The Tragedy of Motorcycle Aerodynamics

Hey, it's the Psycho World Podcast. I'm Mark Hoyer, Editor-in-Chief.

I'm with Kevin Cameron, our technical editor.

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This week's topic, I've wanted to call it the tragedy of motorcycle aerodynamics because they're

horrific. They are pretty terrible for aero.

This is a two-part episode, Kevin. We'll talk about aerodynamics and drag and what we do with

fairings and all of that. Plus, we'll get into MotoGP and what Kevin likes to say about horsepower

wrecking motorcycles, so to speak. The more problems, it's not wrecking them. It's just

causing more problems. 275 MotoGP horsepowers are 300, or as we have now influenced the folks at S&S,

they refer to the horsepowers as toasters now because you

analogized to the Watson. It's so wonderful because a toaster is 750 watts and a horsepower

is 746 watts close enough. So when you say, oh, there's this many horsepower lost in the primary

gear, you think about that in toasters, just put your face right down over a toaster as your

bread toaster. It's impressive. Lots of energy. If you've never seen a toaster later, Kevin,

you should look or audience. Look up the toaster later. A toaster later is a vertical toaster,

has a slot on the side and it has a mineral glass window. So you can see the toast moving through

and it has this series of claws along the bottom and you put your bread in and it goes like this.

The claws just move the bread across the toasting elements and then it falls out toasted on the

other side and if you want it more toasty, you slow down those claws. You want your white toast,

very light toast, make it through, move through quick. I have a toast later at home. It's a

warm bread. A miracle of, well, it's a horsepower at least. Yep. So toasters. Anyway, aerodynamics,

Kevin. Okay. Well, the big problem, of course, is that our planet has an atmosphere and if we had a

way to operate motorcycles on the moon with something other than heavy batteries, mind you,

$8,500 to low Earth orbit, higher prices may apply to lunar. The thing is that there would be no

aerodrag and so you would simply have rolling resistance and on the moon that would be reduced

by 80% because the moon is much lighter than the Earth and therefore its gravitation is weaker.

But we do have an atmosphere which makes it possible to carry just fuel. A rocket has to carry fuel

and oxidizer, but we get ours from the atmosphere. So here we are plowing through the atmosphere on

our motorcycle and we're noticing that, oh, we're doing 225 miles an hour and we're still

accelerating and the front end is awfully light. Hit a good bump and you kind of get an unpleasant

feeling. Many riders have talked about this happening at Kota where the subsoil is clay

and when water hits it, it swells crazily. So the straightaway has these undulations and when

you go over the top of an undulation tendency for the front wheel to come up, oh, no, no, don't do that.

So what's happening when drag is produced, we're getting an echo,

is that you're transferring energy from the moving vehicle to the atmosphere around it.

And I had this graphically demonstrated to me riding my 125 BSA Bantam,

4.95 horsepower at 4500, drafting a box truck.

As the truck forces its way through the air, the air is divided. Some flows over the top,

some flows past the sides, and a confused mass tumbles underneath. But as the flow along the

sides and top reaches the rear edge of the box, it encounters a low pressure

because that area is surrounded by low pressure, namely moving air. When air moves,

its pressure drops as its kinetic energy increases and when it slows down, its kinetic energy

is reconverted back into pressure. Well, that low pressure behind the truck causes those flows

to immediately curl in behind the truck and nothing is perfectly symmetrical in this world. So

one of the two vortices that's forming on the sides grows faster than the other and poof,

it pushes that one off and it streams back and hits me, biff, and then the same process repeats,

right hand rather than left hand, pow, sacco, and I went up the road alternating right and left.

Now that whirling air, the velocity in that whirling air is the velocity basically coming

along the sides of the truck. So it is creating whirling masses of energetic air and just leaving

them behind. And this is analogous to the tip vortex produced by a wing. The pressure on the

lower side of the wing is higher than that on the upper. So air tends to spill off the tip

flowing upward from underneath and curling around the lower pressure on top and this streams back

from the aircraft steadily and woe betide the single engine novice who having looked at his or

her watch and said, I'm clear, pushes the throttle forward and moments later is completely

discombobulated upside down, right side up, etc. upset by hitting one of these powerful vortices.

Well, that energy is taken from the vehicle as drag. Okay, well, we have wing tip devices now,

don't we? Oh, it's much better. But now think of this, the pressure on the underside of the

wing being greater than that atop the wing, there tends to be a net flow on the underside,

a component of flow that is wing tip word. And there is an opposite direction on the

upper surface. So where that when those two flows, one over the top, one along the bottom,

combine at the trailing edge, they form a whole sheet of vortices that are spinning.

They all are energy rich drag. So when I went to the 93 Australian Grand Prix at

Eastern Creek, there was a misty morning practice and I could see that the

wakes of the 500 bikes were just whirling masses of turbulence, nothing like the beautiful,

sinuous lines superimposed on an image of the new model in the brochure that show

beautiful, graceful persuasive streamlining. Oh, yeah. And we've all seen that. This is

a high boost suppress kit. Yeah, the high boost suppress kit has these beautiful like

blue lines and it just looks like perfection and knowing that it's not perfection.

But then we put the motorcycle and rider into the tunnel and we measure their drag and we find

that it is comparable with that of a sheet of plywood of frontal area equal to that of motorcycle

and rider pushing perpendicular to the airflow. In other words, pretty much as bad as it can get.

It's bad. The plywood is better than a motorcycle. Yes. This thing, this tremendous drag is given

the arbitrary number of one. And if we have only half that much drag, which some motorcycles with

fairings and so forth do and maybe even down in the point fours, it's twice as good or maybe a

little bit better than that. Twice as good as sheet of plywood that is cramming through the air. Now,

the aerodynamic coefficient does not tell you the drag. You have to multiply,

you have to put that coefficient into an equation which will give you an idea of the drag. It's

not a precise thing that you can calculate exactly, but it gives you an idea of what it's going to be.

So a point five drag coefficient is comparable to that of a box truck.

And that's where motorcycles are. The rider tucks in and adds a fairing,

maybe point four or something, maybe point five, but about equivalent to the drag coefficient

of a box truck. Pretty good. Now, this is why a Moto GP bike needs

whatever that tremendous horsepower it is that it has to go 225 miles an hour.

And it's still accelerating when it gets to that speed. So that is not its top speed at all. We

don't know what its top speed is. But then again, we turn our minds to that lovely invitation

to end your life early, as some saw it, the BD-5 homebill with its 55 horsepower snowmobile engine.

2.8 square feet, something like that, of frontal area, 200 miles per hour with the pilot.

And the drag coefficient improves enormously in a vertical dive because you don't have to generate

lift. Lift always generates a component of that is drag. So that's the lift over drag coefficient

that you've probably heard of. You want the lift to be generous and you want the drag to be

parsimonious. Well, it's the big compromise in aircraft. Was it the F-104 with this little

stubby little wings? Yep, could go sure fast, but you have to land really fast. You can't get that

40 mile an hour touchdown. And when they put the flaps down, the air refused to fall. No,

they had to blow the flaps. They had to push energetic air out there to

shoo away the turbulent boundary layer. Wonderful phrase, turbulent boundary layer,

makes us all seem so cerebral. Well said, P-51, that scoop on the bottom of the P-51 is not

fared. It is not fared into the airframe. The fuselage, it has a gap because it can't use that

air. It wants to be in the not that air. And all that the boundary layer is, is the molecules that

have been slowed down by colliding with the surface of the vehicle. And they form a layer of

relatively stagnant flow. You don't want that trying to weakly push its way through the radiator

core. I'd like to cool, but I'm just going to sit over here. So Laguna Seca, 1988, 1989,

Grand Prix 500s, cresting turn one. We got up at 4 a.m. to get our spot on the fence,

because the hill had not been cut back yet. So it was kind of dangerous, but you were right on

top of those guys going over one, which is that, you know, it's barely a corner at Laguna. And then

big corners turn two, but they would go over particularly on the plug chop, but a two stroke

was so quiet on overrun that when they would, and then plug chops. So they crest the hill and

everybody's doing a plug chop at the end of practice to check their mixture. And the bikes would go

over and the fairings would go, they would be fluttering and there was no other noise except

aero. And then they'd go and they'd stop at the entrance of two. They just put the brakes on.

And there goes Kel Carruthers walking down to pick up Eddie and pushing the bike. And then Kevin's

walking back and his Kevin Schwantz is walking back and his Pepsi Suzuki is being pushed by the

mechanic. We're yelling, but you could hear the turbulent boundary layer on those little potato

chip fairings going, it was a spectacular word of memory to be there. Yes. So an airplane has a

closes its wake with a tail and the tail, a streamlined body like a fish or a bird,

is essentially a venturi turned inside out. A venturi is a duct which starts large, quickly

tapers down to a small diameter and then slowly expands back to the original diameter. And what

happens is this produces a very low pressure at the point of highest velocity. As we observed before,

if the air accelerates, it's gaining kinetic energy, which means it's taking away pressure

energy. The molecules are going in this direction at a tremendous speed and that speed is subtracted

from their random beating on the walls of the duct. So this thing works well. The pressure in

is very close to the pressure out because accelerating down to that small orifice is

quite smooth. The difficult part is expanding the flow to slow it back down to its original velocity,

turning the energy of velocity, kinetic energy, back into the energy of pressure.

Now, what you're trying to do with a tapered tail is air has had to accelerate to go out around

the bow of whatever it is that's moving. It has accelerated. Now what we would like to do

is get that energy back, not let it become drag. We want to taper the back of the vehicle

such that the airflow will adhere to it and apply pressure to it as it slows back down

and finally leaves at the close to the tail. Well, it's interesting, the airframe evolution,

if you look at your, I mean, look at any 60s aircraft, anything that was designed in that era

from your Cessna 150s, your 421s, twins, and then you'd look at the diamond aviation,

they have a DA42 twin star, it's called, it's a diesel piston engine twin. And if you look at

the tail section of that and the difference between, you know, this kind of World War II fighter look

where it's 30s and it just kind of straight lines back, the DA has a very, and most

current design aircraft like a Cirrus, it goes, and it has quite a dramatic taper.

And I'm imagining that's convert, that's, you know, making the pressure that you're talking

about as well. And on the tail of a fish, if you're, if you're trying to grasp a fish, a fish

is slippery. So your dad puts his two fingers into the fish's gills and holds it up. Look

what we did, we're great anglers. You don't take hold of the body of the fish because it's tapered

and the harder you squeeze, the faster it shoots out of there. What we want the tail for is for

the air to squeeze and some of that vector of squeezing points forward. You are recovering

pressure so that it can push the aircraft forward. A motorcycle has no tail.

And that's why. Except for, except for Dennis Manning's land speed stuff. So I interviewed Dennis

Manning like 20 years ago and I asked him about, you know, I asked him about Arrow and he's like,

well, you know, Sam and another fish have been at it a really long time. So that's, that's,

he's like, that's where we, that's kind of where we start. And, you know, they have to,

they have to be careful about the center of pressure, where the pressure is for stability.

You know, there are, there are, there are things to think about at two, three, 400 miles an hour.

So if the back end comes around, you want the natural aerodynamic forces to tend to push it

back straight, not to make it worse. Now think about this. Sorry. One more related. Oh, okay.

Yeah. More related story. Terry Vance was, I interviewed Terry Vance of Vance and Hines. So

he, he got to start in drag racing. He was, you know, he was with Rich Collins, RC engineering,

and they were doing Hondas. And then he and, and Byron Hines started Vance and Hines. And

they made tons of money and they made zillions of exhaust systems. And he was a successful

drag racer and he went to Top Fuel. And they just decided to go Top Fuel racing and they're like,

yeah, let's make some body work. And so they made some body work. And it was like a fiberglass

wedge thing that they were putting. They had a little tiny nose and had a big spoiler on the

back and they were running a huge tire, but they didn't do any aerodynamic work. And he said the

body wasn't even symmetrical. It was just like, yeah, that looks pretty good. And the guy made

the body and it was sort of like maybe a slightly crooked. And he said, when he ran that thing down

the strip, he's doing 200 miles an hour plus. He said, it was like trying to fly a dart backwards.

He said it was incredibly difficult to run. So that's my story.

Yeah, that's my Terry Manette's aerodynamic story.

Seen in gross terms, drag is the difference between the pressure on the front of the motorcycle and

the pressure on the rear of the motorcycle. And if you don't have any tail, the pressure on the rear

of the motorcycle is like the pressure behind a flat piece of plywood that is being crammed through

the air by a motor. And that means that the drag will be very high. When Craig Vetter,

I think he had, I think he did something impromptu with cardboard and duct tape once

to show how easy it would be to increase the top speed of low-powered, get-around-town

motorbikes. And he started cutting out cardboard and made a tail and he made a sort of rounded

fairing for the front. And pretty soon he had the thing going pretty fast. And all he was doing

was trying to increase the pressure on the back of the vehicle by designing a tail to which the

flow would attach itself. And by attaching itself, exert pressure on it just like trying to hold

on to a slippery fish. Yeah, there was the Craig Vetter fuel economy challenge that was part of that.

And the folks were just trying to hypermile and they were building like big, big little wing

things that you would sit in, completely enclosed vehicles and trying to continue the bodywork.

You know, we're limited by the FIM rules. We don't get dust and fairings that have the big

nose that stick way out in front of the front wheel and we can't extend them off the back.

Yeah. So we have an aero limitation by rules alone, but not on the street. If we want to

get into our cigar, we can't. We can live it up. So it turns out that one of the worst things that

you can do is to have junk sticking out of your smooth aerodynamic shape. And the example that I

like the front wheel, the brake discs, the calipers, all of it. It's just sticking out there. Yes,

the rider's elbows. You know, there are some riders who were called Mr. Elbows. And we have

to bear in mind, of course, that the rider's manner of riding the motorcycle is very important.

And if that's the way he or she feels most comfortable, that's fine. Rich Oliver on his 250

at Daytona said he would come off the seat and arch his back until his leathers stopped having

turbulence. Yeah, you could feel them detaching from your back. He was trying to continue that

arch from the fairing to their, you know, those drooped tail sections that they could still be

seen in MotoGP people putting their butts up on the seat back a bit. Because it looks smooth. You

can draw this line, the windscreen, the rider's helmet, the back. Oh, it's going to be the original

active arrow. Yes, but the air looks at it. This stinks. I'm not sticking to that.

Yeah. I'm out of here. So when excrescences, add that one to asperities and velaset, if you will,

when excrescences jut from the smooth salmon-like contour of our creation,

they are especially drag producing because the awful turbulence that streams off of them

flows down the surface of the vehicle and ruins the flow there as well. So here we are in our

B-47 1950s jet bomber, the US first swing or swept wing jet. And we have, we're preparing to land

someplace, unknown AFB. And we extend the undercarriage, as the British say, gear down.

And if we do this at what is it, 225 knots, the maximum at which the gear is permitted to be

extended, the drag of the airplane doubles. And on commercial airliners, it is said that extending

the gear more than doubles the fuel consumption. So just looking at the front of the motorcycle,

of course, we've been seeing the same look since 1958, which was the first year of the FIM rules that

said the front wheel must be completely exposed. There can be no streamlining ahead of a vertical

plane through the front axle. At various times they changed that, they made it 50 millimeters ahead,

then 100, now I think they've come back to 50, I'm not sure about that. But there is this awful thing

sticking out front. And I went to see some MIT Aero guys. I wanted to put my home-built

H2R into their low speed tunnel, low speed meaning 140 miles an hour, as it then was.

And they were telling me that this was a bad idea. They said there isn't even a dynamic model

for motorcycles yet. What do you want to do? It's foolish. But they gave me an example.

It's foolish. Can we just write that down under motorcycle period? That's why it's so great.

Because with motorcycles we're really on our own. So many of the improvements that have come to

motorcycling have come from the users and not from mighty electronic brains in the

employ of the manufacturers. Not that they haven't made their contribution. But at any rate this

mass of stuff out front reminded these two MIT profs of something that happened during World War II.

Usually painted out of photos for publication at the time were radar dipole arrays. World War II

aircraft with airborne radar did not have little dishes that panned and tilted

underneath a fiberglass cover. They were dipole arrays that were just stuck out into the wind.

And they found that if they put a flat surface behind these arrays that the velocity of air passing

through all those dipoles, you know the phrase the wind in the wires, the World War I fighter plane

movies where you hear the bracing wires of the wings singing as our hero dives to what could very

well be his demise. Keep tuned in folks for the outcome. But off of each of those dipole arrays

streaming vortex shedding. And the tone that you hear is the speed with which those little vortices

are being produced. Anyway if they put a flat plate behind that the airflow tended to be pushed

ahead by the flat plate reducing the drag caused by the dipoles to by a useful amount.

And I showed them a picture of the of Kawasaki's what year was it. There was a year that they had

a chin projection that reminded me of Abyssinian the beards of Abyssinian kings. And they said

it could very well be that that flat radiator reduces somewhat the terrible drag of all that

chunk sticking out in front. So it is almost as though those rules makers in at the end of 57

were trying to increase the drag of motorcycles. The front wheel must be exposed.

There can be no stream lining behind XYZ and all of this business. And so

we we just keep adding power. That's how you go faster. And it's strange. Another thing that

used to bother me is people would put fairings on their motorcycle and instead of shaping them

so the fairing ended quite close to your tucked in knees the fairing was made like a plow getting

wider toward the back so that it was throwing air outward. And I'd say is that do you have a reason

for wanting to do that? Yeah, I like the way it looks. Good. I'll remember that. So

such a good looking bike in 13th place didn't you think?

Stylin man. So the front of the fairing

in a lot of those late 60s bikes was just a huge opening so that all that the fairing was

was a hemisphere for the front number to be painted on with a large plastic windscreen

that most riders made come to the top of their helmets. Honda created quite a stir by making

it come to the top of the rider's shoulders. And the sides of the fairing had no streamlining

purpose whatsoever. They were just like flat sheets that were connected by maybe a six inch tongue

on either side that joined the hemisphere. They weren't streamlined at all. They were covers

and that's what I called them covers. And you could put the numbers on the side.

Well, you know, in recent conversations with Steve McLaughlin and John O'Ritch,

Steve was one of the instrumental guys in making his fairings larger so he could fit

more sponsors on them. So there you go. Good stuff. Good business might have helped there

eventually. 1980, I helped one of the early super cart guys.

Super cart meant that you had a six speed, usually a Yamaha engine at that time

on the back of your cart. And he had an enormous

world of outlaws style wing that was tipped up at a jaunty angle. And I kept saying,

John, you got to take that thing off there. I got to have it on there and sponsors. I got

to put all the sponsors on there. Could we just level it off so that we could reduce the drag

somewhat? I kept after him, eventually said, okay, picked up like 30 miles an hour.

Yeah. Well, what he was doing was carrying that sheet of plywood that we were just discussing.

Well, instead of having it absolutely flat, it was tipped back a little bit.

And this was supposed to produce a downforce that could overcome the fantastic

power of the 250 Yamaha, 40 horsepower. Yeah. So

then along comes Harley Davidson. They have their wonderful moment.

Bunch of guys spending the afternoon at XL shop playing with a Harley flathead.

Dick O'Brien, the Harley racing manager comes out because they found something.

And in the course of trying to

gain as much as they could from this, not only did they put on two Tilletsons instead of one,

carburetors, those were, they also went to the Caltech wind tunnel and a fairing was designed

for this motorcycle, which has not subsequent to that time failed to increase the speed of every

motorcycle it was ever put on because it had a limited opening for cooling. It wasn't just

a hemisphere in the front and two plates on the side. And the widest part of the fairing was at

the front and it tapered inward from that point as though it were trying to create a streamlined

tail. And in effect, what it was doing was reducing its wake area.

And this was not so much science at work as a combination of aerodynamic theory

and ours spent in the tunnel. Well, yeah, I'd like another beer. Thank you.

That looked like it was going to work, but it didn't. So now we've got to think about it again.

So Harley comes in 68. Triumph has won the Daytona 200 twice in a row and Harley's looking like a

pretty tired 1930s POS. And suddenly Harley's efforts, including the Caltech tunnel fairing,

made the triumphs obsolete. Just don't bother. Ride a Cushman. You might do as well. Anyway,

streamlining done carefully can result in gains. But they're going to be relative to that flat

plate of plywood because the motorcycle is so constrained by those rules. So much so that John

Britton came to the conclusion that the main variable in motorcycle streamlining was frontal

area. Reduce it. He took the lower fairing off on that 20 miles straight away where all the white

helmet guys go in New Zealand and picked up speed. That was the same. Well, it makes sense. Air's

getting going between the rider's lower legs and the engine. And there isn't this big thing down there

plowing air. Yeah, that was the same conclusion that the Caltech guys, when Harley did the midget,

Don MD put that story together for us, but they reduced the frontal area. And that was

what they said principally was the advantage was reducing. That was the obsession in the tunnel,

was to reduce frontal area as the first big step. And that was the Harley Davidson Midget,

which you can read on magazine.cycleworld.com. But they just made the tiny wheels. They lowered

the bike just to make it smaller. So we should switch to consideration of the

devices being used in MotoGP at this point. Would you agree? I agree. Okay.

What we see is, first of all, downforce wings or winglets

attached to or near the fairing nose. And the purpose of these is not to exert downforce

to increase tire grip in corners, because when the motorcycle is at 60 degrees, 63 degrees,

65 degrees, any downforce is more pushing the motorcycle off the turn, making it go wide

than it is pressing it down against the pavement. So the real purpose of those wings and winglets

is to keep the motorcycle from wheeling in fifth gear and having to close the throttle to keep

the front wheel steering. Just a little helping hand that presses the front of the motorcycle down

enough to overcome the tendency of the motorcycle to blow over backwards.

And Mike Baldwin and other riders have spoken to me about wheeling over a hill crest at high

speed and having to go for the rear brake because the front wheel wasn't coming down.

I like that one. Real stuff happening. Yeah. Anyway, that takes care of that whole nose business.

That's what it's for. It isn't for in-corner downforce is to allow the use of more power

in higher gears without having the front end go light and lose stability. So

the next gizmo is fairing side panels that are so angled that when the motorcycle is at full lean,

that these panels are parallel to the surface of the earth and form a venturi that can generate

downforce. Now this is going to tend to increase the motorcycle's angle of lean so the rider's

going to have to cope with this. Oh, it's doing something unusual. Oh, that didn't work. Maybe

they say it takes some getting used to. And why not? The air is moving. It has math.

You can generate forces with it. Let's give it a try. And small scoops located on either side of

the fairing, front edge of the fairing at about axle level, which then become ducts that go down

underneath. When the motorcycle is operating on the fairing, on the fairing, on the straightaway,

the ride height is at low. And that means that a flat bottom on the fairing is another prospective

venturi. If only we could get air to it. We can't because the front tire is in the way. Oh,

let's put intakes to some little ducts and run the air down there and see if it helps. They keep

doing it so either I like the way it looks or to some extent it works. And all power to them

for trying something because this is not a contest to see who can design a motorcycle that looks

most like something Agostini wrote in 1966. This is not vintage. It's supposed to be racing. So

the those so-called downwash ducts are trying to use. And of course, when the motorcycle is

photographed, you usually don't see it at minimum height except when they're doing practice starts,

which is how the whole thing started in the first place. So item

number four, a spoon or small airfoil array located just ahead of the rear tire

where it looks like if it moved aft a little bit, it would run itself over.

I don't have any idea what that does. Some people say, oh, it blows cool air on the tire. But

a big problem with the rear tire has always been lack of grip, not too much. So usually,

lack of grip results from cooling off on the straightaway. And Dunlop published and I can't

find my copy, a diagram showing tires temperatureing up as they enter corners.

Because tire temperature is a strong determinant of tire grip. There is a thing that rubber and

other elastomers are subject to which is called the glass transition temperature, T sub G. More

science. And the glass transition temperature is a temperature at which the rubber becomes hard

and inflexible. It turns out that if you can raise the T sub G to something close to the operating

temperature of the tire, you can be in a not quite stiff range of rubber flexibility that

generates a lot of internal friction, hysteresis, which creates grip. This is the wet grip that

all the manufacturers talk about, which is just secret talk for good tire traction under all

conditions. So cooling off the rear tire, I can't, I don't get that. So I just, it's a cold case.

I'm, I'll think about that later, like Scarlett O'Hara said. Various forms of streamlining applied

to fork tubes, calipers, brake discs, what have you. This is to get rid of the appalling load

of excrescences that the 1958 rules burdened our sport with. But if you've got the tunnel

paid for until five and you've been through the program, get the modeling clay and let's start

slapping it on there and seeing what happens if we fill in this and we fill in that. Tape

cardboard around the fork tubes to make a an airfoil section out of them.

And that's what you see happening now is that complicated shapes, no doubt made by

additive manufacturing techniques, aka 3D printing, are covering up the ugly excrescences and

maybe having an effect. Well, various forms of shrubbery affixed to the rider's seatback.

And we have the stegosaurus plates, arrays of jutting airfoils. And I suspect that this

is another area where a little extra downforce when the motorcycle is at lean and the rider is

feeling for the grip to get off the corner, a little helping hand, even a few pounds,

like five, could make such a difference. And for at least five years now, everyone,

not just Yamaha, has been complaining about, well, we'd really like to have more rear grip.

Now, the coming of variable ride height has utterly changed motorcycle,

GP motorcycle, MotoGP braking, because it used to be that Marquez rush up to the corner,

brake like a madman with the rear wheel just hovering in the air, and then started to lean

the motorcycle over and let the rear tire drop on the ground already sliding on the pavement.

Today, people are having to use the rear brake. Well, there's no point in that. I mean,

if you can get the front brake to lift the rear wheel, then that's all the braking there is,

trying to use the rear wheel for a brake, that's not going to help. It is going to help,

because there's such a thing as initial braking. When you first begin to brake,

the front tire is not up to temperature. So if you want maximum braking, you're going to have to

feed in some rear brake, and coordinate the whole thing so that it works out,

looking like you have a mystical ability to get off the corner. There is some rear grip.

How are you going to get it? And all of that shrubbery on the seat back appears to be

intended to give that little helping hand. Now, when you see the rider tucked in,

you know that all of those little airfoils and so forth are probably in separated airflow and

have very little effect. But when they're supposed to help you is when the rider has moved the entire

torso off the motorcycle to the inside, and the airflow comes over the screen,

and there's the seat back array fully exposed. So, good one.

And now the mysterious rubber-lipped oval armrest holes on the Aprilius.

I was waiting for this, Kevin. I was waiting for this, because it's so interesting.

It is interesting, because clearly what happens here is that when the rider is

cornering, he's not tucked in. And so those holes, which appear to be three or four inches long,

and maybe a couple of inches wide, and have what looks like a rubber seal lip,

probably something that comes off of an alpha door in the junkyard. Here's a piece. Give me

those scissors. It just happens to fit. All kinds of the most marvelous analogies are being drawn,

and by which that I mean stretched, to accommodate the view that these are control holes, like those

used in Formula One for some kind of device that could stall the rear wing array to increase

top speed on the straightaway when you don't need downforce, because your tires are 40 inches wide,

or whatever it is now. Rollers, not tires. So, where is the duct leading from these holes?

Where does it go? It goes forward, where it gathers fresh air from the stagnation zone behind

the front tire, and just above the radiator, I think, on either side. Other ducts? Are there

other ducts that plugging those holes up when you're tucked in, and your forearms are sealing

against those rubber lips? We can't see, so we don't know. So then I thought, what special

problem does Aprilia have that its riders complain about constantly cooking the rider?

And then I thought, what if those holes deliver fresh air from the stagnation zone

at .7q, and there is an open-weave section sewn into the rider's leathers that fits up against

that lip, and it blows cooler air into the leathers, and much in the way that the leather's drying

systems that some teams had a few years ago operate. A blower is going, and here's this

thing looking like a rider filled with helium. Very popular at Suzuki 8-hour when I was there.

All the factory guys, you'd see all the castrol suits laying inflated on the floor.

Big fans blowing them up. Good stuff. So, I don't insist that this is the true

purpose of these devices, but it makes sense to me. You think about it and see if it makes

sense to you. And of course, perhaps they'll reveal something that none of us has thought of,

and that'll be even more entertaining. More interesting. Yeah, it is such a fascinating

thing, just that oval. And as you're tucked in, you're putting your arms down on the fairing and

yeah. Well, another thing that has been done in Formula One, there's a lot of energy in the exhaust,

and Formula One cars used to use the exhaust energy to blow the Venturi tunnel.

And when I was, when I had my seventh birthday, my dad took me to New York and we flew down there on

a Convair twin, a pair of 18 cylinder Pratt & Whitney 2800s. And extending back from each engine to

these big tubes. And my dad told me the exhaust pipes from the engine terminate right at the entrance

to those tubes and the rush of exhaust gas at high speed pumps air through those tubes to cool the

engine, greatly reducing the cooling drag in flight and increasing the top speed. So,

a motorcycle doesn't have a Venturi unless it's leaned over, or unless it's upright, and it's a

minimum ride height that, that sort of skateboard underneath the, that forms the bottom of the

fairing. So, where's the Venturi that can be stalled, or where's the, I'm not sure. So, this

there are a lot of people thinking about this now. Ducati kind of started the ball rolling,

but if you look back in history, you could see that downforce wing, winglets were tried by Suzuki

on their 500. There was a fellow who put a wing, it looked like a big dust pan,

up on struts behind the rider, and I don't know what its purpose was, but it had variable incidents

now. Variable incidents is not permitted in MotoGP, but Formula One, which is sort of the

big brother in this business, is now permitting some variable incidents. So, who knows what will

happen next? Because of course, if you have little stubby winglets that have an L over D,

lift over drag of three, it means that for every pound of, of downforce you generated,

you're generating one third of a pound of drag. And at 220 miles an hour, that's

a fair amount. Okay, so you make those, those moustachio wings that the Yamaha and the Aprilia

have, an array of three of them usually. Kind of like what you see on the front of Formula One.

Maybe they have a much better lift over drag, six, seven, I don't know.

My rule of thumb isn't working, but it means that you could get potentially more downforce

for a given amount of drag with longer narrower wings, aspect ratio, because then the tip region

where the losses are becomes less important in relation to the whole wing.

So, it would be very nice to be able to, to vary the incidence of these wings so that they didn't

produce, they produce hardly any drag at high speed. It was at Cheprel 2G, I think was one of those

the K&M car with the strut on it that could change the angle of the wing pretty neat.

There's a great photo of Formula One grid at the height of the, of the wings on stilts movement,

and it's just so silly looking. All these spindly little stilts sticking up with, with these boards,

arrow section planks being carried on high. Why put them way up there? Because the airflow

is cleaner, it is less affected by the car head. So, this whole thing with the aerodynamics

is tantalizing because of the high speed involved, but the advertising people who have to sell these

sport bikes think that their sport bikes would look great with stuff attached to them that really

doesn't have much effect until you're going 150. The rest of the time you're just lugging it around.

It's messaging, Kevin. Yes, it sure is. It's messaging. It sure is. I'm up to the minute here,

folks. I am listening. Well, the supersonic, the whole supersonic look that has overtaken, you know,

hard edges and all these, you know. Yes. It's supersonic. You know, our world is dramatically

subsonic. Yes, it is. Well, Tony Stefinelli, he worked at Buell, and he had an entire career

in Indy as a wing person, and his source document was like a NACA book from the 30s,

because it was all subsonic wing profiles. All those subsonic airfoils, yes. Abbott and Donoff.

And so, he was like, yeah, it was a great book, and we'd try different wing, you know,

airfoils, and, you know, we're turning them upside down because it's downforce.

They were thinking of flight, but that's what Tony did. And so, we have those nice soft curves,

and that's really what our bikes ought to look like is those, you know, bird-like or

fish-like curves. You don't see fishes looking like F-22s. Yes, with those angled forward intakes

on either side of the fuselage, so that work at rearing up angles of attack.

But that looks hot and new. And the Hawker Hunter, which is all Jaguar XKE sinuous curves looks old

and drab. So, the MotoGP guys have to make it work, otherwise it's just a drag.

Well, I liked your Convair discussion because it's one of my favorite planes. There's one,

there's Convair down at the airport where I go on the weekend sometimes, that you know.

And what I like about the cowlings is they open like the petals of a flower.

Oh, yes. You're not unscrewing things and taking off these huge cumbersome things,

they're on hinges, and it just opens like a flower, like the bottom one comes out, and then the top

two kind of go up like this. And there's struts that hold them there so they don't close on your

fingers when the wind goes. So, you just pop the hood, get in there to your thing, close her up,

hit it. Yes. But those ducts you're talking about are plain. And of course, that was the ejector

cooling. A steam ejector was used to drive feed water into boilers against the steam pressure.

Great stuff. But the people who think about this all the time, the aerodynamics people,

here's a whole new field for them, and they're having a ball.

And I don't mind it at all. I've got plenty of pictures of Hailwood on a 1960s Honda. That was

then, it was a tremendous advance in power generation through extreme RPM. The motorcycles

didn't handle very well, but they were fast. And now we have a different, we've paid attention,

and I mean close attention to engine design, to suspension design. The suspension revolution

started in the mid-70s with the revelation that compression valves were becoming rigid

obstructions at high damper rod speeds, which was why people had to make the upshift when they

came out, turned five onto the banking at Daytona. Because if you had the power on,

you were going to have an upsetting impact. And great developments have taken place in tires.

In 84 came the radial revolution. In 74 came the slick tire revolution. In 92 came the silica

reinforcement revolution. Tires began to be,

they automated the production of radial tires around 2000. And it's been a wonderful progress,

and enormous gains have been made. But all this while, aerodynamics has sort of been sitting there

because that 1958 rule said, hands off all these things. Here's a big long list of things you

can't do, whereas Roger Edmondson liked to put it. Modifications not specifically mentioned here

are strictly forbidden. Everything is forbidden, if I didn't mention it. Well, I liked the early

superbike rules, again, going to my recent time with Steve McLaughlin and John Ulrich.

They left a lot open because they knew a lot needed to be done, because we were racing like

motorcycles unfit for purpose. So the rules were broad. Repositioning of the shocks, which

Udo Guido interpreted as, I'll reposition one of them on the BMW to the shelf. So you could

reposition your twin shocks, but would they just stretch the interpretation? And when it got rid

of two shocks and put one of them in the middle, just as it was on a TZ750 in the later models?

So the Japanese took note of all the tremendous work that had to be done to win those

first-era sit-up superbike races. And they re-engineered the second-era bikes to benefit

from the experience in GP racing that they all had by that time, from 83 onward. And

it was a very important step forward. These were motorcycles that were raceable out of the box.

You might want to change the front fork dampers and the tires and the brake pads,

but otherwise that was it. So those motorcycles didn't need all that welding and gusseting and

throwing away the suspension and buying others. They were usable right out of the crate.

And that was a giant step forward. Well, gosh, those are 90Ss. Udo Guido moved the

entire powertrain forward. There's a spacer on the output for the driveshaft. It's about that long

that keeps the driveshaft in the right orientation, you know, distance-wise. So they moved the motor

forward and then you just put a cookie in there that connected the output to the driveshaft

because the engines slid far enough forward that the cylinder is hitting the front down tube.

Yeah. We've run out of room. Well, I went up into the engineering library, which is in that dome

that MIT has. I was working there as a technician, a lowly technician. And it described in the Japan

Society of Mechanical Engineers, it described motorcycle stability testing on a moving belt.

And they discovered that as they moved weight forward, stability was increased.

And at one point they talked about a less successful experiment that they made. And under

result, it said the doll is overthrown. The doll being a human-like dummy placed on the motorcycle to

have similar weight and arrow characteristics. The doll is overthrown.

Yes, the doll is overthrown. Same data out of Buell many, many decades later.

You know, the Buells were going very short trail and very steep rake. They were sort of 21-22

with trails that were quite short to something three-ish, you know, very, very short.

And it was talking to Steve Anderson, who was a longtime contributor for us, an engineer himself,

and also worked at Buell EBR. And he said, yeah, the more weight we put on the front,

the more aggressive we could be with our steering geometries. And they were stable,

I have to say. They were light steering and stable. The Buells.

And if you look at this the other way, turn the telescope around, you see the bevel drive Ducati

with its engine necessarily far back because the front cylinder was at a 15-degree angle

from horizontal. So it acted as a spacer pushing a crankcase back against the rear tire.

So what geometry did they end up with? 31 degrees and four and a half inches.

So sort of touring on the way to chopper hood. Yeah, I think if I'm starting with a frame

for my, you know, notional homemade sport bike, I'm going to stick with 24

and something around four inches. It's pretty pleasant. That's about where it is now.

Pretty pleasant geometry. It's real workable. It does all the things you want. I might go a little

bit longer than your 55.5 or your 54.9 as you do on your sporty bikes. I go to 57 just because

I'm that kind of person, you know. But I'm also a big believer in flywheel mass. We keep taking

all this flywheel mass off and I actually, I find flywheel mass quite workable. I'll go ahead and

say Vellisette. I have the, I have the old flywheels, which are the full circle flywheels,

but I have the hot cam. And so what I, I think I have an advantage the way that bike runs. I think

it is an advantage. Yeah, because there's less crankshaft speed variation. Yeah, and the later

to later cranks with more pork choppy. And one of, you know, our friend Gary Baran over there

at Millennium is building cranks for flat trackers. And he's just piling on. He's making the 450

single cranks full circles, big welds of chunks, all machined and beautifully balanced as he does.

Fascinating. Well, that's not aerodynamics at all, is it?

No, but while you were speaking of it, I was thinking of the aerodynamic experiences that we

all had as children, namely creating winglets with our hands out the car window. And you

discovered that the effect was increased with speed. Oh yeah. How close to the window and then

banking it in, giving yourself a nice face full. Yes. How I missed the wind wing. You know, I have,

I have cars with wind wings. I have my truck, my 8940 has wind wings, my,

my Jag, which I'm driving today, a little, a Corlo quarter. Yes. They were so effective.

Yes, especially in Kansas, if you don't have air conditioning.

Especially in Kansas. Well, I, I have not the fondest memories of crossing canvass,

Kansas in mid, mid summer, while one of my fellow van occupants insisted upon smoking.

I thought I was going to have to stop at one point, but I

manned up. Yeah, I think the, I recall flying on airliners as a kid having a, having a smoking

section inside an aircraft. That was pretty, that was pretty hilarious.

Well, that's not aerodynamics either, but

people write in and they say that digressions are welcome. Yep. So we believe you. Yeah,

we do. We listen as stresses is or not. Well, that's it folks. That's aerodynamics.

Thanks for listening. Share it with your friends. You know, if you like it, share it with your

friends. We appreciate the comments a lot. Likes all that stuff. It helps the whole program,

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The Tragedy of Motorcycle Aerodynamics

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excrescences

asperities and velaset

dipoles

stall the rear wing array

0.7q

Pratt & Whitney 2800s

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