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PeterS · 09-19-2011, 06:25 AM

To summarise,

Tail area helps automatic turn into wind. Good.
High nose side area helps roll out of wind. Bad.
High trail reduces and slows, while Low trail increases and speeds, sidewind-induced counter-steer.
Fast sidewind-induced counter-steer reduces disturbance.

Short trail, small nose side area, and a good tail side area (at least as much as the nose) will produce a strong response, rolling firmly into a side wind. When flow separation features are added the result can be good 'self-correction' which does not intrude on the driver except in truely heroic winds.

For reference, the early Banana bodywork, without a tail, could be blown out of winds, but with later bodywork, including a tail and nose separation features, it did not, self-correcting adequately.
(Royce in the Banana | FF Web)
(Banana with new skin 1999 | FF Web)
Aerodynamic Efficiency

low drag, is usually regarded as the main reason for bodywork. In practice it has a minor role in the efficiency gain provided by the FF layout. At road vehicle speeds, simple frontal area is the main determinant of drag.

Almost all FFs that run as well as the vehicle they share an engine with, return fuel efficiency gains of around 20%. Many, especially high powered ones, achieve similar increases in top speed. Even 001, where drag was hardly considered, comfortably out-performed the Ducati motorcycle. It's always worthwhile keeping frontal area in mind when designing bodywork.

There are detailed ways to improve efficiency. None of these are mysterious. Smooth, clean surfaces and separations, slow surface direction changes, filled voids especially behind the rider, can add up to quite surprising fuel efficiencies - when the vehicle is being run fast enough for these details to matter.

The actual nose shape is least important for efficiency, although it must be carefully shaped to 'set-up' the separated airlfow over the rest of the vehicle.

Fat Jogger was optimised for efficiency more than any of the other shapes. In addition to it's clean lines it also has a sharply cut off 'Kamm Tail' and the resultant low pressure bubble is filled by the hot radiator outlet flow
(03 and FJ | FF Web). The side and centre stands are part of the shape, with the centre stand, when retracted, forming the 'chin' of the radiator inlets.

It impossible to say whether this detailing is 'worth' the effort. Although it has reached 90 mpg it has also returned worse figures than Ian's Production Voyager travelling together Vagaries of old engines and states of tune probably have a greater impact. However the three Voyager shapes are all fairly clean and a computer generated prediction of the Cd for 002 was .3. This level of efficiency is clearly worth having.

09-19-2011, 06:25 AM	#48 (permalink)
PeterS Master EcoModder Join Date: Aug 2011 Location: East coast of Australia Posts: 393 Yella Peril - '80 Mercedes 240D sedan Thanks: 15 Thanked 41 Times in 17 Posts	To summarise, Tail area helps automatic turn into wind. Good. High nose side area helps roll out of wind. Bad. High trail reduces and slows, while Low trail increases and speeds, sidewind-induced counter-steer. Fast sidewind-induced counter-steer reduces disturbance. Short trail, small nose side area, and a good tail side area (at least as much as the nose) will produce a strong response, rolling firmly into a side wind. When flow separation features are added the result can be good 'self-correction' which does not intrude on the driver except in truely heroic winds. For reference, the early Banana bodywork, without a tail, could be blown out of winds, but with later bodywork, including a tail and nose separation features, it did not, self-correcting adequately. (Royce in the Banana \| FF Web) (Banana with new skin 1999 \| FF Web) Aerodynamic Efficiency low drag, is usually regarded as the main reason for bodywork. In practice it has a minor role in the efficiency gain provided by the FF layout. At road vehicle speeds, simple frontal area is the main determinant of drag. Almost all FFs that run as well as the vehicle they share an engine with, return fuel efficiency gains of around 20%. Many, especially high powered ones, achieve similar increases in top speed. Even 001, where drag was hardly considered, comfortably out-performed the Ducati motorcycle. It's always worthwhile keeping frontal area in mind when designing bodywork. There are detailed ways to improve efficiency. None of these are mysterious. Smooth, clean surfaces and separations, slow surface direction changes, filled voids especially behind the rider, can add up to quite surprising fuel efficiencies - when the vehicle is being run fast enough for these details to matter. The actual nose shape is least important for efficiency, although it must be carefully shaped to 'set-up' the separated airlfow over the rest of the vehicle. Fat Jogger was optimised for efficiency more than any of the other shapes. In addition to it's clean lines it also has a sharply cut off 'Kamm Tail' and the resultant low pressure bubble is filled by the hot radiator outlet flow (03 and FJ \| FF Web). The side and centre stands are part of the shape, with the centre stand, when retracted, forming the 'chin' of the radiator inlets. It impossible to say whether this detailing is 'worth' the effort. Although it has reached 90 mpg it has also returned worse figures than Ian's Production Voyager travelling together Vagaries of old engines and states of tune probably have a greater impact. However the three Voyager shapes are all fairly clean and a computer generated prediction of the Cd for 002 was .3. This level of efficiency is clearly worth having.