Author Topic: Aerodynamic motorcycle project fiberglass  (Read 22131 times)

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Offline 4stroke

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Aerodynamic motorcycle project fiberglass
« on: April 18, 2015, 03:06:31 AM »
Hello,

I am interested in motorcycle aerodynamics and my motorcycle crash has inspired me to design and build new aerodynamic fairings.

CBR125R 2007: here is a sketch of what I need to fit inside the streamlined fairing.



I am thinking it'll look something like this:


To ensure my efforts are productive please share your aerodynamic wisdom.

Aerodynamic Questions:

1) Are there any strategies to reduce the drag created by leg cutouts?

2) Are there any strategies I can use to combat overheating with an enclosed front wheel?

3) How much tail/nose overhang is optimal?

4) What guidelines can I use to apply the teardrop shape to my motorcycle (taper angle 7 degree?) ?

5) More on leg cut outs, is it better to have a greater width and minimal foot cutouts or narrower width and larger leg cut outs?

Fiberglass Questions:

1) For 80mph speeds how little fiberglass will be sufficient, what do you recommend?

These are the supplies I am currently looking at: http://stores.ebay.com.au/DIY-Composites/Fibreglass-/_i.html?_fsub=2906329014&_sid=1091254744&_trksid=p4634.c0.m322

2) What would be the most cost effective method for building the fiberglass mold?

Thank you for you time.
« Last Edit: April 18, 2015, 04:36:08 AM by 4stroke »

Offline sofadriver

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Re: Aerodynamic motorcycle project fiberglass
« Reply #1 on: April 18, 2015, 09:04:38 AM »


1) Are there any strategies to reduce the drag created by leg cutouts?Smaller is better but you still have to have room to get in and out quickly

2) Are there any strategies I can use to combat overheating with an enclosed front wheel? street or track?

3) How much tail/nose overhang is optimal? street or track? (there are lots of rules to comply with if you're racing it)

4) What guidelines can I use to apply the teardrop shape to my motorcycle (taper angle 7 degree?) ? a teardrop/raindrop is not a good aerodynamic shape.  it's only shaped that way due to resistance.  google "naca 0021"

5) More on leg cut outs, is it better to have a greater width and minimal foot cutouts or narrower width and larger leg cut outs?  :? )

Fiberglass Questions:

1) For 80mph speeds how little fiberglass will be sufficient, what do you recommend?  very little if you're planning to never fall down

These are the supplies I am currently looking at: http://stores.ebay.com.au/DIY-Composites/Fibreglass-/_i.html?_fsub=2906329014&_sid=1091254744&_trksid=p4634.c0.m322

2) What would be the most cost effective method for building the fiberglass mold?  there isn't one.  check the build diaries on this forum.  good luck.

Mike in Tacoma

"aww, what the hell - let's just do it".............

Bike #833
100cc A/G, A/F and APS/G (in 2019)

Offline Stainless1

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Re: Aerodynamic motorcycle project fiberglass
« Reply #2 on: April 18, 2015, 09:34:53 AM »
Oh... never ride in a gusty crosswind...
Check Sofa's builds, those will help.  And let us know if you plan to race or just trying to make your 125 more fuel efficient.  The fairing shown is not legal in any organization that I am aware of. 
If you look at most of the racing fairings they have a fender and allow air into the motor or they carry a tank of cooling water.
The longer tail will help close the hole, but it may also make it difficult to ride in cross winds.
Have fun and keep us up to date
Stainless
Red Hat 228.039, 2001, 65ci, Bockscar Lakester #1000 with a little N2O

Offline 4stroke

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Re: Aerodynamic motorcycle project fiberglass
« Reply #3 on: April 19, 2015, 01:50:37 AM »
Street.  I aim to improve the acceleration, top speed and fuel efficiency around town (60-80 kph 37-50 mph and in highway travel (110 kph 68 mph).

I was thinking this fiberglass construction method would use less materials: http://www.recumbents.com/wisil/wianecki/velomobile/default.htm

Compared to this fiberglass construction method: http://www.velomobiel.nl/allert/Recumbent%20motorbike.htm

I'll make a drawing with this naca 0021 shape.

Regarding crosswinds.

I was under the impression that a tail balances out the forces on the front fairing making it more stable.


edit:  Here is an overlay of naca 0021 to my drawing.  I stretched it out for the vertical cross section.




The front overhand will be around 10cm, rear overhang will be 30-40cm (I'm not sure yet).

Are there any improvements I can make on this design (I don't want to fly off the road).
« Last Edit: April 19, 2015, 03:11:58 AM by 4stroke »

Offline joea

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Re: Aerodynamic motorcycle project fiberglass
« Reply #4 on: April 19, 2015, 10:14:09 AM »
you likely have seen these pages, seems like nearly every question you have is
covered here in detail, construction, problems, wind, weight, accessibility etc

very detailed dialogue addressing all the questions you have asked, with over 30 years
of development

http://www.craigvetter.com/pages/2011-Streamliner/2011-vetter-streamliner-p40.html

http://www.craigvetter.com/pages/470MPG/Index%20to%20making%20the%20Last%20Vetter%20Fairing.html

Offline wobblywalrus

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Re: Aerodynamic motorcycle project fiberglass
« Reply #5 on: April 20, 2015, 12:14:11 AM »
Read the rules real carefully,

Little bikes are sensitive to weight.  Commercially made fiberglas bodywork often is very light in comparison to home made stuff.  Carefully cut and spliced commercial parts might be the best deal.   

Offline 4stroke

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Re: Aerodynamic motorcycle project fiberglass
« Reply #6 on: April 21, 2015, 01:23:22 AM »
I have been reading Craig Vetter's website and I am especially interested in reading about the fuel efficiency challenge in the 1980s.  However I have not been able to nail down an optimal design.

Enclosed arms and legs, with spring loaded doors for the feet/shoulders


or

Cut outs for the legs


The former has undoubtedly lower Cd but by how much?  Is it insignificant?  The former is more difficult to build due to various doors or sliders to get in and out of the bike. I wonder if they would be about as impractical as being taped into a racing velomobile or if it is not that bad.  The latter requires less reinforcement and is more maneuverable.

Also what considerations determine the airfoil used for the side profile.

Such as with this:


Or this:


I can only guess that the flatter bottom is to balance out the drag produced by the wheels.

Without thorough CFD testing I cannot get it perfect but I would like to get it near perfect.  Like below 0.2 Cd or closer to 0.1Cd.  Then I can make it practical (maneuverable enough to filter through traffic and handle crosswinds) at the cost of some inefficiency.
« Last Edit: April 21, 2015, 01:45:12 AM by 4stroke »

Offline BasementBorn

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Re: Aerodynamic motorcycle project fiberglass
« Reply #7 on: April 21, 2015, 11:35:10 AM »
As many have mentioned before, if you are going to race it the rules state that you have to be able to see the rider's legs from the side which would eliminate the possibility of the doors on the side. Also dustpan style fairings are against the rules unless you run a side car I believe. However, you did say it is a project for street use. In that case you wouldn't have to worry about those rules but you have to think about stopping and maneuvering. I would think the doors would cause issues at stoplights, just one more thing to have to think about under normal riding conditions let alone in an emergency situation when someone pulls out in front of you. Also, another thing to think about would be the handle bars. I am running a Charley Toy fairing on my bike and the fairing wraps around so my forearms are covered. The area for the handle bars is pretty tight and requires them to point down dramatically. It's less of a big deal for straight line but for street riding you don't have much leverage to turn the bars, could cause some issues, especially at low speed. Just a few things to think about.
Gabe Gorton
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Offline joea

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Re: Aerodynamic motorcycle project fiberglass
« Reply #8 on: April 21, 2015, 02:05:44 PM »
4stroke described this for street implementation

"Street.  I aim to improve the acceleration, top speed and fuel efficiency around town (60-80 kph 37-50 mph and in highway travel (110 kph 68 mph)."

Offline 4stroke

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Re: Aerodynamic motorcycle project fiberglass
« Reply #9 on: April 23, 2015, 08:42:27 AM »
I have read that the naca 0010-35 has good laminar flow due to the thickest point being at 50%.  Here is an overlay.  width 60cm, length 220cm.



With leg cut outs, how much clearance is necessary to prevent air catching on the thigh (I have 2.5cm)?
« Last Edit: April 23, 2015, 08:44:02 AM by 4stroke »

Offline RGV

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Re: Aerodynamic motorcycle project fiberglass
« Reply #10 on: April 23, 2015, 11:30:40 PM »
You might want to ask the question "Why are dustpan style fairings banned in all forms of racing"?

Dave

Offline wobblywalrus

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Re: Aerodynamic motorcycle project fiberglass
« Reply #11 on: April 23, 2015, 11:40:35 PM »
It is important to get your feet back a bit so you are not scrunched up.  Also, coverage is needed up high where your shoulders are and down low at your feets.   Scooter Grubb's photos are up on his website and they are worth careful examination.  My bike is #7497.  Originally I tried using a shape similar to the one you are using and practical considerations pushed me to using the shape I have now.

This bike gets road mileage while I fine tune and develop things.  It gets hot in it.  Concerns about limiting the airflow through the fairing would make me hesitant to enclose the front wheel.  The opening at the front behind the wheel captures lots of cooling air and this helps reduce both motor and rider temperatures.  

Offline 4stroke

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Re: Aerodynamic motorcycle project fiberglass
« Reply #12 on: June 12, 2015, 02:54:55 AM »
Update:

After spending some time considering the limitations (and cost) of improving the aerodynamics of my motorcycle I have decided it may be better to purpose build a motorcycle (frame, suspension, exhaust, steering), get it engineered and registered.  That way I can have a roll cage, extremely low frontal area and a frame conclusive to optimal aerodynamics.