Add/remove Gravity with code

HI all ,
I have an plane that work with rigidbody.velocity(forward) and I write this code for increase gravity and decrease height when speed down but when speed is normal can’t see any change for plane and when slow down to min speed again no change and after a short time Suddenly plane fall!!
How can I write code that control speed and down force for plane?
( Speed down and come down slowly and smoothly )

//Control Gravity and height with Speed
	Gravity = -1 / Speed * 110 ;
	rigidbody.velocity.y += Gravity;

it doesn’t matter what you can “See” check the numbers in the editor.

bear in mind your formula for gravity is NOT

-1/ (speed * 110)


(-1/speed) * 110

I only mention it cause the bottom line is pointlessly complicated

you could simply write that

gravity = -110/speed

but I think you want the top line in which case you need to remember your order of operations.