Dropship by StealthWorks ()
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This is my original concept for a DropShip. The huge air-breathing engines on the wings are for atmospheric flight and the ion-engines on the tail fins are for space flight. Loading and unloading of troops and vehicles are via the cargo door in the nose of the craft that pivots down to form a ramp. The figure in the foreground is there just to give a sense of scale.
The ship was modelled in Blender and then rendered in Octane.
Image Comments (5)
wblack () 12:11PM | Wed, 01 May 2013
I’ve been perusing your gallery and you have created some technically superb renders – it is clear that you strive for some sort of realism; it is in that regard, and because I appreciate your artistic sense, that I offer my constructive critique. It is apparent from the human-scale reference figure that this is a fairly massive vehicle and your description “Dropship” proposes that it is capable of both atmospheric and space flight – this being your intent I must point out some design blunders. The forward edge of wing between fuselage and atmospheric engine housing presents a rather thick/large non-aerodynamic blunt forward facing surface, which does not fit with your otherwise aerodynamic design. In atmospheric flight this would generate destructive levels of drag and turbulence – considering hypersonic atmospheric entry velocities (mach 15 or better) this would be catastrophic – resulting in break-up of the vehicle in flight. If you propose some form of hand-wavum force-field technology to lend an aerodynamic the vehicle shape does not possess then your engine choices do not seem to make sense – I will explain why. Your description defines this as a “Dropship” suggesting something with performance akin to the vehicle in the second movie of the Alien saga with a full-up powered atmospheric-entry performance capability – this kind of atmospheric-entry flight dynamic (with respectable cross-range and the capability of combat maneuvers in all phases of flight) requires a rather muscular propulsion system for both atmospheric and space – an ion drive makes no sense for this kind of vehicle. An ion thruster is a form of electric propulsion that creates thrust by accelerating ions. The term is strictly used to refer to gridded ion thrusters, but may often more loosely be applied to all electric propulsion systems that accelerate plasma, since plasma consists of ions. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force. Electrostatic ion thrusters use the Coulomb force and accelerate the ions in the direction of the electric field. Electromagnetic ion thrusters use the Lorentz force to accelerate the ions. Accelerations given by ion thrusters are frequently less than one thousandth of standard gravity. If you want some sense of the amount of thrust power a real world Ion thruster creates hold one hand out palm-up and place a single sheet of standard notebook (81/2 x 11) paper on the palm of your hand. The amount of pressure the weight of the paper puts on your hand is representative of the kind of thrust ion thrusters can produce. All Ion drives are low-thrust. It is a physical limit. Ion drives cannot have high thrusts. Since you are accelerating ions, the acceleration region is chock full of ions. Which means that it has a net space charge which repels any additional ions trying to get in until the ones already under acceleration manage to get out, thus choking the propellant flow through the thruster. The upper limit on thrust is proportional to the cross-sectional area of the acceleration region and the square of the voltage gradient across the acceleration region, and even the most optimistic plausible values (i.e. voltage gradients just shy of causing vacuum arcs across the grids) do not allow for anything remotely resembling high thrust. You can only increase particle energy so much; you then start to get vacuum arcing across the acceleration chamber due to the enormous potential difference involved. So you can't keep pumping up the voltage indefinitely. To get higher thrust, you need to throw more particles into the mix. The more you do this, the more it will reduce the energy delivered to each particle. It’s a physical limit. The visual sense of your vehicle suggests something with a weight/mass on the order of a C-5 Galaxy (at minimum) which has a dry-mass of 380,000 lbs (172,400 kg). Dry-mass is just the mass of your airframe and propulsion system without any fuel or payload. A C-5 Galaxy has a fuel capacity of 51,140 gallon – which is a good ballpark for the kind fuel load required for the dynamic flight maneuvers your description suggests. Aviation Grade A weighs 6.7 lbs/gallon (aviation grade fuels range from 6.4 lbs/gallon to 6.8lbs/gallon –for purposes of ball park design estimates the industry standard is 6.7 lbs/gallon). 51,140 gallon = 342,638 lbs – so a C-5 Galaxy, with its fuel load, has a wet-mass of 722,638 lbs – we are still talking about the mass of the vehicle without any payload. Your vehicle would likely mass higher due to the structural strength required to withstand the thermal stress of atmospheric entry and the aerodynamic loads of hypersonic flight and the implied requirement of performing combat maneuvers through all flight-phase transitional states. Which is why, regardless of your atmospheric propulsion method, an ion drive makes no sense.
StealthWorks () 2:17PM | Wed, 01 May 2013
Wow wBlack - surely that has got to be some kind of a record for the longest comment ever posted on a render !!! I really appreciate your time in setting me straight on these obvious design flaws (and to my shame I have to admit I actually have a degree in Aeronautical Engineering!) However, In the time honoured fashion of Sci-Fi and art - can we just agree that something looking cool far outweighs any technical shortcomings? I'd love to see the letter you wrote to George Lucas regarding the aerodynamic properties of the Millenium Falcon during atmospheric flight ;-) If it really bothers you, we can just assume that a hundred years from now scientists have overcome current ion propulsion limitations, that advanced materials and self generated forcefields can compensate for the stresses caused by atmospheric drag and turbulence and that the air breathing engines aren't powered by inefficient chemical propellants... Of course, its with slight trepedation now that I start designing my next ship! LOL p.s. Maybe I'll post some video footage of this thing in flight just to prove you wrong ;-)