Balloon Design

Kaymont Balloons (kaymontballoons.com) sells differtent models of weather balloons.  The selection of which model to use is based on the weight of the payload, the desired burst height (>100,000 ft), and the desired rate of ascent.  The design of the balloon parameters were determined using three different websites.  Once the model was selected, based on the weight of the payload and desired ascent rate, the Neck Lift was calculated to determine how much helium to put in the balloon at launch.

 

Websites

1.  University of Wyoming, Laramie,WY (http://weather.uwyo.edu/polar/balloon_traj.html)

The first site is available through the University of Wyoming at Laramie.  It is used to predict the likely path of the balloon given the weather forecasts for that day, the starting location (latitude and longitude), and the burst height.  The predicted path is useful in selecting a launch site later, so that we can make sure that the balloon won’t travel in controlled airspace and that it is not likely to land in trees.  The website assumes an ascent rate of 4.5 m/sec (at launch) and a descent rate of 4.9 m/sec.  Since this is not adjustable by the program, we designed the balloon to match these parameters.

 

2. Cambridge University Space Flight (CUSF), Balloon Burst Calculator  (www.cusf.co.uk/calc/)

At this site, you can enter the payload mass (g), balloon mass (g) and target ascent rate (m/sec).  The program will then calculate:

  • Burst Altitude (m)
  • Ascent Rate (m/sec) (may be different than target)
  • Neck Lift (g)

The nice thing about the program is that it knows the mass and burst parameters of several vendors balloons, and in particular, the Kaymont models.  We used the program to select the Kaymont balloon model that will result in a burst altitude of >100,000 ft. given our payload mass and desired ascent rate

 

3. Kaymont Balloons  (kaymontballoons.com/Weather_Forecasting.html)

The Kaymont Balloons site contains useful data on several of their models.We use this to make sure the CUSF site calculations match the manufacturer’s calculations on specific parameters.We can then gain trust in the other calculations from the CUSF site.

 

  • Balloon Characteristics (Sounding Balloons with Payload of 1050 grams)

 

Balloon Size

(grams)

1200

1500

2000

3000

Diameter
(ft. @ launch)

6.0

6.2

6.5

7.1

Volume
(cu.ft. @ release)

113

124

143

187

Rate of Ascent
(meters per min.)

320

320

320

320

Diameter
(ft. @ burst)

28

31

35

43

Burst Altitude
(x 1000 ft.)

109

112

117

125

Free Lift
(grams)

1190

1280

1420

1670

Nozzle Lift
(grams)

2240

2330

2470

2720

 

Content copyright 2011-2012. Kaymont

                                            Table 1.  Kaymont Balloon Characteristics

 

On the CUSF site, if we select the Kaymont 1200 model, and enter a payload of 1050 grams, then adjust the target ascent rate such that the calculated ascent rate equals 5.33 m/sec (i.e. 320 m/min), we see the following results.

 

 

Payload

Burst Altitude

Time to burst

Neck Lift

Launch volume

 

Grams

Meters

Feet

Miles

Min

Grams

Pounds

L

ft^3

CUSF Website

1050.0

33388

109541

20.75

94

2228

4.91

3682

117.9

Kaymont Website

1050.0

 

109000

20.64

 

2240

4.94

 

113.0

Table 2.Comparison of Kaymont calculations with CUSF calculations

 

As you can see, both programs predict a burst altitude of approximately 109,000 ft., a Neck Lift of 228-2240 g., and a launch volume of 113-117 cu. Ft.  From these results we will then trust the CUSF calculator to design around our parameters.

 

Selecting a Balloon Model

Using the CUSF website, several payloads were entered and the ascent rates adjusted to 4.5 m/sec.  The follwing table shows the calculated burst altitudes, time to burst, Neck Lift and launch volumes.

 

Using a payload of approximately 4.1 pounds (1860 g) (see Table 4), we selected the Kaymont 1200 model from table 3.  This will give us a burst height of slightly less than 106,000 feet.

 

Kaymont 1500

Payload Mass

Burst Altitude

Time to burst

Neck Lift

Lbs.

Grams

Meters

Feet

Miles

Min

Grams

Lbs.

2

907.2

35810

117487

22.25

133

1711

3.77

2.5

1134.0

35221

115554

21.89

130

1983

4.37

3

1360.8

34678

113773

21.55

128

2255

4.97

3.5

1587.6

34179

112136

21.24

127

2523

5.56

4

1814.4

33714

110610

20.95

125

2790

6.15

               

Kaymont 1200

Payload Mass

Burst Altitude

Time to burst

Neck Lift

Lbs.

Grams

Meters

Feet

Miles

Min

Grams

Lbs.

2

907.2

34722

113917

21.58

129

1651

3.64

2.5

1134.0

34059

111742

21.16

126

1925

4.24

3

1360.8

33454

109757

20.79

124

2197

4.84

3.5

1587.6

32902

107946

20.44

122

2466

5.44

4

1814.4

32392

106273

20.13

120

2734

6.03

4.5

2041.2

31911

104695

19.83

118

3005

6.62

               

Kaymont 800

Payload Mass

Burst Altitude

Time to burst

Neck Lift

Lbs.

Grams

Meters

Feet

Miles

Min

Grams

Lbs.

2

907.2

31040

101837

19.29

115

1731

3.82

2.5

1134.0

30260

99278

18.80

112

2018

4.45

3

1360.8

29559

96978

18.37

109

2305

5.08

3.5

1587.6

28930

94915

17.98

107

2587

5.70

4

1814.4

28353

93022

17.62

105

2868

6.32

Table 3. Flight parameters with various Kaymont Balloon models and payloads.

 

Payload Estimate

To estimate the weight of the payload, we weighed the components or estimate parts:

 

In the Box

Mass (g)

pounds

Box

257

 

Styrofoam walls

14

 

Plywood

110

 

Camera #1 w/ card

123

 

Camera #2 w/ card

123

 

Cord to Camera #1

49

 

Cord to Camera #2

49

 

New Trent Battery#1

143

 

New Trent Battery#2

143

 

Garmin

49

 

SPOT Meter

97

 

3 lithium batteries for SPOT

23

 

Hand warmers

256

 

Total Inside Box

1436

3.17

     

Outside the Box

   

Parachute

152

 

Radar Reflector

142

 

String from Box to Parachute

42

 

String from Balloon to Parachute

37

 

Bamboo Ring

50

 

Total Outside Box

424

0.93

     

Total Payload

1860

4.10

Table 4.  Estimated Payload