Detect how "hard" a object collides with another object?

How could a detect how “hard” a object collides with another object?
For a aircraft ex. If you fly realy fast and you crash on the nose, how could
you detect how “hard” it collides? So you can make it damaged enough.
I don’t want to use the speed to detect that, because when you land i want it
to detect how “hard” it lands to, so i can’t just make ex. a little damage when you
crashes on anything but the wheels in 40kts or a explosion if the speed is 100kts.

You can use the magnitude of the relative velocity provided as part of the collision class.

You should download Breakable Glass Asset(Unity Asset Store - The Best Assets for Game Making) These scripts in this asset may have answer to your question.

Collision.relativeVelocity.magnitude doesn’t tell you how hard the collision was. If the collision is a glancing blow the magnitude could be very high but the impact quite small.

Collision.impulse is probably a better bet. Otherwise comparing the collision normal with the relative velocity might be the answer.