Fineness ratio vs drag coefficient

[Grant-53]

How does one calculate the finesse ratio of a body with an ovoid cross section and Kamm tail? I learned in technical sales that if I denigrate my competitors I damage my reputation more than theirs. My goal is to get the shell Cd below 0.3 and is stable in cross winds. The primary mounting point is at the bottom of the head tube. I am familiar with sailplane design and construction. I have done coast down tests at 16-17 mph with consistent results on a measured grade.

[aerohead]

Originally Posted by Grant-53

How does one calculate the finesse ratio of a body with an ovoid cross section and Kamm tail? I learned in technical sales that if I denigrate my competitors I damage my reputation more than theirs. My goal is to get the shell Cd below 0.3 and is stable in cross winds. The primary mounting point is at the bottom of the head tube. I am familiar with sailplane design and construction. I have done coast down tests at 16-17 mph with consistent results on a measured grade.

1) Fineness ratio is simply total body length, divided by actual height above the road surface.
2) 'Effective' fineness ratio requires placing the 'vehicle' on top of a mirror (so to speak ), as this is what the atmosphere will 'see;' both the actual structure, plus it's imaginary, mirror-image twin below grade.
3) As to crosswind stability, you'll need to be able to 'come outside the body', using body 'English', shifting your body weight in order to compensate for crosswind loading if you're on two-wheels.
4) Some go to the trike as a solution.
At the IHPVA Annual Speed Trials at Battle Mountain, Nevada, it's quite common to see the top contenders blown into the brush along the highway race course. Stuck inside their composite, Cd 0.11 body shells, there's no way they can transfer their body weight should a gust come along.

[JulianEdgar]

Originally Posted by Grant-53

How does one calculate the finesse ratio of a body with an ovoid cross section and Kamm tail? I learned in technical sales that if I denigrate my competitors I damage my reputation more than theirs. My goal is to get the shell Cd below 0.3 and is stable in cross winds. The primary mounting point is at the bottom of the head tube. I am familiar with sailplane design and construction. I have done coast down tests at 16-17 mph with consistent results on a measured grade.

It might be better if we can see what you have already done with the coroplast.

Stable in crosswinds is a function of the lateral centre of pressure location versus the centre of gravity (on a bike - you). It's why all streamlined (eg land speed) motorcycles have a fin at the rear.

If the comment about damaging reputation is directed at me, you're using a very poor analogy. Or would you rather see misinformation being spread?

[freebeard]

Originally Posted by Grant-53

How does one calculate the finesse ratio of a body with an ovoid cross section and Kamm tail?

I think it's a good question.

The stock answer is length over height, but I notice with vehicles like the Arcimoto, taller than they are wide, the doubled taper on the sides overrules the taper on the top. The result is a vertical edge rather than a tail.

I'd favor length over max width OR height. If you can solve for a full boat-tail you can derive the truncation.

velomoblile need a longitudinal wickerbill on the nose, as well as a tailfin.

[Grant-53]

Anyone is welcome to profit from my experiences. I am working in an area that does not get much attention. I am looking at streamlining commuter bikes that easily fit on bus bike racks as one criteria. Low weight, easy construction, and ease of access are other criteria. Should I start a different thread? Thanks for the input even if it duplicates what I have already discovered.

[JulianEdgar]

Yes, start a new thread.

[Joggernot]

Originally Posted by Grant-53

Anyone is welcome to profit from my experiences. I am working in an area that does not get much attention. I am looking at streamlining commuter bikes that easily fit on bus bike racks as one criteria. Low weight, easy construction, and ease of access are other criteria. Should I start a different thread? Thanks for the input even if it duplicates what I have already discovered.

Please post a link to your thread.

[freebeard]

I am looking at streamlining commuter bikes that easily fit on bus bike racks as one criteria

We need to discuss this in your new thread.

[Grant-53]

I will start putting together the pictures and notes for a new thread.

[aerohead]

Originally Posted by freebeard

I think it's a good question.

The stock answer is length over height, but I notice with vehicles like the Arcimoto, taller than they are wide, the doubled taper on the sides overrules the taper on the top. The result is a vertical edge rather than a tail.

I'd favor length over max width OR height. If you can solve for a full boat-tail you can derive the truncation.

velomoblile need a longitudinal wickerbill on the nose, as well as a tailfin.

Arcimoto is not an ' enclosed' body, and cannot qualify as a candidate for 'template' comparison.