OakenWeld - The place where things get done.

[ParachuteMan]

First I want to say, I wasn't able to locate where the meeting was going to be on the 9th during forum. I had some ideas that I was going to introduce in order to get some input from everybody, but when I went back to the same room where the meeting was last time nobody was there. What happened?

Anyway, here are some of my ideas, let me know what you all think of them:

First of all, lets look at some rough estimates of velocities of various size parachutes. That way we can begin to have an idea of what our needs are. Also this will aid in determining what sort of optimum velocity are we looking at for the project.

Without testing as an option, I think for the time being it would be good to use the standard for emergency parachutes as the starting point for determining the maximum velocity we will allow our load to fall at. That standard is about 5.5 to 8m/s. So by conversion, the optimum velocity that I think we should consider keeping the payload at is somewhere in the neighborhood of 18f/s to 23f/s.

From first hand experience about parachutes, one always wants to use a shoot that is designed to carry atleast 25% more weight then you are. Doing that will help the velocity to stay around 5.5m/s.

Ripstop Nylon about 1.27 yards in Diameter will deliver a load of 9lbs at about 9.875m/s assuming a flat geometry parachute. 9.8m/s is about 22mph to give you a better visualization of the speed. The same parachute at a 6 pound payload will deliver its load at approximately 25.8f/s. In order to bring 6lbs down to the exceptable 18-23 f/s we should have a parachute approximately 65" in diameter atleast. At that size it will deliver it's load theoretically at approximately 18.6f/s. From information such as this we can simulate drops and somewhat accurately test the protection of our load carrying apparatus.

It is important to note that a spherically designed parachute is going to slow the payload down a lot more then a flat designed one, but we would have to buy one rather then make it and that would raise our cost considerably. If you all want me to I could do some calculations for a spherically designed shoot.

So do we want to buy one or make it? I think making it would be the better option. All we really need is a sewing machine. Otherwise we could buy one such as the following:

Prospective Parachute-R7C 3.5 LBS 8 LBS $50.00


But, again, I think it would be nice to make it. (I am interested to know what you used on the previous balloons. If someone could fill me in I would appreciate it):
-In order to do this, we must obtain aproximately 2-3 square yards of rip-stop Nylon, which costs approximately 2 dollars a yard.

Thinking about the FAA regulation on line strength being under 50lbs, and about the strengths and weaknesses of using spyder wire (specifically the possibility of the string to tangle), I came up with a possible alternative. We could utilize loops of Ripstop Nylon sewn onto the parachute infra-structure using just enough stiches for an overload to cause it to breakaway. Securing the parachute cords to the parachute in this way, would be both very easy and satisfy Part 101 of the FAA regulations concerning unmanned baloons.

The Parachute itself could be made in an octagon shape with loops at the corners, to which we could secure eight lines, (making loops on every other straight). We would then bring all the lines together and secure a balance in the chute by knotting the parachute six or so inches above the bottom of the loop. ( I can make a drawing sometime if you all like.)

Another alternative I was thinking about was coating the spyder wire in Parafin in order to give it some rigidity just like is done with parachute lines on model rockets. This could possibly help with potential tangling . However, in my experience growing up fishing, Spyder wire seemed to tangle and snag for no reason at all. For that reason I think it might be better to use something else. But lets talk about it.

A crude measurement of the square yardage probably necessary is somewhere in the neighborhood of 1.5 to 2 square yards, in order to get the load down softly.

A totally different idea I am toying with is possibly a static decent in combination with an emergency parachute. One of the advantages to such a system is an even slower ascent and possibility for more data to be obtained on the way down. (A static decent is using two balloons, one half or 3/4 full so that one pops before the other and allows the net weight to be reduced. This would significantly counter impact force.

-Another Idea that I was thinking about has to do with possibly compartmentalizing the individual equipment a little more then they have been, but I am sure that is something that everyone has been thinking about for a while.

Sorry if this post is a little (or a lot) disjointed. I wanted to clean it up, but this is going to have to suffice because my wife wants me to take her to the valentines dance ....and I am going to be in trouble by her if I don't get going. Let me know what you think about the ideas I have.

PS this is Jared....the Mech. Engineer major.