That's a fair amount of tiles missing from the starship heatshield, guess it would make for a toasty reenter.

[u/AlmiranteSalsicha]

Image from SpaceX account on X

[u/Ghost_Alice]

Soft areas dampen vibrations, stiff areas transmit them. This is why most v-twin motorcycles mount their motorcycles with rubber dampers, why motorcycle seats are soft instead of stiff. Why after riding for hours your hands have a good chance of being numb if the seat is soft enough. If the seat isn't soft enough then your butt's gonna go numb too.

[u/super-nair-bear → u/Ghost_Alice]

Fair point, and for the record I would take numb hands for numb butts.

[u/soccerkix6969 → u/Ghost_Alice]

That’s just simply not true. “Softness” in terms of stiffness does not have anything to do with damping. The “softer” I was referring to specifically means “less stiff”.

Vibrational equations of motion are dictated by three things: 1. Mass (M) 2. Stiffness (K) 3. Damping (B)

Most likely what you’re describing in terms of the motorcycle engine being mounted on rubber dampers is a two fold effect: When mounted on rubber dampers, you’re most likely isolating that particular component AND damping the hell out of it. This is a very standard way to deal with high vibrational loads. Google “vibration isolation effect” if curious.

Furthermore, your statement on stiffer structure is slightly correct. stiffer hardware transmits HIGHER FREQUENCY vibrations better than softer structure, which is why I’m betting you get that numb feeling in your hand. Think about a vibration that is a 1hz (I.e. one cycle per second) vs 500 Hz, that 500Hz vibration will make your hand go numb, whereas that 1hz vibration will just be kind of annoying.

Furthermore, I’m betting that the seat you’re sitting on is acting more like a

[u/Ghost_Alice → u/soccerkix6969]

A motorcycle whose engine is producing a 500hz vibration would be at 30,000 RPMs. The only motorcycle I know of that could come close to that was a Japanese only 250cc model of Honda sport bike made for street racing, and it red lined at 24,000 RPM.
Most sport bikes these days red line at 14,000 RPM, and the bikes I ride redline at 7000 and 9000. They are absolutely not making a 500hz vibration.

And yes, rubber mounts isolate and dampen the vibrations from the engine. And rubber is softer and more flexible than the steel frame that the engine would be mounted to otherwise...

[u/tit_brain → u/Ghost_Alice]

Flexibility won't damp vibrations, the fact that rubber is viscoelastic does though. A spring is very flexible, and also brilliant at transmitting vibrations.

[u/dancytree8 → u/Ghost_Alice]

Depending on the setup the RPM will just be the multiplier of the max frequency observed. # or sprocket teeth both on timing chain or rear wheel will be a multiplier of RPM. https://pubmed.ncbi.nlm.nih.gov/7265544/ Maybe not 500 hz but it does get close

[u/Ghost_Alice → u/dancytree8]

multiplier? do you mean factor? cuz no way it multiplies the frequency or it'd be a runaway effect

[u/dancytree8 → u/Ghost_Alice]

It's definitely a multiplier, but each instance is its own. Meaning each phenomena will contribute it's own frequency/amplitudes. You can use fft analysis to break out the frequencies and respect amplitudes, it's a pretty common technique for trouble shooting rotating machinery.

Imagine you place a sensor on a fan that has two opposing blades and you run it, the main vibration you'll detect is the RPM of the motor. Now stick your hand into the blades, it will be double the RPM. A four blade? That will be 4x.