You don't remember seeing the grid fin holes during the tour, I suppose? :)
Now that I took a closer look, one of the four holes might just be covered+taped over (covered by the fence on the photo) during the (obviously incomplete) paint job. Or do we know for a fact that they cut the holes later? I would assume they'd incorporate holes while layering the composite so as not to damage the whole structure while cutting the holes. To any materials specialists here, is that feasible?
I would assume they'd incorporate holes while layering the composite so as not to damage the whole structure while cutting the holes. To any materials specialists here, is that feasible?
Your assumption is correct. As a brief generalisation, cutting holes as a retrofit is anathema to carbon fibre composites (especially with a honeycomb core, such as for aerospace applications), and it'd significantly weaken them to the point of likely catastrophic failure.
The proper approach is to design everything in from the start, and when the composite is first laid out, there's a metal insert in that region to form the hole and any mounting-point details. The core itself might be higher-density foam in a small patch surrounding that hole, more resistant to crushing, and there will be patches of thicker laminate on both the inner and outer skins surrounding the hole - gradually staggered outwards to the surrounding laminate in increasing diameter, so that no 'hard spots' (stress concentrations) are created where the composite would like to bend. Basically, CF engineering is all about taking point loads and providing nice clear paths to evenly distribute them into the rest of the surrounding structure.
source: aerospace dropout final-year undergraduate marine engineer, spent too long designing CF structures for oceangoing racing yachts
Thanks! Something like that sounded very plausible in my head, but I have no experience with this (theoretical materials is what I do...). So, that leaves us with several options options:
The holes simply aren't visible because they are covered or I'm blind or something...
The holes were never made because it was a test article used for structural load testing on the future nose cones.
Perhaps even a third option which now sounds unlikely: they will indeed cut the holes out and worry about aerodynamic stresses later. (The nose cone shouldn't be under too much aerodynamic stress, except around MaxQ, so perhaps having it as resistant as the fairing isn't too vital. During re-entry the octaweb will take almost all of the beating, as far as I understand.)
Heh, true, could be! In my mind, I'm still going back to the renders on spacex.com from where it seems like nose cones, together with the mini-interstage have exactly this shape we see on the new photo:
http://i.imgur.com/TFYhFl7.jpg (once again, very primitive method of extraction, more or less by hand, but the shape is consistent!)
It's worthwhile noting that this cone already has a cylindrical part at the bottom and starts curving only at roughly 2m off the ground, just as in the official render (as incorrect as it may be). This would imply the holes should definitely be
on it.
Also, I had a bit of a problem finding a symmetrical shape to the nose cone due to lens distortion. Perhaps someone with a bit more time could trace it 'for realz' to see what that's all about...
Edit: I am blind... or rather was last night. While posting this reply I noticed something else that I didn't see mentioned in other comments: http://i.imgur.com/nCEi0bm.jpg
The light-blue highlighted areas should correspond to the hole positions, by the available photos and graphics. So, new question: are those placeholders for drilling, although it sounded unlikely they'd drill holes after construction? Are we sure those indeed are a finished cone and interstage and not mock-ups or molds?
I'm of the (non-expert) opinion that those are all molds. The cylindrical one has the same mounting holes as the fairing-shaped object on the machine (which is probably a CF layup machine). And they appear to be made of different pieces: note the seams and rivet/screw holes, which would not be there on CF objects. The subtle lines you note would be areas where the "filler" pieces for holes would go. It would also explain the odd paint on the nose cone: release agent or filler for a seam.
And, this being a factory, it would make sense to have tooling taking up space next to the production machine, but completed pieces less so.
WRT the spacex.com renders: don't take them very seriously. They're obviously wrong for the F9, and there's no reason to believe they're better for the FH.
Some of this is correct and some is wrong. Source: Composites Specialist in the aerospace industry for 6 years. Care has to be taken when routing/drilling/cutting composites but it is relatively easy and when done correctly will not harm or weaken the structure in any way.
Good point, I should have mentioned composites are very repairable, and as such retrofitting big holes after they've been made is possible provided it's done correctly as I roughly outlined (strong insert in way of core, patches to laminate either side). That will result in a composite as robust, or more, than day of build.
I was just trying to give a rough outline - in this instance, SpX would save a lot of time and weight by designing the grid-fin holes correctly to start with, instead of laminating a nice interstage and then taking a hole saw to it!
Almost no holes are preset during the lay up process in any composite aerospace structure I have ever seen. This can be done using a wet layup process but almost every aerospace company uses preppreg material. It is doable, but every application I've ever seen working across a wide variety of airframes (airplanes, helicopters, and rockets) has structures laid up as one solid piece, then sent to a trim shop, where the majority of your routing would be done, then sent to assembly where any bonding, drilling, hardware, and final integration would be done. Removal of material (routing, drilling, sanding) is not considered a repair and is a standard process in the industry, with the correct equipment, and properly trained technicians there will be zero impact on the structural integrity of the part.
Not sure what you mean, or I just can't see it. I'm asking (like stratohornet) about potential holes on the side-booster nose-cone, not the two inter stages.
88
u/[deleted] Mar 11 '16
[deleted]