Author Topic: looking for suggestions for improved aerodynamics on a naked motorcycle  (Read 8003 times)

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Offline stay`tee

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #15 on: August 02, 2018, 07:28:28 PM »
JimL's ramblings about Don Slinger reminded me of when visiting the National Motorcycle Museum in Solihull UK, thay had Don's twin engine 1500cc Royal Enfield bike on display,, in 1970 at Bonneville the thing set a class record at 194.726,, apparently it was the "first" naked bike to exceed 200mph at 203.16  8-)
First Australian to ride a motorcycle over 200mph at Bonneville,,,

Offline speedrattle

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #16 on: August 02, 2018, 07:45:03 PM »
smaller rider ;)
all the above esp raising your back  and will add rear wheel discs
Friction reduction, ceramic bearings, brakes backed off , non o ring chain ,  

my number-one daughter weighs 107 pounds. we're going to start her on a 300 ninja next year, i hope. i'm likely going to switch to cast wheels sometime.

i know nothing about ceramic bearings. why are they better?

3 spoke mag wheels with aero shape spokes.  Wire wheels are pretty draggy.

Raise your seat position to flatten your back line.  Don Sligger told me to "raise your butt" during Speedweek '69.  I picked up 3-4 mph on the next run.

Clean up all the details.  Everything air flows over has drag....wires, cables, anything at all.  Before I was finished I was running the bikes with no opening in the fairing ahead of the engine.  It was a lot less drag than flowing air over the parts!

Flat blade girder forks are a lot less drag than round tubes.

The tail is an "anything helps" deal.  My 650 pushrod twin (gas engine) ran 164 with the tail and fairing.  I dropped to 134 with the outer aero removed!

Hope this helps.

thanks. everything helps.

i'm looking at cast wheels from something like a 300 ninja. they're 17 inches, which is good, and about the same width as the old dunlop rims i'm running now. i'd have to adapt a disc brake in the back, but i don't need a front brake at all.

i'll be messing with riding position next month. i reinforced the pegs so i can stand up on them, and i tried it out last month. i was messing with pipes, jets, and ignition timing at the same time, though, and didn't pay any attention as to whether it was any better. but i've heard that making a wind tunnel through your legs helps close up the turbulence behind the rider. is that true?

Quote
My 650 pushrod twin (gas engine) ran 164 with the tail and fairing.  I dropped to 134 . . .

i'm intrigued. what exactly was that? i know a guy who does 166 on his 650 BSA, but he uses a turbo to get there.




Offline Stan Back

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #17 on: August 02, 2018, 08:00:13 PM »
Thanx JimL for your comments!

"goes 150-plus with this gigantic tail section"  –  It's probably not as gigantic as yours.
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Offline speedrattle

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #18 on: August 02, 2018, 08:22:36 PM »
JimL's ramblings about Don Slinger reminded me of when visiting the National Motorcycle Museum in Solihull UK, thay had Don's twin engine 1500cc Royal Enfield bike on display,, in 1970 at Bonneville the thing set a class record at 194.726,, apparently it was the "first" naked bike to exceed 200mph at 203.16  8-)

that machine is famous. i didn't know it ended up in the UK. is it still there?

a friend of mine with the second-fastest 650 has also built this. he was first-fastest until last month, but is planning on coming back.



it ran one time last summer, and then ate a crank seal and lost pressure on one motor. but he runs an oil gauge, unlike everybody else, so the rider shut it down without any damage. did 141 on its first and only run. i'm waiting to see it when they bring it back.

Offline JimL

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #19 on: August 02, 2018, 08:56:02 PM »
Before I finished the hobby, I thought about building an "ultimate" open bike....just for the fun of the challenge.  My pushrod Honda V-twins were such a wide engine that I never went onward.

The whole idea was that EVERYTHING has to have air flow across it when you are going fast.  Even things that are out of the direct airflow are still creating some air drag that adds to the total.

Those notes on ceramic bearings and such are very good.  I did go with those on my bike, and every little thing helps.

One of the ideas I had, which would aid aero without adding out-of-rule items, was to install the battery/box as low as possible just ahead of the rear tire (inline mounted).  There is a hard, high pressure area in front of the tire because it drags air around with it....and throws it into the oncoming air ahead of that tire.  That concept is why so many modern cars have spats hanging down in front of the tires.  Aero drag improvements help the mpg ratings and the manufacturers use those details.

When we prepared the Bonneville Prius (in 2004) with Car & Driver, we were told by Toyota engineers to lower the car until the spats could just touch the ground.  They knew very well how much drag a tire can create. 

In the bar cables could reduce a little drag, especially it the bars are not round section.

Anything that air flows across should have sharp rear corners (teardrop idea is great, but doesn't really work on a short bike).  Look at the new cars and you see more sharp corners at the back.  The whole principal of Kamm is a clean break.  As proof of little things adding up, look at the top of pickup tailgates, these days.  They all have added top width, sharp corner, and tuck-in for better air release of the high pressure stream that dives off the top of the roof.  Those folks are good engineers and we should all pay attention to what they are learning.  The latest Tacoma has air straighteners to keep airflow under the mirrors from tumbling through the front door handle.

Everything can make a small difference.  You could really have fun with your project and perhaps open a new chapter in un-streamlined bikes!

Good luck and success, while you go forward.

JimL

Offline speedrattle

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #20 on: August 02, 2018, 10:07:45 PM »
Everything can make a small difference.  You could really have fun with your project and perhaps open a new chapter in un-streamlined bikes!

i'll still be playing follow the leader for some time. i currently have the fastest production-framed triumph in the running, but there is a faster one running in altered that might be within reach before too long:



^^^this 650 triumph went 139 on gasoline and 175 on nitromethane. 139 mph on any naked machine with a naturally-aspirated gas triumph motor is something to be proud of.


Offline stay`tee

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #21 on: August 03, 2018, 01:17:16 AM »
It was 2010 when I was there, not sure if its still on display,, I have some photos that I tried putting up here but this site is telling me thay are too large at over 500kb  :|
First Australian to ride a motorcycle over 200mph at Bonneville,,,

Offline Frank06

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #22 on: August 04, 2018, 07:19:06 AM »
Re: riding position.  I would experiment a bit, try keeping your head centered (just make sure you can see where you're going!) then raising your back, etc.  Hopefully there will be no shortage of runs available to experiment.  Did you try a different helmet (one without the lip)?

I've been told that ceramic bearings make a difference at 200 mph, I imagine the impact would be more significant at lower speeds.  I don't know if anybody has ever made back-to-back runs in an effort to try to quantify.  Wheel bearings are an obvious choice but I've also heard of guys changing transmission bearings.

Offline Stan Back

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #23 on: August 04, 2018, 11:04:59 AM »
Seems like a clever guy could test helmet and riding positions and more at little or no expense with coast-down testing.
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Offline JimL

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #24 on: August 04, 2018, 03:04:30 PM »
Balanced aero on a motorcycle is more important than we think.  Anyone who has ridden in side winds notices that the bike loses a lot of power.  The reason goes back to the basic rule that:  HP = Torque x RPM divided by 5252.

If you have to lean the bike (even a little bit) to keep going straight, you must apply torque into the handlebars to counter the gyroscopic precession trying to turn the front wheel into the lean.  There is absolutely NO way to counter this effect if you are riding on a planet with gravity.

The amount of power absorption is pretty surprising, and explains why side-wind runs at Bonneville are really lousy for our bikes.

Let's imagine you are having to make a 5 pound push into the right bar (and a 5 pound pull on the left), to keep going straight while leaned.  If your bar length were 12" it means you are absorbing 10 lb-ft at the tire contact patch to hold your course.

If you have an engine that makes 50 lb-ft of torque at 5252 RPM, you just sucked up 10 horsepower with your handlebars, if that is the exact rpm you are riding.  I have had runs at Bonneville that I was pushing/pulling on the handlebar with a LOT of pressure, trying to hold my line.  The bike really slows down.....far enough that I have had to downshift to try to recover.  I have pushed the bars far enough to feel the front tire break loose and slide across the course.

That really ruins your run speed.

I had a couple years that the bike was always requiring handlebar pressure to run straight, in no wind conditions.  I reworked the fairing mounts to get both sides in balance....the bike was then easy to ride and went faster.

Food for thought.....and sometimes you can make some decisions based on the NWS isobar map predictions for the day.  When the isobars for the salt flats area are wide, it is time to make your runs.  It seems like it is just impossible to cover all the bases, but you must keep thinking, "everything matters".
« Last Edit: August 04, 2018, 03:12:29 PM by JimL »

Offline maj

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #25 on: August 04, 2018, 03:30:35 PM »
 "everything matters"

Actually i just realised were all talking Bonneville and you run mile events
if you get the chance, go to the salt . A mile is not long enough to try body position changes and see a result
On the salt everything has a visible reaction, just watch the tach , it tells all
think small, knees in elbows in toes in , bum up , head down , can you creep your hands along the bars a little more , lots of time so test it all

I run turbo bikes, harder to tell this sort of stuff , but back in 05 a mate let me take his NA bike for a run , i learnt so much more on that 1 run than i would have in 3 or 4 years of wheelspinning and fishtailing the turbo

Offline speedrattle

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #26 on: August 04, 2018, 11:20:11 PM »
Re: riding position.  I would experiment a bit, try keeping your head centered (just make sure you can see where you're going!) then raising your back, etc.  Hopefully there will be no shortage of runs available to experiment.  Did you try a different helmet (one without the lip)?

centering my head means i have to rest my chin on the top tube, way above the triple tree in the wind. ducking down means my head creates a wind shadow that conceals some of the rest of my body. i've run older-style bell helmets that just bounced from side to side at speed. this one with the lip actually has no discernable buffetting, so i'm guessing they got it right. smooth as glass at speed, rather thnanknocking my head back and forth. the shoei helmets have a kamm profile, and i'm look at the budget for one of those. my bell is getting chewed up from grinding against the fork tubes.

Quote
I've been told that ceramic bearings make a difference at 200 mph, I imagine the impact would be more significant at lower speeds.  I don't know if anybody has ever made back-to-back runs in an effort to try to quantify.  Wheel bearings are an obvious choice but I've also heard of guys changing transmission bearings.

i'm looking at wheel bearings for the winter rebuild, along with all the other small increment stuff. dunno about transmission bearings. the layshaft runs in wet needles, so i'd only get to change out the mainshaft ball and roller. maybe it would be something.

did you run something up there last month? i was busy and didn't have much time to talk to people.
« Last Edit: August 04, 2018, 11:46:14 PM by speedrattle »

Offline speedrattle

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #27 on: August 04, 2018, 11:29:07 PM »
Seems like a clever guy could test helmet and riding positions and more at little or no expense with coast-down testing.

i wish i could. appalachian ohio doesn't have a lot of sweeping downgrades.  that's the main obstacle. but maybe i could figure something out. the race bike isn't even barely street-legal, but i can fake head and tailights.

Offline speedrattle

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #28 on: August 04, 2018, 11:36:43 PM »
Food for thought.....and sometimes you can make some decisions based on the NWS isobar map predictions for the day.  When the isobars for the salt flats area are wide, it is time to make your runs.  It seems like it is just impossible to cover all the bases, but you must keep thinking, "everything matters".

i run whenever i can, make notes of the conditions, and then try to make sense of it afterwards. the fastest runs at loring in july were the last day, when there was a seven mph tail wind and the relative air density was 105, highest of all four days. all our runs are in one direction, one time, so that really makes a difference. when the wind is in your face, everything sucks.

but at loring, we're looking at a 12,000-foot runway, the longest straight paved race course in the world. if the wind is right, and your machine is right, you can do very well.
« Last Edit: August 04, 2018, 11:48:38 PM by speedrattle »

Offline speedrattle

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Re: looking for suggestions for improved aerodynamics on a naked motorcycle
« Reply #29 on: August 04, 2018, 11:42:52 PM »
"everything matters"

Actually i just realised were all talking Bonneville and you run mile events
if you get the chance, go to the salt . A mile is not long enough to try body position changes and see a result
On the salt everything has a visible reaction, just watch the tach , it tells all
think small, knees in elbows in toes in , bum up , head down , can you creep your hands along the bars a little more , lots of time so test it all

I run turbo bikes, harder to tell this sort of stuff , but back in 05 a mate let me take his NA bike for a run , i learnt so much more on that 1 run than i would have in 3 or 4 years of wheelspinning and fishtailing the turbo

i'd love to do bonneville, but it's so expensive for me to get there-- 1920 miles-- that i want to do everything i can on the mile events in the east before i spend the money. i used to live in california, but that was a lifetime ago.

the difference with the short and long events is just as you say-- i don't have time to change things and watch the tach, i have to be right the first time or i'm slow. still, i have 1.5 miles to get up to speed, even though i don't get to run a flying mile at the end.

interesting that you learnt as much as that on a slow bike. my machine is slow by modern standards-- 130 mph or so-- which means i live and die by the wind, not by horsepower. i'm barely accelerating at the mile, and pick up four mph by 1.5. at that point it's all wind.
« Last Edit: August 04, 2018, 11:56:53 PM by speedrattle »