What effect would it have???

What effect would it have???

Post by Joe Pete » Tue, 06 Aug 2002 04:27:45



If I took three "C" type engines, and somehow centered them in the
bottom of a rocket, and got them to all ignite at the same time, would
the rocket go higher than it would with just one C engine??? Would
that be equal to a D or E engine??? What would it really do????

Thanks

 
 
 

What effect would it have???

Post by David Weinshenke » Tue, 06 Aug 2002 05:07:18


Quote:

> If I took three "C" type engines, and somehow centered them in the
> bottom of a rocket, and got them to all ignite at the same time, would
> the rocket go higher than it would with just one C engine??? Would
> that be equal to a D or E engine??? What would it really do????

It's called a "cluster" - it's quite a popular technique!
There would be three times as much thrust as a single C
engine, for the same amount of time. The total impulse
would be the same as 1.5 D engines or 0.75 of a full E,
so it would be the equivalent of a single "medium E".

Some folks have clustered large numbers of engines... the
trick is to use a firing circuit that can provide enough
current to make all the igniters go off rapidly.

The small "controllers" that use AA or 9V batteries aren't really
suitable for anything more than one igniter at a time. At the other
end of the scale are systems that use large lead-acid or nicad
batteries located near the pad, with a relay circuit to get the
resistance of the leads from the firing switch out of the
high-current path between the battery and the igniters.
Such systems can provide enough current to reliably fire large
clusters.

The potential problem added by clustering is that if some but not all
engines fail to ignite (which can happen if the firing system doesn't
have enough "oomph" to pop all of the igniters fast and hard at the
same time), the thrust will not be symmetrical and the rocket will want
to go sideways - as well as being underpowered. That being said, it can
be made to work reliably... and when it works, it works quite well.

-dave w

 
 
 

What effect would it have???

Post by Carsten Glan » Tue, 06 Aug 2002 05:55:52


http://www.wrasp.com

respectfully

Carsten Glans


Quote:
> If I took three "C" type engines, and somehow centered them in the
> bottom of a rocket, and got them to all ignite at the same time, would
> the rocket go higher than it would with just one C engine??? Would
> that be equal to a D or E engine??? What would it really do????

> Thanks

 
 
 

What effect would it have???

Post by Peter Cla » Tue, 06 Aug 2002 06:33:17



Quote:
> If I took three "C" type engines, and somehow centered them in the bottom

of a rocket, and got them to all ignite at the same time, would the rocket
go higher than it would with just one C engine??? >>

You'd have a cluster.  It's fun. People do it quite a lot. Yes, it will go
higher than one C engine.  But in general, you use a cluster to loft a
heavier rocket to single-stage altitudes, and two stages to loft a small
rocket to higher altitude.

Quote:
>>Would that be equal to a D or E engine??? What would it really do????

The "C" in C6-5 stands for a limit of 10 newton-seconds of total impulse --
the total power packed in the motor.  Any motor with more than 5 and less
than 10 is a  C, and the Estes C6 is reportedly 9 or so.  You would add the
three 9's together for a total impulse of 27, equal to a medium E motor, and
very close to the total for the Estes E9.

Now then: the "6" in C6 is the (approximate) average thrust of the motor,
how hard it pushes.  With a cluster, you also add those together, so three
C6's become an E18, meaning it has about the same total power as that E9 but
pushes twice as hard for half as long.  That makes it best for a heavy
rocket (around 10-14 ounces, say).   A cluster of 4 D12's becomes an F48: a
very serious output of power and a popular modification to the Estes Big
Daddy kit.

If you stage them, using C6-0, C6-0, C6-7 one after another, you still add
up the total impuse (9x3=27) but not the average thrust.  In effect you now
have an "E6" that burns longer than an E9 but pushes only 2/3 as ***
average.  The first motor would have a hard time lifting the whole rocket
off the pad, but if it once got going straight up, it would seem to go
forever.   Using a D12-0 in the first stage will give you more thrust for a
stronger liftoff, and then a longer gentler thrust for extreme altitude.
This is the idea of the Estes Commanche-3.

Either way you've left your "little toys" behind and are flying some serious
rockets with perhaps the most commonly available, least regulated motors.

I once wrote a web page on clustering which is now found on InfoCentral.  Go
to http//www.rocketryonline.com and click on the InfoCentral icon at the
top.

Peter

 
 
 

What effect would it have???

Post by R Ted Phipp » Tue, 06 Aug 2002 06:34:27


Quote:

> If I took three "C" type engines, and somehow centered them in the
> bottom of a rocket, and got them to all ignite at the same time, would
> the rocket go higher than it would with just one C engine??? Would
> that be equal to a D or E engine??? What would it really do????

> Thanks

Joe,
   You really, really, really need to get The Handbook of Model Rocketry
by G. Harry Stine, and Model Rocket Design and Construction by Tim Van
Milligan (spelling?).
   Besides good information about building techniques, you'll find lots of
other information about clustering, staging, launch equipment, materials,
and so much more.
   Check out your local library.  But eventually, you'll want your own
copies to keep next to the workbench.

   Hope this helps,
      Ted

--
In the beginning there was nothing... which exploded.  

* remove skates to reply *

 
 
 

What effect would it have???

Post by tater schul » Tue, 06 Aug 2002 08:28:19



Quote:
> If I took three "C" type engines, and somehow centered them in the
> bottom of a rocket, and got them to all ignite at the same time, would
> the rocket go higher than it would with just one C engine??? Would
> that be equal to a D or E engine??? What would it really do????

I am currently bashing a fatboy. 7 (yes SEVEN) engines and an 18" payload
section. rocsim likes, either empty or with 10 oz payload.

That is, rocsim likes if if I use all seven engines. I only have the demo
version right now and i forgot to test for less than the max ammount of
engines. I am alo going to install a choreboy baffle in it too

 
 
 

What effect would it have???

Post by tater schul » Tue, 06 Aug 2002 08:34:37


This is an excelent explanation! I see that this now confirms my belief that
I should go into clusters. Nice big pop and flash on the ground for the big
rockets without having to worry about losing them in the clouds.

currently have a fatboy on the boards with 7     engine cluster and an extra
18 inches of tube for a payload

--
Tater
President of MARS Club
NAR #79654
AMA #747769
EAA #22007969
remove spam spelled backwards to reply


Quote:



> > If I took three "C" type engines, and somehow centered them in the
bottom
> of a rocket, and got them to all ignite at the same time, would the rocket
> go higher than it would with just one C engine??? >>

> You'd have a cluster.  It's fun. People do it quite a lot. Yes, it will go
> higher than one C engine.  But in general, you use a cluster to loft a
> heavier rocket to single-stage altitudes, and two stages to loft a small
> rocket to higher altitude.

> >>Would that be equal to a D or E engine??? What would it really do????

> The "C" in C6-5 stands for a limit of 10 newton-seconds of total
impulse --
> the total power packed in the motor.  Any motor with more than 5 and less
> than 10 is a  C, and the Estes C6 is reportedly 9 or so.  You would add
the
> three 9's together for a total impulse of 27, equal to a medium E motor,
and
> very close to the total for the Estes E9.

> Now then: the "6" in C6 is the (approximate) average thrust of the motor,
> how hard it pushes.  With a cluster, you also add those together, so three
> C6's become an E18, meaning it has about the same total power as that E9
but
> pushes twice as hard for half as long.  That makes it best for a heavy
> rocket (around 10-14 ounces, say).   A cluster of 4 D12's becomes an F48:
a
> very serious output of power and a popular modification to the Estes Big
> Daddy kit.

> If you stage them, using C6-0, C6-0, C6-7 one after another, you still add
> up the total impuse (9x3=27) but not the average thrust.  In effect you
now
> have an "E6" that burns longer than an E9 but pushes only 2/3 as ***
> average.  The first motor would have a hard time lifting the whole rocket
> off the pad, but if it once got going straight up, it would seem to go
> forever.   Using a D12-0 in the first stage will give you more thrust for
a
> stronger liftoff, and then a longer gentler thrust for extreme altitude.
> This is the idea of the Estes Commanche-3.

> Either way you've left your "little toys" behind and are flying some
serious
> rockets with perhaps the most commonly available, least regulated motors.

> I once wrote a web page on clustering which is now found on InfoCentral.
Go
> to http//www.rocketryonline.com and click on the InfoCentral icon at the
> top.

> Peter

 
 
 

What effect would it have???

Post by R. J. Talle » Tue, 06 Aug 2002 15:34:58


Three C-6 motors equals 1.5 D12 motors approx. It's called parallel
clustering and it's done all the time. As cool as it is to do, using one D
motor or an E composite is not only cheaper, it's more effecient. Those
motor cases have considerable mass to them.

R J Talley

Quote:
> If I took three "C" type engines, and somehow centered them in the
> bottom of a rocket, and got them to all ignite at the same time, would
> the rocket go higher than it would with just one C engine??? Would
> that be equal to a D or E engine??? What would it really do????

> Thanks

 
 
 

What effect would it have???

Post by Joe Pete » Tue, 06 Aug 2002 15:58:13


So are you guys telling me that if I were to cluster enough D engines
together, I could essentially have the same power as an L motor???
That's quite a motor, but with D engines, I could get the same power,
without all the red tape. I know that by clustering, you technically
have to still obey the limits and regulations regarding the amount of
propellant on the rocket, but would it be safe to say that by
clustering many engines together, you can get the power of the big boy
engines, with nothing more than the common and modest C and D
engines???
 
 
 

What effect would it have???

Post by RayDunak » Tue, 06 Aug 2002 17:12:50


<< would it be safe to say that by clustering many engines together, you can
get the power of the big boy engines, with nothing more than the common and
modest C and D engines??? >>

Technically, yes. The more motors you cluster, the more total thrust. However,
the performance won't be quite the same, for two reasons. First, clustering
enough D motors to equal an L motor will result in a pretty wide rocket. Much
wider than you'd need with a single L motor. That means there'll be more drag.

Secondly, all those D motor casings might weigh more than a single L motor
casing. I'm not sure about this specific example, but generally speaking
several small motors will weigh more than one big motor of equal power.

Of course, there's also the problem of igniting that many motors. It can be
done, but is tricky. And if they don't all ignite you'll have a sub-optimal
flight at best, and a major crash at worst.

 
 
 

What effect would it have???

Post by Peter Cla » Tue, 06 Aug 2002 18:39:48



Quote:
> So are you guys telling me that if I were to cluster enough D engines
> together, I could essentially have the same power as an L motor???

250 of them, as a matter of fact. Do you think you can get that many
started?

I suggested you could get into the low F range with four of them.  That's a
long, long way from L.

The big motors use AP composite propellant that is 2-1/2 times more powerful
ounce for ounce than the black powder used in Estes motors. And, as Ray
Dunakin pointed out, a single large motor is usually more efficient than a
cluster of smaller ones.  Each situation has its own kind of fun.

Also, the propellant in five or more Estes D's weighs enough to require an
FAA waiver, so you don't escape all the red tape.

Peter

 
 
 

What effect would it have???

Post by Jerry Irvin » Tue, 06 Aug 2002 23:33:04


In article


Quote:


> > So are you guys telling me that if I were to cluster enough D engines
> > together, I could essentially have the same power as an L motor???

> 250 of them, as a matter of fact. Do you think you can get that many
> started?

Easily and comfortably.

Quote:

> I suggested you could get into the low F range with four of them.  That's a
> long, long way from L.

> The big motors use AP composite propellant that is 2-1/2 times more powerful
> ounce for ounce than the black powder used in Estes motors. And, as Ray
> Dunakin pointed out, a single large motor is usually more efficient than a
> cluster of smaller ones.  Each situation has its own kind of fun.

Only far, far, more.

Quote:

> Also, the propellant in five or more Estes D's weighs enough to require an
> FAA waiver, so you don't escape all the red tape.

> Peter

--
Jerry Irvine, Box 1242, Claremont, California 91711 USA

Please bring common sense back to rocketry administration.
Produce then publish.
 
 
 

What effect would it have???

Post by Bob Kapl » Wed, 14 Aug 2002 09:02:41


Quote:

> So are you guys telling me that if I were to cluster enough D engines
> together, I could essentially have the same power as an L motor???
> That's quite a motor, but with D engines, I could get the same power,
> without all the red tape. I know that by clustering, you technically
> have to still obey the limits and regulations regarding the amount of
> propellant on the rocket, but would it be safe to say that by
> clustering many engines together, you can get the power of the big boy
> engines, with nothing more than the common and modest C and D
> engines???

You'd need 256 D12s (or 512 C6s) to get a mid range L motor. That's about
$900!

As was mentioned, the mass fraction of a cluster sucks compared to an
equivalent single motor of the same IT. Add to that that a cluster of 6 or
more D12s, or 4 or more E9s is an HPR and requires a WAIVER due to the
propellant weight being over 125g, regardless of the size or weight of the
whole rocket. Thus it still requires HPR certification, even for something
less than an H equivalent.

A cluster of 256 D12s would be about 19" in diameter compared to either 3"
or 4" for a single L motor. The drag would kill performance.

Then there is the complexity of igniting 4 or 10 or 50 or 256 motors all at
once. But the smoke trail of essentially a BP L3000 would be impressive!

On the final Friday of NARAM, I finally had a chance to fly my Super Ranger
with a 4xE9 cluster. Nice flight, but one of the motors didn't go. Only the
second time that has happened in at least a dozen flights. Flew it oec
before with 2xD12 and 2XE9 because it was an unwaivered launch and I had to
keep it under the propellant limit.

        Bob Kaplow      NAR # 18L       TRA # "Impeach the TRA BoD"
                >>> To reply, remove the TRABoD! <<<
Kaplow Klips & Baffle:      http://www.pleimling.org/le/Phantom4000.pdf
NIRA:   http://www.nira-rocketry.org    NAR:    http://www.nar.org

        26-October, 2001: A day that will live in infamy
        Support Freedom: http://www.indefenseoffreedom.org/

        You [should] not examine legislation in the light of the
        benefits it will convey if properly administered, but in the
        light of the wrongs it would do and the harm it would cause if
        improperly administered -- Lyndon Johnson, former President of
        the U.S.

 
 
 

What effect would it have???

Post by Bob Kapl » Wed, 14 Aug 2002 09:06:50



Quote:



>> So are you guys telling me that if I were to cluster enough D engines
>> together, I could essentially have the same power as an L motor???

> 250 of them, as a matter of fact. Do you think you can get that many
> started?

271 motors would pack into a round hexagonal cluster 19 motors across. For
someone who does a very clean job of prepping such a rocket, I'd say I could
get at least 250 of them lit. That's only a 93% success rate. IIRC I saw a
cluster of 40-50 motors ignited, 100% successfully. And I've heard of
bigger. Might take a whole roll of Thermalite...

        Bob Kaplow      NAR # 18L       TRA # "Impeach the TRA BoD"
                >>> To reply, remove the TRABoD! <<<
Kaplow Klips & Baffle:      http://www.pleimling.org/le/Phantom4000.pdf
NIRA:   http://www.nira-rocketry.org    NAR:    http://www.nar.org

        26-October, 2001: A day that will live in infamy
        Support Freedom: http://www.indefenseoffreedom.org/

        You [should] not examine legislation in the light of the
        benefits it will convey if properly administered, but in the
        light of the wrongs it would do and the harm it would cause if
        improperly administered -- Lyndon Johnson, former President of
        the U.S.

 
 
 

What effect would it have???

Post by Tim » Wed, 14 Aug 2002 10:27:45


Quote:

> 271 motors would pack into a round hexagonal cluster 19 motors across. For
> someone who does a very clean job of prepping such a rocket, I'd say I could
> get at least 250 of them lit. That's only a 93% success rate. IIRC I saw a
> cluster of 40-50 motors ignited, 100% successfully. And I've heard of
> bigger. Might take a whole roll of Thermalite...

What would happen with flashpan ignition on a cluster that size?  That
would be a lot of powder underneath spread over a large area.  I've
played with it before, but never with a large cluster.

Tim