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 .

I would suggest just working with that three view and making a hand sized version by cutting it out of some modeling material, foam/clay/balsa block/whatev, then smooth it out on the corners and see what it looks like in 3d. The proportions don't look too awful, and you can test it in a vacuum cleaner powered air tunnel :)

Now there's a good idea ! :)

Could any of you experienced fellas hazard a guess as to the drag coefficient of what I've drawn ?

I really have no idea but I've been plugging .45 into the calculator. Am I being overly optimistic ? :D

I think you'd find such close proximity of windshield edge and throat to be both uncomfortable and hazardous.

Also I think you'll want more length aft of the rider, for possibly storage and for aero.

You will want a good seat more than you want to be lower for aero. If it's uncomfortable you won't ride it... perhaps the best fuel saving technique of all??? :p

Noises are much amplified inside aeroshells. Prepare for a very noisy interior or special noise mitigation efforts.

I know Allert did it, but personally I'm opposed to adding what is essentially ballast for stabilization. I'd rather try to jockey the weight that needs to be there around to where it does the most good.

I'll build a model of the fairing and see how it performs but the concerns you raise are real especially the internal noise .If I don't do the fairing it will be for the noise .

Just using 10 hp diesel would still give a 36% improvement with the added advantage of being able to use biodiesel for a very low carbon footprint .

Frank ,could you suggest a Cd for the fairing ?

We know that a heavier weight vehicle doesn't suffer reduced fe all that much on the highway, but it does hurt in the stop-n-go, and it makes the go slower. The little diesel is pretty slow in the go dept. already so I'd be after adding lightness. If I found that, say, a more forward Cg is desired I'd look at relocating already heavier stuff like the fuel tank or battery instead of making something heavier than need be.

I forgot what Allert figures his bike's Cd is? Pretty much copy that, and pretty much get that Cd.

Thanks Frank , I have no idea of Allert's cD but I suppose I could try to derive it using the calculator .Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com

.3 sounds likely for Allert if it has 5.5 squ ft frontal area.

http://ecomodder.com/forum/showthrea...rt-c-9287.html

You can cut it off at the wanted length - beyond 70% the gains are minimal anyway.

In that case, you'll have to live with the resulting height.

I just noted this comment Frank .You're right and as I'd actually be looking out over the top of the screen I think I'd modify it to have a wide vertical edge and padding .

Thanks for that link ...I read a bit and am trying to understand but my engineering knowledge is pretty slim and those fellas are pretty good at it .I can't even understand the units ! :D

I did note the template though ,my idea seems reasonable within those parameters .

I've just modified the drawing a little , relieved the area between the rider and screen and added area to the top rear .

How does that look ?

I scrounged a bit of surf board foam last week to make a model from .How do you think she would handle cross winds ?

This looks interesting ,about half way down the page .
Tony Foale Designs, article on motorcycle aerodynamics.

It explains how a well faired teardrop shape develops side forces in a wind even at 15 degrees off straight ahead .Not encouraging !

There appears to be a case for a straight sided fairing or at least one that doesn't generate a side force .

Perhaps scallops in the sides of the fairing to break up lift ? The standard aero template needs spoiling I think .A strange idea but the article I linked above points out some serious problem for a standard aero pattern on a bike .

The scallops could still allow good airflow over the body , perhaps not ideal but without the side lift .

This picture seems to show the problem pretty well .

http://pic40.picturetrail.com/VOL282.../398257078.jpg

It seems that spoiling the aero shape (which would be a horrible pity !) or alternatively leaving a gap between the forward and aft section....it would allow the pressures to equalise across the body and stop there being any side lift .There would still be the straight side pressure but not aero side lift .That might more than half the side forces .

Any comments on this ? I'm just thinking but if anyone can point out my errors I would be pleased and grateful !

Here's another modification, the 2 lines represent the opening in the side, the rear would still move backwards 12 inches or so on draw slides to make getting on easier .

http://pic40.picturetrail.com/VOL282.../398257671.jpg

All bodies EXPEREANCE forces from all directions, the forces they generate are the reaction forces. The question you need to ask yourself is what are they, and how are they managed! Make your self a free body diagram and study it to find the forces and reaction forces. An other thing you might try is accurate description of what actually happens when forces are applied.

The diagram and description are very poor. What you need to know is what are the forces and how do they change for each body. The wing shaped body may only experiance a very low force in the direction of travel and any change in angle of attack will have a proportionally larger change in net force, yet the total force on the body is still less than the force on the rectangle shaped body. So with out some numbers and better explenation you have confusion, rather than understanding.

When you find a straight sided fairing that that does not "generate" side force please let me know. That way I could make that the front of the motorcycle and have no aerodynamic drag force at all.:confused:

PeterS, I think Tony Foale already explained it in his article - the side forces are counterbalanced by leaning the cycle into the wind.

It is the curve that generates the lift ,that being a differential pressure on either side The bike you have built would generate far less side lift than my original drawing .My idea would have a lower overall drag but the forces from side winds would be far higher.The entry areas you use and which will have to use I think reduce the lift from the curved sides .

I'd love to know why Allert works so well!

Flat surfaces generate lift just as well as curved surfaces. You need to find some experemental evidence that quantifies the forces and the derection in which they act. Without numbers I am afraid you do not understand the matter/problem before you.

What you need to know is HOW Allerts' bike works so well.

My next iteration of the rear cargo "box" will have curved surfaces...

Can you offer any link to that ? I'd love to talk to Allert's builder but that doesn't seem possible.

As for understanding ..you are completely right ,which is why I'm asking for comments and assistance here .

1. Statics
2. Dynamics
3. A Brief Intoduction To Fluid Mechanics

Allert LOOKS as if it should be subject to considerable buffeting from side winds but he reports that it is not .From my reading so far this seems difficult to understand ,especially with reference to the last diagram I posted .

Do you have any ideas as to why this is so ?

Personally I'd take Allert's experience over a diagram.

And Allert IS the builder.

''Dutch efficiency enthusiast Allert Jacobs'', thanks Frank ,I hadn't realised that .

I agree that Allert's bike is proof of concept but I just don't understand how !! :confused::)

As well as the designer, test pilot, blogger, etc !

I believe he explained the added side force in the rear counter acts the front effect.
Remember, 2 wheelers use counter steering and leaning to turn. The side radius of the tire is why they turn at speed. The wind pushing the rear of the bike over actuall steers it back into the wind. This can be felt in crosswinds with a rear passenger.
Allert states the problem with front only fairings is there is no side wind ballance. When he had only the front fairing, the bike behaved so badly he almost stopped the project.

He also reccommends putting on the rear one first, then adding the front for safety reasns.

OK ,by those criteria this should work quite well .


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

build a model and roll it down a ramp and measure stuff. Add a couple little diy electric eye timers to make it more like a science.

Note, it needs to be going pretty fast for accurate scaling, moreso the smaller the model, so maybe a launcher and a net at the ends of a bit of track. (air launcher? spud gun?) and note several times and distances (should be decelerating) and figure out the cda curve. Then weigh it and figure out A (and crr with similiar but slower tests)