# Thread: C's twice as high as B's... so on?

1. ## C's twice as high as B's... so on?

Do each letter up on the engines go twice as high as the previous letter?
So when estes says max altitude of 800' feet of standard (A's,B's,C's engines) rocket, which would be on a C to get the max height, so a B engine should be around 400', and an A would be around 200' feet...? Is this right or is there something I'm missing?
I'm just wondering, because this is kinda how I judge altitude with lower engines with my estes rockets.
Thanks for any help!

2. That's a very rough approximation. Cs are twice as powerful as Bs, but twice the power doesn't always mean twice the altitude. However, if all you want is a rough guess, that should be good enough to at least get an idea of the altitude.

3. Also relative to what the actual total impulse is.

For example. Max A is 2.5ns, max B is 5ms, max C is 10ns, 20 for D, 40 for E and so on.

You can have a C motor that is anywhere between 5.1 n/s to 10 n/s, most black powder C motors fall anywhere between 7-9 n/s depending on brand and type; so right of the bat u see that you don't get double the fun if the B is a full B.

4. Originally Posted by [POW]Eagle159
Do each letter up on the engines go twice as high as the previous letter?
So when estes says max altitude of 800' feet of standard (A's,B's,C's engines) rocket, which would be on a C to get the max height, so a B engine should be around 400', and an A would be around 200' feet...? Is this right or is there something I'm missing?
I'm just wondering, because this is kinda how I judge altitude with lower engines with my estes rockets.
Thanks for any help!

Well, it's close enough for government work.

Verna
www.vernarockets.com

5. pretty much, and with the larger estes rockets it's actually fairly accurate, but the small ones that go closer to 1500-2000ft (at least the star dart used to be advertised that way), the C engine will not go exactly twice as high because it'll go faster, so it'll get more drag, but even with that, it's a good approximation, and i'd never thought of it lol.

one thing you can do is go to the apogee website and search for your rocket. they have altitudes for lots of different motors

6. The opposite is also true. I've been flying lots of altimeters in lots of model rockets over the last year or so. I typically see more than double the altitude A to B and B to C on what one might consider small to medium sized models. I actually have the most data on a BMS School Rocket with optional payload section.

My theory about why this is (I have not done the calculations to verify it) is that a greater proportion of the total impulse of the smaller motors is used just getting the thing moving at all as opposed to continuing to accelerate it as the motor burns longer at somewhere near the same sustained thrust. Or, to look at it another way (and looking at time-thrust curves for the most common Estes motors - A8, B6, C6), the initial spike that gets things going takes a much larger portion of the total from the A than from the C.

The case that edwinshap1 mentions just above also can happen - and I see that with the very same sorts of rockets going from a C6 to a (composite 18mm) D10. At that point the drag rise appears to be overcoming the further doubling of total energy delivered and the delta between the C apogee and the D apogee is less than double the C apogee.
Last edited by BEC; 1st July 2011 at 08:51 PM.

7. Originally Posted by n3tjm
Also relative to what the actual total impulse is.

For example. Max A is 2.5ns, max B is 5ms, max C is 10ns, 20 for D, 40 for E and so on.

You can have a C motor that is anywhere between 5.1 n/s to 10 n/s, most black powder C motors fall anywhere between 7-9 n/s depending on brand and type; so right of the bat u see that you don't get double the fun if the B is a full B.
That's correct.

Because the range of the total impulse (power) of the motor also doubles with each letter, it means a motor "one-letter" more powerful can actually be about 1 to about 4 times as powerful as the motor one level below it.

For example, a "Baby C" motor might have only a little higher total impulse than a "Full B" motor. But, a "Full C" motor could have almost four times the total impulse of a "Baby B" motor.

The average difference in power, however, is two times, so, in general, a motor classified one letter higher is twice as powerful as the smaller motor. And that's true for most model rocket motors.

The difference is really only noticible when you start dealing with high-power motors.

-- Roger

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Originally Posted by n3tjm
Also relative to what the actual total impulse is.

For example. Max A is 2.5ns, max B is 5ms, max C is 10ns, 20 for D, 40 for E and so on.

You can have a C motor that is anywhere between 5.1 n/s to 10 n/s, most black powder C motors fall anywhere between 7-9 n/s depending on brand and type; so right of the bat u see that you don't get double the fun if the B is a full B.
n3 is right.

Estes design their:
A's to be 2.5Ns
B's to be 5.0Ns
C's to be 10.0Ns
D's to be 20.0Ns

Actual measured values vary slightly but are close. Total impulse is based
on the mass of the BP used but nozzles efficiencies bring it down a little.

However an Estes E is designed to be only 30 Ns not 40 Ns. I am assuming
this was done to meet a design length on the casing.

Anecdotal information:

The Whatchamacallit on a 1/4A will only get 60-70 feet, the same rocket on
a 1/2A will get between 175-250 feet.

So double the impulse may get you more than double the altitude. In my
example I am assuming the difference is likely the friction on the launch rod.

Larger rockets and engine will like show less of a difference and likely a
reverse of the trend as drag effects take over in particular as higher
velocities are reached.

9. So if a D gets the Estes Saturn V to 100-150' feet, than an Aerotech E-20 should get it to around 300-400' feet... Right???(all rough calculations)
The AT E-20 is not a full E though, it's only like 36 N total, not 40 N like it could be.

10. BTW ... the "Compare Motors" feature at RocketReviews.com might be helpful for exploring some of the ideas explored in this thread. For example, here's a comparison of the 1/4A4 and 1/2A4 motors mentioned in the previous post:

http://www.rocketreviews.com/compare...tes-12a3t.html

And here's an Estes C6 and D12 comparison:

http://www.rocketreviews.com/compare...estes-d12.html

Here's the D12 and E20 compared:

http://www.rocketreviews.com/compare-motors-5998.html

I need to fix the legends which are wrong, but it's easy to see which curve belongs to which motor.

-- Roger
Last edited by jadebox; 1st July 2011 at 09:25 PM.

Estes design their:
A's to be 2.5Ns
B's to be 5.0Ns
C's to be 10.0Ns
D's to be 20.0Ns
Estes C's are more like 9 and the D12 about 17ns
Last edited by Bazookadale; 1st July 2011 at 11:41 PM.

BTW ... the "Compare Motors" feature at RocketReviews.com might be helpful for exploring some of the ideas explored in this thread. For example, here's a comparison of the 1/4A4 and 1/2A4 motors mentioned in the previous post:

http://www.rocketreviews.com/compare...tes-12a3t.html

And here's an Estes C6 and D12 comparison:

http://www.rocketreviews.com/compare...estes-d12.html

Here's the D12 and E20 compared:

http://www.rocketreviews.com/compare-motors-5998.html

I need to fix the legends which are wrong, but it's easy to see which curve belongs to which motor.

-- Roger

13. Originally Posted by BEC
The opposite is also true. I've been flying lots of altimeters in lots of model rockets over the last year or so. I typically see more than double the altitude A to B and B to C on what one might consider small to medium sized models. I actually have the most data on a BMS School Rocket with optional payload section.

My theory about why this is (I have not done the calculations to verify it) is that a greater proportion of the total impulse of the smaller motors is used just getting the thing moving at all as opposed to continuing to accelerate it as the motor burns longer at somewhere near the same sustained thrust. Or, to look at it another way (and looking at time-thrust curves for the most common Estes motors - A8, B6, C6), the initial spike that gets things going takes a much larger portion of the total from the A than from the C.

The case that edwinshap1 mentions just above also can happen - and I see that with the very same sorts of rockets going from a C6 to a (composite 18mm) D10. At that point the drag rise appears to be overcoming the further doubling of total energy delivered and the delta between the C apogee and the D apogee is less than double the C apogee.
In part, that's because for rockets that don't go very fast, the gravity loss is larger than the drag loss. Gravity loss is smaller for more powerful motors, so a motor with twice the power can easily give more than twice the altitude (so long as the drag loss is minimal).

14. How much effect does the rocket's design play into this? I noticed when running sims on one of my recent slim and light rockets that some higher total impulse motors actually resulted in a lower altitude than some others. Looking closely at the thrust curves, it appeared that motors with a higher initial thrust for shorter duration resulted in higher altitude than motors with lower thrust over longer period of time. I'm guessing that the really streamlined and light rockets can coast easier, and with with the higher initial velocity coast a good ways (the sim time to apogee also seem to support this). Some of my less streamlined rockets seem to show the opposite, higher altitudes on a long burning motor. I'm guessing their drag doesn't allow them to coast well at all, so they benefit from longer thrust?

Or am I seeing correlations that aren't really there?

15. Originally Posted by MrGneissGuy
How much effect does the rocket's design play into this? I noticed when running sims on one of my recent slim and light rockets that some higher total impulse motors actually resulted in a lower altitude than some others. Looking closely at the thrust curves, it appeared that motors with a higher initial thrust for shorter duration resulted in higher altitude than motors with lower thrust over longer period of time. I'm guessing that the really streamlined and light rockets can coast easier, and with with the higher initial velocity coast a good ways (the sim time to apogee also seem to support this). Some of my less streamlined rockets seem to show the opposite, higher altitudes on a long burning motor. I'm guessing their drag doesn't allow them to coast well at all, so they benefit from longer thrust?

Or am I seeing correlations that aren't really there?
Yes this seems right, It makes very good sense too.

16. Originally Posted by [POW]Eagle159
Thanks ... but I didn't just find that site. I'm the one who messed up the legends for the charts. :-)

-- Roger
Last edited by jadebox; 1st July 2011 at 11:54 PM.

Thanks ... but I didn't just find that site. I'm the one who messed up the legends for the charts. :-)

-- Roger
Wow, I noticed that...should I ask how

18. Originally Posted by [POW]Eagle159
Wow, I noticed that...should I ask how
I created those web pages. The graphs are drawn based on data from Rocksim and RASP motor files which is why they aren't as smooth as some time-thrust curves.

In addition to the "Compare Motors" thing, you can also "Combine Motors." Have you ever wondered what the time-thrust curve would look like for a two-stage rocket with 1600 MicroMax II motors in the first stage and 800 MicroMax II motors in the second stage? (It's equivalent to a J motor.) :-)

-- Roger

19. Originally Posted by MrGneissGuy
How much effect does the rocket's design play into this? I noticed when running sims on one of my recent slim and light rockets that some higher total impulse motors actually resulted in a lower altitude than some others. Looking closely at the thrust curves, it appeared that motors with a higher initial thrust for shorter duration resulted in higher altitude than motors with lower thrust over longer period of time. I'm guessing that the really streamlined and light rockets can coast easier, and with with the higher initial velocity coast a good ways (the sim time to apogee also seem to support this). Some of my less streamlined rockets seem to show the opposite, higher altitudes on a long burning motor. I'm guessing their drag doesn't allow them to coast well at all, so they benefit from longer thrust?

Or am I seeing correlations that aren't really there?
It all depends on the maximum velocity, or, more accurately, on the drag loss compared to the gravity loss. For faster rockets, even streamlined ones, or for very light rockets, the longer burn motor will win. It minimizes the drag during boost, and thus gives the best altitude. For a rocket that's fairly dense, streamlined, and/or doesn't go very fast, the short burn motor is better however, since it doesn't have substantial drag losses regardless, and the short burn motor minimizes gravity loss. My guess is that in the case of pretty much any altitude rocket (even those on B or C motors), the drag loss is more significant, but I haven't run the numbers for small rockets.

I created those web pages. The graphs are drawn based on data from Rocksim and RASP motor files which is why they aren't as smooth as some time-thrust curves.

In addition to the "Compare Motors" thing, you can also "Combine Motors." Have you ever wondered what the time-thrust curve would look like for a two-stage rocket with 1600 MicroMax II motors in the first stage and 800 MicroMax II motors in the second stage? (It's equivalent to a J motor.) :-)

-- Roger
Now that is scary to think about

21. Yell at me if I missed it, but I don't see anything here yet about how straight (vertically) the rocket goes. That's another BIG factor in altitude.

For a somewhat extreme case, it's very possible for a rocket powered by an E9 to get less altitude than when powered by a D12, because the D12 has enough oomph to get it going vertically while with the E9 it may come over into the wind and mostly fly horizontally.

22. Originally Posted by sylvie369
Yell at me if I missed it, but I don't see anything here yet about how straight (vertically) the rocket goes. That's another BIG factor in altitude.

For a somewhat extreme case, it's very possible for a rocket powered by an E9 to get less altitude than when powered by a D12, because the D12 has enough oomph to get it going vertically while with the E9 it may come over into the wind and mostly fly horizontally.
Well that's usually when something goes very wrong, and you don't bring back a nice one piece rocket like you started with ...

23. Originally Posted by [POW]Eagle159
Well that's usually when something goes very wrong, and you don't bring back a nice one piece rocket like you started with ...
The D12 vs E9 scenario is exactly what I ran into yesterday, and it did not end well. It was however, still technically one piece.

24. Originally Posted by DizWolf
The D12 vs E9 scenario is exactly what I ran into yesterday, and it did not end well. It was however, still technically one piece.
...I remember that... Yes that didn't end well , but now you have something to work on.

25. Well, on a slim, relatively lightweight, well-balanced rocket (neither over- nor under-stable) the E9 will definitely go higher than the D12.... except in gusty conditions! Matching the motor to the rocket and to the launch conditions are two things that are critical for success.
Last edited by MarkII; 3rd July 2011 at 03:34 AM.

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