PDA

View Full Version : Terminoloy primer, what do you think?


Doug Sams
02-27-2007, 02:37 PM
Having witnessed one too many intelligent, respectable people munge motor terms recently, I thought I'd make this up and see if it helps. What do you think? Can we make "average impulse" go away never to re-appear? Will folks finally understand the difference between Newtons and Newton-seconds? Thrust and impulse?

Doug

http://home.flash.net/~samily/stuff/terms2g4.gif

Green Dragon
02-27-2007, 05:18 PM
Doug - you tell em - I agree 127.5 % . I;ve seen MANY knowlegable, and even motor manufacturers, misuse terminology as you note " average impulse " , "total thrust", etc.

Nice thrust curve, too

~ AL

ghrocketman
02-27-2007, 05:44 PM
Agree with Doug also....I see too many terms used incorrectly when relating to motors.
One thing that I do not like about the rating method is that it allows the manufacturer to either rate the motor by average thrust for the whole burn or for the first 30% of the burn.
That is why the A10 is not the A2.5, whereas Estes chose the other route with the C5-3; that could have been the C13-3.

Doug Sams
02-27-2007, 06:00 PM
"total thrust" Good one. Duly added.

http://home.flash.net/~samily/stuff/terms2g4.gif

Nice thrust curve, too Thanks, Al.

Doug

JRThro
02-28-2007, 08:35 AM
Doug, in the description of total impulse on your graph, you misspelled Newton-seconds.

Doug Sams
02-28-2007, 10:25 AM
Doug, in the description of total impulse on your graph, you misspelled Newton-seconds.Thanks, John. Fixed. Doug

JRThro
02-28-2007, 11:23 AM
Now, I think this is a useful thing you've done, and it will probably clear up the terminology a lot.

But that doesn't necessarily mean that everyone will understand the actual physical meaning of Newton-seconds versus Newtons. For that matter, it probably also doesn't mean that everyone will understand the physical meaning of "the area under the curve."

Do you think there's a simple way to show, or describe, the physical meaning of the total impulse number and its units? Like, why do we need to know the total impulse, and how is that number useful to us when we design, build, and fly a rocket?

Green Dragon
02-28-2007, 05:05 PM
Agree with Doug also....I see too many terms used incorrectly when relating to motors.
One thing that I do not like about the rating method is that it allows the manufacturer to either rate the motor by average thrust for the whole burn or for the first 30% of the burn.
That is why the A10 is not the A2.5, whereas Estes chose the other route with the C5-3; that could have been the C13-3.

If I recall correctly, Estes considers the 'tail-off' thrust level on the A10 as 'insignificant' , and indeed counts it into the delay time - such as an A10-3T has a " NAR delay " of 2.2 seconds, since they start counting at the actual burnout ?

a few FSI engines ( motors, lol.. another long-debated terminology :) - such as the D18, had the same ' low tailoff' which some considered useable impulse, and others, such as FSI themselves, used as 'delay time' .

would have to go back and pull out the curves I have someplace and double check, but pretty sure the 'short measured delays' (per NAR ) are due tot his tailoff being counted as burn time.

~ AL ( straying off-topic, sorry :P)