3/8" lifting eye?

… machined aluminum bulkheads and rings seem like the only way to go. …

I’m a big believer in not combining dissimiler materials in assemblies wherever possible. Although attractive when 1st machined, Aluminum sheet is not as ideal (or as robust, in amateur rocketry applications as G10 FR4. first of all aluminum (.098 lg/in^3) weighs more than G10 (.065 lb/in^3) and yet has the same tensile strength, assuming one is using the higher grades of aluminum like 5052-H48 and 6061-T6, otherwise G10 is stronger. For avbay construction, the G10 provides electrical insulation and impact resistance over aluminum.

The biggest concern, I would think, especially when used as centering rings and bulkheads, is that the coefficient of expansion of aluminum is 13×10-6 in/in/DegF as compared with G10’s 6×10-6 in/in/DegF or twice that of G10. A slip fit in the winter could become an interference fit in the summer, and any aluminum sheet bonded to FG could have the adhesive separate, which brings us to the next issue. Most of the time it probably wouldn’t matter.

A bigger issue is that epoxy does not bond well with aluminum, which is why there is a whole family of fasteners available with large backing plates full of holes or other features that allow the resin to flow over many surfaces to make a better grip. I’ve never laid up FG before but have designed many products using it. The last point, is if you need to repair a bulkhead (like moving a hole from one spot to another), G10 is easier to play with, just fill the hole with epoxy and drill a new one.

My take, anyway. (aluminum fins mounted with fasteners excluded)

This bird is all bolt-together except for tip to tip carbon and glass and some incidental epoxy to aluminum joints that have no structural ramifications. In that case though there are little machined grooves all around the ring designed to take the epoxy as well as a rather coarse machining so that the epoxy has something to bite.

Next bird down the pike for me will likely have no epoxy other than what is in the commercial airframe and nosecone and will use bolt on aluminum fins as well unless I get seduced by doing a 4″ MD altitude bird.

Besides, I’m far more afraid of G10 and epoxy dust and breathing it than I am worried about aluminum, which fortunately comes off as rather coarse swarf rather than super-fine dust that floats in the air for hours.

Warren

No welded aluminum rockets, or in other words no rockets constructed primarily of metals at commercial launches. No reason to do that anyways, composites and other forms of construction are easily strong enough to meet the demands of a rocket, they also weigh a lot less.

Art

While I don’t care which I use, U-bolts got me my L3 flight safely and reliably, lifting eyes are actually stronger mechanically. Right ME’s, Warren and Mike? But, when I venture to MD, I’ll definitely use lifting eyes with a locking nut.

I’ve never once had an eyebolt even start to think about coming off. I do use lock washers, blue Loctite, and some serious elbow grease putting them on.

You know, JW, I rub my elbows on screw joints, but I never get any grease. What am I doing wrong? 😯

BTW, blue or red Locktite is good stuff! Used ’em both with success.

No welded aluminum rockets, or in other words no rockets constructed primarily of metals at commercial launches. No reason to do that anyways, composites and other forms of construction are easily strong enough to meet the demands of a rocket, they also weigh a lot less.

Art

So what is this thing you call a commercial launch…? Think I heard the term long ago.. but just don’t remember….