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Joined: 7/3/2003 From: newton,
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Well, finally got started on wing layout. The BirdDog wing is a semisymmetrical airfoil, and is constant chord to the outside edge of the flaps (Rib 7), a bit more than 1/3 of the span. Then it is a double taper, meaning the leading edge tapers back, and the trailing edge tapers forward. On top of that, the section gets smaller from the top surface to the bottom surface. It's impossible to lay out the entire wing flat once the spar is in place, it must be shimmed at the outer end. Ribs 8-15 are all different, they get shorter and narrower as you approach the tip.
The other requirement is that 1.5 degrees of washout must be added to the wing from rib 7 (outside edge of flaps) to rib 15 (tip). One way to do all this is to build a jig. Another way would be to use one of the commercial jigs where you drill all the ribs and insert twin rods parallel to each other, which suspends the ribs off the surface and allows you to add "twist" to set washout.
If I had built a jig, I'd have to build two, one for the right and one for the left (mirror imaged). I came up with something "completely different", to put it as Monty Python would .
First, you have to mark the chord line on each rib, which is shown on the templates on the plans. Then, I drew vertical lines from the top spar notch to the bottom. These are perpendicular to the chord line. At rib 11, which is halfway to the tip from rib 7, I made a line that is 0.75 degrees off vertical at the spar notches, and on rib 15 (tip) I made one that is 1.5 degrees off vertical.
I layed the bottom spar on the plans and secured it, then laid out the ribs from 7-15. Using two squares (actually right triangles) to keep the ribs square front to rear on the spar, I set the washout on R7 at zero, R7 at 0.75 degrees, and R15 at 1.5 and glued these to the spar. Then I placed the leading edge spar in place in the notches in front of the ribs in R7, R11, and R15, and placed the remaining ribs in their spots. This L.E. spar serves to locate the other ribs with their increasing (as they approach the tip) amount of washout. After gluing them , I added the T.E. strip.
Now, I added R2-7, which all have zero washout (Note: R7 is actually two ribs glued together, 7A and 7B, they are slightly different and mark where the flap ends and the aileron begins, and have different chords). After aligning and gluing these, I added R1 which is the root rib. It does not fit vertically, it must "lean" about 2.5 degrees to set the dihedral angle, and there is a special shear web template to make the web between R1 and R2 that has the correct angle. I used this web to set the angle of R1 and glued it in place.
Now, I have all the ribs glued to the bottom spar, and the washout is set. 1.5 degrees isn't much to look at, and you can hardly see it without careful sighting down the wing and measuring. What I have to do now is add the top spar and do it in a way that "pulls" the wingtip off the board about 1/4 " (actually, half the difference of the width of R7 and R15) so that the top and bottom taper of the wings is identical. What I did was to glue the top spar to R8-R15, which now sets the relationship of the spars to the outboard ribs. This makes the top spar divergently unparallel to the bottom spar, so it doesn't want to lay in the notches from R6 back to R1. As I lay the spar into these notches, I pull on the root end of the top spar, which pulls the tip off the board. I had made alignment marks on both spars where the ribs should meet the spar, , so I made sure they were on the marks, and the tip was the corect didstance off the board, and that the section from R7-R15 was not bowed, Then I glued the top spar to R1-R7, and also glued the shear web in place between R1 and R2 and the tip spar from R1-R7.
I now took the assembly off the board and sighted down the wing from the tip end. The leading edge spars were perfectly straight and aligned with each other, and the T.E. strip (where the aileron will be) was also perfectly straight. Rechecking the washout showed that it is still perfect without having to keep the wing shimmed on the board, although as I add structures (aileron and flap servo supports, wing strut attachment point, hardpoint braces, etc) I will keep it on the board and the tip shimmed to maintain the washut and taper. Adding the L.E. strip and remainer of T.E. strips will also stiffen the wing until I can sheet it. I am going to sheet with 1/16" balsa, and do an overlay lamination of G-10 fiberglass in the individual scale panels. (G-10 is also called "Fliteskin" as well as a couple of other brandnames). The flaps and ailerons will be G-10 by itself, so I can get the trailing edge nice and thin. Pics:
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Club Saito #2, WACO Brotherhood #20. What other trouble can I get into?
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Joined: 10/26/2007 From: Hempstead,
TX, USA Status: offline
Ken, As to your wing layout.... Well thought out and executed. I particularly like how you pulled the outer half of the wing with the top spar. Excellant idea for maintaining symmetry. Good luck with the other side..
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Joined: 7/3/2003 From: newton,
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quote:
ORIGINAL: RICKSTUBBZ
Good luck with the other side..
Yeah, if I can do it twice I can say I meant for it to come out that way . Another thing I did after that last post, when I started putting the shear webbing in, I "boxed" the spar from R1 to R7 (where the strut attaches), and extended the shear web out to R12 instead of stopping at R11. Don't know how much difference it will really make, but it sure looks strong.
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Club Saito #2, WACO Brotherhood #20. What other trouble can I get into?
Posts: 301
Joined: 10/14/2002 From: Alexandria, VA, Status: online
Real nice work Ken, the wings should come off the board d#&* near perfect. Your really doing a professional job with the "DAWG". I had to tip toe out to the shop if only for a moment, I needed to clear my eyes. The final report cards have me see grades floating in front of my eyes. Here are a couple of shots of the work I was able to do yesterday. Three more days, just three more and no more students till August. Chic
Posts: 5062
Joined: 7/3/2003 From: newton,
NC, USA Status: offline
Chic, Your cockpit detail gets an A+ from me. The throttle quadrants are beautiful.
Still working on wing #1 right now, but I have the parts laid out on the board for #2, will start tomorrow if my back will let me. I've been out of work all week, can't bend over worth a damn. Today's been the best day since last Friday, hopefully tomorrow will be better and Saturday better still, as it is our club Warbird fly-in.
I've made another change to the plans, has to do with the underside of the wing at the forward edge of the flaps. I've got to make some pics and I'll describe the changes in my next post.
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Club Saito #2, WACO Brotherhood #20. What other trouble can I get into?
Posts: 5062
Joined: 7/3/2003 From: newton,
NC, USA Status: offline
I got the second wing laid out this afternoon, and I was all geared up to get it framed out. One of my spar sticks (1/2 x 1/4 basswood) had a flaw in the exact center that I hadn't noticed and was completely unsuitable to use. A call to the LHS was unfruitful, but he suggested calling one of our clubmembers who builds a lot. I gave him a ring, and sure enough, he had just what I needed. I drove to his house to get it. This is a guy in his 70's who builds all the time, and every room in his house has something going. He is actually building two of these Vailly B-dogs right now, and is finishing up the wings, already sheeted and sanded, he was fitting the flaps today. In addition to the spar stick, he gave me a wing jig he had made for the wings. His wings are works of art, very nicely done. we talked about how he jig built his, and I described how I had done mine, and that while I thought mine were per the plans, I still had a bit of doubt in the back of my mind, since I had used a rather unconventional method.
Anyway, I got out of his way so he could keep working, and went home so I could get started. I laid his jig out on the table which consists of a cradle that R1 sits in, another cradle for R7, and a third for R15. the one for R15 has the washout angle set into it, and the other two are "flat". When I set my framed up wing into the jig, it fit like it had been built in the jig. I'll sleep well tomight knowing that . I will still build my second wing like I did the first one, since I know now the method works, and use the jig to verify that the washout comes out identical to the first wing.
Now, the modification I made in the flap area. Vailly's plans build the "pocket" for the flaps with a vertical trailing edge (1st pic, from the Vailly CD). The full-scale has an angled trailing edge that has curved corners, so the airflow is smooth through the slot created when the flaps are down (2nd pic, fullscale) I trimmed the trailing edge to duplicate this, and used the bottom rear spar and the chord line as reference points to make the cuts on the ribs. I installed the wing portion of the flap hinges, epoxying them to the rib side and making a 1/32 ply gussett on the opposite side of the rib for extra strength (3rd pic). I sheeted the trailing edge with 3/32 balsa and sanded to fit. I'll round off the edge when I sheet the wing and fit the flaps(4th pic)
The 5th and 6th pics show the wing sitting in the jig.
< Message edited by khodges -- 6/7/2008 1:15:50 AM >
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Club Saito #2, WACO Brotherhood #20. What other trouble can I get into?
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Joined: 7/3/2003 From: newton,
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Well, both wings are framed out and both fit perfectly in the wing jig I borrowed from a friend wh is also building this plane. In my last post, I showed how I modified the "pocket" that the flaps fit in. Here are a couple more pics showing where I made the angled cuts, and also the attachment of the flap hinge. (1st and 2nd pics)
Next, I have added the wing strut mounts. On the plans it calls for a single 10-24 screw at each end of the struts to attach them. I opted to use two 6-32 screws at each end, as I can disguise the heads of two smaller screws easier than one larger one, and they should be stronger also. I had also moved the fuselage strut mount 1/4 inch forward, so I have to duplicate that on the wing also. The mount on the wing is a piece of 1/4" plywood that fits between R6 and R7/7A, between the spar and leading edge. This area has notched lite ply doublers on the ribs between the L.E. and spar. I wanted to tie this plywood plate into the spar, so I made it wider than called for on the plans. Triangle stock is also called for to reinforce the construct. I epoxied it all in place. I don't think there's any way it will tear out of the wing. (3rd and 4th pics).
Next will be the servo trays and landing lights, which fits in the leading edge of the left wing.
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Club Saito #2, WACO Brotherhood #20. What other trouble can I get into?
Posts: 301
Joined: 10/14/2002 From: Alexandria, VA, Status: online
What a brillant idea to angle the trailing edge like the full scale. The flaps should really be more effective then the plans set of flaps. Some really great building Ken - based on your wings just falling into your buddy's jig. Sleep well my friend, just imagine how great your next really scale project is going to be. I'm mounting the left aileron will then glass them both. Seems like I glassed the wings but forgot the flaps and ailerons. Daaaaaaa. Finishing up the interior so that I can think about painting the fuse. Just ran the fuel lines, fuel selector switch, ash trays, and elevator trim wheels. Will mount the instr. panel tomorrow. Last day of employment tomorrow for the next 2 1/2 months. Build, build, build, except for the trip to Disney. Chic
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Joined: 8/26/2006 From: Fremont,
MI, USA Status: offline
1/5 Dawg What can I say, the strides you guy's have taken is outstanding. Chic's detailing and Ken's building. WOW !!!! Family matters and physical problems have kept me from my build. Really falling behind. Ah, motor problems to. Had to exchange the G-26, just to big without cutting up the cowl. G-20 although at the bottom of what the plans call for fits except for a small hole that will have to be made on the bottom for plug cap. Most forums say 10.5 max. wt. for stunt, so I am hoping if I can keep it at 12 to 13 it will fly scale. Other wise I might have to try SRE26. Which is suppose to be more compact and with an angled plug. Also have to build a bigger motor mount box, D! ! Did either of you not use the mount for your 1/4 scale, with 2° down trust. First attemp at tail wheel was not good, need more angle on forks, as you can see. Want to follow Ken's build for wing and flap, when I get that far. Rich
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RE: 25% Cessna L-19/0-1 Bird Dog build - 
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