# Help with a design project, dont know where else to go.

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David on 12 Dec 2014
Edited: Image Analyst on 15 Dec 2014
I'm having trouble even finding where to start with this. I kind of have an idea of the equations i need such as net force, drag, PV=nRT, as well as calculating the masses of the ballon and such.
What i have so far is that i will be using a 2m across balloon (assuming a perfect sphere) filled with.748kg of helium. I figure the balloon to weigh .6kg and the package it will carry will be 2kg. I also calculated the mass of the air that will be displaced by the balloon is 5.05kg at ground level and calculated the boyancy force to be 49.54N and the force of gravity to be 32.84N (will this change as it floats away?) Net force = 16.7N
Any help and tips and getting me on the right track will help thank you very much! I attached the assignment i'm following.
Design Project: Corrected Project Document!
Report: -Graphs showing how the balloon will rise and fall. This will be an x vs. y plot in which x is ground distance (downwind) and y is altitude. Point where balloon breaks should be indicated. -Show the pressure versus time. Include a) , b) air pressure at that altitude, -Show balloon volume as function of time. -Plot velocity with time a) vertical velocity, b) ground velocity, c) total velocity -Hand written derivation and equations of how you are describing the motion of the balloon and assumptions made. Be sure to carefully layout the method, show at sample calculations done by hand at two altitudes and show how they match your Matlab answers -Provide hand written narrative about how your balloon works, why you selected the design that you choose, what problems exist with your design, how good are the assumptions that you needed to make to complete this design in a timely manner, which parts each team member worked on with percentage effort.
Programming -The balloon stress – strain physics will NOT need to be accounted for in this project. -The size of the balloon should be selected such that it is much larger than the volume of gas that is placed inside the balloon to start (i.e. it is like a plastic trash bag that is only filled partially). ----Recommended start volume is approximately 1 cubic meter. -Balloon burst should considered to occur at a point when it reaches 10 times the starting volume. This implies that you filled the balloon only 10% full and when it reaches a fully filled point, it bursts. -Drag is given as: Drag = Cd * (Cross sectional Area) * (0.5) * (Air density)* (balloon velocity)^2 -Use condition to insure that Drag is never greater than buoyancy force (set them equal if drag exceeds lift) -Use particle motion equations such that you assume constant acceleration over a small change in time (1 second is a good assumption)
thanks so much for any help!

Joseph on 12 Dec 2014
Start at your initial time with an initial position and velocity: Calculate air density, balloon volume, drag force, etc. Basically anything that causes a force on the balloon. Sum the forces then calculate acceleration = force/mass. Apply the acceleration to the velocity for some delta t (1 sec, 0.1 sec, whatever you chose). Then use that velocity to change the position. Recalculate air density, balloon volume, drag force, etc. Then repeat. Keep track of variables as you go in an array for the final plot vs. time.
Image Analyst on 15 Dec 2014
Look at the error. It tells you why. You have not defined T0. What is its value? After that you need to initialize V to something less than MaxVolume, such as -inf. And you need to get rid of the "do" on the "while" line.