- #1
.:Endeavour:.
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I would like an explanation with this formulas for a rocket engine and any other engine to calculate its exhaust velocity and its specific impulse. I realized that this formulas neglect combustion temperature, engine pressure, speed of the fuel is injected, etc.
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This is the formula that I found in http://www.answers.com/topic/specific-impulse for the specific impulse:
Fthrust = Isp * (Δm/Δt) * g0
>>>
-Fthrust = Force thrust in Newtons
-Isp = Specific Impulse in seconds
-(Δm/Δt) = is the mass flow rate in kg/s (lb/s), which is minus the time-rate of change of the vehicle's mass since propellant is being expelled.
-g0 = is the acceleration at the Earth's surface, in m/s² (or ft/s²).
This another variation to find the thrust of an object:
Fthrust = ve * (Δm/Δt)
This is the formula the exhaust velocity:
ve = g0 * Isp
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I want to know know how do you find the change of mass and change of time in the the formulas, (Δm/Δt). Does this part of the formula translate as: (massf - massi)/(timef - timei)? And my last question is for g0 when it means acceleration at Earth's surface, is it 9m/s2 or is it 9m/s2 * something? I found more equations for an ideal rocket in NASA's page, http://www.grc.nasa.gov/WWW/K-12/rocket/rktpow.html. I would like to see some example using this formulas because you cannot really apply them if you don't know how they are applied. Thank you for your time. This is not a homework question.
-----------------------------
This is the formula that I found in http://www.answers.com/topic/specific-impulse for the specific impulse:
Fthrust = Isp * (Δm/Δt) * g0
>>>
-Fthrust = Force thrust in Newtons
-Isp = Specific Impulse in seconds
-(Δm/Δt) = is the mass flow rate in kg/s (lb/s), which is minus the time-rate of change of the vehicle's mass since propellant is being expelled.
-g0 = is the acceleration at the Earth's surface, in m/s² (or ft/s²).
This another variation to find the thrust of an object:
Fthrust = ve * (Δm/Δt)
This is the formula the exhaust velocity:
ve = g0 * Isp
-----------------------------
I want to know know how do you find the change of mass and change of time in the the formulas, (Δm/Δt). Does this part of the formula translate as: (massf - massi)/(timef - timei)? And my last question is for g0 when it means acceleration at Earth's surface, is it 9m/s2 or is it 9m/s2 * something? I found more equations for an ideal rocket in NASA's page, http://www.grc.nasa.gov/WWW/K-12/rocket/rktpow.html. I would like to see some example using this formulas because you cannot really apply them if you don't know how they are applied. Thank you for your time. This is not a homework question.