing edge. Having the most elevon behind the props screws just makes the most sense..perhaps on the slope, my arrangement would be better, but overall I worry about the Kraken's tendency to pirouette on takeoff rolls. I figure over thinking this will never be a substitute for getting it up in the air right? Weather permitting I'll post some video within the week.
 
#17
Kilroy07 with a Flite Fest deadline I got Krakken on my ....Krakken. I reduced the overall area, and inverted them making the inboard side the widest Bixler style. I have still to program my throttle mixing and build a battery bay. Thats my boy now 21 ...we've been messing with wings for awhile! Flite Fest fever...yeah!
 

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#18
So my efforts to get my Kraken flight ready for FF19 were thwarted this past holiday weekend.

My efforts to program variable thrust just failed over and over. I use a now dated DX7 and the more I tried the more gear I smoked. Very frustrated.

I'll pack it for FF19 and find someone more adept at mixing in Ohio. Like my Kraken's eyes? Anybody ever have a bat kit as a kid? Whaky Kraky sounds fun! Psyched for FF19!
 

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#19
So Flite Fest 2019 is history and we had a fantastic experience. I really really struggled to follow Bixler's video on setting up variable thrust. In the end I met a charming teen named Aiden in my build tent who wrestled my Spectrum 7 to the floor and successfully got the variable set up installed. I installed the Radial Flight Pack C and found the parts and price a good value for the dollar. The plane traveled well and with a 3sa3500 balanced out well with the addition of a 2300mah rx pack. The all up weight is no doubt higher than foam core so a 4s set up is my next step. Any issues with runnging 4s on the FT ESC?
 

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#20
One added thought: My spar addition really worked out well. I placed it just ahead of the servos allowing them to be zip tied to the spar and hot melt glued to the scratched and acetone scrubbed corroplast. Maybe the corro will sag over time but now is when I learn if my substitute material is more tough.