Stiffeners are added so that the appendix will not foul in the rigging. With a fouled appendix the helium cannot be valved, and the balloon after becoming full at its ceiling will burst. These stiffeners are taped to the outside of the appendix just before inflation.
The various appendix types which have been used are given in the following table:
Appendix Data
Appendix Type Stiffeners Effect on Altitude Attained Effect on Descent
None None Ceiling is 10,000 to 20,000 feet lower than computed. Balloon remains full at all times after ceiling is reached by taking on air. Greatly complicates control.
Standard 3 corrugated cardboard battens, $2\frac{1}{2}$ by 15" Computed ceilings attained. Balloon remains full at all times after ceiling is reached by taking on air. Greatly complicates control.
Standard 4 aluminum battens 15 x $\frac{1}{2}$ x .030"24 ST Computed ceiling attained if balloon does not burst due to restriction on appendix. Air excluded during any descent fairly well.
Flattened Tube Metal spring bow to hold appendix flat, like pressed trousers Not yet flight tested. Similitude tests indicate computed ceiling would be reached with no bursts due to appendix at 1000 ft/min rate of rise. Not yet flight tested. Similitude tests indicate almost complete exclusion of air.
Figures 2, 3, and 4 show the various appendices described in the above table.