Estes ejection charge question?

Discussions of motors from single-use and RMS solid propellants to hybrid propellants

Moderator: Moderators

lucifer911
Rocket Flyer
Rocket Flyer
Posts: 134
Joined: Sun Jul 26, 2015 12:49 am

Estes ejection charge question?

Postby lucifer911 » Tue Sep 01, 2015 12:17 am

I am browsing Estes motors and noticed something interesting in the ejection delay charge times.

There is an Estes A8-5 second delay charge motor yet in higher impulse Estes motors there is an C6-3 motor.

Surely the higher the impulse the longer it takes for the rocket to hit apogee correct?
shouldn't the ejection charge delay time always be higher on higher impulse motors?

As in A motors ejection delay charge should be a lower number like 3 seconds... B motors 4 seconds... C motors 5 second ejection delay charge.
It makes no sense an Estes A motor has a 5 second delay charge when it only travels 50m high or whatever vs 200-300m in a C motor.

Am I seeing things correctly? there is also another option for an A8-3 second delay charge.
Why would people opt for a long delay in such a small motor? will the parachute eject when its 10m from the ground or something?

Lister
Engineer
Engineer
Posts: 967
Joined: Fri Jun 05, 2015 5:36 pm
Location: Bendigo, Victoria

Re: Estes ejection charge question?

Postby Lister » Tue Sep 01, 2015 12:33 am

Ejection times depend on alot of different factors.. weight of rocket + motor.. stability, drag, motor impulse v weight of rocket (power vs weight/drag ) is a VERY BASIC way of looking at it.

if the ejection charge time is too short you get an earlty deployment.. and it can wreck your day.. too late and you get a high speed deployment too which will wreck your day.. you want it at apogee.

vance2loud
Rocket Crew
Rocket Crew
Posts: 283
Joined: Wed May 14, 2014 12:44 pm
Location: Devonport, Tasmania

Re: Estes ejection charge question?

Postby vance2loud » Tue Sep 01, 2015 12:38 am

A lot depends on the weight of the rocket.
A lightweight rocket might use an A6-3, B6-4, C6-5
whereas a slightly heavier rocket might use a B6-3, C6-3
With added weight you reduce the time to apogee, reducing the delay required (generally speaking as with most things there are always exceptions)
the other thing that can affect required delay times is the drag of the rocket, search for "Art Applewhite" for some really draggy "rockets" including some free plans.
the best thing you can do is either follow the manufacturers directions or accurately weigh and simulate the rocket and see what the optimum delay time is.
TRA #15165 AMRS #50
I do it because i can, I can because I want to, I want to because you said I couldn't. - Unknown
I have not failed. I've just found 10,000 ways that won't work.
- Thomas Alva Edison

lucifer911
Rocket Flyer
Rocket Flyer
Posts: 134
Joined: Sun Jul 26, 2015 12:49 am

Re: Estes ejection charge question?

Postby lucifer911 » Tue Sep 01, 2015 2:14 am

thanks I think I should use open rocket sim to determine time it takes to hit apogee and use that to help me select which motors I need.

Only thing I don't quite understand is Letter in motor indicates impulse range. First number is average thrust in Newtons and last is ejection charge time.
My question is would there be much difference in altitude and flight in a A8-3 motor vs A6-3 motor? does the higher amount of Newtons make much difference?
I think I will stick with my Low Powered Rockets until I can get my head around with this stuff.

citizenspace
Parachute Packer
Parachute Packer
Posts: 47
Joined: Wed Aug 26, 2015 12:32 pm
Location: Sydney, NSW

Re: Estes ejection charge question?

Postby citizenspace » Tue Sep 01, 2015 2:46 am

lucifer911 wrote:thanks I think I should use open rocket sim to determine time it takes to hit apogee and use that to help me select which motors I need.

Only thing I don't quite understand is Letter in motor indicates impulse range. First number is average thrust in Newtons and last is ejection charge time.
My question is would there be much difference in altitude and flight in a A8-3 motor vs A6-3 motor? does the higher amount of Newtons make much difference?
I think I will stick with my Low Powered Rockets until I can get my head around with this stuff.


If they have the same impulse (In high powered rockets you get stuff like 50% F's, but for low powered motors I think all A's are the same in total impulse) then the lower the thrust the longer the burn.
This is because total impulse is the total amount of thrust produced. A motor with a thrust of 8N and a burn time of 0.2s will produce 1.6Ns of total impulse.
It would take a motor with an average thrust of 6 0.267 to produce 1.6Ns. The difference gets bigger the larger the motor and the longer the burns. Typically a longer burn is good because it reduces stress on the rocket and decreases aerodynamic drag, but I wouldn't worry about it at the size of an A motor.
The best way to do something well is to make sure you've tried all the ways of making it fail.
NASA does it all the time with simulators :D
---

vance2loud
Rocket Crew
Rocket Crew
Posts: 283
Joined: Wed May 14, 2014 12:44 pm
Location: Devonport, Tasmania

Re: Estes ejection charge question?

Postby vance2loud » Tue Sep 01, 2015 3:08 am

the main difference between those two examples is the average thrust not the total thrust.
In an estes Wizard a B4-4 would see 900 feet whereas a B6-4 would see 1000 feet. (Note: in that rocket a 5 second delay would be more appropriate, I am just giving an example).
the only A6 I could find is actually a 1/2A6-2 and that would have considerably less altitude.
A general recommendation is to have at least 5:1 thrust ratio, what that means is that if your model (loaded with an engine ready for flight) weighs 100g you would require 500g of thrust.
In that example to achieve 500g of thrust you require approx 5N of thrust for a safe launch (500g=0.5kg 0.5 x 9.8 =4.9) (to roughly convert Newtons to Kg divide by 10)
That is only a rough guideline but if you aim for at least that amount of average thrust you should achieve a safe launch speed.
In openrocket you will be able to see velocity of Rod . Hopefully someone can chime in with a recommended minimum velocity to help you. (?15 m/s - 45km/h - 40 feet per second minimum?)

Sometimes when you are trying for max altitude a lower Average thrust motor will actually go higher due to the longer burn time,
So for the moment just make sure that you have a safe speed as your rocket leaves the rod and try to get your ejection time as close to optimal as possible.
If any of that doesn't make sense let me know which bits and I will try to explain further.
And to those more experienced, if you can see any mistakes in what I have said please let me know, would rather make the mistakes here than on the launch pad.
TRA #15165 AMRS #50
I do it because i can, I can because I want to, I want to because you said I couldn't. - Unknown
I have not failed. I've just found 10,000 ways that won't work.
- Thomas Alva Edison

lucifer911
Rocket Flyer
Rocket Flyer
Posts: 134
Joined: Sun Jul 26, 2015 12:49 am

Re: Estes ejection charge question?

Postby lucifer911 » Tue Sep 01, 2015 3:28 am

citizenspace wrote:
lucifer911 wrote:thanks I think I should use open rocket sim to determine time it takes to hit apogee and use that to help me select which motors I need.

Only thing I don't quite understand is Letter in motor indicates impulse range. First number is average thrust in Newtons and last is ejection charge time.
My question is would there be much difference in altitude and flight in a A8-3 motor vs A6-3 motor? does the higher amount of Newtons make much difference?
I think I will stick with my Low Powered Rockets until I can get my head around with this stuff.


If they have the same impulse (In high powered rockets you get stuff like 50% F's, but for low powered motors I think all A's are the same in total impulse) then the lower the thrust the longer the burn.
This is because total impulse is the total amount of thrust produced. A motor with a thrust of 8N and a burn time of 0.2s will produce 1.6Ns of total impulse.
It would take a motor with an average thrust of 6 0.267 to produce 1.6Ns. The difference gets bigger the larger the motor and the longer the burns. Typically a longer burn is good because it reduces stress on the rocket and decreases aerodynamic drag, but I wouldn't worry about it at the size of an A motor.


thanks this clears up a lot of things
so to arrive at burn time I simply divide the total impulse in your example 1.6N / 8N (which is the average thrust not Max thrust) which gives me 0.2s burn time.

In another example using the A8-5 SCR single use black powder motor on ausrocketry

Avg. Thrust (N): 3.3 4.1 3.2
Max. Thrust (N): 8.7 8.7 7.2
Tot. Impulse(Ns):2.5 2.5 2.4
Burn Time (s): 0.7 0.6 0.8

I divide Tot. Impulse by Avg. Thrust to get burn time so 2.5Ns/3.3N = 0.757s

So to conclude:
A = total impulse
8 = average thrust in Newtons
5 = ejection delay charge in seconds

vance2loud
Rocket Crew
Rocket Crew
Posts: 283
Joined: Wed May 14, 2014 12:44 pm
Location: Devonport, Tasmania

Re: Estes ejection charge question?

Postby vance2loud » Tue Sep 01, 2015 3:43 am

lucifer911 wrote:thanks this clears up a lot of things
so to arrive at burn time I simply divide the total impulse in your example 1.6N / 8N (which is the average thrust not Max thrust) which gives me 0.2s burn time.

In another example using the A8-5 SCR single use black powder motor on ausrocketry

Avg. Thrust (N): 3.3 4.1 3.2
Max. Thrust (N): 8.7 8.7 7.2
Tot. Impulse(Ns):2.5 2.5 2.4
Burn Time (s): 0.7 0.6 0.8

I divide Tot. Impulse by Avg. Thrust to get burn time so 2.5Ns/3.3N = 0.757s

So to conclude:
A = total impulse
8 = average thrust in Newtons
5 = ejection delay charge in seconds


That looks about right to me.
Can someone clarify for me now though how estes and SCR motors can have an average thrust rating that is higher than their actual maximum thrust?
(ie, an A8-5 should have 8 N average thrust but according to the specs listed it only has about 3.2 N average thrust)
Sorry if this confuses things more, I just always thought that the number after the letter was meant to be the tested average thrust, or at least close to it.
TRA #15165 AMRS #50
I do it because i can, I can because I want to, I want to because you said I couldn't. - Unknown
I have not failed. I've just found 10,000 ways that won't work.
- Thomas Alva Edison

citizenspace
Parachute Packer
Parachute Packer
Posts: 47
Joined: Wed Aug 26, 2015 12:32 pm
Location: Sydney, NSW

Re: Estes ejection charge question?

Postby citizenspace » Tue Sep 01, 2015 6:16 am

Hmmm, actually I don't know... Now that I am looking at the ausrocketry pages for the A8-5 and the B6-4 from SCR, it seems as if that number doesn't have a correlation with any of the stats...
Would anyone be able to correct me on that? I went to the Estes site and it says the 8 in A8-5 should be the average thrust, but it isn't.
The best way to do something well is to make sure you've tried all the ways of making it fail.
NASA does it all the time with simulators :D
---

lucifer911
Rocket Flyer
Rocket Flyer
Posts: 134
Joined: Sun Jul 26, 2015 12:49 am

Re: Estes ejection charge question?

Postby lucifer911 » Tue Sep 01, 2015 11:39 am

citizenspace wrote:Hmmm, actually I don't know... Now that I am looking at the ausrocketry pages for the A8-5 and the B6-4 from SCR, it seems as if that number doesn't have a correlation with any of the stats...
Would anyone be able to correct me on that? I went to the Estes site and it says the 8 in A8-5 should be the average thrust, but it isn't.


to calculate the burn time (thrust duration) it is Total impulse divide by the Average Thrust in Newtons not max newton thrust.

SCR A8-5 the listed tot. impulse is 2.5 and the listed burn time is 0.7
if we divide tot. impulse 2.5 / the incorrect number marketed on the motor after the impulse letter which is 8 the burn time = 0.31
the only way to arrive at 0.7 is by dividing the 2.5 by the average thrust which is 3.3 = 0.757

The number marketed on the motor is meant to be average thrust in Newtons not max Newton thrust.
So technically the motor with the 2.5 tot. impulse and 0.7 burn time should be marketed as SCR A3-5 (3 is the average thrust)

Kind of annoyed they market their products incorrectly. The number which proceeds the Impulse letter on Rocket motors is meant to be the average thrust in Newtons.

citizenspace
Parachute Packer
Parachute Packer
Posts: 47
Joined: Wed Aug 26, 2015 12:32 pm
Location: Sydney, NSW

Re: Estes ejection charge question?

Postby citizenspace » Tue Sep 01, 2015 11:45 am

lucifer911 wrote:
citizenspace wrote:Hmmm, actually I don't know... Now that I am looking at the ausrocketry pages for the A8-5 and the B6-4 from SCR, it seems as if that number doesn't have a correlation with any of the stats...
Would anyone be able to correct me on that? I went to the Estes site and it says the 8 in A8-5 should be the average thrust, but it isn't.


to calculate the burn time (thrust duration) it is Total impulse divide by the Average Thrust in Newtons not max newton thrust.

SCR A8-5 the listed tot. impulse is 2.5 and the listed burn time is 0.7
if we divide tot. impulse 2.5 / the incorrect number marketed on the motor after the impulse letter which is 8 the burn time = 0.31
the only way to arrive at 0.7 is by dividing the 2.5 by the average thrust which is 3.3 = 0.757

The number marketed on the motor is meant to be average thrust in Newtons not max Newton thrust.
So technically the motor with the 2.5 tot. impulse and 0.7 burn time should be marketed as SCR A3-5 (3 is the average thrust)

Kind of annoyed they market their products incorrectly. The number which proceeds the Impulse letter on Rocket motors is meant to be the average thrust in Newtons.

Yes annoying but it's not the max thrust either: The B6-5's second number could only be the propellant mass - it's max thrust is 12.2, total impulse is 4.7 and average thrust is 3.9. It's propellant mass is exactly 6 though.

Doesn't make a whole lotta sense does it...
The best way to do something well is to make sure you've tried all the ways of making it fail.
NASA does it all the time with simulators :D
---

lucifer911
Rocket Flyer
Rocket Flyer
Posts: 134
Joined: Sun Jul 26, 2015 12:49 am

Re: Estes ejection charge question?

Postby lucifer911 » Tue Sep 01, 2015 12:05 pm

citizenspace wrote:
lucifer911 wrote:
citizenspace wrote:Hmmm, actually I don't know... Now that I am looking at the ausrocketry pages for the A8-5 and the B6-4 from SCR, it seems as if that number doesn't have a correlation with any of the stats...
Would anyone be able to correct me on that? I went to the Estes site and it says the 8 in A8-5 should be the average thrust, but it isn't.


to calculate the burn time (thrust duration) it is Total impulse divide by the Average Thrust in Newtons not max newton thrust.

SCR A8-5 the listed tot. impulse is 2.5 and the listed burn time is 0.7
if we divide tot. impulse 2.5 / the incorrect number marketed on the motor after the impulse letter which is 8 the burn time = 0.31
the only way to arrive at 0.7 is by dividing the 2.5 by the average thrust which is 3.3 = 0.757

The number marketed on the motor is meant to be average thrust in Newtons not max Newton thrust.
So technically the motor with the 2.5 tot. impulse and 0.7 burn time should be marketed as SCR A3-5 (3 is the average thrust)

Kind of annoyed they market their products incorrectly. The number which proceeds the Impulse letter on Rocket motors is meant to be the average thrust in Newtons.

Yes annoying but it's not the max thrust either: The B6-5's second number could only be the propellant mass - it's max thrust is 12.2, total impulse is 4.7 and average thrust is 3.9. It's propellant mass is exactly 6 though.

Doesn't make a whole lotta sense does it...


I might try to contact Estes and SCR and get an official response. I will just act dumb and ask them what the first number represents. If they respond with average thrust in N I will ask them for tot. impulse and burn time. I hope these guys who market the wrong numbers do not get a job at NASA. Simple miscalculations like this would lead to disasters in NASA rocket launches...

citizenspace
Parachute Packer
Parachute Packer
Posts: 47
Joined: Wed Aug 26, 2015 12:32 pm
Location: Sydney, NSW

Re: Estes ejection charge question?

Postby citizenspace » Tue Sep 01, 2015 12:27 pm

Good idea, be interesting to see the reply

Except NASA doesn't have any launchers... They buy them
The best way to do something well is to make sure you've tried all the ways of making it fail.
NASA does it all the time with simulators :D
---

martymonsta
Engineer
Engineer
Posts: 709
Joined: Mon Oct 13, 2014 11:57 am
Location: Drouin Vic.

Re: Estes ejection charge question?

Postby martymonsta » Tue Sep 01, 2015 6:23 pm

Ok so how motor codes are supposed to work, and how they actually work.

The way it is supposed to work is eg C6-5 The C relates to the total impulse of the motor, is the case of C it would mean that the motor has between 5.01 and 10 N-s of thrust. The 6 relates to the average thrust of the motor in N's, (it is worth noting that a Newton is a measurement of force required to accelerate 1kg at a rate of m/s^2 and as such the average can only be calculated over a whole second, i'll return to this in a bit) The 5 refers to the delay time in seconds, from motor burnout to the ejection charge being fired (ideally you select a delay that is similar to the estimated coast time so that the ejection charge goes off at apogee). As it has been pointed out the SCR C6-5 (and the Estes C6-5 for that matter) the 6 doesn't seem to relate to average. I'm not certain why it is designated as an average of 6 but it is a manufacturer's designation so it might be due to the original motor design calculations or that 18mm C BP motors from other manufacturers carry the C6 designation while not averaging 6 and it was keep to the norm to avoid confusion in the hobby shop market (the standard for motor designation was updated in 1982 however the BP market was already well and truly established). http://www.thrustcurve.org/motorsearch.jsp?id=1027 actually designates the motor as SCR C3 (C6 Alt). All the actual thrust figures are on the thrustcurve website.

As for the extended motor designation i'll use CTI 68F240-15A (VM) because it will show a few things. CTI is the manufacturer 68 the total impulse is 68N-s which is between 40.01 and 80N-s which makes it an F the manufacturer calculated the average thrust to 240N, however testing by CAR (Canadian Association of Rocketry) found it to be 236.2N. So as for how a motor can have more a higher average thrust then total impulse 68N-s/0.287sec=236.2N remembering that a Newton is a measure per second^2

I hope this helps

Marty
Many years ago the great British explorer George Mallory, who was to die on Mount Everest, was asked why did he want to climb it. He said, "Because it is there."
Well, space is there, and we're going to climb it

MARS #21
AMRS #41 L2/LCO/RSO/CO

lucifer911
Rocket Flyer
Rocket Flyer
Posts: 134
Joined: Sun Jul 26, 2015 12:49 am

Re: Estes ejection charge question?

Postby lucifer911 » Tue Sep 01, 2015 7:06 pm

martymonsta wrote:Ok so how motor codes are supposed to work, and how they actually work.

The way it is supposed to work is eg C6-5 The C relates to the total impulse of the motor, is the case of C it would mean that the motor has between 5.01 and 10 N-s of thrust. The 6 relates to the average thrust of the motor in N's, (it is worth noting that a Newton is a measurement of force required to accelerate 1kg at a rate of m/s^2 and as such the average can only be calculated over a whole second, i'll return to this in a bit) The 5 refers to the delay time in seconds, from motor burnout to the ejection charge being fired (ideally you select a delay that is similar to the estimated coast time so that the ejection charge goes off at apogee). As it has been pointed out the SCR C6-5 (and the Estes C6-5 for that matter) the 6 doesn't seem to relate to average. I'm not certain why it is designated as an average of 6 but it is a manufacturer's designation so it might be due to the original motor design calculations or that 18mm C BP motors from other manufacturers carry the C6 designation while not averaging 6 and it was keep to the norm to avoid confusion in the hobby shop market (the standard for motor designation was updated in 1982 however the BP market was already well and truly established). http://www.thrustcurve.org/motorsearch.jsp?id=1027 actually designates the motor as SCR C3 (C6 Alt). All the actual thrust figures are on the thrustcurve website.

As for the extended motor designation i'll use CTI 68F240-15A (VM) because it will show a few things. CTI is the manufacturer 68 the total impulse is 68N-s which is between 40.01 and 80N-s which makes it an F the manufacturer calculated the average thrust to 240N, however testing by CAR (Canadian Association of Rocketry) found it to be 236.2N. So as for how a motor can have more a higher average thrust then total impulse 68N-s/0.287sec=236.2N remembering that a Newton is a measure per second^2

I hope this helps

Marty


yes this helps and I cross checked the average thrust number with the higher impulse reloadable motors and found the average thrust number to be much more accurate than the average thrust number on the single use black powder SCR / Estes A/B/C motors. I guess its to do with how things were originally manufactured. As someone relatively new to rocketry I don't want to have too many options to choose from when selecting motors in the same impulse range as it just gets confusing. Thanks for your input.


Return to “Propulsion”

Who is online

Users browsing this forum: No registered users and 3 guests