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.

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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Jeffrey Deem
NAR16741
CIA section 527

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!

__________________
Jeffrey Deem
NAR16741
CIA section 527

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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Dale Greene

Mentor, Penn Manor Rocket Club
VISIT SPAAR
2010 Calder Cup
The Old West
2009 Calder Cup

" Speaking the Truth in times of universal deceit is a revolutionary act. " George Orwell

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

Attached Thumbnails

   

Attached Files

	EstesC5.pdf (26.8 KB, 88 views)
	EstesC6.pdf (28.1 KB, 41 views)

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!

__________________
Did the chicken really cross the road, or did the
road move beneath the chicken? Albert Einstein

You Can't break the laws of physics but they can break you. Christine McKinley


Dale Greene

Mentor, Penn Manor Rocket Club
VISIT SPAAR
2010 Calder Cup
The Old West
2009 Calder Cup

" Speaking the Truth in times of universal deceit is a revolutionary act. " George Orwell

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

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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When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL, if you have to ask what is "NORMAL" , you probably aren't !
Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, CHAOS, and HAVOC !

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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-Fred Shecter NAR 20117 (L2)
Southern California Rocket Association, NAR Section 430

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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