Hacker News Reader

Comment by Traster | Hacker News Reader

>- For bidirectional attempts, how can you say that a car has a top speed of C mph when C = A+B/2 mph and A>B? That's an invented figure.

I agree that (A+B)/2 is an invented figure, but I think the logic of "This is the maximum a car can do without external factors" is a reasonable thing to agree on as a top-speed, and wind is an external factor. Otherwise a lot of cars can set their top speed by being dropped from a sky scraper, and the testing would get unreasonably expensive. (A+B)/2 is probably a good first approximation to a wind-neutral value (and a gravity neutral value too).

View on HN

On that note, a Porsche 911 Turbo races 1 mile against a VW Beetle dropped from a helicopter. I won't spoil the ending.

https://www.youtube.com/watch?v=SiAbcw5s9_8

But based on the Beetle's terminal velocity here, this strategy for setting a car's top speed will only work for cars that can't drive particularly fast.

Fun fact: That was probably still cheaper with the Beetle than a record run with the Veyron :)

especially considered the veyron dismantled and crashed in the test run https://www.youtube.com/watch?v=6_3LhIjV6aY&list=LLCR_Dw6p0b...

The Beetle probably cost similar to one tire for the Veyron

Otherwise a lot of cars can set their top speed by being dropped from a sky scraper, and the testing would get unreasonably expensive.

Dropping a $25,000 Camry from an airplane might actually be cheaper than a single speed run of these hypercars, where they burn through a $40,000 set of tires....

I highly doubt the terminal velocity of any production car is even close to the top speed records in discussion here.

I was curious, so I ran the numbers on a Toyota Camry. With a mass of 1447 kg, a cross-sectional area of 2.7 square meters, and a drag coefficient of 0.28, it would have a terminal velocity of 391 mph. Other cars which are both heavier and more aerodynamic (e.g. a Tesla Model S) could reach even higher top speeds.

You'd need some sort of drogue chute or fins to keep it pointed nose-down, otherwise it'd tumble like the Beetle in the Top Gear episode just posted.

Or maybe being a rear-engined car put the Beetle at a unique disadvantage, and the Camry would orient itself just fine.

Junkyards are easy, who's got a helicopter-pilot friend and some land?

Ha! Sorry - I hadn’t seen your comment when I started mine. Yeah that engine up front will help I think!

For it to be aerodynamically stable you need the center of mass to be less than ~25% from one end. I don't think a Camry or Model S will do that, it will need stabilization fins.

For the Tesla, it might help to fill the frunk with water containers. That should bring the center of mass forward and up a little.

So drop an old 50's car with big fins and an empty tank ....

Surely this appears quick, but does this Camry maintain ideal orientation all the way to terminal velocity?

Hmmm, one could imagine using the front wheel drive as a flywheel for some attitude control...

Me thinks a drop test is in order.

Given that you can get away with a production run of 25 and still count just get the cheapest car on the market, stick some fins on it and sell 24 of them at slight discount from cost (include instructions for fin removal). Likely still cheaper than one run of a supercar.

Reply on news.ycombinator.com