FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1927
1927 - 0726.PDF
STTTPLEMKNT TO FLIGHT 60 THE AIRCRAFT ENGINEER SEPTEMBER 22, 1927 In concluding these notes, it must be admitted that it is difficult to cover all the ground in reasonable space. Although span and brake horse-power seem to be the best quantities to use, there are others, such as " Speed range per W/H.P." This would have an advantage over the Area per H.P. basis in that any extra surface or devices carried to extend the speed range would have to be operative, but it has many drawbacks, one of which is the difficulty of determining stalling speeds at the last minute. On the whole, a modification of this year's formula seems the most satisfaetorv solution. HANDICAPPING IN THE KING'S CUP RACE. By H. A. METTAM, M.A., A.F.R.Ae.S. One very important lesson can be learnt from the working of the handicap formula used in the King's Cup Race. This point has already been brought out in the description of the race given in FLIGHT of August 4, but it is so fundamental that it may well be considered still further. If machines of widely differing speeds are taking part in a race, the handicapper must not deliberately underestimate speeds by a constant percentage, as this actually has the effect of ruling out all the fast machines. This is clearly shown by the fact that the "Avenger" would have had to lap at 244 m.p.h.. and the "Vixen" at 165-2 m.p.h., to catch the Anec II, flying at 75-4 m.p.h., which is quite close to her actual speed over the first lap. It seems very curious that this point should apparently have been missed by everybody concerned, but it is, perhaps, not quite so strange when we remember that the handicap speeds must still, in spite of the statement above, be under- estimated when compared with true top speeds over a measured mile. The difference between this true top speed and the speed which can be attained round a course depends on the length and nature of the course, the strength and direction of the wind, and the course-keeping ability of the pilot. The last point cannot be covered by any formula, while windage corrections cannot be applied in a race which goes on all day. A machine will put up a better average round a long course with few turning points, and a relatively small portion of time spent in getting-off, than the same machine would do on a very short course with several turning points and in which getting-off time has an important influence. The change in possible speed from one course to another cannot be simply determined, so here we have another complication to add to the many difficulties of the handicapper's art. It is unfortunate that, owing to the small number of machines completing the course, the King's Cup Race did not provide very much data on which to judge the use of HPppi—:—g——— in the formula ; however, the mere fact that the Moth X started so much before the ordinary Cirrus II Moth, which is well known to be the slower of the two, shows that there is something wrong. It would be interesting to see how the various machines would have come out on the 1926 formula using " wing power," but sufficient data is not available. It was suggested in FLIGHT of August 4 that better results could be obtained by using a higher value of K in the present formula. The values of K required to bring the formula into line with the over-all speeds and best lap speeds of the various machines have been determined. The average value for best lap speeds is 19, and for overall speeds 17-6, so the writer chose K == 18 and worked out the times for the six machines which completed the course. The effect of this is to leave the order of finishing unchanged, but to close up the gap between first and third from 56 mins. to 5 mins., and the gap between first and last from 80 mins. to 30 mins. This increase in K would therefore have made a closer finish, while the fact that the Vixen III closes up on the winning Moth demonstrates that such a change makes ma * rs easier for the faster machines. A further increase of K to 21 would have made the fastest machine also the first home. In FLIGHT of August 4, there is a table of speeds which machines would have had to attain under the K = 12 formula in order to equal the Moth X when that machine was assumed to average 103 m.p.h. It happens that K = 21 gives the Moth X a handicap speed of this amount. The table of handicap speeds on this new basis, given below, may there- fore be compared directly with the original table, and also with the speeds actually attained. Speed, m.h.p. Xo. Machine and Engine. K — 21. 6 Anec II, " Cherub" 79-1 4 Halton Biplane, " Cherub" ... 84-8 27 C.L.A. 4, " Cherub" 87-2 5 Moth, " Cirrus 1 " 97-1 9 Moth, " Cirrus 1 " 26, 18, 15 Moth, " Cirrus II " 12 Avian, "Cirrus I" ... 10 Widgeon III, " Genet " 2 Bluebird. "Genet" 3 Moth, "Cirrus II " 22 Widgeon III, "Cirrus II "... 23 Avian. " Cirrus II" 8 Avian II, " Cirrus II " 13 Alpha-Avian, " Alpha " 14 Avian, " Cirrus II ' ... 24 D.H. 9, "Nimbus" 19 Vespa, '" Jupiter " 7 Horsley, " Condor '" ... 1 F. 6,'"Viper" 16 Tiger Moth, " Cirrus II " ... 20 Vixen, " Lion " 25 Boreas Martinsydc, " Nimbus " 21 Badminton, " Jupiter " 11 Avenger, " Lion " A great variety of speculative results may be deduced from these comparisons, but there does not seem to be any reason for thinking that the higher K would really give satisfactory results over the whole range of machines. We are therefore forced to the conclusion that handicapping can only be done satisfactorily by scrapping the formula and working from known performances. 99 • 3 103-0 105 1 105-2 106-3 107-5 108-8 110-0 110-0 114-0 115-2 133 1 139-0 141-9 144-0 148-0 149-5 159-3 177-8 198-2 A SIMPLE THEORETICAL METHOD OF ANALYSING AND PREDICTING AIRPLANE PERFORMANCE. By IVAN H. DRIGGS. (Continued from p. 54) Maximum Rate of Climb Similar to the ceiling there is a rate of climb corresponding to every value of V throughout the range, but it is the maximum of these values which Is the most interesting. We know from experience that variations of speed between quite large limits about the best speed have but little effect upon the rate of climb due to the fact that the curves P,, and PR are nearly parallel for a long distance. If a line be drawn from the origin tangent to the PK curves, the point of tangency will very closely determine the speed of best climb. Point E^,K. Fig. 1." p The slope of such a line equals ', and since this line is tangent to the curve of PK its slope is a minimum. Therefore dividing equation (7) by V, differentiating ^ against V, and placing the differential equal to zero, a value for V at climb or Vw is found. , (27) R.C. = Rate of Climb in feet per minute. Following a reasoning similar to that used in the case of the ceiling proof :— 668d
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
