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-   -   converting single engine to cluster engine. (http://www.oldrocketforum.com/showthread.php?t=18021)

metlfreak 08-08-2019 10:25 AM

converting single engine to cluster engine.
 
I was thinking about building an Aerotch Initiator but instead of using the 29mm motor mount I want to use a 18mm 4x cluster motor mount and use 4 Q-jet engines which I think would be pretty neat. My question is though would I need to add weight to the nose for this or would it be stable enough without? The rocket can hold up to a G motor without mods and is pretty heavy built standard.

LeeR 08-08-2019 10:53 AM

Assuming you have not done much clustering with composite motors, I would recommend starting with a model rocket converted to a cluster mount. Id try a Big Bertha, and put two 18mm mounts in it. Do some BP clusters first, then substitute the Q-Jets. Composites are more of a challenge.

Estes used to sell a Bertha-like rocket called the Ranger. It looked like the Bertha, but had 3x18mm mounts. One other differences was that the 18 inches of body tube included a payload section, where the Bertha is just one tube. But the Bertha would be something you can buy today, and could easily convert to a cluster.

tbzep 08-08-2019 11:03 AM

It is a stable rocket so you could stuff a pretty big and heavy motor back there and be fine. Your configuration won't weigh as much as a full G motor. Four full 20Ns D's are equivalent to a full 80Ns F in impulse. The Quest D16's are a little under 13Ns so you are looking at the equivalent impulse of a 50Ns F motor.

The total weight of your four Quest D16's are 102g. An average G motor probably weighs about 150g. A full reloadable G will be considerably more. However, if you don't feel comfortable with it, sim it in OpenRocket (free) or ask a member with RockSim to do it. They can figure in the motor mount differences too.

ghrocketman 08-08-2019 11:27 AM

The Astron Ranger actually predates the Big Bertha.
The Big Bertha was a simplified (and far more BORING with no cluster/no payload) version of the Astron Ranger.

tbzep 08-08-2019 11:44 AM

Quote:
Originally Posted by ghrocketman
The Astron Ranger actually predates the Big Bertha.
The Big Bertha was a simplified (and far more BORING with no cluster/no payload) version of the Astron Ranger.

Back when the B3 (aka B14) was king.

metlfreak 08-08-2019 01:02 PM

Quote:
Originally Posted by tbzep
It is a stable rocket so you could stuff a pretty big and heavy motor back there and be fine. Your configuration won't weigh as much as a full G motor. Four full 20Ns D's are equivalent to a full 80Ns F in impulse. The Quest D16's are a little under 13Ns so you are looking at the equivalent impulse of a 50Ns F motor.

The total weight of your four Quest D16's are 102g. An average G motor probably weighs about 150g. A full reloadable G will be considerably more. However, if you don't feel comfortable with it, sim it in OpenRocket (free) or ask a member with RockSim to do it. They can figure in the motor mount differences too.

Do you know how much an Estes D motor weighs? I had also thought about using a 2x 24mm mount and using two D12-3 which would be basically the impulse of an E.

metlfreak 08-08-2019 01:04 PM

Quote:
Originally Posted by LeeR
Assuming you have not done much clustering with composite motors, I would recommend starting with a model rocket converted to a cluster mount. Id try a Big Bertha, and put two 18mm mounts in it. Do some BP clusters first, then substitute the Q-Jets. Composites are more of a challenge.

Estes used to sell a Bertha-like rocket called the Ranger. It looked like the Bertha, but had 3x18mm mounts. One other differences was that the 18 inches of body tube included a payload section, where the Bertha is just one tube. But the Bertha would be something you can buy today, and could easily convert to a cluster.

Interesting you bring that up. I was actually thinking about building a Big Bertha with 2x 18mm as well. It's def. on the list.

tbzep 08-08-2019 01:41 PM

Quote:
Originally Posted by metlfreak
Interesting you bring that up. I was actually thinking about building a Big Bertha with 2x 18mm as well. It's def. on the list.

Two A8's will perform similar to an early B14!

Flash 08-08-2019 03:39 PM

1 Attachment(s)
Aerotech Rocket wouldnt be a good choice, the fins and interlocking motor mount system would be a problem. It could be done, but fins would need a lot of mods and wouldnt be as strong.

How about North Coast Rockets Cluster Duck?

LeeR 08-08-2019 05:07 PM

3 Attachment(s)
Here is my Astron Ranger, barely visible on the right, taken in 1965. Most of these rockets are brushed Estes butyrate dope. Im really wanting to do another rocket with brushed-on dope. Great memories.

The second picture is my upscale Astron Cobra, prior to assembly. Went with 4x24mm cluster instead of 3 motors like the original. With four, the fins can be thru-wall on all four, and sit in the valleys between motor tubes.

The last picture is my take on the LOC Viper. Its 3x29mm. I show it with nozzles, but those are only for show. A friend has a CNC lathe and these are actually 29mm aft retainers. I have not flown to test, since it is not manufacturer approved. And I really built this rocket to fly on Estes F15 black powder motors.


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