moderately high performance nosecones

[G_T]

I'm having a devil of a time getting Goggle search to come up with anything relevant tonight. I was trying to research wood or wood core nosecones... Nothing useful. I know it has been done; the Russians used them for some high performance rockets or ICBM reentry nosecones/shields. I believe some amateur projects have used them as well, including Proteus if I recall correctly. But I found nothing this time, courtesy of my lack of coming up with the right persuasion.

I'm tentatively considering a minimum diameter Black Rock project. Crude RasAero numbers are slightly over M3 and at least 90Kft, possibly over 100 and a bit faster if I can keep the rocket light enough. ~5" 80%O3000 for an unoptimized motor starting point... I can make the motor. I'm more concerned about the nosecone.

I'm used to working with composites, including bladder molding to decent pressure (as in, a sub-par mold = exploding bomb), vacuum bagging, and have equipment and materials for this sort of work. I could do a high temp painted in the mold seamless bladder molded layup of some sort that would possibly suffice. It is a lot of work to get there.

What I'm curious about is an old, simpler approach - using a solid or near-solid wood core for the actual nosecone. I understand Oak has been used and that makes sense to me. It is ring-porous, so as it outgasses under extreme heat it won't internally pressurize and split. I believe it also forms a char layer. What I don't know about this construction method can fill a book of what I'd need to know about it!

Oak? Some other wood? Limitations? Treatment, such as possibly pre-cooking it to remove low temp volatiles? Infusion? Solid or laminate? Orientation? If laminated, using what as an adhesive? What sort of surface finish is done, if any? Can it be done as a shell or does it need to be solid or nearly so? How much degradation is experienced in use? Deformations or dimensional changes? How does this construction method compare to other nosecone construction methods?

Essentially nearly clueless, asking for practical feedback and/or research papers on the subject. What works; and what doesn't!

More generally, what have people found working well for nosecones at >= M3 that fly fast for long enough to get some serious heat soak? I'm looking at max drag force showing up around 12Kft and motor burnout happening at around 24Kft, AGL. And then a long coast... Anyway using a long burn motor should be helping the situation out a fair bit vs using a fast burn motor design.

With wood (and in general) I'm presuming a metal tip at least. So to prevent the tip from burning away the support, it should be centrally stabilized on a rod or tube. That turns the wood cone into a fairing. Yes, no?

How about survivability of commercial filament wound nosecones, internally reinforced, under these expected conditions? I'm not super inclined to go that way but it is certainly the easiest method!

I apologize for such an open ended set of questions, and thanks for any help/guidance.

Gerald

 

[COrocket]

As far as I know, no one has exceeded the "speed limit" on the filament wound nosecones that are available from rocketry warehouse/wildman/PR. The one advantage of the filament wound cones is the uniformity and lack of weak spots. There is no seams to worry about in a homemade cone and no woodgrain geometry or material flaw that might be present in a solid wood cone. All of the projects that I've seen in this range are usually composite or metallic nosecones. Plus you get a bit more volume to stuff recovery/avionics gear inside the rocket.

Oak is a fairly dense (but strong) wood compared to wood like birch or balsa, so the weight savings probably isn't there. One option is to buy wood from a place that supplies furniture makers. The wood is dried and it eliminates a lot of warping/splitting that you would get using wood from say a lumber yard when making a laminated piece. At room temperature, using a regular wood glue like Titebond II/III results in a bond that is as strong as the wood itself, but I'm not sure what would happen at elevated temperatures. One thing I would worry about is a crack developing along one of the glue lines or along the grain of the wood at Mach 3+. Disclaimer - I've never used a solid wood cone on a rocket beyond lower power kits, just pulling from general woodshop knowledge. Hope this helps.

You could contact Roachwerks (Sandman) https://roachwerksmachining.com.istemp.com/index.html about doing a nosecone.

 

[CCotner]

Kosdon used to run wood nosecones, if I've heard correctly. That was before my time. you're correct, it will (probably) outgass and char, ablating nicely, but the surface you're going to be left with is going to be very rough and crappy probably. At mach 3, and probably not getting to Mach 3 until 15,000+ (msl) feet with an O burning that slowly, I think a better option might be to take a standard filament-wound FG nosecone, one of the metal-tip versions, and go for adding some basic protection to that-multiple layers of high-temp BBQ paint carefully applied with full cure times in between each one, or to be extra safe, mix up a syntactic foam of sorts using some laminating epoxy, glass microballoons, and some TiO2 powder, paint it on, and sand it smooth on a lathe (you want the metal tip version so you have a place to center the part on the lathe-if you add a bunch (like a 1/16" is what I would add) of material, you can also lathe a new metal tip so you have a seamless transition from metal to the ablative).

Just my 2 cents; you've been in this hobby a lot longer than I have.

 

[G_T]

Using a filament wound nosecone would certainly be a major plus with the internal volume being usable. I have this mental picture of a lathe and the entire surrounding area coated in a layer of tenacious TiO2 residue from refinishing a coated nosecone! :eyepop:

Anyway, TiO2 + downwind aluminum + elevated temperatures = mild thermite, so I'm not certain I'd want to use TiO2 for that job. But at only a little over M3 the stagnation temperature may well be too low for a reaction to occur.

Part of the reason I was looking at making my own nosecone is I was looking for a shape closer to conical than VK. But at only M3 the CP doesn't shift too badly as long as the cone doesn't become particularly rough during the burn. VK would probably be just fine. IIRC the CP difference was only about an inch at that speed anyway. The extra volume is likely worth the tradeoff. Earlier sketched out versions of the potential rocket were much faster, some > M4. I've done nearly all I can to slow the motor without starting to sacrifice performance. I can slow it down to perhaps 16 seconds burn instead of 12 with major propellant formulation changes - but I lose density and ISP in the process so I expect it to have a negative impact on final altitude. Plus the greater time of the burn likely more than offsets the lower combustion temperature when it comes to heat soaking the assembly. I'm prepared to try for 12 seconds; I'm not sure I'm prepared to try for 16.

Tonight if I get the chance I'll look at some of the ramifications of nosecone shape to see how the tradeoffs come out. A little shorter rocket with VK, vs. a little less CP shift with conical and fins could likely be a hair smaller...

I haven't been super fond of the filament wound nosecones for this sort of project due to the exposed fiber ends from the grinding process, the high air inclusion in the layup, and the sub-optimal fiber orientation for the expected load. But mostly that would just mean it would need a surface coating, possibly a bit of internal reinforcing, and be a bit heavier than need be.

Gerald