Determining Thrust in Pounds

Having brain farts today; 3:00 in the afternoon'll do that to you when you work overnights.



Not having any luck searching either.



And OK, so this probably makes me a



But....

Remind me how one determines thrust in pounds from motor designations.

Just noticed there seem to be no "Thank You" smilies in Xtra4 so see the attached.

Greg

edit: Whoever first posted the Smiley Xtra idea, you're BAD.

Well, the first number in the motor designation (I.E. the 12 in D12) indicates averge thrust in newtons. To get average thrust in pounds, take the thrust in newtons, and divide by 4.45. For a D12, this would be 12/4.45=2.7 pounds average thrust.

I did find to multiply the N by 0.224808943 which works out to almost what you posted to divide by.
OK.
So does it go like the attached?

Greg

Not really. That would be impulse in pound-seconds. That is the same error as saying a D12 has 20 newtons of thrust, when it really has 20 newton-seconds of impulse. That is the correct conversion to pound-seconds, but you would then take the total impulse of the motor (that number you posted) and divide by the burntime in seconds to find the average thrust in pounds. (if you can easily visualize units in equations, you can see that pound-seconds divided by seconds is pounds)

i can't believe you're not in college cjl...

Originally posted by cjl
snip....(if you can easily visualize units in equations, you can see that pound-seconds divided by seconds is pounds)....snip

Click to expand...

That I can. Stooooopid math.
Even though I still haven't slept it's getting to be vampire time and I'm coming more awake now.

Thanks,

Greg

BTW- goto-
https://www.grc.nasa.gov/WWW/K-12/airplane/rktengperf.html
and about halfway down there is a cool anigif of a model rocket moter showing the flamefront as the motor burns.
I'd just copy it and post it here but it's too big to be attached.

Originally posted by r1dermon
i can't believe you're not in college cjl...

Click to expand...

Lol - I still have a couple more years to go.

On line unit converter. Very useful...

https://www.digitaldutch.com/unitconverter/

I just use google for online unit conversions. It can do just about any conversion. Very handy.

that might be right...but its too late for me to do math, anyway, there doesnt have to be that many lbs of thrust to equal 1 horsepower, for instance, depending on how far your vehicle(motor) is traveling, all it as to do is move 33,000ft-lbs per minute. so if it moves 1000lbs 33 feet in one minute, that's a horsepower, if it moves 100lbs 330ft in a minute then its a horsepower.

horsepower is an arbitrary number devised by james watt in the 1700's...it's equal to about 746 watts, about 2,545BTU (british thermal units), and several hundred thousand joules, since one BTU is around 1000 joules.