Now here's a crazy idea.

[Senior Space Cadet]

I suppose I'm getting ahead of myself. Haven't even finished the first rocket, but I made a trip to Walmart and got some needed supplies and am feeling a lot better about it.
But, anyway, I was thinking a multi-engine rocket might be fun. Lots of flame and smoke, etc.
Then I started thinking about all that engine weight at the rear and how much weight I'd need to put in the nose cone, Then it hit me, what if I put most the engines in the front? I'm thinking three.
They'd need to be spaced out from the body, so it isn't started on fire. But how far? And how strong would the struts, or whatever, need to be? 1/16" inch sheet plywood, similar to fins in shape, two for each engine?
The fins, at the back, would need to be pretty large. Would the flame start these on fire? If the three engines in front were centered between the three fins in back, maybe not a problem.
I'd probably put an engine at the back of the main, central body, and this would fire the parachute. And what of the other engines? Just pop out the nose cone or have them pop out a streamer?
The whole point of the exercise is to occupy my mind and time, so this is already working.

 

[boatgeek]

Congratulations sir, you have (re)invented tractor motors! There's a long and storied history of using tractor motors in unusual rockets, and @Daddyisabar is probably the king of tractors on this forum. Some classics: the giant squid and the undead Pict. He can school you more in the mysteries of the tractor.

Also, using the words "crazy idea" in the thread title will definitely get some views.

 

[neil_w]

Tractor motor rockets are cool, not sure if I'd do one as my second build though.

Multi-engine clusters in the rear are fine as well, just need big enough fins and perhaps some nose weight and you're good. Modeling the rocket in OpenRocket can help you get it right.

If you want a really *fun* cluster rocket, might I suggest the Fliskits Deuce's Wild: https://www.fliskits.com/WPRESS/product/deuces-wild/. Two canted motors produce two distinct smoke trails.

 

[Nytrunner]

Or the Tres

 

[BABAR]

If you haven’t already got it, given your enthusiasm I’d recommend

Handbook of Model Rocketry

By Harry Stine.

It’s actually an enjoyable read for a technical book. Will save you much more than the cost of the book in money, time, and boo boos (you’ll still make some, but not as many!)

 

[Senior Space Cadet]

Next chance I get, possibly in the morning, I'll see if King Soopers still caries poster board and I can work on a mockup. Just for kicks, at this point.
I think mine will look more like a futuristic space station than something from the deep.

 

[Funkworks]

They'd need to be spaced out from the body, so it isn't started on fire. But how far?

If you're looking for a semi-technical answer: "d such that Torque = dF1 + dF2 + dF3 = dF = 0", meaning the farther it is, the more likely the slight variations from one motor to another will cause the rocket to veer off to neverland.

The problem is that since no two motors are perfectly identical (F1 ≠ F2 ≠ F3), there will be a slight torque causing the rocket to turn. But no one can predict how much (including the manufacturer, beyond an error percentage), so most people choose d = 0, meaning as close to the center as possible. This minimizes the risk of losing the rocket or having to walk a mile (or a km).

 

[Nytrunner]

so most people choose d = 0, meaning as close to the center as possible.

And canting the motors so the exhaust goes away from the body tube

 

[mbeels]

Although, to minimize torque from a tractor engine arrangement, you'd want to cant the motors towards the body tube (and the CG).

 

[Nytrunner]

Rockets is a world of tradeoffs. Lowest torque or bbq'd tube, pick your con!

 

[Senior Space Cadet]

Sounds like a real can of worms.
My biggest concern is safety. Will the engines come off and go flying out of control? Will the rocket start on fire? There might be solutions to all the problems, but looking pretty complicated.
I'll probably still make a mockup, but that may be the end of it. I don't want to kill anyone.

 

[Senior Space Cadet]

I started work on it. I'm going for a ride on my Trek. I might work on it some more this afternoon.
Final parts coming for my current build on Sat.
Estes emailed me and said they now have C5-3 engines again, so I ordered some of those too, and some stands.

 

[Nytrunner]

Sounds like a real can of worms.
My biggest concern is safety. Will the engines come off and go flying out of control? Will the rocket start on fire? There might be solutions to all the problems, but looking pretty complicated.
I'll probably still make a mockup, but that may be the end of it. I don't want to kill anyone.

What you describe has been attempted (successfully and not) in the past.

If the motor tubes are mounted solidly, then the motors shouldn't fly off.

Folks have had success putting shiny aluminum tape on the parts that will be exposed to the motor exhaust. (Or just angling the motor so it points away from the tube, but still upwards)

Experiment and have fun! If you have doubt when trying it for the first time, strap the rocket to a post in the ground and do a static burn test.

Things may not work the first time, but you'll learn from each sucdess and failure

 

[neil_w]

Sounds like a real can of worms.
My biggest concern is safety. Will the engines come off and go flying out of control? Will the rocket start on fire? There might be solutions to all the problems, but looking pretty complicated.
I'll probably still make a mockup, but that may be the end of it. I don't want to kill anyone.

Rockets like this will work (and hold together) just fine if build correctly. I wouldn't really recommend this sort of thing though until you have some more build experience. Something like the Deuce's Wild will give you a bit of experience with (a) clusters, and (b) a canted motor mount. The Fliskits Tres is good as well, albeit quite a bit larger.