Talk:Reaction engine

Pump-jets

Would it be correct to add water pump-jets as examples of reaction engines? The Jet-ski (and equivalent) uses a pump-jet for propulsion, i.e. it obtains thrust in reaction to the ejected stream of water. But then this is really so different from a propeller on a shaft external to the engine? (Sdsds - Talk) 18:58, 26 May 2007 (UTC)

dE/dt is not F v

In a discussion on the Talk:Conservation of energy page, I made the point that the time rate of change of the kinetic energy of the rocket engine is not simply Fv where F is the thrust and v is the engine velocity. A second term which constitutes an energy loss due to the mass of propellant being lost to the exhaust must be included. The correct statement is:

$dE/dt=Fv-{\frac {1}{2}}\mu v^{2}$

where $\mu$ is the rate at which propellant mass is converted to exhaust mass. As noted by 95.134.115.203, the total power P and thrust F produced by the engine can be assumed constant, so, assuming no heating effects, if Po=Fv is the rate at which the engine increases its kinetic energy, and Px is the rate of energy increase of the exhaust train, then P=Fv+Px or Px=P-Fv and at a high enough velocity, the rate of change of energy of the exhaust train is negative. Thats impossible.

I would edit the article myself, but I am not familiar enough with it to trace the implications of this throughout the article. PAR (talk) 21:53, 9 April 2010 (UTC)

What is I_sp ?

It is introduced in paragraph 3 without any explanation. Nor is there any mention of I_sp in the referred article "Propulsive_efficiency". Mesdale (talk) 11:03, 19 August 2015 (UTC)

Merge content from Spacecraft_propulsion#Reaction_engines

The Spacecraft_propulsion article has a large (too large) section on reaction engines. I would like to see the bulk of that content moved here to this article with only a short summary left on that page. Any input like warnings or encouragement would be appreciated. Somebody doing it would also be VERY appreciated. If not, I'll give it a try, but I have a lot of propulsion studying to do before I could pull it off. Thanks. JaredHWood💬 22:47, 3 February 2021 (UTC)