As always, there are many things which could improve the project 'The Airship Simon'. A few very interesting points have been mentioned through e-mail by Cezar, a fellow airshipian, in January 2002. With his permission, we cite them below:
- "Welding mylar is difficult but not impossible: only one side of the foil is
metalised - you can weld two foils if they touch each other with the
non-metalised sides. To figure out what side is metalised you can
scratch it gently with your fingernail. If you scratch on the metalised side the
scratch will be visible in light. The difficulty of welding comes from mylar's
tendency to shrink at high temperature, obtaining the projected shape being difficult."
UPDATE April 2002
"Regarding what I said on welding mylar - well it is partially true, depending on what kind of mylar you have. I did some research on Dupont's site, they are one of the biggest mylar manufacturers and they have dozens of types of mylar. All mylars have a main polyester layer, but may have (or not) one or two additional 'welding-friendly' plastic layers, with or without the metal layer too. So to be fair - some mylar-based membranes can be welded - due to the additional layers - as you said, mylar itself doesn't [get] weld[ed] well."
- "[...] ordinary transparent 5cm wide adhesive tape
is the best and simplest way to patch blimp holes. If it sticks
neat, without folding the hull or the patch, helium has a
difficult way out. It should provide also a good reinforcement along
the lines [when] glueing the mylar pieces of the hull.
"What I remember reading on another web page was about a product called 'Heat and Bond' or 'Heatnbond' or so. It is a heat glue adhesive tape used to glue fabrics, so strong that in some cases is used as a sewing replacement."
- "The Cr (resistance coeficient) of 0.35 is amanzingly high for how
streamlined Simon looks. I would guess it somewhere below 0.2 - but that's just a guess."
- "Your engine/propeller combination is underpowered.
If the 'Robbe hauptkatalog 98/99 - page 397' isn't bullshiting,
a Power Plus 410 is capable to push between 210g (at 10V, 15k rpm,
5.8A) and 460g (at 16V, 24000 rpm. 11.3 A) with only a tiny Rojet 75mm impeller. A
propeller should be much more efficient. [...] I bet you should get more thrust using the
recommended 7x3 propeller size (for 'Segelflug' at page 378, same
catalogue). At the same rpm, a 9x6 propeller needs >10 times more power than a 7x3
one. I bet 9x6 goes at much lower rpm than it should - somewhere above
15000 rpms. Probably this is also the cause for the engine overheating you