Newbie question

[Rneuwirth]

Just started my PPL training, with 8hrs in so far (and loving it).
My question: it would seem that with a heavier weighted plane, sudden movements would increase the angular momentum and stress the wing/fuselage junction more than a similar but lighter loaded aircraft. Why then is the VA higher as the weight goes up?
Thanks in advance.

 

[Jim Logajan]

Think about it this way... if you hit a beach ball (light) and a bowling ball (heavy) with the same amount of upward force with your hand, which one displaces further?

Now, extrapolate that to an airplane getting bumped around by turbulence / up and down drafts. How does increased weight affect the amount the aircraft gets displaced? As the airplane gets lighter, does it get bounced around more? :yesnod: Thus, as we slow down (lower Va with decreased weight) we limit the impact of that displacement on the aircraft structure.

Then why doesn't maximum structural cruising speed (Vno) change with the weight (or mass) of the airplane?

I think the above explanation can cause confusion because it refers to turbulence - not to control movements. Otherwise Vno and Va would be referring to the same thing. In the eyes of design engineers (or the FAA; some concepts originate from them rather than the physics of the situation) they are different values.

I'd post a clarification if I understood the difference myself, but am too lazy/busy to sort through CFR section 23.335 and its related kin. Besides, I'm not an aeronautical engineer and don't know anyone who is.