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Old 12-11-2016, 03:40 PM   #1 (permalink)
HP economizer
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Minimizing drag at 140mph+

Hello folks,

I am an amateur motorcycle racer, and at the end of the 2017 season I plan to enter the Race of Champions at Daytona. Unlike other tracks on the calendar, Daytona has long full throttle sections where you will hit and hold the maximum speed of your motorcycle for a relatively long time. Drag is not an area that amateurs put much effort into- we buy "race bodywork" and worry about other issues like tire costs, lean angles, and why there aren't more ladies in the grandstands.

So I have been doing some reading and think I have a general understanding of streamlining, but am hoping you can help me stay on track. My goal is to produce a second tail section (over these winter months) that I can swap on and test in race conditions for benefit to top speed.

I will try my first image upload in a moment to support the following questions:

1) Given the side view, how far off from "ideal" is the curvature of my back- does it even matter what the tail section looks like?

2) Assuming the back curvature is a workable aero shape- what should the tail section look like? It seems to me it should be taller, at a height relevant to the air flowing off of me and onto it smoothly. Thoughts? How about the gap between me and it?

3) My tail bodywork probably can't extend more than an inch or two further from the back without setting the race officials after me- so is a Kamm the way to go? How do I know what angle it should decrease by, and is it a speed-adjusted answer?

Thanks, Jake

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Old 12-11-2016, 03:52 PM   #2 (permalink)
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race tuck

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Old 12-11-2016, 05:27 PM   #3 (permalink)
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With a bike, youre never going to have enough rear length for attached flow, you should focus on frontal area.

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Old 12-11-2016, 10:04 PM   #4 (permalink)
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1)aero template Overlay found at the top under tools .Im working on an android so not as easy but doable
2a) that is pretty good-looking down to about the love handle area ,wight stripe on your lethers, things get too steap from there adding a spacer to fill the Gap behind your hips and continue the transition to the tip of the tale. Think like a fish. (|) not like a whale (--) your+bike are so short you don't realy have room for reattachment vertically.,However horizontal taper ,your setup is small, and you are tapering on 2 plains L&R. 12°per 10%length ea.take it as farback and down as the rules alow..
Tuck. your helmet has a cam built in , the gold wing, to reduce buffeting caused by the uneven separation of a standard helmet. However in the pic its more of a trip edge /spoiler. It needs ~(aproxamitly) 15° rotation clockwise. Based on the brick wall as levle this 15° will reduce frontal area and move the template 6" forward, allowing more room for taper=better CdA

2b) add a tail to your lether with industrial velcrow make follow the 3d template on 3 sides T,L,&R. Botom contorted to matchrear faring. Was thinking semi dense open cell foam.

2c) gap should be interference fit. Ast why I suggested the gap garde be attached to you . And with this attachment it must give in a crash and be brake away to prevent further injury.

3a,b)see 1 and 2a
3c) idk Aerohead or others may chime in.
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Old 12-11-2016, 10:17 PM   #5 (permalink)
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I would think if you have more fairing, just enough to cover hands, legs, and shoulders more completely when in full tuck you'd have made significant progress. Fairing the front wheel and a more significant tail than you have would probably also help you slip through. Your suit/gear could do more to reduce separation beind your helmet in full tuck. Here are two images (you may well have seen before):

See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

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Old 12-12-2016, 03:19 AM   #6 (permalink)
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Those Hayabusas are blazing fast yes, until they encounter a corner...
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Old 12-12-2016, 04:19 AM   #7 (permalink)
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I have a few observations on your dilemma

1. Congratulations on even thinking carefully about this subject, because aside from windtunnel testing rider position, even the MotoGP teams have made no serious attempts to "streamile" bike designs

2. Unlike cars, motorcycles have a different geometry, with much lower width/height ratio. For this reason it makes more sense to focus attention on smooth airflow down both SIDES not over the top. We have become accustomed to diagrams, templates and side-view photographs, all borrowed from the car industry which has led the way in all things aero. However, much of this is irrelevant.
Have a photographer snap you from above for a plan view, this will help you more.
As gumby says: Think like a fish!

3. I think the "dirtiest" part of the airflow will be aft of your arms above the elbows. This is the widest part of your plan profile and has no chance of re attachment and plan taper due to the abrupt cut-off. To mitigate against this you could consider filling the area from upper arms back to your hips
Think of flying suit wings, as used by the base jumpers. A strong flexible membrane would smooth the airflow back to the point of separation on your butt
It would mean modifications to your leathers not the bike, no problems with scruitineering and you'll get plenty of attention - make the membrane black. If it doesn't work you'll have to give up bike racing, because you'll forever be known as the "batman biker", but if it does work you will be instantly famous when Rossi and Marquez copy you.
One problem I foresee is that when you get your trophy, you won't be able to hold it up for all to see!
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Old 12-12-2016, 10:58 AM   #8 (permalink)
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You are pretty limited by class rules.

I don't think any significant mods are going to be allowed, but I would study the Rule Book. It's all in there.
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Old 12-12-2016, 12:08 PM   #9 (permalink)
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Airtech has nice aero fairings: Motorcycle bodywork, 6000+ fairings, tanks & tails, USA built!
Maybe you can find something over there that might find, post it and we'll give it a quick comment.
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Old 12-12-2016, 05:45 PM   #10 (permalink)
HP economizer
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Thanks for all of the input, everyone.

As noted, I am indeed constrained by the rulebook, the key quotes are:

1)The front wheel must be clearly visible from both sides except for the portion covered
by the fender. [I might be able to add a little material without attracting attention,worth it?]

2)The rider must be visible from the side and above, while
in a normal riding position, and transparent material may not be used
to allow for such visibility.

I have finished races to find that I wore paint/fiberglass off the sides of my bodywork from the lean angles, so I have to consider width to already be maximized.

Working on more imagery, will be back to add to thread.

Sorry, new users are not permitted to post links in their signatures.
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