|
|
Thread Tools | Display Modes |
#11
|
|||
|
|||
Air breathing Engines
In article ,
Allen Meece wrote: Surely this can not be purely justified on the bases of reduced fuel (oxidiser) payload? ... Well, If oxidiser is 1/4 to 1/3 of the weight you're trying to get off the ground, it makes sense to burn the oxygen in the air. No it doesn't, not when you consider the extra technical problems and the extra engine mass. What we care about is *cost*, not *mass*. LOX is cheap. Tanks to contain it are cheap and compact. There is no inherent virtue in reducing how much LOX gets carried. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
#12
|
|||
|
|||
Air breathing Engines
Well, If oxidiser is 1/4 to 1/3 of the weight you're trying to get off
the ground, it makes sense to burn the oxygen in the air. No it doesn't, not when you consider the extra technical problems and the extra engine mass. Well, the theory out of the AFRL is that PDE combined cycle air-breathing rockets will have *less* mass than rockets with turbopumps and *big* LOX tanks. [air breathing rockets will still need tanks above the atmosphere but no *big* pumps because the injection occurs at low chamber pressure] Also, less fuel mass means less horsepower required which means less engine weight. It's very hard to see why Henry says it's fine to go big and heavy if it's cheap. Weight's never cheap in the space game. ^ //^\\ ~~~ near space elevator ~~~~ ~~~members.aol.com/beanstalkr/~~~ |
#13
|
|||
|
|||
Air breathing Engines
Stephen:
Hi, Just like to say cheers for all the messages :-), they will certainly keep me thinking. I have one final question, I know that the Brits have flown a scramjet engine (missile scale model), but, I also know that the Australians and the Americans (X-43) have had several attempts. I was just woundering if anybody could tell me who did it first! -------- For air-augmentation the earliest I have found is the PR-90 (Russia) 60's. An ICBM version (Gnom) was designed but did not see production. http://www.astronautix.com/lvs/gnom.htm Reading the above the air-augmented stage was to range between Mach 1.75 to Mach 5.5 lasting less than 70 seconds at an impulse of 550 seconds. It could only work for that short period of time the craft was still in useful air. -- |
#14
|
|||
|
|||
Air breathing Engines
Anvil wrote:
For air-augmentation the earliest I have found is the PR-90 (Russia) 60's. An ICBM version (Gnom) was designed but did not see production. http://www.astronautix.com/lvs/gnom.htm Reading the above the air-augmented stage was to range between Mach 1.75 to Mach 5.5 lasting less than 70 seconds at an impulse of 550 seconds. As they noted in the text, that's about twice that of a solid rocket over that regime; 550 seconds is extremely respectable; and the first 70 seconds is the thick/heavy end of a rocket. Imagine what an airbreathing Kerosene or even a hydrogen version would be like. You'd be looking at perhaps 600-800 seconds and 900-1100 seconds. With luck you would have spare fuel to send it back home with. It could only work for that short period of time the craft was still in useful air. Clearly, however the ISP over that time is extremely high for a solid, and reduces the GLOW of the vehicle quite a bit- the vehicle delivers a fairly respectable payload fraction on what must be nearly an orbital trajectory. |
#15
|
|||
|
|||
Air breathing Engines
"Anvil" wrote in message om... Stephen: Hi, Just like to say cheers for all the messages :-), they will certainly keep me thinking. I have one final question, I know that the Brits have flown a scramjet engine (missile scale model), but, I also know that the Australians and the Americans (X-43) have had several attempts. I was just woundering if anybody could tell me who did it first! -------- For air-augmentation the earliest I have found is the PR-90 (Russia) 60's. An ICBM version (Gnom) was designed but did not see production. http://www.astronautix.com/lvs/gnom.htm Reading the above the air-augmented stage was to range between Mach 1.75 to Mach 5.5 lasting less than 70 seconds at an impulse of 550 seconds. It could only work for that short period of time the craft was still in useful air. -- Interesting reference. They had a GLOW half that of comparable rockets with similar payload. It took me several minutes to figure out why their numbers were different than what I have read and figured out. They were comparing low performance solids against air augmented solids. Better rocket performance is available for space launchers that don't have to be on alert for several years. This tends to drop the value of air augmentation to parity or less compared to all liquid rockets. |
#16
|
|||
|
|||
Air breathing Engines
In article ,
Ian Woollard wrote: It could only work for that short period of time the craft was still in useful air. Clearly, however the ISP over that time is extremely high for a solid, and reduces the GLOW of the vehicle quite a bit... And we care about that... why, exactly? A great many misconceptions, superstitions, and outright myths about launcher design can be traced to the habit -- inappropriately inherited from the missile business -- of thinking of gross liftoff weight as an important figure of merit. Especially when the reduction in weight is coming out of the propellants, the cheapest and most easily-designed part of the whole vehicle. "Gross weight is not a primary consideration in the design of space vehicles... paper studies based on weight optimization have ... vastly overrated the importance of weight, particularly for the booster stage, which is of course the heaviest stage..." -- Del Tischler, 1962 -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
#17
|
|||
|
|||
Air breathing Engines
|
#18
|
|||
|
|||
Air breathing Engines
A great many misconceptions, superstitions, and outright myths about
launcher design can be traced to the habit -- inappropriately inherited from the missile business -- of thinking of gross liftoff weight as an important figure of merit. Especially when the reduction in weight is coming out of the propellants, the cheapest and most easily-designed part of the whole vehicle. "Gross weight is not a primary consideration in the design of space vehicles... paper studies based on weight optimization have ... vastly overrated the importance of weight, particularly for the booster stage, which is of course the heaviest stage..." -- Del Tischler, 1962 -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | keep on preachin brother! especially when ultralight, high performance aerospace widgets are measured in thousands of dollars per ounce and fuel and normal metal parts are measured in dollars per pound! Blll "big dumb booster fan" Fish |
#19
|
|||
|
|||
Air breathing Engines
Henry Spencer wrote:
In article , Ian Woollard wrote: It could only work for that short period of time the craft was still in useful air. Clearly, however the ISP over that time is extremely high for a solid, and reduces the GLOW of the vehicle quite a bit... And we care about that... why, exactly? Only because the GLOW suggested that the airbreathing was working. The GLOW is reasonably unimportant, but ISP clearly isn't. Airbreathing for a first stage (*not* an upper, orbital stage) is a much more respectable concept, atleast two launchers use that- Pegasus, and SpaceShip One; and several others, such as Black Horse (fuel would be lifted using a transport plane) have proposed to use it. It was seriously considered for the Space Shuttle and the N-1 IRC. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Multiple Engines??? | Charles Talleyrand | Technology | 125 | February 4th 04 06:41 PM |
State of the art Ion Engines | Charles Talleyrand | Technology | 5 | November 25th 03 10:35 PM |
Ultra-Low Oxygen Could Have Triggered Mass Extinctions, Spurred Bird Breathing System | Ron Baalke | Science | 0 | October 31st 03 05:34 PM |
Air breathing re-entry concept | Zoltan Szakaly | Technology | 15 | September 27th 03 07:19 PM |
Do NASA's engines destroy the Ozone Layer | Jim Norton | Space Shuttle | 1 | September 27th 03 12:00 AM |