Quiz - estimate the Cd
 

Donald Campbell's Bluebird Land Speed Record Car (jn second version form).

https://i.postimg.cc/4nCXTpKT/bluebird-1.jpg

https://i.postimg.cc/jqBfj9PR/bluebird.jpg

https://i.postimg.cc/nhJQ4D35/Bluebird-2.jpg

What was its measured Cd?

(And a hint: it had no lift or downforce.)

Yay, an actual poll. I went with 0.20-0.24 because there has to be some massive internal airflow for cooling, and no wheel spats.

edit:
Can't change my vote. I just noticed it's a turbojet.

Well.... I was wrong once before.

People don't seem to be being very brave - 63 views and only 5 votes!

Land Speed Record cars of the 1930s, 1950s and 1960s are among the most streamlined cars ever produced, so very relevant to those for whom ultra low drag shapes are important.

From a contemporary pamphlet:

Bluebird's shape is of advanced aerodynamic design, evolved from a long series of wind tunnel experiments at the Imperial College of Science & Technology in London.

Bluebird was constructed by an extension of a method employed in the aircraft industry. Absolute accuracy was paramount; to achieve this Motor Panels [the maker] evolved a technique whereby the car was built over a heavy steel base plate mounted in concrete.

Four jacking points, one just inside each wheel, carried the body whilst it was being assembled, and formed the main rig and datum. Wooden formers were made to maintain close limits and uniformity on individual panels. These formers were used for shaping and flanging the alloy sheets. Where panels had to be shaped to match the outer contour of the car, wooden ''egg box'' jigs were employed.

The problem of skinning was solved by hand-forming the outer panels to the diaphragms and stiffeners already in position. After fitting, the individual skins were riveted into position. Particular care was given to the smoothness of the surface to avoid unnecessary air turbulence while the car is travelling at high speeds.

I wouldn't worry too much. Consider:
I like the idea of starting with a box with a jacking point at each vertical edge and transitioning to an aeroform. When done you have four built-in jacks. :thumbup:

It was a fantastic car.

https://i.postimg.cc/43ZSDkcW/Bluebird-1.jpg

https://i.postimg.cc/t4P00NM4/bluebird-10.jpg

https://i.postimg.cc/9X8HyM9C/bluebird-11.jpg

https://i.postimg.cc/DZxHQj8B/bluebird-3.jpg

https://i.postimg.cc/Gmvfgh4B/bluebird-4.jpg

https://i.postimg.cc/L6YwfVR3/bluebird-6.jpg

https://i.postimg.cc/X7tMDzxP/bluebird-9.jpg

Slightly awkward canopy was a replacement after the car rolled at Utah. It had a lovely teardrop acrylic canopy before that...

I usually view as guest because I get logged out when I leave, I only log in to post.

edited bit: I realised after I posted that there is a thing at the top where you can put your guess in, I really should log in before viewing.

My guess is under 0.2, I will go for 0.18 because it looks more aerodynamic than the EV1 but is quite long so friction drag will occur.

But with the internal flow path I doubt the numbers are completely accurate.

I have seen that car several times but I don't remember reading about its drag coefficient, I doubt most people would have any idea whether drag coefficient of 1 was good or bad. The frontal area must have been pretty big though, that car was huge.

Each time you log in, isn't there a Remember Me button?

I backpedalled on the internal airflow when I remembered it's a turbojet.

I hadn't seen its Cd quoted before, until I came across it in the printed discussion shown after a tech paper presentation (1978 book).

I too have seen the car twice - the colour photos here are mine.

I wanted to penalize it a bit for those wheel fairings, but .20-.24 seemed too high, it's the domain of ordinary passenger cars that are neither tad pole trikes nor demand rear seat passengers lop off the tops of their heads to fit.

Most cars don't have a rudder though. That's got to disrupt some air.

I can't believe that car was built by cartoons!

I guess it depends on how the drag is measured. Does the propulsion sucking in the front hole negate what that would show if you placed that car in the tunnel without it running and the air just stacked up against the turbine?

VW XL1 = .189

I went one step lower than the above in a contextual comparison.

I think you guys are right about the air intake being a variable outside of our familiar norms.

I do not recall Cd's of aircraft being posted in the forum. However, isn't a body this close to the ground a doubling factor?

Bluebird
 

Might have that at home, so I won't guess.
This car may have been in the shootout with another streamliner 'Thunderbolt,' which Alex Tremulis ( himself a world motorcycle speed record holder ) wrote about in the 1980s.
During the 'duel,' one of the teams took the risk of removing the rear stabilizing fin and radiator, attempting to shave enough drag for a world record run. They were both in 357-mph territory if memory serves me.:)

The Bluebird CN7 originally had no fin, and crashed at 365 mph. The car was rebuilt and the fin added before its record run; it ran only one more time after that as a demonstration on an airstrip where it overshot the end of the runway and crashed at low speed. (According to an article in Motorsport magazine I found yesterday. That article, published in 2002, also reported the drag coefficient and drag area).

A turbojet > the Meredith Effect.

Enquiring minds....

And the answer is....


"near to 0.16" - the the most definite value I have.

Here's the link to the Motorsport article. Of interest is this passage:

But also interesting:

And here's the article mentioned there, by Ron Ayers, on Goldenrod (which you should read in its entirety, because it's fascinating):

https://www.uniquecarsandparts.com/i...oldenrod_2.jpg

This car has cD = 0.1165 and area A = 8.5 ft^2.

Interesting article. When we did some travelling a few years ago we had on our list to see as many LSR vehicles as possible. They're all glorious in their own ways.

newatlas.com: Jessi Combs breaks 48-year old land speed record
By Angus MacKenzie October 15, 2013

Jessi Combs burnt her candle at both ends, but in 2013 she piloted a grounded F-104 on four wheels made of solid aluminum. On the Alvord Desert in Oregon.

The 1000mph Bloodhound and others do the same.

no go on Bluebird
 

I didn't have anything for Bluebird.
* It's competitor Thunderbolt was Cd 0.174
* Reid Railton's Mobil Special was Cd 0.18
* MG EX-181, Cd 0.12
* Mickey Thompson's Challenger-I was Cd 0.16
* I had Cd 0.117 for Goldenrod