Forces Acting on an Airfoil

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This video's topic covers the Forces Acting on an Airfoil. In doing this it also covers quite a lot of terminology associated with airfoils as well.
Starting with the basics we have a basic airfoil shape. This can come in either symmetric or asymmetric shapes, each with their own benefits. From the leading edge to the trailing edge of the airfoil we have what's known as the Chord Line. This line gives us a baseline for how to measure forces in relation to the blade. As the rotor turns about the mast it creates a Rotational Relative Wind (also known as the Tip Path Plane). This is generally perpendicular to the axis of rotation when the aircraft is level. Due to the fact that the rotor blades follow each other along the same path around the mast with pitch applied, a downwards velocity of air is present known as Induced Flow or Downwash. What's leftover is now the Resultant Relative Wind, or the wind that has been modified by induced flow.
It is from here that we can find the Angle of Attack. This angle is the angle between the Chord Line and the Resultant Relative Wind. This angle depicts the amount of Lift the airfoil is producing. Angle of Attack should not be confused purely with pitch angle in the blades. The difference between the Chord Line and Rotational Relative Wind is the Angle of Incidence. As pilots we control the Angle of Incidence with cyclic and collective inputs because this is a mechanical angle. On the other hand, Angle of Attack is an aerodynamic angle which is a product of our Angle of Incidence and Induced Flow.
From here it's necessary to note that Lift acts perpendicular to the Resultant Relative Wind. It's from this point that we can compare Lift to Drag in order to find our Total Aerodynamic Force on the blade. This is sometimes referred to as the Resultant Force and is generally inclined up and to the rear. This is the basic structure of the forces acting on an airfoil. From here you can see how changes in flight profiles can affect Lift. For example, if you were to have an increase in Induced Flow with no change to Angle of Incidence, the Angle of Attack would be reduced and therefore Lift would be reduced. This is exactly what would happen if you made an approach to an OGE (Out of Ground Effect) hover with without an increase in collective.
While I wouldn't expect every pilot to actively think about this diagram during every flight maneuver, it is good to understand this diagram in order to have a better understanding of how Lift can change depending on the flight profiles you find yourself in.
That wraps up Forces Acting on an Airfoil! Thanks for watching! Don't forget to hit like and subscribe below. Be sure to like us on Facebook as well. As always, safe flying!
If you're just getting started and want more information, pictures, and more explanations, I'd recommend reading the Rotorcraft Flying Handbook - amzn.to/2ifPlnZ. If you've already got a basic understanding, and want to further your professional helicopter education with advanced helicopter concepts, I'd recommend reading Cyclic and Collective, by Shawn Coyle - amzn.to/2ifQGLx

[@Scottpulliam]

Dude! I am just starting my journey as a pilot, and I found your video while I was studying. Thanks so much for posting this. It really clarified what I was reading and made it all the more understandable.

[@kevinwatkins6510]

Had so many questions after looking into the Helicopter Flying Handbook. I feel like the FAA should just put a link of this video in their section of aerodynamics. That would make it easier for everyone. Thanks so much! Greetings from Germany

[@TheGroceness]

loving being able to go back and watch these

[@claramelb7476]

That's interesting. I've never watched a video about helicopters and only clicked because it was talking about airfoils. It's fascinating to know that unlike airplanes, you can actually manually change the AOI for helicopters. I always assumed the AOI was fixed once the aircraft is designed/manufactured but then again I'd never paid much attention to helicopters until now Thanks for sharing your knowledge!

[@ddtddt8493]

Well done Jacob. A little in depth understanding never hurts. Keep these videos coming as I’m sure even those who do not comment enjoy them as much as we do. Thumbs up.

[@falconry44]

All your videos are so helpful. Getting ready for my private check ride

[@clisdan]

Thanks for this pls keep uploading. i have Engineering license exam tomorrow and am binge watching your videos before going to sleep wish me luck 👌

[@diegoplata5570]

best instructor

[@melanesianstory-time7205]

Best explanation. Thanks for the video. May God bless you more.

[@agonizedanguish6267]

Thank you! Taking my SIFT test soon and I'm extremely excited for flight school. If I pass my SIFT it'll be like a dream come true. I was told I'm overestimating the difficulty of it dramatically, but I'd rather be over-prepared than fail it and only have one more chance at it. Definitely going to be watching a lot more of your videos and putting a binder together with drawings and explanations.

[@THEUSMCMOTA]

How’d it go?

[@PLISNO]

I wish I could give you more thumbs up but it's not possible. You look like a great guy, thanks for sharing your knowlege. Best regards from Brasil!

[@adolfconradigharas439]

Thankyou brother this helped a lot. May you always follow GOD and His guidance. keep safe

[@ddtddt8493]

Hi Jacob, I went and found all the recordings of my flight lessons and are in the process of posting them on my channel. Hopefully answering questions and showing lesson by lesson that it can be done, I’ll inspire someone to pursue their dream of flying a chopper. Hope it helps like your channel helps everyone.

[@jean-louiscavallera4733]

DDT DDT very cool, but all in Italian, unfortunately. Thanks for your efforts.

[@antoinecamus51]

Great video again, clear and precise, helps a lot to learn and understand! Thanks mate!

[@jds1002000]

Keep ‘em coming man!!

[@crawford323]

I would like a comparison discussion of the airflow transition during the process of forward flight to that of auto-rotational flight. As a gyroplane pilot, I find such complete explanations such as you provide very sparsely addressed in our industry.

[@waxinggibbous7820]

Nothing like a cushion creep departure and some jazz

[@Ab-ml1kd]

Thanks Jacob,another awesome lesson...!!

[@brianschwarm8267]

These are so helpful, thank you!

[@stevehoughton3854]

Love your explanations. Thank you!

[@charliekeyes6206]

Thanks Jacob

[@VitorMoura]

One more great lesson!

[@jaytheman3]

The FAA rotorcraft handbook is so dry and hard to understand at times. Thank you for this.

[@jaytheman3]

becawse cool bro not everyone learns the same 🤷🏼‍♂️

[@CC-bq7wk]

GREAT VIDEOS... Would you do a break down video of an approach plate and how it relates to helicopters....

[@jantzen.]

Great video keep it up

[@mariojorgepiresdasilva9956]

Good vídeo 👍🏾🚁

[@TheRailroaddan]

Thanks Good video

[@beingbhutanese]

Thank you sir

[@serg3y]

Even i can understand this! Thank you

[@fit_tit9902]

Nice explanation! However, is there a mistake in the official FAA Helicopter Flying Handbook? Figure 2-21? It says "Lift is perpendicular to resultant relative wind" but it clearly isn't on the picture (it's perpendicular to rotational relative wind). Am I missing something? faa-h-8083-21A.pdf is free online

[@fit_tit9902]

Found a new version of the book "FAA-H-8083-21B" and they corrected the mistake! All clear now!

[@fit_tit9902]

But I think they got the pictures wrong way round - because induced flow seems to be lower in OGE hover and higher in IGE...

[@dirkbastardrelief]

A diff channel's vid about fixed wing AoA took care to distinguish the path of the plane's movement through the air vs the pitch of the plane/wing vs level ground vs relative wind. In your (this) vid, I didn't hear mention of the heli's path thru the air -- is this because (in a discussion of AoA in helicopters) we're concerned about the path of the blades, not the path of the heli body?

[@davidwallace5738]

Thanks again sir. I understand the diagram but can you please explain how the induced fly is created. I've listened to all of your lessons and if I missed a previous explanation please direct me back to that lesson. Thanks again, sir.

[@davidwallace5738]

Induced flow

[@helicopterlessonsin10minut10]

David Wallace. Sure thing. I'll see about making a video that explains it in more detail.

[@davidwallace5738]

Thank you sir. Looking forward to it!

[@johnwerner8752]

@helicopterlessonsin10minutesorless Was the footage used in the beginning of this video from Katterbach Germany?

[@jeremylakenes6859]

Angle of Incidence on airplane is defined differently than helicopter?

[@skyloveglobalnelsonbarbonc8009]

Its good verynice im learning🚁🚁🚁🚁🚁🚁🚁🚁🚁🚁🚁🚁🚁🚁🚁🚁🛎

[@alexandramilne6032]

So, Rotational Relative Wind is the Induced Flow, or downwash, that an airfoil will come intact with, caused my the airfoil before it? So, the airfoil is being effected by the relative wind in addition to the Induced Flow of the airfoil before it? These two combining to make Resultant Relative Wind?

[@helicopterlessonsin10minut10]

Alexandra Milne. Rotational relative wind is the wind the blade experiences as it rotates around the mast. This velocity is affected how much airflow is being pushed downwards through the disk (induced flow). The resulting airflow is the Resultant Relative Wind. Imagine a helicopter with engine running and flat pitch sitting on the ground with zero wind. At this point rotational relative wind is the same as resultant relative wind. But as pitch is applied and induced flow begins to occur, or as blades flap, induced flow is introduced and there is a difference between the rotational relative wind and the resultant relative wind. I hope this helps clarify.

[@tmanf22]

If lift and drag are always 90 from each other then the TAF never changes in powered flight, correct?

[@gehadqaki]

The TAF can change based on the size of the the Lift and Drag Vectors

[@vlatkopopovski2685]

The authors have two wrong scientific approaches: researching the creation of Lift force and Low pressure at upper side of the wing, relative to the ground surface and Earth. I explain the aerodynamic cavitation and existence of Lee side aerocavern, and creation of Aerodynamic force.

[@ahmadbems]

thanks jacob..may i know which direction drag acting actually? some book mention its against the chord line, some other book mention its against the rotational relative wind. can you explain or give any reference?

[@AmbientMorality]

Drag is always in the same direction as the airflow coming toward it, so the rotational relative wind for a helicopter (basically, this video is correct). Drag for any object is always parallel to the direction that air (or any fluid) is hitting it. In engineering, forces relative to the chord line are normal and axial, where axial is the force along the chord line (a value close to drag) and normal is the force perpendicular to the chord line (a value close to lift). I'm not sure if those terms are ever used in aviation; they're generally not as useful.

[@angelomagalona6049]

Andrei Sunga shout out syo hahaha

[@mawsoncasey7347]

10 thumbs up

[@mawsoncasey7347]

And I just bought your book! Watch the videos then read the book it really makes the book so useful in getting to a really thorough basic understanding of helicopter flight and it makes doing your PPL Theory H course work a cinch!

[@miller745]

My brain hurts

[@kuyacopter]

What’s the song in the beginning?

[@helicopterlessonsin10minut10]

Chris Perry VI. I don’t remember the exact song name. But it’s one of the free ones included in the Splice app.

[@tonyollier7098]

AEROFOIL!!! FFS!

[@crawford323]

Yikes induced flow is not clear to me.