I sampled the curve with a software tool to make this table. Read the table into an array for speed w {rad/s} and array for torque T {N-m} (note 9.807 Conv factor applies):
This code builds arrays for Force and Power versus velocity:
Note I added 250 {N} rolling resistance estimate in 3rd...
You mean the tire circumference? On the R/C boards they calculate the rollout but I don't use it in my models. In this case we're only looking at top speed equilibrium, so driveline intertia is neglected. The best case force at the drive axle as a function of velocity is then approximately...
Good data. I need to install and test a software application to convert your torque-speed plots to a lookup table, or else create a piece-wise linear approximation, so I'll get back to you as time permits with a graphical study.
Just to confirm my initial understanding I would multiply to get...
Frontal area Af = 1.8{m^2} was an estimate based on a modern (199?) CV2 design that I saw in a web site or the Wikipedia. If you provide some more system parameters I'll revise the model to your values.
I can overlay the source transformer force-velocity curves on the drag loads in these...
So my model confirms Lsos' basic analysis. I misread your post above since you said the engine would require 43 HP (my bad). Now I see the point you were making. The graphical comparison is attached.
Numerical Code
Plots are converted to show newtons and horsepower versus kilometers per...
As Jeff said the radius of the drum on the take-up cable is relevant to the torque leverage. It should be possible to caculate the minimum starting torque required if the drum radius is known.
Chicago,
I'd like to generate some drag and wind power estimate curves to post to the board if you provide these input values:
A = ?, car frontal area in square meters
Cd = 0.51 per above
rho = ?, air density in kilogram per cubic meter
this will give a comparison to your values in a...
RIGHT! But without stalling or seriously loading down the engine, she could not drive it in 4th gear! She probably could not drive it in 3rd gear! She maybe could drive it OK in 2nd gear and probably could crawl along against the 120 km/h headwind in 1st gear at the rpm in which the engine power...
True if the particles don't travel very far or exist for very long. But measurements show that the Sun's gravity bends the light from distant stars during an eclipse. I think the concept of constant velocity is treated in terms of Newtonian versus Non-Newtonian reference frames. My understanding...
I remember learning the geometric definition of a line as a youngster. A line was drawn on the blackboard and the teacher said it is defined as infinite in both directions. Of course constant velocity over infinite time would require an infinite line and no acceleration due to gravity or any...
Do you know the mass of the load? Are you lifting it with a cable on a drum? If so what is the drum radius? How thick are the gears you're using and are they heavy compared to the chain and sprockets? (Are the sprockets relatively heavy or light?)
Do you think the gears increase the rotational inertia in the driveline? Or the stiction force when starting the load? These two factors impact the sufficiency of starting torque.
Chances are the driveline friction is a nonlinear function of velocity. But that may not be the primary cause of your ability to go faster in 3rd gear into a headwind.
Suppose the axle speed is omega in radian per second and the wheel damping is linear with a factor D in standard SI units...
The motor does not make more power or torque in a headwind. It develops power according to the torque speed curve. For simplicity, at constant speed, let there be 1 power source and 2 power sinks.
Pin = P1 + P2
where P1 is power dissipation due to friction in the driveline. If this depends...
This is correct. If you're only making 30HP, and it is geared to push air, you can't push more air by changing gears. However, picking a gear ratio to make maximum use of available power at speed is a design problem which may not be optimized for your car. You probably have an overdrive 4th gear...
No. The factor 1/2 is part of the formula for quadratic drag force:
http://hyperphysics.phy-astr.gsu.edu/HBASE/airfri2.html#c2
and to get power (in coherent unit system) multiply by velocity.
When this happens to me, I copy the text/code/message to clipboard, delete the "glitchy" post...
Convert peak horse power to watts and measure relative velocity in meters per second. The relative velocity into a head wind is the speed of the car plus the speed of the head wind.
The power caused by drag is:
P = \frac{1}{2}\rho C_{D}Av^{3}
where rho is air density, Cd is drag...
Right. To get instantaneous power you would sample crank speed and torque sensors at least a few times per second. If you have a good model of mass and rotational interta, and do an acceleration run on a flat surface to sample the crank speed data, it would be possible to estimate the power via...
Maximum power need not occur at maximum force or torque. For example say the bike is driven by an electric motor. Maximum torque occurs at zero velocity (start-up) for a DC motor and maximum power peaks later as the torque decreases but the speed increases.
Are you looking for raw power input...
Try applying this analysis as the first case approximation. I think you can find the bouyancy as a constant proportional to the amount of water displaced by air inside the ball, and ignore pressure differences at shallow depths. This requires solution of the differential equation on a computer...
DH, thanks for the information. My background is EE but this is a potential educational concept for high school level. I follow your logic and it should enable me to better explain the basic rocket concept while removing a numerical integration from the simulator model.
In the attached sketch I have a comment for the OP and a question for D.H.
I'm looking at rocket launch and vertical flight from the surface of the earth. The gravity radius is rE + h, which can be converted to approximate gravity function g(h). I draw a continuous-time (CT) computer diagram...
I agree with Stonebridge and DaveC. You could think of the problem in two parts, start up (transient analysis) and steady state. During transient analysis an object inside the cylinder must somehow gain or lose momentum. During steady state an object moves as if stationary with respect to the...
Well, I have caught air on my motorcycle unexpectedly when crossing elevated train tracks at ordinary road speeds! But I agree a road should not have a 50 foot jump built in at 78 mph, so that part of the Myth/stunt is totally busted. In regard to getting a bus to jump 50 feet I watched the...
Tonight the Mythbusters tried to skip a sports car across 100 feet of water. The cars at 1/12 scale and full scale worked best with high velocity and no jump ramp.
The jump ramp caused cars at 1/1 and 1/12 to flip and land roughly nose first, what we used to call an "endo" when I raced...
Great writeup. Thanks diazona. One thing I noticed in the episode was the short run to accelerate the model bus to 23 mph, and no clear reading on the radar gun. The radar gun could be off by +/- 1 mph according to some specs I've read. Also, once the front of the bus starts downward it is...
When you release the pendulum it converts gravitational potential energy (GPE) of the raised weight at 45 degrees, to kinetic energy (KE) of impact. You can easily find GPE and KE but if I recall properly the force during collision depends on the elastic properties of the bodies. Also it is not...
I'm looking to do personal computer (silicon) simulations that explain and predict Mythbuster results with reasonable accuracy. This is engineering modeling problem with components such as fluid capacitor (air tank), fluid inertor (gun barrel), fluid resistor (heat transfer losses), ideal power...
Let the donut shaped spacecraft rotate with constant angular velocity \omega about a central axis. A dude of mass m stands on the floor at radius R as shown in the sketch. The floor pushes the dude toward the center and the dude pushes down on the floor. Tangential velocity at radius R is...