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  #1  
Old 07-07-2011, 08:01 AM
Scott6060842 Scott6060842 is offline
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Default Motor confusion

I'll be the first to admit I never really fully understood motor coding and I guess I still don't (although I am making an attempt to try).

I have been reading about how great Estes c5 motors were, but I wondered "how much different can they be from the c6?"

So I went to the internet and printed out the NAR data:

c5 Peak thrust 21.85 newtons, max lift weight 226.4 g
c6 Peak thrust 14.09 newtons, max lift weight 113.2 g

What the? Thats backward from what I would have thought....and that much difference between a 5 and a 6. Talk about confusion...am I missing something? I guess I need to print out all the data on every motor and study up.
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Old 07-07-2011, 09:10 AM
jdbectec jdbectec is offline
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The number in a motor designation is the average thrust not the maximum.

In most cases a motor with 5 newton seconds of average thrust would have a lower maximum lift-off weight than a motor of 6 newton seconds but, the C5-3 is an exception. It has a cored design that gives it a very high initial "spike" then drops off to a lower , and slower burn which gives it a lower average thrust than the C6-3. If you go to http://www.thrustcurve.org/ you can compare the thrust curves of many different motors
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Old 07-07-2011, 09:30 AM
jdbectec jdbectec is offline
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I just visted that site and realized you have to download the thrust curves to a suitable program to veiw them. It is the NAR site that has ones that you can veiw.

Sorry for the confusion.

It is interesting to note that based on the actual testing data, the C6 is just under 5 N-secs average thrust, and the C5 is slightly more than 5 N-secs,

So in reality the motor designations should be reversed.

Boy, would that add to the confusion!
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Old 07-07-2011, 11:30 AM
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Bazookadale Bazookadale is offline
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Quote:
Originally Posted by jdbectec
I just visted that site and realized you have to download the thrust curves to a suitable program to veiw them. It is the NAR site that has ones that you can veiw.

Sorry for the confusion.

It is interesting to note that based on the actual testing data, the C6 is just under 5 N-secs average thrust, and the C5 is slightly more than 5 N-secs,

So in reality the motor designations should be reversed.

Boy, would that add to the confusion!



Estes and Quest both "fudge" their numbers at times. The A10 is really an A2 they call it an A10 so the user knows about the really high initial thrust spike. By that logic they could just as easily called the C5 a C7 or something like that - C5 is actually an accurate designation for a change.

Rocketeer beware! you should always check the actual data on a motor rather than trust the manufacturers code
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Old 07-07-2011, 11:33 AM
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For one of the best web-based explanation of rocket motor classifications:

http://www.thrustcurve.org/motorstats.shtml

Attached is a motor comparison between the C5 and C6.

The C5 (green line in the graph) has a higher initial thrust spike (significantly), so it can lift more due to that. The sustain level is about the same after the spike, just a tad shorter.

By my calcs, the average thrust of the C5 is actually a little higher.

So, if you have a rocket that is marginal on a C6, a C5 would be better.

Greg
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File Type: pdf EstesC6.pdf (28.1 KB, 41 views)

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  #6  
Old 07-07-2011, 11:37 AM
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Interesting - that is the first time I've seen a C5 with a shorter duration than a C6 - it's supposed to be a full 2 seconds - but that's Estes numbers again!
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  #7  
Old 07-07-2011, 11:45 AM
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GregGleason GregGleason is offline
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If we wanted to increase accuracy in the distinction between the C5 and C6:

C5-x --> C5.5-x

C6-x --> C4.9-x

Greg
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  #8  
Old 07-07-2011, 01:57 PM
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There is literally nothing a C6-3 can do that the C5-3 does not do better.
Many rockets that are marginal on the C6-3 are fine performers on the C5-3.
Two examples are the full-stack Estes #1284 Space Shuttle and the Estes/Semroc Mars Lander.
It was a stupid decision by Estes to ever discontinue the C5-3 and keep the C6-3 in the line.
Estes had one bad batch of C5-3 motors that went "explodo" on every launch and instead of FIXING THE PROBLEM, they just discontinued the motor.
They got it backwards; the one that survived should have been the one discontinued.
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Old 07-07-2011, 03:02 PM
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Quote:
Originally Posted by ghrocketman
There is literally nothing a C6-3 can do that the C5-3 does not do better.
Many rockets that are marginal on the C6-3 are fine performers on the C5-3.
Two examples are the full-stack Estes #1284 Space Shuttle and the Estes/Semroc Mars Lander.
It was a stupid decision by Estes to ever discontinue the C5-3 and keep the C6-3 in the line.
Estes had one bad batch of C5-3 motors that went "explodo" on every launch and instead of FIXING THE PROBLEM, they just discontinued the motor.
They got it backwards; the one that survived should have been the one discontinued.


That is not correct. The bad batch was in year "X" and they continued to make the C5-3 motors for many years afterwards. They simply corrected the problem that led to the catastrophic failures in year "X".

The decision to discontinue them was related to the difficulty in manufacturing them with such a deep centerbore. In business "difficulty" = "expense".
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Old 07-07-2011, 03:02 PM
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Quote:
Originally Posted by ghrocketman
There is literally nothing a C6-3 can do that the C5-3 does not do better.
Many rockets that are marginal on the C6-3 are fine performers on the C5-3.
Two examples are the full-stack Estes #1284 Space Shuttle and the Estes/Semroc Mars Lander.
It was a stupid decision by Estes to ever discontinue the C5-3 and keep the C6-3 in the line.
Estes had one bad batch of C5-3 motors that went "explodo" on every launch and instead of FIXING THE PROBLEM, they just discontinued the motor.
They got it backwards; the one that survived should have been the one discontinued.

I'd like to have them both, but like you, if I had to choose one or the other I'd choose the C5-x.

However, there is the issue of a 7 second delay. The current C6-7 is just about filled to the top. The C5-x has more propellant and it is cored, both contributing to a need for more space in the casing than a C6-7. A 7 second might not fit. My vintage C5-3S (Centuri labeled) motors are filled as full in the casing as my current C6-7's. Estes could cut the amount of propellant, like the classic D11-9, but then we'd have the whiners that would complain about the motor being crippled or dumbed down.
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