After the tantalizing first description of the problem of how to deploy the parachutes effectively to stop the BLOODHOUND Super Sonic Car, I asked Dr John Davis for more details. Specifically, I asked what is the objective of the choice of chute opening times and what constraints apply.
John replied with the following information:
1) We want to stop at exactly 10 miles so we are ready to turn around to go back
2) We can not deploy the parachutes above a certain speed, definitely not supersonic
3) We can stop at 10 miles by two methods
a) Airbrake at the end of the measured mile and wheel brakes at about 150 mph. This is the preferred option.
b) Parachutes: first just sub-sonic, second almost immediately afterwards, followed by wheel brakes maybe a bit faster than 150 mph
4) If the airbrake only partly deploys we will need one parachute, but not necessarily at high speed. This will be very dynamic
5) The air-brake has one good mode of deployment and four possible failure modes, three with a reduced function, one with no functionLike many real-world problem (or Dr Who's tardis!), the problem gets bigger once you get beyond the front door. How would you interpret the additional information? What additional questions would you ask? Comments below please.
In my next blog post, I'll write about how I interpreted the above information and the questions I asked next.
What about the weight of the device?
ReplyDeleteHi Tiggerboy0301,
ReplyDeleteGood question: weight (or mass) of the device is an important to know when you are understanding motion. For example, the deceleration of the car and the drag forces acting on it are related via Newton's 2nd law of motion:
Force = Mass x Acceleration.
At the start of the run, the mass of the car, driver, and fuel is expected to be 6422 kg.
However, the mass of the car will reduce as the jet and rocket fuel burn. The total fuel mass is expected to be 1752 kg and most of this will have burned off by the time Andy reaches the end of the measured mile. The exact amount of fuel left at the end of the measured mile will depend on design choices still to be made e.g. when to fire the rocket.
For now, we'll use the round figure of 5000 kg for the mass of the (car + driver + remaining fuel) at the end of the measured mile.
More details on the masses involved with BLOODHOUND are available here:
http://www.bloodhoundssc.com/car/facts_and_figures/vehicle_technical_spec/vts_part_2.cfm#VTS_7
For an explanation of the difference between mass and weight, see here:
http://en.wikipedia.org/wiki/Mass_versus_weight
Here is more details on Newton's 2nd law of motion:
http://www.grc.nasa.gov/WWW/K-12/airplane/newton.html
If anyone knows of any better links than the ones used above, then please include them in the comments below.