The Theory and Practice of Model Aeroplaning Part 15

6. For all-round efficiency nothing but a good all-round model, which can be absolutely relied on to make a dozen (approximately) equivalent flights, is any good.

7. In an open distance compet.i.tion, unless you have a model which you can rely on to make a _minimum_ flight of 200 yards, do not enter unless you know for certain that none of the "crack" flyers will be present.

8. Do not neglect the smallest detail likely to lead to success; be prepared with spare parts, extra rubber, one or two handy tools, wire, thread, etc. Before a lecture, that prince of experimentalists, Faraday, was always careful to see that the stoppers of all the bottles were loose, so that there should be no delay or mishap.

9. If the rating of the model be by "weight" (1 oz., 2 oz., 4 oz., etc.) and not area, use a model weighing from 10 oz. to a pound.

10. If there is a greatest height prize, a helicopter model should win it.[52] (The writer has attained an alt.i.tude of between three and four hundred feet with such.) The alt.i.tude was arrived at by observation, not guesswork.

11. It is most important that your model should be able to "land"

without damage, and, as far as possible, on an even keel; do not omit some form of "skid" or "shock-absorber" with the idea of saving weight, more especially if your model be a biplane, or the number of flights may be restricted to the number "one."

12. Since the best "gliding" angle and "flying" angle are not the same, being, say, 7 in the former case and 1-3, say, in the latter, an adjustable angle might in some cases be advantageous.

13. Never turn up at a compet.i.tion with a model only just finished and practically untested which you have flown only on the morning of the compet.i.tion, using old rubber and winding to 500 turns; result, a flight of 250 yards, say. Arrived on the compet.i.tion ground you put on new rubber and wind to 750 turns, and expect a flight of a quarter of a mile at least; result 70 yards, _measured in a straight line_ from the starting-point.

14. Directional control is the most difficult problem to overcome with any degree of success under all adverse conditions, and 15 per cent., in the writer's opinion, is far too low a percentage; by directional I include flying in a straight line; personally I would mark for all-round efficiency: (A) distance and stability, 50 per cent.; (B) directional control, 30 per cent.; (C) duration of flight, 20 per cent. In A the compet.i.tor would launch his model _in any direction_; in B as directed by the judges. No separate flights required for C.

FOOTNOTES:

[48] The better way, undoubtedly, is to allow the compet.i.tor to choose his direction, the starting "circle" only to be fixed.

[49] Or 10 per cent. for duration of flight.

[50] In another compet.i.tion, held under the rules and regulations of the Kite and Model Aeroplane a.s.sociation for the best all-round model, open to the world, for machines not under 2 sq. ft. of surface, the tests (50 marks for each) were:--A. Longest flight in a straight line.

B. Circular flight to the right. C. Circular flight to the left. D.

Stability and landing after a flight. E. Excellence in building of the model.

[51] On the a.s.sumption that the model will fly straight.

[52] If permitted to enter; if not see Fig. 53.

CHAPTER XIV.

USEFUL NOTES, TABLES, FORMULae, ETC.

-- 1. COMPARATIVE VELOCITIES.

Miles per hr. Feet per sec. Metres per sec.

10 = 147 = 4470 15 = 22 = 6705 20 = 294 = 8940 25 = 367 = 11176 30 = 44 = 13411 35 = 513 = 15646

-- 2. A metre = 3937079 inches.

_In order to convert_:-- Metres into inches multiply by 3937 " feet " 328 " yards " 109 " miles " 00006214 Miles per hour into ft. per min. multiply by 880 " min. " sec. " 880 " hr. into kilometres per hr. " 16093 " " metres per sec. " 044702 Pounds into grammes multiply by 453593 " kilogrammes " 04536

-- 8. Total surface of a cylinder = circ.u.mference of base height + 2 area of base.

Area of a circle = square of diameter 07854.

Area of a circle = square of rad. 314159.

Area of an ellipse = product of axes 07854.

Circ.u.mference of a circle = diameter 314159.

Solidity of a cylinder = height area of base.

Area of a circular ring = sum of diameters difference of diameters 07854.

For the area of a sector of a circle the rule is:--As 360 : number of degrees in the angle of the sector :: area of the sector : area of circle.

To find the area of a segment less than a semicircle:--Find the area of the sector which has the same arc, and subtract the area of the triangle formed by the radii and the chord.

The areas of corresponding figures are as the squares of corresponding lengths.

-- 4. 1 mile = 1609 kilometres.

1 kilometre = 1093 yards.

1 oz. = 2835 grammes.

1 lb. = 45359 "

1 lb. = 0453 kilogrammes.

28 lb. = 127 "

112 lb. = 508 "

2240 lb. = 1016 "

1 kilogram = 22046 lb.

1 gram = 00022 lb.

1 sq. in. = 645 sq. millimetres.

1 sq. ft. = 00929 sq. metres.

1 sq. yard = 0836 "

1 sq. metre = 10764 sq. ft.

-- 5. One atmosphere = 147 lb. per sq. in. = 2116 lb. per sq. ft. = 760 millimetres of mercury.

A column of water 23 ft. high corresponds to a pressure of 1 lb. per sq. in.

1 H.P. = 33,000 ft.-lb. per min. = 746 watts.

Volts amperes = watts.

{pi} = 31416. _g_ = 32182 ft. per sec. at London.

-- 6. TABLE OF EQUIVALENT INCLINATIONS.

Rise. Angle in Degs.

1 in 30 191 1 " 25 229 1 " 20 287 1 " 18 318 1 " 16 358 1 " 14 409 1 " 12 478 1 " 10 573 1 " 9 638 1 " 8 718 1 " 7 822 1 " 6 96 1 " 5 1153 1 " 4 1448 1 " 3 1945 1 " 2 3000 1 " {square root}2 4500