Aircraft lift

I am moving on from writing about SEATs. I want to spend some time talking about retardants that airtankers -- SEATs and multi-engine airtankers -- drop on wildfires. But, before doing so, I need to spend some more time on the aerodynamics underlying “aircraft stalls” for reasons that I hope will be apparent in later posts. I will be spending a couple of weeks on this sequence of posts before I move on writing about multi-engine airtankers around the third week of March.

To review, I wrote about stall speed in my post of February 12:

“As I understand it from my correspondence with TL Stein, stall speed for an aircraft is the speed where the forward speed of the aircraft is not producing enough air flow over the wings to produce lift or support the airplane at its altitude.

When a pilot is landing an aircraft, the plane is just over stall speed.”

The engine provides the power or thrust to move the aircraft forward through the air, but it is the aerodynamic properties of the wings that provide the lift: chord, dihedral and anhedral, wing loading, and the shape of the top and bottom of the wing. The leading edge of the wing is thicker than the trailing edge. Recall that the flaps are usually on the trailing edge of the wing. The distance from the leading edge of the wing to the trailing edge of the wing is known as the chord.

Dihedral is the angle, usually upward of the wings of an aircraft in relation to the body of the aircraft. The wings of a bird also are dihedral. Anhedral are when the wings are at zero or negative dihedral. See this wikipedia article on dihedral for a more detailed explanation and some pictures.

Wingloading is the loaded weight of an aircraft divided by the wing area. TL Stein tells me that “the chord, length and ‘hedral aspects determine the amount of lift that can be generated by the wing for any given aircraft.

But, we are not done with lift yet. The standard wing design is a curved top and a smooth bottom, creating a high pressure area under the wings and a low pressure over the wings. TL Stein explains:

“the faster the air moves over the wing, the more lift is created. Air speed is in direct relation to lift. Lift enables flight. Lose lift and the aircraft sinks, When the forward airspeed no longer produces enough low pressure over the top of the wing to sustain flight . . . this is stall.”