Can I have a few comments on this ?
 

As you can see it's pretty obviously inspired by Allert but is drawn to fit over a 500cc Enfield that will be fitted with a 10hp aircooled diesel .These diesel Enfields get around 1.8 l/100km at 45 to 50 mph cruising .130mpg US without any fairing or aero mods at all .

As drawn the rear would slide out on heavy draw slides around 24 inches /600mm,adequate to throw a leg over .There would be storage against the rear of the frame and also in the sliding section .The fairing would be fibreglass just possibly with a bit of extra weight added low done to damp cross wind buffet .

The frontal area is around 7.5 squ ft .,the diesel has a theoretical efficiency of .3 and I have no idea at all of the cD.

.5 ?

Please excuse the basic hand drawing ,I'm not good with CAD.

http://pic40.picturetrail.com/VOL282.../398246014.jpg
http://pic40.picturetrail.com/VOL282.../398090017.jpg

THIS HAS BEEN MODIFIED TO INCLUDE MORE SPACING AROUND SCREEN AND ADDED AREA AT THE REAR .

I think you will have separation on the rear section because it tapers in too fast (especially behind the shoulders of the rider).

You might try making just a rear faring to start with and not have it slide back seeing as how the largest chunk of your aerodynamic drag is the rear of the vehicle.
The more mass you have at the front of the motorcycle the worse it will handle and the harder it will be to control in side winds.
Smooth touring tires will also help, try to find some silica rubber LRR motorcycle tires, they cost a little more but they have great traction and last.

What is the maximum angle of taper ? I seem to remember it from somewhere but can't remember .

I really do need CAD or at least a big lump of modelling clay .It's hard to do this on a piece of paper .

Oops, I didn't see the pic with the top view. That shape would probably be OK.

I thought from the side view that the sides came together at a point.

You could probably cut the drag down some more by actually bringing the sides to a point further back than your current drawings.

There are several free cad programs out there - even for Linux guys like me.

Heck I'd stick with some fullsized drawings - head to Home Depot and get their red rosin or brown building paper and work on that. Get a piece of wood trim or a 3/8" x 3/8" x 8' long stick to use for fairing your lines from point to point. Measure from a center line and use that to determine how to build your building form for the fiberglass. Look around at older traditional boat building articles about "fairing"; you might find some good ideas there.

You could kamm the back behind the rider possibly instead of a long tail - it would make it less susceptable to cross-winds and could be used for helmet storage etc.

Those Enfields are nice little bikes, I haven't seen a diesel yet - are they loud?

OP, you can get a good idea of how everything would fit together by making an orthographic drawing as shown here: BBC - GCSE Bitesize - Drawing 2: Formal drawing techniques

Although a drafting table would be ideal, you can do it with some regular paper and a ruler as long as you keep everything at right angles.

Did you use the aero template for the top view ?
It could be the hand drawing, but it looks a bit too fast
Follow that as closely as possible in all aspects (topview, sideview)
I'd extend it a bit further too, to reduce the wake.

See if you could lower the seating position, it'll greatly improve aerodynamics as seen on Burt Munro's or Allert's bikes.

If the helmet sticks out of the main shell, give it a fairing as well and blend that into the body.

Loud ?:D I suspect they are very loud .I've found someone on DieselBike Net .DieselBike.net • Index page who lives a couple of hundred km away so I'll ride down and have a look soon .It might be possible to enclose the engine in sound dampening material and cool it with directed vents ,maybe with fans on them .

I have a bit of boat building experience of the old school variety so lofting and fairing are within my capabilities .

I'm interested in diesel because I can make biodiesel and if I got 1.5 litre /100km (150 mpg US )from a diesel bike on bio it would be the carbon emission effect of 375ml per 100km (600 mpg US ):)

The fairing is my main concern as I'm actually have very little idea except what I've been able to derive from Allert's site and this forum .I'm concerned about cross winds and would very much like to know if there is a particular side shape that will help .

There has been a recent discussion here http://ecomodder.com/forum/showthrea...e-16754-3.html about centre of pressure and centre of gravity which i grasped some of .As a result it seems as though there might be some advantage in a bit of ballast down low ,below the c of g ?

Where do I find the aero template ? That was just a guess on my behalf .

I've drawn that with a thin seat right down on the frame ,my State is very strict about frame mods so I'm really restricted to the diesel engine which gives a 36% efficiency increase and anything I can gain from a bolt on aero fairing ...which is really the place to look if i can't do much with my frontal area .

Extending it would be good aerowise but is there a balance between that and reduced cross section for winds ? I was trying to keep it as short as possible .