Aluminum can wrap on booster, is this a safety code violation?

From NAR
https://www.nar.org/safety-information/model-rocket-safety-code/

Materials. I will use only lightweight, non-metal parts for the nose, body, and fins of my rocket.

If I cut a piece of an aluminum can to wrap around a booster engine to protect it from charring from sustainer (I am looking at a three engine each stage [total 6 engine] black powder one to one booster-to-sustainer ignition, each of the three boosters separates independently and may be slightly delayed) and I place a wrap of aluminum from a can around say the upper 2 inches of the booster tubes, is that a code violation?

I don't see a problem with your idea, since its not a substantial amout and its light weight. Aluminum HVAC tape would work as well but probably have to be replaced every so often.

I'd be concerned about the can material in the event of a CATO. The HVAC tape likely has some fiber reinforcement in it that would hold any parts of it from flying away.

KennB said:

I'd be concerned about the can material in the event of a CATO. The HVAC tape likely has some fiber reinforcement in it that would hold any parts of it from flying away.

Click to expand...

HVAC tape is nothing more than heavy foil with adhesive, at least the stuff I have is. Also a AT Hobbyline case is made from aluminum for the reason that aluminum doesn't really fragment well, it tears and ruptures with few fragments, and even those have a very limited travel distance. Most BP motors I have seen CATO either blow the nozzle out or up into the body of the rocket gutting it, they don't seem to rupture radially, but I also haven't seen more than 30 or so BP catos.

My Estes motor (D12-0) split down the length when it Cato'd on me, but it didn't disintegrate like a hand grenade. The outer body tube managed to keep the destroyed motor mount inside it. So, I doubt that there'd be any real risk from shrapnel in such a CATO with your idea.

BABAR said:

From NAR
https://www.nar.org/safety-information/model-rocket-safety-code/

Materials. I will use only lightweight, non-metal parts for the nose, body, and fins of my rocket.

If I cut a piece of an aluminum can to wrap around a booster engine to protect it from charring from sustainer (I am looking at a three engine each stage [total 6 engine] black powder one to one booster-to-sustainer ignition, each of the three boosters separates independently and may be slightly delayed) and I place a wrap of aluminum from a can around say the upper 2 inches of the booster tubes, is that a code violation?

Click to expand...

In a word YES I believe using a piece of alum can to wrap your boost would violate the safety code.
That said I would think the adding a wrap of Aluminum or stainless Steel adhesive backed tape would not violate the code as they are .002" thick but would help insulate your outer airframe from the momentary heat and gas at separation. Aluminum tape would need to be replaced every so often. Stainless steel tape holds up much better. Stainless is much more expensive but I've found it has more then paid for itself in several different Mod-Roc applications.

I agree, aluminum can metal is not allowed. If there is space, consider simply rolling up some paper to act as flame insulation, and replacing it when necessary. You can soak the paper in a borax/boric acid solution to make the paper fireproof like crepe paper or Estes wadding.

You might reconsider your design a bit. Consider a gap staging design so that all motors will ignite at the same time from the hot breakthrough gases.

You can also coat the inside of the airframe expose to the hot gases with epoxy. That will protect the airframe.

Bob

Thanks for the input. I think steel tape sounds great

After scratch building and then flying a triple 24 mm clustered engine within a BT70 airframe, I noticed some exterior paint bubbling and softness in the area above where the ejection charge happens and before the baffle which also functions as a body tube coupler. Additionally, the large through the wall balsa fins had a long half span in order to move the center of pressure aft and would usually split upon touchdown. So, rather than make constant repairs I decided to salvage what I could and make some changes.

When I rebuilt it I made the fins from 3/32" aircraft plywood rather than balsa and lengthened the distance from the top of the engine mount to the baffle/coupler. I also made a heat shield from a large aluminum iced tea can by cutting off the end caps with a razor saw and slitting it lengthwise with a utility knife. When compressed this longitudinal cut overlaps itself and when released expands within the body tube without any adhesive being required. So far, so good.

Whenever you have more than one ejection charge within the confines of a body tube you will have an excess of hot gas and fire within the confines of a flammable container, albeit for a short duration. This is aggravated by the addition of the baffle so I thought some sort of heat shield might prolong the service life of this bird. As far as shrapnel that might result from any KAY-TOW I doubt that any pieces of this thin aluminum would travel any further than the paper that restrains them because they lack the substantial mass needed to maintain inertia.

If M80 artillery simulators were still available to the public this could make an interesting experiment. :kill:

[video=youtube;oeAsY_D6un0]https://www.youtube.com/watch?v=oeAsY_D6un0[/video]

I cannot give you a definitive answer on rule breaking, but by the looks of it think no, but ask your club! Aluminium beer can sides are .004 thick, so not much thicker than aluminium tape

Yeah, I think I will definitely continue to use the technique of a rolled up aluminum can piece for gap staged rockets, just above the booster engine. In my case for my gap staged rockets I have a very high risk of burn through since I use a smaller diameter "chimney" just above the booster engine (for a 24 mm booster engine will have a 20 mm (BT-20) "chimney", for an 18 mm engine a BT-5 "chimney.") This smaller diameter tube gets a lot more char. This rolled up aluminum makes sense since it fits "inside", and basically "self sizes" to the internal diameter and stays pretty much in place (I do add a touch of glue for security, probably not needed.) This is likely to be my standard from now on out. As regarding concerns for "shrapnel" injuries from metal in case of a CATO, as a military radiologist who saw a whole LOT of shrapnel injuries from IEDs in IRAQ, a big part of the injury from metal is due to metal pieces (sharp or otherwise) which are carry significant mass/velocity product. Since the aluminum is about as light as the cardboard, don't see this being a real issue.

Regarding my primary post here, was looking more at the OPPOSITE end of the booster, specifically the area around the FRONT of the booster tube which is likely to get charred by the jet of the sustainer engine (or the next upper stage in a multistage rocket.) Here the exposure to flame is both inside and OUTSIDE the tube. I like der Micromiester's idea of tape here on the outside. First, it is a heck of alot easier to put tape around the outside of a tube than to stick a piece of aluminum around it, particularly a small tube. If needed could add a piece of aluminum INSIDE the tube as this part self-sizes to the internal diameter easily, unless you are "recessing" the upper engine into the tube (in which case you can't mess with the internal diameter.) But even if you are not recessing or "nesting" the upper engine into the tube (I usually leave a straight "gap" here between the chimney and the upper engine), the outside metal tape should hole the shape okay, even if the inside cardboard part chars out.

Stay tuned, I have bench fired a 74" gap stage (to see if it would work) and it did, so that should be flying sometime next month. Yup, 6 foot 2 inch gap. Don't know what the record for gap staging is. It is really pretty simple, I think this will be the most I will go for, as the rocket is just getting to big for me to work with (total rocket length about 8 feet.) More to come.

My apologies for thread-bumping, but steel tape would work fine. If you are going to use aluminum use aluminum tape, because it is less dangerous. I also believe it doesn't violate the safety-code.