About this Plan
Buttercup. Free flight scale model for .049 power.
Scale is 1/12. Wittman's Buttercup.
Direct submission to Outerzone.
Update 18/12/2019: Added article, thanks to theshadow.
Quote: "Lightplane designers figure Steve Whittman must use black magic to get sensational performance from the home-builts. Try this old favourite on an .049. Buttercup, by Steve Lambert.
Buttercup is a two-place utility airplane designed and built by Steve J. Wittman of Oshkosh, Wis. Readers of MAN will recall him as a prolific designer of very successful Goodyear Racers, namely 'Buster' and 'Bonzo.'
Through Mr and Mrs Wittman's courtesy and efforts (mainly that of crawling about hangar rafters to get measurements, details and the like) I have been able to gather, over a period of three years, authentic information to present here with an exact scale model of Buttercup, as witnessed by Mr Wittman's signature in the lower right-hand corner of the drawing.
In order to eliminate hassles with scale judges at contests, the original penciled drawing was sent to Mr Wittman for his approval. The necessary changes were made and now appear in the drawing. A word of thanks also goes to Cal Smith for his original sketches of Buttercup which he was kind enough to lend me for double-checking.
This is a one-inch to the foot flying-scale model and its construction is conventional and straightforward.
Start by making a metal template of the full size wing rib as shown on the plan, then cut and sand to shape (pinned together as a unit) 20 ribs. Make the spar slots slightly oversize by using a #11 Xacto blade to cut out the notches; .003 is about the blade thickness and will make a good tight fit on the spars. Wax paper should be used to atop the plans to prevent the cement from stick-ing to the paper.
Space the ribs correctly on the spars and, using scrap 1/18 inch sheet balsa under the spars, pin the spars to the drawing over a flat board. Pin the 3/16 x 3/4 shaped trailing edge in place after applying cement to the rib ends. The leading edge is done in a like manner. The wing tip is shaped from a soft balsa block. The .045 pins are bound to the spars after first bending a small 'L' in each pin end and pushing it into the spar. The .020 wire hook on the root rib goes into the 3/16 inch diameter aluminum tube which is cemented to the fuselage ends, Hush with the root rib. A rubber band is passed through this tube and attached to each hook. These hooks I Ad the wing in place during flight but will allow the wings to pull loose in case of a crack-up or rough landing.
Notch the top of the 34 sheet wing strut brace 1/16 inch deep where it meets the spars and cement in place. Sand this to the rib shape and insert the female section of a #3/0 dress snap as marked on drawing. Be careful not to get cement inside the snap or it will not work properly. Sand the whole unit and give it two coats of clear butyrate dope, diluted 40 to 60 per cent to eliminate any fuzz on the balsa. Sand with very fine sand paper and wet cover with yellow silk. When dry, give the silk about five coats of clear dupe cut 50-50 in very light brush coats to fill up the pores of the silk.
This can be done only in small sections and by using the proper technique. if the brush is too full, the dope will just go through the silk and form large globs of dope on the underside. Dip the one-inch flat brush only about 3/16 to 1/4-inch in the dope to get the proper effect. When the silk no longer absorbs this cut dope, you may then use three or four coats of clear dope as it comes from the jar. Cub Yellow finish should be sprayed on if possible. Cut it about 40 per cent with thinner and apply as many coats as necessary to get the finish you want - bearing in mind the more dope you use, the more weight you get!
The green wing letters and numbers NX 18268 are 2-1/2 inches high, 1-1/4 inches wide. They are placed with the last number 8 between the last two wing ribs. Note that the root rib is tapered to the shape of the fuselage at the joint where they meet.
Fuselege is conventional. Build two sides one atop the other, noting that the door is on the bottom half ( if you want to use it). I like to build one side first, then remove thepins and sand the whole side with a wide block wrapped with fine sandpaper to remove any irregularity that might occur in the wood. Then replace on the plans and build the second side on top of the re-worked first side. Actually 3/32 inch dowels would be more scale-like but this, and the 1/8 or 5/32 wood, is left to the builders discretion. I used 1/8inch square spruce on this model since it was to be flown and the weight was con-sidered unimportant in relation to flying characteristics.
The windshield struts are 1/32 and .035 wire. The floor is 1/32 inch sheet balsa and the seat is either balsa or post card stock. Control stick is 1/16 brass tubing. The exhaust stack is 3/32 brass tubing with the flange of shim stock brass. The ends of the wing struts have hooks that fit into the 3/16 aluminum tubes in the fuselage and a rubber hand pulled through the to holds the struts in place.
Stabilizer and rudder are exact scale outline in construction and soft iron wire or aluminum can be used for hinges. The yellow rudder numbers are 1/4 inch high, 3/16 inch wide.
Use the same procedure in covering the fuselage with silk only this time use white silk (green if you can find it). Cessna Green mixed with Stinson Green in equal parts is almost leaf green and the two colors make a fine contrast. Again, use only the necessary amount of dope. Stabilizer and rudder are covered in the same manner.
You will notice that for true scale there is no dihedral. I would suggest at least 5/8 inch and possibly 3/4 inch for each wing for good flying.
Make necessary arrangements to start the motor and be able to fill the tank, so that the cowling will not have to be re-moved each time you fly. Model pins can be used on the cowling and windshield to represent rivets.
Cockpit details are shown on the draw-ing with the exception of rudder pedals and the safety belt. The safety belt is of two-piece construction. One-half of the belt is attached to the sides of the seat and both passengers utilize the same belt. The rudder pedals are hinged and either one of the set can be folded down and out of the way when not in use. The instruments can be either hand made or cut from other printed commercial plans of various kits. For the opalescent green mix some Silver and Swift White with the Cessna Green to get the proper color for the instrument panel.
The Berkley kit of the Pitts Special has a good drawing of the tail wheel detail - if you want to go to the trouble of building it up.
The model weighed-in at 11 ounces which give it a fast yet stable glide. I used an Atwood .049 Shriek with a Tornado 6-3 prop. Balance is about 30 per cent of wing chord."
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User commentsThanks to Pit for the date and publisher on this one.
SteveWMD - 06/08/2019
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