Material strength is measured in units of force per area. Nails are pointed to make them overcome material strength and penetrate in. Mass/weight in combination with rigid points sticking out is deadly. A person might be able to deflect a flat heavy object with rounded edges, potentially still suffering some injury, but there is no chance doing that with a sharp point or edge that can penetrate the skull.
Oh, I fly too much. The stuff people carry.
One can pack clothing around the bike. If I go for a 100% clean/waxed chain, I would consider this for additional capacity.
If you don't feel you can easily heft a Brompton into the overheads, you shouldn't try.
The good news is that British Air, Southwest and Virgin America (haven't flown on them since the takeover) have great overheads.
I don't know why people object to this? I have literally done the "Brompton in the overhead" with flight attendants asking me about it and being OK with it, for years now. And I'm not the only one.
I do own the hard shell case, but that kills the "fly to the place, use the train, ride bike to hotel/conference thing."
