thanks for joining me today for ground lesson 14 on the free pilot training channel in this episode we're going to be discussing ground effect and wing tip vortices this is information you'll want to know for both your check ride and your written exam we'll start this lesson by talking about wingtip vortices which are a byproduct of lift which we discussed in a little bit more detail in lesson two now we discussed how the wing makes a low pressure area on top of the wing and a high pressure area on the bottom but what we didn't talk about is that it can also create lateral flow this just means that that high pressure air underneath the wing rushes out then up to meet that low pressure area on the upper surface of the wing when this happens downwash from the top of the wing catches those updrafts and pushes them back down causing the air to spiral around the wing tips these are called wingtip vortices and they're what causes induced drag the bigger your wingtip vortices are the more induced drag you'll have and the size and the strength of these vortices completely depend on the angle of attack so if you have a higher angle of attack you'll have bigger and stronger vortices which means more induced drag now if you watch lesson one you're probably thinking hey i thought induced drag was related to our airspeed yes it is when we're at lower air speeds we need a higher angle of attack so that the lift equals the weight in our airplane then if we increase our airspeed we don't need a steep of an angle of attack to maintain level flight so this gives us less induced drag next let's talk about one of the hazards of wingtip vortices which is wake turbulence now i'm sure you probably could have guessed that you don't want to fly through another airplane's wingtip vortices but you especially don't want to get caught in this behind a larger heavy aircraft takeoffs and landings can be particularly dangerous if you run into this wake turbulence flying through these spiraling vortices can cause you to flip over or lose control of your airplane if your airplane gets flipped over that low to the ground you may not be able to recover so let's look at a few things we need to know in order to avoid wake turbulence first of all the most dangerous airplanes you can encounter are ones that are heavy clean and slow heavy airplanes need to maintain a higher angle of attack in order to produce enough lift for flight and we already mentioned how that higher angle of attack causes bigger and stronger vortices both clean and slow airplanes must also have a higher angle of attack to produce enough lift to fly so angle of attack is the big culprit here so how do we avoid the wake turbulence from these crazy death machines the first way is to avoid flying through another aircraft's flight path these vortices sink at a rate of several hundred feet per minute so if you can fly above that airplane's flight path you'll stay out of that turbulence the faa says you should avoid following another aircraft at an altitude within a thousand feet personally i think that's a little bit close and if i stay above their flight path i'll stay out of their wake turbulence now let's see how we can avoid wake turbulence on takeoff and landing an airplane begins to make wake turbulence after it rotates then upon landing once the wings no longer create lift the wake ends so the best way for us to avoid that airplane's wake on takeoff is to leave the ground before we get to that airplane's rotate point then when we land we want to land beyond where that airplane touched down well what if i'm not sure where the airplane in front of me took off or landed a good rule of thumb is to wait three minutes for the vortices to dissipate that'll give you a good margin of safety on the ground when there's little to no wind these vortices dissipate by moving away from each other laterally this movement is somewhere between two and three knots something you really want to be aware of is that a one to five knot crosswind could cause that upwind vortices to stay on the runway for an extended period of time in this situation i would wait the full three minutes just like we talked about then just be prepared to go around if you need to do so now that we've talked about wingtip vortices we can expand on that and talk about ground effect because ground effect is caused in part by our wing vortices being disturbed by the ground when you first start practicing landings you're going to notice the airplane does not want to land it just wants to float down the runway that's because your airplane is subject to ground effect once the height above the ground is about the wingspan of your airplane let's look at a couple reasons for that now we just talked about some of the airflow patterns around our airplane and how these wingtip vortices are produced but when we get in close proximity to the ground or water some of these airflow patterns get disrupted for example one thing that it does is it reduces the size of our wingtip vortices and with that we get less induced drag and more lift and we already kind of talked about why another thing that happens is you get reduced down wash this just means less induced drag with all these reductions in drag that means less thrust is required because of that and because we have increased lift if you're above the recommended landing speed you could get considerable floating which may not be an issue if you're learning to land on a really long runway but you can see how it would be an issue if you wanted to land somewhere where there was a short runway it makes sense why we want to consider ground effect during landing but we also want to think about it on takeoff too first is that if you don't use proper techniques you could become airborne before the recommended takeoff speed if you do then you also leave ground effect a couple things can happen first of all you immediately need a higher angle of attack to maintain your lift second it will increase your induced drag which will lower your air speed it will also reduce your stability which means it can be tough to control your airplane and lastly it can make you think you're flying faster than you are because of the pressure change that being said there is one time where we want to become airborne before the recommended takeoff speed and that's during a soft-filled takeoff but the important thing to note here is that we never leave ground effect until reaching a good climb out speed let's look at a couple more things to keep in mind about ground effect first is that ground effect affects low wing airplanes more than it affects high wing airplanes and that's just because the closer the wings are to the ground the more susceptible they are to ground effect there's one thing you want to remember from today's lesson remember that ground effect is caused by interference of the air flow patterns around the wing from the ground or water i hope you got something out of today's lesson if you did please smash that like button for me don't forget to subscribe and hit the bell notification so you don't miss out on more free pilot training