Bonneville and Weight.....

[1FATGMC]

   

( RICK'S WEB SITE  ) ( Check out his runs on video  )

Guys I've been one of the ones preaching weight doesn't matter a b'ville and weight is a good thing, but I now have reason to wonder about that with my car.  

I was talking to Rick Yacoucci shown above with his motorcycle motor streamliner.  He has run over 330 mph and said that his exit speed at the end of the 5 mile was greater than his entry speed and he was still accelerating.  He has the traction he needs, but not enough course.  So he has to view it as a 5 mile drag race and tries to accelerate as fast as he can the whole 5 miles.  So in his case the weight is hurting the acceleration rate and he is unable to reach his top speed that would be limited by the  power needed to overcome the air resistance.  If he would have peaked by the end of say the 4th mile and would have held that speed through the 5th mile then his weight wouldn't of effected his top speed.

If I end up with too much weight and can't accelerate to top speed by the beginning of the 3rd mile (and last mile) on the short course then I'll be limited in reaching the true top speed potential of the car by the car's poor acceleration due to the weight (and also somewhat the aero).  Now even if that happens, but I'm able to run 175 in the first quarter of the 3rd mile on the short course I could move to the long course where I would have more time to accelerate.  Streamliners have an advantage since they can choose to run the long course with out having to qualify on the short course.



( Other Bonneville Pictures  )

Now weight on some cars is vital and they have to have it.  When the Burklands ran the stude in the picture above they were not allowed to have the rear spoiler for down force.  They had a thick steel plate for the whole belly pan and I believe over 60 gallons of water on board for weight (over 1000 lb. total).  After the rules allowed the addition of a rear spoiler on cars in this class all of that weight wasn't needed.  The reason the weight is needed or other down-force is that if the speeds of the car get high enough the aero pressure on the front of a car gets so great that the tires loose traction trying to push the car through the air.  Remember the tires in most cases are only 5 to 6 inches wide.  It is like putting the nose of your car on a concrete wall and putting water/bleach under the rear tires and see how easy it is to light up the tires.

If you take a high speed roadster that is shaped like a brick and you can't run a spoiler on it you are going to have to add a lot of weight to make it stick.

So every car and situation is different.  We are making provisions to add weight to Hooley's stude this year, but I don't think we are at the place where we need it yet and the car is pretty light at 3000 lbs.

Tom Burkland told me someone once told him something to the effect "if your tires spin add weight and if they don't spin add nitro"   .

c ya, Sum

[Elmo Rodge]

Good point, Sum. In the design of my Tank I'm paying close attention to weight and weight bias. I want just enough on the *-end for bite but enough forward to stay ahead of the center of pressure. By the way, the move to Utah has begun. Richfield. Just got back from taking another load up yesterday. Wayno

[Crosley.In.AZ]

Very good post....... it is a large equation on weight needed and acceleration desired/needed.

[av8]

This makes my head hurt!  

I recall being astonished when I learned just how much ballast the slippery Studebakers were running to help them grab hold of the salt. We added 240 pounds of steel ballast to "Salt 'N Peppers" in 1995 to settle it down and improve grip as it approached 150 mph. Clearly it wasn't enough because the car continued to do its little salt dance at that speed.  

In retrospect, with what we've since learned about going fast and steady at Bonneville, doubling or even trebling the ballast probably would not have helped much, and in fact might have made the little Nash treacherous by increasing the problem rather than solving it. Kent Fuller pegged the problem about the time Vern Tardel sold the car: As clean and low as the little racecar was, there was nothing to prevent air from getting under it and lifting it to the extent that traction was reduced. The change in front-to-rear weight bias, from additional ballast in the rear, might possibly have turned the Nash into a real handful at 150 mph.

Fuller recommended a fix that now seems so obvious: A rigid vertical air dam extending down from the front bumper to within a couple of inches above the racing surface, to prevent air from getting under the car and lifting it.

Operating as I will be in the lower speed registers, and with any form of air cheating not allowed, I'll do everything I can to exclude air from getting under my truck, and will probably carry several hundred pounds of ballast ahead of rather than over or behind the rear axle so as not to lever the front end up at speed.

Mike

[1FATGMC]

This makes my head hurt!  

I recall being astonished when I learned just how much ballast the slippery Studebakers were running to help them grab hold of the salt. We added 240 pounds of steel ballast to "Salt 'N Peppers" in 1995 to settle it down and improve grip as it approached 150 mph. Clearly it wasn't enough because the car continued to do its little salt dance at that speed.  

In retrospect, with what we've since learned about going fast and steady at Bonneville, doubling or even trebling the ballast probably would not have helped much, and in fact might have made the little Nash treacherous by increasing the problem rather than solving it.

Mike it probably wasn't just the air getting under the car, which was probably some of it.  You were probably moving the center of gravity further back.

On these cars there is the "center of pressure", think of that as the center of the area of the car as viewed from the side.  They add fins on the back to move the center of pressure rearward as that adds more area in side view further back on the car and is also flat.  With the Nash the center of pressure is probably about 2/3's of the way back on the the door (back past the middle of the Nash, front to back) as the top goes back quite a ways.  On your pickup I'll bet the center of pressure is probably a little forward of the middle of the truck front to back with the bed in the back not adding much area from the side.

You want the center of gravity forward of the center of pressure.  Think like an arrow.  Heavy point in the front and the feathers in the rear move the  side view area rearward.  

If the center of pressure and center of gravity are in the same place front to back on the car and the car is upset by wind, tire spin, etc.  the car can go into a flat spin, spinning about that common point.  You see this pretty often there with the roadsters.

Worse if the center of pressure is ahead of the center of gravity and the car is upset it will be real hard to keep going straight as the front of the car will want to take off in different directions.

   

We finally understood this concept last year and made the spill plates (the vertical pieces on each side of the rear spoiler) as large as the rules would allow.  We also have the rear spoiler about as large as allowed, although at this time we aren't running much angle on it at the rear.

If you have to add weight for traction you are going to probably have to add it so you are increasing the weight on the front as much as the rear.  Not to hold the front down, but to keep the center of gravity in the same place on the car.  It would be tempting to hang is as far behind the rear axle as possible, but this could cause real handling problems as it would move the center of gravity rearward.

With your pickup I would work to get it as low to the ground as possible.  As you said the rules don't allow you to do much.

c ya, Sum

[av8]

Mike it probably wasn't just the air getting under the car, which was probably some of it.  You were probably moving the center of gravity further back.

Yes, the CG was definitely moved rearward with the addition of the ballast which was well aft of the rear axle. That's why I will locate my ballast forward of the rear axle.  

On these cars there is the "center of pressure", think of that as the center of the area of the car as viewed from the side.  They add fins on the back to move the center of pressure rearward as that adds more area in side view further back on the car and is also flat.  With the Nash the center of pressure is probably about 2/3's of the way back on the the door (back past the middle of the Nash, front to back) as the top goes back quite a ways.  On your pickup I'll bet the center of pressure is probably a little forward of the middle of the truck front to back with the bed in the back not adding much area from the side.

I'd place the center of pressure at about the rear cutline of the doors -- the B pillar. That area just aft of the cab and ahead of the rear fenders is an unknown for sure. It would be interesting to see what goes on there, either with smoke or tufting in a wind tunnel.

You want the center of gravity forward of the center of pressure.  Think like an arrow.  Heavy point in the front and the feathers in the rear move the side view area rearward.  

If the center of pressure and center of gravity are in the same place front to back on the car and the car is upset by wind, tire spin, etc.  the car can go into a flat spin, spinning about that common point.  You see this pretty often there with the roadsters.

Worse if the center of pressure is ahead of the center of gravity and the car is upset it will be real hard to keep going straight as the front of the car will want to take off in different directions.

I'm confident the CG will be well ahead of the center of pressure, due in great part to the nature of a pickup truck.

We finally understood this concept last year and made the spill plates (the vertical pieces on each side of the rear spoiler) as large as the rules would allow.  We also have the rear spoiler about as large as allowed, although at this time we aren't running much angle on it at the rear.

If you have to add weight for traction you are going to probably have to add it so you are increasing the weight on the front as much as the rear.  Not to hold the front down, but to keep the center of gravity in the same place on the car.  It would be tempting to hang is as far behind the rear axle as possible, but this could cause real handling problems as it would move the center of gravity rearward.

This is why we're placing the ballast well ahead of the rear axle. I'm currently thinking about a 1/4-inch thick steel "platform" at the front of the bed that will serve as mount for the fuel cell, the batteries, and a ballast rack.

With your pickup I would work to get it as low to the ground as possible.  As you said the rules don't allow you to do much.

That's been the plan all along, Sum. Fuller has been drumming this into my head ever since we began talking about a pickup project.

Mike

[1FATGMC]

I'm confident the CG will be well ahead of the center of pressure, due in great part to the nature of a pickup truck.

This is why we're placing the ballast well ahead of the rear axle. I'm currently thinking about a 1/4-inch thick steel "platform" at the front of the bed that will serve as mount for the fuel cell, the batteries, and a ballast rack.

A pickup will probably have the center of pressure farther to the front compared to almost any other vehicle, since there isn't a lot of side area past the cab.  This will move the center of pressure and center of gravity closer together.  A coupe for instance would also have it further forward than say a sedan or station wagon.  Like in Tony's case I would pick one of his wagons from his Crosley fleet for b'ville.  

I would be tempted to have provisions for additional weight, but not put any in unless it is needed.  I can't remember ever seeing a pickup spin at b'ville   .

c ya and it is going to be fun,

Sum

[WZ JUNK]

In addition to the large spill plates that Hooley made, I made some additional panels that fit under the rear quarter panels behind the rear wheels to increase the side area.  We were trying to make up for some of the area we added to the front profile when I made that huge ugly scoop that works so good.

I know the added weight at Bonneville can make the car go faster but it is so hard for me to add weight to a car.   We have talked some on how and where to make provisions for the ballast but I do think the final decision is made.

[WZ JUNK]

In addition to the large spill plates that Hooley made, I made some additional panels that fit under the rear quarter panels behind the rear wheels to increase the side area.  We were trying to make up for some of the area we added to the front profile when I made that huge ugly scoop that works so good.

I know the added weight at Bonneville can make the car go faster but it is so hard for me to add weight to a car.   We have talked some on how and where to make provisions for the ballast but I do think the final decision is made.

John

http://purplesagetradingpost.com/sumner/hooley/hooley-2005.html

http://purplesagetradingpost.com/sumner/bvillecar/bonneville-Index.html

[Crosley.In.AZ]

A pickup will probably have the center of pressure farther to the front compared to almost any other vehicle, since there isn't a lot of side area past the cab.  This will move the center of pressure and center of gravity closer together.  A coupe for instance would also have it further forward than say a sedan or station wagon.  Like in Tony's case I would pick one of his wagons from his Crosley fleet for b'ville.  



Sum

The Crosley would need a 50 or 60 mph head wind to get into trouble aerodynamically if the car could run 90mph too.