Wing Assembly

From "Construction Notes" Falco Builders Letter, June 1991

George Barrett stopped by the other day to pick up some kits, and he got to talking about the process of building the wing, which he has just finished. He pointed his finger at me and said that a major omission of the construction manual has to do with the installation of the cove ribs and cove skin on the aft face of the aft wing spar. He had read in this newsletter that the way to do that was to install the ribs and skin on the aft wing spar before you begin the assembly of the wing.

That way you can do it on the table, and it's very easy to do. Do it on the wing-like Howard Benham did, chuckle, chuckle-and you've got a real bear of a job on your hands. So everybody go mark up your construction manual with a note about this. Anytime you can do it on the table, it's better than doing it on the wing.

From "Construction Notes" Falco Builders Letter, September 1993

Glyn Russell asks about how to attach the plastic tube to the pitot tube. The pitot tube that we used in the past was made by Cessna and had a plastic fitting bonded in place. That model is no longer available, and the pitot tube that we use now has a tube coming out of the top of the thing. We ask them to supply it with just the plain copper tube so you can shove the plastic tube over the copper tube. If there's a fitting on the end of the copper tube, then just cut it off.

From "Construction Notes" Falco Builders Letter, March 1992

Stephen Friend notes that where the side load strut mounts poke through the wing bottom, part of the plywood is unsupported and wants to know if this is correct. That's right, but you can always epoxy some blocks of wood to the metal fitting and glue around it. That's what I would do.

From "Construction Notes" Falco Builders Letter, March 1992

Stephen also asks if it is strictly necessary to paint such aluminum parts that are buried in the wing. He's noticed that some larger aircraft are leaving nose gear forks and similar parts unpainted for easier crack inspection. My answer to that is that it is not strictly necessary but very foolish. Since the part is buried in the wing, you can't even get in there to inspect it, so why eliminate the corrosion protection? Also bear in mind that the lack of corrosion protection paint inside the wings of many metal airplanes is simply a cost factor-many aluminum 'spam-cans' don't even have zinc chromate paint on their wing spars.

From "Construction Notes" Falco Builders Letter, June 1992

Occasionally we hear from a builder who reports that their control cables are just a smidgen too long for their airplane, and that the cables bottom out before the correct tension is reached. This usually happens on the forward aileron cables. If this happens to you, you can file about 1/8" off the threaded ends of the studs that go into the turnbuckles. This will probably take care of the problem, and if not, then you can do the same thing to the aft cables. Many builders have had this problem and have solved it this way.

From "Construction Notes" Falco Builders Letter, September 1991

Steve Wilkinson reported that the stall strips on his Falco weren't giving him the sort of warning I get on my Falco, so the other day, I measured the stall strips on the Corporate Disgrace. They have an included angle of about 55° and are 25mm on each exposed face. They are planted on the leading edge of the wing with no noticeable up or down cant.

From "Construction Notes" Falco Builders Letter, December 1990

George Barrett discovered a minor omission in the construction manual. We fail to tell you to install the aileron pulley brackets on wing rib No. 2 before you install the rib in the airplane. So in Chapter 24, somewhere after Figure 5 and before wing rib No. 2 is installed, make a note to install the pulley brackets on the wing rib. Once the wing rib is installed, it's difficult to install the brackets, even with an angle drill.

From "Construction Notes" Falco Builders Letter, March 1988

Elsewhere in this builder letter there's an article by John Devoe on his experiences. In case you miss it, he makes a point that bears repeating. John found that when he was installing the aft wing ribs to the spar, the alignment string at the trailing edge of the ailerons and flaps was inconvenient to use. Others have used it, but you have to clamp a straightedge to the rib. John simply used an extra alignment string at the forward face of the aft wing spar. He located the string by using the 200mm offset line.

John also found that it was much easier to install the wires in the plastic tubing conduit by sprinkling them first with talcum powder. Thus lubricated, they pushed through the tubing very easily.

From "Construction Notes" Falco Builders Letter, June 1988

No sooner had I given my admonition about using the sequence of the Falco Construction Manual I found the need to deviate from it. I was about to glue an aft wing spar to the ribs when I gave some thought to other work needed on that spar. Building the wing in the upright position has much merit, but it does put that aft spar pretty close to the floor. The cutting, fitting, sanding which is required for the small pieces which support the aft end of the wing skin and the 1mm fairing skin which encloses those supports, is work better done on the bench. It also makes it easier to do whatever sanding might be required to get that 8mm gap betwixt the coving and the leading edge aileron/flap ribs. Do the whole ball of wax, then glue it on. I took a tip from Bob Bready and glued the little pieces at right angles to the aft wing spar, thus saving angle-sanding of the end which is glued to the spar and the curved angle required at the end. Only at openings is the angle needed. The skin does not know the supports are not lined up with the ribs!

John Devoe

From "Construction Notes" Falco Builders Letter, March 1986

In a recent letter Mr. Frati mentioned that at Oshkosh he noticed the way some builders have installed the wing on the fuselage, building the wing and fuselage as separate assemblies and then gluing the wing spars to the appropriate fuselage frames. Mr. Frati does not care for this procedure since the critical glue joints between the wing spars and fuselage frames are not made under optimum clamping conditions.

The method that Mr. Frati recommends is this: The wing is built on the wing jig and skinned on top. The front, main and aft wing spars are glued to the appropriate fuselage frames before putting them in the fuselage jig. The wing-and-fuselage-frame assembly is placed in the fuselage jig and aligned with the other fuselage frames, then you proceed to skin the bottom of the fuselage and wings. This is the method used to build the Falco during production.

Mr. Frati emphasizes that the bottom center longeron must be continuous and if any joint is required, it should be located outside the central part of the fuselage, where the loads are lighter.

Mr. Frati also suggests that when gluing the aft wing spar to fuselage frame No. 6, you consider using one bolt and large washers. This is not necessary for strength, but it may assist in clamping the odd-angled joint, and you may leave the bolt in place. It will also serve as an alignment pin.

Mr. Frati says that this procedure is the only method that will give the proper structural strength to the assembly. "Any other procedure, due to the unavoidable tolerances, may result in a weak or overstressed glue joint, that may considerably reduce the structural integrity of the joint."

I still prefer the method of gluing fuselage frames No. 3 and 4 to the wing spars before the wing is assembled. It seems to be easier to align these two fuselage frames when the spars can be clamped to each other. Some builders prefer to align the frames and drill all necessary bolt holes, and then leave the gluing of the frames until after the wing is assembled. But either way, the message is that the glue joint will be better if the fuselage frames are glued to the wing spars before they are assembled in the fuselage.

The normal procedure that our builders have used is to skin the bottom of the wing first. Thus, any masking mistakes will be on the upper wing skin, out of reach of standing water. I believe that the method described by Mr. Frati was used to avoid turning the Falco over any more times than necessary. I may be wrong in this assumption, but I think that Mr. Frati is talking about doing the initial fuselage assembly and wing bottom skinning with the airplane upside-down. Take a look at the construction photo in our booklet Stelio Frati, a Designer's Portfolio.

From "Construction Notes" Falco Builders Letter, June 1986

John Harns also mentioned that he had a problem with the lower wing skin where it glues to the fuselage skin. He did not install a spruce gluing strip as shown on Sheet B2, and just cut the plywood to the angle and glued it in place. He only had a problem in front of the front wing spar. On inspection, he found a slight blister in the fabric so he pulled off the fabric and found that the plywood had come un-glued. He re-glued the skin and then covered the joint with several layers of fiberglass cloth. Particularly at the forward end, the skin needs some additional support since it hits the fuselage skin at about 30°. If you use epoxy, you can reinforce the joint with epoxy and cotton flox on the inside.

From "Construction Notes" Falco Builders Letter, March/June 2002

In the flap correction package are two precision bolts AN173-20, to be used to connect the control tube to the P/N 765 support. Even after buying a new 3/16" reamer, they won't fit. Is this normal? I could reduce the diameter in a lathe.

Marcel Morrien

I don't know what to tell you on this one. The bolts are supposed to go in a hole produced by a standard reamer. I would try to increase the inside of the hole diameter slightly, rather than change the bolts.

From "Construction Notes" Falco Builders Letter, March/June 2002

The aft wing spar has to be fitted to the fuselage. In the drawing, you give two different angles, 34:250 and 35:250. Is one the cut in the vertical plane and the other cut in the horizontal plane?

Marcel Morrien

The slopes are measured relative to the forward and aft face of the spar, and the spar is slightly tapered. This is the reason for the difference.

From "Construction Notes" Falco Builders Letter, March/June 2002

Is there a drawing presenting a view inside the wheel well, a cross cut? I'm trying to figure out where the upper laminate will go.

Marcel Morrien

I don't have a specific drawing, but they are fitted to the upper wing skin in the end. So you glue them to the airplane and then sand them to the shape of the upper wing surface.

From "Construction Notes" Falco Builders Letter, March/June 2002

While installing the main landing gear side load fittings on the main wing spar, Dave Burchette noticed that the center hole of the block in the spar did not line up with the large hole in the side load fittings. Many others have noticed and commented on the same thing. In fact, both are just lightening holes, and they are not intended to be directly aligned with each other.

From "Construction Notes" Falco Builders Letter, March/June 2002

I am confused as to how the skins on the underside of the wing -- below the cockpit floor -- are fitted. It appears that there are packing pieces glued to the bottom of the main spar. Is this correct? If so, what drawings are they shown on? Is it carried forward and scarfed to the forward part of the fuselage? Furthermore, the fore and aft blocking for the sides of the wheel wells forms part of this supporting structure. Again, I am confused as to what shape this should conform to. I can roughly guess how it all comes out, but some guidance would be appreciated.

Alan Powell

Between frames 3 and 4, the fuselage is skinned with plywood that wraps around the lower longeron, thus you have a skin that continues the fuselage shape back to the main wing spar.

The lower wing skin then continues the wing shape directly into the fuselage and where it hits the fuselage shape, you scarf the plywood to fit the fuselage and also add gluing strips as necessary.

For the area covering the main wing spar and back to fuselage frame 6, the skin must go over the bottom center longeron, so it needs tapered shims to carry the skin over the bottom center longeron.

Then the walls of the wheel wells are extended to where the skin is, and thus you shape and sand the rings of the wheel well to the shape that the wing skin takes. Some of this is simply a matter of sculpture and sanding things smooth for the skin to cross the bottom of the fuselage. It's a difficult thing to visualize, but it is shown in a number of places in the drawings for the fuselage and wing, and also you will see many photos of this in the Falco Skunkworks. I'd suggest looking at Al Dubiak's and Mel Olson's entries in the Falco Hangar.

From "Construction Notes" Falco Builders Letter, March 2003

I'd appreciate some advice about the wheel well laminate rings. I've looked on the web, but find that most people show off finished stages rather than divulge the intermediate process. I plan full doors and therefore have made hockey stock laminates. On the bottom hoop, at the inboard end do I cut an 'L' shape so that the laminate hooked underneath the 20x20 stringer, or does it just butt up against the 20x20.

Angus Buchanan

It's not terribly important, but I would butt it and then when you get plywood on it, everything will be very strong.

On the top 'hoop', at the other end I'm a bit confused about the notch in the frame.

Angus Buchanan

Again, it's not terribly important, but the hockey-stick laminate follows the shape of the upper wing skin and you notch frame 5 where they cross. The intent here is to get a laminated piece of wood to glue to the upper wing skin (in the fuselage) and the wheel well wall.

And I'm confused about its shape and its connection with the 'hoop'. (Not so easy to explain.) The frame 5 top outboard notch was cut vertically and horizontally. However the rib sits against the frame at right angles to the dihedral. The resulting hole is therefore not a nice square for the hoop to sit on (with its own notch, too). Instead the hole is a trapezium with the inboard corners 90 degrees. Should I 'improve' the frame 5 notch to suit the hoop, or have I missed something more fundamental about the geometry?

Angus Buchanan

It's the same answer as above. I would notch frame 5 to the size shown, then position the lamination so that it will sand to the contour of the upper wing skin in the fuselage. This will mean that you will notch the lamination where it crosses frame 5. You are getting into sculpture here, but just remember that the intent is to create a curved gluing block that joins the wheel well wall to the upper wing skin in the fuselage.