Turning during terminal descent

Bill :>

As no-one else seems to have leapt in here I thought I'd do the polite thing and offer a suggestion.

Frankly, I have no idea, never having flown a balloon in my life, but it's almost certainly some sort of Coriolis effect caused by the Earth spinning.

Does it go round the other way in the other hemisphere? (No idea where you did the descending...)

One clue in the previous post - the balloon was a Cameron, so it was equipped with a scoop. It has been my experience that balloons with scoops tend to turn more than those with skirts. Releasing the scoop snaps from the burner frame reduces that tendency.

One friend has 2 Thunder & Colt balloons - one with a skirt, and another with a 'mini-skirt' or almost a scoop. The balloon with the scoop spins, while the one with the skirt does not. My Cameron Viva with a scoop tended to spin, while the Eagle, Balloon Works, and Aerostars with skirts did not.

Alan :>

You suggest that the scoop acts like a rudder to turn the balloon when the air-flow is upwards relative to the envelope?

Makes perfect sense. Out of interest, can it be made to spin one way or the other by adjusting the scoop?

Interesting. I have flown Raven and Aerostar with skirts for over 20 years, every one spun on any kind of rapid descent. So did my Thunder with a skirt. I used to believe it was the side vent leaking air that did it until I got the Thunder. Certainly one could speed up the spin, and even do it in level flight with the side vent. I believe Coriolis!

No balloon is perfectly symmetrical, and neither is the weight distribution in the basket. This by itself will always cause some tendency to make the balloon rotate during a fast descent (and to a lesser extent, a fast climb). When fitted with a scoop, the ballon is deformed very asymmetrically by the airstream flowing upwards around and into the envelope. You get a large deformation on one side of the balloon, and as a result it will a) rotate and b) slow down as it loses some of its aerodynamical (drop-like) shape. This will usually occur at a descent speed of between 800 and 1200 ft/min, depending on the load. If the balloon is decently loaded (i.e. not too light), you can actually increase the rate of descent by using the burner: putting just enough heat in to create some internal pressure and regain normal shape, but not enough to gain lift. Due to reduced drag the scoop-equipped balloon will then descend faster. It will also rotate less. The slowing down at 1100 FPM is a result of the denting of the envelope/increased drag, not of hitting 'denser air'. Tell him to look up into the envelope, burn at that point and he may learn something from you. I found this out during paraballooning competitions, where skydivers jump from balloons onto targets and the balloons then have to drop markers on targets at virtually the same spot - resulting in the need for very fast descents from a minimum of 4000 ft AGL.

Regards, Frank Schweppe

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