Mo'Best wing - laminated spar construction

LAST EDITED ON Oct-24-04 AT 10:47 PM (CDT)
 
((OK, Dan, some more blatant self-promotion!))

I'll readily admit that more time is required to assemble the laminated spars for the wing. However, it isn't all that bad, and it has its rewards.

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Like all the laminated spars in this design it has a 1/32" plywood center laminate piece. This is laminated between two 1/4" x 1/8" balsa strips. The center laminate has notches to locate the ribs. (a la Tom Morris's Lincoln Log method).

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My method for gluing these involves three steps. First, the laminated balsa strip is tack glued with drops of medium CA. In this case, the strip edge is aligned with the top edges of the rib notches in the 1/32" center laminate.

The next step is to carefully stream thin CA along the joints, to actually glue the bulk of the area.

Finally, I use a long T-Bar metal sanding block to true up the external edge. The 1/32" plywood edge serves as a great guide for doing this.

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The resultant spar is about 9/32" thick, actually slightly thicker due to the CA glue. This compares with the 1/4" square strip balsa stock I traditionally use for top and bottom with spars. However, one big advantage is that the glued spar is very straight, and I don't have to select a bunch of spars. They are all made using 1/8" sheet stock.

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Here you see the first 3 ribs, just dry fitted - set into the notches. I am pleased with the fit, which is not loose nor too tight. The finished assembly should almost stand together, without glue, in good alignment.

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Here's the outboard portion of the wing, with just top and bottom spars, just sitting there, nothing glued. All self-aligning. (Poor focus on the photo..)

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"By working faithfully eight hours a day, you might eventually get to be a boss and work twelve hours a day." -Robert Frost

Show me the Brodak bellcrank installation????

The 4" Brodak bellcrank is mounted on a rectangular piece of 1/8" Lite Ply, which sits on 1/4" square balsa sticks, between Rib #1s..

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Here's the side view, showing the optional tilted bellcrank configuration.

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Here's the top view; the bellcrank is mounted "Rabe-style".

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Note that you can download a 10-part detailed builder instruction series for the laser-cut Mo'Best from the PAMPA web site. The PDF files are compressed and you need Adobe Acrobat 6.0 or later to read them. (These are NOT the better profile series, nor the original Mo'Best construction article, they are newly released.) Above are screen shots from Parts 6 and 7.

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"All men are frauds. The only difference between them is that some admit it. I myself deny it." -H.L. Mencken

Here's another reason I love laminations. The Mo'Best has a removable gear and the gear block (also of laminated construction) is suspended between ribs 2 and 3 in the wing. The front portion of these ribs has 1/64" plywood laminates, with the 1/8" thick balsa rib center section.

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You can see the rectangular cutouts for the gear block, which would be difficult to cut without the laser. But this arrangement is super accurate, and quite strong and light.

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Notice also that the gear block (which I previously butted against the front edge of the bottom spar) is no longer aligned with the top/bottom spars (which sweep aft). Instead it sits exactly perpendicular to the ribs 2 and 3. This simplifies my gear wire bend (which previously had to sweep like the top/bottom spar) and allows me to use Lite Ply vertical gear retainer blocks to secure the top of the gear wire (instead of the other leg of an L-shaped gear block). Again, this is equally strong, but lighter, and easier to align.

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The original Mo'Best uses wheelpants, which are carved from balsa blocks.

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An alternate gear treatment is "Mustang-style" gear strut covers, which are (curiously enough) very easy to construct with laminated sandwich construction.

The kit will probably choose one or the other, since the gear wires have to be bent opposite directions for the two versions. The Mustang-style gear is extremely easy to build, which may be the choice for the kit. I'll build one of each so you can see them both, and post them here later.

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"Ninty percent of the politicians give the other ten percent a bad name." -Henry Kissinger

Great stuff, Larry! For the record, I prefer the LG Door setup. I'm looking forward to another of your usual striking paint schemes. Keep up the good work. Steve

>((OK, Dan, some more blatant self-promotion!))
>
>I'll readily admit that more time is required to assemble
>the laminated spars for the wing. However, it isn't all that
>bad, and it has its rewards.
>
>[photo not recovered: 417b28943b9397ec.jpg]

Is this .007 CF tow or sheet between the wood?

Robert,

It is 1/32" plywood, whose thickness works well for the gap for the nylon hinge. 1/32" is .03125 (31 thousandths). .007 unidirectional CF is 7 thousandths.

Also note that the center laminate has notches to locate the ribs, and .007 uni CF would not be suitable for that at all.

(That said, a center laminate of uni CF does make a very strong spar. I have constructed them in that manner, but normally would glue it to the vertical external surface of a 1/4" square or 1/4" x 1/8" section balsa stick.)

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"I could tell that my parents hated me. My bath toys were a toaster and a radio." -Rodney Dangerfield

>Robert,
>
>It is 1/32" plywood, whose thickness works well for the gap
>for the nylon hinge. 1/32" is .03125 (31 thousandths). .007
>unidirectional CF is 7 thousandths.
>
>Also note that the center laminate has notches to locate the
>ribs, and .007 uni CF would not be suitable for that at all.

I see thank you. Now one question how much more does it weigh?
Looks to be a good Idea.

I've tried searching the PAMPA website and can not find the files or pictures. Can anyone help the computer ignorant? Thanks a lot.

FLY SAFE, JOHN

>I've tried searching the PAMPA website and can not find the
>files or pictures. Can anyone help the computer ignorant?
>Thanks a lot.
>
>FLY SAFE, JOHN

John,

Try clicking on this link: http://www.control-line.org/DesktopDefault.aspx?tabid=22

The last 10 items on that page are the laser-cut Mo'Best builder instructions (about 88 pages worth). Be sure you have Adobe Acrobat Reader 6.0 or greater. (You don't have to be a PAMPA member or logged in.)

Let me know if that doesn't work for you.

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"I love being married. It's so great to find that one special person you want to annoy for the rest of your life." -Rita Rudner