There is a somewhat popular notion that one pound of freelft
provides an acceptable ascent rate for a small amateur radio
equipped balloon.

This is a good approximation if the balloon is close to 4 feet
in diameter at release, but most of the payloads now with GPS
onboard and one or more radios will need a bigger release diameter
to obtain the necessary lift.

Here is a small table of values obtained by using LIFTWIN that
shows the dependence on release diameter for the proper value
of freelift required to achieve an ascent rate of 1000 feet/minute.


Release diameter            Freelift for 1000 feet/minute

    3 feet                              .7 pounds
    4                                  1.2
    5                                  1.9
    6                                  2.7
    7                                  3.7
    8                                  4.8

Hank Riley, N1LTV
04/24/00
