Parachute design for BACAR III
By CJ Kriek – ZR6LJK
Sam Baxter have written two programs essential to parachute design namely rate.exe and gore.exe.
Rate.exe works out the decent rate of the payload with specific diameter parachute.
Once you have the aimed decent rate and the corresponding diameter you can move onto the next
phase to design the parachute of matching diameter.
Using rate.exe we entered 10 pounds for the payload weight and 84 inches for the diameter of the
parachute, this resulted in a decent rate of about 5ms-1.
Next you need to design the parachute. This we do with gore.exe and we enter the diameter info in
from rate.exe.
The gore program will take the diameter info and use that and other useful data to design a pattern
to cut and stitch the parachute together.
First you need to enter the diameter of the parachute, you can guess or use the rate.exe output for
the diameter.
Next you need to enter the number of sections of the parachutes or as this program calls it gores.
My suggestion is to use at least four but more than 8 becomes an issue with the sowing.
Overlap is the length of material overlap between the gores, 1 inch is working great this allows
enough room for dual double stitching next to the rope inlay.
CH or chord is the length of the gore this gets calculated by the program.
Chord
Finally to be able to draw a pattern on paper you would need reference points from a centre line by
entering: 1, you will get references for every 1 inch.
Below is the output from the program
By using MSexcel I converted the inch to millimeter in the tables below.
For a big 5kg payload.
inches
chain
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
L
L+Overlap
37.699
39.699
37.688
39.688
37.656
39.656
37.603
39.603
37.528
39.528
37.432
39.432
37.315
39.315
37.177
39.177
37.017
39.017
36.837
38.837
36.636
38.636
36.414
38.414
36.171
38.171
35.908
37.908
35.624
37.624
35.32
37.32
34.996
36.996
34.653
36.653
34.29
36.29
33.907
35.907
33.505
35.505
33.084
35.084
32.644
34.644
32.186
34.186
31.71
33.71
31.215
33.215
30.703
32.703
30.174
32.174
29.627
31.627
29.064
31.064
28.484
30.484
27.888
29.888
27.276
29.276
26.649
28.649
26.006
28.006
25.349
27.349
24.678
26.678
mm
chain
0.0
25.4
50.8
76.2
101.6
127.0
152.4
177.8
203.2
228.6
254.0
279.4
304.8
330.2
355.6
381.0
406.4
431.8
457.2
482.6
508.0
533.4
558.8
584.2
609.6
635.0
660.4
685.8
711.2
736.6
762.0
787.4
812.8
838.2
863.6
889.0
914.4
25.4
L
957.6
957.3
956.5
955.1
953.2
950.8
947.8
944.3
940.2
935.7
930.6
924.9
918.7
912.1
904.8
897.1
888.9
880.2
871.0
861.2
851.0
840.3
829.2
817.5
805.4
792.9
779.9
766.4
752.5
738.2
723.5
708.4
692.8
676.9
660.6
643.9
626.8
L+Overlap
1008.4
1008.1
1007.3
1005.9
1004.0
1001.6
998.6
995.1
991.0
986.5
981.4
975.7
969.5
962.9
955.6
947.9
939.7
931.0
921.8
912.0
901.8
891.1
880.0
868.3
856.2
843.7
830.7
817.2
803.3
789.0
774.3
759.2
743.6
727.7
711.4
694.7
677.6
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
23.992
23.293
22.581
21.856
21.118
20.369
19.608
18.836
18.053
17.26
16.457
15.645
14.824
13.995
13.157
12.312
11.461
10.602
9.738
8.868
7.993
7.114
6.231
5.344
4.454
3.561
2.667
1.771
0.874
25.992
25.293
24.581
23.856
23.118
22.369
21.608
20.836
20.053
19.26
18.457
17.645
16.824
15.995
15.157
14.312
13.461
12.602
11.738
10.868
9.993
9.114
8.231
7.344
6.454
5.561
4.667
3.771
2.874
939.8
965.2
990.6
1016.0
1041.4
1066.8
1092.2
1117.6
1143.0
1168.4
1193.8
1219.2
1244.6
1270.0
1295.4
1320.8
1346.2
1371.6
1397.0
1422.4
1447.8
1473.2
1498.6
1524.0
1549.4
1574.8
1600.2
1625.6
1651.0
609.4
591.6
573.6
555.1
536.4
517.4
498.0
478.4
458.5
438.4
418.0
397.4
376.5
355.5
334.2
312.7
291.1
269.3
247.3
225.2
203.0
180.7
158.3
135.7
113.1
90.4
67.7
45.0
22.2
25.4
L
L+Overlap
23.876
25.876
23.843
25.843
23.744
25.744
23.579
25.579
23.349
25.349
23.054
25.054
22.695
24.695
22.274
24.274
21.791
23.791
21.247
23.247
mm
chain
0.0
25.4
50.8
76.2
101.6
127.0
152.4
177.8
203.2
228.6
660.2
642.4
624.4
605.9
587.2
568.2
548.8
529.2
509.3
489.2
468.8
448.2
427.3
406.3
385.0
363.5
341.9
320.1
298.1
276.0
253.8
231.5
209.1
186.5
163.9
141.2
118.5
95.8
73.0
For a small 1kg payload.
inches
chain
0
1
2
3
4
5
6
7
8
9
L
606.5
605.6
603.1
598.9
593.1
585.6
576.5
565.8
553.5
539.7
L+Overlap
657.3
656.4
653.9
649.7
643.9
636.4
627.3
616.6
604.3
590.5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
20.645
19.985
19.27
18.502
17.683
16.814
15.899
14.94
13.939
12.9
11.826
10.718
9.581
8.417
7.23
6.023
4.799
3.562
2.315
1.062
22.645
21.985
21.27
20.502
19.683
18.814
17.899
16.94
15.939
14.9
13.826
12.718
11.581
10.417
9.23
8.023
6.799
5.562
4.315
3.062
254.0
279.4
304.8
330.2
355.6
381.0
406.4
431.8
457.2
482.6
508.0
533.4
558.8
584.2
609.6
635.0
660.4
685.8
711.2
736.6
524.4
507.6
489.5
470.0
449.1
427.1
403.8
379.5
354.1
327.7
300.4
272.2
243.4
213.8
183.6
153.0
121.9
90.5
58.8
27.0
575.2
558.4
540.3
520.8
499.9
477.9
454.6
430.3
404.9
378.5
351.2
323.0
294.2
264.6
234.4
203.8
172.7
141.3
109.6
77.8