Chap 85: Truncating the tail

What does it do to streamlining? How does it feel? How does it look?

Real streamlining is round at the front, pointed at the rear
Streamlined shapes go thtough the air the easiest - consuming the least energy. Streamlined riders go twice as far, at higher speeds than non streamliner riders. The pages of this web site are full of reasons to streamline and they far outweigh the disadvantages. Of course, there are problems.

Observed problems with Streamlining:

1) Parking: I live in the country and seldom go downtown. When I do, I either take up a car spot or the tail extends over the sidewalk. Not good. My streamlined Helix takes up more space in the garage, too. I have to be careful how I push it.

2) Winds: Streamlined bikes can blow it over more easily when parked. Ultimately, I will probably add a lightweight strut to add support in awful winds.

Imagined problems with Streamlining

1) Weight: Because streamlining looks big, people assume it is heavy. My streamlining is not heavy. Airplane builders have learned how to keep airplanes light. I have learned how to keep streamlined motorcycles light.

2) Streamlining is not cool. Consider this: You are helping to make electric bikes cool. When you streamline bike, you will be helping to make streamlining cool, too.

It seems that you like partial streamlining but not full streamlining

Doubling your range at 75mph is not as important to you as I had expected.

Your idea of a useful load seems to be limited to two helmets and a duffle bag

Streamliner #2 seems to be the closest to what you want

Race Streamlining..... Street Streamlining

Altho you want to look like a racer... you may have to settle for Design #2

The common feature is the tail has been truncated.

What would riding be like without the tail? Certainly it will be easier to park. It will not be as streamlined which means it will probably consume more energy at speed. How much more? Nobody knows. Terry, Alan and I discussed this. Who wanted to cut their tail off? Nobody. They know the value of Real Streamlining.

I volunteered

The entire rear streamlining the seat and bodywork on my Helix - in aluminum - weighed 56lbs. The portion we cut off weighed 10lbs. For reference, the vinyl coated paper tail on Alan's 250 Ninja Streamliner weighs 36lbs. The Vinyl-Paper tail is much lighter, and seems to hold up just as good as the metal.
Riding impressions without the tail
So far, I have not been able to feel any difference in riding.
However I did notice that the rear surface (made of 1" Ethafoam pressed in place ) was always pushed forward when I stopped.

This is an indication that the air is coming around the cut-off tail, reversing its direction and going forward.

This reversed flow will probably reduce my top speed and consume more energy.

Note: I have nobody to ride side-by-side with so all impressions without a tail will be subjective.

But what is actually happening?

Time for more Tuft Testing
Test #6 Feb 5, 2015: What is the air doing without the last 40" of the streamlining?

To find out, I mounted a thin piece of plywood in down the centerline of my Helix and drew a line representing the part of the tail removed. I left the plywood big so I see where the air was going all around the area. Then we took high speed videos at 65mph of the results.

We were all surprised that about 30" back, the air was flowing straight again. This was good.

Did this mean that my original tail could have been 10" shorter?

AirTabs

Many have suggested that a product called AirTabs would help to streamline truncated bodywork and make the long tail unnecessary. This seemed to be the perfect time to see what AirTabs would do.

We installed AirTabs as per instructions and rode the same day, within the hour ... again videoing at high speed.

Test #7 Feb 5, 2015: AirTabs: Do you see a difference?

Five of us closely observed. None of us could see any difference. I took the AirTabs off.

The road is my Wind Tunnel

As I write, I am waiting for some powerful winds so I can go for a long ride. I need to know what winds will do. I need to get an idea if there is any noticeable effect on mileage. A winter storm is predicted. Stay tuned. There is more to come.

We are learning things nobody else seems to know. Isn't this fun?

Master Index to the Last Vetter Fairing Story

End Chapter 85

Updated April 10, 2015

Posted Jan 30, 2015

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