[Realestfake]

I’d love to get discussion going on this. Do rockets move by pushing off the air?
It sure makes sense.

[Tom Bishop]

They probably move though multiple mechanisms. They propel themselves through inertial mass ejection, and also push off of air when available near the exhaust port yes.

[Action80]

I’d love to get discussion going on this. Do rockets move by pushing off the air?
It sure makes sense.

Rockets eject a plume of gas from the bell nozzle. This allows them to move.

Jet engines do the same.
“After compression it was heated, augmented by additional burning fuel(reported in the press to be kerosene), and finally discharged from the aft vent in a monstrous jet of energy pushing against the atmosphere.”


As long as either a jet or rocket engine can eject gas that is capable of forming a plume, then work (i.e., movement) can take place.

If a plume cannot form (i.e., no external pressure facilitating the formation of a plume), no work (i.e., movement) will take place.

[Realestfake]

They probably move though multiple mechanisms. They propel themselves through inertial mass ejection, and also push off of air when available near the exhaust port yes.

Would intertial mass ejection work in a vacuum?

[Realestfake]

As long as either a jet or rocket engine can eject gas that is capable of forming a plume, then work (i.e., movement) can take place.

So air resistance is the force that is moving rockets? Air resistance being the “pushing off the atmosphere”?

[markjo]

Jet engines do the same.
“After compression it was heated, augmented by additional burning fuel(reported in the press to be kerosene), and finally discharged from the aft vent in a monstrous jet of energy pushing against the atmosphere.”

The atmoplane doesn't seem very solid to me.  Wouldn't that "monstrous jet of energy" just push the atmoplane out of its way, especially at higher altitudes where the air is much thinner?

[DuncanDoenitz]

I began training as a Jet Engine Engineer in 1969; it was my career. 

I've no idea what the "plume" is that Action80 refers to in respect of a gas turbine engine.  They categorically do not rely on "resistance", or "pushing off the atmosphere", but please don't allow facts to get in the way of a good theory. 

Contrary to its title, "Popular Science" is not a professional scientific journal, it is a digest of scientific articles written for the layman.  The issue in question appears to date from the 1940s, and the article admits that much of the technology discussed is still secret.  The statement that thrust is obtained by a ("monstrous") jet of energy pushing against the atmosphere" is incorrect, as well as employing hyperbole. 

The diagram top-left of the article is false; there is no such component as a "carburation chamber (C)" in a gas turbine engine, nor does it illustrate the turbine. 

And Tom; "They probably move through multiple mechanisms"?  Glad we nailed that. 

[markjo]

I've no idea what the "plume" is that Action80 refers to in respect of a gas turbine engine. 

My guess is that he's referring to this:

[Action80]

As long as either a jet or rocket engine can eject gas that is capable of forming a plume, then work (i.e., movement) can take place.

So air resistance is the force that is moving rockets? Air resistance being the “pushing off the atmosphere”?

As long as a plume is capable of being formed (and this can only take place in a pressurized environment, external to the engine exhaust), then the craft can move.

I began training as a Jet Engine Engineer in 1969; it was my career. 

I've no idea what the "plume" is that Action80 refers to in respect of a gas turbine engine.  They categorically do not rely on "resistance", or "pushing off the atmosphere", but please don't allow facts to get in the way of a good theory.

Ah yes, please do not allow the facts I posted prevent you from straw-manning the living bejesus out of the post.

Pathetic.

Contrary to its title, "Popular Science" is not a professional scientific journal, it is a digest of scientific articles written for the layman.

True.

The issue in question appears to date from the 1940s, and the article admits that much of the technology discussed is still secret.

True.

The statement that thrust is obtained by a ("monstrous") jet of energy pushing against the atmosphere" is incorrect, as well as employing hyperbole.

The statement was true then, it is true now, and will remain true as long as jets or rockets remain in use. Nobody gives a good goddamn about your protestations otherwise. 

The diagram top-left of the article is false; there is no such component as a "carburation chamber (C)" in a gas turbine engine, nor does it illustrate the turbine.

Ignoring the fact it is a simplified diagram sourced from "Flight," magazine and not meant to be technical at all, I forget whether it was Heinkel or Messerschmitt, but fuel delivery in the early days did take place by using carburetors rather than injectors, so it does not qualify as "false."

Nobody gives a damn whether it illustrates the turbine or not.

Nobody gives a damn whether you think the word "monstrous," is hyperbole or not.

The jet engine and the rocket engine accomplish their work (i.e., movement) by ejecting a gas, which in turn forms a plume (which can only take place if there is an externally pressurized environment).

[Realestfake]

Ah yes, please do not allow the facts I posted prevent you from straw-manning the living bejesus out of the post.

Pathetic.

Nobody gives a damn whether you think the word "monstrous," is hyperbole or not.

Why the negativity? You’re the first one to be disrespectful in this thread. That truly reflects on your character.

The jet engine and the rocket engine accomplish their work (i.e., movement) by ejecting a gas, which in turn forms a plume (which can only take place if there is an externally pressurized environment).

Interesting. So would ejecting a gas to move a rocket work in a vacuum?


Ill actually be more concise to what I’m getting at:
What does “pushing off of something” actually mean? Why should something move if it pushes against another object?

[Action80]

Ah yes, please do not allow the facts I posted prevent you from straw-manning the living bejesus out of the post.

Pathetic.

Nobody gives a damn whether you think the word "monstrous," is hyperbole or not.

Why the negativity? You’re the first one to be disrespectful in this thread. That truly reflects on your character.

Did you start a thread about character or how rockets push off air?

The jet engine and the rocket engine accomplish their work (i.e., movement) by ejecting a gas, which in turn forms a plume (which can only take place if there is an externally pressurized environment).

Interesting. So would ejecting a gas to move a rocket work in a vacuum?

No, a plume cannot form in an environment where there is no pressure.

Ill actually be more concise to what I’m getting at:
What does “pushing off of something” actually mean? Why should something move if it pushes against another object?

There is nothing more "concise," about this additional query.

[Realestfake]

No, a plume cannot form in an environment where there is no pressure.

They are called plumes regardless of being in a vacuum or not. The actual shape doesn’t make it not a plume.

To cite this paper, for example: https://doi.org/10.1016/j.cja.2012.12.016

“In vacuum environment, the exhaust flow of the attitude control thrusters of satellites, spaceships, space stations and deep-space probes would expand freely and produce the plume. The vacuum plume would possibly cause undesirable contamination, aerodynamic force and thermal effects on the spacecraft, which would debase the capability of functional components and even make the flight missions fail. Therefore, for spacecraft designers the effects of the plume must be taken into account.”

I have no idea why you would make this claim.

[Action80]

No, a plume cannot form in an environment where there is no pressure.

They are called plumes regardless of being in a vacuum or not. The actual shape doesn’t make it not a plume.

A plume cannot form in a vacuum.

To cite this paper, for example: https://doi.org/10.1016/j.cja.2012.12.016

“In vacuum environment, the exhaust flow of the attitude control thrusters of satellites, spaceships, space stations and deep-space probes would expand freely and produce the plume. The vacuum plume would possibly cause undesirable contamination, aerodynamic force and thermal effects on the spacecraft, which would debase the capability of functional components and even make the flight missions fail. Therefore, for spacecraft designers the effects of the plume must be taken into account.”

I have no idea why you would make this claim.

First, your paper clearly states the altitudes are at "60–80 km..." which is not a "vacuum environment."

Second, rocket engines can and do indeed work in lower-pressure environments than jet engines.

[Realestfake]

A plume cannot form in a vacuum.

It’s literally just the word for the gases that come out of a propulsive engine. If it makes any shape, that shape is called a plume.

[Action80]

A plume cannot form in a vacuum.

It’s literally just the word for the gases that come out of a propulsive engine. If it makes any shape, that shape is called a plume.

There is a shape in both of your pictures, of course. One is more defined. but again, your paper is specifically writing, ""60-80 km...". Not an outer space vacuum environment.

[Realestfake]

There is a shape in both of your pictures, of course. One is more defined. but again, your paper is specifically writing, ""60-80 km...". Not an outer space vacuum environment.

What’s the altitude where the plume stops being a plume and why? Why is the shape of exhaust arbitrarily no longer called a plume to you if you go higher?
And I say “to you” because I linked the article in the first place to cite usage of the word “plume” relating to, quote: “the exhaust flow of the attitude control thrusters of satellites, spaceships, space stations and deep-space probes would expand freely and produce the plume.”

[Action80]

There is a shape in both of your pictures, of course. One is more defined. but again, your paper is specifically writing, ""60-80 km...". Not an outer space vacuum environment.

What’s the altitude where the plume stops being a plume and why? Why is the shape of exhaust arbitrarily no longer called a plume to you if you go higher?
And I say “to you” because I linked the article in the first place to cite usage of the word “plume” relating to, quote: “the exhaust flow of the attitude control thrusters of satellites, spaceships, space stations and deep-space probes would expand freely and produce the plume.”

"Deep space," is your first clue.

"60-80 km..." does not constitute "deep space..."

It seems your article is inserting contradictory adjectives.

[Realestfake]

What’s the altitude where the plume stops being a plume and why? Why is the shape of exhaust arbitrarily no longer called a plume to you if you go higher?

It seems your article is inserting contradictory adjectives.

The article is talking about different things at different times. These aren’t contradictory.
What aren’t you getting about calling a plume from a deep space probe a plume? Is it because they, in the same article, describe the simulated altitude (60-80km) of their low-pressure chamber? Does that undo them calling a deep space probe’s plume a plume? Is that the road you’re going down?


“In the space vacuum the exhaust gases form a large free jet, called a plume, which can impinge on neighbouring surfaces.”
https://doi.org/10.1016/0376-0421(91)90008-R

[Action80]

What’s the altitude where the plume stops being a plume and why? Why is the shape of exhaust arbitrarily no longer called a plume to you if you go higher?

It seems your article is inserting contradictory adjectives.

The article is talking about different things at different times. These aren’t contradictory.
What aren’t you getting about calling a plume from a deep space probe a plume? Is it because they, in the same article, describe the simulated altitude (60-80km) of their low-pressure chamber? Does that undo them calling a deep space probe’s plume a plume? Is that the road you’re going down?


“In the space vacuum the exhaust gases form a large free jet, called a plume, which can impinge on neighbouring surfaces.”
https://doi.org/10.1016/0376-0421(91)90008-R

Listen, if you don't understand the words, "deep space," are not synonymous with "60-80 km," then maybe you should check another forum instead.

[Realestfake]

”In the space vacuum the exhaust gases form a large free jet, called a plume, which can impinge on neighbouring surfaces.”
https://doi.org/10.1016/0376-0421(91)90008-R