Apologies on behalf of us Yanks for desperately clinging to the English
system, ironically abandoned long ago by the Brits. I expect that sometime
in this millenium, we'll join the rest of the civilized world in fully
adopting the metric system, perhaps even before the only other hanger-on,
By "stalling", I mean a significant loss of ascent rate to the extent that
burst and descent may be delayed until the flight is much farther downrange
I pointed out the most effective measures to avoid stalling, but I must
emphasize the importance of carrying a commandable cutdown device if all
else fails. This device has been used even on otherwise normal flight to
avoid landing in an unaccessible area. The EOSS cutdown device also
incorporates a DF beacon - it transmits a DF signal for 30 sec every
minute, and listens for a DTMF cutdown command for the remaining 30
sec. The DF beacon has paid for itself many times where the APRS beacon
has failed - most recently on our last flight.
IF you have run LiftWin, you may have noticed that for a given balloon and
payload weight, one may fill for a range of ascent rates. A more generous
fill will yield a faster ascent rate due to greater lift, and will result
in burst at a lower altitude due to the greater volume of fill gas; the
envelope will burst at a fairly predictable expanded maximum diameter.
EOSS has achieved its 100% recovery rate largely because we deploy the
tracking and recovery teams out to the vicinity of predicted landing before
we even start the fill. This has allowed the teams to witness the descent
and landing on nearly all flight in recent years. During the summer, the
upper winds are easterly, which causes the balloon to return towards the
launch site, sometimes even passing directly overhead. On those flights,
the trackers typically will deploy from the launch site after assisting the
launch team. Winter flights, however, can be expected to travel at least
100 km downrange.
I'm not aware of any amateur balloon group who have successfully flown a
latex release valve, but a company in New Mexico, US, Space Data, uses that
method to float mobile phone cell sites in the stratosphere for up to 3 days.
Both latex and plastic balloon envelopes must be as light as possible, and
thus rarely survive a flight and landing intact. And latex deteriorates
rapidly in solar UV radiation - and often to the extent that a lightly-filled
and slow-ascending balloon may burst at a lower altitude than a faster one,
contrary to the assumption of a fixed burst diameter noted above.
Accordingly, re-use of balloons is hardly worth a second thought.
In the US, Kaymont Inc in New York distributes the Japanese Kaysam line of
latex balloons. A 1200 gm balloon, suitable for flights under 5 kg, costs
about US$65.00 plus shipping. You might check with some of the other EU
balloon groups listed on Ralph Wallio's web site for their sources. Beware
of bargain basement latex balloons which may not have been stored properly
or have exceeded their expiry date. They may have deteriorated to the
extent that they won't survive a fill, or may burst much earlier than
expected. But there are some valid bargains out there. Caveat emtor.
I've cc'd this to the GPSL reflector, which has become the ad hoc forum for
technical issues related to ARHAB.
73 de Mike W5VSI
Thomas Scherrer wrote:
> Hi mike, thanks for getting back to me,
>> HEre's a link to all of EOSS's balloon-related software:
> super thanks !
>> LiftWin is quite handy for computing a fill for a variety of balloons
>> based on the weight suspended from the balloon neck.
> great, I am just a bit sad about it dont handle metric mode :-)
>> Both He and H2
>> are supported. As a rule of thumb, one should aim for about 1000 ft/min
>> ascent rate to avoid stalling when flow separation occurs at high
> aha ok, stalling, you mean stabelicing at a height under the burst height
> so I get a problem ?!
>> A latex balloon can "stall" either due to an inadequate fill, cooling
>> after sunset or a gas leak. It's an excellent idea to include a
>> commandable release device to bring the payload string down before
>> it soars out of sight and its batteries die.
> exactly what I am affraight of, first of all I need to understand all
> fundamentals into full datail,
> to first prevent getting any issues, and then also add safety devices,
> a commandable feature will need a two way radio, and add more weight,
> something I dont understand, using the LiftWin:
> changing a payload weight I dont see the peak height change soo much ?!?!
> that is wierd to me..
> it is clear the time to get up goes much slower when the payload gets bigger,
> but I would expect a much heavier payload to go much lower,
> that is not the fact with that program.
>> It's also possible to get a substandard fill if there is over about
>> 10 kt wind over the balloon during the fill; this creates "false
>> lift" due to the top of the balloon acting like an airfoil. Best
>> plan is to avoid filling under such conditions; winds are typically
>> calmest shortly after sunrise.
> yes I see, I expect to perform my flight an erly morning with as low
> wind ad possible
> so I get long time to find it again, and also make my car hunt for it,
> as short as possible.
>> And yes, the long-duration fligths typically use "zero-pressure" plastic
>> balloons which have vents at the bottom. But it's also possible to
>> cause a latex balloon to float at some desired altitude by controlling a
>> dump valve in the neck. Another scheme is the super-pressure balloon
>> which has a fixed, sealed volume - but it must withstand the excessive
>> pressure of the fill gas during the day.
> have anyone tried to mount a pressure sensor inside a weather balloon ?
> and an electronic controlled valve to let the gas out again?
> with this added bursting can be avoided,
> and it can even be commanded down again, and even reused ?
> and then you can save the parachute, is this a bad idea ?
> I think the large balloons are quite expensive so reusing them seems
> like a cool idea, or not ?
> have you any idea where I get the 800gr to 1200gr large size weather
> balloons cheap ?
> (maybe we should copy some of this into the balloon skeed forum as well ?
> might help others too)
Mike Manes mrmanes@...
"Things should be made as simple as possible, but not more so."