Scorpion Major (oz12811)


Scorpion Major (oz12811) from Bunch 1937 - plan thumbnail

About this Plan

Bunch Scorpion Major. Free flight power model. Wingspan 57 inch, for Mighty Midget engine, or similar.

Direct submission to Outerzone.

Scorpion Major (upright engine). Scorpion Senior (inverted engine).

Note the Scorpion Major is shown (illustrated) with floats fitted. These were sold separately, see Gull Float Gear (oz12812)

Planfile includes detailed build instructions.

Quote: "BUNCH MODEL AIRPLANE COMPANY Instruction Sheet: Scorpion Major: Design No. 3601

It is important that you study the plans of your airplane thoroughly. The aerodynamic and engineering design of this airplane has been carried out with the same thoroughness that is used in the design of a full-size airplane. Use sharp razor blades for cutting wood and trimming tissue, and a sharp knife to trim propeller. Cut all longer lengths of material first. Study sketch and photos of airplane to have an accurate conception of its general assembly and design. At all times work accurately and carefully.

Start construction with the fuselage. Build the sides first. Cut longerons to length and pin in place right on drawing. Install struts, then diagonals. Cement well. Note bamboo inlays (Z). Note reenforcement (b) running from station B to E. Make a 1/4 in sq and taper as shown. Next install horizontal struts at stations C and E. Align fuselage carefully. Install temporary cross struts at (A). These are removed when fuselage is dry to make room for engine. Finish primary frame as shown. In process of assembly leave out forward fuselage diagonals until landing gear radius rod is installed. Next, install bulkheads. (AL) is 1/16 plywood. The remaining bulkheads are 1/16 hard balsa sheet. Bulkhead pattern may be transferred to wood by tracing with carbon paper. Note (BL), (C), (D), (E) and (F) are shown in halves. Make one for right and one for left side. Fit bulkheads carefully before cementing in place. Note: Fill open space of bulkheads B and C in solid with TV sheet to keep oil spray out of fuselage cabin. See (F).

See Figs. No. (25) and No. (26) for landing gear assembly. Main strut (L1) is bent of .125, music wire. Match carefully to Fig. No. (25). Auxiliary strut is .125 music wire. Solder washers in place as shown. Notch fuselage to receive main strut and bind in place with thread. See (L4). Radius rod (L2) is bent of .095 music wire. Fit accurately and bind to fuselage with thread, see (L4). At (N) bind with fine wire and solder. Install tail skid. See Fig. 12. Make motor beams. Note (H): Notch to fit over radius rod. Cement beams in place. Fit carefully. Install bamboo splints for stabilizer support. See extra longerons at rear of fuselage to properly space these splints. Make fitting, Fig. 19, for rudder adjustment. Cinch nut is soldered to clip (K). Use 4-40 machine bolt. Make Hooks H1 for wing support rubbers. Use needle and thread to sew through bulkheads. Bind in place securely and cement. Hooks H2 are cemented in place and secured with patch of 1/16 sheet balsa. See (a). See (aa), flooring of 1/16 balsa for battery trough.

Cut wood parts for wing and assemble right over drawing. Note: spars are tapered. Therefore, notches in main ribs very. Study patterns carefully. Note: top spar is cut at rib (7) and bent down to meet tip. First make right and left panels, less drag bracing. Next, block wing up as shown in front view and butt joint center section parts in place. See Fig. 14 for assembly method. In finishing wing frame see Fig. 15. Sand edges as shown. Install bamboo inlays on top of center spar, and bottom of lower spars, also on leading and trailing edges. Next, install drag bracing. This bracing is in the plane of the lower spars and the intermediate ribs are notched out to allow drag struts to pass through. Construct each side of stabilizer and the rudder over drawing. Note spars are 'I' section. See Fig. 10. Rear rudder spar webbing below base rib is double. Rudder hinge eyes (P) are made from 11/16 cotter pins. Cement well. (L6) hinge is .034 music wire.

The motor cowling, Fig. 17, is hollowed out of a solid block of wood. This method is best, as there are no metal parts to short out the ignition. This cowl is fastened in place with large spring snaps (See U), and also rubber bands about pin heads shown as (J). Thus it is readily removable. The windshield cowl frame is assembled as a permanent part of the fuselage and the top cowl is removable. Fasten top cowl in place with rubber band to (J). See Fig. 16.

Landing gear fairing (L3) is made of balsa. Cement pattern shapes in place as shown in Figs. 23 and 24 (Q) and (R). Above dotted line (m) on inner pattern, change grain direction to horizontal. When dry, sand to cross-sections (Q') and (R').

Before final assembly, the airplane is covered with bamboo paper. First recheck all framework. Be sure every part is complete and in alignment with nothing warped. Cement about four large-diameter, big-hole fibre washers to covering and cut out inside for oil drains. Paste bamboo paper on with special cement made as follows: use 3 parts standard cement and 1 part thinner. Trim carefully to insure smooth covering job. When dry, water-spray paper lightly to draw it taut. Check parts and hold wing and tail surface while drying so they do not warp. Dope covering as follows: Fuselage, 4 coats; wing, 3 coats; tail, 1 coat. Dope cowling, interior of fuselage from bulkhead A to C, and landing gear fairing 4 coats. Also give top of wing one additional coat from top center spar to trailing edge. This later to control tip to progressive decrease in incidence.

Next install power plant and wiring system. The installation shown is for the Mighty-Midget Motor. Set motor and tank in place as a unit. Bolt motor in place with four 6-32 machine bolts..."


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Scorpion Major (oz12811) from Bunch 1937 - model pic

  • (oz12811)
    Scorpion Major
    from Bunch (ref:3601)
    57in span
    IC F/F Floatplane Cabin
    all formers complete :)
  • Submitted: 03/02/2021
    Filesize: 1836KB
    Format: • PDFbitmap
    Credit*: TomRyan

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User comments

Holy Maxwell, this the largest fin in side area proportions that I've ever seen! Two possibilities are open here: a) terrific FF knife-edge flying, b) calculate the accurate bearing for great-circle navigation from say Singapore to Murmansk, adjust the orthodrome for expected trade winds, point it in the right direction and with enough fuel it will unfailingly arrive at said Murmansk, hopefully this century! By the way, flat-earth navigation is much easier than spherical geometry, that's why I'm a fan of the former!
I also liked the attempt at trussed structure, but the author says "Also give top of wing one additional coat from top center spar to trailing edge. This later to control tip to progressive decrease in incidence.". This contradiction makes me doubt the author's self confidence!
All in all a fantastic shape and this goes right into my collection of "to-build in Eternity". I wonder where I can get supplies in the Other World .:-)
Miguel - 17/02/2021
There is very little history available for the land based Scorpions as freeflight models. I suspect that has to due with the large fin which gives it its name.
However, as an R/C assist model, famed competitor Eut Tileston was very successful flying ROG and ROW. The thin airfoil gives it very little induced drag and a climb performance unlike any other OT model. While the glide is not up to what one expect from a Lanzo Bomber, he used to get high enough to max with little difficulty. Then, he would perform all sorts of maneuvers to kill altitude, including flying inverted. That should make people reconsider the notion of switching the OT rules to make them altitude limited events!
Eut always removed the leading edge incidence and used a flying stab. As hot as his Scorpions were, they were quite docile and he often loaned them to the wives to compete against their husbands. He claimed that there didn’t exist a better R/C trainer than the Bunch Scorpion.
Danner Bunch was better known for his engines and taking his own life. Requiescat in Pace.
John - 17/02/2021
The tall fin was obviously carried over from the company’s rubber models, see
Tom - 17/02/2021
J. Eut Tileston was RC Grand Champion one year flying nothing but Lancer 45s, Gross Flying Wings, and several Scorpions. I don't think I ever saw an Old Timer climb the way his big plum colored Scorpion did.
Lance Farlow - 17/02/2021
The Senior , with the higher thrustline, makes a much nicer transition from climb to glide.
Max Washington - 17/02/2021
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