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        Build Log Yardbird!!!!!

#1 schrederman Dec 19, 2006 11:14 PM

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Well, as promised, here comes the Yardbird build thread. Please don't reply here and fill the thread with oooohhhs and aaaahhhs.... as flattering as they are, they only clog the actual build. If you want to post that kind of thing, please post it in the original Yardbird II thread. I'm not trying to quell anyone's enthusiasm, just trying to help those that are actually trying to get through the build. And, we're oficially dropping the "II" designation... it's just the Yardbird.

Not as promised, I will be starting with the wing. I tried to get going on the fuselage, first, but I just ain't built that way for some crazy reason. I had also decided to do the whole build, and then post it all at once. My job and the holidays are going to make this tough enough without trying to do that. Besides, if I do it this way, people will bug me enough to keep me working on getting through it.

Rule # 1.) If you add lots of beef, it will fly like a cow. I can't take credit for that. I saw it on the builders board today while watching it ice over... :eek:

Rule # 2.) Building is an art, and some basics will be addressed here. If you don't agree with my techniques, please argue on the other Yardbird thread, and remember that old free-flighters never die, they just smell that way... :p

Rule # 3.) Sanding 101 is a required subject. I'll discuss that a lot. Again, if you don't agree with my methods and techniques, please pee in my socks on the other Yardbird thread... :p

Rule # 4.) Whether you think you can build this, or you think you can't... you're right. If you expect exacting perfection, please build something else... I haven't walked on water and probably never will...

We'll begin with the outer panels to get warmed up for the other stuff... I know that AJ had some problems with flutter at super winch loads and we will be trying to address that as part of this build.

Here's a pic of an outboard panel just about complete.

Jack Womack
Professor Emeritous of Goofing Off :D

#2 schrederman Dec 19, 2006 11:18 PM

Getting started
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You can't build a straight wing on a crooked table or without a good strait edge. Here's the outer panel beginning to be laid out.

#3 schrederman Dec 19, 2006 11:32 PM

Outer Panel - continued
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Once the Double - D sheeting... :D ... and tapered lower spar cap are set, the lower .007 X .25 carbon fiber can be tacked down. No need to glue it down it's entire length, yet. As you add the ribs and 1/16 shear webs, you'll be using thin CA and it will run under it as you go. That will save a gram or two, at least. The spar cap that you tapered may be a touch wide for the ribs. Wood thicknesses can also vary. Make sure the ribs fit, by removing material from the front and top of the spar slot if necessary... do NOT notch the spar...

#4 schrederman Dec 19, 2006 11:36 PM

Moving on...
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It's now time to add the ribs... simple, you say? Well, let's do it correctly. That means straight and square, so our wing will maintain that beautiful 3014 airfoil that seems to fly so well...

Yes, I really do build with triangles and straightedges...

#5 schrederman Dec 19, 2006 11:42 PM

Still more...
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Ribs are in... Seems that the shear webs don't fit well, and that will be resolved. However if you have a current wing kit, you will have to fit the webs... Heck, I drew this mess and I'm having to do it... :p

Be absolutely precise on these. They need to fit and be perfectly aligned with the bottom of the top spar slot. NO VOIDS...

#6 schrederman Dec 19, 2006 11:54 PM

Got ahead of myself...
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Sorry, but while laying all this out, I forgot to cover preparing the trailing edges. They are a sandwich of 1/16 balsa and a little 3/4 wide piece of carbon tissue. Use the .5 oz stuff. I am using the .2 oz. and it's not helping as much as I'd hoped. If you don't use cf, use a 3/4 strip of 1/64 plywood in between the sheeting, with the outer grain running chordwise. I'll be building my next one that way.

Anyhow, the trailing edge sheet tapers slightly in width. It also needs to be tapered in thickness from where the rib ends out to about 1/64 at the actual trailing edge. Draw a line on it using the first and last ribs as guides. Make a matching pair... one bottom, and one top. You may want to make them for both outboard panels at one time. Sand it across the grain at first and then with the long block lengthwise to smooth out any irregularities. This is important for airfoil accuracy.

#7 schrederman Dec 19, 2006 11:58 PM

T. E. Continued
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Here's what the next step looks like. The cf tissue is laid on, tacked with fast CA at each end, and th trailing edge upper is glued on with slow ca.

#8 schrederman Dec 20, 2006 12:14 AM

Finished T. E. - Upper spar cap
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Here's the finished T. E. with a good shot of the upper spar cap. Since we're through with the T. E. we'll discuss fitting the top spar.

The top cap is just like the bottom, except that it's spruce, and not hard balsa. Al the caps should have been tapered at the same time, so they should be uniformly tapered. Again, fit needs to be precise. If the slot needs to be modified, remove material from the front of the slot, keeping the aft slot edge perfectly straight. If the slot isn't deep enough, chances are your webs are also too tall. I would use an emery board to remove the material very meticulously... remember... NO VOIDS! The spar integrity is dependent on fit. If you've read this far before beginning, you're in luck. You can set the depth of your spar slots before beginning, and avoid a lot of unnecessary work... yes I should have mentioned it... :o

By the way, the entire spar of the outer panels should be done with wood glue... no CA. The rest of the structure can be done with ca or wood glue, except the cf D-tube doubler. That needs to be done with CA. The top sheet needs to be done with wood glue or Gorilla Snot used sparingly...

#9 schrederman Dec 20, 2006 12:26 AM

Spar complete
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Should look like this before proceeding... note the crossed pins for a little glue pressure...

Take a look at the sanding block... it's aluminum, 1/2 X 3 X the length of a piece of sandpaper... I use it because I know it's straight, hard, and will give me the desired result. A wood block isn't precise enough for my taste. Again, and I stress this, use only the weight of the block for pressure when sanding something like a sheeted wing. If you use a lot of force, you'll end up with the sheeting sanded almost all the way through at the ribs, but almost full thickness of sheeting in between. This is because the unsupported sheet between the ribs will move down. The thinner it gets over the ribs, the more the middle will move down away from the sand paper... and don't ask me how I know this... :eek:

#10 schrederman Dec 20, 2006 12:40 AM

Leading edge
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Well, we're ready to do the leading edge. If you followed the Houston Hawk project, you already know I love my jack plane. I could comfortably shave with it. Sharp blades are necessary for soft woods... nuff said... Because of the shape of the airfoil, I tried something with the leading edge I've not done before. This is a minor ureka... Instead of bending the bottom sheetng down to match the 1/4 square leading edge, I have planed a bevel onto the bottom edge to match the upward curve of the bottom of the airfoil before installing it. Three quick passes of the plane and one quick lengthwise pass with the sanding block and you're done.This is probably something someone else had thought about before me but I'm kinda slow, sometimes... :o

This pic shows the wing ready for upper sheeting. We'll get into the shear webs and upper cf cap in the next frame. The leading edge has been beveled on the bottom, installed, and beveled on top to accept the sheeting.

#11 schrederman Dec 20, 2006 12:48 AM

Double D...
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:eek: Double Ds!!! Well, OK, doubled D-tube... The bottom cf cap was laid down when the sheet was laid out. After the ribs were done, I did all the shear webs at the same time, because it's tedious... The front webs are added with thin CA, and it will run around and glue the cf to the sheeting... and to you as it travels up the grain of the wood... Make absolutely certain that the webs are straight, and don't protrude over the rib tops. Use a straight edge to check, and an emory board to take them down if necessary. The cap is added with slow CA... and when all else is done...

#12 schrederman Dec 20, 2006 01:13 AM

It's time for the top sheeting
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I use Gorilla Glue for this... This is a neglected glue joint. I have heard of all kinds of ways to do this, and some of them give me the shivers. I hate to think of all that work going to waste because of no torsional strength... no strength because someone wanted to hurry this step. If you use contact cement or try to use slow CA... call it something else... not a Yardbird...

Here's how I avoid problems with this joint. On this model, some of the upper sheeting extends beyond the aft edge of the spar... my contribution to thinking outside the box... CA is fine there, and in fact helps this process. First, I cut the sheet a little oversize. Then I trial fit it. Then I coat the rib tops, and the cf spar top with Gorilla Glue... sparingly... I use a stick and barely have a bead at all. I smooth it off the cf spar so as not to build up weight. Next I use slow CA on the wood spar and the rib sections behind the spar. Then, I dampen the inner side of the sheet and apply it, using the heat gun to heat the Gorilla Glue up a touch. After the slow CA has the aft part of the sheet held firmly to the wood spar and aft portion of the ribs, I smooth the sheeting down to the leading edge, and use fast CA to attach it, beginning in the middle, working outward, about 3" at a time. Then I place the whole thing on the work bench, with about 1/2" of the leading edge hanging over the edge, and stack on the weight... in my case, I have 20 years worth of Saoring magazines... I use about 6 years worth... :D

Leave it at least overnight. The Gorilla Glue expands and forces it's way into the pores of the wood, and fills tiny gaps. The urethane then actually shrinks slightly pulling the joint even tighter together.

#13 schrederman Dec 20, 2006 01:15 AM

Tomorrow, if I survive this winter weather, I'll do a tip panel. Not nearly as involved as this, but fun, none the less... We'll join it when I can get the table saw out...

#14 schrederman Dec 20, 2006 10:40 AM

Well, no pics but the second outboard panel is as rigid as the first, so tonight I'll be building a tip panel, and beginning the center section... with all that pretty carbon...

We'll also look at the spar bumps we created last night and talk again about sanding them out.


#15 schrederman Dec 20, 2006 07:13 PM

Tip Panel Framed
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Well there's not much to explain here. The spars are tapered in thickness, not in width. They're only 1/8 sq. to start with and taper to 1/8 X 1/16. They are webbed with 1/32 hard sheet, on the face of the spar between the sheeting, not in between. Eveything still goes, with the exception of the second d-tube. I will add that if I feel I need to in a future version. I thought about it and feel that the stiffness of the center and intermediate panels should be sufficient. I'm going to sheet this and start the center section. If I have time, I'll post a few more tonight and some tomorrow. Then we'll close down for a while so Santa can do his thing... :D

Here's the tip panel, framed up.

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