- Description of contents
JUNE Model Ships – Cars – Yachts Radio Control . Engineering Sse tlt tw 1959 nl MODEL MAKER) RADIO CONTROLLED YACHTS Part One of an interesting, factual series by one of the best-known R/C yacht exponents, J. C. Hogg | eee in Radio Controlled Yachts has gained added regattas impetus which with includes this season’s the first programme national event of for R.C. Yachts, which will be held at Poole on 29th and 30th August. Some thoughts on the design and performance of yacht control equipment may help to stimulate new ideas. The main control requirements for a yacht are firstly the movement of the rudder and secondly the control of the angle of the sails to the wind, which involves the operation of a sheet winch. Let us consider what is required for each function. First Function—Steering Since the aim is to control the model as one would a full-scale yacht the method of the operation of the rudder is of prime importance. R.C. yachts, although at present mainly of the displacement types, undergo far more manoeuvring when racing than do their full-scale counterparts. They are, in fact, made to behave more like sailing dinghies For example, a typical R.C. yacht triangular course may have legs of 60 yards or 30 boat lengths, compared with 250 boat lengths for a 6 metre race and 530 boat lengths for a 12 metre race. The figures are approximate, but the point here is that to get the best advantage in their manoeuvres and tactics the models’ steering systems should be lively and yachts should be able to tack quickly even in choppy water. In addition to this it is almost impossible to get the feel of a boat with a slow-moving rudder. One tends to give “too much, too late”. On the other hand the temptation to “pump the tiller” must be resisted, as it is as fatal to speed in the model as it is in full-size sailing. After trying Progressive, Self-centring, and Proportional steering systems over a number of years I think that the Proportional is the satisfactory—and Sunray II certainly the most satisfying——-way of sailing yachts. In a fully proportional system the rudder on the boat behaves as if linked to the tiller held in the hand on shore. The use of the other types mentioned is governed more by the practical problems of control design than by choice. The radio assisted vane steering should be mentioned, but I think that what it gains on keeping a fast course it loses during other features of the race. Also the idea of two skippers— one in the boat and one on shore—seems unsound. However, there is room for all types of systems to be developed. The mechanism for steering an “A” size yacht should operate the rudder from 35° port to 35° starboard in about one second. Recent tests carried out under radio with a form of tensometer fitted to the rudder show that 3 1b. inch torque is necessary. This value will of course depend on the rudder area, its aspect ratio and its position in the hull, but forces of this order can be expected and can be met with a margin to spare by a good midget 4-6 volt motor, provided an efficient reduction gear train is used. The gears can be quite light with thin shafts as the wear is extremely small even after several seasons (it is wise to protect them with a friction clutch as described later), The screw and nut principle is a simple form of reduction and an easy one to make, but is less efficient than a gear train. The gear ratio c= MAIN One yacht used _ for these tests was the JIB required will vary with the type of motor used, but a typical ratio is 400:1 reduction, to give a final speed of rotation of the rudder equivalent to 20 r.p.m, These little motors should be run fast and the reduction gear designed accordingly. In. this way the GEARBOX current consumption is low and efficiency is near its peak. The articles and the graphs on motor performance in the MopEL MAKER are of value in this respect. The servo motors can be connected to the gears either by a small pinion, by a flexible coupling, or by thin elastic bands in deep groove pulleys. Since only some 1/1000th horse-power is being transmitted the bands are quite adequate and compare with a single vee-rope drive in full-scale motors. Obviously, bands should be changed before they deteriorate, JIB oe +g / CIRCULAR PLASTIC BELT BELT Cc en Fs 278 UNE, 1959 Right are photos A and B, showing the winch and rudder gears from a Marblehead and a tensometer micrometer screw type but if not overtensioned they form a protection for the little motors. system with Proportional described later. Rudder control is Second Function—Sail Control Fortunately the angles of the the mainsail to the wind should the sheets controlling these two by one winch (proper allowance greater travel foresail or jib and be similar, so that sails can be moved being made for the of the mainsheet). This greatly sim- plifies the equipment. It may be argued that individual sail trimming would be an advanta ge, but in practice, at a distance the accura cy of individual trimming would be low and the advanta ge, if any, small. In the cutter “Sunray” two headsails and the mainsail are controlled from one winch, carrying drums of different diameters. In the “M” “Sunray II” and the “A” “Sundial” the main and jib sheets are led to one lever, the jib sheet directl y and the mainsheet via a pulley which doubles its travel. The main feature in sail contro l is that at times considerable pulls have to be exerted on the sheets and that much power can be lost in inefficient pulley systems. The pull required has been measured on each of the models, while sailing. On the “A”, for example, up to 4 Ib. is needed at the main boom end and 3 1b. on the jib. These sails should be able to be hauled in, in say 5 second s, even when running. As with the steering, an efficient gear train is needed. Clock mechanisms make excellent purpose, the gears being sized and ing to their duty. the main spring trains for If a clock is used for a lever winch may be retained and wound up shows the winch and of some +4 Ib. rudder gears from “Sunray II”. These are mount ed on one removable unit which can be withdrawn from the control box for cleaning. The connections for the limit switches are plugged into the socket, the switches being built into the mechanism. There are (Fig. 1):— 1, 2. 3. three main Lever Winch Drum Winch Belt Winch ws _… sale FA Lever Winch Method 1 has the methods advantage we ks ost of sheet ment from the yacht in one box. The lever type is the least likely to cause jamming or entang- ling of the sheets. Limit Switc hes are easily fitted at the ends of the lever move ment. The limit switches prevent the winch over- running and possible dama ge and secondly to give two known positions for the sail control, namely, “close hauled” off” for for beating running to windward before and the wind. fully It is particularly important to find accurately and quick ly the close hauled position because if sails are pulle d in further than this posit ion the yacht’s performa nce drops considerably, (Continued on page 308) Photo C, tig, 2 (qe=== === showing the dial tensometer whic h is simply graduated for easy reading from the shore . Inset is picture D, showing installation and regis tration 279 === 5 ke yet | lng PAXOLIN \ it is useful to be able to lift out the whole of the equip “squared ~~ DECK compact ROLLERS 3″ ALL 18.S.W.G. STAINLES WIRE Gear ratio. 2900:1 40:1 80:1 of being FREE FIXED control enough to go in the radio control box on the model— Serve two purposes, firstly to TO WINCH this inches on the winch—a valuab le help to the system. “A” DECK weighted accord- permanently when it will exert a pull Photo TO JIB SCREW TO SK Nis Oh Yq “4 DIA. DIA.PLASTIC ROD DRILLED N° 54 ET — |I | ] | ———— =) 4] Sn 8 BA.C vie < IMPROVING THE PERFORMANCE OF MODEL YACHTS Part Three By R. H. MORRELL point at which pressure will cause the boat to move evenly sideways through the water. This point, the C.L.R., can be lightly marked on the side of the hull. across the deck it is By resting a ruler squarely then easy to transfer this point to the centre-line of the deck, making a slight mark. Great accuracy is not called for, as any slight discrepancy will have small effect on our result. The distance of this mark from the bow can now be measured, but this is not the final result we need, Ee our next attention last instalment we dealt at some length with the means of checking the alignment of the fin and skeg of our model, and the verifying of this is of real importance if our yacht is to attain its proper efficiency, and to sail similarly on both tacks. Our is given to a factor which calculate what per is vane, etc., so that is floating on her correct either the bow or the stern swings away first, but a little experiment will show that there is just one of This, the C.L.R. however, is than trying to smaller than our first one, difference may be 7-10 in. the deck from the bow and obviously easier and more measure along the side of cent. a matter, as the position of the C.L.R. (which is not little longer. she position L.W.L. a fixed point) is not very critical. If its position is found to be above, say, 57 per cent., I would advocate altering it, and this can generally be done easily by cutting away a little from the rear edge of the fin. Needless to say, the after part of the fin will have to be cleaned up to good streamline shape again, care being taken to get its after edge truly vertical. But if the leading edge of the fin is incorrectly placed, or if the C.L.R. is much too far forward (say less than 51 per cent.), action is To check factor 2, float the model in a bath, using suitable weights on deck to represent mast, sails, L.W.L. Then hold a sharpened pencil horizontally with its point near the L.W.L. just aft of amidships , and push gently. It will probably be found that the There the C.L.R. falls on a point 55 per cent. along the length of the L.W.L.; quite a normal figure. Let us suppose that, after making these tests, the skipper finds that the C.L.R. of his boat is too far aft. Now, provided that the position of the leading edge of the fin is satisfactory, this is not too serious 30 per cent. of the L.W.L. (i.e, L.W.L. x 30/100) and then measure this distance along the L.W.L. from its forward ending. The point found is the correct placing for the root of the fin. In cases where the plans are not available no difficulty arises, but the operation may take a the 27 in. Now the L.W.L. measured 49 in., so:— If 49 in. represents 100 per cent. of the L.W.L., then 1 in. would be 100/49 per cent. of the L.W.L.. therefore 27 in. will be 100/49 x 27/1, equals 55 that the root of the leading edge is approximately this, know of We now have a measurement in inches, and can easily convert this into a percentage of the L.W.L.. as the following example shows :— On an “M” class yacht the C.L.R. was found to be 28 in. from her bow. As her forward overhang was | in., the C.L.R. was 28 in. minus 1 in., or easy. If he first ascertains that the angle of inclination of the fin’s leading edge is not very much steeper than 45 degrees, he has then only to check do to the hull to the forward end of the L.W.L. Fin Incorrectly Placed under Canoe Body Quite a different approach is called for in checking the model for this defect. The first check is a straightforward matter of measurement, and the second a simple practical test. The two factors which we desire to verify are:— (1) That the leading edge of the fin is correctly placed in a fore-and-aft direction; also that its shape is satisfactory. (2) That the centre of lateral resistance (C.L.R.) is reasonably placed under the canoe body. Where the reader has the plans of his model readily available, checking factor 1 becomes extremely To desire percentage accurate properly. placed. we a will not be very much but for a 10-Rater the To thus measure along deduct the overhang, is largely determines whether a yacht will hold a good course, or whether she will insist on constantly working up into the wind or, alternatively, refuse to point up correctly as as easily found. We know the distance of the C.L.R. from the bow, so if we deduct the length of the forward overhang from this figure, we shall have the distance of the C.L.R. from the front ending of the L.W.L. In the case of classes without much overhang, such as the “M” class, the amended figure necessary. In only answer, made. 290 some but cases often a new suitable fin may alteration be the can be JUNE, 1959 Heading photograph shows two Bristol M.Y.C. members trimming for a run. Note set of sails. Fig. 1 (right) shows the lamination removed from the Marblehead fin as detailed in the sketch (Fig. 2) below The model illustrated in Figure 1 needed alteration, as the leading edge of her fin was too far forward. This presented something of a problem, if recasting of the lead keel was to be avoided. In any case, it did not seem practicable to move the fin bodily aft, as the keel bolts passed through two strengthening floors inside the hull, an arrangement one would not wish to alter. The difficulty was successfully overcome, and the sketch in Fig. 2 shows the solution found. This model had a rather deep fin (deeper than the original design) and it was felt that a small reduction in draught would not be detrimental, so a 4 in. thick layer was cut out. This resulted in the lower portion of the fin moving upwards to close the gap,, this having the effect of moving the leading edge back a little, as is clear from the sketches. It will be seen that it was now possible to carve away the root of the fin considerably, and a small slice was also removed from the front of the lead keel, the result being a well placed leading edge to the fin. Actually, its angle of inclination is a little steeper now than previously, but the angle is not excessive. Two further problems had to be overcome, and these were inter-related. The adjustment of the leading edge resulted in the loss of a few ounces of lead and, furthermore, left the keel rather bluntnosed. Rectifying this resulted in a little further loss of lead, tthe final total loss being about 10 oz. This was satisfactorily overcome by the removal of a suitable area of deadwood above the top face of the lead keel, and a piece of lead was cast to replace the wood. When all was cleaned up, the result was quite satisfactory, and the various had all been successfully overcome. success, the model’s waywardness having Incidentally, difficulties the modifications proved a complete pletely cured, and Inefficient Sails As emphasised been com- her full performance restored. in the opening section of this article, sails are the determining factor as to what propulsive effort a yacht receives in any given strength of wind. The very best of hulls cannot be really effective if its motive power is seriously reduced. Assuming, then, that it is accepted that sail efficiency is of first-class importance, we will consider the factors involved. The first consideration is the sail plan—a somewhat controversial subject! Two main points arise here (a) the aspect ratio (A/R) and (b) the proportion of headsail to mainsail. Designers of equal eminence have different views as to what constitutes the ideal proportions. As on all points of design, the author feels that the most profitable course is to carefully weigh the various opinions, giving due regard to the reasonings advanced, and then to carefully seek been found very effective to windward, especially since the introduction of improved sail materials, such as varnished terylene, etc. In recent years A/Rs have steadily tended to increase, creeping up until 4 to 1 is quite common. However, in all spheres it is possible to have too much of a good thing, and there is now a strong trend towards more moderate ratios. Certainly no one will go far wrong if they adopt an A/R of either 34 to 1 or 34 to 1, according to their circumstances (for difficult ponds where winds are “fluky” there is much to be said for the lower ratio). A similar swing has been apparent in the matter of headsail/mainsail ratios. Starting, some years ago, with the headsail (or jib) having 27 per cent. or 30 per cent. of the total sail area, the percentage of headsail has steadily increased until it sometimes reaches as much as 40 per cent. Here again designers recently appear to have become convinced that there are advantages in moderation, and less extreme sail plans are more evident. The author would suggest that a proportion of 35 per cent. to 36 per cent. of headsail will be found very suitable in most cases. Although the question of sail plans is interesting and by no means unimportant, we feel that it is much less vital than are the sails themselves, Firstclass material; good cut, with just the right amount of “flow”; skilful making; and good “‘set”; all these combined are necessary for really efficient sails. All this adds up to the conclusion that for really good sails one needs to go to a specialist (several, who turn out a first-class job, advertise regularly) It is true that some experienced model yachtsmen can turn out good sails at home, but it is well to realise that few people get sufficient practice to become really first class at the very tricky art of sailmaking. The moral is—give your model really good sails, and notice the difference! LAYER TO BE REMOVED Saas say ie ‘\ . \ re a balanced judgment which, so far as possible, reconciles the different views. For the benefit of the novice, the term aspect/ ratio refers to the height of a sail in comparison to its width. For example, a sail having both, the luff and the foot each measuring 30 in. would be said to have an A/R of 1 to 1; whereas a sail whose height was 60 in. with a width of 15 in. would have an A/R of 4 to 1. For many years model yacht designers favoured an A/R of about 3 to 1, but higher A/Rs ORIGINAL FIN have 291 i \\ DRAUGHT REDUCED FIN RAISED & NEW L.E. FORMED AFT. JUNE, 1959 Readers Write... The elegant little plastic wallet containing chrome vanadium double-ended B.A. spanners in the hard-to-get model sizes Readers Write” correspondents. the left-over bits of plastic first. It is so easy to ruin the whole lot with two shots of the spray. A. Kay. Peterborough, Northants. POSHING UP PLASTICS Dear Sir, I am finding the articles dealing with the construction and improvement of plastic car kits very interesting, and would like to mention my own modifications. I have made the complete Merit Range, and find that the following additions make the models even more attractive. On the majority of the Grand Prix Models, coil springs can be inserted between the upper and lower wishbones of the front suspension. These can be made from thin copper wire, which is first coiled around a suitable size of dowel or rod. Slip the dowel or rod from the centre of the coil, and gently pull the wire outwards, so as to form a neat looking spring, then cut to the correct length. I find it easier to paint the spring matt black first, and glue in position after the model is completely painted. j All the cars in the series are fitted with hydraulic braking systems, and the fluid pipes are visible running from the back of the brake drums, into the body through the front suspension cut-out. These pipes can be represented by lengths of plastic string or the thin plastic coated wire found inside telephone cable. f Body modifications can be carried out on the Ferrari, and 250F Maserati. The Ferraris had varying exhaust systems, and the one I used had two large diameter exhausts protruding from holes cut in the body, just in front of the rear wheels, on both sides of the car. The shape of these holes varied, but can easily be picked out from photographs. The Maserati, which is one of the nicest looking models when completed, was raced in various forms, and extra vent holes can be cut in the body under the splashers. ‘ It is also possible to carry out drastic modifications to convert the 250F to the V.12 Maserati raced two or three times by Fangio and Behra. Regarding the books dealing with Model Car Construction, I would like to point out that Rex Hays has written an excellent little book called ‘‘Racing Cars in Miniature’’ which caters for the pen-knife and razor blade brigade. Although enamel paints give a good finish, one is often troubled by air bubbles appearing on the surface whilst painting, and also the waiting, before the paint hardens. After much experimenting, I have found that it is possible to break the golden rule of plastics and spray the model with cellulose. The finish is superb and is comparable with enamel as far as appearance is concerned. The main advantage with cellulose is that the model is dry within 10 to 15 minutes. One word of warning. Don’t start spraying a 12s. 6d. kit without experimenting on YACHTERY Dear Sir, Mr. Thomas (February) complains about lack of interest by the Model Yachting Association, and lack of subjects by the MODEL MAKER. Model Yachtsmen I find, treat their sport in a different manner according to their personal interest in a particular class. In addition to Club racing all over the country, there are six events sponsored by the Association during each year. The MopeEL MAKER also arrange a Marblehead trophy. Subscribers to the “A’’ class regatta are sent a daily report of this event, otherwise a full report is given in the M.Y.A. News and the MopeEL MAKER. Mr. Thomas would appear to be a member of the Bristol club in the Western Region of the M.Y.A. A member of this region is entitled to attend each council meeting of the M.Y.A., so that Mr. Thomas can obtain up-to-date information through his club. Mr. Thomas evidently refers to the Marblehead class as not being a thing of beauty. This class was instituted by the M.Y.R.A.A. of America, which has a limit to its overall length, and as waterline length is important, its full use is made of. I suggest that Mr. Thomas has a week’s holiday in Fleetwood from August 16th to the 23rd, when he will see as lovely craft as any in scale or full size, so much so, that the Yacht Racing Association have called into conference our members with a view to sailing models of prospective full-size craft for the America cup. This is fully explained in an article in the February issue, by N. D. Hatfield of the Y.M.6 club on whose lake the trials will be made. F. SHACKLETON, M.Y.A. Ipswich. NORTHERNERS NEGLECTED? Dear Sir, I would very much like to attend a Power Boat Regatta, but most of them are at Bournville or somewhere near London. Perhaps, through the medium of your magazine, the opinions of other modelmakers in the North could be voiced on this subject of too distant regattas. May I suggest that Manchester may have a suitable venue and is centrally placed for most Northern enthusiasts. Yacht regattas are held at Birkenhead, why not power boats? What do other Northern readers think about this subject? E. L. KNOwWLEs. Moreton, Cheshire. BLOP-BLOP-BLOP-BLOP-BLOP! Dear Sir, When I got the latest edition of the MoDEL MAKER today, I was very surprised to find there the nice article by A. H. Caistor about his submarine. When I read it, I found that it contains the description of a principle which happens to be exactly the same as an invention of mine patented in Germany since 5.9.58. I know that this is not the first time that two or more people have had the same idea at the same time and the reason for my writing is to prevent trouble for any readers of MopEL MAKER who intend to build a similar submarine. The use of carbide to form gas is not only poisonous to fish; the acetylene produced makes the whole boat as explosive as a grenade and together with the electric 307 which will be presented to our devices, which can easily act as ignition, may destroy or ruin a life. I am a chemist and know the properties of acetylene very well. In my patent there is mentioned a much better substance to produce gas which is non-poisonous and non-inflammable; this employs a mixture of sodium bicarbonate and citric acid to interact with the water. Both substances can be bought for pennies at any chemist. The exact formula is to mix three ounces of sodium bicarbonate with two-and-a-half ounces of citric acid. Both are powders and both must be waterfree. Keep the mixture in a dry glass away from moisture. If you have a chemist friend he may be able to press tablets for you. Calculations from Mr. Caistor’s design indicates that .05 ounces tablets should be adequate, each of which will produce about sixteen cubic inches of carbon dioxide. Figures are very approximate. If you cannot get tablets pressed, quantities can be weighed out on a letter balance and wrapped with tissue or other non-waterresistant paper to form little balls. Incidentally, if you are thirsty, take one teaspoonful of the mixture, add to a glass of water and make yourself a soda! In my own boat, submersion is achieved by flooding a ballast tank by means of pressure from the bow-wave and the gas provides surfacing, timing being arranged by coating the tablets with a substance which needs to be dissolved before the carbon dioxide can be generated. Dr. HELMUT ZIEGLER. Leverkusen-Schlebusch, Germany. MASK-ER-AID Dear Sir, On page 251 of the May issue it is suggested that cellophane tape is unsitable for masking in certain circumstances. In this case I should like to recommend the plastic insulating tape, now available in various colours from Woolworths, and probably elsewhere. It has a much better edge to it than either cellophane tape or gummed paper tape, and is not so strongly adhesive, and pulls off ordinary enamel painting quite easily. Incidentally, it can be pulled round into slight curves—an added advantage. R. S. FARMER. Rothley, Leics. INVITATION TO TEES Dear Sir, The car section of the Tees-side Model Engineers are just completing an electric car track layout, the construction of which may be of interest to readers. The difficulty of cutting an accurate slot and getting a good electrical continuity was overcome by using }-in. square brass rail set for jan -in. slot; the rails are bolted to a hardboard base with 10 BA csk. screws. A simple jig kept the drilling and slot accurate, and screws were placed at i-in. centres on straights but rather closer on bends. Three sets of rail were laid, then the “roadway”’ between filled in with Redimix Plastic Flooring. In later stages of construction for economy we filled in with scrap material and finished with a ;4-in. layer of plastic. This method of construction may not be the cheapest, but for neatness and efficiency I think it takes some beating. For readers in the Tees-side area, may I say we would be pleased to see them Tuesdays and Fridays at 8 o’clock in the Settlement House, 130 Newport Road, Middlesbrough. R. THOMAs. Grangetown, Middlesbrough.
