Effect of Wind Resistance. AN INTERESTING EXPERIMENT FOR THE BENEFIT OF MOTORISTS.

Progress, Volume III, Issue I, 1 November 1907, Page 29

Effect of Wind Resistance. AN INTERESTING EXPERIMENT FOR THE BENEFIT OF MOTORISTS.

[To THE FDITOR ] *>ir — During the past motormg season I have watched with considerable interest a large numl'ei of events take place handicapped under formula which take into consideration wind resistance. I was wondering whether anyone had any reliable data ii. regard to the wind resistance of rapidly moving motor cars, and as there did not seem to be much available I thought some test at Brooklards Track would be useful to motorists, and therefore on Fnday last, thanks to the courtesy of Mr. Rodakowski and the Brooklands authorities 1 was allowed the use of their finishing straight, for timing trials on a 38.4 hp. (R.A.C. Rating) Napier I had the advantage of the assistance of two R.A C. Official timekeepers, Messrs. F. f. Bidlake and A C. Reynolds, who timed the car over each test. The six-cylinder Napier driven by Mr. Tr^ on as shown in picture No 1 had a wind screen erected on it of 30 sq. feet, the dimensions being 6ft. wide bv o ft high and being built up of laths 6ft. long and 2m wide, so that each lath represented one square foot. Sixteen runs were made commencing with the total area exposed to the wind, and after each run 2 sq feet, i c two laths were removed, and the result of these runs came out as follows .—. —

Besides these 16 runs there were two otheis, the results of which were very interesting First, a run with each alternate lath removed leaving a total wind-resisting area of the screen of 15 sq. ft. The time however for this run was 15 4-5 sees, giving a speed of 57 m p.h. showing very clearly that although there was actually only 15 sq. ft. of resistance on the screen, owing to the arrange ment and apparent extra skin and corner friction, etc., -the resistance was the same as if it had 18 sq. ft. of continuous surface. Motorists should take special note of this, as it is pretty good proof that a large number of small protuberances on a motor car are detrimental to its free running. The next test was to have the total are? exposed of 24 ft., but arranged in two portions, the top one consisting of 13 sq ft solid then a gap of 6 sq. ft and then the remaining 11 sq. ft, the total solid area exposed thus being 24 sq. ft. but the actual effect on the car was as if about 27 sq ft. were exposed. It will be noted in gomg through the accompanying table that the slowest speed recorded with maximum wind resistance was 47 85 miles per hour, whereas the highest was 70, a variation of over 31 miles per hour merch/ by the addition, of wird resistance and practically no additional weight ; so all owners of large touring cars with wind shields, limousines, etc., must realise the enormous extra work they are giving their engines to do, and incidentally their driving tyres, when they travel fast against a strong head wind. This extra work is of course only obtained by the consumption of con biderably more petrol, and so the varying petrol results that motor-car users sometimes get must be very carefully considered, and the direction of the wind when petrol consumption tests are being made ; m fact, the only useful ones are when an " out and home ' course i*- ehus'n The accompanying pictures show. No. 1 the si\cyhndei Napier car end on showing the full capacity of the wind screen. No 2 some of the B r- ooklands men showing how the laths were removed No. 3 the gnd'ron type of wind screen referred to m test No 17 No 4. is a group of gentlemen round the car who assisted me to make the experiments a success, and reading from the left tn right they are as follows — Messrs. Reynolds Bidlake, two of the Brooklands mechanics, Staner, Edge, Smith New and Tiyon I can only oonclude by thanking those who assisted, and particuiarlv the Biooklands track people for allowing the uninterrupted use of their finishing straight It is merely another example of the extraordinary value that th<= Brooklands track can be to British Automobihsts and I hope at an early dcte to carry out ver}' much more exhaustive experiments m many other directions, including the effect of w eight on speed and petrol consumption without increasing wind area. If there an* any details not mentioned here (which of course I have m a very elaborate degree) that would be useful to other British manufacturers who have not had the opportunity of attending at Brook-

lands, I shall be very happy to supply them as it is only by attention to details of thi^ sort that the British motor car can continuously improve. Yours truly.— S. F. EDGE. [ P.S. — The front area ot the car and the driver outside the wind screen area was about 1 14 to 12 sq. ft. in addition.

Aiea of wind le- Time over fly- i sisfcmg screen. ing i mile. Ist run 30 square feet 18 4-5 sees 2nd „ 28 „ , 18 3id „ 26 , „ 17 4th „ 24 , , 16 sth , 22 „ , 16 3-5 „ bth „ 20 , , 10 1-5 „ 7th , 18 „ 15 4-5 , Bth , 16 , ,15 3-5 , Speed in miles per hour. » 47.85 moh 50.0 ,/ 52 9 „ 56 15 „ 54 0 , 55 5 57 0 „ 57 B „

Wind-resistance tests carried out August Joth 1907 on a 38.4 (R.A.C. Rating) six-cylmder Napier car Timed by F. T. Bidlake Esq., and A J Reynolds Esq., official timekeepers Royal Automobile Club. Total area of wind screen 30 square feet

9th run Oth „ Ith „ •2th „ 3th „ :4th „ ioth „ L6th „ 17th „ 1 8th „ Area of wind le- Time over Hi- Speed in mile sisting scieen mi? J-mile pel hour 14 square feet 15 sees. 60 mp 12 „ „ 14 2-5 „ G2 5 „ 10 „ „ 14 „ 64 2 , 8 „ „ 13 3-5 „ 06 15 , 6 „ „ 1-3 4-5 „ 70-23 „ 4 „ „ 12 , 7.1 0 , 2 „ „ 12 1-5 , 73 8 „ Normal 11 23 „ 79 0 „ 15sq ft cTrai - 15-4 3 „ 57 gpd as gridiron 24 sq ft in two 17 3-5 „ 51 1 „ blocks with 6sq f* interval between them.