# Cluster vs Large Motor...

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#### bronicabill

##### Well-Known Member
TRF Supporter
I have been contemplating this question for quite a while, and after just seeing a post regarding a member's first flight of an Estes Patriot using 4 D-motors... well, I just have to ask... WHY?

Why would you build a rocket using clusters vs a single larger motor of equivalent (or better) total impulse power? Why risk one or more of the motors in a cluster not igniting before the remainder shove it off of the pad? Why deal with the complexity of a cluster vs reliability of a single larger motor? Why deal with the COST of a cluster vs a single larger motor?

Not trying to be critical of ANYONE who chooses to fly cluster models; I'm just trying to learn about an area of model rocketry that I have never ventured into. I've flown single-motor models most all of my life, including up to G76 AeroTech RMS motor systems, but never a cluster.

Thanks!

#### DabCat

##### Well-Known Member
For me, my clusters have all been for that extra "wow" factor and the added challenge. Who doesn't like seeing multiple flames on the way up? Clusters just look so cool. Especially the larger clusters like the one at blackrock. Who can argue that big clusters aren't cool???

#### rklapp

##### NAR# 109557
TRF Supporter
Who can argue that big clusters aren't cool???
Especially when one doesn't light and the rocket goes sideways.

#### 6inchmonster

##### Well-Known Member
Clusters: stupid but fun.

I for one cannot think of any primary (read: non-visual, non-artistic) reason to go with a cluster over a larger single motor. That said, I have had a ton of fun with clusters, and intend to keep doing so (on occasion at least)

#### jimzcatz

##### Boss, Carolina Rocket Mafia
Just because I can.

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#### samb

Clusters ARE cool. But they do require you to up your game in many areas - design, construction, motor selection, ignition system, launch operations, range safety ....

#### 6inchmonster

##### Well-Known Member
Clusters ARE cool. But they do require you to up your game in many areas - design, construction, motor selection, ignition system, launch operations, range safety ....

View attachment 486455
Great shot!

##### Well-Known Member
Caveat: I have not purchased any engines larger than E so this may be a totally incorrect impression on cost of larger engines... I am also doing low powered, smaller rockets.

I have not done many clusters but the few I have designed into models were about:

1) Cost vs Lift (there seem to be some lower weight ranges where a pair of engines are cheaper than, or comparable to, a larger engine. For example, it seems hard to beat a pair of D12-3s w/ nearly 800grams of max lift for $7.19. Similarly a pair of mini A10-3T with 170 or so grams of max lift for$3.08 is only beat by the C5-3 w/ 227 grams max lift for $2.36. Also a pair of C5-3 engines packs punch with 454 grams max lift for$4.72. (EDIT: Removed bulk pack comments since I misread site)

2) Design (prototype had a pair of engines so a 2-engine cluster looked better). Pogo w/ pair of mini engines and Ultraman Space VTOL w/ pair of 18mm engines.

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#### Banzai88

##### Lvl 1,Wallet....Destroyed
TRF Supporter
Clusters ARE cool. But they do require you to up your game in many areas - design, construction, motor selection, ignition system, launch operations, range safety ....

View attachment 486455
This. Clearing all of the various technical hurdles is reason enough to do it. Sorta like "Why climb a mountain?"

#### Funkworks

##### Low Earth Orbit, obstructing Earth's view of Venus
Why would you build a rocket using clusters vs a single larger motor of equivalent (or better) total impulse power?
I got one of those 1:100 Saturn V's from Estes that came out 2 years ago (as a re-release) and converted it to a cluster to mimick the real thing.

The real thing is a cluster because it's easier to build 5 smaller motors (already some of the largest ever) than to build 1 motor with equal power. Humanity still isn't at the point of building 1 motor that can replace 5 Saturn motors. In other words, until we have ostrich farms, it's easier to find a dozen chicken eggs than an ostrich egg. That's my analogy and I stand by it.

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#### ghostfather

##### Well-Known Member
TRF Supporter
There was a time many years ago after the Aerotech factory explosion and before Cesaroni stepped up production, that there was a shortage of APCP motors. There were still plenty of Estes black powder motors.
I've seen and heard stories of some clusters and staged clusters that were launched, things like a cluster of 50 Estes D's, roughly equal to an I motor. And all lit by using a layer of black powder in a pie tin.....
Rocketeers got to launch, and will be creative, I guess.

Otherwise, I've done some clusters just for the technical challenge. I used a large central motor with sufficient thrust to fly everything if the other motors in the cluster did not ignite, or did not all ignite at the same time. This was to insure some measure of safety, that the rocket would still fly reasonably safe and straight in the event of uneven thrust.

#### samb

Great shot!
Thanks. My friend and ace photographer Stuart Powley took that picture.

##### Well-Known Member
TRF Supporter
C5-3 w/ 227 grams max lift for $2.36 ($2.12 now that they come in bulk packs).
I am not finding the C5-3 bulk pack. Can you point me to it? I could sure use that...

#### billeblurzz

##### Well-Known Member
TRF Supporter
The flight of my Estes Pro Patriot cluster was just the latest of many flights over the years I've had it. My only problem was the first flight where I used the wrong delay on the motors. I've never had a misfire of any motor and love the satisfaction of multiple motors. I use the Estes Command Launch Controller that came out the same time as the Estes Pro Patriot models. Another cluster rocket that is fun is my Launch Pad Nike Ajax that uses 3 D12-5s. I even deploy 3 mylar chutes with each flight. CLUSTERED motors and CLUSTERED chutes!!! What FUN!

##### Well-Known Member
I am not finding the C5-3 bulk pack. Can you point me to it? I could sure use that...
Sorry, maybe I am going crazy -- I guess I accidentally thought C6-5 bulk pack said C5-3 (did not get home till like midnight last night after teaching in Philly till after 9pm)... AC Supply's price per engine for C5-3 in 3 packs is still $2.38 per engine which is pretty good... Last edited: #### DigBaddy ##### Well-Known Member TRF Supporter Sorry, maybe I am going crazy -- I guess I accidentally thought C6-5 bulk pack said C5-3 (did not get home till like midnight last night after teaching in Philly till after 9pm)... AC Supply's price per engine in 3 packs is still$2.38 per engine which is pretty good...
Ah, no worries. C6-5 bulk pack is a frequently bought item in this household

#### mtnmanak

##### TRA & NAR L3
TRF Supporter
For LPRs and MPRs, I build clusters because, as was already mentioned, it is just cool, fun, and I enjoy the challenge. In the past 50 years, I have built hundreds of LPR/MPRs and it is just more fun now to build practically everything as a cluster.

At the other end of the scale, on really big rockets, a cluster can give you a bigger punch than a single motor. I have two ongoing cluster projects in 8 inch diameter rockets and one 12" diameter project that will have a 4 x 98mm cluster.

An example:

In a Wildman 8 inch airframe, you can fit 4 x 75mm MMTs (barely, but they fit). I am currently doing an 8" build with a 4 x 75mm cluster with a 60" booster. If your booster is 60" long, the largest single 98mm motor (physical size) you can fit in there is an Aerotech N3300. The other commercial motors larger than that won't fit because of the Ebay. If all we consider is total impulse (I realize there are other factors, but the total impulse is a good single measure), the N3300 has a total impulse of 14,035 NS. A very respectable N.

The highest impulse 75mm I can fit in the cluster would be a Cesaroni M2245. 4 of these bad boys nets a cool total impulse of 39,912 NS - almost a max O motor.

Now, granted, an N3300 costs about $990 and those M2245s cost about$690 each, so the cost of flying 4 of them is crazy high (although, still less than a single O motor...), but this represents a scenario that you can't even achieve with a single motor.

If we want to compare based on impulse parity, 4 x Aerotech L1150 motors is just about the same flight profile as that single N3300. The L1150's go for $210 a piece over at Sirius (cheapest I could find on the web). So, to fly a 4 x 75mm cluster that is the same as the largest single 98mm I can fit in the airframe, it is about$100 less per flight.

I am not counting the price of the hardware because it is a sunk cost. Even so, the cost of 4 x Aerotech 75/3840 cases isn't all that much more than a single 98/15360 case.

Additionally, the use of a cluster in HPRs brings in a whole other capability - air starts. (I have not tried air starts in LPR/MPRs, but I am sure they are possible). Once you start air starting clusters, it is difficult to go back to just "normal" single motor rockets. Whole lotta fun!!!

#### Back_at_it

##### Well-Known Member
I have been contemplating this question for quite a while, and after just seeing a post regarding a member's first flight of an Estes Patriot using 4 D-motors... well, I just have to ask... WHY?

Why would you build a rocket using clusters vs a single larger motor of equivalent (or better) total impulse power? Why risk one or more of the motors in a cluster not igniting before the remainder shove it off of the pad? Why deal with the complexity of a cluster vs reliability of a single larger motor? Why deal with the COST of a cluster vs a single larger motor?

Not trying to be critical of ANYONE who chooses to fly cluster models; I'm just trying to learn about an area of model rocketry that I have never ventured into. I've flown single-motor models most all of my life, including up to G76 AeroTech RMS motor systems, but never a cluster.

Thanks!
I completely agree with you. Why use 2 when 1 will do just fine. Keep in mind that I'm a low and mid power flier.

I've built and flown various cluster rockets. The Estes Pro Series Impulse, Maxi Force, etc. I went through a phase where I thought they were different so I bought and built a bunch of them. They were different and fun for a very short period of time. The novelty of clusters wore off in about 3 months time and I knew there had to be a better way to get these heavy rockets to fly. It was about this time that I found Aerotech and got into composite motors. Next thing I knew I found myself sitting at the bench with a hobby knife and Dremel removing the cluster mounts and replacing them with single 24mm and 29mm mounts.

#### DabCat

##### Well-Known Member
My first cluster was a scratch built. It has 3 18mm motor tubes, but the entire motor mount is removable so I can make different configurations. It barely had enough power on 3 Q-Jet D motors. I flew it for the last time recently when only 2 motors lit.

Even though it failed, it was still spectacular.

#### Steve Shannon

##### Well-Known Member
TRF Supporter
I have been contemplating this question for quite a while, and after just seeing a post regarding a member's first flight of an Estes Patriot using 4 D-motors... well, I just have to ask... WHY?

Why would you build a rocket using clusters vs a single larger motor of equivalent (or better) total impulse power? Why risk one or more of the motors in a cluster not igniting before the remainder shove it off of the pad? Why deal with the complexity of a cluster vs reliability of a single larger motor? Why deal with the COST of a cluster vs a single larger motor?

Not trying to be critical of ANYONE who chooses to fly cluster models; I'm just trying to learn about an area of model rocketry that I have never ventured into. I've flown single-motor models most all of my life, including up to G76 AeroTech RMS motor systems, but never a cluster.

Thanks!
It's just another facet of a fascinating hobby. Different strokes for different folks. And of course there are many people who simply wish to master as many different technical challenges as possible.

#### neil_w

TRF Supporter
Common possible answers to many questions:
1) Because it's fun
2) Because it looks cool
3) Because it's a challenge

For a hobby, any of these is more than sufficient.

#### Lee

##### Well-Known Member
My first cluster was a scratch built. It has 3 18mm motor tubes, but the entire motor mount is removable so I can make different configurations. It barely had enough power on 3 Q-Jet D motors. I flew it for the last time recently when only 2 motors lit. View attachment 486511View attachment 486512
Even though it failed, it was still spectacular.
Curious about your interchangeable motor mounts - how are they designed and held in place?