Weight and Bonneville:

[Sumner]

Sumner and anyone who wants to help,
Here are some views of the current scoop.  The engine is a 258 cid GM V6 with Hilborn EFI, naturally aspirated.  We run in E/STR and after two years of hard work finally set a new record of 168 plus.  And since this thread started with an inquiry about weignt, we added 500 lbs of lead between the frame rails and in the middle of the car.  The result was the ability to use full power on the short course.
Robin

Robin how many square inches is the scoop??

Is the volume increasing from the inlet backwards??

Do you think you are getting turbulence from the top of the grill shell at the inlet point??

I think the rules allow it and if so I would try and move it down into the top front of the grill shell and sticking out into clean air.

I've heard 2 lbs. of possible boost at 200 from a properly designed scoop, so at 170 you might only be gaining 1 to 1 1/2, but still worth going after.

On our last run we data logged a hair over 8 lbs. of boost, so I'm thinking we were only making 6-7 with the blower.

c ya, Sum

[hotrod]

You may want to look at this NACA report:

http://naca.larc.nasa.gov/reports/1927/naca-report-247/naca-report-247.pdf

It lists maximum theoretical ram pressure for speeds up to 1000 mph.
As you can see maximum theoretical ram pressure (incompressible flow) at 200 mph is 102.326 lbs/ft^2 or about 0.71 psi.

Best probable pressure recovery is about 70% so your realistic ram pressure at 200 mph ~= 0.49 psi.

Best pressure recovery is supposed to happen with diverging angles of about 8 degrees inside the inlet (angles can be a bit higher with guide vanes).

To get full pressure recovery you need to nearly bring the air to rest.

John Bauman of Chrysler designed the boundary layer scoop they used in drag racing in the late 1960's and details of that scoop design is included in one of the Chrysler direct connection books. (I have a copy and would be willing to scan those pages if you think they would be useful).

Also simply putting a flat plate on the bottom lip of the scoop, might help as you probably have a bow wave of air coming off the radiator and its true velocity vector (direction) might be very much upwards at your scoop location and striking the inlet at a significant angle. (tuft test would help determine that).

If so you could "droop snout" the inlet so its inlet opening is normal to the air flow at speed or put a splitter plate on the bottom edge of the scoop to send clean air flow toward the inlet.

Larry

[PorkPie]

The cross section is fixed to allow room for growth on the drivers part  and the aero is yet to be determined


You mean a McDonalds aerodynamic shaped body......also called solid... or as some people said.......belly tank body.......  ....fixed to every engine up to 61 cubic inch.......

[PorkPie]

Do you think you are getting turbulence from the top of the grill shell at the inlet point??


Sum, give me some time to prepare the picture....will be done to the end of the week.

[hawkwind]

Small displacement and power can only fixed with proper aerodynamic and cross section

PorkPie could you please expand on this statement , I think I understand what you mean ,but again I may be way off track
Gary

[Cword]

Maybe Mike will elaborate on where and how much weight they added to the 1149 car to get them over 200 .

c ya, Sum

Thanks to Lockhart Enterprises (801) for sourcing the weight for us and Tom Burkland for sourcing the mounting holes.  We were finally able to see the top side of 200 this year.
We came down with more power than we'd ever had on hand before and then proceeded to struggle to reach 190 for the first few days  of Speed Week.  Until the light came on and we clued in to the traction problem.

While in line Tuesday we were introduced to Jerry Lockhart who arranged to source some steel plates for us. We ordered up 6 one inch thick 6 inch by 36 inch plates. We already had mounting points on the car for ballast, and these would fit easily.  
The plates arrived Wednesday and we spent the day drilling (thanks to the Burklands for the holes).
The plates added near 400 pounds to the truck. We also had scrounged about 150 pounds of smaller steel (from 974) and lead from 6666 and others, which was all fastened down in the truck box.

The first pass with the weight in place showed us we'd been lacking traction.  Our 2-1/4 speed went from a best of 177 without weight  to 197.  

The plates that the Lockharts sourced for us were mounted 3 per side under the cab of the truck, as shown below.


Mike

[PorkPie]

PorkPie could you please expand on this statement , I think I understand what you mean ,but again I may be way off track
Gary


It means.....if you got no power against the wind.......you better gave him no resistance.....

Or you can say..........with less power get a shape which is the aerodynamicly best to the necessary cross section........sometimes a smaller cross section could be wrong when you kill therefore the aero shape.......so we got a again a compromise

the smallest number from drag and cross section together gives you the right speed......if you got also enough length....you can go faster....

[Richard Thomason]

You can only apply the amount of forward thrust that is the product of weight (whether actual scale weight or the combination of scale weight and aerodynamic loading) on the driving wheels times the coeff. of friction of the tires. Big HP without load equals spinning tires. That was one of the main reason we went with front wheel drive, so we would have max weight on the driving wheels and keep the CP way behing the CG. We still have had to add weight, oh well.

[LittleLiner]

Interesting and informative thread.  

Adding weight to gain traction sounds good but I am wondering what effect adding weight can have on the severity of a crash.  

I don't pretend to imply that I have a clue about the physics involved but I am guessing that additional weight will add to the severity of a crash.  

Consider two cars with the same aero characteristics (Shape, size, cd, frontal area, etc), one weighing 2000 pounds and other weighing 4000 pounds.  Both going 250 mph and crashing.  What is the effect of the additional weight?  All other things remaining equal (roll cage design and structure, belts, helmet, etc) can we expect that the driver of the lighter car will have less injuries?

I don't know the answer but am interested in other opinions . . . .

Thanks

[PorkPie]

LittleLiner,

this questions is not complete and also a little bit strange, too - normally we try to stay on the wheels .

The question is not complete, due to this that the kind of incident is missing. But this is not necessary to get you an answer.

It's doesn't matter if you be in a light or heavy car, the reaction, movement of the car depends how the car crashed .
The weight on the heavy, placed on the right place, can keep the car on the wheels, due to a lower weight centerpoint.
A light car can loose the contact to the ground faster. A heavy car can move longer uncontrolled, due to this that the weight is still pushing.

So you see, that there is no answer, due to the not knowing the cause of a so possible situation .

By the way - much more critical is a aerodynamic mistake in the shape of the racer - the result will be a nightmare. So mistakes produce flips or hard rollings - the #77 lakester went out of aerodynamic balance - we know the result.

[John Burk]

My opinion on weight

There are three conditions LSR vehicles can be in :

(1) Traction limited with acceleration
(2) Power limited with acceleration
(3) Power limited with no acceleration

For cars that peak (3) weight isn't too important . For medium cars that almost peak adding weight for handling is good . For 300 mph cars lighter means more acceleration when the wheels arn't slipping . For 400+ mph cars which are 100% traction limited  less weight means fewer psi at the contact patch which means better acceleration .

[836dstr]

Robin,

I have a '27 D/STR with a modifed Pro Stock"Aero Scoop" and was comtemplating going to a NACA duct. After talking to some people really into aerodynamics I found that this would actually hurt performance. NACA ducts require a long smooth surface approaching the duct, in other words very smooth air. With air hitting the top of the '32 grill & shell and spilling up and over the hood there would be a lot of turbulance.

I'm planning on lowering the scoop and extending it about 5 inches beyond the grill shell into clean air. A scoop thru the upper portion of the grill shell would be ideal, but with the requirement in STR class of a functional radiator filling the greill shell and having 530 Sq.In. area this would not be easy unless using a flat top radiator tank and punching thru the grill shell, but this might violate the stock panel definition.

Good luck!

Saw your Roadster @ Bonneville, very nice.

Tom

[robin dripps]

Tom,
Thanks for the information.  I have been getting advice very similar to this and will be following an approach along the same lines as you have determined.
Robin

[836dstr]

Robin,

A couple of months ago, between runs at El Mirage a asked Russ Eyres about scoop design and optimum opening size. Previous discussions on this thread got into scoop design and internal sizing.

Russ ran some calculations based on a 301 Cu.In. engine turning 7,500 RPM @ a speed of 185 MPH. Based on a lot of other scoops I have looked at his answer blew me away! The optimum would be 6 Sq. Inches + 10 % error margin or 6.6 Sq. In. or just over a 2" diameter circle.

Obviously engine effieiency enters into the equation. Assuming optimum placement of the scoop openning to get clean air the larger the openning the more aero drag. We have enough of that already with our boxy Street Roadsters.

As I recall you said you are running Injection. I tried and after floging them for a while went back to a single 750 Race Demon 4 barrel. The air flow characteristics inside the scoop are different.

Hopefully this will generate some additional comments that could help us both.

Tom

[Stainless1]

So we have learned Bonneville is a balancing act.  
Too much weight and you are still accelerating toward your top speed at the end of the last timed mile. (terminal speed much higher than average)
Not enough weight and you don't get traction to accelerate to you top speed.  (wheel spin, your gearing formulas don't work out)
But there is also a requirement to have enough weight to maintain enough traction to overcome your aero drag at your top speed.  Excess wheel spin makes the ends want to swap places.  So too much power is not a good thing either.  (it is possible)
So build in some downforce if possible.
Have some weight, add it as you need it.

Sumner, build for the fast speeds, 1500 lbs is not too heavy for the 45 inch class if you have some areo.