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.

Assuming you have not done much clustering with composite motors, I would recommend starting with a model rocket converted to a cluster mount. I’d 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.

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.

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.

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.

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!

Aerotech Rocket wouldn’t 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 wouldn’t be as strong.

How about North Coast Rockets Cluster Duck?

Here is my Astron Ranger, barely visible on the right, taken in 1965. Most of these rockets are brushed Estes butyrate dope. I’m 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. It’s 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.

Wow Lee! I see you were a DOM plans fan back then. Noticed a few of Design Of the Month rockets in your lineup. Very nice, BTW!


Joe

Thanks Joe! I was a big fan of the DOM /Free Plans. Growing up in Colorado, my first purchases were mail order to Estes. Then my friends and I found a hobby shop in Denver (Tom Thumb Hobbies) that carried everything in the Estes catalog. With plans coming in MRNs and in my orders, I found that I could go to the hobby shop, get all the parts I needed, and build the rockets from the free plans pretty cheap. Of course, kits were also pretty cheap at the time!

One favorite plan (Free Plan #28) was the Augie II. For those unfamiliar, it’s the yellow and black rocket. Featured “thrust augmentation” and what I’ll call “internal CHAD staging”.

Another fun rocket, (not shown in my picture), was the Tiger Shark (Free Plan #22) whose booster glided after staging.

I’ve wanted to upscale both of these for a long time. Maybe a BT-50 based moderately upscaled Tiger Shark. Semroc has an upscale called the Lil Augie (really an Augie II, and nit the L’il Augie shown in Free Plan #10) that is 29mm motor-based. F15 to F15 would be pretty amazing.

A 2x24mm mount will not fit in a BT-60 based Ranger/Big Bertha.
The most it will fit is either 3x18mm, or single 24mm, or single 29mm.

Yeah I would modify the fins. Ive built several Aerotech rockets would def have to cut some of the fin through part down.

The Tiger Shark was always one of my favorites, too. The first one I built back in 68-69 is long gone (the booster glided pretty well, surprisingly), but I have a replacement that's been sitting around waiting for a paint job for 25 years or so.

ghrocketman,

You need to think outside the tube! A “Dueces Wild” type of mod would be right up your alley, in terms of “unwimpifying” a Big Bertha.

In her nakedness, she’s a thing of beauty. :)

Apologises if I missed it, but I didn't see anyone mention that Semroc makes a Ranger kit:

https://www.rocketreviews.com/ranger-1958.html

As I did see mentioned, it is a good choice for a first cluster-powered rocket.

I’d forgotten about the Semroc Ranger. But, a 2x18mm Bertha would be at least one less motor to worry about if someone wants to get a taste for clustering.

Speaking of Rangers, I have a Semroc Brighton, a really incredible upscale (BT-80) of the Ranger. It has interchangeable motor mounts. It included a 4x18mm mount, 3x24mm mount, single 29mm, or you could fly it with single 24mm using the 29-to-24mm adapter.

Good luck flying a Semroc Brighton on a single 24mm anything short of an RMS24 F24 reload.

The F39 Blue Thunder in the 24/40 RMS is another good choice. I’ve also got the 24/60 RMS and there are a several high thrust F reloads for it, in a variety of propellant formulations.

Agree with the F39 and 24/60 statement.
Just don't go trying to fly it on any Estes 24mm LOW thrust BP motors.

Ideally, to keep the fin-lok units, a 4 engine cluster, one central 24/29, with 18mm mounts between the 3 fins would be great. A quick calculation shows this probably wouldn't work - CRs are 2.558" with a 1.210" hole, leaving just 17mm. So the central tube would need to be 24mm, and fin-lok units couldn't be used. Still, though, the fins could be nestled between the 18mm tubes, making for a fairly solid attachment with some creative assembly.

An easier route would be 3x24mm, ASP makes plywood cluster centering rings that should fit. That gives you options from 3xC11 to 3xE12, or even 3xE28/E30. The fins should nestle between the 24mm tubes, with some trimming.

The four fins nestled between motor tubes is how I did my upscale Astron Cobra. I poured epoxy into the valleys between two fins, and attached one fin at a time until epoxied cured, then I added the next.

These are 24mm motor tubes in a BT-80H heavy wall tube.