"SpaceShipTwo could be single stage to SUBorbit"
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From: Pat Flannery on 18 May 2010 16:40 On 5/18/2010 4:57 AM, Sylvia Else wrote: > Probably ought to be comparing rates for hydrogen airships in general, > rather than just Hindenberg. Alternatively, only consider those shuttles > that were lost. That would be almost impossible to do for the hydrogen airships, due to the large number that were built in WW I and between the wars, and the fact that many were shot down while on military missions during WW I. Passenger airships were comparitivly few in number; but is the Shuttle considered a passenger carrying vehicle, as its crew does space-related work on every flight? As far as the two lost Shuttles themselves go it can be done though. Columbia flew a total of 28 missions, carrying a total of 160 astronauts. So vehicle loss rate was 1 in 28, or 3.6%, and crew fatality rate was 160/7=22.86 or 4.4%. Challenger flew a total of 10 missions, carrying a total of 60 astronauts, so loss rate was 1 in 10, or 10%, and crew fatality rate was 60/7=8.57 or 11.7%. Pat
From: Pat Flannery on 18 May 2010 18:49 On 5/18/2010 8:45 AM, Rick Jones wrote: > In sci.space.history Pat Flannery<flanner(a)daktel.com> wrote: >> As part of that project, I started looking up installed horsepower >> on airships of various sizes required to move them at various >> speeds, and made a most interesting finding...as the size of the >> airship increases, it takes proportionally less horsepower to move >> it at the same speed. > > I presume you mean its length and not its cross-section right? In > broad terms, it sounds a bit like a boat and hull speed. "Size" was a combo of both length and beam, giving the total amount of cubic feet of air it displaced. As an example of the two ends of the spectrum, the original Goodyear blimp "Pilgrim" from 1925 had a volume of 55,000 cubic feet and could cruise at 40 mph with a max speed of 50 mph, on the power of one 60 hp engine, so cubic foot capacity to hp ratio was 917 to 1. "Hindenburg" on the other hand had a envelope volume of 7,062,000 cubic feet and could cruise at 76 mph with a max speed of 86 mph, on a total of 4,800 hp, so its capacity to horsepower ratio was 1,471 to 1...despite its 53% greater cruising speed. Figures for the present-day Goodyear blimp "Spirit Of America" are a capacity of 202,700 cubic feet, a total of 420 hp, cruising speed of 30 mph with a max speed of 50 mph, and a volume to horsepower ratio of 483 to 1. Pat
From: Greg D. Moore (Strider) on 18 May 2010 23:45 Pat Flannery wrote: > On 5/17/2010 5:40 PM, Alain Fournier wrote: > >> >> From the above I conclude that the Shuttle must go about 6 times >> faster than the Hindenburg :-) > > Long time back, a friend and I were designing future dirigibles > powered by solar energy derived from lightweight solar cells covering > their exterior (during daylight some of the electrical power would be > used to break down water into hydrogen and oxygen; at night these > would be recombined in fuel cells to allow the electric motors to > continue to drive the airship). As part of that project, I started > looking up installed horsepower on airships of various sizes required > to move them at various speeds, and made a most interesting > finding...as the size of the airship increases, it takes > proportionally less horsepower to move it at the same speed. Probably more accurately, the longer it gets in relation to its width. This is probably the same equation that drove schooner design. > To give you some idea of just how efficient a large airship can be in > horsepower usage, the Hindenburg's total installed horsepower(4,800 > hp) was _less than half_ of that of a single NK-12 turboprop engine > off of a Tu-95 "Bear" bomber (12,000 ehp), yet could drive the > 803-foot-long airship at 85 mph. > > Pat -- Greg Moore Ask me about lily, an RPI based CMC.
From: Pat Flannery on 19 May 2010 04:16 On 5/18/2010 7:45 PM, Greg D. Moore (Strider) wrote: As part of that project, I started >> looking up installed horsepower on airships of various sizes required >> to move them at various speeds, and made a most interesting >> finding...as the size of the airship increases, it takes >> proportionally less horsepower to move it at the same speed. > > Probably more accurately, the longer it gets in relation to its width. Not necessarily; our modern submarines used wind-tunnel data from the 1920-30's navy dirigible program, and the best shape isn't like a torpedo, with a domed nose and tapered tail on a cylindrical body, as was thought in WW I, but rather a smoothly curving teardrop shape that can be surprisingly wide at its maximum diameter compared to its length. (called a laminar flow body of rotation) If you look at a side view of a modern Goodyear blimp and the Hindenburg, they are fairly similar in proportions except for size: http://www.wolfsshipyard.mystarship.com/Misc/Airships/Airships.htm http://blog.miragestudio7.com/wp-content/uploads/2007/07/goodyear_blimp.jpg In the case of our nuclear subs, the best shaped one from a hydrodynamic point of view was the Skipjack class: http://www.motionmodels.com/ships/sub/skipjack.html But although very efficient from a drag point of view, it was also hard to manufacture due to its smoothly curving lines, so later ones added a airship-form bow and stern to a basically cylindrical midsection to speed up manufacture, and allow the sub to dock in shallower waters in comparison to its length: http://motionmodels.com/ships/sub/la-class.html To the point where they are beginning to resemble WW I style airships again. > This is probably the same equation that drove schooner design. There's a big difference though in that the schooner pierces the water surface, whereas both the submarine and airship are totally immersed in the medium they travel through. I think the efficiency improvement with size has something to do with the density of air and how smooth the boundary layer is compared to the airship's size. Smaller airships tend to "drill a hole" through the air generating drag, as it doesn't have time to accelerating up to the speed the airship is traveling at before reaching the back half of the hull, and therefore generates drag and turbulence, whereas the giant ones allow near-laminar flow as the air flows smoothly down their hull, adhering to it via the Coanda effect. Pat
From: Robert Clark on 20 May 2010 13:25
On May 14, 9:47 am, Robert Clark <rgregorycl...(a)yahoo.com> wrote: > On May 13, 6:50 pm, Pat Flannery <flan...(a)daktel.com> wrote: >... > > And since when did 50,000 feet become outer space? > > I like the part about it using a "liquid chemical propulsion system", > > without specifying what those chemicals are exactly. > > You could certainly make a ground takeoff rocket plane that could climb > > to 50,000 feet, but since numerous types of jet aircraft are capable of > > flying to 50,000 feet also, what would be the point of doing this? > > > Pat > > The article mentions "50,000 ft and above". But to do suborbital > flights means above the sensible atmosphere and a longer time for the > period of weightlessness. > The author Rob Coppinger may have given the 50,000 ft. number to > remind the reader of the altitude WhiteKnightTwo reaches. I'll ask him > about that. > I got an email response from one of the scientists at GasDynamics about the suborbital study they did on the SS2. As I thought, the reporter Rob Coppinger only mentioned 50,000 ft to remind the reader that is the altitude WhiteKnightTwo took SS2, which wouldn't be needed for the version of SS2 that used higher performance liquid-fueled engines. In the GasDynamics study they used the [URL="http://en.wikipedia.org/ wiki/Vinci_%28rocket_engine%29"]Vinci hydrogen-fueled engine[/URL] being developed by the ESA as a new upper stage engine for the Ariane. They said by truncating the nozzle they could get adequate sea level performance to allow a horizontal takeoff from the ground to reach >100 km altitude for the SS2. Note that since the LOX/LH2 propellant is actually less dense than the solid/nitrous propellant now used with SS2, the takeoff mass would actually be less than the initial mass of the air launched SS2. Bob Clark |