Team Go Dog, Go! Modified Partial Streamliners

[wobblywalrus]

During my early 20's race tires were tried for street racing by some of my friends.  They almost killed themselves so I did not use them.  The problem was lack of grip.

These videos I am watching during lockdown.  They show and discuss race tire vs track temperature vs performance.  My friends probably did not get the tires hot enough to grip.  These racers pre-heat the tires prior to racing and do a warm up lap to get them ready to race.  Some of these videos are in Spanish and most are in English.  The lady doing the commentary is Suzy Perry.  She was one of the first women that presented the races and has been doing it for over 20 years.   

https://www.tokyvideo.com/series/moto-gp-2020-full-race

[manta22]

WW;

When I was drag racing my '65 Pontiac GTO, I used M & H Racemaster slicks but one time I was in a hurry and did not replace them at the track with my street tires. They were great on the street until it started to rain. I drove home at 15 mph....

[wobblywalrus]

That car must'a been fun to race.  There were a lot of drag strips in the old days.  The tracks were dry in the first five races on those videos and those are what I have watched until now.  They used soft, medium and hard slicks.  Hopefully it will rain for a race and I can see how they set up the tires. 

[wobblywalrus]

The featured bike in this article, the John Player Norton, has a fairing that was developed using extensive wind tunnel testing.  Note how it gives the rider good coverage and the trailing surfaces, just before they end, are parallel to the direction of wind flow.   

https://www.motorcycleclassics.com/classic-british-motorcycles/john-player-norton-monocoque-replicas-zmmz13sozbea

[wobblywalrus]

This article shows the current MotoGP fairings.  There is much less coverage and the trailing edges are angled to the wind flow.  This seems like backwards progress from that 1070's Norton.  The new fairings look to be inefficient.  I asked about this during the wind tunnel visit.  The answer was to keep the fairing large so as to give good coverage.  "The fairing is more streamlined then you are" was the answer I remember hearing.

https://www.crash.net/motogp/feature/928481/1/wings-chins-remain-under-stricter-2020-motogp-aero-rules   

[wobblywalrus]

Surface roughness vs smoothness was discussed at the wind tunnel.  The tail section may have a small area of attached flow with a turbulent boundary layer.  Most or all flow will be detached turbulent flow.  No appreciable benefits will be gained by a smooth surface in these conditions.  The rivited plate surface will be used.  It is easy to make and repair or modify and it is light and strong.

F = ma or force equals mass times acceleration.  Reduction in the force to overcome aero drag allows the bike to go faster and this means the mass of air disturbed by the vehicle must be minimized as well as the acceleration of the disturbed air.  Acceleration is a change in air velocity or in the direction of air flow.  Creating a wake vortex or disturbance accelerates air in both velocity and flow direction.  Wake disturbance needs to be minimized.  Tail shape does this and not tail finish smoothness.

The vehicle from overhead view was designed to conform to a NACA shape.  The vehicle as viewed from ahead and the sides is a "do the best as I can" shape.  The rider is part of the vehicle during the design.  It was developed using years of experience and book learning before it went into the wind tunnel.

The wind tunnel cost big money to use.  Most of us can afford to use it to validate our design and to test easily made modifications, like I did.  It would take mucho dollars to develop a shape in the tunnel.

Tufts of yarn were attached to the bike to show flow direction across the surface.  The first tunnel test was used to photograph the yarn tufts during air flow.  Also, a smoke wand was used.

"The best modification you can make is to get your head and shoulders down and behind the fairing" I was told after the smoke test.  The seat pan was lowered to do this.  It is about a millimeter above the frame tubes and it is an inch or two lower than it was before.  It was narrowed, too, to allow my knees to tuck in better along the bike sides.

Posting pictures with the narrative is problematic after the website crash.  The post following this will be an attempt to post pictures.       

[wobblywalrus]

The first picture shows the old seat pan.  It is higher and wider than the new one.  The new pan is in the second picture.  It is so close to the frame that there is no room underneath the front for bolt heads.  Countersunk head screws are used with acorn nuts on top to hold it together.  The seat pad will prevent nut-to-nut contact between me and the bolts.   

[wobblywalrus]

The FIM regulations say the tail upper surface cannot be higher than 150 mm from the seat.  The tail is redone to lower the top.  The aluminum is 0.019 to 0.020 thick and there are either flat surfaces or single radius curves.  A single flat sheet could have been formed to cover the top.  It would be easily dented.  Instead, the sheet is cut up into scales.  Each scale is pounded on an anvil with a hammer on both sides and then flattened with a rubber mallet and then sandwiched between a wood block and the anvil.  The block is pounded down to further flatten the metal.  Then, the piece is bent to curvature of left flat before being riveted on.  The work hardening from the pounding and the overlapping seams make the surface strong and dent resistant while using thin aluminum..

[wobblywalrus]

The bike is primarily built to run as an FIM entrant.  Constructing it to meet USFRA and SCTA requirements, too, seems like a good idea.  The SCTA classes page, and bike tech checklist are available on the SCTA website.  The bike rulebook could not be found and I need some help to find it.

It is nice to see that the site is up and functioning and that Bob and Slim are OK.   

[salt27]

The bike is primarily built to run as an FIM entrant.  Constructing it to meet USFRA and SCTA requirements, too, seems like a good idea.  The SCTA classes page, and bike tech checklist are available on the SCTA website.  The bike rulebook could not be found and I need some help to find it.

It is nice to see that the site is up and functioning and that Bob and Slim are OK.   

Bo, just go to the SCTA or USFRA website and order a rule book, same book.

  Don

[wobblywalrus]

The bike was run naked and streamlined in 2018.  It went 129.02 and 149.63 without and with the tin.  The sheet metal helps a lot.  The wind tunnel guy said "Put on as much streamlining as you can before the testing.  It is a lot quicker and easier to take it off than to put it on."   This adding was done after the 149.63 run.  Quite a bit of thin aluminum roof flashing, duck tape, and cardboard was used.  The drag coefficient for the first test with all of this in place was 0.494  The smoke wand showed a lot of power robbing turbulence behind me.  The second test was made with me holding my chest lower down onto the fuel tank.  The drag coefficient dropped to 0.457

It was hard for me to hug the tank and I doubt if I could do it during a race.  So, the seat pan was lowered a little more than an inch, the bum stop was moved back an inch, and the front of the seat pan was narrowed so it is easier to keep my knees against the tank.  This I did last week.

My weight was between 210 and 220 pounds when my leathers were originally made.  Now I weigh a lot less.  The scrotum like folds of the excess cowhide caught the wind.  Duck tape was used to tighten up the leathers during the tunnel work.  The operator mummified me.  The smooth leathers dropped the drag coefficient down from 0.457 to 0.445  Bates remeasuerd the new slimmer version of me and altered the leathers.

A speed hump was made on my leathers behind my head using more cardboard and duck tape.  It raise the drag coefficient from 0.445 to 0.463  A speed hump does not work for me.  The speed hump was removed.
   
The tail end was open during all of my racing including the 149.6 run.  It was closed with roof flashing during the initial tunnel tests.  The drag coefficient went up from 0.445 to 0.453 after the tail was opened.  The tail was closed up with 0.020 thick sheet aluminum this week.

There are power robbing turbulence vortices behind the tail end.  Closing the tail reduced the size of this turbulence, is my best guess.  The next post will have pictures.         

[wobblywalrus]

Roof flashing is great to make mock-up parts and patterns.  It is cheap and easy to work with.  It is far to thin to use for a final product.  This is the end section used for tunnel testing and the final end section in place.

[wobblywalrus]

Dzuz fasteners were used to hold the fiberglass sidecovers onto my old BSA.  They worked great if I remembered to push them down to lock.  Otherwise the side cover flew off while riding.  Nuts-n-bolts have a similar issue.  They do the job if someone remembers to tighten them down.  Both Dzuz fasteners and screwed ones are not obviously loose during a visual inspection.

Some guy used pin and clip fasteners to hold down the hood on his race car.  I copied the idea and use it for all body panels.  It is obvious from a glance if the connection is complete.  It is more "idiot proof" than other fasteners.         

[manta22]

WW;

Where do you find those?

[wobblywalrus]

Google "clip and pin hood latches" to see lots of manufactured versions.  My ghetto style version uses pins that are stainless steel bolts with the threads ground off and holes drilled through them, stainless steel washers, and safety pin clips.  All can be got at Ace Hardware.