Trade-offs

I’m creating my own velomobile for varied reasons, whether for customizing the fit or trying to wring out any aerodynamic improvements I can. Most decisions have a trade-off though; I may gain some aerodynamic advantage by making a change, but that may mean I give up something else.

Some of the aerodynamic tweaks that I’m working in may only provide small improvements in efficiency, think tenths of a MPH improvement in average ride speed for instance. Barely able to notice a difference if only one change is made. But a couple tweaks added together should be noticeable in my ride data.

I’ve made decent progress on the plug over the last week. From the nose back to the shoulder bumps is ready, with the exception that I haven’t made the heel bumps (I need to rotate the plug again for that). Before I can fill in low spots with auto body filler (ABF) I need to give the plug a boundary layer of paint, since ABF will dissolve the polystyrene foam.

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From the nose back to the shoulder bumps is ready for a boundary layer.
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The white areas are wallboard joint compound (Gypsum). Someone suggested it for a low spot filler and it works OK, at least it doesn’t melt the foam. But it takes over a day to dry if it’s a thick application. I’m going to fill the rest of the low spots with ABF after the plug has a boundary layer of paint on it.

Perhaps the largest aerodynamic change I’m making is the angle of the body sides as they relates to the front wheels. I’ve measured the negative camber of the front wheels at 12 degrees, whereas the WAW body is more like 6-8 degrees. To address this I’ve widened the lower edge of the body by about 1.5cm each side, and increased the slope of the sides so that they match the negative camber.

This morning I put the WAW up on some crates at the same height as the plug. You can see that the wheel has more camber than the WAW body. By widening and increasing the slope I hope to fair the wheels into the body better.

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Increased the slope of the sides to match the negative camber of the wheels.

And while I was thinking that my design would have a nose about 15″/38cm shorter than the WAW, it looks like the final design will be 8.5″/21.5cm shorter. Acceptable, and it should help reduce sensitivity to side winds. Sculpting the bodywork lower between the knee and toe bumps should help reduce side wind sensitivity as well. The view over the nose will be better since it’s shorter and slightly lower.

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One trade off is that my nose cone design is wider than the WAW at the same point (directly below the toe bumps). The WAW nose slopes gradually back to the wheels, and is only barely as wide as the wheels before the air-stream gets disturbed by the front wheels.

I’m designing the bodywork in front of the wheels to match the body slope behind the wheels, so that the air-stream hopefully is already traveling straight back past the velomobile, and the front wheels won’t disturb it much (so I hope!).

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And of course adding in shoulder bumps doesn’t help aerodynamics, but certainly will make my ride more comfortable for me.

I’m still waiting for the rear suspension kit to arrive from Katanga (wire transfer delays on my side), so I can’t work on the tail design until that arrives. Just getting ready to start cutting out and shaping the turtledeck.

My turtledeck design will be very similar to the Milan’s turtledeck (that part of the velomobile body behind the rider’s head). This should be another strong aerodynamic improvement. In warmer weather I prefer to ride cabriolet style (as seen in the photo) with no hood. You can see here with the WAW and Milan next to each other that the WAW’s turtledeck could be considered an air brake, with those flat surfaces left and right of where my head would be. (Either side of the white velcro strips). The blue tape on the WAW is where the front edge of the hood will be; mirror stalks will be moved forward as well.

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And while discussing trade-offs, I should discuss target weight for the Zephyr. Since this will be the only velomobile I’ve built from the ground up, I expect that I will be slightly heavy with my resin application, and even though I want the machine to be as light as possible it’s being built with the intent of riding it regularly on the roads with all manner of vehicles and distracted drivers. I will be adding more CF in key areas to insure I’ve got a safety cage around me. I won’t be building super light for track-only race use (cause, I don’t even know where there is a racetrack near me!)

Also I have decided on lights and electrical system for the Zephyr. I am going to use Kellermann brand lights with a Kellermann control module (I won’t have to design my own electrical system, Yay!!) System also will control horn and even offers an alarm function. This is one of the rear lights; 12 volt LED, with running/brake/indicator lights all built in. I’ll most likely be going with chrome finish; I wish they still offered the brushed nickel finish…

Here is a photo of Kellermann lights on a Milan; thanks to Marc S for discussing these lights on his blog: https://etrike.wordpress.com/2018/11/05/lights-for-the-milan/ That rear facing light is identical to the one in the above photo. I will be using different Kellermann lights on the front (Atto).

Kellermann designs these lights as custom add-ons for motorcycles. I figure if they can survive the rattling around on a rumbling motorcycle then I will have great luck with them. They are somewhat heavy, but I’m going for durability, brightness and simplicity over light weight. I will post a more in depth blog about it at a later date.

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