Thanks for Erich Hartman to show the pictures
http://www.hostelshoppe.com/images/tech/df_vs_volae.jpg
I am trying to assemble my dream recumbent, which would have as small drag as possible without
extensive fairing. In that purpose I was sitting on my prototype in front of a mirror and trying to
outline correctly the cross sectional areas in different alternatives. A camera in my hand directed
to the the mirror was intended to document the result.
But after a while I started wondering why my shoes were so large compared to my head.
I was positioned only about 2 metres from the mirror, and therefore everything nearer the mirror
looked considerably larger than things farther away. I could not 'draw' the profile correctly e.g.
to the surface of the mirror.
You might notice the same effect by looking Erich's pictures, the width of the helmets of the two
riders at the right. Quite different number of pixels. Tthe helmet of the rider nr 4 from the left
(nr 2 from the right) is 57 pixels wide and the same helmet in the rider nr 5 from the left is 46
pixels wide, the difference 11 pixels is 100*11/46 =24 percent.
The effect of the camera distance can be minimized by going very far away from the rider and using a
zoom lens.
In practice the errors average out somewhat, but for serious developement work this effect should be
considered. To strengthen our belief in the supremacy of recumbents vs DF these images work
wonderfully. Mäy be too wonderfully.
?
At first glance a human being looks at the face or head of the other human being. In the image the
head of the DF rider looks huge and the head of the recumbent rider very tiny.
We want to believe
the cross sectional area of the recumbent bike and rider is tiny, so we are happy to see this
.
The miracle is seen again. Our belief is stronger. Amen.
Do not consider this as a deconstructive criticism of the work. I do not suspect the honesty of the
authors, of course.There were adequate remarks of the effect in the posting. I am grateful for the
steps they have done and the publication of the results, we are going to the same direction. I say
this to emphasize how easy it is to see what one wants to see. Strengthen one's old beliefs. But to
make scientific and technical progress we must be careful about hard facts all the time.
Erich's images are actually very useful to provoke thoughts about recumbent developement.
One sees that the recumbent rider could drastically diminish the cross sectional area of his (upper)
body by being more horizontal. In my quick and dirty prototype (the web page will be there soon,
perhaps within a week) I have the possibility to adjust the angle of the backrest during riding from
almost vertical to fully horizontal (in vertical position the seat is low so that my feet can reach
the ground, horizontal position is about 25 cm higher) . The effect of drag can be measured and also
felt. When coasting downhill (without pedalling) the rider can keep the legs straight and together
like a diver jumping legs first into water,just before hitting the water surface ('diving throught
the air legs first'). The suit can be aerodynamic (think of the suits of ski jumpers, who fly at the
speed of 100 km/h).
The cross sectional area with legs straight might be half of the currently 'good' recumbent
constructions without fairing , and thus the air resistance or air drag perhaps also half. Diving in
the air without cumbersome fairing, perhaps with small wings, aerofoils here and there, all parts of
bike and rider (!) made as aerodynamic as possible. Like waterdrops, like aeroplanes. Fly low. (wild
idea: add some lift to minimize rolling resistance also if necessary?. Or vice versa). Birds,
dolphins...
But sigh, those legs. Any ideas to eliminate their drag or utilize it?
In any case, pedals/shoes should be optimized like a water drop. If the speed is in the calm air
e.g. 36 km/h (10 m/s) and pedalling rate 60 /min, the length of the pedal arm about 175 mm, then the
air flow towards the shoes is about 9-11 m/s from the approximate front direction in all positions
of the pedal.
One could experiment with different aerodynamic forms in the handlebars (if they exist) , frame
tubes, seat, pedals,helmets, legs,hands, etc eg. using some suitable foam. Ideas about materials?
Any of these ideas can be freely used even commercially. I develope these as a hobby, as ' computer
freeware' or 'careware' (careware?
http://www.arachnoid.com/careware/index.html )
"Erich Hartman" <
[email protected]> kirjoitti viestissä
news:[email protected]...
> Rolf and I were in the photo studio shooting pictures for the Volae manual and discussing a thread
> I'd read on this message board about recumbent frontal area in relation to DF bikes. (Cutting out
> all the discussion to keep the story short) we eventually ended up taking a series of shots of him
> on a Volae and in various positions on a nice upright racing bike. We've been circulating this
> photo around the Hostel Shoppe for a while, but we've had such a reaction from everyone we've
> shared it with, that I thought it might be time to show it to the rest of the world. While it's
> definately not a technically perfect study, it is a pretty visually-compelling illustration of the
> incredible frontal area advantage that performance recumbents enjoy over performance uprights.
>
>
http://www.hostelshoppe.com/images/tech/df_vs_volae.jpg
>
> NOTE: While this wasn't intended to be public and is by no means a scientific study, we were
> careful to leave the camera and bikes in the same relative position throughout the photos. I
> cleaned up the images (removed the trainer and background) and merged them into one. Also,
> note that he doesn't actually have aero bars in the last DF photo - we simulated the
> position by having him rest his forearms on the handlebars.
>
> Have Fun,
>
> Erich Hartman
http://www.hostelshoppe.com
