Round bottom versus flat bottom aero

[JackD]

The Modified was built for his son Danny to drive and featured many things not common to the Modified of the day.
I think it was the first one built to take advantage of the new SCTA rule that no longer required the wheel base be a % of the track width.
It was a pioneer with respect to a lot of things for example the 4 OHV billet, twin head, push rod 37 Nash motor, and the belt driven conversion from a turbo charger that was not allowed in Vintage engines, to the Mercedes mechanical fuel injection with the rack.
The quick change feature on the rear drive was made by  him on the input shaft.
He also had the ability to put a Dyno pump in the car in the place of the transmission and could load all the motor systems on board  without spinning the wheels.
All of this and some real thought to aero features that were never really proven against a similar classed car because there were none in it's short life.
It was interesting but under utilized.
As Bruce is prone to do he quickly went on to other things including his Reno Air Racer and the Exhaust heat recovery engine.
They say his imagination is never ending and most of his projects are waiting for an end.
This is not to avoid the subject but to give him suitable credit for the project as far as it went.

[russ jensen]

 8-)Thanks to you  Jack, as usual helpful info - that  T looked  real good to me @ time & still does- I know Bruce thinks up a lot of neat stuff , and probably hasn't the time to thrash out one good idea before another looks more interseting. isn't anybody else following up  with the aero ideas on that car???

[Sumner]

8-)Thanks to you  Jack, as usual helpful info - that  T looked  real good to me @ time & still does- I know Bruce thinks up a lot of neat stuff , and probably hasn't the time to thrash out one good idea before another looks more interseting. isn't anybody else following up  with the aero ideas on that car???

Are there pictures somewhere of the car (Internet?? or a  program??)??  I don't know if I've seen it or not.

c ya,

Sum

[Dean Los Angeles]

This is a tough essay question. All things engine related can be tested on the dyno. All things aero related can be tested in the wind tunnel. Except underbody aerodynamics. In the wind tunnel you sit on a non-moving plate, nothing like the ground whistling under you at 200 mph.
The flat bottom concept also lends itself to the possiblity of ground effects down force.
Because we always see the static car sitting in the wind tunnel with the smoke streaming over it, we always seem to think of the air moving over the car, instead of the real world where the air is static and the vehicle punches through it. It is easier sometimes to picture the world filled with water so that you can think of the flow over things. Much easier to visualize.
So the answer is all about drag and how to reduce it. We can all picture the super slick shape of the streamliner and picture the smooooooth air flow. When it comes to the underside, it's anything but smooth.
The flat bottom concept leans toward keeping the air out from underneath, but there is still air under there, and it's subject to a shear layer between the stationary ground and the moving vehicle. You still have a 200 mph difference in speeds. Picture what a small pebble would do. Picture it bouncing between the ground and the underside, and then picture the air doing the same thing.
The round bottom concept treats the underside the same as the top side. Pick the bottom up out of the ground effects, let the air bleed out.

The Blue Flame is the ultimate in round bottom, least possible ground effects design. JCB and Goldenrod are not even close.

Ecofire

Which one is better? Have you looked at the speeds these guys are going?  Whichever one you think is better, look at the speed the other design is going.

[ddahlgren]

getting the car 'off the ground' has it's limits as well. consider the handling dynamics of a car that is long has a narrow track and a high CG.. Close your eyes and see the thing starting to get just a little sideways then do the lateral load transfer calcs.. It won't be pretty.  a 4 inch change in CG is a big deal when the track is only 28 inches. There is no way to change this with suspension or anything else the load transfer does not car how it is suspended or if it is at all. See 'Race Car vehicle Dynamic' W. Milliken and D. Milliken........

As far as wind tunnels and rolling roads it can be done just not cheap. It is not completley idendical but very close. See 'Race car Aerodynamics' by Joseph Katz.. An interesting read. mostly sporty car stuff but as a result lots on underbody flows as well.
dave

[Richard Thomason]

Bruce's liner is the only one that I've seen or ever heard of that actually spun without rolling and crashing. That in and of itself was and is quite interesting. His body shape was based on that of a trout. On another note, Roger Lessman's liner, had a flat bottom and a down force suction tunnel. When boost really came on, he spun the wheels and as soon as it started to get sideways, it flew big time. His new car has a different set-up on the bottom but will still use aero downforce. We have a semi-flat bottom but rounded edges and sides that hopefully lets air spill out from underneath. According to our computer analyisis, at 300 mph in free air we generate 300 #s of lift but next to a plane surface it's 700 #s of downforce. So far it has worked pretty well.

[Rex Schimmer]

When you start getting really close to the ground like Yacoucci's and Main's cars you have both the bottom of the car and the ground plane that have a boundry layer and they start to mix and this is the area and that is difficult to define. If you look at pictures of Yacoucci's car at El Mirage there is very little apparent turbulance along the sides of the car which would indicate that the air going down the side of the car is still attached, which is the least drag and most desirable situation. On cars like the JCB and the Golden Rod I would think that the air going under the car is  at a higher velocity than the air going along the sides and therefore it is at lower pressure and is drawing air from the edge of the car to the bottom area. This is how ground affects works, you accelerate the air under the car to make it lower pressure than the air going over the car and the differential pressure times the plan area of the car is down force. Aero down force using ground affects is probably not a good idea for a Bonneville car. As Dave Dahlgren said, you get a little side ways and the down force goes away and now the "pencil" rolls follow.

On round bottom cars if you run them to low then the air that is trying to go under the low spot is interferred by the boundry layer of the car and the ground and it becomes turbulent and un-attached. This can make the lower rear half of the body act as a "bluff" body which means that this part of the body is now subject to "pressure drag" as it is no longer a "streamlined" body, i.e. the air stream is attached to the body completely from the front to the back. This can increase the total drag of the body by 100% in some cases.

At the speed that are ran at Bonneville very little of the air flow around any of the streamliners or lakesters is laminar, most is turbulent but to be an efficient stream lined shape the air needs to remain attached. It is when the air becomes turbulent and then becomes un-attached that drag is signifigantly increased.

Rex

[PorkPie]

This is a tough essay question. All things engine related can be tested on the dyno. All things aero related can be tested in the wind tunnel. Except underbody aerodynamics. In the wind tunnel you sit on a non-moving plate, nothing like the ground whistling under you at 200 mph.

This is the kind of wind tunnel 20 years ago - today the wind tunnel are rolling wind tunnels and the scales are so sensitive that the react when you forgot a small nut on the floor...

[PorkPie]

Aerodynamic, shape, flat or round bottom, all is a question of the overall package - and by the way, the Golden Rod nearly starts to flip when he was at 425 mph. The Blue Flame design has nothing to with car design - a rocket powered vehicle needs a totally other shape as a racer which brings the power to the ground. The JCB - at last they found out that theorie and reality is sometimes different.

What is really important - how you go thru the air and how you got out of the air....

Some years ago a streamliner went up in the air when his chute opens during the acceleration in the 2nd mile - the chute lift the car for a short time on the front and the rest was historie...

[russ jensen]

Are there pictures somewhere of the car (Internet?? or a  program??)??  I don't know if I've seen it or not.

c ya,

Sum

[/quote]I have a couple of blak&white   pics that  have been looked to death, I will try to take a pic  of & send to you, if it works you could post so people know what we are talking about{ I don't know how to post pics}  apparently not that many people have seen this car, I paid particular attn as it fit program I was interested in, Okland is a bit bigger than T but a rare roadster these days, specialy an origional tin one,: that still has the "true blue " paint still on it. Off to see if I can get a usuable pic.Sent pics- not good qty- does't pork have some? he seems to have pics of about everything- pics were 1988- car no=118 agmr qualified@230.4 & cracked a head on 1931 nash eng.

[Sumner]

I have a couple of blak&white   pics that  have been looked to death, I will try to take a pic  of & send to you, if it works you could post so people know what we are talking about........................

That sounds good.  Are you e-mailing them or snail mailing them???  If you e-mailed them before this post I didn't get them,

Sum

[russ jensen]

 :evil:sent to email drs on your h, pg,{sumner1@purpletradingpost.com}. but am on slowwwww ll and some pics have been known to take 12 hr to get there.

[PorkPie]

:evil:sent to email drs on your h, pg,{sumner1@purpletradingpost.com}. but am on slowwwww ll and some pics have been known to take 12 hr to get there.

Old Indian way - one cloud....yes....two clouds......yes yes.......three clouds....stop......four clouds....no......five clouds.....no PayPal..........

[Sumner]

:evil:sent to email drs on your h, pg,{sumner1@purpletradingpost.com}. but am on slowwwww ll and some pics have been known to take 12 hr to get there.

Old Indian way - one cloud....yes....two clouds......yes yes.......three clouds....stop......four clouds....no......five clouds.....no PayPal..........

Russ I got the pictures after they got thru the smoke. Here they are.

     



   

Here is what you also put in the e-mail.  It might help someone:

Paper is shiny & worn so this is best I can seem to get front is like soapbax derby shoving air off to sides and as near as I can tell from pics there appears to be lexan slide plates on sides that are on slots that let it ride on salt keeping air out. maybe I can get a photo shop to do better??

c ya,

Sum

[RidgeRunner]

:evil:sent to email drs on your h, pg,{sumner1@purpletradingpost.com}. but am on slowwwww ll and some pics have been known to take 12 hr to get there.

Old Indian way - one cloud....yes....two clouds......yes yes.......three clouds....stop......four clouds....no......five clouds.....no PayPal..........

     Now I know where Pork Pie learned his Aero.  From the Indians   Enter the forest quietly, make no large disturbances while passing through, and leave as few traces as possible after having done so..................