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FOR “TELECTRA” ALL CRUISER : BALSA RADIO CONTROL ALL WORLD’S CABIN MODEL “R.N.L.B. PLYMOUTH” NEW LIFEBOAT DESIGN : “SLITHA” SPACE MODEL : LANCIA AURELIA DETAILED CAR =: RADIO CONTROL IN A ANGLES AND APPARENT WIND TUCKER’S TOPICAL TALKS : M.M. MOTOR TEST : COOPER 1100 DESC RIBED : RHYTHMIC ROLLING READERS’ LETTERS : : : y 7 REGULAR : ELECTRIC MODEL RAIL CAR RACING : VANE FEATHER BOAT MAKE MODELS LEADING MAGAZINE © LITTLE FIAT 600 : RUSTON BUCYRUS EXCAVATOR MODEL WHO “SPACE” @ er a ae ies FEATURES MODEL MAKER] Wane FEATHER ANGLES & APPARENT WIND fine author’s recent articles (July, August, September, 1955, MoDEL MAKER) gave rise some to correspondence with Mr. H. E. Andrews, Commodore of the Newcastle M.Y.C. regarding vane feather angles. This in turn has prompted the following series, and due acknowledgements are made to him for raising this somewhat complex subject. The optimum feather angle is dependent on the following main factors which will be dealt with in order:— (1) The direction of the apparent wind. (2) The linkage ratio between the vane mechanism and the rudder move- ment. (3) The mast position. The first article will be confined to the beating trim. Let us deal first with the apparent wind and its relation to the true wind. Having had considerable experience of wind conditions on London waters where it is liable to turn up from the most unexpected quarters, one must make it clear from the outset that the true definition of apparent wind has nothing to do with where the wind is apparently coming from when you don’t expect it—those are flukes—flukes have nevertheless to be taken into consideration in trimming if they are persistent, such as are produced by the avenues of trees round the Round Pond, Kensington, or rows of houses in other cases. The true wind is only readily observable when you are stationary and observing in an area clear of obstructions. A “weather cock” or vane gear set up on a point will “fly” in the direction to which the wind is going and the direction from which it is named is directly m.p.h. strength would the wind to scale, direction the same and scale, when BC is the direction of the apparent wind and. TRUE scaling off the length will” give its apparent strength. This WIND E. So example has been chosen both for its simplicity and also to indicate how far removed the apparen t wind can be from the true wind (in this example 45°). In Fig. 1 it is fairly evident that the wind would appear to blow in the direction BC and not CB, but all cases are not so evident, so that our physics books give us a simple rule which determines the directi on for us. It can be stated as follows. From a point draw the “ object’s” motion to scale in the appropriate direction and put on it an arrow facing outwards; from the same start- ing point draw away from the point the true wind direction to scale, but put an arrow on this pointing to where the wind is coming from (that is the starting point in all cases). Complete the triangle and put an arrow on that line so that all the arrows face round the triangle. The length (to scale) of the completing line and the arrow on it define the knowledge to the beating model yacht. wind of say 15 m.p.h. It is Now the course taken for a close beat is If on a perfectly windless day you move at four miles per hour (m.p.h.) in any direct ion the wind feels to be facing you. This is the its some convenient to consider a Northerly its how to assess both these qualities. and is strength this strength. From what follows it will be seen apparent wind, to N-E. say lin. per m.p.h., and AC course of a of a model yacht in motion. Not only does the also motion ¥) cet Me This is at 4 m.p.h. North and the wind same effect is felt by the sails and vane feather but your is 8 m.p.h. from North East. We are now ready to apply This is the apparent direction of the wind. The change and its strength would appear to be 5.6 m.p.h. This is illustrated in Fig. 1 where AB is Fid 1 illustrated in Fig. 2 where the object moves wind appears to come from a different point to the true wind unless you are moving directl y into the wind, or with it directly behind you. effectively to come from the North East apparent wind strength and direction. opposite. When you move in a wind stream, the direction the wind is blowing from the East at 4 m.p.h. it will appear be 4 This of course cannot occur to a model yacht, but it is an excellent startin g point for understanding the apparent wind. If you move directly North at 4 m.p.h. when 188 about 45°, the axis of the boat however, is probably about 30°, the reason for making a 45° course being the leeway made. Both these figures are important since the apparent wind direction and strength (graphically) taken, while are calculated from the course the vane feather Fig 2 APPARENT WIND tl-2 M.PH. 30° E. OF N. APRIL, 1956 setting must be relative to the axis of the boat. In Fig. 3 AB defines the wind—15 scale divi- poor, as high as 4°. We will take 3° as an average. Fig. 5 illustrates a series of vanerudder linkages in which 5a shows a 1:1 ratio sions from A with the arrow pointing to where the wind comes from—while AC in which to obtain 3° of helm the vane must be 3° off wind to give it, assuming the wind is the boat strength and feather area are strong enough course at 45°. At this point we wijnp ” meet the most interesting feature of this exercise. It is this. If We have a constant 15 m.p.h. wind from the North and set off one boat 1OR”, ALMOST iin and each “M” of the “A”, large enough to overpower the water pressure on the rudder. This is never likely to be so, therefore something more than 3° ane offset would be required to give 3° of working helm. 5b shows a more powerful linkage with the vane arm shorter and the and 36 in. classes rudder arm longer. from a starting buoy all trimmed In turn, however, one sees that to move the rudder 3° the vane must for a close beat they should all follow the 45° course but at different speeds, therefore in be offset 9° assuming that the vane has sufficient power to move to the neutral position against the water pressure on the rudder. As mine the apparent wind direction we shall have points C,, C,, Cs. C,, which have in the example any additional offset need be smaller than in the previous case. To a close approximation the multiplying factor for the vane offset for completing our triangles to deter- tpi, linkage is stronger in favour of the vane been taken as 5, 4, 3, 2, mp.bh. which is probably a fair approximation. The triangles for these have been completed in Fig. 3 B and the apparent wind directions and strength quoted in m-p-h. and degrees the linkage ratio is the ratio of the distance from the rudder post to linkage pin, to the distance from the linkage pin to the vane pintle (three in tha case of Fig. 5b). Fig. 5c jjjustrates a bad linkage ratio to which I grew attention in a previous article. Here the ferred to Fig. 4 which shows the outline of a hull set at 30° to North and the directions ment for small angles (with which we are concerned) and because of the adverse leverage West of North. These angles are now trans- of the apparent winds. It will be noticed how these differ for the different classes of boat. We can now turn our attention to the second point, i.e., vane linkages. One of the great advantages of vane steering is the ability to give a small amount of weather helm to keep on firm steerage and the sails full and drawing. The amount of helm to do the this skeg and is finish. lining dependent and If is the good stream- the may be as low as 2° TABLE (a)| —(b) © | Apparent Class Axis ot BoattoN on _ rudder design | Wind West of | helm and if yane movement is less than the rudder move- the vane requires considerable offsetting to overpower the water pressure on the rudder ; nevertheless a small wind shift gives a large rudder movement and steering is erratic. Overcome water pressure the more susceptible the gear to variations in wind strengths, is which is to be avoided. It is clear that the 5b arrangement is desirable and this is one that enables one to calcu- late pretty accurately the degrees of offset for 3° of helm plus a very small additional offset for overcoming water pressure, say 2°. case we get the settings shown in Table 1. | | RUDDER POST (d) (e) Vane Offset rom Apparent Wind | almost 11° | (3×3)+2=11 30° | 9° | (3×3)+2=11 | 32° M 30° 7 ag | Gx3)+2=11 | 34°° (3×3)+2=N1 | Bee | 5° (Continued on page 208) 189 3° a 30° eck 3° VANE PINTLE —s – relative to Boat’s axis =b-c+d 30°. 30° ° Vane setting 10r | 36” These figures can now be applied to Fig. 4 in which “A”| | In addition the more the vane has to be offset to 5 ? APRIL, 1956 Calm conditions and breeze steady a the Northern favour SA”? boat Black Tarquin, here demon- strating the circumstances under which rolling com- rhythmic frequently this Left, mences. simple diagram will aid you to follow the explanaingenious tion below RHYTHMIC ROLLING The phenomenon of rhythmic rolling is peculiar to model yachts, and has provoked many a long dis- cussion wherever yachtsmen gather. A feasible explanation is here put forward by one of the model yacht world’s better-known original thinkers, Guy Blogg. f ® HE cause of Rhythmic Rolling when sailing before the wind can be satisfactorily explained aerodynamically without introducing other minor factors. Let us first consider the effect of wind on a single vaned balanced windmill. The illustration represents the vane in the same position as this paper and in a 2 o’clock position. The axis on which the vane axle (A) can rotate is perpendicular to this paper. If the reader were to blow air on to this vane it would remain in the same 2 o’clock position, but the axis (A) would tend to change direction. If the end of the axis below this paper could move horizontally only, it would tend to move to the left. Let us now imagine that the vane is still in a 2 o’clock position but its lower long edge is further from the reader than the upper long edge. If the reader now blew air on to the vane, two things would tend to happen, (1) the vane would rotate about (A) anti clockwise, and (2) whilst the vane moves from 2 o’clock to 12 o’clock the axis (A) perpendicular to this paper would change direction so that its end below this paper would move to the left. In the example given, the axis at (A) perpendicular to this paper represents the longitudinal axis of a yacht and A.B. represents the mast. Let us now view a yacht from her stern with her mainsail set on the starboard side, 205 travelling away from us with a following wind. She will obviously tend to head slightly to port which will cause the wind to be shed across the leach of the sail. This will cause the mast to heel anti-clockwise, and the centre of effort will pass from starboard to port side. This will cause the yacht to turn direction slightly to starboard on account of the driving force being out to port. This change of direction will now cause the wind to be shed over the luff of the sail, which in turn will cause the mast to heel clockwise. Repeat these incidents and we _ have “rhythmic rolling.” Under ideal conditions, i.e. wind light and steady in intensity and direction, it is conceivably possible to sail dead before the wind (1) with mainsail dead transverse to wind and mast erect with a degree of weather helm of course, (2) with mainsail out less than 90°, heeling over to boom side with a greater degree of weather helm because C. of E. is further out to lee owing to the heel, (3) with mainsail out more than 90° heeling so that the boom is lifted. If, in this last case, the C. of E. is vertically over the yacht, little or no helm is required, but if the C. of E. passes to the opposite side of the boom, then some Iee helm will be required. MODEL MAKER) Tucker’s Topical oh Mae Talks ;.. MAINLY ON ew 2 : ” 3” 10Z./1N. Fig 6a 3 OZ,/IN. oz 2″ ~ (Coutinued from page 189) and in turn it will not be blamed for the idiosyncrasies of a hull. As a postscript it may be useful to analyse the action of the vane described under Mr. Week’s name in the November 1955 “ Model Maker”. It is clear from his performance in the 1955 “M” National Championship that he had good control of it and with knowledge and experience others can do the same. The reason for commenting lies more in the fact that unfortunately the gear is not, as he suggests, balanced—that is, balanced in both the fixed and self tack positions. If it is balanced in the fixed position the conditions will be approximately as shown in Fig. 6a where the weights and moments about the pintle balance. When, however, the feather is released, its centre of gravity moves towards the pintle and the counter weight moment about the pintle is now the greater and will give weather helm. This no doubt accounts for the feather being set at such a close angle. We then get the condition of the wind on the feather trying to give lee helm to counterbalance the weather helm given by the counterweight. This form of feather mounting when released can only give effectively lee helm where it is driven against a stop as in the other direction it can fly free. Clearly a setting can be found where the counterweight and feather are nicely balanced to give the required helm. In making these comments the author hopes that. all readers and in particular Mr. Weeks will not take them as critical comments on the capabilities of the gear but rather as an appreciation of the possibilities of this unconventional gear and the unconventional settings required. ARM & STOP PLATE P/ NTLE anoe WIND FEATHER WEIGHTS 102. 3° 10Z./IN. IMOMENTS While not suggesting that Mr. Week’s Marblehead is unbalanced there seems little doubt that a boat which tends to “screw up” into the wind on heeling would be happier with such a gear than with the perfectly balanced type. 30z/IN. = —— LAST MONTH’S ADVERTISEMENTS March MODEL MAKER was so lucky to get out at all that a certain number of errors unfortunately crept into the advertisement section due to the unaccustomed hands responsible for the final stages. In particular We 10z. i %oz. t 30Z/iN. 10Z/iN. NOTE BALANCE IS IN THE WEIGHTS MOMENTS 02, 102. 1 oh N. \, oz/| N. we OF 102.OF TOTAL WEIGHT OF 4075S. BASE WHICH IS ALWAYS must apologise for anticipating a price change by Messrs. Wolf Tools, and also to the Crown Silver and Guinea Gold Lacquers whose price change worked the other way. BALANCED 208
