Boom sock - work in progress

[hamishbarker]

I was looking for cheap, simple, light and removable aero cleanups to the bike. Yes a fairing blah blah, but that's a big project and makes the bike almost impossible to put in a car.

The vendetta boom hits the air, then some bits of cable and the hole under the boom, then the head tube, then the rider. Why not clean it up aerodynamically with a stretchy cover at least back to the handlebars?

I just draped it over and a put in a couple of pins - it worked ok (please ignore the wrinkles at the back end and at the fork crown, of course the final version will be cut to clean these up). I went for a short test ride, no problems, front derailleur works, no chain snags, tiny tire rub but easily fixed. The lycra is not particularly airtight, but is possibly enough to prevent eddies shedding from the back of the boom.

The sock is only the width of the boom. Sort of a splitter plate. The center of pressure would be forward of the steering axis, so it might be a liability in crosswind - testing (covert! - my other half has declared that I am not to ride around town with that horrible colour on the bike!) will tell.

It could be extended down over both left hand fork/chainstays, but I suspect that might make just too much unstable area ahead of the steering axis in crosswind, and might also actually increase drag due to forcing more airflow onto the forward advancing spokes. Easily tested anyway.

I would leave the back end open, to allow access to the bottle cage (and keep the bottle out of any airflow ).

Will post again when i have installed press studs instead of pins and taken it for some aero power test laps.

 

[Charles.Plager]

Find a nice big hill. Run down pedaling backwards with and without the sock (5 times each). Report back.

(I don't have a problem with power meters, but calibrating them well is non-trivial - maybe not so much of an issue in this case.)

I find aerodynamics confusing enough that I'm not particularly good at guessing what works well and what doesn't. This isn't what I would have thought to do, but that really doesn't say much about whether this helps or not.

 

[battleaxe0]

Pardon my non-existent MS Paint skill, but what about the area in red?
Passing the chain would be the sticky part.

.

 

[trplay]

It's begging for a front wheel Disc.

 

[Lief]

love this idea Hamish.
Been thinking (lightly) about the clutter in that frontal area for quite some time.

about 6 weeks back I did a ride with a battery taped to the boom.
Once I got up to about 20mph every stroke with my right leg would cause a whistling noise thorough a gap in that tape.
It was damned hard to pin down (sounded like a fender hitting the tire) but was only there when I pedaled.

Anyway - it just pointed out how much turbulence is flowing around that whole area.

Also recently, I was coasting at 47mph and I suddenly surged forward when I changed from both knees up (hugging the boom) to one leg straight (the other hugging the boom). It almost felt like I released the brake a bit.

I'm eager to hear about results as well - I think you are on to something.

 

[JOSEPHWEISSERT]

This is an excellent idea. You could turn this into an add-on item and sell it to Vendetta riders. If it looks cool and makes me faster, I would buy one.

 

[battleaxe0]

Another thought - since you're using fabric, you might want a fender to prevent puddles splashing into there.

 

[hamishbarker]

@battleaxe re extending down over the fork/chainstay area isnt appealing for couple of reasons
1. the top spokes entrain air as they move forward. this airneeds a path to escape. extending fabric down would mean,the onlyway out is forward = more drag.
2. one could extend a support down from the chainstay bridge, allowing
fabric to wrap right around and shield the front wheel. but the projected area would be larger. first rule of aero is dont increase frontal area.
3. all that red triangle area would be in front of the steering axis. stability could be a problem.
4. hassle to route the chain through a hole, snag potential. ugh.

 

[Robert Holler]

Hmm, I am not sure this is a realistic idea in real riding. In a wind tunnel under controlled conditions maybe but otherwise the fabric would likely fill full of air and act like a giant sail. It is already rough with a full disc wheel and a wind (which rarely hits dead on). It will be interesting to see what your experiment turns up. Ride with caution.

In a blustery wind there might be a lot of extra energy expended controlling the front end.

Even in a mild side wind there is a significant difference between the feeling of the fat tube front end V2.0 and the new skinnier front end V20 - the old version was more impacted by side winds.

 

[hamishbarker]

i agree robert. then again, tom traylors bikes have had fully faired boom (actually sheet metal/cfrp structures) - i wonder how they were to ride.

if full boom socking is no good, at least fairing of the messy area ahead of and including head tube, cables and boom cage holes should be worthwhile and easy.
re the fabric ballooning, i plan to have it quite tight. the idea is to disrupt vortex shedding and interaction of the wake of the boom with downstream parts.

on a related topic, this is a very interesting study about drag testing for various spoke counts and disc/trispoke wheels:
http://www.google.co.nz/url?sa=t&source=web&cd=7&ved=0CC0QFjAG&url=http://www.personal.soton.ac.uk/aijf197/Wheels.pdf&rct=j&q=reynolds number spokes&ei=jfdwVb6BNobs8gWjyIKADw&usg=AFQjCNHH4a718hK33FzjjPKbC6hI6B6KAw&sig2=yK8aWpqzg0uhDPiw1HGkgg

 

[JOSEPHWEISSERT]

Somebody was also talking about closing off the area under the seat just in front of the rear wheel. That wouldn't take much fabric. Would that help with aerodynamics as well?

 

[ratz]

Somebody was also talking about closing off the area under the seat just in front of the rear wheel. That wouldn't take much fabric. Would that help with aerodynamics as well?

Would be an excellent cargo enclosure. Should be testable with a roll down hill and duck tape

 

[hamishbarker]

ratz, jim parker did tape test of enclosing the rear triangle enclosure, see his recent post about giro air attack and other variations.


easy to fabric enclose that area, or better, heavy gauge plastic film carefully taped to avoid wrinkles.

all of this certainly makes the v less asthetic.

 

[super slim]

hamish, I think that a tail-sock that is shaped closely to your shoulders and hips like the photo below, + a covered rear wheel, will give you more speed, as the cross section of your body is much greater than the Cross section of the extendable tube to the BB.

http://www.wadler.org/Biking/Bike_AddOns/TerraCycle.php

OR a corflute tailbox

http://users.tpg.com.au/pheal/Tailbox/Tail_Box.htm

http://users.tpg.com.au/pheal/Tailbox/SV300045.JPG

 

[hamishbarker]

sure, but a tailbox is a bigger project (and will weigh more and make the bike take up more space in our garage.

It can still be done after this project. And if this project improves aero by a repeatably measurable amount, it's cheap and easy gains, and I can sew up a few repeats to post to other vendanauts. Makes more area for a company logo on the bike (tax deduction!) but I guess a tailbox would make MUCH more!