Fevair (oz3879)

About this Plan

Fevair. 48 inch span FF rubber powered Wakefield contest model. Model Aircraft, October 1960.

Quote: "A most attractive and viceless Wakefield design. Comprehensive notes will enable you to duplicate this really successful model. Fevair, by Geof Lefever.

THIS model is the result of logical development of a line of Wakefields. First started when the amount of rubber used was in the region of 50 per cent of the total weight, they have been modified and redesigned as made necessary by subsequent reductions in the amount of rubber that could be used. The Ottair (oz9395) was designed to accommodate 80 gm (2.8 oz) of rubber, and was flown in the 1956 Wakefield Cup contest. Fevair retained many of the features incorporated in Ottair, but modifications were made to take advantage of the new rubber weight reduction to 50 gm (1.75 oz).

The result was a much cleaner design with detail refinements which resulted in a performance comparing very favourably with the 80 gm motor Wakefield. The average evening performance of Ottair was in the region of 3.30-4 min., whereas the performance of Fevair is between 3.15 and 3.3o min.

Modellers who cannot afford to spend several seasons developing a design, may well find Fevair a good basis for further development. The design is completely free from vices and will prove to be a most simple model to trim for contest performance, providing the following points are religiously adhered to.

(1) The rigging angles should be carefully checked, and with the CG in the position shown, no more than 1/32 in packing under the LE or TE of the tailplane will be required for final trim.

(2) The tailplane mount is fixed so that the tailplane is not horizontal. The starboard tip being raised to give right turn. This gives right hand turn proportional to the lift generated by the tailplane, and is far less sensitive to changes in flight speed between power and glide, than rudder turn. A small amount of trim tab turn will be needed, but this should be used sparingly.

(3) The tailplane and fin should be free from warps but the warps which are built into the wing are most important. A small amount of washout (approximately 1/8 in of packing under the TE) should be built into both wingtips. The port wing inner panel should be flat, while the starboard wing inner panel (ie the inside wing when the model is turning to the right on climb and glide), should be given 3/8 in washin. The model cannot be trimmed properly without these warps.

(4) A schedule of weights of the component parts of the model is given on the plan. These should be followed fairly closely as a wing or tailplane which is much lighter than tabled will not be strong enough. On the other hand a propeller assembly which varies much from the given weight will affect the rigging angles and alter the trim. The model should certainly not be overweight or the performance will be seriously affected.

(5) The contest performance can only be achieved with first class rubber motors. Each batch of rubber varies in quality and must therefore be tested before being made up into motors for contest work. Also each batch varies in density and cross sectional area, there-fore, motors can only be made up by weight. Allowing 2 or 3 gm for lubricant, the skein is cut up into lengths weighing about 47 gm each. When these lengths are made up into 12-strand motors, the length will be in the region of 26 in. It is a sound practice to keep each motor in a small labelled polythene bag. A note of the date, batch, number of times used and number of turns applied can be noted on the label and the motor is always returned to the same bag after use. Motors last much longer this way and, of course, it is invaluable for contest work to be able to see the history of each motor at a glance.

(6) With the exception of the quality of the rubber, the final performance of the model will depend on the efficiency of the propeller more than on any other single factor. Care should be taken to ensure that the pitch is correct and the blades well balanced. It will be found that an extra coat of dope on one blade will usually provide the final balance. The blades should be quite thin and very light. Because of this it is advisable to remove the propeller assembly before winding the motor, thus avoiding any risk of damage to the blades..."

Supplementary file notes

Planfile includes article.

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