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Terminal velocity calculator
wombatone - January 24th, 2006 at 08:27 PM

Has any one seen a program that can calculate the terminal velocity of a bug.

hellbugged - January 24th, 2006 at 09:58 PM

ask dave- he knows things- aka "dangerous"

crewcabconnection - January 24th, 2006 at 10:07 PM

what altitude will you be dropping it from?

dangerous - January 25th, 2006 at 06:31 PM

The only formula I have is for terminal velocity in the standing 1/4 mile.
You will need engine power and your vehicle mass in lbs.
Answer will be in MPH.
Get the cubed root of (HP divided by weight), and then multiply your answer by 234.
So if your Volksy has a 60hp engine and weighs 1870lbs (850kgs)
=cubed root of (60 divided by 1870)
=cubed root of .0321
=.318
Then multiply by 234=74mph.
This will be a rude shock to all those people who think their engines make more power.
If you have a chassis dyno figure then you can add between 10 and 15 percent (depending on calibration and correction factors),
to get flywheel power to use in this formula.

[ Edited on 25-1-2006 by dangerous ]

lohoon - January 25th, 2006 at 06:36 PM

Isn't there a "table" that speed dudes use that considers final drive ratio + wheel diameter + top engine revs?

modulus - January 25th, 2006 at 06:48 PM

Quote:
Originally posted by lohoon
Isn't there a "table" that speed dudes use that considers final drive ratio + wheel diameter + top engine revs?


Yes and no. What 'dangerous' is referring to above is a way of estimating trap speed at the end of 1/4 mile of full acceleration.

Of course, the car may go on to achieve a higher top speed, which can be calculated from the top gear ratio, final drive ratio, top rpm, tyre size etc. *provided* that the horsepower curve of the engine is able at all points in the top gear rev range to deliver more kW than required by the sum of rolling resistance (usually small) and aerodynamic resistance (usually big).

I can't guess what wombat wants to know, so I'll go with:- if you drop it from a C4 transporter at 10,000 m, it should top out at about 180 kph before it hits the desert floor.

[ Edited on 25-1-06 by modulus ]

dangerous - January 25th, 2006 at 06:48 PM

Gear ratios can be used to calculate theoretical top speeds but
unless the engine makes enough power to overcome the frictional losses
(air and other), then it is just theory.
A 60 hp vw beetle would probably max out at less than 90mph
.....well unless "gravity is your co-pilot"

dangerous - January 25th, 2006 at 06:50 PM

Well said Peter, you beat me to it and described it better.

VWCOOL - January 25th, 2006 at 06:50 PM

Yeah - it's called a speedo :P

speedster356 - January 25th, 2006 at 08:00 PM

If your looking for theoretical top then the final drive, tire size, and max engine revs are used. I have a formula some place that then uses your theoretical top speed along with Cd, and frontal area and gives you the required HP to reach that top speed. This dosen't take into account rolling resistance (tire on surface) but is used by the salt lake speed guys. Remember that drag squares by the velocity....:o