cbr125r improve efficiency + top speed

[D.O.G.]

OUCH!

I hope your leg heals OK and that the bike damage is only cosmetic .


Pete.

[Grant-53]

Sorry to hear you were injured. Our thoughts and prayers are for a complete recovery. When you feel up to it I would be interested in the accident report as I design fairings with some crash protection. The use of aluminum honeycomb can help absorb energy and good geometry is critical. The concept of a lap belt on a motorcycle does not have much support yet.

[Spaghetti Man]

I am walking now so I did some measurements and took out my pen and paper.

I could fit the naca 0021 airfoil to the bottom diagram, 60cm wide, 240cm long, 10cm overhang at the front and 40cm overhang at the back.

However the airfoil did not fit well to the above diagram and required stretching. I do not think the airfoil will work quite as well when distorted like this.

How can I improve this design so it is optimally safe and aerodynamically effective?

If I can settle on a design I can make a CAD model and get a quote for cnc routing (if I try to build the mold it'll look like paper mache). I am thinking of using a door rather than cutouts to maximize efficiency.

[sendler]

Very slick and close to a pure airfoil form. 200 mpgUS should be possible. Crosswinds will be tough with such a pure design. You can use a spoiler up the nose and will still probably need to vent across the width in front of the radiator and behind the engine where your feet need to be free anyway.
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And adding side area below the cg on the roll axis will actually help the bottom of the bike to translate over so the bike retains more of it's trail induced tendency to automatically lean into side winds. Modern race bikes have body work streamlining the exit of the front tire and attack of the rear tire right down to the point where it is just shy of dragging on the ground at full compression.
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[Spaghetti Man]

I'll definitely experiment with stall strips.

I will scrap the idea of feet doors as being too dangerous at this time.

This change will reduce the shell frontal area from 0.565486686 to 0.4241150145m or 75% the size (excluding wheels). I am not sure if this makes up for the air separation caused by the leg openings.

As for increasing side area below center of gravity I am thinking of an enclosed rear wheel but beyond that I am not sure. I see what you mean about adding pressure below the center of gravity. It will cause the bike to self correct itself in crosswinds. I like that idea.



I thought that extending the nose beyond the front wheel causes terrible instability which requires computer assisted controls like that seen modern jet fighters. Is this the case?

Also if I can get 0.1 drag coefficient I'll be looking at speeds of over 200kph and a fuel efficiency of 1.12L/100km at 113kph. This is much better than 125kph top speed and 3.5L/100km on the highway.

http://ecomodder.com/forum/tool-aero-rolling-resistance.php?Weight=230&WeightUnits=kg&CRR=.02&C d=0.1&FrontalArea=0.565486686&FrontalAreaUnits=m^2 &FuelWh=33557&IceEfficiency=.22&DrivetrainEfficien cy=.98&ParasiticOverhead=0&rho=1.164&FromToStep=5-200-5

[sendler]

Minimize the overhang in the front. The best self correcting behavior will be had when the center of side lift in cross winds is close to the center of the steering head. The same place you will probably end up needing cross vents. Right across the front of the radiator. It might take as much as 1 square foot of area to make it effective. The trick would be to design the vent shapes to be nearly invisible to the air when there is no pressure differential side to side, but flow with minimal resistance when there is a pressure differential.

[Spaghetti Man]

I have discovered the vetter rifle fairing mold was created by vacuum blowing plastic to give the terrific rounded shape. I am trying to determine if this is a cost effective method of creating the fiberglass mold.

Also I wonder if vacuum formed plastic is lighter and or cheaper than fiberglass because if it is it will eliminate the need for fiberglass.

Update: The company is incapable of producing a shell without a mold and has quoted about $3000 for the mold and $2000 for the first unit then $800 thereafter. This will not be economical as I could probably build and register a ICV recumbent motorcycle for that instead of improving my existing bike.

[sendler]

Originally Posted by Spaghetti Man

Also I wonder if vacuum formed plastic is lighter and or cheaper than fiberglass because if it is it will eliminate the need for fiberglass.

It would also be much quicker and cheaper for mass production but you are limited to the sheet size of ABS that you can buy.

[Grant-53]

I am in the process of integrating the HPV shell design program from Recumbents.com, a CFD program, and the Pepakura paper model software to make skin for my fairings.

[Spaghetti Man]

Originally Posted by Grant-53

I am in the process of integrating the HPV shell design program from Recumbents.com, a CFD program, and the Pepakura paper model software to make skin for my fairings.

Sounds good.

I have considered developing a recumbent chassis with integrated roll cage but the red tape in Australia is too costly and troublesome for it to be viable.