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Avid C HH wing build 101

93 posts in this topic

Posted

If I was in your situation I would just order a small sheet of plywood and make what you need, If you are trying to keep it original that is, Kitfox uses the 17 3/4 centers on all there planes, if your in a hurry just do that, but you got a long long long ways to go before your flying, at this point you can make it how ever you want,

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Posted

Right you are, sorry, (9) ribs outboard the tanks is 12" o.c. HH spacing. With the tank notches 18" o.c. an the correct # of trailing edge ribs, I might be tempted to just use what you have if you don't mind the aesthetics. I do however agree with you on the overall construction using TE ribs at flaperon hinge locations, less than favorable IMO. Actually, I opted to replace my Avid Mk-IV wing tanks with Kitfox 3 slip in wing tanks (made by Skystar) to use full length long ribs for the flaperon hinges and strengthen the wing. They are not a perfect swap due to washout and slight rib differences, but can be made to work with a little finagling. It's been a while but, IIRC, you could not simply use long ribs outboard of the old Avid tanks because the tank was too wide to allow proper hinge spacing. The KF/Skystar tank was made to fit between the ribs. A couple other 'between-the-rib' options might be the new E-resistant Airdale F/G tanks or Rocky Mountain Wings poly tanks. The later would even allow an additional rib between the smaller tanks. Search around, some info HERE   

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Posted

HI guys! 

Finally back to wing buildin! I've cleaned and inspected the spars. There were some minor scratches which were lightly filed and sanded out. I'm thinkin' they're in good shape, no major defects. Got the ribs ready to go and am sliding them on. There is a small place on the trailing end where the rib web comes through the cap strip that could use a little filler. What should I use? Before I get 'em all on I need to whittle on rib #8 so it will fit over the strut attachment. The front spar end of the rib is no problem, but the rear spar opening is gonna be a little hairy, I've got to take down the inside of the cap strip so it'll go over the bracket. There sure ain't gonna be much left when it goes over the bracket. I think I can cheat a little on the opposite cap strip (top) to slightly enlarge the OD. I don't think it will change the profile enough to make any difference. When I get #8 fit, I'll get the rest of them on. Do you guys still think a 1" washout is good? I even thought I read, 3/4" would be better!

I'm figurin' on making a couple of more trailing edge ribs to stay consistent with the wing design. By gusseting the forward end and using the the aluminum trailing edge I think the ribs would be structurally sound. I bought 1/4" marine plywood for all the gusseting, the drag tubes too. Is good, or do I want different? It'll be birch ply for the ribs themselves.

The gun's gone off and we're out of the blocks.....26K!

Wyatt

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Posted

Wyatt,  While you are mixing 9460 and flox to glue the ribs you will probably have some left in the mix cup - use that to fill in the capstrip voids.   EDMO

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Posted (edited)

dreamel works great for making the number 8 rib fit

Also I'm not sure if avid did it like kitfox or not but on all the hanger ribs there is a small piece of plywood that goes between the rib and the spar on each side, Needs to be glued in at the same time your gluing the ribs to the spar,

Edited by TJay

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Posted (edited)

dreamel works great for making the number 8 rib fit

Also I'm not sure if avid did it like kitfox or not but on all the hanger ribs there is a small piece of plywood that goes between the rib and the spar on each side, Needs to be glued in at the same time your gluing the ribs to the spar,

Trying to clarify what TJay said, these are 3/8" or 1/2" wide x about 2" or 3" long pieces about same thickness as capstrip and glued under the capstrip on each side of the rib where the rear spar is located.   May not work on an Avid?   Clear as mud??  EDMO

Edited by EDMO

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Posted (edited)

Won't work on the Avid rib. The rear spar cutout is too high, right at the very top of the web, and the capstrip actually sits right on the spar. The cutout on the Kitfox 1-3 rib is just a tad lower in the rib web, leaving about 1/8" space between the spar and capstrip. Ie, enough space to glue in the doubler. 

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Edited by dholly
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Posted

Great picture Doug,  I tried to find some pics in my stuff but didn't have anything as good as this.  JImChuk

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Posted

#8 wasn't bad. You can use the laminations of the cap strip to gauge your depth when takin' them down with the Dremel. They turned out fine. I'll get the rest of the ribs on and fit the drag tubes. Then, I gotta ask again, 1" WASHOUT? I did read somewhere 3/4" may be even better.

I am gonna use my tanks and build a couple of more TE ribs outa birch plywood just like the others. Should I use the 9460 I bought to glue the cap strips to the web or use something else? The glue on the rest of the ribs is kind of a light brown. When it comes to using the cotton flox, that's just a thickener not for strength isn't it? Also, on the strut attachments, microballoons were mentioned to use when gluing them on the spars. I must confess, I'm not familiar with either one.

Keep an image.thumb.jpeg.99c3da833ba91ff0e643ff4eye on me boys! 

Wyatt

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Posted (edited)

I believe the original glue used in making the ribs is T-88 epoxy.  It's a real good glue for wood.  I wouldn't hesitate to use the Hysol though, it holds the wood ribs to the aluminum spars, so it should hold  the wood to the wood.  I've used it that way myself.  The reason for the microballoons mixed into the hysol for glueing on the strut brackets is to keep the dissimilar metals from touching each other.  That will stop them from corroding like they would if they were able to touch. Microballoons are small fiberglass spheres that will keep the metals away from each other while still allowing a glue joint.    As far as wash out, I'm not sure how much is best, but the tanks have a certain amount of twist built into them, so I think they will begin to stick out above the spars if you don't have enough wash out in the wings.   Edit:  yes,  cotton flox is a thickener so the hysol doesn't sag or run out of a glue joint.  It takes hours for the hysol to harden, and its slightly runny when mixed without the flox.  JImChuk

Edited by 1avidflyer

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Posted (edited)

I cant tell you exactly how to mix the flox - you may think you put too much flox in the mix the first time you try it, but continued mixing will give you a fairly stiff paste that don't run when it starts to warm up and set.   You may need to experiment with the mix.  The mix I use, and I use a $25 digital scale from Harbor Freight, is for every 10 grams of epoxy and 10 grams of hardner I add the amount of flox I can hold on a large craft stick bought from Walmart - I buy both the popsickle sticks and the larger sticks there.  The small ones are nice for putting a radius on the rib/spar joints and elsewhere.  They say to use 100 grit sandpaper to sand the spars before gluing, but I like the purple scotchbrite pads better, and they don't contain aluminum oxide which is bad for aluminum, so I am told.  The old 2216 instructions say to wipe the sanded spars with alcohol, but I dont remember what 9460 instructions say - that is your call, but I did that.   I have used 9460 for lots of rib repairs and capstrips.

I don't think there would be much difference in performance between 3/4 and 1" twist.   EDMO

I believe the original glue used in making the ribs is T-88 epoxy.  It's a real good glue for wood.  I wouldn't hesitate to use the Hysol though, it holds the wood ribs to the aluminum spars, so it should hold  the wood to the wood.  I've used it that way myself.  The reason for the microballoons mixed into the hysol for glueing on the strut brackets is to keep the dissimilar metals from touching each other.  That will stop them from corroding like they would if they were able to touch. Microballoons are small fiberglass spheres that will keep the metals away from each other while still allowing a glue joint.    As far as wash out, I'm not sure how much is best, but the tanks have a certain amount of twist built into them, so I think they will begin to stick out above the spars if you don't have enough wash out in the wings.   Edit:  yes,  cotton flox is a thickener so the hysol doesn't sag or run out of a glue joint.  It takes hours for the hysol to harden, and its slightly runny when mixed without the flox.  JImChuk

 

Edited by EDMO

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Posted

Myself and a mechanical engineer buddy did some testing with various wood glues and epoxies including the T88.. Gorilla glue won hands down.  I used gorilla glue to do all my wing rib repairs in 09 and they are still holding strong and they have been put to the test. 

:BC:

 

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Posted

Gorilla glue? Really! With a name like T-88, it's got to be better. Just kidding! Good is good.Thanks Leni! Hey, what are your thoughts on washout? 1 1/2", 1", less? Heavy hauler undercambered.

Wyatt

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Posted

I wouldn't put in more than .75"  I would cut mine down to 1/2" if I had it to build again   I'm not sure what the kf washout was changed to but I would go with that.  I have 1 3/4" in mine and I know I'm leaving a boat load of performance on the table just by the way it flys.  if your worried about stall break you can always put vgs on the last few bays to keep the tips flying.  I don't think it would have a nasty break without them though.

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Posted

BHi Guys! Back at it again, wing buildin'!

I'm ready to start gluin' ribs. Got a couple of questions before I start. First, the washout: Are y'all in agreement that 3/4" would be good? And second: Degreaser for 9460 glue prep. I have what came with the kit and I also have this paint surface cleaner that I have leftover from my Challenger.

What'cha think?

Wyatt

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Posted (edited)

I just rubbed my spars with purple scotchbrite and wiped with alcohol where the ribs connect - my wings have been handled a lot and sometimes got banged around and seems like the 9460 is holding good.   I think it bonds better than the original 2216 Avid used.  

3/4" Washout should be better than the original amount.   EDMO

Edited by EDMO

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Posted

If my memory is correct, scotchbrite and alcohol (to clean the spar, not to drink)  I think Kitfox said green scotchbrite  though.  Not sure if it's finer or courser then the purple.  JImChuk

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Posted (edited)

If my memory is correct, scotchbrite and alcohol (to clean the spar, not to drink)  I think Kitfox said green scotchbrite  though.  Not sure if it's finer or courser then the purple.  JImChuk

Jim,  I could be mistaken, but I think I read that Purple Scotchbrite is about same as 100 grit .  Somewhere there is a chart that compares different  colors with sandpaper.   Probably don't matter as long as it is not the pads with soap in them.  EDMO

Edited by EDMO

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Posted (edited)

I think 3/4" twist is good. To prep the spar tube surface for fresh Hysol, clean with MEK then Acetone, rough up the bonding points in a cross-hatch pattern with maroon Scotch-Brite #7447 pads only (other pads or sandpapers that contain metals other than aluminum oxide can imbed metal and cause stress risers in the aluminum spar tubing). Clean with MEK and Acetone again. Mark the rib locations with a ball point or felt tip pen (graphite from lead pencils is a no-no on aluminum) by wrapping a piece of heavyweight paper around the spar tube and tracing along the edge for a perfect line around the spar. Then mix up a small batch of Hysol epoxy 1:1 by weight (don't eyeball, use a digital postal or diet scale with tare feature) and spoon it into a freezer weight zip top sandwich Baggie. Clean spar with MEK and Acetone again. Cut the tip end off one corner slightly and use like a piping bag to lay a bead of epoxy all around the spar just outside your rib location line. Dragging the rib into position through the epoxy ensures a good bond between spar and rib. After the Hysol has skinned over slightly but is still pliable, wet your finger with Isopropol Alcohol and run it around the joint for a perfect filet. Clamp a straight edge along the top and bottom capstrips of several adjoining ribs to make sure they cure flat, will save a lot of sanding and make for a visually appealing end product!

[edit] A couple things I didn't mention above is that you should use a garrote to hold the spar tightly against the rib while the epoxy sets and you must go back after the Hysol filet on the first side has set up to apply and smooth the filet on the other side. I find it easier to do this way rather than trying to glue and smooth both sides then straighten/brace etc. all at once. That was a recipe for getting glue all over everything!

Edited by dholly

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Posted

Thanks guys!

I sure look forward to smelling MEK again! I've missed it since my Challenger rebuild. I bought some syringes down at Wicks that I was gonna try to use to apply the glue. Do I want to use cotton flox too? Doug, what do you mean, a garrote? I have fiber reinforced strapping tape to strap and twist the front and rear spars tight. Is that what you meant? 

Wyatt

On my way to buy the stuff. Ain't gonna get much else done today. It's a nice day here in central Illinois and I'm flying!

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Posted

Yep, you got it.

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Posted

Use the flox - Without it, your glue will get thin when it starts to heat up and will drip out of the joints.  EDMO

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Posted

Excellent pictures and cotton flox it is!

Thanks! 

Wyatt

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Posted (edited)

If you have any roughness, or glue joints that need to be smoothed more, wait a little while to let it set some, and you can wet your finger with water and smooth out any roughness.  Another tip - at the joint of the capstrip and front spar, you can put some blue tape over the joint and smooth it out by rubbing the tape while the glue is wet - after the glue hardens, the next day, pull the tape off and sand a little if you need to.   EDMO

Edited by EDMO

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Posted

Also, if it wasn't mentioned already, make sure the flaperon fits the rib tails.  JImChuk

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