Paul Tupker's VT Air Racer

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An important name in the history of Dutch control line modeling is that of the late Paul Tupker. Tupker's own stunt model designs are internationally recognized. One of his elementary designs was published in the final copy of the well-known Dutch do-it-yourself magazine “VT” (abbreviation for “Free Time”): the VT Air Racer. The solid balsa plank model is the subject of this web page.

Informal meetings organized around these simple models triggered me into building one. In this particular instance there were only 3 weeks to do the job – and those 3 weeks were already rather busy. Anyway, a working copy of the plan was made by scanning A4-sized overlapping areas with my 15-year old HP scanner (HP build great peripherals) and printing them at 105% of the original size to compensate for shrinkage. Overlaps were cut away and the whole thing taped together.

Having noted sheet balsa fuselage and fin fractures on the flying fields, I chose to accept the weight penalty and build a laminated fuselage with a 1,5 mm plywood core that incorporates the fin.

The fuselage nose and wing mount area is reinforced on both sides with 1,5 mm plywood cheeks, as on the original design.

The assembled fuselage lamination and profiled wing and tailplane are treated with sanding sealer. Tissue, cut slightly oversized, is moistened, laid out over the balsa and then secured with thinned dope. After cleaning up the edges, several coats of dope are applied with light sanding between coats. The hole in the wing accommodates a hardwood plug reinforcement, the bell crank mount.

Here all elements have been glued together, except for he elevator which is fixed to the stabilizer using suitable cloth strips that act as hinges.

Accustomed to using aluminium for wear-sensitive parts, this time I risked the use of plywood as per the original. - after all, Tupker knew what he was doing? Below are images of the leadout guides and elevator control horn.

The plan shows balsa strip fuselage reinforcements which are also applied here but only for the sake of authenticity. Now more dope is applied, mixed with Humbrol enamel to create colour dope and always with gentle rubbing down between coats.

Often I default to yellow/red schemes, but this time it's a classic red-white-black job..

Flipped on it's back, the model shows it's metal steering system parts. Bell crank and push rod guide are aluminium, the push rod and leadouts are made of music wire. The laminated plywood engine mount is supported by a aluminium sheet doubler which also resists the pressure exercised by the engine bolt nuts.

The 1,5 cc Webra diesel was acquired secondhand around about 1980, an early example with a serial number. It runs very well but the cylinder loosens when hot – probably because no gaskets are present. Adjusting the compression or needle valve while the engine runs is dangerous because these controls are difficult to access and the model has no undercarriage to rest on. No undercarriage is present because it often induces cartwheel landings on grass strips.

All-up weight as displayed with engine and prop is 250 gr whereas the plan states a guideline of “around 200 gr”. No problem at the end of the day, because the VT Air Racer is easy to control, even in gusty weather.

Thanks to Paul Tupker!