Da Magic

No..... because your weight vector is still down.

shdw

Since drag is caused by the wing tip vortices being disrupted by the ground I would have to say yes you still experience the effects of ground effect. As long as forward speed above stall speed exists, the wing will create lift, and that lift will have resulting vortices. They will still deflect downward with respect to the aircraft because of some angle of attack to sustain this lift. Gravity doesn't pull the vortices down, at least not appreciably.

How did I do?

PS I went at this like I am 100 percent sure, I am not. However,I was always taught to be assertive even if I am wrong!!! :sarcasm:


Cubdriver: Sure you hit it by accident, I call BS! Power hungry DickTators these days...lol

bubi352

Nice try shdw but DA_Magic is right. If you were to fly straight up parallel to the cliff you would not produce any lift and as a result no ground effect would take place. How do I know you do not generate lift in this case? Well if you did, you would fly away from the cliff because gravity is not there to oppose it. Gravity in this case is pointing straight down.

ryan1234

Crazy as it sounds, I agree with shdw in this case. Lift generally is 90 degrees from the relative wind, not really gravity (remember this is how you turn). Anytime the vortex is disrupted the loss of induced drag results. The aircraft by the cliff would be increasing AOA as thrust energy was reduced - as long as you had enough energy to maintain a non critical AOA (which should be a lot!) you could "feel" the "ground effect". Guess we could try it and find out.

Pitts S2B

Time to go get the Masters Degree and make this your Masters Thesis. ERAU offers a great MSAE program....

Aerospace Engineering Master's degrees at Embry-Riddle in Daytona Beach

Do that and I'll show you how to make $80k+ a year for the rest of your life...

bubi352

Alright. Draw a simple diagram of an airplane in straight and level flight with all four forces: thrust, lift, weight and drag. To compare it, draw now this same airplane flying along this cliff straight up (90 degrees in relation to the horizon). Do you see any differences?

You are right to say "lift" is 90 degrees from the relative wind - BUT - does it apply to us in our case? Are we really generating lift? Just like straight and level - you maintain straight level because you have a balance of two forces: Lift and Weight.

If you fly now straight up, the weight vector is pointing right to the center of the Earth. If we did generate any lift even a small amount, we would then in this case fly away from the cliff. There is just no force to counteract it. So how can we fly parallel to this cliff? By simply flying the angle of attack (ie no lift line) that will generate no lift. If no lift is generated, ground effect is impossible.

ryan1234

I think you're confusing the vertical component of lift and the vector quanity - lift
is a force and as such it has a magnitude and direction. Lift acts from a flow, it is always 90 degrees from the relative wind. Even if a plane is upside down in a 1g loop the aircraft is still producing lift towards the ground not opposing it. There is a big difference between not producing lift and lift not being equal to weight.

bubi352

Ryan1234, it's ok to be wrong

ryan1234

Just curious where you got your information from?

Here is a reference about lift in turns:
Banking Turn
It basically says that there is two components of lift; the vertical component of lift that opposes weight and the unopposed component. In a turn the wings generate lift, we know this as the horizontal component of lift or unopposed force. The vector of lift has a direction and magnitude thus making the airplane turn. This is very fundamental in aerodynamics. As the NASA website says, in a turn, the lift vector is tilted in the direction of the roll.

The mechanical forces of lift do not matter which direction they are in relation to the ground, it matters that there is some type of flow direction. For example, a rudder doesn't need to be opposed by gravity to work, yet it functions much like a wing like being subject to circular flow/vorticity (the things that are subject to ground effect).

Induced drag (from the ground effect) is ironic to this discussion because it is actually the lift vector tilting aft as a result of the tilting movement of local flow (local relative wind) from the vorticity. That aft part of the lift vector quantity is induced drag because it is starting to oppose thrust.

bubi352

Ryan I was just being a smart #$%. It's just that most pilots have only flown straight and level and can think only in this dimension. I just hate this representation of an aircraft with the four forces with lift going upward. That was just my point. Just like you said, lift has no relation to the ground yet we make it appear this way in every flight training books.

Up for another trivia question? From straight and level flight, what is the fastest way to accelerate? (be precise in the answer)