Sproose Goose (oz14451)

About this Plan

Sproose Goose. Radio control sport biplane model. Wingspan 55-1/4 in, wing area 884 sq in, for .60 engine. An experiment in spruce construction.

Quote: "Sproose Goose, by Bill Northrop. The SG proved one thing for sure; you can build a light, and obviously very strong model out of spruce. Although a little more tedious to build, we've had many requests for plans. Here they are, updated.

If this airplane happens to look familiar to you, it's probably because you were a reader of Model Airplane News in early 1969. The March issue contained our construction article on the T'Winger, for which the Sproose Goose (I'm a licensed poet) was the prototype.

SG, which was completed in the winter of 1966-1967, was the result of an all-out effort to avoid the use of balsa as much as possible and/or practical. The experiment in our opinion, was a complete success. Essentially, the only balsa in the plane is the sheeting around the wing dihedral ioints (bottom center section is mostly 1/16 ply), the fuselage sides and decking back to the cockpit, and the headrest. Other than a few more scraps here and there, the plane is built entirely of spruce.

The finished plane, ready to fly except for fuel in the tank, weighs 6 pounds, 10 ounces. With a wing area of 880 sq. inches, the loading is in the 18 to 22 ?z/sq. ft, range, depending on the percentage of total area you may assume is effective in this biplane configuration.

The T'Winger, which was developed from the S.G., was of more conventional construction, using mostly balsa, with the usual scattering of ply and hardwood. The 'SG TWinger' was first redesigned in balsa for fellow Delaware R/C'er Arnie Lipschutz, who has since gone on to build somewhere in the neighborhood of 5 or 6 in the past 3 or 4 years. This design, being of more easily obtained materials, was chosen for the MAN article. It's interesting to note that to date, except possibly for Arnie's two latest modified versions, none of the balsa models came out as light as the Sproose Goose!

With today's skyrocketing balsa costs, the spruce experiment has even more meaning now than it did six years ago, when SG was completed. Actually, ready-cut spruce from your hobby supplier won't save you a great deal. In addition, many shops don't carry a very complete line of sizes. And of course, if you're going whole-hog with the idea, you'll need some sheet stock, which you just cain't hardly git nowhere!

The trick to all of this is the old do-it-yourself bit. Obviously, this isn't a 'crashed last week and need a plane for Saturday' type project, so anyone tackling the job shouldn't mind preparing their own spruce material.

First of all, you'll need to beg, borrow, or steal the use of a table saw. Obtain a small-tooth, plywood cutting blade. This blade will leave a smooth finish on the cut wood that won't require sanding prior to use.

Better lumber yards carry clean, unknotted spruce. Select your own if possible. We prefer nominal 1 x 4 material in 6 foot lengths (Oh, the beautiful R/C glider wing spars!) Cutting 2-inch wide sheets of 1/16, 3/32, 1/8, etc. is quite easy. Incidentally, when you start figuring costs, based on lumber that runs around $1.00-$1.75 a board foot, you can also see some economy.

Now comes the big surprise. Compare your spruce strips in weight and strength with balsa. The spruce is only a little bit heavier, but many times stronger. Consequently, you can go to smaller wood sizes, resulting in stronger and lighter construction.

By the way, we have checked with Dwight Hartman, Hartman Fiberglass Products, Argenta, Illinois 62501, and the cowl is still available for $4.50 post-paid. Carve your own it you care to, but the fiberglass one is hard to beat.

The coat hanger wire used for the cabane struts is the unpainted type, slightly over 3/32 diameter. Don't let its softness fool you. Once the unit is completed (those eyes in the ends are very easy to form) and bolted in place, its as rugged as music wire, with much less effort. As an alternative, you may cut out the 'N' pattern struts from 1/16 sheet aluminum.

Top and bottom wing panels are exactly alike, only the center sections differ. Dihedral Joiners may be cut from I/4-inch spruce, tapered to match the sweepback of the wings. Alternately, 1/16 aluminum joiners may be cut, bent, wrapped onto spars with button thread or copper wire, and epoxied.

Outboard struts are necessary in order to maintain proper spacing of wings, thus keeping ailerons lined up. We chose to make all horns and aileron connecting rod fittings from 1/16-inch micarta, but who follows the designer's ideas?

Most important thing about fuselage alignment is to start out with an absolutely flat 1/4-inch ply firewall bulkhead. Note the extra large holes for the should be obvious that SG is not a project for anyone without a great deal of building experience.

Since publishing the T'Winger we've had many requests for plans for the spruce version, and since these were kinda rough, we figured it was time for an update.

The plane is an excellent flier, extremely comfortable on the controls. If the weight is kept down to a reasonable figure, it is an agile acrobatic performer, very realistic in appearance and manner. Under dead-stick conditions, it doesn't sink like a brick, and ground handling is quite precise for a tail-dragger.

The Sproose Goose is the twelfth biplane we have designed, and in our bottom wing dowels in bulkhead B. For easy alignment, the ply rings are lightly epoxied over these large holes with the wing in place. After setting, the wing is removed and the rings are further epoxied for maximum strength.

This was not intended to be a full-blown construction article, because it opinion, from an overall performance viewpoint, the best of the lot. If you decide to tackle it, we'll be glad to offer any verbal assistance you may need. Let's hear from ya!"

Direct submission to Outerzone.

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