MODEL AEROPLANE NOTES and General Hobbicrafts

Auckland Star, Volume LXIV, Issue 237, 7 October 1933, Page 3 (Supplement)

MODEL AEROPLANE NOTES and General Hobbicrafts

CARVING PROPELLERS' FROM AN OBLONG BLOCK. Qi.l'e a long time ago I gave you some advice about carving a Scotsman type of propeller, and many of my readers expressed their appreciation of the hints for curving contained in that article. A few more, words about propellers will never be amiss, so this week I am giving you some data which will be interesting to the beginner and the more experienced builder alike.

In the following list of propeller block sizes I have given you, a number of what we might call standard sizes far model aeroplanes. These are, of course, only

intended for a guide, but will undoubtedly help you to see the difference in the sizes of the blocks required to give a. low jiitcli, a high pitch, or a medium pitch to your propeller.

l.ow Medium- High Lfjth. pitch size. pitch size. pitch size. I «in 0-82x9-10 3-8 x 0-1 ft >9-16x0-16 7i» 5-16x5-8 7-1,0x5-8 f 5.-Bxs-3 Sin 3-BiM 5-Bx3-4 3-4x3-4 Oin 7-16 x 7-8 11-1.6 x 7-8 7-S x 7-8 lOiii 1-2 xl 3-4 xl Ixl 1 liu 0,16 x 1 1-8 J 3-16 x 1 1-8 1 1-S x 1 1-8 12in 3-S x 1 1-4 1- 516.x 11-4 11-4xll-4 Fig. 1 show? the method of carving one of those blocks according to the latent ideas on propeller design. Fig. 2 shows the block diagonally pencil marked and the centre hole bored. B shows the waste wood cut away. C shows the concave sides carved and sanded to a finish. D indicates plainly th* convex sides carved away, to give a rough finish. E shows the finished propeller with tips rounded off and boss narrowed to about half its original size. BALANCING A PROPELLER. Fig. 2.—This is a very important part of the work, and one not always, thoroughly dona by beginners, although the old hands know how important it is.

Before trying to balance a propeller it should be completely carved and sanded. Xo excessive amount should be removed while cheeking. Balance by sandpapering from the outside of the blades only. Hold propeller to a strong light. This will show the variations in thickness and assist in keeping the blades even.

After carving the propeller, the next step is to make it balance at least four ways as illustrated in Fig. 2, Xos. 1, 2. 3 and 4. After the propeller has been tested as illustrated in Xos. 1, 2. 3 and 4 it .should be tested as in Xos. 5 and (i. A propeller that is out of balance will cause the ''plane to shimmy and so hinder the duration and speed. After propeller is balanced a coat or two of dope applied to the blades will

help to stiffen and strengthen them. This added weight is negligible, although not recommended for indoor duration models.

When properly balanced, the propeller) shaft can be inserted and the washers or collects placed in a position ready for use on the machine.

. For a fuselage model of the heavier type, that is, weighing about IJoz to 2oz. the blades should be left about l-Bth inch thick at the boss, and tapering to about 1-lGtli to the tips. On the other hand, for extremely light duration models the propeller need not be more than about 1-1 Otli inch at the boss, and thin away almost to paper thickness.

A good rule to follow is to allow approximately 1-Sth inch inside "caniba" (or curve) within an inch ot' blade width. Later on I will go. more fully into this question, but I will here merely- mention that the greater the blade area of the propeller in proportion to the wing area of the model, the higher the model's rate of climb will be, so that to get a good climber use a widebladed propeller. Conversely, if you are limited for height in a hall for duration flying, and do not want your model to climb rapidly, a narrow-bladed propeller is essential.