Team Go Dog, Go! Modified Partial Streamliners

[wobblywalrus]

The open area for the rider creates turbulence on the tail.  There is no way the tail can be designed to prevent all tuft fluttering.  At best, turbulence can be minimized and not eliminated.  The smoke and tuft tests were done when I was wearing baggy leathers.  Wrinkles at the knees and arse hung out into the breeze.  Hopefully that will not happen now.

The tail cannot be higher than 150 mm above the seat pan.  The area behind my back cannot be enclosed.

There were plates on the sides behind my knees.  There was nothing behind these plates except braces.  Now the voids are boxed in.  This should help to reduce turbulence.   

[wobblywalrus]

These are the layout drawings for the 2010 fairing and tail redesign.  This bike is short in length, tall, and wide.  It is not the ideal starting point for a land speed motorcycle, for sure.

[wobblywalrus]

The NACA shape is shown.  It sort of resembles the bike below the nose.  Extra room is needed for the nose and it cannot extend forward beyond the front rim.   A rounded shape is chosen.  It allows air to flow off of the nose and directly back to the sides of the tail.  The trailing edges of the nose and windshield are parallel, or nearly parallel to the direction of travel, and this is needed.  Noses with more triangle shapes push air off to the sides and away from the tail.  This reduces the aerodynamic advantages of the tail.

The photo shows the bike from the front.  It was measured to determine the frontal area.  The picture was taken at a distance, enlarged, and cropped.  This reduces the parallax distortion as compared to a closeup shot. 

[wobblywalrus]

This is a side view.  The table is a crude way that I keep track of the aerodynamics on a year-by-year basis.  The rear wheel horsepower reading from the dyno is multiplied by 0.85 to get horsepower at Bonneville.  The rolling resistance loss horsepower is calculated for the speed on the timing slip.  It is subtracted from the rear wheel horsepower.  The remaining horsepower is assumed to be aero drag horsepower.  The formula at the bottom of the page is used to calculate the aero drag coefficient.  The "175281" multiplier is adjusted to account for the thinner air on the salt flats.

The lowest aero drag coefficient was in 2014.  That was when the tail with the higher hump was used and it is shown in the side view photo.  The regulations outlawed the high hump and it was trimmed down to the flat topped tail shown in the wind tunnel movies.  The high hump helped the aero a lot and most of my recent work is getting it back to where it was in 2014.   

As seen on the table, the last few years have been a struggle to get more speed.     

[wobblywalrus]

These next posts are about using the wind tunnel data.  The main reference is "The Racing Motorcycle" by John Bradley, Volume 1.  The first task is to calibrate the rolling resistance curve based on the wind tunnel drag coefficient.

Page 1)  The bike with me on it was weighed in 2017 and it was a hefty 755 pounds.  A diet and some shop work reduces this 57 pounds, to 698 pounds, total.  This weight and the tire pressure are put into a rolling resistance equation refined by Kevin Cooper in the early 1970's.  A 125cc Can-Am was used on the Bonneville Salt Flats to collect data.  The equations were originally developed by a fellow named Hoerner in the 1960's.  The Goldenrod streamliner used the original Hoerner work during its development.  Bradley discusses this and includes references to the older research papers.

Page 2)  The rolling resistances directly from the equations are listed.  Both are on pages 172 and 173 of Bradley's book.  These equations are what I used for the table in yesterday's post.  Experience has shown they are an overestimate of rolling loss.  The Triumph has a very efficient drive system and uses radial tires, rather than the bias ply ones used in the 1970's.  That might be the reason for the high calculated values.

A run was made in 2018 with streamlining similar to Run 2 on the wind tunnel spreadsheet, the "Baseline" run.  Scooter Grubb took a picture of it and I had my head up high just like in the wind tunnel photos.  The speed was 149.61 mph.  No big problems happened during that run so it will be used for curve calibration. 

The 2018 dyno horsepower is converted to atmospheric conditions during that run.  The aero drag for 150 on the spreadsheet is converted, too.         

[wobblywalrus]

Page 3 has the horsepower and drag correction factors.

Page 4 has the wind tunnel aero drag.  The tunnel data spreadsheet that was posted a few days ago has an EXCEL error in calculating drag and some other values.  This sheet shows the correct values.   There is a reason that I do hand calculations.

[wobblywalrus]

Page 5)  The rolling resistance for the 2018 run is 16.2 horsepower.  The same calculated by Cooper's equation is 18.1 hp.  Dividing the two gives the correction factor.  The tire pressure or bike weight may change in the future.  If so, Cooper's original equation will still be used to calculate rolling resistance with the 0.895 conversion factor.  The factor will be reexamined after 2021 Speed Trials using the 2021 timeslip, dyno results, and bike weight with the tunnel Run 5 aero drag.

Page 6 shows the two rolling resistance drag curves.     

[wobblywalrus]

The safety inspector at World of Speed wants to know how fast I expect to go.  Also, there is the need to figure out the optimum sprocket combination.  Additionally, the tunnel data shows that there are issues I need to address if I go a lot faster than I am now.  The next step will be to figure out how fast I will go at the Speed Trials and World of Speed. 

Page 7)  The bike will be built to tunnel Run 5 configuration.  Spreadsheet Run 5 aero drag values are converted to typical Bonneville atmospheric conditions.  The rolling resistance is added to the aero drag to get the anticipated total drag.

Page 8 shows the conversion factor.  The tunnel uses the Motorsports Standard Atmosphere (MSA) and the dyno uses the Standard Day (STD).  They are not identical but similar.  Some of the newer SAE atmospheres are quite different than either.  Although I could have used a 0.820 factor throughout this work, it is good practice to be careful and to do all of the conversion factors.     

[wobblywalrus]

Page 9)  The graph.

Page 10)  The 2018 engine horsepower is used for a first estimate.  It looks like all of that weight loss and aero work is good for 4 mph more than 2018.  Unless some motor work is done...

Next will be a look at the tunnel data with a 165 mph target speed.  An aerodynamic expert on the forum has been discussing some of this with me and developed some graphs.  This is a big help.  I am not the brightest bulb on the X-mas tree, so any advice is welcome. 

[Old Scrambler]

Bo....very informative work your doing for us

The side view in the wind-tunnel tuft video VERY STRONGLY shows that you should be able to lower your hand-grips by several INCHES......thereby lowering your head and reducing frontal area. The edge of the windscreen will likely need to be trimmed to fit your helmet.......remember to push the chin-bar upward to increase the view area. The hands foreward and lower will also move a slight amount of weight for improved frontend bias. Some fairing trim and detail will likely be the hardest work.   

[wobblywalrus]

Thanks, Dennis.  Next winter I will look at lowering the fairing top.  I am making a chin rest so I can keep the helmet viewport tilted up and my head down.

The wind speed is adjusted to 165 mph.  This is maybe 5 or 10 mph higher than the bike will go.  The side loads are shown on the spreadsheet.  Theoretically, there should be no side loads if the bike is perfectly symmetrical and I am centered while sitting on it.

The tunnel test and front view photo were taken before the alignment jig was developed.  The jig was shown four or five months ago on this build diary.  The bike was almost always out of alignment before the jig was used.  Note how it is tilted to one side in the photo.  This can cause side forces in the wind tunnel.

In the jig, both wheels are clamped between the channels and measured with a spirit level to make sure they are vertical.  All bolts holding the bike together are loosened.  A plumb bob is dropped down from the center of the steering head or a central location on the frame near the head.  The bike is twisted around in the jig, as needed, until the plumb bob is exactly halfway between the channels.  Then, the bolts are tightened up and the bike is in alignment.  This should eliminate or reduce side loads.

[wobblywalrus]

The attached shows the X-14 Shoei helmet that I use in the wind tunnel.  Aerodynamic performance was part of its design objectives.  Note how the top of the airfoil at the back of the helmet is horizontal.

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

[wobblywalrus]

The top of my X-14 is not horizontal in the wind tunnel movies and my head was higher than optimal.  The duckbill at the back is sticking up and it is creating turbulence.  This tilt gets worse when my head position is low.  I should have foreseen this and brought a round helmet to the tunnel test for comparison.

This Cd comparison chart was made by Woody.  It was nice that he helped me with this.  The biggest drag coefficient differences are due to head position with lower the better.   Rider posture is important for drag measurements and it is impossible for me to sit on the bike exactly the same way during each test.  The measurements with taped leathers, the speed hump, the open tail, and the covered sidestand hole are very similar and a small change in my crouch could influence those results as much as anything.  Really, those tests should have used a dummy like in the Shoei movie rather than a smart guy like me.  The dummy would have a more consistent seating position.

 

[wobblywalrus]

There is lift on the front end due to the air drag.  The attached table shows this.  The bike steered OK in 2018 with 46 percent lift.  That was when my head was in a higher position.  With it lower, the same lift occurs at around 165 mph speed.  The fairing is OK, liftwise, for the speeds the bike can go with a naturally aspirated engine.  The front end is almost off of the ground at speeds like 230 mph.  It would lift completely off the salt if I sat up in the seat at the end of the run.

What I learned from the tunnel test.  The bike shape is the most important thing and it is basically OK.  Finish is not important.  I was going to spend a lot of time making the surface smoother so the tunnel work saved me a lot of effort.  Riding posture is critical and the lower the better.  Lift will be an issue if I use forced induction or nitrous to get a lot more speed.  Side force may continue to be problem.  Another wind tunnel test is needed to verify the aero is OK before use of the blower or laughing gas.

In the early years I sat up at the end of the run and used air braking to slow down quickly.  Often that resulted in a massive speed wobble.  Trial and error told me to get below 100 mph before sitting up.  What I learned from the tunnel work is that, by sitting up, I was moving the center of pressure forward and upward.  This resulted in instability. 

The cost and inconvenience of the work was justified.  It gave a bit more speed an a lot more safety. 

[Old Scrambler]

We are running at similar speeds.......my best is 147+........I gently apply my 'air-brake' after a few seconds of slowly closing the throttle.....never a handling problem......but my forward weight bias is thought to be several points greater than yours.