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Effect Of Gores In Hot Air Balloons

hot air balloons buoyancy

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#1 sgor22

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Posted 17 January 2018 - 10:05 PM

There are many types of hot air balloons. I realized that some of them contain many gores (as much as 24) and some contain less which makes a great difference in the shape.

image.png.8eb9eaae4ba8bfb8de8ad1cd973c82         image.png.2f73d65494481ca8b2a784dc36985e      image.png.1a4402ee2cc5e1b1b47e5f08da7c53     

18 gores                                                  3 gores                                               24 gores

 

What I am wondering is the difference that the number of gores make in the flight of hot air balloons. 3-gored balloon's shape is much different than 24-gored balloon, does it affect its flight in any way? (e.g. buoyancy or air resistance) If not, what else might it affect? Why might people choose to make balloons with more/less gores?

 

The images are taken from <https://www.apexballoons.com/balloons/>



#2 exchemist

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Posted 18 January 2018 - 02:14 AM

 

There are many types of hot air balloons. I realized that some of them contain many gores (as much as 24) and some contain less which makes a great difference in the shape.

image.png.8eb9eaae4ba8bfb8de8ad1cd973c82         image.png.2f73d65494481ca8b2a784dc36985e      image.png.1a4402ee2cc5e1b1b47e5f08da7c53     

18 gores                                                  3 gores                                               24 gores

 

What I am wondering is the difference that the number of gores make in the flight of hot air balloons. 3-gored balloon's shape is much different than 24-gored balloon, does it affect its flight in any way? (e.g. buoyancy or air resistance) If not, what else might it affect? Why might people choose to make balloons with more/less gores?

 

The images are taken from <https://www.apexballoons.com/balloons/>

 

Since balloons are blown by the wind I would not have thought wind resistance would be relevant. What does strike me, though, is that the number of divisions may affect the stress on the fabric of the balloon. I presume that as the load is borne at the seams dividing one gore from the next, the fewer of them you have, the more lift has to be transferred to the adjacent seam by the fabric itself. So more divisions would spread the stress out more . But I have no idea if this is an important factor in practice.



#3 spartan45

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Posted 26 February 2018 - 04:46 PM

The gore numbers are driven by 4 factors:

·         Fabric width (usually only a factor in vertically cut balloons – which have gone out of fashion)

·         Aesthetics

·         Load tape strength

·         Panel length

·         Cost

o   Fabric Width: if you cut the balloon with vertical panels then the number of gores must greater than balloon diameter / fabric width

o   Aesthetics:  Smooth balloons are better for putting artwork onto.  The gores need a bit of “bulge” to shed the load into the vertical tapes, so more gores means a smoother balloon.

o   Load tape strength:  One load tape per gore, so the tapes in 12 gore balloon carry twice the load of those in a 24-gore.  That’s why we go from 24 to 32 gores on our larger balloons.

o    Panel length: The fabric contains flaws,  it’s more economical to fit 24-off 3 metre panels into a length of fabric with some flaws in it than 12-off 6 metre panels.

o   Cost:  The more gores, the more panels, so the more work to be done.

Generally 8 panels is a practical minimum.

 12-16 gores brings the panel length down to a sensible size.  24 are needed for a good smooth surface for an advertising balloon.

This information was given to me by a well-known hot air balloon company.