Introduction & Cross wind solutions to motorcycle Streamliners?

[godscountry]

Originally Posted by Teri_TX

Hi everyone,

I recently joined and have been lurking a while before making a fool of myself by posting :-)

I stumbled on to this site via a stumble on to Craig Vetter's site after stumbling on another site ... I forget what I was orginally looking for. That's the beauty of serendipity! Anyway, I'm a retired engineer (mechanical and electrical) with even more time now to ponder things. I have never had a motorcycle or ridden one (except once on my brother's dirt bike many moons ago) but I'm considering one (Honda CBR250R is my current choice) for high FE so I can putter around and explore the countryside. Having weather protection would extend the utility of the motorcycle instead of just being a joy riding toy.

Allert Jacob's velomobile is probably the most documented successful and beautiful aero bodied motorcycle/scooter (sorry Craig Vetter !) to date (in my opinion). He reports that side winds have minimal effects on the handling and this is without a long tail. After reading about many of the other similar projects I started wondering why his aeroshell is least affected by side winds.

Others have mentioned in passing that the side forces from side winds is from the lateral lift forces after a vector analysis of the apparent wind direction. This got to me to thinking of why and how minimize the lateral forces. Craig Vetter's "last Vetter Streamliner" had door fairing temporarily until he decided the side gusts were too much with them. He is also a veteran motorcyclist and probably prefers the open feeling of not having door fairings anyway.

The above ramblings got me to thinking that maybe the lateral lift is the real problem and I started Googling about wings and various lift and spoiler devices. Today, I stumbled across a "spoiler" type device called a stall strip which is just a simple triangular piece of metal (usually) placed at the stagnation point of the wing root to improve stall behavior. Even the U2 spy plane has a retractable stall strip to assist in landing since it simply just wants to keep flying which I found in my Googling..

After reading about "stall strips" I looked again at Allert's aeroshell to verify something I had just thought was simply a "styling" look he placed on the sides. The swoopy creases and resultant slight concavity probably cause any lateral lift to be ruined or minimized at least. I wonder if Allert deliberately put them there for aero reasons or that he just thought they "looked good". Anyone have an email address for Allert Jacob or other means to relay this question to him? Theo22? I'll PM him.

Back to Vetter's streamliner, I wonder if a stall strip or even a low vertical fence on the centerline of the nose section would serve a similar purpose to disturb the low pressure side airflow in a side wind gust condition and yet not have any perceptible parasitic drag in the forward direction? I hope Craig Vetter reads this or I may have to email him directly if he doesn't respond to this post.

On another thought, I did a search of the archives for "DIY wind tunnels" and many replies were rather negative, pointing out the Reynold numbers etc. The original posters were usually asking to determine Cd's and such to "compute" forces on their "finished" project. I was wondering if instead of the utility in studying flow conditions and "relative" forces between different designs. The operative term is "relative". I have a 42" shop fan which might be used as the fan for a modest wind tunnel. Of course, where I live, the wind blows rather hard most of the time from the south and I could probably just set up models outside.

Sorry for lengthy post and look forward to an intelligent discussion.

-- Teri

Yes you maybe on the right track,looking at photos of the Ecomobile in crosswind testing and reading the commentary,it sounds like the body was acting like a big wing,providing lateral movement,instead of vertical lift.They said it turned into the wind.Could it be a little of both,the design of the side panels and the somewhat open cockpit[cockpit area,if enclosed would be like the leading edge of a wing]?The open cockpit and or side panel design,breaks up the airflow and resulting actions,eliminating the side movement

[sendler]

Originally Posted by godscountry

They said it turned into the wind.

Every good motorcycle does this due to the trail in the front end geometry.

[Teri_TX]

Originally Posted by ;418782

Yes you maybe on the right track,looking at photos of the Ecomobile in crosswind testing and reading the commentary,it sounds like the body was acting like a big wing,providing lateral movement,instead of vertical lift.They said it turned into the wind.Could it be a little of both,the design of the side panels and the somewhat open cockpit[cockpit area,if enclosed would be like the leading edge of a wing]?The open cockpit and or side panel design,breaks up the airflow and resulting actions,eliminating the side movement

Hi godscountry,

Thank you for the encouragement. Starting with message #45 by Theo22 and Ironside's experiments (starting with message #67) I have little doubt now of my original theory. The question is how much and if there is some other simple thing that could be done to further reduce cross wind sensitivity.

I'm waiting for Vetter's latest blog after he privately told me that his preliminary testing indicated that a stall strip was helping.

-- Teri

[godscountry]

I'm a little confused, so is the streamlined body, acting like a big wing on its side,with the top of the body[canopy,roof area] acting like the leading edge of a aircraft wing. The reason I say that,is looking at the early testing of the Ecomobile in crosswinds,the bike moved into the wind,as if it was providing lateral lift instead of vertical lift like a aircraft wing would do, if it were in a horizontal plane..So what your saying is the shape of the side panels[maybe the open cockpit] of his body design,is changing the airflow and reducing that lateral movement?Sorry guys,but I'm not too well versed in aerodynamics,but after reading about Rogers crash,I want to learn a little more .Thanks for your time

[Teri_TX]

Originally Posted by godscountry

I'm a little confused, so is the streamlined body, acting like a big wing on its side,with the top of the body[canopy,roof area] acting like the leading edge of a aircraft wing. The reason I say that,is looking at the early testing of the Ecomobile in crosswinds,the bike moved into the wind,as if it was providing lateral lift instead of vertical lift like a aircraft wing would do, if it were in a horizontal plane..So what your saying is the shape of the side panels[maybe the open cockpit] of his body design,is changing the airflow and reducing that lateral movement?Sorry guys,but I'm not too well versed in aerodynamics,but after reading about Rogers crash,I want to learn a little more .Thanks for your time

Hi godscountry,

I'll leave the explanation of the Ecomobile moving into the wind to the motorcycle gearheads which I am NOT!.

As I understand it, the trail of a motorcycle's front wheel causes it to move into the wind when pushed by it. My theory is based on the idea that a streamlined motorcycle body behaves as a wing which in a cross wind develops lateral lift in the downwind direction. This is a good thing as the opposite is bad. However, too much can be BAD if it moves you right into an oncoming vehicle or off the road.

My theory of having "stall strips" is to ruin the downwind lateral lift by spoiling the wing effect. Vetter's open sided streamliner is one way to minimize lateral lift in a cross wind situation. However, the big gap causes more drag and thus lower fuel efficiency (we're here for FE). All previous fully streamlined 2 wheeled vehicles suffer from cross wind sensitivity to the point of causing them to crash. Videos of streamlined HPV's show some spectacular crashes from cross winds. HPV's are especially sensitive because of their light weight.

Motorcycles are heavier and the Ecomobile's weight (1000+ lb) and wheelbase (3m) make them less sensitive but still vulnerable. Roger's crash is because his vehicle is light and is vulnerable to cross winds because of his aerodynamics.

I hope stall strips will become a defacto part of the bodies of streamlined 2 wheelers. I say "largely prevent cross wind sensitivities" because there is always the simple bluff body wind forces of cross winds. Traditional kites have simple flat planes for lift but still fly as they always have.

Hope this clears up your confusion.

-- Teri

[sendler]

Originally Posted by godscountry

the early testing of the Ecomobile in crosswinds,the bike moved into the wind,as if it was providing lateral lift

All good motorcycles lean and corner into a side wind due to the trail in the front end geometry. The ecomobile does this because of this steering geometry and despite of it's aero bodywork. I will post the link again to read about it here :
.
http://ecomodder.com/forum/showthrea...tml#post285297
.
Here are some ramblings on the subject pasted from various threads:
.

More related ramblings from another forum:
.
Motorcycle aerodynamics, a slippery and windy, slope? - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com
.
I am not a suspension designer but I can tell you this from riding 6,000 miles this year. Most of it on relatively straight divided highway at 65mph and often in side wind conditions. My motorcycle is very noticeably self correcting in side winds. I could demonstrate this to you "no handed" by laying on the tank and momentarily letting go. But you have to lay on the tank while riding to get the best effect which most people find self conscious or uncomfortable. Other riders suggest "riding with your knees" to take the weight and stiffness of your upper body off of the handle bars. This helps free up the steering but doesn't work quite as well. Maybe this is why you haven't personally ever noticed it.
.
If your upper body is sitting high and free from the bike as most people do, it will spoil the effect that the steering geometry has to roll the motorcycle into the side wind. Cross winds pushing on the side area of the bike/ rider/ luggage that is above the center of gravity of the roll axis will cause the bike to lean over and actually turn off line the wrong way. Worse yet, blowing the rider's head and torso to one side of an upright, yet comfy riding position of a standard bike, pushes the rider out of position from over the balance line which has made the system lean and turn the wrong way. The next thing that probably happens is that the rider will try push their upper body back over the bike against the wind with their far side arm which applies a counter steering manuver to the handle bars. The wrong way. Which makes the bike lean the wrong way even further. All of this happens in a domino effect very quickly, blowing you off line. If you sit up.
.
Super Sport bikes with their ultra low and narrow clip on handle bars place the rider in a better position to avoid all of this in the de facto riding postion they impart by lowering the rider's upper body, and so, the side wind center of pressure. And further, reducing the leverage that the side wind has to push the rider's upper body off the bike. My CBR250R offers the best of both worlds with high, wide bars for sitting up in traffic, and, perfect ergonomics to lay down on the tank to get out of the wind in order to let the suspension use it's trail to lean the bike into the wind.
.
To answer your questions:
Motorcycle dynamics of turning and balance are very complicated.
.
Bicycle and motorcycle dynamics - Wikipedia, the free encyclopedia
.

Motorcycles have trail. The contact patch of the front tire is behind the steering axis. When the side wind pushes the whole bike to the right, the contact patch is stuck to the road behind the steering axis. The steering axis, which is in front of the patch, is free to move to the right more than the contact patch which is stuck to the road. The wheel has just torqued and steered to the right. Which causes a counter steering lean of the bike to the left through the combination of gyroscopic precession leaning the the wheel,
.
Precession - Wikipedia, the free encyclopedia
.
and the tire steering out to the right from under the cg on the roll axis which stayed where it was.
.
Camber thrust - Wikipedia, the free encyclopedia
.
Cornering force - Wikipedia, the free encyclopedia
.
The motorcycle has just leaned to the left into the wind. Automatically. The same as if you had consciously pulled on the right handle bar to initiate a counter steering maneuver. If the center of pressure of the side area of the rider/motorcycle is below the cg of the roll axis, this would also tend to lean the bike into the wind. Or at least stop the distribution of the wind pressure from fighting the roll force of the counter steering trail if the wind pressure is at least neutral to the cg.
.
Trail also tends to make the bike stand up from a lean. When the bike leans to the left, there is an increasing vector of gravitational force pulling on the left side of the bike. To the side of the steering axis. Which is again free to move more than the patch. Causing a counter steering torque to the left which makes the bike lean and steer it's tires back under the bike until it is upright again.
.
The more the bike leans, the less area is presented to the side wind and, the more gravitational force is applied to the trail to make the bike stand up. Careful design has made a nice balance in the amount, and vertical distribution of the side area of the CBR250R, and the amount of trail, in order to balance the forces so the bike "knows how much to lean" into a side wind.

[Teri_TX]

Originally Posted by sendler

...
<big snip>
...
If your upper body is sitting high and free from the bike as most people do, it will spoil the effect that the steering geometry has to roll the motorcycle into the side wind. Cross winds pushing on the side area of the bike/ rider/ luggage that is above the center of gravity of the roll axis will cause the bike to lean over and actually turn off line the wrong way. Worse yet, blowing the rider's head and torso to one side of an upright, yet comfy riding position of a standard bike, pushes the rider out of position from over the balance line which has made the system lean and turn the wrong way. The next thing that probably happens is that the rider will try push their upper body back over the bike against the wind with their far side arm which applies a counter steering manuver to the handle bars. The wrong way. Which makes the bike lean the wrong way even further. All of this happens in a domino effect very quickly, blowing you off line. If you sit up.
...
<really big snip>
...

If we are DAMMED to glue our torsos to the gas tank to ride in cross winds, then I'll have no part in it. My back and neck wouldn't tolerate it for more than few minutes. Besides, as an adult, I wouldn't want to be mistaken for some wannabe boy racer poser idiot.

I want a feet forward (to use Creasey's term) position for comfort with a real seat. I don't have an iron butt. I suppose having the body more connected to the bike could be done with side bolsters like car racing seats or a "grippy" fabric seat back. The 1982 VW Jetta diesel I once owned had a grippy "mouse fur" (to use some reviewer's term) upholstery fabric that I liked.

Furthermore, personally I'm interested in a fully enclosed body for FE and ultimately to have air conditioning in the southwestern US heat. When you're brain addled from the heat, FE is a secondary consideration. With a full body, I also want crash protection which is possible with suitable structure and Kevlar. In other words, I want to be a "cager" and not road meat for the buzzards. Cager is not a pejorative term for me.

Those interested in "motorcycle dynamics" should start another thread, otherwise just post a permalink. That's the link beside your message number.

Back to our regular scheduled programming of "Cross wind solutions to motorcycle Streamliners" as this thread title reads ...

[sendler]

I offered an answer and further reading to correct the other poster's misconception that the Ecomobile was somehow flying into cross winds because of it's shape. It is not. Motorcycle steering dynamics is fundamentally tied to this discussion. Your question is how to mess them up the least when adding a streamlined body. But you must first know about the effects of trail in sidewinds which most people do not. Which is why I keep bringing it up. I'm not saying that you have to lay on the tank of a streamliner. But I am here to say that if you want the safest performance out of an off the shelf motorcycle in bad weather, you can get it by taking all of the weight off of the bars and by keeping your torso from getting blown to the side with the wind. And I also offered an explanation as to why most long time riders have never noticed it because they are being blown off balance to the wrong side of the bike. An automotive "seat back" style seat in a streamliner will anchor the rider and get the weight off of the bars so the steering can work it's magic.
.
Well I didn't really want to sit and type for hours but your hesitance to read and study other good threads has compelled me. I would link some excellent threads Aerohead has written about the rapidly diminishing returns of Kamm tails but you don't like links so let's skip it.
.

To summarize what we have already discussed in the other threads:
.

Motorcycles automatically lean and corner into a side wind due to the trail in the steering geometry as shown by the dramatic correction of the ecomobile video. As long as the handle bars are not burdened with a terrified rider's rigid arms.
.

Keeping the CG on the roll axis high accentuates this.
.

Keeping the side CoP low helps push the bottom of the bike out from under the top which accentuates this.
.

Streamlining a motorcycle turns it into a vertical airfoil which generates horizontal lift when sidewinds combine with the headwind of forward motion to create an angle of attack. This increases the force beyond what a normal bike would see.
.

The greatest lift of an airfoil is located just behind the max thickness. So "spoiling" with a fence along the top and back section of the tail isn't going to help anything. In fact, that is just adding extra area for the side wind to push on above the CG and will act like the winglets on the tips of modern airplanes that will actually increase the undesirable side lift in that area. Pushing the top of the bike over with the wind the wrong way. It was also noted in another thread, (no link) by someone who made a tail with a sharp edge along the top that it tended toward severe oscillations as it knifed through the air. The rounded top of the ecomobile is much better. Modern Moto GP bike have a Kammed off under belly that almost drags the ground under full compression to carry the streamlined air behind the front tire with a ground effect and to lower the side CoP to the minimum (no photo).
.

Venting the max pressure differential from one side of the wing to the other across the engine bay or the riders lap is the easiest way to make the increased side lift of a streamliner a complete non issue.
.

Bikes corner from leaning and camber thrust. Not from steering and slip angles. The concept of an airplane like rudder on the back of a full aero motorcycle makes an interesting thought experiment for my stance on the futility of an extended fin behind the rear wheel for the purpose of straight line tracking in side winds. A big fin in the back makes the bike into an arrow when it is going straight down the road except for the fact that arrows don't have two tires stuck to the road. The rear tire is fixed and can only roll straight ahead so even with the tail fin, your bike is not really like an arrow. The tail fin can only push the rear of the bike with the wind but it is forcing the rear tire to go sideways in order for anything to happen. Now look at the rudder sticking up high above the cg and far behind it like the low fin is. Which way would you actuate the rudder if you were flying the bike and got hit by a side wind? Would you actuate the rudder to amplify the force of the wind at the rear as you are trying to do with the tail fin? Again, this is not an airplane. The rear wheel is stuck to the ground and the most effective way to generate the lateral force needed to push back against the side wind is to LEAN the bike so it is camber thrusting and steering into the wind. You would actually use the high mounted rudder in the opposite direction that the tail fin provides by trying to rudder the top of the bike, even though it is behind the rear wheel, to ROLL INTO the wind. Think about it. Maybe counter intuitive. The rear of the bike to roll INTO the wind. I also wonder what any yawing action that did make it sideways past the tracking rear tire would do to the trail in the front geometry. If you could have the cg at the steering axis it would tend to stay neutral like the arrow. But the cg will probably be closer to midway between the wheels with a feet forward design. And the yaw force from the tail will have the stuck rear tire patch as the fulcrum. The yaw will pivot on the cg and the contact patch of the rear tire, forcing the steering axis laterally into the wind, causing the trail to counter steer and precess and lean the wrong way, with the wind.
.

But I have seen that the full tail is very quiet to turbulence when following big trucks. And it is the most aero. But makes the bike easier to blow off the stand when it is parked.
.

Longitudinal CoP, contrary to Foale, provides the best use of the steering trail if centered at a point which is low and directly beneath the steering head. This was demonstrated by some HPV guys (no link) by tying a string at various points along a bicycle and tugging on it while someone was riding. Top speed runs on salt flats are an extreme case where the rear tire is completely at the limit of traction and so the vehicle is essentially flying as it skips along the ground.
.

In lieu of venting which still could be done even if the rider is fully enclosed, Spoiling on either side of the nose could also reduce the side lift at a slight compromise of cd if the spoilers are carefully run along the lines of flow. They will have to be much larger than a piece of rope. More like Sheepdog's design at the early part of the thread (no photo) but two of them and moved part way around to the side of the nose.
.

That's enough for now. I will edit this post as time goes by when I think of any other things we already knew and forgot.

[PeterS]

Originally Posted by sendler

I offered an answer and further reading to correct the other poster's misconception that the Ecomobile was somehow flying into cross winds because of it's shape. It is not. Motorcycle steering dynamics is fundamentally tied to this discussion. Your question is how to mess them up the least when adding a streamlined body. But you must first know about the effects of trail in sidewinds which most people do not. Which is why I keep bringing it up. I'm not saying that you have to lay on the tank of a streamliner. But I am here to say that if you want the safest performance out of an off the shelf motorcycle in bad weather, you can get it by taking all of the weight off of the bars and by keeping your torso from getting blown to the side with the wind. And I also offered an explanation as to why most long time riders have never noticed it because they are being blown off balance to the wrong side of the bike. An automotive "seat back" style seat in a streamliner will anchor the rider and get the weight off of the bars so the steering can work it's magic.
.
Well I didn't really want to sit and type for hours but your hesitance to read and study other good threads has compelled me. I would link some excellent threads Aerohead has written about the rapidly diminishing returns of Kamm tails but you don't like links so let's skip it.
.

To summarize what we have already discussed in the other threads:
.

Motorcycles automatically lean and corner into a side wind due to the trail in the steering geometry as shown by the dramatic correction of the ecomobile video. As long as the handle bars are not burdened with a terrified rider's rigid arms.
.

Keeping the CG on the roll axis high accentuates this.
.

Keeping the side CoP low helps push the bottom of the bike out from under the top which accentuates this.
.

Streamlining a motorcycle turns it into a vertical airfoil which generates horizontal lift when sidewinds combine with the headwind of forward motion to create an angle of attack. This increases the force beyond what a normal bike would see.
.

The greatest lift of an airfoil is located just behind the max thickness. So "spoiling" with a fence along the top and back section of the tail isn't going to help anything. In fact, that is just adding extra area for the side wind to push on above the CG and will act like the winglets on the tips of modern airplanes that will actually increase the undesirable side lift in that area. Pushing the top of the bike over with the wind the wrong way. It was also noted in another thread, (no link) by someone who made a tail with a sharp edge along the top that it tended toward severe oscillations as it knifed through the air. The rounded top of the ecomobile is much better. Modern Moto GP bike have a Kammed off under belly that almost drags the ground under full compression to carry the streamlined air behind the front tire with a ground effect and to lower the side CoP to the minimum (no photo).
.

Venting the max pressure differential from one side of the wing to the other across the engine bay or the riders lap is the easiest way to make the increased side lift of a streamliner a complete non issue.
.

Bikes corner from leaning and camber thrust. Not from steering and slip angles. The concept of an airplane like rudder on the back of a full aero motorcycle makes an interesting thought experiment for my stance on the futility of an extended fin behind the rear wheel for the purpose of straight line tracking in side winds. A big fin in the back makes the bike into an arrow when it is going straight down the road except for the fact that arrows don't have two tires stuck to the road. The rear tire is fixed and can only roll straight ahead so even with the tail fin, your bike is not really like an arrow. The tail fin can only push the rear of the bike with the wind but it is forcing the rear tire to go sideways in order for anything to happen. Now look at the rudder sticking up high above the cg and far behind it like the low fin is. Which way would you actuate the rudder if you were flying the bike and got hit by a side wind? Would you actuate the rudder to amplify the force of the wind at the rear as you are trying to do with the tail fin? Again, this is not an airplane. The rear wheel is stuck to the ground and the most effective way to generate the lateral force needed to push back against the side wind is to LEAN the bike so it is camber thrusting and steering into the wind. You would actually use the high mounted rudder in the opposite direction that the tail fin provides by trying to rudder the top of the bike, even though it is behind the rear wheel, to ROLL INTO the wind. Think about it. Maybe counter intuitive. The rear of the bike to roll INTO the wind. I also wonder what any yawing action that did make it sideways past the tracking rear tire would do to the trail in the front geometry. If you could have the cg at the steering axis it would tend to stay neutral like the arrow. But the cg will probably be closer to midway between the wheels with a feet forward design. And the yaw force from the tail will have the stuck rear tire patch as the fulcrum. The yaw will pivot on the cg and the contact patch of the rear tire, forcing the steering axis laterally into the wind, causing the trail to counter steer and precess and lean the wrong way, with the wind.
.

But I have seen that the full tail is very quiet to turbulence when following big trucks. And it is the most aero. But makes the bike easier to blow off the stand when it is parked.
.

Longitudinal CoP, contrary to Foale, provides the best use of the steering trail if centered at a point which is low and directly beneath the steering head. This was demonstrated by some HPV guys (no link) by tying a string at various points along a bicycle and tugging on it while someone was riding. Top speed runs on salt flats are an extreme case where the rear tire is completely at the limit of traction and so the vehicle is essentially flying as it skips along the ground.
.

In lieu of venting which still could be done even if the rider is fully enclosed, Spoiling on either side of the nose could also reduce the side lift at a slight compromise of cd if the spoilers are carefully run along the lines of flow. They will have to be much larger than a piece of rope. More like Sheepdog's design at the early part of the thread (no photo) but two of them and moved part way around to the side of the nose.
.

That's enough for now. I will edit this post as time goes by when I think of any other things we already knew and forgot.

I take on board what you say and have said often but Ironside DID report and improvement with that little bit of rope .

How come ?

[sendler]

Originally Posted by PeterS

How come ?

A little rope works a little bit. More would be better.