Smooth Landings and Ground Effect

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Hello again everyone, just wanted to share my thoughts and advice on how I make those tires squeal when I touch the pavement. So the problem a lot of people have is once they get close to the ground they flare way too aggressively which causes their aircraft to go back up in altitude, loose airspeed, and then drop like a rock back onto the runway. Trust me, I have done this countless times in real life and on IF. If you have ever heard of the term “ground effect” and know what it means then this is what is causing your “almost perfect landings.” For those of you that do not know, ground effect is the effect of added aerodynamic buoyancy produced by a cushion of air below a plane (or any vehicle) moving close to the ground.

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This “cushion” of air produced from vortices is what holds an aircraft from touching down right away. Because of this, you need to be more gentle with your flare and let ground effect work with you. One of the things that lots of people struggle with is they see the ground coming up and want to flare early so they do not hit the pavement hard. But they do not consider the fact that ground effect will slow their rate of decent down before that happens. As everything does, it takes practice to master smooth landings and each aircraft is a little different considering size and weight, but knowing how ground effect works is a key component when learning how to land.
Thanks for reading! I would love to see your comments!

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Great tutorial!

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Thanks! I love to help people out when it comes to aviation.

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Thank you so much for this tutorial. It was really helpful! 👍

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Happy to help! 😊

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Good article. It happens a lot when you land in cockpit view!

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Good article!

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Yes it does. But you need to know how to land in cockpit view for more realism! I never land using outside view.

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Always do. Was weird at first.

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Hmm very interesting idea! Never thought about this!

I have a question though: does having the jet engines below the wings affect the vortices under the aircraft? Don’t the engines suck those winds and blow them to the back of the aircraft?
If so, only the back part of the aircraft gets the cushion, not the front. The back part of the aircraft receives an uplifting force (or “cushion”) and this would create a torque that pushes the front part downwards towards the runway. If it actually happens then wouldn’t you need to flare up even higher to counter the torque that pushes your nose downwards?

I’m not really sure about my hypothesis–it’s probably a stupid one since I don’t really know a lot about aircrafts and physics. I just enjoy playing flight simulators.

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When I flew a 747 simulator the training pilot told me that there’s no need to flare, just maintain 2-3 degrees of positive pitch and it’ll land itself…this goes for many aircraft not just the 74

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Engines under the wing of the aircraft do not make a difference. You will always have have the cushion of air under you when landing. 😉

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Whilst very well written it is not ‘entirely’ accurate! Sorry!

The vortices’s created by the wing occur at the wing tip and are an effect caused by the acceleration of air over the wing (the aerofoil shape forcing the air traveling over the wing to move faster than that traveling under the wing) creating an area of low pressure over the wing and high pressure under the wing. This is what causes lift and ‘effectively’ ‘sucks’ the aircraft airborne!

The high pressure under the wing wants to fill the void of the low pressure over the wing and the leakage around the wingtip from underneath to above generates the wing tip vortices’s.

What happens with ground effect is that you are, for all intents and purposes, ‘pushing’ a body of air beneath you at high angles of attack with the plan form of the aircraft, particularly at the wing root. As you get close to the ground this air has nowhere to easily escape and causes a very localised high pressure area under the body of the aircraft cushioning the descent slightly.

The bigger the aircraft the greater the effect and Delta wing aircraft (Concorde) used this effect during landing.

The effect on the flare as detailed above by the OP is correct just a small correction as to why it occurs ‘aerodynamically’.

HTH.

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can you make a video?!

What you have to say is mostly accurate. I think we can both agree ground affect is what happens when there is an area a condensed air under an airfoil causing an aircraft to want to “float” when near the ground . However, a big reason why ground affect happens is because of the high pressure that forms under the wing. Because of this, the area of high pressure under the wing upon landing has a smaller space to form in because of the ground being so close to the wings. This causes it to push up on the bottom of the wing. Here is an example I made:

The blue represents low pressure and red represents high pressure.

This next picture shows a test I ran with the same airfoil only above the surface of the ground. As you can see the pressure is much higher underneath the wing when close to the ground.

I do think ground affect is caused to a certain extend by the angle of attack, but very little compared to the high pressure already under the wing that is formed by the low pressure over the wing.

As to vortices, they are not produced only on the wingtips. Vortices are everywhere on an aircraft. The biggest ones are on the wingtips though (as seen in my diagram).

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A vortex flow (rotational flow around an axis) is caused by the air flow from the ‘high’ pressure environment under the wing to the low pressure environment above the wing.

Due to the speed of the aircraft through the air the flow from either the trailing edge or the leading edge can be effectively discounted. The body of the aircraft gets in the way of Vortex generation at the wing root as there is no flow to be found from high to low hence the major vortex generation takes place at the wing tip. This has led to a large industry developing wing tip extensions and fences as the energy lost in the generation of the circular motion is large and the induced drag huge thus having a direct influence on fuel efficiency.

There is little to decelerate the air under the wing as to do so would introduce parasite drag and be counter productive, Hence the ‘pressure’ under the wing is pretty close to ambient in level flight.

In your final picture you show a convergent duct which is the difference between the horizontal landing surface and the angle of attack of the aerofoil. This effectively ‘compresses and accelerates’ the air during the landing roll providing a cushion, something I perhaps over simplified but effectively it can be taught as the ‘air’ not having the space to get out of the way.

The vortices’s produced by, for example, chines, or vortex generators on older fighters are done by mounting the chines and strakes at a slight angle to the airflow to produce a high and low pressure side enabling the generation of vortices’s which, normally, are used to reinvigorate the boundary layer to improve laminar flow and reduce drag overall. Nothing to do with flare effect and everything to do with stability and efficiency. As an ‘aerodynamacist’ you want to reduce vortex generation to an absolute minimum as the constant acceleration toward the centre of the vortex requires energy which is provided from the aircraft in the form of induced drag.

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Well, rest assured we both agree the high air pressure under the wing has less room to escape when close to the ground which causes ground affect. 😂

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Pretty much.

What a lot of ATP/ATPL aerodynamics teachings fail to take into account is that air, like all other fluids, has mass and therefore inertia.

In most courses they will teach Bernoulli but that is in a stationary environment. Once you get 200 tonnes in motion then the physics of mass and inertia start to play and you get ground effect.

In Helicopters it’s easy as you have a large induced flow to create the ground effect, much like in the original description of generated vortices’s however modern airliners don’t ‘generate’ down flow in any great quantity so the effect has to come from somewhere.

HTH

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What app is it that allows you to draw stuffs and simulate the vortices? I’ve been looking for this app for years!

“WTunnel Free” I have it on iOS so im not sure if its on Android.

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