Quote:
Originally Posted by PeterS
Thus far Ironsides little Honda is looking the most practical. His cd is around .44 by his calculation and this without much work yet on the rear section and with open sides.
Frankly that's a very good result and yesterday I was mentally comparing it to Jacob's ultimate Velomobiel and thinking about the rear of Jacob's bodywork and wondering if it was too rounded. A heretical thought of course but as Ironside and Jacob are running superficially similar machines although the Velombiel had fuel injection and is fully enclosed while Ironside's is quite open .
The Vetter body above has a hard rear edge and from my reading this appears to be very important and possibly a fault with the Velomobiel ???
Any comment ?
Ironside . Do you have a finished rear fairing shape in mind ?
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Hi Peter,
I too have wondered about Allert's rounded tail. It seems he is loosing the benefits of the Kamm effect as I understand it. I notice his and Theo's (they are business partners) velomobiles have rounded back ends too. Theo may be able to expound on the reasoning if any. My attempts to email Allert at the address Theo gave me failed several times and I gave up.
I think Allert's rounded tail is more for appearances although tastes in styling differ. I wonder more about the swoopy creases on the sides. They
COULD be for lateral lift spoiling but as I said, I couldn't ask Allert in my email attempts. If Theo is reading this, he could clear this up.
Terry Hershner's Zero with the Vetter nose has a classic Kamm tail. Obviously he (Terry) is of a different opinion than Craig about long tails. I notice too that Terry's transition from the cockpit back opening is rounded compared to Vetter's sharp edges. I think Terry is on the right track in that regard. Reading the recumbents.com site, some of the HPV folks also have rounded edges on their transition from the open cockpits to the tails.
The Kamm effect works as I have a day sailing catamaran (Nacra 5.2 -- 5.2 m long) with a stern that is cut off like a Kamm back. At speed, the hole in the water can be seen to close up about 10' or so past the edge, effectively making the hulls that much longer. For boats, hull speed is a direct function of waterline length. A boat operates in water of course where skin friction is very important. A catamaran goes fast largely from having a lot power driving it. A brick can be pushed fast too, the Space Shuttle was such an example. Had the glide ratio of one too!
-- Teri
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