Cluster flash pan

[Sooner Boomer]

I really hate launching cluster motor rockets with a flash pan because it cooks the aft end of the body tube. I'm hoping to get an alternative for our local launches, but until then... How do I prevent/reduce the scortching? Let's use my 7-engine Fat Boy as an example. I didn't build the rocket with a flash pan ignition in mind. It's a "conventional" build where the aft centering ring sits a way up the body tube, and the engine mounts stick down almost to the edge of the main tube.


(OK a flash pan won't work with all those igniters in there!)

I've seen a lot of cluster projects where there are just a bunch of engines glued together and stuck under a rocket. I can see how a molded flash pan would work for that. Would my rocket above be better with the centering ring and engines flush with the aft? Centering ring flush, but with engines sticking down below the aft?

 

[kalsow]

I really hate launching cluster motor rockets with a flash pan because it cooks the aft end of the body tube. I'm hoping to get an alternative for our local launches, but until then... How do I prevent/reduce the scortching?

A "spider" should reduce the scorching. But it needs to be custom built for the individual rocket.

http://meatballrocketry.com/pvc-spider/

 

[Donnager]

I really hate launching cluster motor rockets with a flash pan because it cooks the aft end of the body tube. I'm hoping to get an alternative for our local launches, but until then... How do I prevent/reduce the scortching? Let's use my 7-engine Fat Boy as an example. I didn't build the rocket with a flash pan ignition in mind. It's a "conventional" build where the aft centering ring sits a way up the body tube, and the engine mounts stick down almost to the edge of the main tube.

View attachment 489871
(OK a flash pan won't work with all those igniters in there!)

I've seen a lot of cluster projects where there are just a bunch of engines glued together and stuck under a rocket. I can see how a molded flash pan would work for that. Would my rocket above be better with the centering ring and engines flush with the aft? Centering ring flush, but with engines sticking down below the aft?

You may be able to choose a pan size and use some tape judiciously to prevent some of the excess flame over the sides.

 

[user 35280]

https://electricmatch.com/rocketry/see/23/6/bp-rocket-starters

 

[heada]

I've heard some people say this method violates safety rules but since it is electrically started, my view is that it is still within the rules....

I use fast paper fuse that is chain-linked from a central starter and then to each motor. I have also set it up so all the BP motors have a section that goes to a central AP motor which has a standard starter. The fast paper fuse burns at 0.1 to 0.4 seconds per foot so near instantly for the short distance we're working with. It burns so fast it whips around so secure it to each motor well.

https://www.skylighter.com/products/quick-fuse-white-gn1207
Currently sold out but it becomes available several times a year from multiple sources. This isn't the cheapest source but it's a reputable company.

 

[K'Tesh]

Would it be possible to construct a custom metal cone that fits over the motors, and shields the fins and airframe from the flash?

 

[Troy3003]

Just make a lid for the flash pan with a cutout shaped to your motor configuration. As long as there is some means of keeping the lid from flying off.

 

[kuririn]

I use fast paper fuse that is chain-linked from a central starter and then to each motor. I have also set it up so all the BP motors have a section that goes to a central AP motor which has a standard starter. The fast paper fuse burns at 0.1 to 0.4 seconds per foot so near instantly for the short distance we're working with. It burns so fast it whips around so secure it to each motor well.

I like this idea. Also if one motor ignites a split second earlier than the others it will not negate the ignition of the rest. Also no custom spider to fabricate. I wonder if a fast cannon fuse would work?

 

[heada]

I like this idea. Also if one motor ignites a split second earlier than the others it will not negate the ignition of the rest. Also no custom spider to fabricate. I wonder if a fast cannon fuse would work?

Most fuses don't have the burn speed. Quickmatch (black power infused cotton string encased in a tube) is ideal but its a regulated item. Next closest is fast paper fuse (flash-like comp infused in cotton or paper, encased in a paper wrap). Both burn at sub-second per foot. Nearly all other fuses are seconds per foot or even seconds per inch. For this application we need the speed to help ensure ignition as close to the launch controller start command for safety.