Quiz - estimate the Cd

[JulianEdgar]

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







What was its measured Cd?

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

[freebeard]

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.

[JulianEdgar]

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.

[freebeard]

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

I wouldn't worry too much. Consider:

Currently Active Users: 415 (6 members and 409 guests)

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.

[JulianEdgar]

It was a fantastic car.















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

[AeroMcAeroFace]

Currently Active Users: 415 (6 members and 409 guests)

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.

[freebeard]

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

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.

[JulianEdgar]

Originally Posted by AeroMcAeroFace

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.

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.

[jakobnev]

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.

[redpoint5]

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