Voo Doo (oz10049)


Voo Doo - plan thumbnail image

About this Plan

Voo Doo (Voodoo). Wakefield rubber competition model.

Quote: "Voo-Doo is the ultimate in streamlined-slabsider design, representing the limit in the development of this particular breed of Wakefield layout which started with the 1946 Gamage Cup and Canten Trophy winner. Still air duration is just over four minutes on 1,000 turns with good rubber and a superior grade of rubber would undoubtedly push this up to over the five minute mark.

On the folding propeller-retractable undercarriage scheme, the designer believes that this is the ultimate - although it is doubtful that such measures are necessary, or even desirable. For all normal contest work a freewheeling propeller and fixed undercart are recommended. This is less critical and makes for easier trimming.

The article details a very interesting and original propeller scheme - the folding-freewheeler.

PEDIGREE of my streamlined-slabsider Wakefields dates back to 1944, when I first used a shoulder wing layout on a lightweight rubber model of around 150 square inches. The first Wakefield to this layout was built in late 1945 and flew in the 1946 contest season with considerable success.

Since that time the basic design has been developed continuously, first concentrating on adequate stability and then on drag reduction. The latter was carried to the extreme of actually producing a decrease in performance, this by slimming down the wing section to a degree where the glide was so fast that sinking speed was higher than with a thicker section of higher drag values.

By 1948, the design had become more or less standardised for competition work, both as regards aerodynamic layout and structural design. Furthermore it had become possible to duplicate the model readily at 8-1/4 ounces total weight with a 3-3/8 ounce motor and 1/4 ounce parachute.

For comparative purposes an 8-1/2 ounce streamliner with the same propeller, wings and tail unit was built, trimmed and flown alongside the slabsiders during 1948, and without exception all the slabsiders outfiew the circular-fuselage job in still air. Most noticeable difference is in climb, where the streamlined-slab gets on average 100 to 150 feet more altitude with both machines at best trim. There is very little apparent difference on the glide.

Looking to 1949, therefore, the question of developing the streamlined-slabsided layout does not arise, other than as regards minor structural modifications which might be tried out. First rate contest performance with the model then boils down to two things - first, enough time to properly trim for best performance (and the trimming difference between a 3-minute flight and a 4-minute flight in still air is very small); and second, using the best possible rubber obtainable for consistent performance.

One of the few problems requiring attention is the very slight change in trim which can take place unnoticed. For example, a model trimmed to 4-minutes in still air may do considerably less than this at a later date on the same motor and in better conditions. It may, in fact, require slight re-trimming to get back to its original 4-minute mark.

Having studied this for some years, it would now appear that the most probable cause is difference in relative humidity of the air under varying conditions, causing a small and quite unnoticeable change in tailplane incidence which can make just that difference in performance. The answer to this again is structural design - not aerodynamic.

However, returning to the original layout. With the streamlined-slabs showing a better performance than a comparable streamliner, it would seem that the drag figure of the former is at least comparable..."

Voo-Doo, Model Planes Annual, 1949.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.


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