Hot Air Commuting            

 

blimp r 2

 

This started as a vague idea for an urban mass transit commuter.

The idea was to have a very elongated dirigible with a narrow cabin where passengers are seated only 2 to 4 abreast in a pattern that extends 20 or 50 or even 100 instances.

The balloon would be semi-rigid and would generate lift at about 80% plus of the tare weight ( empty) of the entire craft. The rotors would mostly lift the cargo and thus would require lower power input. The rotor discs would also be comparatively large and slow turning for reasonably quiet operation in urban environments.

 

blimp r 11

 

The lifting balloon would be pressurised with nitrogen which is heated to high temperature by exchanging thermal energy from the exhaust of the turbines that power the main rotors. Hot air balloon principle.

By applying the exhaust energy for lifting, the efficiency of the engines is vastly improved and the strain on the rotor mechanisms and integrating structures is much reduced.

This craft would then be quite ideal for extended periods of continuous operation doing short hops all around urban and suburban environments to collect and drop-off passengers in a regular commuting service.

 

blimp r 1

 

  A tremendous advantage of such a service would be the complete disconnection from traffic! Another fantastic coincidence would be the panoramic view that the passengers would be treated to.

Since the rotors would also transit to horizontal operation the craft has a reasonable higher altitude cruising capability which then also makes it ideal for shorter, inter-city commuting. In this application the advantage of requiring very limited grounding facilities adds to the charm of the concept.  

 

blimp r 7    

 

 

                                                                                   blimp r 10

This vague idea for a 3 dimensional commuter was then used as a subject in a self ascribed tutorial for studying and familiarisation of surface functions in 3D design software.

(The component shown below - 4 images - constitutes one single model-part entirely developed in surface functions)  

singlepart 1

singlepart 3  

 

                        singlepart 4singlepart 5

   

After intermittently considering the crudely modelled concept  through multiple dozens of lunar phases it was decided to formulate another model more dedicated to the function of practical form rather than the operation of 3D design software.

In this evolutionary increment the craft is powered by one or two turbine engines which are entirely dedicated to driving AC electric generators. The exhaust thermal energy is similarly directed to generating lift by transference to the balloon gas but the rotors, and there are now three of them, are driven by electric motors. 

dirigible t 3

 

 dirigible t 10

Above: Port side turbine with electric generator. Note the passenger cabin seating arrangement.

 

Each rotor is driven by a dedicated electric motor but the jury is still out on whether the two main rotors should be interlinked with a synchronising drive shaft. For the sake of safety the bias is to insist on interlinking the main rotors. This obviously brings about complicating configurational permutations about which the (as yet phantom) design team will have to make hard, ( course setting) decisions.

The capacity for generating electric power will allow additional heating of the lifting gas during certain operational cycles and conditions. For example: where the upper limits of gross weight is reached at take off the electric power will, for a short period, be exclusively directed to heating coils associated with the gas envelope until a certain determined temperature is reached before the rotor motors are energised for take-off. 

Also in colder climates where the thermal radiation from the vast surface area of the balloon could cool the lifting gas too quickly.

In a hot ambient environment additional heating of the lifting gas may be required in order to increase the differential for lift.     

 

dirigible t 13

 

  dirigible t 23

 

 dirigible t 26

 

 Speculative, idealised configuration of dirigible operation and construction.

The first consideration is obviously always on the mass properties but since the gas balloon is not the sole lifting component on the craft there is some leeway in the final construction configuration with regard to overall weight.

The centre tube (see images below) is of a material that will withstand extremely high temperatures (300 to 500 deg C) and it should have good thermal conductivity properties.

It should ideally also have high tensile strength and resistance to tearing (obviously).

The first material that comes to mind which is most likely to conform to these criteria would be a specialised aluminium foil combined with a carbon fibre netting.

The idea would be to pressurise that centre tube to about 2 to 5 bar (?) at a gas  temperature of a few hundred degrees C. The pressurisation causes elongation and structural rigidity to the centre tube. 

The thermal energy immediately starts radiating into the large gas cavity of the  outer envelope of the balloon and that causes pressurising tension on the outer skin. The radiating (sic) fibre tendons are attached to strips that act as longitudinal ribs to shape the outer skin fabric for aerodynamic optimisation. 

The outer gas envelope will also be electrically heated at start-up and whenever required during operation to keep the gas density at the lowest value in relation to the maximum temperature that the outer skin fabric can safely bear. 

 

 crossect 2     crossect 5     crossect 3

 

 dirigible u 11

 Above: Section throught outer envelope to show inner high pressure, high temperature tube with two verticle ducts to link the lifting gas to the flow of the turbine exhaust stream. 

 dirigible u 15

dirigible u 5 

dirigible u 6

Standard 6m freight container built from aluminium and carbon fibre

 

 

...............Please watch this page for further hot air developments........

 

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Come on already! It is dissolution of inertia that we want - not cumbersome, combustion driven hot air contraptions!

 

 Kindly express your opinions on the practicality and desirability of such a commuting craft.