How Center of Gravity Affects Flight | Tail Down Force | Aircraft Stability

[@rickestabrook4987]

Outstanding. This whole concept is usually made in a complicated, muddling progression of principles and explanation. You have once again cracked the code for comprehension and more important, application.

[@jonathantwining3799]

From an ATP/CFII and former flight school chief pilot, I have always been disappointed with most resources that try to explain W&B, and find most CFIs do not properly understand the concepts when they start instruction. This is the most comprehensive and clear explanation and I wish it was required for all pilots to watch! Well done.

[@keithmeline7485]

I’m a current student and I absolutely love this explanation. Seriously, every ground school/audiobook/podcast has basically said what to memorize when it comes to CG, but this video actually shows you, plus your explanation is very easy to understand of the more important WHY. Things really clicked when you showed a forwarded loaded airplane and how (because of this) it would easily recover in a stall. And the opposite with a CG on the CP getting you to that critical AOA faster.. yet harder to recover ect. Anyway this was exactly the explanation I needed and will be sure to share with others. Thanks!!

[@Homoskedastic1]

First time coming across your channel. I'm a trained CFI myself (as well as a university lecturer and educator for my career), and I just wanted to congratulate you on an exceptional video. Very impressive resource. The script, the graphics, the pedagogical approach as well as the scaffolding were first class. Well done! Off to look at your other videos now hoping they are just as excellent.

[@RegularItemShow]

Just busted my oral because I said aft CG will make it harder to recover from a stall, but did not mention that it also gives the aircraft better performance since less lift is required. (I also blanked on who to call before takeoff during a tfr, clearance delivery, and incorrectly stated that SVFR needs instrument rating..without stating night or day). I did "pass" the rest of the oral. So the retake will just cover these 3 areas.

[@RegularItemShow]

If anyone reading this is curious, I went back and did the 3 questions I missed, then flight portion. Am a pilot now.

[@jonathanb.1215]

@@RegularItemShowcongrats 🎉

[@thenelsonbruhs722]

@@RegularItemShowfor your private ride?

[@haithemesmail5547]

What a great video. I have my CPL skill test tomorrow, and was not 100% sure how to explain why forward cg had the influence on the stall speed and fuel flow. Thanks to you, I feel much more confident. Cheers!

[@kylebeatty3466]

The best explanation of CG I’ve seen or read. I found information on on take off - CG vs landing gear particularly interesting.

[@TridentCapital]

Super clear explanation!

[@tomevans5]

Well done. Clear, concise, and most importantly... accurate.

[@christiangraves9340]

you guys are seriously the best and helped me understand concepts like this throughout my pilot training

[@yuval159]

Juat want to let you know how much i appreciate you guys thanks !

[@benjaminmartz3595]

Not a pilot but I learn a bunch from you guy's. Hopefully one day I get to start training for my private.

[@js9550]

Just do it. Dont wait or you never will

[@miguelgt2002]

@@js9550 he is probably saving money or doesnt have the economic stability to do the ppl, its not as easy as "just do it"

[@clayton4115]

Very interesting ! Easy for an novice to follow.

[@xXSiNiSteRXx1]

I'm very impressed with how this was explained like no other video. I feel like I almost got it. So will be rewatching this later today. Thank you. P.S I will be checking out the website.

[@BerndSchmitt-Martinique]

Excellent! It can't be done better! Greetings from Germany

[@flightinsight9111]

Thanks for joining!

[@dmarcodegross]

Very good explanation, excellent video

[@stacereading2477]

Great video while studying fort ppl, thanks!

[@Ishan-l8r]

Thank you for this video! It was really helpful! Please make more such videos!

[@IanHorsford]

Bro you are a phenomenal instructor👏🏾👏🏾

[@clydecessna737]

Very well explained.

[@jordanthomas5353]

This is an excellent video

[@nataliesanchez7997]

rad video- not even finished watching it and already makes sense and subscribed haha! thx

[@E39520IA]

Nice and clear explanation. Thank you!

[@marc-andrefortier1869]

Really well explained, great work!

[@jakew9887]

Excellent presentation. Thanks

[@smsfrancis]

Excellent video

[@Valentin_MeL]

Very nice explanation of cg. So both bars green and white is calculated to max take off weight. I am curious is this also true for any other plane. For example primary flight displays and it's red bars in A320 or B737?

[@jr800w]

I still don't quite understand how the CoG is where the plane swings around in flight or at least pitch around. Maybe for the other axis such as yaw and rotating. I keep thinking that the CoL is where the plane pitches around. I bit like a see saw is held up by a rope which provides enough strength to counter gravity and this see saw has a heavier short left arm vs a longer lighter right arm but the moments balance out. As you start loading the left side, it becomes heavier and will start to dip towards the left but is then balanced out by adding a corresponding load on the right. To apply this to a plane on the ground, the weight is held up by the main wheels and nose wheels. You load up the plane and it doesn't collapse on the nose because it is still held up by the nose wheel. As you take off and the wings start generating lift, the force of off-setting the gravity is transferred from the wheels to the wings, and as you pull back on the controls gently it applies a downforce on the horizontal fins which increases the moment of the right side. Lift force continues to increase and the planes ascends. Obviously it is way more complicated than that given the dynamic relationships between lift force, COG, moment and arms not to mention also CoL shifts back and forth and so does the CoG. But that's just how I see it intuitively without having to bust my brains studying it at the mathematical level.

[@patrickpowell2236]

Imagine that while flying, you move 3 one-gallon jugs of water from the front seat to the rear seat. 25 pounds has moved 30 inches aft. By definition, the CoG moved aft a little. If you don't re-trim, the plane will start a small climb. So, you trim a little nose down to fly level. Since you now have less AoA, your wing makes less induced drag, and your horizontal stabilizer needs to make less down-force, so it also makes less induced drag, so you will gain forward speed.

[@jr800w]

@@patrickpowell2236 I think I am starting to sort of get it. Planes are designed so that there is a downward pitching moment to aid with stall recovery. Under normal circumstances, and flying at normal cruise speeds, there is a slight angle of attack ( 4 degrees ) to generate enough lift to counter weight plus down force on horizontal stabilisers. However, the CoP moves forward to align above the CoG during equilibrium(L = W and T = D), allowing the plane to fly straight and level. When the speed drops enough eg descending, so does speed and the CoP moves rearwards, giving the plant a pitch down moment.

[@ed2800ed]

At 4:04 You said that moving the center of gravity aft towards CP would create almost no tail down force, I think that’s a misleading statement. As far as I can tell, moving the CG aft would Increase tail downforce and require the pilot to increase forward pressure on the controls to lower the angle of attack. Moving the CG aft does not magically change the tail down force, we have to physically apply more pressure forward on the yoke

[@rjhinnj]

You are getting aerodynamic force confused with weight forces. If the CG is moved back, closer to the CP of the aircraft, you need LESS tail down force (TDF is an aerodynamic force caused by the tail). There is a point if you move the CG behind the CP of the plane to the Neutral Point NP, where the plane is not affected by any pitch control of the rear elevator… not a good situation! Many an aircraft and life has been lost due to poor CG placement at or rear of the NP.

[@davidwallace5738]

Outstanding. Thank you!

[@luiscosme1154]

It feels so good to understand this finally! lol... Thank you!

[@hmabboud]

WOW!!!!!!! You are the best by farrrrrrrrrrrrrrrrr! Can you be my instructor?

[@Uncommon_Sense01]

Great explanation, thanks!

[@Darryl_P_]

Great video

[@ParamjitSingh-fb3ou]

GREAAAAAT Knowledge.

[@FlyNAA]

I didn't follow the stability-during-a-stall explanation at the 3 minute mark. If we "cut the string" pulling up behind the CG, while the weight acting at the CG remains the same, the body would rotate up and not down. The change in force behind the CG (reducing an upward force) is downward.

[@ShonMardani]

I believe Parasite drag is produced by VERTICAL surfaces and Induced drag is created by HORIZANTAL surfaces ONLY, please let me know if you think I am correct. Thanks

[@FPIPedit]

Hello, can you say do we have a calculation for the center of pressure? How can I calculate the place of the pressure center with my hand?

[@devansh8846]

Thanks for such informative videos👍🏻

[@guliyevshahriyar]

thank you

[@hemalghedia3713]

Amazing!!!

[@adiliraliyev5882]

Thanks!

[@wangbang2356]

Very good!

[@mtnairpilot]

Placement of the landing gear vis a vis the CG also affects landing characteristics. Look at long body vs short body MU2s as an example. The former is fairly easy to land while the latter takes a different technique.

[@michaelboerger671]

I love this video

[@thepenmen22]

So I don't get it, is it better to have a more tail or nose heavy aircraft? Or does it matter on the type of plane? Also, what happens when you're on a long flight and the fuel is decreasing and changing the CoG. How do you account for that?

[@FlyNAA]

Tail heavy is better for efficiency. Nose heavy is better for stability. The limits are established to respect both. If the CG changes in flight, you just keep controlling the pitch to maintain the altitude you want. You're always controlling it to cont correct for slight bumps, etc. anyway. This is just one more slight disturbance.

[@TheodoreCuartas]

So good

[@mblaber2000]

A novice here attempting to understand the basics of flight. You state center of pressure is typically 50% chord location. However, other sites seem to state 25% chord location (particularly with symmetric airfoils). I must admit confusion with Cp and center of moment. I notice that in model airplanes that I am familiar with, placing the C.G. at 25% chord typically makes them nose-heavy. Moving to around 30% chord location makes for better flight. Moving C.G. behind Cp seems like a bad outcome; thus, ~50% chord location for Cp seems right to me empirically. Can anyone comment? Thanks

[@alk672]

Yes! Yes! One pilot in 10 understands this.

[@jamesmcgurrin8160]

what simulation tool is used in this video?

[@rcdenis1]

At 7:55...while in flight the aircraft rotates around the center of lift and not the center of gravity.

[@daviddavids2884]

at :59, cg is at the WING.!!!! c-m is in the fuselage.!!!

[@daviddavids2884]

at 2:00, you are Incorrectly referring to the c-m as the 'pivot point'. IN FLIGHT, the pivot point is the cg; at the WING.!!!!!

[@mrrobertwolfiii1079]

Nice recovery Cessna KMTJ hello from

[@maritestaylor8458]

Awesome 😎😎😎😎😎😎 thanks

[@LoganKnapp-y7v]

turn the music up i cant hear it

[@Jet-Pack]

I'm sorry but parts of this representation are incorrect. You do not need a constant downforce to have a stable airplane! Let me explain: The lift of the wing does not attach at the CP as shown in this video, instead it usually acts at about 25% chord line which is in front of the CP of the wing+tail configuration. Any increase in lift on the wing produces a pitch up moment and a decrease in lift pitches the plane down, e.g. in a stall condition. And the correlation is inverted for the tail, because it is located aft of the CG. A wing with positive camber also produces a moment that pushes the nose down (Cm0). The tail also has a Cm0 but it's usually zero unless the tail has camber as well. Looking at the new equilibrium moment equation this yields: L_wing * distance( 0.25 chord_wing, CG ) + Cm0_wing = L_tail * distance( 0.25 chord_tail, CG) + Cm0_tail To have a stable airplane the right hand side just has to grow quicker than the left hand side as angle of attack increases. And because the moment arm of the tail is soooo much larger than that of the wing you can have a positive wing and positive tail surface lift and the longer tail arm with the increase tail lift still pushes the nose down. This balance is affected by the tail surface area, wing surface area, distance of the center of pressure of the wing and tail surface as well as the downwash effects of the wing onto the tail and other effects such as propwash. Example: You have an angle of attack of 0 degrees. The wing still produces lift because it has a positive camber, lets assume the tail is symmetrical and cm0 and down wash are irrelevant, then the tail produces zero lift. Now if you increase the angle of attack your wing produces more lift but the tail also sees a positive angle of attack and it too produces an upforce, not a downforce. The tail upforce pushes the nose down with a very long moment arm where as the extra lift of the wing is located close to the CG and doesn't add that pitch up moment. This configuration is stable even if the tail produces an upforce.

[@alk672]

Well I guess their explanation still kind of holds if you don't take "downforce" to always be positive. Obviously it's about the balance between the two down(up) forces and the gravity, and certainly tail won't produce literal downforce under many flight conditions, but I think their version is accurate enough (and easy to understand/remember).

[@Jet-Pack]

@@alk672 My issue with it is that most people and pilots think the tail only produces a down force because a textbook told them so. Most textbooks are not correct in this regard though. It's like you get more lift when you add flaps but in reality lift is still just as large as before, because it equals the weight. Your just flying at a lower speed or lower angle of attack.

[@alk672]

​@@Jet-Pack well aren't all widely used training materials for pilots basically a bunch of BS when it comes to aerodynamics, or weather, or pretty much anything else? Have you seen the explanation of transonic aerodynamics and shockwaves in PHAK? It's basically satire. The target audience is not technical enough for any explanations to be real, so it is what it is.

[@moeinmemphis]

But to increase the angle of attack, you have to increase the downforce to the tail, don’t you? And if the wing produces a nose-down moment when producing lift, don’t you need a down force on the tail to counteract that moment? Am I just confused?

[@Jet-Pack]

@@moeinmemphis The pitching moment can also decrease as you increase angle of attack, depending on airfoil. If the aircraft is stable then you need more downforce to increase angle of attack yes. But then as angle of attack rises and the tail also sees that increase in angle of attack you decrease the downforce on the tail again and a net positive tail surface lift might remain.

[@paulhetherington3854]

A balanced cg = "No problem, and barrel roll - parachutes || Airplanes.

[@VanPray]

5:53 "More room to pitch up and diminish speed"? Better statement in my opinion. As the CG moves aft, Less tail down force is required, reducing total load, lift requirement of the wing, reducing stall speed. Correct me if Im wrong. Hopefully taken as constructive criticism. Thanks for putting this together. Good work. My 206s elevators are 3deg down from counterweight streamline and use a large elevator down spring to aid the pilot in control forces. This allows the horizontal-elevator to create upward lift with the CG at the aft limit at cruise speeds.

[@ShonMardani]

I think CG in front of CP makes stall recovery easier but the main reason is the speed above the stall speed. For example if a Cessna 172 is in level flight at 70 m/h, if you increase the power and its speed while keeping the wings level, the aircraft will climb as well. To stop the climb in level flights above the stall speed (weight = lift) we need to lower the nose which requires less elevator (less drag) if CG is forward of CP.

[@paulhetherington3854]

TDF >> ttCH'f' -- Native origin - of dialect and, made. No US(taxans) - own any - SHT'! In our landmas.

[@sblack48]

There is so much wrong with this I don’t know where to start. Any aeronautical engineer would shake his head at this. You can have an upload on the tail or a download and still be perfectly stable. Stability and trim are often confused when pilots try to explain engineering and that’s what is happening here. The stability equations don’t even include center of pressure. It only comes up when flight instructors try to explain trim and stability which they inevitably jumble together into a dog’s breakfast that “makes sense” to them but has no bearing on reality.

[@daviddavids2884]

at 1:52, this is gobbledy-gook and misinterpretation of reality. NO moment is produced by a stab (at zero-degrees aoi). like cg, the center of lift/pressure Should be at THIRTY percent. googletranslate

[@daviddavids2884]

information. at :53, in order to balance, the vertical line should connect with the wing at THIRTY percent of chord. the distribution of mass (dom) of a typical, conventional, aircraft NEEDS to be OPTIMIZED, so that the location of the center of mass (c-m) vertically aligns with 25 percent of chord. ideally, the c-m should also be ON the thrust line. ideal location of c-m indicated, in this illustration. googletranslate s3.amazonaws.com/assets.flitetest.com/article_images/medium/truecg-jpg_1384168691.jpg if the center of MASS of an aircraft is 'too' near the cg, an aircraft will be Less stable. this is a reason that most fighter jets are inherently less stable.