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Balloon Design

Kaymont Balloons (kaymont.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 (https://weather.uwyo.edu/upperair/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.habhub.org)

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 (kaymont.com)

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

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