Why does Va go up when the aircraft weight increases?

Question

Why does Va go up when the aircraft weight increases?

Answer 1

I see someone now knows that Va and max turbulent penetration speed are different in jets...cool.

Answer 2

well said Capt.

Answer 3

Load factor is Lift/Weight.  If, in a turn, a 4000lb airplane is producing 8,000 lbs of lift, the load factor on the airframe is 2 (or 2 G's).  For a given value of lift (usually engineers set a vertical gust factor when determining Va), an increase in weight lowers the load factor.

Ever watch that video of the Air Tanker C-130 snap it's wings after dropping retardant on a fire?  Imagine pulling out of a dive (while banking) in a valley and then within a second losing 10,000 lbs of cargo... when the weight is reduced, load factor goes up for a given value of lift.  In the case of the C-130 there may have been other factors such as metal fatigue but the increased load was the primary cause.

EDIT: Capt & Coffee:  your answers should be summed it up perfectly without making it confusing... wish I had worded it that way when I was teaching

Answer 4

an aircraft with a higher weight will stall before an aircraft of less weight for a given airspeed.  

At Va or below, the aircraft will stall before the load factor limit is reached, so any speed above Va can cause structual failure.  Because weight is oppsosed by lift, a lighter weight will stall at a lower airspeed, and vice versa, so a lighter aircraft's Va is less than a heavier one.

Also, in small a/c- not jets- Va is also for rough air penatraion , as it is the highest airspeed that full and abrubt control movements will not exceed the load factor limit, and heavier aircraft have more inertia, and are less prone to deflection.

Answer 5

You have a lot of good answers.  I'll try to put together all of the pieces.

Va is nothing more than a stall speed.  It's the stall speed of the airplane at its limit load factor (usually includes a small safety buffer).  The point is that below this speed, a plane will stall before its G-load limit is exceeded.  Above this speed, it is possible to put enough stress on the wings to cause structural damage without the plane stalling.

If you just think of it as a stall speed, this speed increases with weight.  A plane will stall at a higher speed at heavier weights (for any given load factor), so there is an extra so-called stall protection at heavier weights.  The other answers explained it pretty well from here, so I won't restate what others have said.

Answer 6

Va calulation

Max Va X the square root of New weight( Weight with you, occupents, fuel and baggage in the airplane) divided by the old weight (weight of the aircraft sitting on the ground no fuel)

This will give you ne new Va. Dosn't really asnwer the question but it works!