If it's minimum diameter, use JB Weld or Cotronics or similar high temp epoxy for the fin roots and fillets. You can still use West Systems for the laminating epoxy for your tip to tip. I'm starting to lean towards Aeropoxy's high temp stuff though - no specific reason, just my tendancy towards conservative overkill.

Warren

I've flown a lot of minimum diameter stuff and flown K250s, K185s, and L330s and have never lost a fin. Aeropoxy is good stuff, but ALWAYS make sure your c-slot or moonburning core is oriented between, and not underneath, a fin.

Rough the tube and fins up good! A well sanded surface goes a whole lot further then most think!

In your case, you might consider the long cure (standard) JB Weld.

Art

Batman, to clarify - for my part (and perhaps what others are suggesting?) I use JB Weld *only* for tacking the fins on. Not the fillets, and not for the actual wetting of any fabric 😯

Here is my sequence:

a.) JB Weld the fin roots into slots - I generally wrap a motor with Mylar and slip it in there
b.) Add fillets with your favorite epoxy. Pull out your motor.
c.) Lay fabric tip to tip. More layers of more exotic stuff as you push the envelope further and further.

Until my current project, I never used more than 3 layers of satin weave glass (no kidding). No carbon, Kevlar, etc. I have gone to AeroPoxy now for heat resistance and the occasional layer of carbon (because I had carbon envy) 😀 To date, I have never flown a personal project that had any carbon or Kevlar on it.

I've flown a lot of minimum diameter stuff and flown K250s, K185s, and L330s and have never lost a fin. Aeropoxy is good stuff, but ALWAYS make sure your c-slot or moonburning core is oriented between, and not underneath, a fin.

c-slot??
Whats that?

Scotte

I'm sure James, Conway or Elvis (Eric) will correct me here, but there are essentially 5 or 6 basic core types in solid propellant rocket motors. The Bates Grain I'm sure you're familiar with - a hollow core of even diameter that runs the length of the motor. There are variations on that theme including star grains (of various numbers of points) and tapered grains (rare). These motors all burn from the inside through the web towards the walls of the case. The burn time, in a gross generalization, is determined by the thickness of the web of propellant between the inside core and the wall of the casing (actually the liner).

Longer burn motors are either Moonburners where the grain is typically one piece with an arc cut out of one side (sometimes an offset hole in the core); C-Slots have a slot cut into the propellant all the way along the length of the motor; and end burners have no core or slot at all and burn from the back to front of the grain like a cigarette. Except for end-burners, all these grain geometries burn along the length of the motor. With Bates and other central core geometries, the propellant itself insulates the case from the flame front and heat created by the burning propellant. However, we Moonburners and C-Slots, the area where there is no propellant is where the flame front is and as a consequence, it heats up the casing a lot more. Certified motor cases and reloads are limited to a maximum of 400 degree F after 5 minutes or else the motor / reload combination won't be certified. You would not want this hot spot to be located underneath a fin joint as the heating would impact the structural integrity of the epoxy.

Heat both cures epoxy when you mix it and it can soften the epoxy after it has cured. Heat from a motor case won't soften the epoxy during flight, but afterwards as the heat soaks out of the case. Some epoxies are better than others for handling this heat without softening. JB Weld is one of them, Aeropoxy makes a good high temp epoxy and Cotronics is probably the best. The temperature at which epoxy begins to soften from heat is called the Td or glass transition temperature.

West Systems, while a very good laminating epoxy, has a Td of only 126 degrees F. I've seen a black rocket laying in the sun on a hot day go well above that temperature. 400 degrees F will most definitely soften West Systems and regular Aeropoxy. Higher temp epoxies are a good idea when doing minimum diameter birds as the structural joints between fin and airframe will definitely be subject to the heat soak from the motor case following the flight. Some builders who roll their own airframe tubing from glass and carbon will build a phenolic or paper liner into the tube which provides substantial insulation from the heat to the airframe epoxy. Non-minimum diameter birds don't have this problem because the air gap (or foam) between the motor mount tube and the airframe provides more than enough insulation.

It's always a good idea to use a high temp epoxy for any joints to the motor mount tube and for minimum diameter projects. The one problem is finding a good high temp laminating epoxy. Cotronics is very expensive and the high temp Aeropoxy is as well.

Warren

Has anyone ever used High Temp Ez-lam? ACP sells it.... ?

id love to learn this compression style(duct tape) fiber/or carbon lay up, gotta wait til Conway has a little seminar.......

Jb weld I think has high temp stuff now too? (I think I have seen it???)