Ascent rate 4 to 6m/s - sources?

[Steven Boonstoppel]

Hi folks,

Steven here - Nick's "remote puppet" that makes perfectly fine vero boards: size doesn't matter. Only weight.

Anyhoo, I am making lesson materials around a HAB launch. All good and well, but I'm looking for some explanation around the recommended ascent rate of roughly 5 m/s. Surely it correlates with the average retrieve distance being pretty optimal versus the amount of data collected. But I've heard whispers about "aerodynamic stability". Now I would like to add some argument in my materials about why we are looking at 5m/s, and I'm lacking a somewhat physics-related explanation. Stable pics, sure, but why is it stable with this speed?

Does someone here have a useful source that has some high- or low-level explanation of this stability? Thank you very much in advance!

Cheers, Steven

[Steve]

I must check my unread emails more often**.  

Its not that 5m/sec is actually stable - its just that stability gets disproportionately worse with ascent rate.  In fact from a payload stability point of view he slower you can ascend the better - but there are other reasons not to ascend too slow:

    the balloon may enter a "float" rather than bursting (that may, or may not be desirable depending on what you want to achieve).

    the drift is more - recovery distances longer and may take your landing spot into the sea.

    the maximum altitude is less.

The wash of air going round the balloon causes turbulence underneath it  - which makes the payload swing around in a sort of conical pendulum motion (while sometimes also rotating) .  I believe that air motion around the balloon can set up a circular wash.  Totex even used to sell a device that attached to the balloon envelope that was supposed to reduce the problem. 

It becomes increasingly difficult to achieve fast ascent rates - as more gas you put in (giving more lift) is counteracted in part by the increased drag of the balloon - its a square law (drag) vs cube law (lift) thing.  I have a feeling that the amount of turbulence is more proportional to the free lift force than ascent velocity.

There is actually an optimum (average) ascent rate to achieve maximum burst altitude - above this rate the balloons burst early as they reach burst diameter lower.  Below this optimum rate the balloon ascent will slow as it approaches burst (I believe this is the latex becoming a constraining factor).  This rate varies by manufacturer & balloon size and is one of the secret sources of balloon altitude records ;-)

4  - 6m/s is a good range to stay in - noting that some balloons may float at 4m/sec.  5m/sec (circa 1000ft/min) is also what the manufacturers use a reference for their data. 

If you want stability with a fast ascent rate then look to other methods such as a boom (not that I recommend that in the confined spaces of the UK) or some form of active control. 

    Steve G8KHW / AJ4XE

** I get inundated with posts from the [picoballoon] group taking about the minutiae of twiddling WSPR message bits (or the 3 main protagonists are having an ego war).

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[Nick McCloud]

On Sunday, 15 March 2026 at 18:20:43 UTC Steve wrote:

If you want stability with a fast ascent rate then look to other methods such as a boom (not that I recommend that in the confined spaces of the UK) or some form of active control. 

All good info - also explains the line lengths to try to get the payload as far as reasonably possible from the balloon wash.

Steven's question was more out of curiosity because he won't be bikeshedding the parameters until he's done a couple more if he knows what's good for him!

** I get inundated with posts from the [picoballoon] group taking about the minutiae of twiddling WSPR message bits (or the 3 main protagonists are having an ego war).

The latter I suspect. Groups.IO has split out a separate group for them to duke it out.

[Nick McCloud]

On Sunday, 15 March 2026 at 00:23:06 UTC Steven Boonstoppel wrote:

Hi folks,

Steven here - Nick's "remote puppet" that makes perfectly fine vero boards: size doesn't matter. Only weight.

Larger piece of VeroBoard still weighs more and then needs a larger box. Target weight 110g but ends up at 160g says it all.