Need a Parachute Calculator?

[RebelRockets]

Hi,

Can anybody use a parachute descent calculator? I was in a programming mood so I put together something using equations that I found at

http://web.archive.org/web/20011027124518/www.execpc.com/~culp/rockets/descent.html

The screen shot should pretty much explain what's in it. Any suggestions for things to add or change?

Parachute Calculator Screen Sample1.jpg (85.46 KiB) Viewed 63 times

This is a 'Windows' program, tested so far to run on versions ME & XP . If anybody is interested, I believe that my WordPress page can be set up to download from there. I will post here again if and when it is available for download.

Here's a question for the "physics majors" out there. If the equation says that you need a chute of 500 square inches, would using two identical chutes that combined total 500 square inches give the same results? I put an option in the program to use multiple chutes to evenly divide the weight and I'd like to know if that makes sense.

Dennis

[U.S. Water Rockets1]

Hi,

Can anybody use a parachute descent calculator? I was in a programming mood so I put together something using equations that I found at

http://web.archive.org/web/20011027124518/www.execpc.com/~culp/rockets/descent.html

The screen shot should pretty much explain what's in it. Any suggestions for things to add or change?

Parachute Calculator Screen Sample1.jpg

This is a 'Windows' program, tested so far to run on versions ME & XP . If anybody is interested, I believe that my WordPress page can be set up to download from there. I will post here again if and when it is available for download.

Here's a question for the "physics majors" out there. If the equation says that you need a chute of 500 square inches, would using two identical chutes that combined total 500 square inches give the same results? I put an option in the program to use multiple chutes to evenly divide the weight and I'd like to know if that makes sense.

Dennis

Thanks for creating this application. This is definitely the kind of thing that we need to have available for people to use so they can make parachutes that are predictable. We would otherwise use trial and error by dropping weighted parachutes from a rooftop so we could get the size correct for our chutes.

[Brian]

maybe research equations for different shaped parachutes. maybe also a an equation for the force parachuting object has when hitting the ground.

[RebelRockets]

Hi everybody,

I've enabled downloads for the calculator from http://rebelrockets.wordpress.com
Look for the Box.net "DOWNLOADS" widget at the bottom of the right sidebar on any page. I've tested the download myself, it seems to be working now, but at first Box.net sent me strange very small files instead.
I hope it was just a setup problem because I had no prior experience with Box.net. Any Box.net experts here?

The correct file should be 1.07 MB in size. Be sure to read the 'Program Information' from within the program itself.

Dennis

[RebelRockets]

maybe research equations for different shaped parachutes. maybe also a an equation for the force parachuting object has when hitting the ground.

Hi Brian,

The program itself takes all shapes in the same equation, BUT somehow you have to determine the rating number for your parachute yourself. The person who wrote the original equation, Randy Culp ?, says that a "parasheet" ( not to be confused with a parakeet ) made from a single flat piece of material, has a drag coefficient of 0.75 and I've set that as the default in the program. He rates a dome-shaped parachute made from fitted pieces at 1.5, so is that the maximum possible?
If anyone knows how he arrived at those numbers please say how and it will be included in updates of the program.

I suppose you could put a known weight on a known size parachute, drop it from a known height and measure its falling speed. Then compare that speed to the one predicted by the program to adjust the drag coefficient to get the same result in the program. If you work with the program that will make more sense.

As for the force of the object hitting the ground, would that be momentum?
A quote from Physics Essentials For Dummies®
"All you have to do to get the momentum of an object is to multiply its mass by its velocity. Because you multiply mass by velocity, the units for momentum are kilograms-meters per second, kg·m/s."
The program uses and displays grams and meters per second, so that could easily be added to an update

Dennis

[U.S. Water Rockets1]

We use mostly cross-form parachutes, which don't see to be supported. The program could use other parachute types to round out the offering. Otherwise, it is good to have this type of program available.

[RebelRockets]

Hi everybody,

The latest version 1.1 of the calculator has been uploaded to my web site today. It was in the works already before the last response, and yes there are now options for hexagon and octagon shapes. There are also more bits of information displayed along with the options. I believe I now have the correct formulas for the new geometry, but if anyone sees something they disagree with, please let me know.

Calculator v1_1 screen.jpg (118.46 KiB) Viewed 34 times

I've been researching cross-form parachutes and have been wanting to add them to the options. If you consider them to be made of two equal, long rectangles over-lapped at the center, Length and Width refer to the rectangle itself and you would figure the area of the parachute to be

Area = ( 2 x Length x Width ) - ( Width x Width )

You could work with the program before the option is added by adjusting the circle parachute until it has the same area as you get from the equation above.

Looking at pictures of cross-forms in the air, it seems like some have more material at the sides of the open parachute than basicly round ones do. Would this mean that their area of material was proportionately less effective than round parachutes? That would effect the overall accuracy of using the program unless you entered a different drag coefficient for cross-forms. Anybody have any data from using cross-forms that would help here?

Dennis

[U.S. Water Rockets1]

Hi everybody,

The latest version 1.1 of the calculator has been uploaded to my web site today. It was in the works already before the last response, and yes there are now options for hexagon and octagon shapes. There are also more bits of information displayed along with the options. I believe I now have the correct formulas for the new geometry, but if anyone sees something they disagree with, please let me know.

Calculator v1_1 screen.jpg

I've been researching cross-form parachutes and have been wanting to add them to the options. If you consider them to be made of two equal, long rectangles over-lapped at the center, Length and Width refer to the rectangle itself and you would figure the area of the parachute to be

Area = ( 2 x Length x Width ) - ( Width x Width )

You could work with the program before the option is added by adjusting the circle parachute until it has the same area as you get from the equation above.

Looking at pictures of cross-forms in the air, it seems like some have more material at the sides of the open parachute than basicly round ones do. Would this mean that their area of material was proportionately less effective than round parachutes? That would effect the overall accuracy of using the program unless you entered a different drag coefficient for cross-forms. Anybody have any data from using cross-forms that would help here?

Dennis

Dennis,

Thanks for the updated software. Adding cross form chutes is a big help.

One thing though... it seems that the formula you used to computer the area left out the fact that the overlapping area of the two rectangles should be halved because it shouldn't count twice.

Otherwise, nice work!

[RebelRockets]

"If you consider them to be made of two equal, long rectangles over-lapped at the center, Length and Width refer to the rectangle itself and you would figure the area of the parachute to be

Area = ( 2 x Length x Width ) - ( Width x Width )"

You can also consider them, generally but not always, to be 5 squares attached together in a + shape. So that area would be 5 square units. So in this case Length = 3, Width = 1.

Area = ( 2 x 3 x 1 ) - ( 1 x 1 ) = 6 - 1 = 5

If Length = 6, Width = 2, one of its 5 squares is 4 square units in area.

Area = ( 2 x 6 x 2 ) - ( 2 x 2 ) = 24 - 4 = 20

If you have a different, thicker + shape, Length = 5, Width = 2

Area = ( 2 x 5 x 2 ) - ( 2 x 2 ) = 20 - 4 = 16

That one layer of material that overlaps is always subtracted by ( Width x Width ).

[U.S. Water Rockets1]

"If you consider them to be made of two equal, long rectangles over-lapped at the center, Length and Width refer to the rectangle itself and you would figure the area of the parachute to be

Area = ( 2 x Length x Width ) - ( Width x Width )"

You can also consider them, generally but not always, to be 5 squares attached together in a + shape. So that area would be 5 square units. So in this case Length = 3, Width = 1.

Area = ( 2 x 3 x 1 ) - ( 1 x 1 ) = 6 - 1 = 5

If Length = 6, Width = 2, one of its 5 squares is 4 square units in area.

Area = ( 2 x 6 x 2 ) - ( 2 x 2 ) = 24 - 4 = 20

If you have a different, thicker + shape, Length = 5, Width = 2

Ok, that's what we were wondering about. That looks good now!


Area = ( 2 x 5 x 2 ) - ( 2 x 2 ) = 20 - 4 = 16

That one layer of material that overlaps is always subtracted by ( Width x Width ).