Micro Rocket Motor and Model Jet Resources
Plan: Twizzler



by Dick Twomey

Reprinted from Aeromodeller, November 1951 (p. 593)

For a near-vertical climb with Jetex 200, try Dick Twomey's latest, the Twizzler – an easy to build, easy to fly, high performance JETEX model, 28 inch span, with detachable wing, designed for competition work with the JETEX 200.


  Two ways to get the Twizzler plan:
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CONVINCED that the high thrust line layout is the best for Jetex duration, Dick Twomey has developed the "Twizzler" (a name born recently in the excited broadcast commentary of the Supermarine Attacker upward roll at the "Daily Express" Air Show) from his renowned "Firecrest" design. He has found a simple way of doubling the power, while halving the engine run, which is perfect for open ratio competitions. The climb of the "Twizzler" is thus stepped up to over a 60 degree angle, and recently it established the best ratio in a power contest with a 3 min. 27-56 sec. flight giving a ratio of 20-5 : 1. The chief differences between this and other Twomey designs are reduced drag, with a slimmer fuselage, less fin area, faster wing section, enlarged tailplane with dihedral tips, light weight, and the off-set Jetex unit. Last year's model won the R.A.F. Championships, and "Twizzler" is undoubtedly an improved version. Study the designer's trimming gen on the plan [also reprinted below] for his novel system of boosting Jetex power.

Fuselage. Cut two fuselage sides from 1/16 in, sheet (medium) join them with former A and add 1/16 in. cross spacers. Cut away as shown for wing, which slides into position in one piece. Add ply Jetex platform, formers B and C, noseblock fin and rudder. Sand finished fuselage all over.

Wings. Build whole wing in one piece, flat on the plan. Then crack at dihedral points, prop up to required heights and cement dihedral gussets in place. (A "turbulator" was tried on the original model, but has been discarded as having no beneficial effect on such a small model.)

Tailplane. Simply constructed and must be kept free of unnecessary weight. Do not neglect to build in 1 in. dihedral under each tip as shown on the plan. Failure to do so would have grave effects on stability.

Jetex Mounting. Offset the unit 10 degrees to starboard, as shown. Then by "balancing" rudder against motor sidethrust you can achieve the best and most safe trim, a straight steep climb followed by a left-circling glide.—Happy "Twizzling"!

With c.g. in position shown test glide with Jetex unit empty until satisfactory left circle is achieved. All alterations to glide trim are made by giving positive or negative incidence to tailplane. Do not touch thrust line or wing incidence.

Now cut one 200 charge in two and try power flight. Make alterations to rudder to obtain straight stable climb. Note that rudder alterations may also entail tailplane alteration (the tighter the turn, the more negative incidence required to keep nose up). Increase power by inserting two 200 charges but not launching until the first has completely burnt out and the second charge is under way. Trim until this is satisfactory.

For final power trials cut down the diameter of a 350 charge until it just fits. You can thus fit two 350 fuel capsules into the 200 unit and the result is astonishing. Complete engine run will now be 10-15 secs with a corresponding increase in power. Length of engine run depends on how much air gap there is between the fuel and the inside cylinder walls of the unit. The less close the fit the more the power and the shorter the power run. Warning:- With the 350 fuel the Jetex metal end cap will not last forever and also the asbestos washers must be continuously replaced.

  Designer Twomey and Twizzler
Designer Twomey and Twizzler will be a pair to watch at the Jetex contest. [1951]
- Aeromodeller, Oct. 1951 (p. 593)

And for a contrast in what the best-dressed Jetex contestants wear, compare Dick's gear above with Dave's gear below…

Dave Hegarty and Twizzler, Jetex winner, Australian Nationals 1960
Dave Hegarty and Twizzler, Jetex winner, Australian Nationals 1960
- photograph from Peter Lloyd
Plan for Twizzler (A larger copy of the plan is also available to view or download).



 - Article, plan and photograph of Dave Hegarty contributed by Peter Lloyd
 - Additional material from the MAAC Archives, via Bill Henderson


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