3Dreaming wrote: On a airplane like a LSA an increase of 200 pounds will reduce your safety factor by about 15%.
Actually (and you know this, Tom; this response is for the benefit of others), that's only part of the story. Yes, a 15% increase in weight will reduce safety factor, but by far more than 15%. Here's why:
What leads to fatalities in aircraft accidents is the kinetic energy which must be dissipated while decelerating. Some of that energy (we can debate the percentage, but clearly some
of it) gets absorbed by the occupants, leading to traumatic
injury. And KE = 1/2 m v^2.
So, increasing m by 15% starts by increasing energy 15%. That's Strike One. (Stick around; the other strikes are related to velocity).
What velocity do planes crash at? In LSAs, most accidents occur during takeoff and landing, so they occur at or near stall speed. This is one of the reasons for the safety-motivated 45 kt LSA stall speed limit. And stall speed varies with load factor, which in turn is a function of mass. So, when weight went up 15%, stall speed also went up 15%, compounding the Kinetic Energy problem. That's Strike Two.
But wait, there's more. KE = 1/2 m v squared
. So Strike Three happens because that 15% safety degradation happening from the v factor occurs twice
The total increase in KE becomes (1.15)x (1.15) x (1.15) = 1.52. That's a 52% total increase in KE, resulting in a 52% decrease in the margin of safety for occupants in a takeoff or landing LSA accident.
Think about that when someone tells you the LSA rules are arbitrary.
Corollary: all else being equal, a plane flown 15% below
it's safe design weight will thus have a 52% greater
safety margin in a takeoff or landing accident.