Estes C11 vs D12

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Kruegon

Well-Known Member
Joined
May 20, 2014
Messages
1,885
Reaction score
5
Perhaps I just have bad info, but the numbers just aren't lining up.

Looking at the numbers, the C11 and D12 seem to perform similarly. The only thing I can see is the C11 seems to burn longer at a little lower thrust while the D12 burns shorter at a slightly higher thrust.

I simed both engines in a rocket with RockSim and got nearly the same result from both. I've never played with the C11 and I'm trying to figure out why it even exists.
 
I love the C11. For my small BT-50 based 24mm rockets it's perfect for testing them in my local park which is'nt as big as I'de like it to be.

Regardless of what the Sims say, they are notably different in real life flight characteristics.
 
Last edited:
I think your info must be off. Look them up on Thrustcurve.org. The C11 has about half the burn time and a little over half the total impulse of the D12. It's a real and very noticeable difference.
 
Looking at the thrust curve data on the NAR site - isn't the initial thrust quite a bit higher with the D? Perhaps it doesn't make much difference on your existing design - but I suppose it has it's place, right?

As TopRamen noted - the C-11 might be nice in an application that doesn't need a lot of initial thrust off the rod.
 
Even my glassed 24mm Patriot can ride one for a nice low altitude flight.


[video=youtube;Rm5Z3X47B_M]https://www.youtube.com/watch?v=Rm5Z3X47B_M[/video]
 
Last edited:
And here is the same rocket on a D12.


[video=youtube;7DUWn3hupgY]https://www.youtube.com/watch?v=7DUWn3hupgY[/video]
 
Last edited:
I love the C11 in certain applications. For instance, the Estes Goblin came out when I was a kid. I wasn't nearly smart enough to build an 18mm adapter, so I was stuck using the D motor (the C11 didn't exist yet). Bye bye. Smallish 24mm birds like the Goblin fly great on the C11.

Substitute a 24mm mount in a rocket like the Big Bertha and you increase its versatility greatly. A C11 gives an overly-stable rocket like the Bertha a nice kick off the pad with less weathercocking than a C6. And Bertha on a D12 just rocks!

I also have a Quest Li'l Grunt (D12 motors only recommended) that flies great on the C11-3. I wouldn't dream of putting a C6 in it.
 
The C11 is good for a nice solid kick, but not much total impulse. I have a Silver Comet that I like to fly on the C11. It gets off the pad nice and straight, but it doesn't go very high. That's a nice flight in a small park or on a day with a bit of wind. I've flown the same rocket on D's and E's when conditions are right.

It seems like the C11-0 would make a good first stage motor if you wanted to stage to an 18mm upper stage. You could get a nice kick and still stage at a low enough altitude to see it happen.

The motor definitely has it's place.
 
My minimum diameter 24mm Alpha will get a C11 for its first 24mm flight. It nearly goes out of sight on a B6-4 with an adapter, so there's no way I'm going straight to D power for it.
Sims put it at 877ft. on the C11-7 and 1495ft. on a D12-7.
 
Last edited:
I often fly my Der V-3 on a C11-3. Fairly slow lift off for a fat, heavyish rocket, easy to track with a camera. It puts it up about 250 feet. A D12-5 is great in that rocket, but you can see the entire flight clearly on a C11.
 
Here's a comparison of the thrust curves of the C11 and D12:

https://www.rocketreviews.com/compare-estes-d12-to-estes-c11.html

-- Roger

I have one problem with that, and that is the classification of the D12 as a "68%" D. That sounds rather wimpy indeed, until you consider that, with that scale, a full C would be considered a 0% D, which is really kinda silly. A full C is 50% of the power of a full D, so the D12 should be about a 84% D, since 16.8 is 84% of 20.
 
I have one problem with that, and that is the classification of the D12 as a "68%" D. That sounds rather wimpy indeed, until you consider that, with that scale, a full C would be considered a 0% D, which is really kinda silly. A full C is 50% of the power of a full D, so the D12 should be about a 84% D, since 16.8 is 84% of 20.

It seems like a really weird convention to me, but apparently that's the standard. If you are comparing two motors of different classes, like a C and a D, it's better to just look at their actual impulse, not these percentages.
 
I have one problem with that, and that is the classification of the D12 as a "68%" D. That sounds rather wimpy indeed, until you consider that, with that scale, a full C would be considered a 0% D, which is really kinda silly. A full C is 50% of the power of a full D, so the D12 should be about a 84% D, since 16.8 is 84% of 20.

As the parched savage pointed out, it's just the conventional way of rating the power of a motor within its classification. The scale runs from 0% to 100% - i.e. a D motor is classified as a 0% D through a 100% D. The way you propose would have the scale running from 50% to 100% for each letter.

-- Roger
 
Last edited:
I agree with you, Roy.....but as Roger points out if we did it the way it makes sense to us the minimum would be 50%. I've decided to just grit my teeth and accept the convention....

C11-3 in a Maxi Alpha 3 makes for a very amusing demo flight - maybe 100 feet up, pop, and landing almost right back on the launch pad (in little wind).

The extra kick of the 24mm C11 (vs. an 18mm C6) can be very useful. I wonder if that would be the way to make the Astron Farside and Farside-X work well - have the first stage be 24mm mount. One would have to figure out a clever way to stage a C11-0 to an 18mm second stage, with the first stage being minimum diameter for the motor though.....
 
50% of a full D is 100% of a full C, so I like the scale running from 50% to 100%.

I just use total impulse and do not attempt to create my own scale of reference since the scale is already there.


As the parched savage pointed out, it's just the conventional way of rating the power of a motor within its classification. The scale runs from 0% to 100% - i.e. a D motor is classified as a 0% D through a 100% D. The way you propose would have the scale running from 50% to 100% for each letter.

-- Roger
 
The letter ratings are a nice guide, but it's best to just look at total impulse and not an arbitrary scale. You can have J and K motors separated by less than 20N/s.

The scale is good for a general guide, but best not to entirely rely on it.
 
The letter ratings are a nice guide, but it's best to just look at total impulse and not an arbitrary scale. You can have J and K motors separated by less than 20N/s.

The scale is good for a general guide, but best not to entirely rely on it.

This^^^
When I'm mind-simming I look at stuff like the thrust curve and motor weight before and after burn rather than concern myself with arbitrary and useless tidbits of information like "What percent of a full whatever" any given motor is.
That figure tells me NOTHING about the performance characteristics of the motor.:)
 
The letter ratings are a nice guide, but it's best to just look at total impulse and not an arbitrary scale. You can have J and K motors separated by less than 20N/s.

The scale is good for a general guide, but best not to entirely rely on it.

This^^^
When I'm mind-simming I look at stuff like the thrust curve and motor weight before and after burn rather than concern myself with arbitrary and useless tidbits of information like "What percent of a full whatever" any given motor is.
That figure tells me NOTHING about the performance characteristics of the motor.:)

Correct.

The purpose of the percentage convention, at least as I understand it, is just to tell you where the motor lies in the arbitrary letter classes. So if a motor is a 90% D, then it is almost a "full" D, and if a motor is a 10% D, then it is closer to a "baby" D. It's just to give you an idea of where the motor is within the motor classes, and it's not really useful for any kind of calculations, as far as I know.

I don't see the 50% - 100% system being any more useful than the current convention. For example, if you are comparing the C11 to a D12, how helpful is it to say one is a 88% C and the other is an 84% D? Is that more useful than saying one is a 76% C and the other is a 68% D?

The best way to compare them is go directly to the impulse --- one is an 8.8 Ns motor and the other is a 16.8 Ns motor. The C is 52% of the D. Using the actual impulse means you can also compare the E9 and E12 as well, without your comparison having to be in terms of a motor class or a percentage of 3 different classes! This is one of the reasons I like CTI motor names --- the name starts with the impulse, not the letter.

I had all the same questions when I first saw this percentage convention. I thought it was stupid too. Now I understand it as just a guide, a way to add a bit more info to the letter classes, but I still don't think it is very useful. It's definitely not for making calculations or detailed comparisons between motors.
 
I'd love to see motors listed more like CTI does, but yank the letters. (total impluse) - (average thrust) - (burntime) - (delay) would be nice. Though you could omit the burntime with the first two being there, it'd still be nice.
 
the 24 mm x 70 mm long C11 and D12 motors are essentially the same motor with different amount of BP.

The nominal 10 Ns C11 has nominally 0.40 oz of BP propellant and the nominal 20 Ns D12 has nominally 0.9 oz. of BP propellant in the same motor casing.

BP motors are end-burners but have a small partial depth bore in the propellant grain to give an increased thrust to quickly get the rocket off the launch pad.

The efficiency of the propellant burn is dependent on chamber pressure. During the initial thrust spike the chamber pressure is more than 2 times higher than the lower plateau level, and the specific impulse is higher. This is the reason why the D 12 has slightly more than twice the propellant of the C11 (125% more versus 100% more).

The same is true for the variants of the 18 mm x 70 mm BP motors. The 1/2 A6, A8/ B6 and C6 motors are nearly identical except for the amount of BP propellant: 0.06 oz., 0.11 oz., 0.22 oz., and 0.44 oz. respectively.

https://www2.estesrockets.com/pdf/Estes_Engine_Chart.pdf

Bob
 
I had an application where I think that the burn-time of D12's versus C11 was important. As I recall I had a PerfectFlite minitimer, which used an accelerometer to activate a timer for second stage ignition. The model was a Nike Hercules with four 24 mm BP motors in the first stage and one 24 mm motor in second stage. In order to keep the altitude down I used four C11's in the first stage on the first launch, however, the second stage was not electronically ignited. The PerfectFlite timer requires a certain G-load for a certain time, in excess of 0.5 seconds. I did have some second stage issues that I corrected, but I also decided to go with four D12's on the second flight to insure that the G-load was present for a longer period of time. The second flight was successful.
 
I often fly my Der V-3 on a C11-3. Fairly slow lift off for a fat, heavyish rocket, easy to track with a camera. It puts it up about 250 feet. A D12-5 is great in that rocket, but you can see the entire flight clearly on a C11.

Me too. First launched my V-3 on a D12 and it went too far for my liking given the field size. I did not know about C11s at the time. They go great with that rocket.
 
the 24 mm x 70 mm long C11 and D12 motors are essentially the same motor with different amount of BP.

The nominal 10 Ns C11 has nominally 0.40 oz of BP propellant and the nominal 20 Ns D12 has nominally 0.9 oz. of BP propellant in the same motor casing.

Bob

Isn't the nozzle size also varied? Larger nozzles for faster burn motors and such?
 
Isn't the nozzle size also varied? Larger nozzles for faster burn motors and such?

I believe you are correct sir. As the BP for all Estes motors is most likely the same formulation, the only way to control the thrust would be via nozzle diameter/shape since all the motors are endburning.
 
Back
Top