i should know this... but.. cluster question

[lppa2006]

i should know this.. but im havin a brain fart today... when clustering do you just multiply the motors to come up with total imp and thrust... For example would three C's be greater in power than one E. The reason im asking is im thinking about doing a Big Daddy mod with a 3x - 5x cluster... this will be my first attempt at clustering so i want to make sure i know the science behind it as well

 

[Balltip]

Each step in lettering means double the power (roughly). So three C's would be just between D and E. To equal that single E you need 4 C's. That is in total impulse, the average thrust would be greater using the C's (6N x 4 motors = 24N) but you get a shorter burn time (as they expell their propellant more rapidly than a black powder E)





...hope I did not mess things up now

 

[Handeman]

The general concept is each letter doubles the total impulse. Two Cs = 1 D, 2 Ds = 1 E, so four Cs would equal an E That's the general concept and works sort of, kind of as long as you're talking Estes A through D motors. It starts getting a little out of whack with E's and above.

In your case, you're correct. Three Cs at 10N equals the 30N total impulse of the Estes E9 (middle of the E range). Four of them would hit the maximum for E motors at 40N.

Another example would be a 24mm RMS F12J reload with a total impulse of 43N. It should take 2 Fs to make a G and four Fs to make an H. In this case, four F12Js give a total impulse of 172N, still in the G range.

The most accurate method is to add up the total impulse of all the motors you'll be using and do your calculations with that.

 

[cjl]

Actually, handeman, 172Ns is a baby H motor. 4 F motors will ALWAYS make an H, but it may not be a very big one (the cutoff is 160Ns)

 

[Handeman]

I stand corrected. I was thinking 180N, don't ask me why

 

[Bigander]

Calculator under cluster totals!!
https://info-central.org/index.cgi?propulsion

 

[jraice]

Originally posted by Handeman
I stand corrected. I was thinking 180N, don't ask me why

I wont ask you but Ill tell you ...

The most common small H casing is the AT 29/180, I am sure thats why you got confused...

The big daddy is a pretty solid rocket so I wouldnt worry to much about strength, but make sure it is still stable.

At the least find the CG (balancing point) when loaded with a standard D12 motor (stock kit) and then make sure your cluster rocket is either the same, or closer to the nose.

Or use rocksim...

Unless you want to have to reinforce the fins I would probably stick with 3 18mm motor mounts... You could do 4 but three is nice and easy, because that is how many come in the pack !

And 3 B's would be just a bit less total impulse then the D12, but with more kick... And 3 C's would be about the same but also with more kick then the D12... So build it tough!

Would be a fun rocket...

 

[Handeman]

Originally posted by jraice
I wont ask you but Ill tell you ...

The most common small H casing is the AT 29/180, I am sure thats why you got confused...

By jobe, I think he got it!

 

[kandsrockets]

Go with six 18mm tubes...... Here is my Big Daddy on 6

 

[Motörhead]

Originally posted by krsconstruction
Go with six 18mm tubes...... Here is my Big Daddy on 6

WOT THAAAAAAA .... ??????

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NICEEEEEEEEEEE!!!!!!

 

[Handeman]

Originally posted by krsconstruction
Go with six 18mm tubes...... Here is my Big Daddy on 6

With that big washer for retention, it just looks like it should be a 24/29mm center motor...

 

[adrian]

If you're going to do that, you have plenty of room to angle the motor mounts a little so that they point up and slightly inward toward the CG. That way, if one of them doesn't light for some reason, the result of the unbalanced thrust from the opposite motor won't be so great. Just make the upper centring ring with the holes closer to the centre.

 

[jraice]

not cant the motors...

Its got 6, if one or even two dont light (as long as they are not next to eachother) it will still fly straight, as long as it is enough thrust to lift it in general...

Canting would help if say only 1-3 lit, but in that case it probably wouldnt even be able to get off the pad with half the speed to fly straight.

I say go 5-6 18mm's... 5 would be cool because you could do one in the middle with 4 around it, so you could do flights with just a D21 (believe thats the aerotech load for that size) or do the D21 with 4 BP motors around it!

Or go with a 24mm central and 3 or 4 18mm's, I would do three just because the rocket has 3 fins (easier to orient with the TTW tabs) and thats how many come in a pack...

Very versatile setup, D12 or E9 in center with 3 B-C motors, just 3 B-C motors, just a D12 or E9, an E15 (E30 might be to much), or really go for it with the E15 and 3 C6's!

Lots of combo's with a setup like that...

 

[adrian]

Originally posted by jraice
Its got 6, if one or even two dont light (as long as they are not next to eachother) it will still fly straight, as long as it is enough thrust to lift it in general...

In that case, don't cant the motors a little. Cant them a lot. If you like the angled motors of a Deuces Wild, just imagine what this would look like.

Very versatile setup, D12 or E9 in center with 3 B-C motors, just 3 B-C motors, just a D12 or E9, an E15 (E30 might be to much), or really go for it with the E15 and 3 C6's!

Lots of combo's with a setup like that...

The only thing I'm uncertain about there is nose weight. If there's enough nose weight for the rocket to be stable with a maximum load of an E15 and 3-4 C6's, will it have enough thrust to be stable with just the C6's or just a single D12?

I certainly like the idea of a central 24mm with flanking 18mm motors, though. I've built my own model based on BT-80 with a 24mm and two 18mm motors. Being somewhat longer than a Big Daddy, it doesn't need much nose weight to be stable on a full load, and has flown on everything from 2xB6 to D12 plus two C6's. Mind you, although the extra weight isn't necessary for stability, it generally only gets the full load if it's carrying a heavy payload and needs the power.

 

[kandsrockets]

My BD has 2oz of nose weight and flies perfect on 6- C6-5's

 

[Bohica]

Not a BD....but an impressive cluster none the less....

 

[Stymye]

this is a really cool cluster , I've seen at some club launches

https://v-serv.com/usr/kits/weightlofter.htm