The Lift Equation - Part 2

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This video's topic covers part 2 of the Lift Equation. If you missed the first part I'd recommend watching that first. Here's the link ( • The Lift Equation - Pa... ).
The next element in the Lift Equation deals with air density using 1/2p (Greek symbol for "rho"). At this point I note that math buffs may see the "1/2" and say this doesn't necessarily have to be here in the formula and could technically be put anywhere else in the equation while still making sense. You're right. But I'll get in to it later about why this is normally found at this point in the equation. Back to the topic, Rho covers density. Density is the measure of the thickness or viscosity of a substance. For Helicopters specifically, air density affects how easily the rotor can move the air molecules around it. For helicopters, more air density = better performance. Denser air is simply easier to move. The blades grip and push the air better. Let's cover what makes air denser.
1. Atmospheric Pressure: higher pressure means there are more molecules in 1 given area. This fluctuates day by day and region by region. Higher pressure increases air density and increases performance.
2. Altitude: as altitude increases, the air is thinner because molecules are spaced farther apart. Lower altitude increases air density.
3. Temperature: warm air expands and moves farther apart which decreases air density. Low temperatures increase air density.
4. Moisture: water vapor weighs less than dry air and displaces it. As moisture increases air density decreases. Lower moisture content increases density.
Summary: High Pressure, Low Altitude, Low Temperature, and Low Moisture increase air density and therefore improve performance.
The last element in the equation is by far from most important. This part is Velocity Squared. This is the relative velocity of the air over the airfoil. As I mentioned in other videos this can affect lift more drastically than any other variable because it affects exponentially. If speed over the airfoil doubles, lift quadruples. If speed is halved, lift is quartered. This loss of air velocity could even affect the Coefficient of Lift by causing a stall condition due to the Angle of Attack in the blade now exceeding the critical angle. The loss of air velocity could cause a reduction in surface area as well if rotor RPM is allowed to slow enough for coning to occur.
The last part I wanted to address is that the part of the formula 1/2p X V squared" is actually the measure of Dynamic Pressure. This is the same formula used to calculate airspeed in your pitot tubes. Some references even cite the Lift Equation as using Coefficient of Lift times Surface Area times Dynamic Pressure.
The biggest takeaways from this formula is that each variable can increase or decrease lift and that Velocity Squared has the greatest impact. That wraps up part 2 of 2 if the Lift Equation. Thanks for watching! Don't forget to hit like and subscribe below. As always, safe flying!
If you enjoyed the video or have any questions or comments, hit the like button and comment below.
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

[@dirkbastardrelief]

My girlfriend likes your video format. She wishes everything was 10 minutes or less. Anything more is just showing off and she has to fight to stay awake.

[@sharonburns4788]

Good job, hurry back with more.🤙🏻

[@svmik]

Brilliant video, thank you!

[@davidwallace5738]

Thanks again sir.

[@mariojorgepiresdasilva9956]

Good vídeo 👍🏾🚁

[@kandyfleming1490]

Great explanation of the lift equation. Thank you!

[@Practicaltrain]

I love it(by son of the users) ! Well explained!

[@lp1485le]

Interesting, living in the UK I always associate high pressure with higher temperatures. Need to look into this next I think. Thank you.

[@zulqarnayeenschaftler9323]

Helpful video☺

[@Scott.Farkus]

Hey man, I like your videos on helicopters. Could you do some on helicopter flight maneuvers, flight patterns, advanced maneuvers like R2T turns a walk through of how to do those type of maneuvers?

[@helicopterlessonsin10minut10]

Ken Quesenberry. Those are some good ideas. I'll add them to the list. I've got quite a few more basic aerodynamics lessons set up before I expand into advanced maneuvers though.

[@Scott.Farkus]

Awesome!

[@Littlewings01]

This is great thanks a lot bro❤️❤️❤️❤️

[@justicewarrior9187]

Brilliant

[@everardoarredondo539]

Thanks for all the videos. I have used your videos during my training and have been transitioning to the AStar. There is little information on the difference between power on Vne and power off Vne and why they are different. Could you do something on that. Thanks

[@davidwallace5738]

I would like to see a real world application of the formula as used in flight planning. Thanks again for your efforts.

[@helicopterlessonsin10minut10]

David Wallace. For real world application I don't think many pilots will sit down and do the math by plugging in each of the variables. But I think it's important to consider these factors if you find yourself operating towards the extremities. By that I mean, imagine flying a helicopter in hot, high altitude, mountainous environments where the aircraft is near its max gross weight and in flight profiles where hovering OGE is not even an option. In these situations it's important to understand that Lift does not come easy and your engines will be working very hard to maintain flight. And if you demand just a little bit too much from them you could find your rotor drooping, Lift being lost exponentially, and aircraft control being lost. So the flight planning comes down to performance planning and map analysis so that you don't find yourself in situations that are unrecoverable.

[@davidwallace5738]

Helicopter Lessons In 10 Minutes or Less Thanks so much for the prompt reply. This lesson just goes to show how important pre-flight planning is. Was a great lesson.

[@sahjadkhan3133]

Hi Jacob, it was really informative. I am working on rc engine powered helicopter. Can you please make a video on how to do the thrust calculations of helicopter and what dimensions should be of main and tail rotor? What dimension and thrust ratio should be between main and tail rotor? Please if you give some clarification on it, that will be very helpful for me. Thank you.

[@vinnynguyen7846]

Hi there, great videos. I wonder what velocity to consider here because the velocity is different at every point on the blade? For the sake of calculation, should we use the mid-point of the blade? Thanks

[@helicopterlessonsin10minut10]

Vinny Nguyen. With the exception of aircraft engineers and designers I've never heard of anyone doing an exact calculation for a specific rotor system. The video is meant as more of an explanation as to what factors affect Lift. But if you wanted to calculate it I would recommend breaking the blade down into sections and adding up everything for total lift. Obviously the further away from the hub, the faster velocity and more lift produced. You'd require the dimensions of your rotor diameter as well as the revolutions per minute it rotates in order to apply appropriate velocities to each section. I hope this helps.

[@karlfriedrich7758]

Thanks for such a good explanation of the variables! To be clear, this is only for a single blade, correct? In a 3 blade system you would assume (roughly) slightly less than triple the resultant force?

[@helicopterlessonsin10minut10]

Correct. But it goes even further. Because the tip of the blade travels faster than the root, there’s differences in lift all along the blade. To calculate lift you’d have to divide the blade into regions and calculate for each region.

[@kentgladden4316]

@@helicopterlessonsin10minut10 Or... you could calculate the speed at Tip & Root, add together, & divide by 2 to produce a Median speed for the entire blade. EX: Tip travels 12.57 ft/rev @ 200 rev/s (12,000 rpm) = 2,514 ft/s. Root = 3.14 ft/rev @ 200 rev/s (12,000 rpm) = 628 ft/s. 2,514 + 628 = 3,142. Divided by 2 = 1,571 ft/s. That's 1,071 mph. Which, for a conventional rotor design, would be prohibitively problematic. For the obvious reason. Fortunately, there is a rotor that does not suffer from that effect :)

[@FireFlashX32]

@@helicopterlessonsin10minut10 is there a calc example vid of this? Also how is the area calculated? Is the surface area a single/multiple blades length×width? Is the area the area of the full circle at the top of the cone? Or the area of two circles subtracted (cone cirle for a certain width). Or is it the surface area of the entire skirt of the cone?

[@waitdaniel]

thanks for your explaination, why 0.5 p tho?

[@muttnjeff2]

Hi Jacob, Your programs are excellent! I flew helicopters for the Navy and Army for 8 years. How can lift vary by velocity squared at air speeds beyond translational lift? In other words, how can lift increase velocity squared from 30 knots to 40 knots? What have I missed here?

[@helicopterlessonsin10minut10]

I’m not sure I fully understand your question. I outline lift more thoroughly in my Dissymmetry of Lift video if you’d like to take a look. But I believe the answer to your question would be that blade velocity has the biggest effect of lift because it is the only thing that increases or decreases exponentially. The 2 ways velocity of the blade is influenced is by rotor RPM and airspeed. Blade RPM is relatively constant. At higher airspeeds there’s a significant difference between the velocity of the blade on the advancing side and retreating side. At 100 knots that’d be Blade RPM + 100 knots on the advancing side and Blade RPM - 100 knots on the retreating side. That’s a drastic difference in lift created so the rotor system would have to be compensated for in the form of flapping and feathering. I hope this helps.

[@ftmhaidar5181]

Hi , thanks for your useful videos . Ive a question , how do you know how much weight is required to make the right amount of lift to avoid it from unstable flight?

[@helicopterlessonsin10minut10]

Proper performance planning is a must before flying. You should know how much power your engines have available with the current environmental conditions as well as how heavy your aircraft is. By knowing this you know what maneuvers you can and cannot perform.

[@Captainziadkhan]

Velocity square but how to calculate it for rotating blade ? V= r*w(omega) but what is r ? Half dia ? But that’s going to be just tip velocity ?

[@ddtddt8493]

hi Jacob. if i may be allowed a suggestion could you please find a way to suggest the order in which you believe all the videos should be viewed. i just subscribed and i'm still a novice as i'm still in the sign up and medical of my heli PPL, i obviously do not have the experience to fully understand which order would be best for a newbie like me

[@helicopterlessonsin10minut10]

DDT DDT. Sure thing. My Playlist "The Basics in Helicopter Aerodynamics (Start Here)" addresses the basic topics and sets the foundation for all the other videos. Thanks for watching!

[@jakubgaaska7752]

How does the number of blades affect the lift? No matter the amount the surface are of disc remains the same as well as the speed, is it just the matter of maniuplating center of weight?

[@PennsylvaniaPanda]

I know this is late but what measurements do you use? mm, cm, or inches. Km or Miles.

[@Scott.Farkus]

So we know that some rotor systems have better performance than others; are more efficient rotor systems less susceptible to VRS?

[@iandavison6617]

That explanation helps a lot in understanding lift. But does it not imply that at zero velocity (= hover) there is no lift?

[@helicopterlessonsin10minut10]

There are 2 types of velocities affecting the blades. One is rotational velocity from the rotor blades spinning around and the other velocity from movement in any direction. At a hover the blades have plenty of rotational velocity to produce lift.

[@iandavison6617]

Of course! Thank you .

[@paulrun111]

What would the velocity be durring take off? Your not moving so wouldn't the velocity be zero. How would you use this equation to consider a helicopter getting off of the ground ?

[@bencrawshaw1227]

I still don't get how you can come up with a number for lift coefficient. Do you use the angle of attack or the angle of incidence. Sorry I'm slow

[@mikkopousi3002]

How does the equation take the rpm of rotor blades into consideration? Since that also matters to the amount of lift generated. Rigth?

[@helicopterlessonsin10minut10]

Generally you find the circumference of the rotor system and the rounds per minute it travels. This gives you the speed of the blade. From there you can convert and apply it to the rest of the equation.

[@ahmetogurtan3886]

I am a little confused since the velocity of the blade isnt same everywhere if we simply multiply the "rpm" and "Circumfrance of rotor system" we will get the maksimum velocity shouldnt we suppose to find average velocity??

[@kareemsalessi]

In general, do you know how much power (bhp, or Newton) is needed to lift one kg-mass?

[@helicopterlessonsin10minut10]

I’m not sure. I haven’t looked into it that closely. When I pull the collective, I go up haha.

[@kareemsalessi]

@@helicopterlessonsin10minut10 Thanks. I found out meantime. It is one horsepower of lift-force for each 2.3kg of mass. You can see it at my new comment under this clip in KZbin::: (The CH-47 Chinook Proves It Can Lift 50K Pounds )

[@SPOTONWEALTH]

I want a complete calculation and design for one seater helicopter plz provide me plz

[@helicopterlessonsin10minut10]

I want a lot of things. But I don’t quite have time to personally design you a helicopter and explain the exact aerodynamic calculations lol.

[@SPOTONWEALTH]

Sr plz not more some calculations🙏

[@rohailqamar8930]

How to calculate density of air?

[@helicopterlessonsin10minut10]

The most basic density formula is by dividing the mass of air by its volume.

[@TuongNguyen-ep5eo]

the basic density of air is 1.29

[@britty1969up]

Does gravity not have an impact? Are you assuming the helicopter is on earth. Is it possible to fly a drone on Mars? Looking at that equation, a ten times rotor velocity, would overcome the 1/100th "air" density on Mars. Anyone?

[@gregduplechain7932]

gravity on mars is .375 that of earth

[@shadowolf7023]

I was bored and wanted to figure out how fast a dnd charcter would have to spin a staff to fly. I have now realized that I should study for my math test tommorow instead of doing this.

[@manzoorhussain2703]

I'll man,

[@christopherpeters5916]

Air speed is king

[@atulmaurya3437]

The intro music sounds like that of "money heist " 🙊