The Lift Equation | Aerodynamics in X-Plane 11 (1/4)

X-Plane 11 has an awesome UI which allows you make graphs in real time. Using the Zibo 737 in X-Plane, this allows for some really interesting demonstrations of flight dynamics. Here we take a look at one of the most important equations which describe how aircraft work.
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[@dean2387]

For someone who's now studying ATPL and about to do my CAA exams, It made me happy seeing this and see how aviation impacts people's lives in different ways! keep the good work and hope to see more!

[@FlyByMax]

Thank you! Good luck with your exams!

[@minater247]

These are amazing! High-quality work, I actually felt like I understood the concepts you put out relatively well in less than 10 minutes. So glad I found this channel, thank you for all your awesome work here!

[@FlyByMax]

Awesome comment, I'm so glad you stopped by :) Have a good one, and thanks a lot!

[@triangleenjoyer]

This is the best explanation of this I've seen. I've studied this and struggled with how to put all the factors together in an intuitive way. I finally see it now!

[@flyingfs888]

Really awesome that you use Xplane to explain those things. Really interessting! :)

[@julians9362]

If i understand the question correctly, the "right" AOA is being held by the aircrafts design. The horizontal stabilizer counter acts any disturbances along the longitudinal axis and creates an equilibrium of forces. Given the pilot trimmed the aircraft for level flight and holds a constant airspeed, this will allow the wing to hold the correct Angle of Attack, needed to create the required amount of lift. This will only apply on aircraft with some sort of positive stability and these properties are being manipulated by stabilizer size, shape, positioning, incidence etc. This however comes to the prize of manouverbility. A Cessna for example is a perfect example for a stable aircraft whilst modern FBW assisted fighter jets are so unstable, they wouldnt even be controlable without computer assistance. I always found this concept of balancing out forces and finding compromises striking and very interesting, shows how much engineers got to weigh out facts to each other and compare in order to find the best compromise. Happy Landings to you guys!

[@FlyByMax]

I think you explained this really well! I think you're absolutely right. We as the pilots (or autopilot) control the elevator so that we maintain an equilibrium of forces (level flight), which corresponds to a certain alpha. I'm actually looking into doing a couple of videos on Cm_alpha, which is the change in longitudinal moment due to a change in angle of attack. So to hopefully add to what you're saying - for a positive change in alpha, you would want there to be a decrease in longitudinal moment (since this would counteract the initial disturbance in alpha). You can also program a stability augmentation system in a feedback loop (alpha as input - elevator deflection as output), exactly as you explained with FBW aircraft. I'd also like to look at dynamic stability (phugoid, short period) at some point. Awesome stuff, very cool that you already know so much about this!

[@julians9362]

Shows that i might have taken something out of ATPL class :) These would be topics i would be interested in as well for sure. I really enjoy the whole subject of aerodynamics, it can be rather confusing at times however, especially when learning such topics on paper only without any visualization. For that i find XPlane and explanatory videos very helpful. Any new topic would be highly appreciated. You are doing a great job at breaking them down so thank you very much. Shows how far our little FlightSim community has come, that is for sure!

[@FlyByMax]

@@julians9362 I had a feeling you must have had some real world experience with these concepts by the way you were describing them :) Hopefully I can find some topics that can challenge even people like yourself, who are already very knowledgeable about aerodynamics. I'm going to try and build my way up to some more complicated stuff, although as things get more complex I'll need to become better at simplifying and visualizing things so that a broad audience can understand. Very cool to know that an ATPL-er is watching though, that'll definitely keep me on my toes to not make any mistakes ;) in all seriousness, your feedback would be really useful. Thanks a lot for stopping by!

[@julians9362]

​@@FlyByMax Sounds amazing, i am going to listen a bit more closely from now on then, i guess... just kidding of course! I am truly looking forward to those future videos then, that is for sure. The less academic approach really helps consolidate some of that new learned knowledge! Keep up the great work, cheers mate!

[@simonniewind7769]

I think there is a small mistake at 6:04. The aoa relevant to the lift of an airplane is the one between the the flow of air and the chord line of the wing and not the angle between the airflow and the fuselage. Great work though, please keep on doing so.

[@FlyByMax]

You're absolutely right. In this case I chose to align it with the fuselage because it makes it clearer to see in the video, and the cord line is more or less parallel to the fuselage (so the angle wouldn't change much). I'm going to try and do this better in the future though, I've been reviewing some of my content recently and I'm not particularly happy with some of the simplifications I've made. Thanks!

[@bsswandgaming1730]

I think another interesting thing to note (and maybe you cover it in later videos) is you can see when you have the lift vectors on (at least I assume that is what the green lines are) that the force distribution across the wing is some what **elliptic**, and this goes into why wings have twists, and sweep, etc to try to mimic the most efficient lift distribution. Great video! edited: corrected parabolic to elliptic

[@FlyByMax]

This is a good point and something I hadn't considered yet, I might touch upon it in a future video. Thank you!

[@olafzijnbuis]

Nice video! I learned the lift equation for my PPL In fact it is very related with the kinetic energy equation: E = 1/2 m. v2 What you do is convert the kinetic energy of the air passing over the wing in a force. If you fill in all the SI units you end up with kg.m/s2 (Newton). S is m2 Rho is kg/m3 V is m/s Cl is a unitless factor

[@FlyByMax]

That's really interesting, I've never looked at it that way before. A question that is often asked is why V is squared in the equation, makes a lot of sense when you think about it from a kinetic energy perspective as you explained. Thanks :)!

[@olafzijnbuis]

@@FlyByMax that is also the reason for the factor 1/2 in the lift equation. It could otherwise be included in Cl

[@himneeshchowdhary820]

how could i not subscribe! impressed!

[@FlyByMax]

Thanks!!

[@vodka5598]

Great video🔥

[@lilithasmith7077]

Qqqqqqq

[@piloto_loco]

nicely made.appreciate.

[@isaiah9572]

i love planes and i was trying to figer this out thanks for teaching me and keep up the good work

[@FlyByMax]

Thank you!

[@thecometcuber8462]

Very informative thank you… earned my subscribe 🤩🤩

[@fitme6650]

Awesome video bro! keep it going! greetings from germany

[@FlyByMax]

Thanks a lot!

[@xforcepc]

Just found your channel. Subscribed. Thanks for your enthusiasm.

[@FlyByMax]

Thanks!

[@FlyByMax]

Hi Michael, just posted another video which I think you might like as well :). Take care!

[@RogerMentol]

very good video.

[@haxlow5420]

my 082 study thanks you ALOOOOOOOOOOOT

[@sbrensbeve2388]

Un👏der👏ra👏ted👏

[@59vijaiyaaravindthsr39]

super bro

[@chillegaming1837]

Hey mate ! How did you plot the graph on a separate window ?

[@lucasd3658]

Really interesting video! How would you describe how MSFS2020 physics work then?

[@FlyByMax]

Good question! Well since both simulators are trying to replicate the same reality, you'd expect similar results. An interesting experiment would be to try out the things I did in the video over in MSFS2020 and see if the results line up.

[@lucasd3658]

@@FlyByMax yeah would be interesting indeed! Curious to see what is wrong with that system lol

[@davidrose1993]

I agree with other commentators that you are really good at explaining things. I thank you and also encourage you to keep going with this work. You mentioned elsewhere that Xplane's virtual flight dynamics are superior to those of MSFS 2020. I was wondering if it might be possible to create a superior flight dynamic engine for MSFS 2020 as a plugin? I don't expect you to be as brainy at programming as you are at physics, but you never know ;-) Obviously it would be preferable for the creators to make it better over time. I haven't even virtually flown yet. I bought Xplane 11, yoke, quadrants & rudder pedals only to discover that my 2012 iMac running Ubuntu can't power a flight sim. (I don't mind if you chuckle.) I have to wait a little longer to get a new machine so I have spent the last few months watching hundred of aviation and flight sim videos on KZbin. MSFS 2020 looks mightily impressive and fun, especially for a beginner. Maybe the add-on jets that I need to buy (when I graduate to that level) will have better flight dynamics. My point is that it would be nice not to have to have 2 flight simulators. I am starting to understand that I am getting into quite an expensive hobby ;-)

[@FlyByMax]

Thanks for your comment! As it happens, I can do a bit of programming and I have some understanding of how physics and flight dynamics can be implemented in a flight simulator (see future video :)), although I am definitely not a developer by any means. In my opinion the realism of an aircraft probably has something to do with 1) how it was modelled within the simulator, 2) which data was used to verify and validate it, and 3) how the developer tuned his model to fit real life data. But again, I'm not a developer at all so this is just intuition. But I think that eventually we'll be able to get realistic aircraft in MSFS, it just takes a lot of time to get these things right I assume. X-Plane also has a lot of aircraft (even payware) which do not fly realistically at all, so in my opinion it's mostly down to the quality of developers on that platform. Right now X-Plane has more developers who can really exploit the capabilities of the simulator. But who knows, we'll see what happens over time :)

[@treynolds94]

You will not get realistic physics in a simulator. You don't get gforce and input is all based off what controls and sensitivity your using.

[@FlyByMax]

You're right that sitting behind a computer screen, we will never be able to feel g-forces or the force feedback of the flight controls. However in the video I'm talking about something else. I look at the aerodynamics behind X-Plane and the physics of flight, i.e. how lift is generated. In fact, in the video I barely control the aircraft at all. The aerodynamic forces behind an aircraft can be studied separately from the controls and feedback systems of that aircraft, which is what you're describing (humans in a control loop).

[@TamilFlightSimmer]

Worth a watch doing good keep on going with lots of videos want to learn more. @FlyByMax