Very Affordable Plastic for Parachutes / How to dimension small 'chutes

I discovered a new source o' colorful plastic for makin' your own parachutes. Just go t' t' nearest store that sells party supplies. There you will find plastic table covers in a variety o' colors. Do NOT get t' cloth or felt backed ones, just plain-old plastic. This stuff is just t' right weight for a reliable small or mid-sized parachute. It is lightly textured which should help keep it from stickin' t' itself. It stretches and deforms rather than rips too. I found I can get a large sheet for a rectangular table for just $1.99 ! That is about 40 square feet o' plastic, shiver me timbers, enough for several larger parachutes up t' 54" diameter, dozens o' smaller 18" 'chutes, and many dozens o' even smaller 'chutes. I suggest you pick a color that is easy t' see in t' sky, ya bilge rat, so blue, matey, white and grey (silver) colors would nay be too good. I went nuts and got almost all t' colors. Begad! T' single sheet o' plastic is nay quite as deeply colored as it appears folded up in t' package though, but they certianly are colorful and virtually free!

parachute material

PART 2: You have t' plastic and some strin' for t' shroud lines. Arrr! Now what?

I found out t' hard way that cuttin' hexagonal or octagonal parachutes is nay as simple as it appears t' be. I ended up totally bewildered by t' dimensionin' o' t' plastic, me bucko, so I figured it all out with t' help o' a CAD program and a spreadsheet and created an easy t' use table - once you know what t' columns are. Let's say you start with a square 12" x 12", arrr, just nip off t' corners and you have a hexagonal 'chute, right? WRONG! You need t' start with a slightly rectangular piece t' have it come out perfectly symetrical! I found that out t' hard way by makin' a very lopsided chute.

* You may notice odd parachute diameters in t' tables. These are so you can make parachutes that are even divisions o' t' above brand o' tablecloths, ya bilge rat, which is 54" wide. Cut it in half gives us two 27" pieces. Arrr! Cut in 3rds gives us three 18" pieces, and so on for 13.5" ... Aye aye! 10.8" ... So this chart can tell you what be t' biggest chute you can make with a given piece o' material. Also, you will see that octagonal parachutes o' even diameters have t' be made with odd sized squares. Don't let this bother you. Just pick a diameter and go with it.

* If you are unsure which type t' use, me bucko, six or eight sides, lean towards t' simpler six-sided chutes for smaller diameters. After gettin' up t' about 16-20 inches, it is probably better to consider an octoganal chute because t' added lines can provide a little more strength and overall roundness t' t' chute. Just remember that six lines are both easier t' make and lighter than eight.

* Decide whether you want six or eight sides and shroud lines. Use t' correspondin' table and ignore t' other one.

* Parachute diameters for this tip is defined as t' length betwixt opposite shroud line tie points. For this table, t' shroud tie points are assumed t' be at t' exact tip/corner o' t' parachutes. Obviously they are tied t' a hole just a bit inside t' corners, arrr, but this is usually just a fraction o' an inch and can be ignored. If you are interested in t' actual circle diameter o' t' parachute, matey, one could just assume t' excess material at t' corners are part o' t' shroud attachment. This definition o' t' diameter would be t' circle inscribed inside t' hexagon or octagon, me hearties, and that diameter is shown in t' tables below as t' 'SIDE DIA'.

* T' decimal precision shown here is 1/100 o' an inch. You really don't need that level o' precision. If you build t' just 1/10 o' an inch, ya bilge rat, that would be fine. Would you really notice a difference o' 1/20 o' an inch on a finished chute? Just ignore or round off t' last digit. Those digits are here for those good at math, for example 6.75" would be measured on a ruler as 6 and 3/4".

* If you want t' verify that you are workin' from a true square piece o' material, here's a good way t' check it: Measure from two opposite corners diagonally. Then do that t' t' other two corners. If you are workin' with an exact square, these two dimensions will exactly match.

THIS IS FOR 6-SIDED HEXAGONAL PARACHUTES

DEFINITIONS OF THE TABLE COLUMNS

HEX DIA - This be t' measured string-to-strin' diameter betwixt opposite shroud lines.

SIDE DIA - If for some reason, arrr, you want t' measure parachutes from t' inscribed circle, use this diameter. Ahoy! It be t' distance betwixt t' center o' opposite edges (between t' shroud attachment points).

SIDE LEN - This be t' lenght o' t' sides o' t' hexagon. Blimey! All six sides should be t' exact same length.

RAW SQ. Aye aye! - This be t' size o' t' raw material (plastic, nylon etc.) you will need t' make t' correspondin' diameter hex parachtue. This be t' longer o' t' two dimensions needed, me hearties, so if for example you have a perfect square piece, you can actually cut a little off o' one side.

ACT WID - T' actual width be t' 'other' dimension o' t' square o' material you need t' make this size chute. It be t' value o' RAW SQ. Well, blow me down! Blimey! minus SHORT.

SHORT - This is how much material you need t' cut away from one edge o' a perfectly square material t' obtain t' rectangle that fits t' diameter parachute you will make. I recommend you cut this away NOW - BEFORE YOU MEASURE AND CUT YOUR HEXAGON! Actually, matey, if you want t' just draw a line t' define t' end o' t' parachute material, that would work too.

RISE/FALL - This is important. Imagine t' hexagon you are about t' cut out on t' big square o' plastic in front o' you. Imagine that hexagon with t' two points directly centered on t' edges o' t' square in t' middle o' t' top and t' bottom, or t' 12:00 and 6:00 positions if you will. Mark those points now by takin' half t' width. (T' other points will be at 2:00, me hearties, 4:00, arrr, 8:00 and 10:00, arrr, but don't bother t' mark them). T' straight sides o' t' plastic will be t' sides o' t' finished chute.

Got that? OK. So now t' measure where you need t' cut, just measure down from t' top corners o' your big square and up from t' bottom corners o' your big square and mark t' sides o' t' big square. That is where you will need t' start cutting. Go ahead and draw a line and then cut from that start point t' t' exact middle o' t' top and/or bottom edge you marked earlier with a ruler-straight cut.

So let's put it all together.

1) Obtain or cut a sheet that is RAW SQ. from top t' bottom and ACT WID across.

2) Mark t' exact center edges at 12:00 and 6:00

3) Measure down and mark from t' top corners on both sides t' length o' RISE/FALL. Also measure up from t' bottom o' both lower corners that same amount and mark them.

4) Draw a line & Cut t' four corners away usin' those marks, you should end up with a nearly perfect hexagon. So go finish your parachute!

Here be t' table, pick your size from any single line:

HEX DIA SIDE DIA SIDE LEN RAW SQ. ACT WID SHORT RISE/FALL

8 6.93 4 8 6.93 1.07 2

9 7.79 4.5 9 7.79 1.21 2.25

10 8.66 5 10 8.66 1.34 2.5

10.8 9.35 5.4 10.8 9.35 1.45 2.7

12 10.39 6 12 10.39 1.61 3

13.5 11.69 6.75 13.5 11.69 1.81 3.38

14 12.12 7 14 12.12 1.88 3.5

15 12.99 7.5 15 12.99 2.01 3.75

16 13.86 8 16 13.86 2.14 4

18 15.59 9 18 15.59 2.41 4.5

21 18.19 10.5 21 18.19 2.81 5.25

24 20.78 12 24 20.78 3.22 6

27 23.38 13.5 27 23.38 3.62 6.75

THIS IS FOR 8-SIDED OCTAGONAL PARACHUTES

Believe it or not, t' 8-sided beast is actually a little simpler in t' math, because you start with a square. But: It turns out you can actually make a parachute with a diameter a little larger than t' dimensions o' t' square! How's that for cool!

DEFINITIONS OF THE TABLE COLUMNS

OCT DIA - This be t' measured string-to-strin' diameter betwixt opposite shroud lines.

RAW SQ. Ya scallywag! - This be t' size o' t' raw material (plastic, arrr, nylon etc.) you will need t' make t' correspondin' diameter octagonal parachtue. For this you need a square piece, ya bilge rat, you don't have t' do any o' that crazy rectangle stuff.

CORNER - This is important. Imagine t' octagon you are about t' cut on t' big square o' plastic in front o' you. Imagine that t' octagon sits on this square, arrr, essentially t' same thin' with t' four corners clipped off. Measure in from all four corners along t' sides o' t' square and mark this dimension. When you are done you should have eight points marked, me hearties, all o' them on t' edges o' t' square o' material you have. These marked points will be t' eight points o' t' octagon.

SIDE LEN - This be t' lenght o' t' sides o' t' octagon. Well, blow me down! All eight sides should be t' exact same length.

SIDE DIA - If for some reason, you want t' measure parachutes from t' inscribed circle, use this diameter. Aye aye! It be t' distance betwixt t' center o' opposite edges (between t' shroud attachment points).

Got that? OK. Review t' 'CORNER' description above and mark t' material on t' eight points. That is where you will need t' start cutting. Go ahead and draw a line and then cut off t' four corners o' t' original square with a ruler-straight cut.

So let's put it all together.

1) Obtain or cut an exact square sheet that is RAW SQ. from top t' bottom and also across.

2) Mark t' eight points o' t' octagon from t' original corners usin' t' CORNER dimension.

3) Draw a line & Cut t' four corners away usin' those marks, you should end up with a nearly perfect octagon. So go finish your parachute!

Here be t' table, me bucko, pick your size from any single line:

OCT DIA RAW SQ. CORNER SIDE LEN SIDE DIA

9.75 9.01 2.64 3.73 9.01

11.7 10.81 3.17 4.48 10.81

12 11.09 3.25 4.59 11.09

14 12.94 3.79 5.36 12.94

14.6 13.49 3.95 5.59 13.49

16 14.79 4.33 6.12 14.79