questions about thrust
questions about thrust
(OP)
hello everyone,
is the thrust produce by rocket engine(thrust produce by exhaust gas)dependent on the outside environment. or is the amount of thrust produce in a vacuum space also the same in pressurized space,
thanks,
is the thrust produce by rocket engine(thrust produce by exhaust gas)dependent on the outside environment. or is the amount of thrust produce in a vacuum space also the same in pressurized space,
thanks,





RE: questions about thrust
RE: questions about thrust
another day in paradise, or is paradise one day closer ?
RE: questions about thrust
Every action has an equal and opposite reaction.
So throwing a bunch of hot gas out at very high velocity has a given momentum. The rocket itself sees equal momentum in the opposite direction.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: questions about thrust
it's harder to run in water (than in air) 'cause it takes more work to move the water out of the way. similarly, a rocket exhaust in space doesn't have to push an atmosphere out of the way; and the added aerodynamic drag is another "loss" ... there's no drag in space, so the rocket thrust (which is higher in space) accelerates the rocket more (without aerodynamic drag).
another day in paradise, or is paradise one day closer ?
RE: questions about thrust
so youre saying that the jet velocity and thrust is at maximum when the jet is near the water surface, my thought on this is that when the jet of water strikes the surface of the water it creates an upward force towards the vehicle and this adds to the thrust. just my analysis, correct me if im wrong...
RE: questions about thrust
No.
When the jet of water is accelerated out the back of the vehicle, that in itself causes thrust in the opposite direction.
The column of moving water doesn't carry force like a support pillar.
I suppose if the jet of water somehow bounced off the surface, then it might subsequently ricochet off the vehicle adding an imperceptible additional thrust for a few miliseconds, but that's nothing to do with what's really going on.
Why are JetSki questions here?
RE: questions about thrust
in nay case, if the exhaust hits a nearby water surface, pushing this water out of the way won't increase the rocket thrust ... it'll create a lot of spray ! it might reduce the thrust as I can see some back pressure building up (increasing the pressure near the exhaust, reducing the delta_p of the exhaust ...).
another day in paradise, or is paradise one day closer ?
RE: questions about thrust
RE: questions about thrust
RE: questions about thrust
RE: questions about thrust
note: in answering this question please neglect for awhile the effects of drag to the body of the vehicle and other factors, just focus on the exhaust gas ITSELF and the effect of the outside environment to the flow or performance of the exhaust gas ITSELF, because my goal here is to find the effect of the outside environment pressure to the exhaust gas ALONE.
thank you so much...
RE: questions about thrust
TTFN
I can do absolutely anything. I'm an expert!
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RE: questions about thrust
Each Space Shuttle Main Engine operates at a liquid oxygen/liquid hydrogen mixture ratio of 6 to 1 to produce a sea level thrust of 179,097 kilograms (375,000 pounds) and a vacuum thrust of 213,188 (470,000 pounds). http://www.nasa.gov/returntoflight/system/system_S...
based on the above info from NASA it seems that the difference of thrust at sea level and outer space is really big. is this mainly due to the effect of drag or resistance against the body of the vehicle and not the resistance between the exhaust gas and the outside environment pressure?
RE: questions about thrust
RE: questions about thrust
TTFN
I can do absolutely anything. I'm an expert!
homework forum: //www.engineering.com/AskForum/aff/32.aspx
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: questions about thrust
The OP asked about the effect of the ambient environment on thrust produced by a rocket engine. However, I would agree that the velocity of the exhaust gas exiting the nozzle is an important consideration for the engine performance at various ambient conditions, such as sea level versus the upper atmosphere.
RE: questions about thrust
Cheers
Greg Locock
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RE: questions about thrust
If one took a ship equipped with a typical rocket motor down near the surface of Jupiter for a flyby, one might find that the atmospheric pressure near the surface of Jupiter was higher than one's rocket chamber, let alone tank, pressure. So when one opened the valves, atmosphere would be sucked up into the chamber and into the fuel and oxidizer tanks. This would cause a short pulse of thrust in the direction opposite of what one would want. It would of course end very badly.
This is not intended to be practical, but it may help clarify the extreme cases.
RE: questions about thrust
RE: questions about thrust
The SSME flight nozzles would ring like a bell (but much more violently) when starting into atmospheric pressure, causing fatigue failures of the coolant tubes, so the number of starts on any flight nozzle were limited. A steam ejector called the "SLAM" ring was used to reduce the exit pressure for engine tests at NASA Huntsville (Stennis). The variable back pressure of the Huntsville test stand also allowed some verification of thrust vs. altitude.
Engine thrust is never quoted as net, no more than a car's engine horsepower would be. Airframe losses (drag, gravity) are the aerodynamicist's/vehicle designer's problem, the engine company tells them the thrust available on the engine mounts.
RE: questions about thrust
RE: questions about thrust
another day in paradise, or is paradise one day closer ?
RE: questions about thrust
is the 2psi you mention refers to the outside environment pressure or atmospheric pressure because 2psi is very small for the exhaust gas, just clarifying...thanks,
RE: questions about thrust
Every part of the Shuttle "rang like a bell" when the engines ignited. I worked in mechanical systems on the Shuttle, and the worst load environment was often from engine noise for the few seconds before it left the pad.
RE: questions about thrust
Tbuelna, it was fun to stand about 1/2 mile from the SSME test stand at Santa Sue, and watch the shock waves bounce off the cliff behind the flame bucket. And to look down at your chest and see it vibrate. You could shout as loud as you could at the person standing beside you, and they couldn't hear anything you were saying. As loud as the SSME's were, the SRB's were much noisier, and probably a bigger component of the vehicle vibration. I watched a "small", 50,000 lb thrust chamber test that ran LOX/RP-1 (kerosene), and the noise from that was much more alarming - it crackles and snaps and snarls at you. The hydrogen/oxygen flame from the 10x higher thrust SSME was just a big bass roar.
RE: questions about thrust
Did you get involved in the linear aerospike engine program for X-33? I knew the Orbiter TPS SSM at Rockwell/Boeing and he spent some time working on the ramp surface TPS for the X-33 engine. He explained to me the aerospike engine gave better performance overall for the X-33 than a conventional nozzle. Since there was no fixed outer surface constraining the gas flow, the gas expansion continually adjusted to match the current atmospheric pressure at all altitudes.
I recently saw that Firefly Space Systems successfully ground tested their RP-1/LOx aerospike engine.
RE: questions about thrust
I wish...and then again I don't. The NASP and X33 programs were staffing up in a big way, right about when I started. Just before leaving ~ 2 years later, they had the project cancelled, and people were coming begging at our door (I was in the Advanced Combustion Devices group by then). Aerospikes are neat. I had a picture (may still, somewhere...) of a test of (I think) an early SSME (or might have been a J-2) combustion chamber with an aerospike nozzle (circular, not linear). It was done as a proof of concept for some Air Force contract or another. Cooling is a bit tricky, but has been proven do-able by now. The 2D nozzle is interesing in that you can do 2-D attitude control/thrust vectoring by throttling one side or the other.
In some ways, I am very heartened by the likes of Rutan and others who bring grass roots and bootstraps (and ex-software barons with oodles of spending cash) to the aerospace world. I got out of the biz as it was always a roller coaster ride, wondering when your meal ticket gee-whiz project would get cancelled by congress critters.
RE: questions about thrust
Back in 2014 I was working at a company doing design of the LH2/LOx ducts for the SLS booster first stage, which uses the SSME. The chief engineer on the project was a middle-aged PhD that had spent his career working on engines designed by someone else. On my last day of work there I stopped by his office to say goodbye, and he told me it was also his last day at the company. I asked where he was going to work at and he told me (with quite a bit of enthusiasm!) that he had been given a once in a lifetime opportunity to do a serious clean-sheet-of-paper rocket engine design. It was something he had dreamed about his entire career.
RE: questions about thrust