Skew Ball (oz12153)

 

Skew Ball (oz12153) by Gordon Rae 1994 - plan thumbnail

About this Plan

Skew Ball. Radio control racing or aerobatic slope soarer model.

Quote: "Skew ball. 60 inches of slope agility. Gordon Rae's racer with a difference.

Skew ball is a racing aerobatic slope soarer and is intended as an introduction into the newly established 60 in slope racing class.

This type of model, together with a variety of model types with differing spans, was used in the UK in the 1970s for mixed class, mass start, slope racing. The introduction of a specific 60 in span class on the West Coast of the USA has started the ball rolling over here again. The compact dimensions of these aircraft enables conventional materials and construction methods to be used in the production of a competitive model.

Skew Ball presented here is the result of development work done to achieve a fast aircraft with optimum stability, together with the ability to be reasonably aerobatic. The wing loading and particularly the section are the major factors in the speed ultimately obtained and the Eppler 205 is used with a 2 degree reflexed trailing edge. This has turned out to be an excellent all round choice, with the reflex providing speed together with a good inverted performance.

For the ultimate in speed, other low cambered sections can be used, such as the RG 14 and Selig 2052 etc. However, remember that with these thinner sections, beam strength becomes a problem if the wing loading is increased much above 10 oz/sq foot. The built up wings are OK with the 9% thick Eppler 205, while a simpler solution is to use foam veneer skinned wings which can additionally use glass or carbon skinning for the thinner, racier sections, to give the required strength.

No there is not a bit missing! During development, various tail layouts were experimented with, including conventional vee and latterly, the asymmetrical. The latter proved so good that it was retained as apart from its excellent control, compared to conventional layouts, it also offered a reduction in weight, less interference drag and smaller total area compared to the other two. The latest interpretation of this layout has even less interference drag. (See photo/sketch).

When I'm interested in a design, I usually miss out the stick A to B bit and go on to the flying, so let's do that.

Flying: Despite its unconventional tail, Skew Ball's flying characteristics are quite normal, without any detectable asymmetry in handling. The 'bank and yank' turns are crisp and controllable. Straight line flight is stable with ample fin volume to maintain a straight course and yank control in turns.

For fast racing, Tx rates are recommended set for half control surface deflection. The control movements shown are required for maximum control in 'slow flight' and aerobatic modes.

With the reflexed E205 'Skew Ball' has a good inverted performance and will do nice large diameter loops, bunts, etc. The roll rate is good, dependent on the aileron surface deflection and aircraft speed while the small fin enables 'Skew Ball' to do nice stall turns without the use of rudder.

Spinning performance is normal, inverted or upright, left or right with the inverted ones the better. She is not fully stalled in a spin with the centre of gravity at the 3 1/2 in root balance point, therefore the ailerons give instant recovery. Do remember to 'push' not 'pull' in an inverted spin recovery, otherwise things get exciting, especially low down inverted.

If ailerons are used in the flapperon mode, 3 degree pos. flap/elevator mixing can be used to advantage in turns at higher loadings. A further two degrees neg. flap for speed, then down two degrees, to neutral, for cruise and light conditions (remember this represents 2 degree reflex) while up to 30 degrees can be used for landing.

Flaps do extend the flight envelope and are well worthwhile, particularly with the thinner sections though with just aileron control 'Skew Ball' is still a great performer upright or inverted. Apart from the improved inverted performance the built in reflex gives, it also stabilises the 'centre of pressure' movement, improving pitch stability and permitting a smaller tail area..."

Skew Ball, Silent Flight, August/September 1994.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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Skew Ball (oz12153) by Gordon Rae 1994 - model pic

Datafile:
  • (oz12153)
    Skew Ball
    by Gordon Rae
    from Silent Flight
    August 1994 
    60in span
    Glider R/C
    clean :)
    all formers complete :)
    got article :)
  • Submitted: 18/02/2020
    Filesize: 646KB
    Format: • PDFbitmap
    Credit*: Circlip, RFJ
    Downloads: 770

Skew Ball (oz12153) by Gordon Rae 1994 - pic 003.jpg
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Skew Ball (oz12153) by Gordon Rae 1994 - pic 004.jpg
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