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Old 09-30-2014, 07:30 PM   #1 (permalink)
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Motorcycle Aero Question

I've been reading old posts about using "the template" tool to evaluate aerodynamic shape for cars but have lost track of how it might be used for motorcycles. There's almost too much info available. In any case, I thought there was another template that someone suggested could be used (in plan view) to look for streamlining ideas. In my case it's an EV with some of the batteries in saddlebags (at least for now) and I'm considering extending the outside edge aft then bringing them together somewhat for more efficiency.

I would appreciate any comments, ideas, etc.

thanks,
Frank

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Old 10-01-2014, 11:17 AM   #2 (permalink)
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Template #2 should give you what you want.

Here is a link. For future reference, its under the "tools" link up top in case you didn't know.

http://ecomodder.com/forum/tool-aero-template.php
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Old 10-01-2014, 11:31 AM   #3 (permalink)
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Last Vetter Fairing

The "Last Vetter Fairing" build might help with a few issues. Check out more chapters down at the bottom.

He ends up building this and selling fiberglass nose cones.

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Old 10-01-2014, 10:25 PM   #4 (permalink)
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Are you considering just the saddelbags or the whole vehicle?

For an alternate template, I nominate Mair:



For a contrarian take on The Template, try this:

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Old 10-02-2014, 08:34 AM   #5 (permalink)
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[Dark Secret]: I have two motivations for this project. One is to improve efficiency, I've been trying to keep up with Vetter's work. It's been pretty effective in helping out folks like Terry Hershner.

Second is that I've done some land speed racing. LSR is essentially power versus aerodynamics. Here's the bike I'm talking about up at Loring:



I'm carrying a *lot* of battery (100 mile range) and am considering changing that some day (mainly to reduce weight) but in the meantime it's what I have. Here's a lousy plan view of the bike taken in my garage. It's a bit truncated but you can see what I'm working with:



It's a first generation Hayabusa which has a documented Cd of around .5 (without the saddlebags obviously.) I can extend bodywork to 10" behind the rear tire. I can also increase the wheelbase to get more length.

freebeard: that's an interesting graphic. I've been sketching out designs like that. FWIW, "d" is presently 28" and "l" is (6 + 10) = 16". I thought the optimum "closure" angle was closer to 15*?

(thanks everyone)
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Old 10-02-2014, 11:06 AM   #6 (permalink)
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This shape is a low drag glider fuselage similar to the Morelli/Aperta profile. The Motorcycle/Scooter threads have some excellent discussions. Looking at your top view we want to use a 3:1 L/W or longer symmetric airfoil section. The typical max width on a motorcycle is 26 in. at the handlebars. If possible the lower battery boxes should be as far forward without contact the feet. Reducing ride height and the gap between a rider's back and the tail are critical.
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Old 10-02-2014, 02:46 PM   #7 (permalink)
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Inflatable boattail backpack.

OP -- Your two motivations sound identical to me. I don't think ecomodding, as such, imposes speed limits. My own ambition is to run an electric baja bug at Bonneville.

I can see why you want to change the saddlebags. What's inside? If it's a single battery, that's a problem. If they were packed with Tesla 18650 cells, then you could curve at least the outward face.

Do they need to be separated, or could you make a single U-shaped piece that wraps around the rear tire? Worst case, just rotating them to horizontal might be an improvement.

Quote:
I thought the optimum "closure" angle was closer to 15*?
You're not going to see optimum on the back end of a motorcycle IMHO. Too much upstream turbulence. A rounded rear, 30's style (Dymaxion/Volkhart Sagitta), might reduce crosswind response. Then you get the flat Kamm bullet shape (good for low fineness ratio), the full template boattail and finally the reverse camber to shift center of pressure backward. You get to choose from the first two.

Last edited by freebeard; 10-02-2014 at 02:59 PM..
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Old 10-02-2014, 09:13 PM   #8 (permalink)
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Yes, the two boxes are as far forward as I can get them. The back of the fairing is about 24" wide so the saddlebags protrude about 2" more on each side. My legs are sticking out there as well. Some type of gaiter to move airflow outboard?

Quote:
Originally Posted by freebeard View Post
Inflatable boattail backpack.

I can see why you want to change the saddlebags. What's inside? If it's a single battery, that's a problem. If they were packed with Tesla 18650 cells, then you could curve at least the outward face.
I'm using Enerdels and each side has two assemblies of six "elements." They're not that granular. They are butting up as close to the side of the bike as I can get them. They could be a *bit* lower but that would compromise ground clearance.

Quote:
Originally Posted by freebeard View Post
Do they need to be separated, or could you make a single U-shaped piece that wraps around the rear tire? Worst case, just rotating them to horizontal might be an improvement.
I don't understand "rotating them to horizontal"?



Quote:
Originally Posted by freebeard View Post
You're not going to see optimum on the back end of a motorcycle IMHO. Too much upstream turbulence. A rounded rear, 30's style (Dymaxion/Volkhart Sagitta), might reduce crosswind response. Then you get the flat Kamm bullet shape (good for low fineness ratio), the full template boattail and finally the reverse camber to shift center of pressure backward. You get to choose from the first two.
I'll have to think about this! I always thought I'd have to end up with some sort of Kamm tail. I don't understand fineness ratio, have to study...
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Old 10-02-2014, 11:31 PM   #9 (permalink)
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Quote:
I don't understand "rotating them to horizontal"?
Level.

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Old 10-03-2014, 06:23 PM   #10 (permalink)
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symmetrical wing section

Here is a table made from the table Freebeard posted.The center image is the drag minimum profile not listed in the original table.
Craig Vetter's body is close to this drag minimum profile.
If I were to do a body in white bike,this would be my starting point.

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