Aerodynamic Body Construction

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Ray Brock

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by Ray Brock

We of Motor Sport are believers in the achievement of high performance by weight reduction and streamlining. But this entails a new conception in coachbuilding. Consequently, we are glad to publish this most interesting article by Ray Brock on how he built the required aerodynamic coupé body for his 1 1/2-litre H.R.G. The methods of construction and the weights of individual components quoted will be of much interest to those contemplating similar body-building activities. — Ed

Have you ever thought of the car you would really like to have, and then decided that no one appeared likely to build it? Thought of all the things you liked in several different cars, and then all the things you disliked in those same cars? How hopeless it always appeared to expect any one manufacturer to see things in the same light.

I had this phobia during the war, and then after the war decided, as usual, that I must put up with the best alternative, if I could even get that!

After a while I decided that, much as I disliked an open car, I could tolerate the Aerodynamic H.R.G., if only because of the other good points, and I finally placed an order. The months rolled by . . . there seemed no hopes of delivery . . . and then I met a fellow who had made several bodies for his “special,” and it all appeared just too easy as he described it. I also discovered that there were plenty of chassis if only I dared. The time came rather late in my life for this sort of thing, and I must make it plain that I have had no engineering training, and had never done anything like this before. Moreover, I knew that the result would have to carry my wife and pass her criticisms! However, I ordered a 1 1/2-litre chassis.

I set out the essential and the desirable points of the body pretty clearly before I even got the chassis, and later had to modify them as various snags arose.

(1) I wanted a two-seater with really comfortable seats and air cushions.
(2) It must be either coupe de ville if not fully enclosed.
(3) It must be well streamlined.
(4) It must have superb brakes.
(5) It must have an air heater. (As you will see, I got it !I!)
(6) It must have extremely good visibility, including very thin screen pillars and a really large rear window.
(7) It must have as little wood as possible in its construction.
(8) It must have really light doors. This ruled out winding windows, but I had expected to use sliding windows, anyway.
(9) Above all, it must be lively and light. After driving the chassis this point had added importance.

I saw the method of construction used in the Aerodynamic H.R.G., with thin steel tubes welded to form a framework of the full shape with an alloy coverwork, and decided that this could hardly be bettered, so I bought a welding outfit and learned to weld. Actually, I found that I preferred to use Sifbronze for thin steel, and used this throughout. There are some “dud” welds, I expect, but they are still holding together!

The great adventure started on December 18th, 1947, when I collected the chassis and couldn’t resist a trial run. This in forgotten motor-cycle clothing, on an ice-cold day! The French have a word — epatant . . . it was! Up a local hill of 1-in-7, where many years ago my fastest racing motor-cycles used to do 50 m.p.h. after the bottom corner, I got 65 m.p.h. in third before cutting out. This coloured all my subsequent work, and made me terribly weight-conscious, far more so than before. It meant that I was now prepared to sacrifice many luxury details to reduce weight, and I fear that the final job is definitely less well finished in consequence.

Later I ran the car at each stage in the building, and noted only too well how each piece added cut down the shattering acceleration! In fact, the complete chassis weighed about 12 cwt., and the engine gave about 55 b.h.p., so that the power-per-cwt. was pretty high, and any addition made an appreciable percentage increase to the total weight. It is only fair to point out that the H.R.G. chassis is really complete, with all instruments on a full dash, and with lamps (unfitted) and all tools and accessories. I had the Aerodynamic chassis with the side petrol tank, and brackets for the wide body, but without any fittings for the spare wheel as they are a part of the bodywork. By these standards the chassis is one of the lightest there is, the tendency elsewhere being to remove everything before weighing.

From December 29th to February 8th the chassis remained in the garage while the framework was made and the minimum panelling, etc., fitted to make it drivable. I wanted to drive it earlier, but so many chassis parts had to be removed to fit the framework that it wasn’t safe, and I spent quite a while at the end trying to make sure that I hadn’t forgotten anything vital.

The work was all done in an ordinary single-car garage usually without heat, and the only tools used for most of the structure were electric drills, hand shears, a rubber mallet (the mug’s best friend) and vices, together with all the usual car tools. The windscreen was built by a works foreman in his spare time, as I really did want this to look nice, while the outer aluminium panels were cut exactly to shape and welded, also at week-ends, by two experts.

I was lucky enough to acquire quite a lot of the actual wing panels, etc., already rough-shaped, so that there was comparatively little serious “panel-bashing” to do, and the expert who came for several Sundays taught me enough to enable me to do all the panels which did not show. Actually, although the panelling is the part that makes or mars the car, from the appearance point of view, the time spent on this was only a very small fraction of the total time required. It is the frames and scores of oddments which take up the time.

The first major task was the front frame. I particularly wanted to copy the H.R.G. shape, which seemed to me to be exactly right, and I got the loan of the main jig for this for one Sunday only. I had one fitter for help and we worked from 8.30 a.m. to 7.30 p.m. with one break for a drink! No food, tea, or anything, as the café we relied on was shut! It was imperative to finish that day, so we just got down to it, and I was quite scorched from welding while the fitter cut and fitted the tubes.

Later, when I made the rear frame myself, there was no such rush, and I was able to bend the tubes nicely in the hinges of the garage door, but fitting and holding while welding was certainly a trial of patience.

I was lucky enough to find that my gardener was really keen on cars, and later he came as an assistant for all the work needing another pair of hands, and, finally, he made quite a lot of the under shields. This, of course, eased the troubles of assembly, where previously I had had so much trouble clamping things in alignment during welding.

For four months I worked from 5.30 to 9 p.m. or later, for three evenings at least, and all week-ends, and there is still a little work going on, so that there was an impressive total of man-hours. In general, I got down to all the bending, fitting and welding, while the more refined work required was done at odd times by the aforementioned works foreman. I knew it wasn’t worth wasting time learning to turn and mill, so what little of that was needed was left to an expert!

All parts were weighed before final fitting, and we were very pleased to find that the front and rear sections, complete with panelling, weighed nearly the same — 57 and 59 lb., respectively. While the experts were finishing-off the outer panels, we got on with the undershield, and this was the greatest weight-saver. It was constructed of 1-mm.-thick aero plywood, doped with thinned chlorinated rubber solution, which makes it completely oil and waterproof. To give it the necessary rigidity, I first tried sticking on specially-bent dural angle 1/2 in. by 1/2 in. by 26 gauge, but while this gave astonishing results, the Bostick softened with oil, and rivets were not sufficient. We cured the sticking trouble later with Boscoprene, which is oilproof, but then found the ideal stiffeners. These are now made from 24-gauge dural tube, 5/6 in. i.d., stuck, and fastened by screwing through with dural washers and self-tapping screws. While I hate these screws for steel, they grip dural really well, and the way dural tubes can be delicately bent to curves in the wooden door hinges is delightful.

Anyway, the complete undershield with supports, which were also very light of course, saved about 40 lb. over the normal type, and the experiments were well worth while.

The floors were made from alloy sheet of too light a gauge, and had to be stiffened later with dural sheet at the more heavily-loaded points, but it must be remembered that I deliberately tried to run at the flimsiest stage possible, and was expecting to have to stiffen many parts after test.

On Sunday, February 8th, everyone was present for a special effort to get the car on the road, and this meant fitting the front undershields, the windscreen, and the rear section of body. Memory is a little blurred, but I recall that at 8 p.m. we thought that we should finish by nine o’clock, but did not start the engine until about 11 p.m. Three remained, and we crowded in, with a temporary roof (very), no doors, and no time for final adjustments. After two miles we had to stop to refix the roof, as we couldn’t hear ourselves shout, and also because I couldn’t declutch! Five miles on, the gardener and I dropped the works foreman and decided that we couldn’t stand the roof any longer, so we folded it up and put it in the back, and then went on home, wondering what our wives would say and keeping our fingers crossed in case something major fell off.

In fact, all went well, and from then the car was normally used all the time, each piece being prepared and fitted as ready.

Most of the work up to this stage had gone pretty steadily, but we did have one shocking afternoon fitting the underbonnet screen wipers. Lining these up, and continually raising and lowering the whole front body, caused more fury than anything else, and we finally finished up with a spare hole that had to be welded up and beaten out the next week-end!

We then found the next major snag. The windscreen was far too large and with too much outward slope. The point is that I had planned a certain size to suit my streamline, and had not intended to have “tumblehome,” but the windscreen looked so queer without any inward slope that it simply had to be rebuilt. It should be realised that there are two factors involved in these windscreens. If you have a greater backward slope you must have more glass to give the same visibility, and, apart from the weight, you come to the time when it just isn’t rigid enough. You can then stiffen up with a centre strut or use a vee-screen, but there are severe aerodynamic objections to the vee, and I finally compromised on a more upright screen than I like and which I should certainly slope more if I started again, using a centre strut.

The panel expert made up the door panels and I welded up the structure from thin sheet-steel. They are a tremendous success, weighing 9 lb. each! Being so light they never give hinge trouble, and are held by rubber-mounted locks, to allow for chassis whip.

It was at about this stage that I was persuaded to have a solid roof instead of the special spring-loaded hood which I had designed to hold its shape and yet roll back in coupe de ville fashion. The expert was so hurt at the thought of all his beautiful curves being spoilt by an ugly wrinkled hood that I gave in, and he made up an amazing set of pieces from templates of brown paper. These, in turn, were made from thin steel pieces which I bent up to get exactly the streamlines I wanted. They are unusual, I realise, but the beetle-browed effect is necessary to gather the overspeeded air as it comes over the top of the windscreen. It is not generally appreciated that it is not sufficient merely to provide a suitable way for the air to flow. It is equally important to provide such curves that the air will not have an opportunity to leave the surface and form a vortex, and this cannot be done with the usual method of cutting off the head immediately after the top of the screen. Likewise, if you have a vee-screen, it is necessary to bulge out the sides of the top of the body to gather the air shot off the sides, which makes the vee-screen a bit of a problem aerodynamically.

It was appreciated that the H.R.G. chassis is decidedly flexible, and provision had to be made for this by making the body in two completely separate halves, and then fixing the doors with rubber-mounted locks to permit relative movement of the two halves. This was quite simple, but it meant that I was either faced with the alternative of using the roof to hold the chassis rigid, which was impossible with my method of construction, or else devising some way round the problem. Finally, I decided to allow the roof to be a part of the front assembly, i.e., fixed to the top of the windscreen, and to allow it to ride over the front of the rear assembly with a sliding joint. This was done, despite much sniffing by friends, by means of swing bolts and an oiled leather strap as a bearing material, and after some early troubles, the structure has settled down, and appears nicely permanent. It is not very obvious, and after I got out of the habit of loading the belts heavily to damp the movement, the stresses in the roof itself appeared quite reasonable, but of this more anon!

It was while the final rough work on the body was being done that I began to realise how excellent the performance seemed, and I thought of using the car in some competition or other. Until this stage I had merely been making a controllable two-seater for ordinary use, but Peter Clark needed another enthusiast for an H.R.G. team for the Belgian 24-hour race, and I decided to try, if the body seemed good enough on test. I should like to put, on record how I appreciated Peter Clark’s trust in my handiwork, at, a stage when I seemed to be more doubtful than he was. This decision made the rush more serious than ever, and with this fresh impetus we finished the major body items on March 20th. This included rebuilding the windscreen, and also removing the roof and fitting steel reinforcing pieces in the front corners where the strain was greatest.

Then I had to devote a little time to the chassis details in time for a full-scale speed test with the rest of the team at Moreton Valence aerodrome on April 10th. Still unpainted, but finished except for lots of details, the car did quite well, although naturally it was not as fast as the other two. Very satisfactory, and no serious alterations called few, so that on the Monday the car went in to be partly painted. I had wanted to do everything like this myself, but there was no time left, and I had to be content with doing some of it only. Probably as well . . . I’d never have made it look quite as nice!

During the next period I was doing all the oddments like final undershields, rear floorboards, felt coverings, door locks, etc. There is an amusing point about the locks. I invented several ingenious but poor methods of eliminating external handles, and then had advice on further streamlining refinements, including the proper way to use deflectors on the sides or the windscreen. These covered half the space I had intended for the sliding windows, and as these were also a flop from the appearance point of view. I had to think again. It was as well that I did, as I think that the solution will find approval. I decided that outside door handles were quite unnecessary if you had an open window, and that doors need not be locked if you could not reach the handle. Therefore, I merely close and lock the windows!

The windows are, therefore, of two distinct parts. There is the front third which is hinged by an ingenious method worked out by the works foreman, and is permanently there, and the rear two-thirds which are instantly detachable and are kept in special pockets behind each seat. The most remarkable part is that the hinged flaps do not need any rigid support at any speed and now have merely a friction hold. They open to a small amount according to the conditions and remain without flapping, and the rear section is merely steadied in position in felt-lined grooves by a phosphor-bronze clip. It jusl shows what a steady airflow will do to relieve stresses!

When I was getting advice on true streamlines, I also got suggestions on air extractors, particularly noting that the ordinary louvres are the most hopeless method of extracting air ever devised. As a result of the extractors on the bonnet and sides, engine temperature dropped from 85 to 65 deg. under identical conditions, and this despite the fact that there were already lots of louvres before I fitted the extractors. There are snags, however, as if sited wrongly they spoil the flow along a good piece of panelling, and they should certainly not be put on just anywhere.

On May 20th, my wife and I loaded up with three suitcases and did 3,500 miles in France, Belgium (including a test over the Spa circuit), Switzerland and Italy. This was a holiday and a final test to see what would break . . . but nothing did! We did however, encounter what is proving one of the most bothering troubles of all in closed fast cars with undershields and streamlining. It appears that the heat from the enclosed exhaust pipe cannot be prevented front overheating the interior of the car except by impossible weight penalty from insulation. The very lovely Cisitalia now wears its exhaust system outside the undershield and is reputed to have only three inches ground clearance! We didn’t know of this snag, and in hot weather in Milan we nearly cooked. Imagine a 24-hour race like this . . . so I got to work with alloy-foil insulation and asbestos for the pipe. Fair results, but not good enough, and we have now had to rebuild the undershield with a tunnel to take the pipe, which is now out in the airstream. This may do the trick, but otherwise we must use even more insulation, us the result of an undershield in improving streamline is too great to ignore.

The seats were another source of interest. I tried the usual sponge rubber and found it was useless in thicknesses of less than four inches. As I had designed for 1-in.-loaded height from the floor, this would not do, so I tried experiments with air cushions. Finally I got “Float-on Air” cushions made to measure to fit between 3-in, edges of sponge rubber, and this gives nice support to prevent rolling from the seat on corners, and yet permits very low seating. The real leather upholstery, however. has been a shock. The seats are specially made and weigh perhaps 2 lb. each, but the padded upholstery for each weighs about 20 lb.! I would like to alter it but it’s too nice.

In its finished form, the complete car lives up to my original requirements very nicely, but I fear that it will not bear really critical inspection. Most of the work is very amateurish, but it is quite strong even if not up to professional coachwork standards, and it certainly has a far better streamline than anything else of this sort.

The weight, complete with water, oil, spare wheel but no petrol, is 15 cwt. 7 lb., and of this, I might be able to save perhaps 50 lb. if I started again. The framework, however, could not be any lighter, as even now it will bend if pushed hard. It makes things difficult when crowds gather round when I stop, and with people who will lean on the bonnet.

The acceleration is, of course, exceptional, and the brakes will lock all four wheels at any speed and without starting a skid, even after 7,000 fast miles without, adjustment. Of the other original points, the air heaters are left. I ducted in air from in front of the radiator through 2 1/2-in. tubes and at first heated one by passing it through a 16-in, jacket round the exhaust pipe. This was startling . . . on the first burst of full throttle, the air got so hot that it burnt the floor mats!! We then removed the jacket, and took the air from behind the fan, and this has been very successful, while for hot weather this duct, and another the other side, lead cool air from in front of the radiator, and come in at the occupants’ feet. In really hot weather this is still not enough, even at 90 m.p.h., because of the heat from the undershield, but I hope that the latest modification has cured this.

Finally, on July 4th, we left for Spa, as the third car of Peter Clark’s team. Our adventures make another story, but we were successful, despite one hour and twenty minutes spent removing the roof after the windscreen was broken in the night.

The streamlining certainly seems to do its stuff, as the car beat all the other standard H.R.G.s at Brighton and Goodwood, and appears to be about 8 m.p.h. faster than the Aerodynamic without a roof. Very pleasing, but how I should like to start again and build another, altering all the things I know now to be wrong. But I fear that this body-building really was a case of “once in a lifetime.”

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