To: (Separate email addresses with commas)
From: (Your email address)
Message: (Optional)
Send
Cancel

Thanks!

Close

4 Common Aerodynamic Misconceptions

Boldmethod

When you're first learning to fly there is undoubtedly a lot of information to conquer. In order to make learning a little easier, complex aerodynamic concepts are often simplified. And while that's not a bad thing, there are some common misconceptions out there.

Here are 4 common misconceptions, and what really happens in each scenario:

1) Ground effect is a "cushion of air"

If you've spent any time flying you're probably already familiar with ground effect. It's the thing that makes you float way past your touchdown point on landing.

You've also probably heard that ground effect is a "cushion of air", and that your wings compress the air beneath them as you get close to the runway.

Here's the real story: As you fly through the air, your wings create wingtip vortices. As you get closer to the ground (within a wingspan or less) your wingtip vortices are much smaller, because the ground limits the size of the vortices. This also means your wings create less downwash. With less downwash, your induced drag is reduced.

Your lift vector will always be perpendicular to the relative wind. Why does that matter? Because with less downwash, your lift vector isn't pointed rearward as much. This means you will have more vertical lift which will oppose your aircraft's weight, and less lift pointing backwards, which creates induced drag.

2) Bernoulli's principle is the complete answer to "how lift is generated"

Regardless if you are a thousand-hour airline pilot or a newly minted student pilot, you've probably heard that lift is created through Bernoulli's principle, by creating an area of low pressure on the top part of the wing and a region of high pressure on the bottom. This is true...partially. However, to fully explain it, your plane's lift is not created by just one method. It's a combination of several.

Even NASA acknowledges that the debate over how lift is generated is not definitively settled. But you should know that it is a combination of Bernoulli's principle, Newtonian deflection, and the Coanda effect.

The two main schools of thought are Bernoulli and Newton. Bernoulli's explanation for lift is that an area of low pressure is created on the top of the wing because the air moves over the top at a higher velocity. On the bottom of the wing, a region of higher pressure is created as a result of the lower velocity of the air moving on the underside of the wing. The difference in pressure is what creates lift according to this theory

The theory called "Newtonian deflection" or "Skipping Stone" can be easily modeled by putting your hand out of the window of your car while it's moving. As you increase the angle of attack you get more lift, until suddenly your hand stalls. This phenomenon is a product of Newton's Third Law; the one about equal and opposite reactions.

Lastly, there is the Coanda effect. Coanda effect is the tendency of a fluid (like air) to stay attached to a curved surface (like your wing). Coanda effect deflects incoming air that's coming over the top of the wing downwards at the back of the airfoil, providing lift.

Check out this great visualization of Coanda effect below:

The interesting thing about lift theories is that currently there is not an individual theory that matches the measurements taken by scientists in the field. Even when combining them there is still an unknown.

3) Maximum demonstrated crosswind component is a limitation

You should always have a healthy respect for your aircraft's published "maximum demonstrated crosswind component". That being said, unless your POH specifies it, the maximum demonstrated crosswind component is not a limitation.

As a Part 91 pilot, it's up to you, the pilot in command, to determine how much crosswind you are comfortable handling.

However, for insurance and safety reasons, many aircraft fleets, flight schools, and commercial operators have crosswind limitations that their pilots must comply with. Always think twice before you choose to land in conditions beyond your plane's maximum demonstrated crosswind component.

4) The most likely place to stall in the pattern is base to final

You should always be aware of your airspeed and stall characteristics in the pattern. After all, you are close to the ground, so stall recovery can be difficult or impossible.

According to the AOPA Flight Safety Institute, 51% of all unintentional stalls occur in the pattern.

While downwind-to-base and base-to-final turn stalls are the most likely to be fatal (66% and 80%, respectively) they are not the most likely place to stall in the pattern. According to AOPA's data, 89.3% of traffic pattern stalls occur on, over, or beyond the runway.

What are the scenarios where these stalls might happen? Takeoff and go-around are two of the most common, when you're low and (relatively) slow.

Boldmethod

Want to learn more about aerodynamics in the pattern, as well as during takeoff and landing? Sign up for our Mastering Takeoffs and Landings course here, and get your knowledge up-to-speed today.


Nicolas Shelton

Nicolas is a private pilot from Southern California. He is currently studying at Purdue University, where he is working on advanced pilot ratings. You can reach him at nicolas@boldmethod.com.

Images Courtesy:

Recommended Stories

Latest Stories

    Load More
    Share on Facebook Share on Twitter Share via Email