"SpaceShipTwo could be single stage to SUBorbit"
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From: Robert Clark on 21 May 2010 06:56 On May 20, 1:25 pm, Robert Clark <rgregorycl...(a)yahoo.com> wrote: > ... > 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. > ... That link should be: Vinci (rocket engine). http://en.wikipedia.org/wiki/Vinci_%28rocket_engine%29 Bob Clark
From: Greg D. Moore (Strider) on 21 May 2010 11:29 Pat Flannery wrote: > On 5/20/2010 2:21 PM, Bob Myers wrote: > > >> >> Of course, someone should point out that the Hindenburg didn't >> really "use" ANY hydrogen; it was pretty much all still there >> whenever the thing got where it was going, save for that little >> mishap in New Jersey. Were it not for the fact that they wanted to make >> round >> trips, it could have been used as a hydrogen delivery system. > > I would have to check to see if Hindenburg ever did it, but it wasn't > unusual for Zeppelins to vent hydrogen to reduce their buoyancy, as > hydrogen was pretty cheap to replace, unlike the very expensive helium > used on US airships. > That used to be standard practice as they burned off fuel on the > Zeppelins, but after WW I they used water recovered from the engine > exhaust to act as ballast to replace the weight of the burned fuel. > The really odd one was the first Graf Zeppelin (Hindenburg sister ship > was also named Graf Zeppelin) which had some of its gas bags filled > with coal gas instead of hydrogen, and used the coal gas to power its > engines to eliminate the fuel weight loss problem. Huh, interesting. I thought they also collected atmospheric water (either rain or condensate) for ballast also. > > Pat -- Greg Moore Ask me about lily, an RPI based CMC.
From: Pat Flannery on 21 May 2010 19:34 On 5/21/2010 7:29 AM, Greg D. Moore (Strider) wrote: >> That used to be standard practice as they burned off fuel on the >> Zeppelins, but after WW I they used water recovered from the engine >> exhaust to act as ballast to replace the weight of the burned fuel. >> The really odd one was the first Graf Zeppelin (Hindenburg sister ship >> was also named Graf Zeppelin) which had some of its gas bags filled >> with coal gas instead of hydrogen, and used the coal gas to power its >> engines to eliminate the fuel weight loss problem. > > Huh, interesting. > > I thought they also collected atmospheric water (either rain or condensate) > for ballast also. I seem to remember reading that also, but have never read up on the details of how they would capture the rainwater. Here's some more info on the gaseous fuel system used on the Graf Zeppelin, from this webpage: http://www.nlhs.com/mail-p5.htm "The Germans did use "Blaugas" fuel with the HINDENBURG's predecessor, LZ127 GRAF ZEPPELIN, which flew from 1928-1937. A gaseous, hydrocarbon fuel, it weighs the same as air and is roughly the same molecular structure as ethane. By using it, an airship could fly for several days and have its weight/balance ("equilibrium") remain relatively constant, providing for great economies in the use of lifting gas and ballast. Built as a demonstration airship with limited funds, GRAF ZEPPELIN was restricted in size by the overall dimensions of the largest World War One vintage construction hangar at Friedrichshafen. Seeking the achieve maximum range for intercontinental flight, the designers determined that gaseous fuel taking up roughly 1/4 the lower part of the gas space in the hull would power the engines for over 100 hours' flying time, while the equivalent space, if used exclusively for hydrogen lifting gas, would only lift about 60 hours' worth of gasoline. The gas cells were made of light cotton fabric lined with "goldebeaters skin" (cattle gut membrane.) There were 17 gas cells positioned in bays between the transverse frames of the GRAF ZEPPELIN, held in place by netting and wiring which transmitted their lift to the airship's structure. The difference with this ship is that the 12 largest cells had a lower section so that out of a total of nearly 4-million cubic feet hull volume, only about 3,037,000 cubic feet was used for hydrogen and the rest for Blaugas. Conventional gasoline tanks were also fitted in clusters along the lower keel and the Maybach engines were equipped with dual-fuel carburetors which accepted either fuel with the flick of a lever. Because Blaugas weighed roughly the same as air, ventilation of the hull was critically important. Being lighter than air, any leaking hydrogen gas would go "up and out" through vents and apertures all along the outer skin, but Blaugas would tend to settle and lay in the lower part of the hull by the keelway and work spaces. As an aid to leak detection, the Blaugas was usually scented with a strong garlic-type odor. It burned very "clean" in the engines (oil, valves, etc stayed deposit-free) but the engine mechanics used to joke that running on Blaugas the exhaust often smelled like they were cooking cabbages! A new construction hangar was built at Friedrichshafen and an upgraded commercial airship, LZ128, was on the drawing boards in 1930. The Zeppelin Company was so satisfied with Blaugas that this airship would have used it too. Then, in October 1930, the British R101 suffered a fiery crash in France. Dr. Eckener took stock of the situation and decided that his next airship should have safe non-flammable American helium and diesel engines. LZ128 was never built, and the company moved on to the bigger LZ129, which was launched in 1936 as HINDENBURG. (For various reasons, political as well as economic, the HINDENBURG ended up flying with hydrogen and her performance was so superior that helium became something of a back-burner issue; until the spectacular disaster at Lakehurst. Subsequent attempts to get helium for sister ship LZ130 ended up being thwarted by political considerations.) While successful in the GRAF ZEPPELIN for nine years, the Blaugas fuel was inflammable and rather dangerous and it posed something of a logistical headache when refueling the airship at foreign stops. Union Carbide was one of the few companies that manufactured Blaugas commercially; very often the Germans "bootlegged" the stuff using a mixture of hydrogen and propane gas set up at a "field kitchen" with cylinders and tank cars on the landing field (notably on their stops in South America.) The U.S. Navy tried Blaugas in its helium-inflated non-rigid airship (blimp) K1, which flew from 1931 to 1940. The engines ran well with it, but there were occasional problems with Blaugas leaking from its bladder ("ballonet") and contaminating the helium gas in the bag. This led to some bizarre purification problems when they tried to purify the helium in the Lakehurst helium purification plant, a state-of-the-art facility in its day, which pressurized and liquefied the helium to remove impurities. (On one occasion, a Blaugas explosion in a gas line sent a manhole cover flying 50 feet into the air next to the Lakehurst hangar! ) The Navy eventually concluded that Blaugas was more trouble than it was worth and all subsequent Navy airships used aviation gasoline." It's obvious that the person who writes that page knows airships backwards and forwards. :-) Pat Pat
From: Fevric J. Glandules on 21 May 2010 16:41 Greg D. Moore (Strider) wrote: [burnt fuel / weight problem with airships] > I thought they also collected atmospheric water (either rain or condensate) > for ballast also. I must confess that I don't understand the problem. It occurred to me that you can simply pump air into and out of a balloon *inside* a lifting gas cell to alter its bouyancy. A quick google revealed that this is the way blimps operate. What am I missing?
From: Pat Flannery on 21 May 2010 20:39
On 5/21/2010 12:41 PM, Fevric J. Glandules wrote: > Greg D. Moore (Strider) wrote: > > [burnt fuel / weight problem with airships] > >> I thought they also collected atmospheric water (either rain or condensate) >> for ballast also. > > I must confess that I don't understand the problem. It occurred to me > that you can simply pump air into and out of a balloon *inside* a lifting > gas cell to alter its bouyancy. A quick google revealed that this is > the way blimps operate. What am I missing? On a blimp the "ballonet" doesn't alter the ship's buoyancy much, it keeps the outer envelope stretched taut as the gas swells or contracts either due to its changing temperature, or climbing and descending making the exterior air pressure change around the airship, meaning the lifting gas will take up more or less volume. The Wikipedia article seems to place too much emphasis on the pressurization of the gas bag, which is pretty slight...I would imagine well under a pound per square inch. In a rigid airship the gas cells need not be taut as the interior framework maintains the airship's shape, so the gasbags can swell or contract as it changes altitude. What you do have to watch out for is going above "Pressure Height", where the lifting gas expands to the point where it completely fills the gasbags, and any further increase in height will cause them to burst from over-pressurization unless you vent gas out of them. Once you do that, you of course lose lift, and have to dump water ballast to compensate for that. If that happens repeatedly...like it did in the crash of the Shenandoah...you find yourself out of water ballast, and at that point you start dropping fuel tanks as a last resort. In the case of the fuel, the airship's lift stays the same, while its weight decreases as fuel is burned off, so unless it can lose some lift, it won't be able to land at the end of its trip. Most large airships tended to operate a bit "heavy"; that is, the gas's lift didn't quite equal the actual weight of the airship, and the last few hundred pounds of lift were generated by angling the airship slightly upwards as it flew forwards under the power of its engines. On landing, some water ballast was dropped to bring it back into near neutral buoyancy. Although their crews kept very careful track of all weight and lift changes during the flight, if the airship was going to be light or heavy at arriving at its destination was always a bit of a unknown. Pat |