Team Go Dog, Go! Modified Partial Streamliners

[wobblywalrus]

A few questions...

Is the data adjusted for a 175 mph speed?  Are the drag coefficients and lift reasonable for this type of bike?

The SCTA rule book arrived a few days ago and the bike was discussed with the tech inspection team.  There are only two cases where it does not comply with the rules for 1000cc APS-F.  The FIM tail is about 4 inches too long.  Also, the class record is well over 200 mph so the rule book says I need road race tires.  The tires are new (W) rated road tires that are rated for faster than the bike can go.  I am allowed to run with these shortcomings.  The run is for "time only" with a safety inspection for the speed the bike can do.   

[Koncretekid]

Wow! - -"taped leathers" - 2.7% reduction in Cd.  Also, speed hump was worse than none. 

Were your leathers extremely loose, or in what way were they taped that made that difference?

Where did you get wind tunnel tests done?

Were the subsequent tests after # 5 inclusive of the previous changes?  In other words, was the speed hump in addition to head down and taped leathers?  Ditto the last two changes?

Tom

[wobblywalrus]

The A2 wind tunnel in Mooresville South Carolina was where it was done.

The leathers were very loose.  How loose they were can be seen in the video.

The operator folded the loose parts against my skin and taped the folds down by wrapping duck tape around my arms and legs.

The circuit breaker for the fan tripped during run 1.  It is invalid.

Me sitting in my normal position, with loose leathers, no speed hump, a closed tail, an open hole at the base of the windshield, and an open slot for the side stand is Run 2.  It is the baseline for comparison.

Me crouched down lower, with loose leathers, no speed hump, a closed tail, an open hole at the base of the windshield, and an open slot for the side stand, is Run 3.  Unfortunately I could not see forward from underneath the top edge of the helmet opening in this position.  The seat needed to be lowered so I could see where I where I was going while down and behind the windshield.  This was done a few weeks ago.

The leathers were taped.  A run was made and I crouched about midway down between where I was in Run 2 and 3.  This is Run 4 and it is rejected.

Me crouched down lower like on Run 3, with taped leathers, no speed hump, a closed tail, an open hole at the base of the windshield, and an open slot for the side stand is Run 5.  This is as good as it got.

A speed hump was made from cardboard and duck tape.  It was taped to my leathers behind the helmet.  Me crouched down like on Run 3, with taped leathers, a speed hump, a closed tail, an open hole at the base of the windshield, and an open slot for the side stand is Run 6.

The speed hump did no good and it was removed.  The vertical plate at the end of the tail was removed.  Me crouched down like on Run 3, with taped leathers, no speed hump, an open tail, an open hole at the base of the windshield, and an open slot for the side stand was Run 7.  It can be compared to Run 5.

There is an open slot at the base of the windshield.  It is big enough to stuff a fag pack through on end.  It's intent is to bleed some air into the low pressure area behind the windshield, reduce low pressure there, and consequently to lower the aero drag.  It is an idea I got from a WWII era NACA movie.  Run 8 is me crouched low like on Run 3, with taped leathers, no speed hump, an open tail, a closed hole at the bottom of the windshield, and an open slot for the side stand.  It can be compared to Run 7.

Closing the hole did no good.  The side stand was retracted and the slot for it was taped over.  I do not remember if the hole at the base of the windshield was opened.  Run 9 is me crouched down like on Run 3, with taped leathers, no speed hump, an open tail, an open or closed hole at the base of the windshield, and a taped slot for the side stand.  It can be compared to Runs 7 or 8.

Taping up the side stand slot did no good.  The best combination was during Run 5.                 

[Koncretekid]

Thanks, Bo, that is extremely telling  about what is important about partial streamlining.  I'd love to get my bike down there, but not much chance of that as I am stuck in Nova Scotia (safe) while the bikes are in Colorado.
Tom

[wobblywalrus]

This is a 1941 movie that explains a lot about wind tunnels.  First, log into You-Tube.  Then in the search function type in "Aerodynamics - Forces Acting on an Airfoil."  The movie will pop up on the selection list as a 1957 military video.

The sensors attached to the bike measured horizontal and vertical loads on the wheels.  All testing was done with the bike unskewed to the relative wind.     

[wobblywalrus]

The tail is long on this bike and a rudder was considered.  Lets say the bike is going 100 mph down the track into still air.  A side wind gust of 20 mph hits the bike as it goes past the slot in the mountains.  The angle of attack is arctan 20/100 = 11.3 degrees.
At 175 mph this would be arctan 20/175  = 6.5 degrees.  This is a worst case scenario.  It does illustrate that the angle of attack into the relative wind can be significant.

The movie shows a flat plate canted into the relative wind.  There is high pressure on the windward side of the plate and low pressure on the other.  A rudder would be a canted plate, too, and these pressures would tend to push the tail into alignment with the relative wind.  The fins on a dart or a weather vane do this.  They point the object they are attached to into the wind.

This self aligning feature is great if there are no side winds.  The tail is flicked around to point me in a direction I do not want to go if a gust of wind hits the bike from the side.  To counteract this, I am trying to steer the bike where I want it to go with a lightly loaded front tire contact patch.  This looks like it will be nothing but a problem.  There will be no rudder on this bike.
 

[stay`tee]

rake plays a significant role in correction from the blast of a sidewind,, in that more rake gives slower steering, thus aiding in negating the negative effects of correction,,

 Modern Sportsbikes typically have rake angles in the sub thirtys, great for the backroad Twisties but problematic to sustained high speed wind effected passes on salt

[wobblywalrus]

The Triumph's rake angle is 29 degrees static and it goes up a degree or two when the bike rock back due to relative wind pressure.  That seems to work OK.  I have never ridden a modern sportsbike.

Viewed from the side it is almost impossible to get a NACA profile although there are some talented builders who have.  In bird's eye view, a NACA shape is feasible.  There are four numbers to designate NACA shapes.  The ones that are 00XX describe symmetric profiles where both sides have the same shape.  The last two numbers describe the airfoil's width to length ratio.  A 0012 airfoil would be 12 percent as wide as it is long.

A bike's airfoil length is limited by race organization regulations.  The SCTA rules say "there shall be no streamlining forward of the front edge of the rim."  At the back "... the seat/tail section cannot extend further to the rear than 10 inches beyond the rear edge of the rear tire."  The FIM allows a longer tail.

The airfoil width needs to be enough to enclose the rider and bike.  Width at the shoulders was most critical for me.  Rose measured me while I sat on the bike and I transferred this width and other measurements to graff paper.  Several copies were made of this drawing of bike and rider measurements.

Many NACA profiles were plotted over the bike and rider measurements.  The dilemma arose:  a NACA profile with large angles of convergence toward the tail could be fitted.  The tail would be pointed.  Or, a profile with lower angles of convergence could be used with a truncated tail.

There are complex variations in flow characteristics on each side of a pointed tail at different angles of attack, and this is exacerbated by acute angles of convergence.  Nights of hand calculations and watching NACA videos showed this.  In other words, small variations in the angle of attack would result significant changes in the attached vs detached pressure distributions.  The bike would be unstable and hard to ride in a side wind environment.

There are no movies of truncated airfoils that I could find.  It was hand calcs, only.  There is an engineer saying that "a hand job is better than no job" so that is what I did.  A NACA shape with a truncated tail has a less acute angle of convergence and air flow stays attached to it better at reasonably expected angles of attack.  The attached/detached flow patterns on the tail, and the turbulence patterns behind the tail, are much more consistent at varying angles of attack.  The bike's handling in sidewinds, and especially gusty side winds would be much more predictable with a bobtail NACA shape.  This was figgered out over ten years ago and it seems to be working.           

[wobblywalrus]

This is the NACA movie that showed me the problems with a pointy tail.  Note the Von Karmann vortices.  The movie needs to be reeled back to the start to see the whole thing.  It is midway through if you use the link without doing this.

https://www.youtube.com/watch?v=dUhiDctsyfs&t=322s

[wobblywalrus]

This recent paper, on Pages 15 and 25, shows with a wind tunnel picture what I was trying to do with the truncated tail.  I wish I would have found this paper back in 2010 when I did my design.  It would have saved me a lot of work.  https://lfgss.microco.sm/api/v1/files/04ab9d14181f94ab35ee081bc22abae99ae72b17.pdf

[Koncretekid]

An interesting article, for sure.  Realize, of course, that it is the work of a commercial enterprise (Trek bicycle manufacturer).  The most amazing conclusion is that they were able to get negative drag at yaw angles between 10 and 15 degrees.  This implies that if we were able to replicate the KVF shape that they are hoping to patent, that we could go faster with a head wind at 10-15 degrees off the front of our machines than we can with no head wind.

 "At the core of its low-drag performance is the Kammtail Virtual Foil (KVF) tube shape, which itself is the result of a nine month project dedicated to low-speed airfoil development. The KVF is an unconventional aerodynamic shape proven to have incredibly low drag, with a light, stiff profile. In fact, the Speed Concept?s KVF tubes themselves are proven to have negative drag (thrust) in a wide range of common wind conditions. "

Unconventional?  I believe that the Kamm tail has been around for years. 

However, that KVF shape looks a lot like the profile that we are trying to perfect.



Tom

[wobblywalrus]

The wind tunnel pictures illustrated what I was attempting to do.  They probably are legit.  It is possible to do calculations that show negative drag.  I have done it.  The problem was that I was using simplified assumptions.  Some research showed that to correctly figure drag out requires at least two of Newton's laws, Bernoulli's equation, and some Euler math.  There is a book by a Boeing Engineer that give details on how to do the calcs correctly.  If you are interested I can find the title and ISBN number.

My work was done 1n 2006, 2007, and 2008.  There was not a lot of info on the i-net at that time.  There is now, and most of it is about wind generator propellers.  The truncated airfoil helps them, and being props there is an angle of attack involved.  The physics is real interesting 'cause the Reynolds number of a prop blade increases with distance out toward the blade tip.  This stuff is 10,000 rpm problems and my brain has a 5000 rpm redline.  I reach for a beer to put into the mental radiator before I figure anything out.       

[wobblywalrus]

This is the tufts test.  Note the attached flow on the front fairing, the detached flow on the tail, and the turbulence behind the rider. 

https://www.youtube.com/watch?v=tqyDQ_5i9uo

[Lemming Motors]

This stuff is 10,000 rpm problems and my brain has a 5000 rpm redline.  I reach for a beer to put into the mental radiator before I figure anything out.     

   

[gowing]

Questions from a aero novice:
Looking at the tuft test video, turbulence behind the riders legs seems to be pretty extreme.
Would widening the bodywork behind the riders legs (filling the void) smooth out the turbulence?

I know that there are rules limiting the height of the bodywork to the top of the seat, but it also looks
like the riders butt is the source of a big low pressure area.
How would one address that area?