Rocket Thrust Conversions

[smonsterj]

I'm having a weird brain fart with thrust conversions, if someone can point out what I'm doing wrong...

please ignore rounding errors for the sake of brevity.

 

My issue is that I'm getting different values for thrust in Newtons when I convert using the following two paths:

lbm-->lbf-->N

lbm-->kg-->N

 

e.g.

lbm --> N = (6000 lbm) * (32.174049 ft/s^2) * (4.44822 N/lbf) = 858704 N
lbm --> kg = (6000 lbm) * (.45 kg/lbm) = 2700 kg

 

Right?

Now here is the contradiction that I'm seeing with whatever I'm doing wrong:

however,
kg --> N = (2700 kg) * (9.81 m/s^2) = 26700 N
2700 kg was calculated from 6000 lbm...
but we already showed that 6000 lbm leads to 858704 N, not 26700 N

and,
N -- > kg = (858704 N) / (9.81 m/s^2) = 87533 kg
858704 N was calculated from 6000 lbm...
but we also showed that 6000 lbm leads to 2700 kg, not 87533 kg

wuuuuuuuut the heck?

[studiot]

Why are you converting lbs mass if you are talking about thrust?

 

6000 lbs of thrust (US units) convert to 26700N, the conversion factor is 1lb of thrust is 4.45 Newtons of thrust.

 

https://simple.wikipedia.org/wiki/Thrust

[Janus]

I'm having a weird brain fart with thrust conversions, if someone can point out what I'm doing wrong...

please ignore rounding errors for the sake of brevity.

 

My issue is that I'm getting different values for thrust in Newtons when I convert using the following two paths:

lbm-->lbf-->N

lbm-->kg-->N

 

e.g.

lbm --> N = (6000 lbm) * (32.174049 ft/s^2) * (4.44822 N/lbf) = 858704 N [/size]

Here's your problem. If you are using lbm, then the unit for force is the poundal, and there are 0.13255 Newtons to a poundal. Thus if you change the 4.44822 to 0.13255, yo get an answer of 26689 N

If you wanted to use lbf, then the mass unit is the slug. lbm and poundal belong to the absolute FPS system of units, while the lbf and Slug belong to the gravitational FPS system of units.

lbm --> kg = (6000 lbm) * (.45 kg/lbm) = 2700 kg [/size]

 

Right?

Now here is the contradiction that I'm seeing with whatever I'm doing wrong:[/size]

 

however,[/size]

kg --> N = (2700 kg) * (9.81 m/s^2) = 26700 N[/size]

2700 kg was calculated from 6000 lbm... [/size]

but we already showed that 6000 lbm leads to 858704 N, not 26700 N[/size]

 

and,[/size]

N -- > kg = (858704 N) / (9.81 m/s^2) = 87533 kg[/size]

858704 N was calculated from 6000 lbm...[/size]

but we also showed that 6000 lbm leads to 2700 kg, not 87533 kg[/size]

 

wuuuuuuuut the heck?[/size]