shdw

I got you bud, careful though cause the initial pull does have lift involved and wouldn't leave you at a no lift AOA. But I get what you mean once pointed up the cliff if you orient the nose to have no AOA or slightly negative in the case of a non symmetrical wing you can make the wing produce zero lift and thus no ground effect.

Next question, precise really? Point the nose down 90 degrees and if you want to die put in full power. When the wings rip off you will get a real good reduction in drag.

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bubi352

shdw, you got it

For the second part, you are half way there. I will give you a hint. It has to do with induced drag.

shdw

Reduce to a zero lift AOA, I figured that was inherent with the push the nose over and align the direction straight down. I see what you mean by be specific now.

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bubi352

yep you got it. Pitching down with zero Gs unloads the wing generating no induced drag.

ryan1234

To give the greatest acceleration you would pull back on the stick as hard as possible...loading the airplane with as many units of gravitational acceleration (g's) as possible.

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bubi352

The last thing you want to do to gain airspeed quickly is loading the wing. You should rather push forward on the stick for Zero Gs at full power.

ryan1234

You said accelerate... Refer to any aerobatics manual, physics, or engineering book to understand the concept in depth.

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727gm

A report I remember from a SSA Convention presentation:

[PDF] AIR FORCE- INSTITUTE ýOF- TECHNOLOGY

Glider Ground Effect Investigation
Thesis
Nathan H. Jones
Captain, USAF

They used a Blanik & a Grob glider in flight tests to investigate Ground Effect (at KEDW)

runge

RE: Thin Airfoil Theory

Note: I'm omitting equations and explaining things in terms that are hopefully understandable, because, well, no one likes equations.

There's some good reading on this topic here:
Thin Airfoil Theory

Basically, thin airfoil theory is a way of approximating the performance of a given airfoil to get the lift and moment coefficients for both symmetric and cambered airfoil.

Assumptions:
1. Thickness is neglected, but the derivation is still considered relevant for airfoils with a thickness-to-chord ratio of 10% or less.
2. Inviscid (approximately valid for Re >> 1)
3. Irrotational (fluid lines do not curl; they are parallel to one another at any given position at any moment in time)
4. Incompressible (that rules out anything moving faster than about M=0.3)

Basically it is only applicable to 2-D airfoils, not 3-D finite wings. This in turn neglects induced drag from wingtips, as well as a handful of other tip and root-interference related factors.

Basic steps to the derivation:
1. Place a vortex sheet along the chord line of an airfoil.

2. Calculate the variation of the vortex strength per unit length along the vortex sheet, such that the camber line becomes a streamline of the flow and the Kutta condition is satisfied at the trailing edge (vorticity strength = 0 at the trailing edge).

3. Obtain the velocity distribution due to vortex strength along the length of the airfoil.
4. Find pressure as a function of velocity.
5. Calculate the lift coefficient and the moment coefficient for the airfoil.

Conclusion
Thin airfoil theory provides a simple, practical, reliable method of calculating airfoil properties, within the limitations of its assumptions. It is extremely useful for designing and analyzing airfoils. All you need is the mean camber line for the airfoil, and you can calculate all of the important properties of that airfoil. The major weakness of thin airfoil theory is its inability to calculate drag; that must come from later analysis.

Cubdriver

Thanks Runge.

If someone wants a mathematical breakdown including how the Laplace Equation is satisfied by the flow on a thin airfoil, feel free to speak up. Not many pilots care at that level although it makes for interesting reading if you happen to have your old Calc III book in the house.

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