From: aewhelan@icaen.uiowa.edu (Andrew Whelan)
Subject: Re: Controlling Airship Lift
Date: Tue, 26 Jan 1993 15:52:49 GMT
Organization: Iowa Computer Aided Engineering Network, University of Iowa

In article <kkobayas.727919759@husc.harvard.edu> kkobayas@husc8.harvard.edu (Ken Kobayashi) writes:
>kamprath@space-grant.sprl.umich.edu (Michael F. Kamprath) writes:
>
>>In article <1993Jan21.074446.15421@nuscc.nus.sg> Perry Morrison,
>>swkmorri@nuscc.nus.sg writes:
>>>Some time back I posted a query about dirigible/blimp control surfaces.
>>>Now I have another query- could a helium filled airship control its
>>>lift by having some internal heat delivering device such as an electric
>>>radiator.
>>>
>>>I'm aware hot air balloons generate lift by heating the enevelope with
>>>LPG flame. Could sufficient expansion be delivered by an electric/non
>>>combustion method?
>>>
>>>cheers
>>>Perry Morrison
>>>
>
>>Lift is not a good choice of words to describe why hot air/helium balloons and 
>>dirigibles "fly" -- try buoyancy.
>
>>Anyways, yes they can, but an electric heater would weigh temendous amount.
>>It would probably weigh less just to bring more helium along for the ride.
>
>
>   And thtow away expensive helium when you want to go down?  I think the
>point of the original poster is that if heaters are used the dirigible can
>go up or down without loss of helium.  But if electric heaters are too
>heavy, how about gas burners, like the ones used on hot-air balloons? 
>Those should be light enough, and it shouldn't be too hard to construct a
>safe heat-exchange system...

Hang on a sec! As Kamprath wrote, the important part here is the bouyancy.
Blimps, like the Goodyear bunch, keep a constant (or nearly so) amount of
helium in the envelope and regulate the volume of the heluim to regulate 
the lift. By pumping more air into pockets in the envelope, the pockets
expand, compress the heluim, and lower the bouyancy. 


               ______________________________
              /      |              |        \  ______
             /       |              |         \/      \
            /   Air  |              |   Air    \      |
           /         |              |           \_____/
           \_________/    Helium    \__________ /     \
            \                                  /      |
             \                                /\______/
              \______________________________/
                    |      |
                    |______|
                      


If you have seen the Goodyear blimps on the ground, there are two 
chain-saw sized motors that hang near the gondola and appear to 
start randomly. These motors regulate the helium/air ratios.

Back (way back) to Morrison's original question: could heaters be used
to expand the heluim? Yes, but since a source of energy would be needed
to maintain altitude, it would be less practical than regulating the
helium/air ratios.
-- 
________________________________________________________________________ 

   andrew whelan                                                   
     aewhelan@icaen.uiowa.edu    
       university of iowa, idaho city, ohio
________________________________________________________________________

                                                                    
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