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Author Topic: Craft-Air Windrifter SD100 Kit  (Read 768 times)
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Donjamin
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« on: December 22, 2014, 11:38:46 PM »

I just picked up a complete Craft-Air Windrifter SD100 kit off of eBay.  Does anyone who has built and flown this model have any tips or lessons learned that you are willing to share?  This kit has the epoxy-fiberglass fuselage.  Unfortunately, the fuselage had a lateral crack just behind the wing root.  This should be pretty easy to fix with a bit of light fiberglass cloth and resin.

Don
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Donjamin
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lincoln
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« Reply #1 on: February 11, 2015, 08:13:12 PM »

Sounds like fun. If possible, straight grain popsicle sticks glued inside might be stronger and invsible. Wash off any mold release or amine blush first. Or is it polyester? You can probably treat that the same way. In my experience, epoxy that's made for gluing works best. Also, Goop or similar might be good. Held a servo tray in an Ava that went in almost straight down right after launch.

Caveat: this is all based on relevant
experience with other models.

P.S. taper the ends of the sticks. Roughen inside of fuse where gluing of course.
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kukailimoku
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« Reply #2 on: February 13, 2015, 12:42:42 PM »

I always have a surfboard ding repair kit nearby for this sort of thing. Sets up hard as nails and sands like wood. Two thumbs up on adding bracing as well. You might consider chopsticks if you have the room, they're pretty stiff.
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Pit
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« Reply #3 on: February 13, 2015, 01:41:52 PM »

Looks like only the resin has been damaged - the fibers seem to be still intact.  CA might be all you really need, depending on whether or not the "break" goes thru to the interior layers.  Can You see the inside at the break?

Not familiar with the 'glass Windrifter fuselage, but if you can access the kink thru one of the fuselage openings the strongest - and probably lightest - method for repair is an inside lamination of carbon weave that extends about an inch fore and aft of the damaged area.  The outside can be fixed before doing the inside with CA - just apply a few drops and press the area together under a layer of Monocote backing (just don't press so hard that the surface is deformed).  Proper surface prep, inside and out, is required as already stated.  The outer area of the kink can be then sanded smooth again and painted.  For a bit more confidence building, a single wrap of lightweight glass cloth can be added around the break and the edges feathered in (try to keep the weave at 45° to the fuselage axis - for all laminations).

This aircraft isn't a racer, so it doesn't need a ton of strength in that area - even for winch launches.  Popsicle sticks and "chopsticks" were fine back in the 60's and are still ok in a pinch, but look cobby (even tho "hidden") and take up a lot of room plus getting them to stay stuck along the whole length is uncertain at best.
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lincoln
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« Reply #4 on: February 13, 2015, 11:44:33 PM »

Not sure how hidden popsicle sticks are "cobby". If they're inside, you can't see them.

I'm sure that carbon weave is a good way to go, and better than most, but for the fanatic there are stronger and lighter ways to go. Such as using unidirectional carbon fiber. Tapering the ends to avoid stress concentration might be harder with the weave or even the uni than with the sticks. I suspect most gliders like this are lighter than optimal, considering the kind of airfoil they have, so more weight near the c.g. may make them fly better instead of worse. I expect a straight wood grain stick would be stiffer for the weight than a woven carbon sleeve. And stiffer is the name of the game when buckling is the failure mode. Might be good to use a long stick along each side of the fuse from  about 50 percent chord back most of the way to the tail, though the optimum may vary depending on exact proportions. I understand a really light way to prevent buckling is to make up a long balsa piece, maybe only 1/16" thick, with the grain crosswise, just to keep bends from starting. It would be like a horizontal deck inside. One might also attach pushrod housings before inserting it.

If you can get the carbon weave in and stuck, you can also probably get the popsicle sticks in and stuck down. You could put threads across a few of them, insert with glue, and use a balloon or something to hold them against the inside of the fuselage. And they don't have to be full length. This method would probably hold the fuselage in alignment, too. If the paint is sanded off, you can generally see through the glass to see if the glue is in contact everywhere.

If I was trying to get something into the weave, I'd use epoxy, with maybe a bit hot air from a heat gun so it could wick in better. Use sparingly and with ventilation. I'm pretty sure it's stronger than CA.

Launching loads are not the highest loads. Unless you are landing in very long grass or deep, fresh powder snow, landings are the big load on fuselages. Usually sideways from one wing tip hitting the ground first.
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Donjamin
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« Reply #5 on: February 16, 2015, 08:28:16 PM »

Quote
Looks like only the resin has been damaged - the fibers seem to be still intact.  CA might be all you really need, depending on whether or not the "break" goes thru to the interior layers.  Can You see the inside at the break?

Thanks everyone who has posted a response.  The fiberglass is actually cracked through the threads and resin.  I received this model from an Ebay seller and as things like this goes, the crack was not disclosed.  Fortunately, the two fuselage halves have joined together and who ever did the work did a nice job in bonding the two parts together.  The bad part is that there is this crack in the tail of the fuselage.  I was thinking of applying a small spot of fiberglass cloth and covering it with a small amount of resin to close the crack from the inside of the fuselage.  I'd then use some auto body epoxy to cover the outside crack and then sand the outside of the tail smooth to cover it.

Since I'm now building a Sagitta 600, the Windrifter will have to wait a few more weeks before I can start the build process.

Don
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Donjamin
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cbhank
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« Reply #6 on: May 11, 2019, 10:55:48 AM »

Yes this is an old thread, but ...

I want to build a windrifter from the plans on this site. But there are no rib templates in the plans ...

Does anyone have the rib templates they can share with me?

Thanks in advance!

Mark
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lincoln
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« Reply #7 on: May 11, 2019, 01:05:38 PM »

Have you checked the 3 Windrifter plans on Aerofred? You could also shrink that one rib from the plans. Or look at other Craft Air designs.
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cbhank
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« Reply #8 on: May 11, 2019, 03:11:18 PM »

Have you checked the 3 Windrifter plans on Aerofred? You could also shrink that one rib from the plans. Or look at other Craft Air designs.

I will do that, thank you! Didn’t know about that site until you told me.
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