Safety performance of open cockpit, FF single track vehicles
Definition; “FF”
A single track vehicle with a seat base less than 20” above ground level at ride height, fitted with a seat back capable of supporting the rider. The front suspension should not be steered.
Application.
This information applies only to basic 'open cockpit' FFs of the type shown on my site www.hightech.clara.net Open cockpit FFs give the least protection of the various FF types but offer the least weight/size and greater agility. Crash protection is concentrated on initial impact mitigation, mainly cockpit features. In this respect it is at a similar technology level to late twentieth century open topped cars, without seat belts.
Sources.
All this knowledge is derived from the Quasar and Voyager production projects, during which several real accidents occurred. Information from accidents was added to published knowledge of car safety features and these features have worked in subsequent accidents. This process was engineering, rather than academically, based and the accidents were not necessarily representative of any other accidents. However the evidence strongly suggests that FFs are much safer than conventional motorcycles and that simple safety features work.
“Active” safety.
A properly designed FF (see also Basic Dynamics) will be far more agile than a motorcycle of similar size. It will turn faster and brake harder, at the same time if required. The rear wheel will not lift under braking. It is very difficult to 'High Side'. The rider is far more secure in the vehicle and has better control, These features increase the safety performance by making it easier to avoid accidents.
“Passive” Safety.
Foot clearance.
Very early in the Quasar programme it became clear that the footboards were a hazard if the vehicle was dropped as they trapped the riders foot. This caused serious injuries in some cases. It also prevented riders putting their feet down at a standstill if stopped between cars. Subsequent designs allow riders to put their feet down within the widest part of the vehicle. It is important to confirm that the feet will not be trapped at any point if the vehicle falls over.
The resulting cut-outs cause minor aerodynamic problems which are discussed in 'Aerodynamics'
Frontal impact.
This common form of accident kills most motorcyclists, usually due to head contact with the roof edge of a target car. It is primarily caused by the poor design of the motorcycle and in particular the front forks. In such impacts the front of the motorcycle collapses downwards, pitching the rider into the car. On an FF, even a 'cut'n shut' with telescopic forks, this pitching effect is largely absent due to the lower CG and the forks will collapse more rearwards.
This provides an opportunity for the rider to be 'caught' by the cockpit of the FF rather than be pitched out and over it. If 'Hub Centre Steering' (HCS) is used it will transfer far more energy into the target vehicle and may push it out of the path of the FF. It will also collapse downward but lever the front of the FF upwards in so doing. This makes rider capture quite easy and it becomes relevant to provide padding and collapsible structures at the front of the cockpit, especially the hand controls.
In accidents like these, where the vehicle remains horizontal or pitches up at the front, the rider will move forwards until contact is made with the cockpit. This should happen as soon as possible and a steeply sloping seat will immediately capture the rider's pelvis. Further forward movement of the lower body can be prevented if the knees contact the inner face of the footboxes which should be suitably deformable. This immobilises the lower body but provision should be made for progressive structural collapse of the seat nose and the footboxes.
The rider's upper body is more problematical. There is inevitably some distance between the rider's chest and the hand control yoke. This has been addressed on the Voyager design by providing a friction clamped pivot allowing the entire control yoke to hinge upwards under crash loading. The underside of the control yoke is a flat panel which, in the prototype at least, is heavily padded. It is assumed that the rider will be resisting the forwards movement of the upper body and thus the clamp will already be loaded towards the point at which it will slip by the time the riders chest hits it.
The control yoke on the Voyagers pivots in a structure that will itself deform under crash loads and the instrument panel, seen as the 'target' for the riders helmeted head, is too fragile to cause injury.
These features can be seen deployed on the post-crash photos in 'early prototypes' on www.hightech.clara.net There were no injuries to the rider as a result of the impact with the cockpit. In this accident 002 hit the rear wheel of a Fiat 132 which had turned into it's path, with an impact speed of about 50 mph. One might expect a modern production version of this vehicle to feature an airbag on the hand control.
After this impact the rider was ejected from the cockpit, at ground level, and slid for some distance along the road. This produced minor 'road rash' injuries and these are typical of most accidents involving open cockpit FFs where the rider has left the cockpit. However these have all been accidents at fairly high speed (40-60mph) and the 'urban accident at less than 30 mph' that kills most motorcyclists are clearly more survivable in these vehicles than on a motorcycle.
Leg injuries
At the time of the Voyager project (1988-9) leg injuries were the second most common cause of death. Usually the leg would be trapped between the two vehicles and ripped off. Initially this was countered by enclosing the footboxes in the frontal bodyshell (Banana) then steel footplates inside foam-filled bodywork (001, 002), then as a result of the 002 accident the production design was a steel structure that supported the footboxes and the nose bodyshell and was intended to improve the progressive collapse of the front of the vehicle. All these designs were intended to give protection from side impacts and prevent the feet being trapped,
There have been no leg injuries in any of these vehicles and until 2006 none of the production Voyagers has suffered a frontal impact, making it impossible to evaluate the crash performance of the later features up to that point. In the 2006 event a production Voyager slid, on one side, into a concrete block that impacted on the side of the nose bodywork, the right hand footbox and the right hand leg of the front fork. All the steel components were unrepairably damaged. The rider suffered a slight injury to a toe. The footbox collapsed roughly as intended, preventing serious injury to the riders foot or leg. The accident also demonstrated the value of a 'bolt-on' footbox system for repair purposes.
Non-impact crash performance.
As performance, rather than safety, was the primary interest of early English FF development the majority of accidents involved going too fast rather than hitting other traffic. As a result there is plenty of information about the performance of FF's sliding along the road on one side.
In this mode, if the rider is still seated correctly, there have been several occasions where the edges of the wheels have remained on the ground and some control has been retained. Several riders have reported a belief that in the right circumstances a sliding FF could be recovered onto it's wheels.
From the safety point of view there are two considerations that should be borne in mind by designers.
First that any slide should stop as soon as possible. This to avoid painful and damaging contact with road furniture or kerbs. This requires consideration of the detail of the ground contact points that the vehicle will slide on. These should resist, sacrificially if needed, being dragged along the road. The production Voyagers used convenient brackets, shaped to slide, sledge-like, fore and aft, while resisting being dragged sideways. These have worked in 'going too fast' accidents. 001 had alloy caps designed as friction contact pads and these also worked well in a demonstration slide. GRP does not resist slide well and will skate for some distance along a normal road surface.
This ability to slide illustrated the second requirement for a slide on one side. In the Banana crash in the I.o.M. (Creg Na Ba) the vehicle not only slid freely after losing grip but also rotated so that on impact with the straw bales it was going top, or cockpit,-first. This is undesirable. A stable, keel-first, slide can be ensured by fitting the ground contact points well to the front and rear of the vehicle. This means that whether it goes down in under-or over-steer the first point to contact will tend to return it to a stable keel-first slide.
Later, ad hoc, development and some minor low-speed drops have shown that the slide attitude can be quite easily controlled by selection of the friction materials. A slightly 'tail-down' keel-first slide, suitable for damage limitation and potential recovery, and be achieved by fitting some high-friction rubber at the front with just a metal contact point at the rear..
One might see some advantage in racing , in using rotating contact patches (or “Skateboard Wheels”) but in practice, on the road, stopping the slide as soon as possible has to be the priority.
Practical crash padding.
Polyurethane foam, also known as 'Brown Foam', Seat Foam', is the perfect material for deformable crash padding. Enclosed in a Glass/Polyester or Glass/Epoxy envelope it makes stiff, light and fire-retardant bodywork and it is an easy matter to adjust the GRP skin thickness to give appropriate strength for either outer skin or a target for part of the riders body. It's progressive collapse qualities are excellent. It can be poured, as a self-foaming liquid, into existing body sections, or used as a carved shape to build GRP onto.
Pressure on manufacturers to reduce toxicity in their products in the late nineties and early noughties has resulted in a new form of PU foam, used for house insulation. One trade name is 'Seletex' This type of foam is just as suitable for bodywork but does not produce an irritant dust and is much cheaper than 'brown foam' 'Room Temperature curing' Epoxy resin is also now available for GRP, lighter and stronger than Polyester resin. It tends to cause eye irritation as a dust but is not toxic like early epoxies. FJ has a new nose using these materials.
Seat belts and beyond.
The apparently obvious step of fitting seat belts, to prevent the rider being ejected after the initial impact means that the rider may find themselves unable to keep their arms and legs in the cockpit of a cartwheeling or tumbling vehicle. Even sliding into an obstacle strapped to the vehicle may be injurious. This may not be a problem, or seat belts may lead to increased arm, leg or head injuries. Seat belts have been fitted to a Quasar and much more recently to the production “FF-like” BMW C.1 scooter, both open sided at least but I have no information on their crash performance. It may be that the addition of a roof alone will make seat belts safe.
Prioritising safety, inevitably at the expense of cost, weight, complexity, etc., leads to consideration of other rider restraint systems that can be used in conjunction with seat belts. These might be doors, enclosing the side of the vehicle and containing arms and legs or total enclosure up to the level of the Swizz Ecomobile.
All these features, seatbelts, the simplest side doors, and definitely roofs, also compromise basic features of the vehicle. Seatbelts, unless quite sophisticated will prevent body movement needed for easy low speed control. even simple sidedoors are actually quite difficult to do achieve without leg fouling problems. The problems of roofs on FF's are almost legion!
Individual designers must make their own decisions about their design priorities, these basic safety features on open cockpit FF's have however demonstrated a very reasonable standard of protection in real-life accidents and will be of particular interest to designers chiefly interested in the vehicle dynamics.
Copy free for credit
Royce Creasey. Jan. 2005