CCotner
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A comment Bandman444 made in a previous thread about painting on epoxy reminded me of my interest in starting a thread on this topic. The basic idea I have seen in lots, lots of places: if the underlying structure is somehow inferior or insufficient, adding some sort of surface treatment will make it better. I'm going to describe surface treatments as any sort of non-structural component which nonetheless improves performance (adding layers of fiberglass or carbon to existing airframes, for example, would not count, as it is adding structure in the form of the fiber-resin matrix. Some examples of what I have seen:
What have people done before, what was the rationale behind the decision, and how did it turn out? I want to hear from everyone. Troj? Tfish? Bandman444 et. al.? cjl? New Ocean? butalane? Frozenferrari? KenBiba? Everyone else I'm forgetting?
I'll start out. The only rocket I've designed or worked on whose' underlying structure was insufficient for aerothermal reasons was Bare Necessities, the N5800CS minimum diameter we are currently re-designing to take advantage of both our newly developed knowledge of high-altitude recovery and payload design and some exciting new recovery electronics (the AIM EXTRA). I calculated that, based on a worst-case (highest-performance) simulation of the first few seconds of flight, the rocket would spend approximately 14 seconds under conditions where aerothermal loads on the nosecone would be doing permanent and irreparable structural damage to the fiberglass/resin matrix. To combat this, we chose a surface coat of the same 300F laminating epoxy we used in the bulk nosecone, mixed >%50 by volume with hollow glass microballoons. My rationale for this was that the surface coat (~1mm thick, or over 4700 individual microballoons thick by quick estimate) would have a very, very low thermal conductivity-because the stuff was mostly air inside the bubbles-and that as the epoxy melted out from around an individual microballoon, it would simply strip off-exposing the next microballoon to the airstream, which would be still relatively cool, due to the low thermal conductivity of the matrix. I figured that the ~1mm thick layer would provide the required protection time, and even after it stripped off, the underlying structure would still be cool, certainly well below its softening temperature. We had considerably difficulty applying the stuff neatly, and it required extensive sanding, resulting in an unattractive and un-aerodynamic lumpy finish; overall the experience felt unprofessional. And of course, we never got the chance to test it, and that nosecone will not be flying ever, because we see no reason to risk it (we're pretty confident it would be fine; however, we have time and eventually will have the money, so why not do it over again to be better?)
- Painting on neat (unfilled and without fiber) laminating epoxy
- 'High-temperature' paint
- High-temperature (Cotronics/JB-weld/Proline) leading edges formed from neat epoxy
- Metalized (often aluminum) tape
- Filled laminating resin (fumed sillica, glass microballoons, milled fiber)
- Purpose-formulated ablative coat
What have people done before, what was the rationale behind the decision, and how did it turn out? I want to hear from everyone. Troj? Tfish? Bandman444 et. al.? cjl? New Ocean? butalane? Frozenferrari? KenBiba? Everyone else I'm forgetting?
I'll start out. The only rocket I've designed or worked on whose' underlying structure was insufficient for aerothermal reasons was Bare Necessities, the N5800CS minimum diameter we are currently re-designing to take advantage of both our newly developed knowledge of high-altitude recovery and payload design and some exciting new recovery electronics (the AIM EXTRA). I calculated that, based on a worst-case (highest-performance) simulation of the first few seconds of flight, the rocket would spend approximately 14 seconds under conditions where aerothermal loads on the nosecone would be doing permanent and irreparable structural damage to the fiberglass/resin matrix. To combat this, we chose a surface coat of the same 300F laminating epoxy we used in the bulk nosecone, mixed >%50 by volume with hollow glass microballoons. My rationale for this was that the surface coat (~1mm thick, or over 4700 individual microballoons thick by quick estimate) would have a very, very low thermal conductivity-because the stuff was mostly air inside the bubbles-and that as the epoxy melted out from around an individual microballoon, it would simply strip off-exposing the next microballoon to the airstream, which would be still relatively cool, due to the low thermal conductivity of the matrix. I figured that the ~1mm thick layer would provide the required protection time, and even after it stripped off, the underlying structure would still be cool, certainly well below its softening temperature. We had considerably difficulty applying the stuff neatly, and it required extensive sanding, resulting in an unattractive and un-aerodynamic lumpy finish; overall the experience felt unprofessional. And of course, we never got the chance to test it, and that nosecone will not be flying ever, because we see no reason to risk it (we're pretty confident it would be fine; however, we have time and eventually will have the money, so why not do it over again to be better?)
