Projects: HOSSACK 1
The HOSSACK front suspension system consists of 2 wish-bones, an up-right and steering linkage. Similar components are found on the front of all racing cars, the only significant difference being in the up-right which has its geometry rearranged.
The wish-bones look and work exactly like their racing car equivalent The up-right performs the same task as its racing car equivalent but has its axle rotated through 90 degrees and over hung. There are few limits on how the up-right is made or what its made from, it could be fabricated, cast or layed-up. The steering link is a little clever though, as it has to pivot on roughly the same axis as the up-right. There is a handle bar pivot but this carries none of the suspension loading and only has to handle the weight of the riders upper half. Norman has run the spring/damper element in several different positions to achieve different conditions as is also common in the racing car world.
In all but HOSSACK 1, the up-right has been made of welded pressed steel profiles making a very strong and light weight shell structure. Detailed stress analysis later showed the up-right could not be made lighter even if it was made in aluminium, indeed an up-right designed for a 125cc racer, made for destruction testing weighed under 1.5 Kg. Further analysis done in Germany for the TUV approval which the HOSSACK BMW was awarded, showed Norman got his numbers a little wrong because the axle structural stiffness was 25 times stiffer than a standard BMW (over kill)!
Before Norman left McLaren he raced a 350cc Yamsel at club level. He found that when braking very hard into Druids for example, the bike could be made to judder. This he attributed to flex and as it happened the March Atlantic cars of that era did the same thing, leaving the familiar judder marks on the circuit at the braking points. Norman was involved in chassis stiffness tests at McLaren to investigate the March problem and it was found that increasing the bulkhead stiffness was the answer to the cars problem.
So Norman set out to stiffen up the front end of the motorcycle. His first design (1974) was a braced telly which he never built because it became clear that an additional and real weakness was the steering head structure itself. Just compare: the back end of a bike can carry:- most of the rider, a passenger and luggage on little bronze bushings less than an inch in diameter.
He knew that there had to be 'triangulation' in the structure, only that way could he achieve the stiffness to weight ratio he wanted. Wish-bones on bikes were GO. Norman drew several different designs but settled on this one. With this design, full triangulation was available therefore low weight as well as a major stiffness increase. Tellies back then were very flexible and no match for today's up-side downs (NOTE: first seen on that little BSA bantam Norman started out on) but even the best telly could never come near the stiffness to weight ratio this design could achieve.
NOTE: once you have real stiffness inherent in a design you can both soften and direct that stiffness by using rubber bushings; the reverse is not possible.
Here the design opened up new opportunities that others could only dream about.
It could have constant wheel base
It could have constant trail
It could have constant head angle
It was possible to juggle with these and even have:- non dive, anti-dive, or pro-dive or all 3 in one set up. It was even possible to imitate the geometry that tellies provide. By choice Norman ran the axle path near vertical to limit dive but here there is an introduction problem:- riders born on tellies can't get used to bikes that don't nod on braking, this is after all how they have learned how hard they are stopping. However after some exposure to this non-dive characteristic the gains become obvious.
The story behind the first bike
Designed in the mid 70's from ideas worked out with a bent coat hanger nailed to a piece of wood, the first parts were made just to test the function. Later Norman found wheels in
a scrap yard and made it movable so it could be pushed down a hill to see what it would feel like.
Much later a friend bought the project an engine, a Honda XL500. It took some cunning but Norman managed to squeeze it into the frame and made it a runner. It ran first up and down the roads of the Slough trading estate late 1979 - it worked!!
At that time the only other innovation on bike front ends was the Defrazio system which deserved much more credit than it got, and later came , the ELF fiasco which Norman blames for the demise of the 'alternative suspension movement'.
Why? the question was asked could ELF with all their budget and influence not match the Honda they were up against in weight or stability. Answer "crap design", Norman doesn't have much better to say about the Bimota effort.
Next came some proper wheels from Tony Dawson : Astralites. Eventually it became a racer, which it had to be if it was going to go any further. It took time because Norman had no way to fund it properly and what funds there were, were stretched to cover 3 patents at the same time. It showed in Motor Cycle News in 1980 after it had been round Brands Hatch a few times.
It made an appearance on the BBC's Tomorrow's World in 1981. Norman raced it in 1981 but it didn't attract much interest. Later a friend introduced Norman to Vernon Glashier who became its owner and then, thanks to his skills, things began to happen. Glashier won the Bemsee single championship in 1983 and in the same year the next HOSSACK a 250cc Rotax engined machine won the Bemsee 250cc championship. Two out of two! He went on to win the British Single Cylinder Championship in 1986, 87 and 88 and set lap records everywhere. It won its last championship when it was almost 10 years old! Vernon retired it when the class changed to 600cc- a bigger engine would just not fit.
The frame design started with some observations then some theory.
Observation 1 - the McLaren M23 had a front wheel weight of approx. 250lbs on each front wheel and the structure which held that wheel (top and bottom wish-bone) weighed approx. 3lbs and provided huge stiffness. Now the front end of a bike has similar weight but the forks are heavy and worse, they were not very stiff.
NOTE: Why this preoccupation with stiffness?:- answer the other side of the same equation is low weight! So Norman set out to design a system that could be triangulated and just as importantly symmetrical.
Observation 2 - essence of a good wishbone is that metal goes directly between the load points in straight lines, the curvy devices on the front of the ELF for example are not wishbones.
NOTE: the ELF, the Yamaha and Tony Foales machines were all non symmetrical - this means more metal is required to achieve the same stiffness.
HOSSACK 1's frame started as tetrahedron, pyramid like but on a triangular base:-which is a collection of triangles, the strongest possible geometry. One vertex became the steering axis, and opposite axis at 90 degrees to it became the rear axle pivot. Next these 2 axis were stretched and tilted. Then some engineering compromises were required ; at the front some wishbones were needed and at the back a swing arm pivot. The frame as a whole almost obeys Norman's rules of what a wishbone should be; the only compromises were that direct lines between the load points could not be achieved. Still the frame design was good enough to win a championship 10 years later, so though Norman claims he could have made it lighter there was no need. The bike weighed 215lbs in race trim, the engine being close on half the total.
Norman managed to avoid the inventors obsession to rethink everything and stuck to the basics. "Inventors seem to have the compulsion to have a go at everything:-we have seen different handle bars, different steering geometry, different brakes, you name it". Norman kept it simple and used the known numbers and hardware where possible. Norman does not have fixed views on steering head angle;trail; c/g etc, all of these need to be tested and re-evaluated in the light of the extra stiffness the HOSSACK system offers.
After HOSSACK1 Norman built several other racing machines, though the closest he ever got to a true racing engine was in the 3rd bike which had an RD350 Yamaha engine, this was his favorite bike. This machine performed well in the hands of Ray Knight, Mat Oxley and Alan Cathcart, though they all complimented it and were competitive straight away, nothing came of it.
NOTE: it's making a fine show for itself these days, 20 years later, with its new owner Steve Burge.