Hot answers tagged

60

I think there's a mix-up in the labeling of the photo. Here's the photo and caption from a copy of "Ignition" that I just downloaded: Here's the photo and caption from the next page: Seen together, those two photos and captions make sense. Somebody mixed up the images and the captions in the copy you are reading.


29

One reason the L-1011 was chosen was that the keel beams on the L-1011 are spaced such that they could create an opening inside the aircraft for the verticle tailfin of the Pegasus when mated to the bottom of the aircraft and do so without jeopardizing the structural integrity of the airframe. This allowed them more clearance than other aircraft although the ...


26

As the source linked next to the image in the other question says, it is a C-130 performing a "rocket assisted takeoff". These are performed to safely achieve V1 on short airfields, where the aircraft would not be able to take off otherwise. The rockets (or "bottles") use solid fuel, so they are usually single-use. I have no data on the thrust provided by ...


19

For one, don't only look at the engine, but at the whole propulsion system. This includes tanks, piping, controls, pumps and the actual engine. Now the rocket looks much less favorable, especially if you size the tanks for equal running times. The rocket does not need any of the parts which are ahead of the combustion chamber of a jet and also does not need ...


17

This C-130 is with the Blue Angels demonstration team. Affectionately nicknamed Fat Albert. The rockets are JATO(Jet Assisted TakeOff) bottles, and basically jets/rockets that provide a temporary thrust boost for shorter take-offs.


16

Seems as though everyone has missed the simple, obvious answer: the rate at which the engine burns fuel. To take a concrete example, the Saturn V's first stage carried 205,400 gal/770,000l of kerosene fuel, which it burned in a bit less than 3 minutes: https://www.space.com/18422-apollo-saturn-v-moon-rocket-nasa-infographic.html By contrast, a Boeing 747 ...


15

(Source) The initial carrier was NASA's DFRF B-52-008 – aka Balls 8. As the rocket increased in size and weight, Orbital needed a more capable carrier. A detailed study considered the B-52G, 747, DC-10, and L-1011. A study was initiated in late 1991 to identify the optimum carrier aircraft for long term Pegasus launch operations. Some of the aircraft ...


11

Despite the scene in Moonraker the Shuttle orbiter carried no fuel for the main engines. Further, the orbiter sat nose down on its landing gear, lacked the elevator authority to raise the nose off the ground at landing speed, and could not retract its landing gear (it used a straight-fall gravity deployment). The OMS didn't have enough thrust or delta-V at ...


10

Maybe wings never mattered... Altitude: The answer depends a bit on the design of the craft in terms of control surfaces/wings. Atmospheric reentry begins at the Karman line at an altitude of 100 km (62.14 mi / ~ 54 nautical mi) (327,360 feet) above the surface. Which is generally when air resistance starts to matter but that does not mean control surfaces ...


8

The temperature of the environment doesn't have a significant impact on the performance of a rocket engine. Air breathing engines have better performance in cold air because the mass density is higher at a given pressure, which allows them to ingest more air, and because the thermodynamic efficiency of a heat engine increases when the temperature of the cold ...


7

It needed ground clearance for the rocket limiting the choice to the largest of the widebodies. At the time of selection (mid 1990s) the L1011 was already out of production and much cheaper to purchase than a 747 or MD11. Operating cost was immaterial due to infrequent use. You can see here that even with size, they still had to jack up the aircraft to get ...


7

The rocket engine produces the same thrust regardless of the speed it moves. Differently, the thrust of the jet engine depends on velocity and declines as velocity increases, because of the ram drag. It is largely useless if the engine speed approaches the exhaust velocity. The exact formula for efficiency can be found here: $$ \eta_p = \frac{2}{1 + \frac{...


6

Interesting topic. Rockets and spacecraft are still highly experimental vehicles and are recognized as such under 14 CFR §1200. The laws, liabilities, and regulations for private spaceflight are largely uncharted territory at this point, though §1266.102 requires all participants aboard the ISS and NASA launch vehicles to sign a liability waiver prior to ...


5

The answer is simpler than others mention here. It is simply that the rocket operates at much higher temperatures than gas turbines do. This translates to more thrust at the greater temperatures. Turbine blades in turbojets would melt at such high temperatures. Rockets cool the outer lining of the rocket combustion chamber. This is done by using liquid ...


5

The first, and most significant reason, is because more fuel is pumped in and burned. Why does a car battery have more stored power than a AA battery? Because, it is designed to be bigger, because that it necessary for the design requirements. But, this is not always the case. The mercury-redstone rocket, that carried Alan Shepard had 78,000 lbs of thrust,...


4

It depends if you are asking about rocket ships or rocket planes. On any note, its unlikely in the lower atmosphere, but in orbit, quite possibly. There are a few issues you may encounter, Some rockets use solid fuel which cant be pumped from one tank to the next so you would not be able to refuel on the go. As @TomMcW mentions in the comments most ...


4

From the link you provided: Specification: Rotor Diameter: 90mm Fan blades:11 blades Weight: about 350g Working Voltage:6s(22.2V) lipo battery Motor:Brushless Motor 3553 1450kv No Load Current: 4.1 A Load Current: 83A No Load Speed:32190 rpm Load Speed:16095 rpm Thrust: 3300g G/A:45.16 Assuming that 16 * 6/4 = 24 18650 ...


4

It wasn't a lack of technology. The technology to automatically fire the rockets is not actually very complicated: a radar altimeter, airspeed data and maybe input from the landing gear load sensors hooked up to a simple computer. All of that existed back then, and the rocket system was in fact computerized: The Lockheed test crew then assessed that the ...


3

A rocket stabilized by fins alone needs a certain amount of lift at the rear to ensure that if it is disturbed from a nose-first attitude, it returns and damps out the resulting oscillation. Adding mass at the rear of the rocket increases the amount of lift (hence fin area) required, as well as increasing the inertia factor that counters damping. If a ...


2

This answer may not be what you are looking for, but I think the issue is we aren't really talking about the rocket as a "wing" here since these rockets fly ballistically. I think the term CP in the NASA article would be better expressed as "neutral point", the point at which aerodynamic moments are in balance when the rocket is not aligned with the ...


2

Speed or altitude is relative. To me the answer to this question is "At whatever speed or altitude the flight control surfaces cease to be effective due to insufficient relative wind or atmosphere and only thrust from the propulsion system can have an effect on the craft."


2

SpaceX launches from Cape Canaveral Air Force Station (CCAFS), Vandenberg Air Force Base (VAFB), and Kennedy Space Center (KSC). All three have Restricted/Warning areas overhead and out to sea, from the surface to "unlimited" (i.e. space). It is illegal to fly through active Restricted airspace without permission. Warning areas are used over international ...


2

Refueling is done a few times per year on the ISS. A visiting spacecraft arrives, docks and transfers some of its fuel to tanks on the ISS for its engines. Refueling while in orbit is relatively simple: docking is a solved problem, and there is no turbulence etc. to make things difficult. Refueling while a rocket engine is running is more difficult. You ...


2

Welcome to Aviation Stack Exchange, and interesting question. I assume you know something about the ballistic process for vehicles such as ICBM's and so I'll start my explanation from there. Firstly, ballistic anythings don't account for the acceleration's effect on humans. Only machinery and weaponry has been transported in this manner, and I don't see ...


2

It is simply the rate at which fuel can be burned. For instance, the Saturn V's first stage carried 1.37 million kg of liquid oxygen (along with the kerosene fuel), which it burned in about 165 seconds. Imagine the size of the jet intake you'd need for a comparable amount of air.


2

Yes, solid fuel rockets are very different from liquid fueled rockets. A solid fuel rocket is basically some solidified rocket fuel and oxidizer wrapped in a non-combustible cylinder (hence the name). Once it's lit, there's no way to throttle it or shut it down, it just burns until all the fuel is consumed. On the other hand, in a liquid fuel rocket (...


2

Sure, you could, but for that kind of mission these days there are far better choices. For instance, a Bell-Boeing V-22 Osprey could be used for such a mission, is rack ready now, far easier to control during takeoff and landing, and makes use of modern avionics and mission systems.


2

I'll just answer my own question thanks to Koyovis' comment :) Koyovis was right - I didn't realise the difference between how dynamic pressure is calculated for compressible vs incompressible flows. There are some useful notes on it on pages 4-8 of this link (http://mae-nas.eng.usu.edu/MAE_5420_Web/section5/section.5.5.pdf) In summary: Bernoilli’s ...


1

The cargo payload capacity of the Shuttle is about 22 tonnes when external tank weights 760 tonnes when full and is used up in 8.5 minutes. Hence it would be enough fuel for 14 seconds of flight. The thrust of the single engine, RS-25, 1860 kN, is more than three times that of the 777's GE90, 513 kN. Hence for 14 seconds we have near 5 times more thrust for ...


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