# Stupid (?) question: How do planes really fly? **URL:** \ **Category:** Factual Questions\ **Created:** [May 7, 2026, 2:37pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890 "2026-05-07T14:37:34Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [May 8, 2026, 12:43pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/21 "2026-05-08T12:43:51Z")
> [@robby](#): > > My understanding is that it is both the shape of the wing (and the Bernoulli effect) _as well as_ the angle of attack of the wing, which pushes down on the surrounding air, and which by Newton’s third law pushes back to create the force referred to as lift. Yep. Wings push air down. Same with helicopters… the spinning blades push air down. For decades, there was a popular belief that “lift” was primarily due to the longer path on the top of the wing vs. bottom of wing, thus less pressure on the top of the wing, the air splits at the leading edge and rejoins at the trailing edge, etc. That explanation is mostly incorrect. ---
**Author:** ![yendis](https://avatars.discourse-cdn.com/v4/letter/y/ed8c4c/32.png) [@yendis](https://boards.straightdope.com/u/yendis)\ **Post date:** [May 8, 2026, 1:04pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/22 "2026-05-08T13:04:08Z")
> [@Measure\_for\_Measure](#): > > Still confused. I trust this has been studied statistically in wind tunnels. Put a wing in a wind tunnel and attach it to a scale so that upward force can be measured. Hold wind speed constant. Vary angle of attack. Vary shape of wing: a flat plate would eliminate the “Wing curve effect”. (Use hidden weights to equalize weight of wing across different shapes.) Take dataset and estimate equation: This has been very thoroughly studied in wind tunnels, NACA (NASAs predecessor organisation), generated tonnes of empirical data on airfoils. For each and every one you can get a range of values for lift, drag, efficiency etc. in the form of graphs. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [May 8, 2026, 1:59pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/23 "2026-05-08T13:59:22Z")
A plane flying is somehow countering the force of gravity. That means the air is balancing that force. Air is a fluid, and the only way it is going to do this is if it is being driven downwards from the plane such that the change in momentum of the air balances the force of gravity. It doesn’t matter how the momentum of the air gets changed, whether it is a barn door effect, Coanda, or Bernoulli, or all three, the air mass must be diverted downward, and its momentum changed enough to balance the plane. The niceties of air flow are such that keeping the flow attached to the wing maximises the amount of air being diverted. So much so that we generally really try to avoid stalling wings. The attached flow on the upper wing surface is diverting a heck of a lot of air downwards. Same logic for sail boats. Bend the wind around the sail. Wind changes direction, momentum is conserved in the system, sail boat moves. ---
**Author:** ![RTFirefly](https://avatars.discourse-cdn.com/v4/letter/r/c77e96/32.png) [@RTFirefly](https://boards.straightdope.com/u/RTFirefly)\ **Post date:** [May 8, 2026, 2:07pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/24 "2026-05-08T14:07:37Z")
> [@Dorjan](#): > > L=Cl⋅(ρV^2)/2⋅A where: > > CL = coefficient of lift - the complicated part. It is a function of flow conditions, wing geometry, and angle of attack, and can be mathematically determined for a range of geometries and simple flow conditions, but usually ends up being determined experimentally for a given lifting body. > > ρ = air density > > V = velocity > > A = wing area. > > density times the square of the velocity, and then divided in half, is the dynamic pressure and the Bernoulli equation part. Just wanting to make sure I’m reading the formula as intended: 1. Cl in the formula = CL = coefficient of lift, right? 2. Is the A factor in the numerator or the denominator? It looks like it _might_ in the denominator (but not clear because no parentheses), but I’d think lift would increase as wing area increases, which would put it in the numerator. I appreciate your providing this formula, and I just want to make sure I’m reading it right. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 8, 2026, 2:18pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/25 "2026-05-08T14:18:34Z")
Yeah, area belongs in the numerator. This article is big, but not too technical for the interested reader: > **[Lift (force)](https://en.wikipedia.org/wiki/Lift_(force))** > > When a fluid flows around an object, the fluid exerts a force on the object. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the force parallel to the flow direction. Lift conventionally acts in an upward direction in order to counter the force of gravity, but it may act in any direction perpendicular to the flow. > If the surrounding fluid is air, the force is called an aerodynamic force. In wa... ---
**Author:** ![Elmer\_J.Fudd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmer_j.fudd/32/1211_2.png) [@Elmer\_J.Fudd](https://boards.straightdope.com/u/Elmer_J.Fudd)\ **Post date:** [May 8, 2026, 2:23pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/26 "2026-05-08T14:23:06Z")
I still think it’s the Tinkerbell effect. Manned flight only exists because enough people inside the metal tube believe in it. Kinda the same way American government works…well worked. ---
**Author:** ![Dorjan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dorjan/32/12440_2.png) [@Dorjan](https://boards.straightdope.com/u/Dorjan)\ **Post date:** [May 8, 2026, 3:27pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/27 "2026-05-08T15:27:39Z")
> [@Dorjan](#): > > L=Cl⋅(ρV^2)/2⋅A This should be clearer, I forgot the board supports LaTeX! L = C\_l \left(\frac{\rho V^2}{2}\right) A ---
**Author:** ![Marvin\_the\_Martian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/marvin_the_martian/32/2898_2.png) [@Marvin\_the\_Martian](https://boards.straightdope.com/u/Marvin_the_Martian)\ **Post date:** [May 8, 2026, 3:44pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/28 "2026-05-08T15:44:39Z")
> [@Elmer\_J.Fudd](#): > > I still think it’s the Tinkerbell effect. Manned flight only exists because enough people inside the metal tube believe in it. Kinda the same way American government works…well worked. No, it’s the Dumbo effect. That’s why all the successful aviation pioneers carried a feather. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [May 8, 2026, 3:59pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/29 "2026-05-08T15:59:55Z")
> [@LSLGuy](#): > > An airplane, even a highly manueverable one, is indeed optimized for upright flight. As such the wing is installed at small upward angle to the fuselage. This is called the angle of incidence. > > The purpose is to align the fuselage at the cruise condition with the relative wind for minimum fuselage drag, while also aligning the wing at an angle of attack relative to that relative wind that will produce the cruise lift requirement. So both the wing and fuselage work together to produce the needed lift with minimum drag. Typical angles of incidence are just a couple of degrees. It’s not much, but it adds up. Here’s a visual that may be pertinent to the conversation. The wing cross-section of a typical airliner like the 737 varies between the wing root and the midsections out to the wingtip, but at no point is there a really dramatic difference between the top and bottom curvatures as one might expect if the Bernoulli effect was dominant. OTOH, in the bottom image, looking at the wing root one can pretty clearly see an angle that is partly due to curvature but substantially due to the aforementioned angle of incidence. [![](https://i.imgur.com/scUjCxT.jpeg) ](https://i.imgur.com/scUjCxT.jpeg) ---
**Author:** ![Measure\_for\_Measure](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/measure_for_measure/32/557_2.png) [@Measure\_for\_Measure](https://boards.straightdope.com/u/Measure_for_Measure)\ **Post date:** [May 8, 2026, 5:57pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/30 "2026-05-08T17:57:25Z")
Agreed, that visual is highly pertinent IMHO. So is wingshape design primarily driven by a desire to avoid stalling, and lower drag and turbulence? How much does variance in wingshape affect lift? (Also, stating the obvious, I wouldn’t want to dismiss 1% or 2% increases in lift or even less. Aircraft are highly optimized for fuel efficiency, appropriately.) ---
**Author:** ![md-2000](https://avatars.discourse-cdn.com/v4/letter/m/9d8465/32.png) [@md-2000](https://boards.straightdope.com/u/md-2000)\ **Post date:** [May 8, 2026, 6:27pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/31 "2026-05-08T18:27:08Z")
There’s a reason airfoils are asymmettric - the curvature also does figure into it. The Bernoulli effect was well-known and was adequately demonstrated when Britian started building faster trains in the 1800’s - they could not put the parallel tracks too close together, because two trains passing were sucked toward each other by the pressure difference. Anyone who’s sat in a left turn lane being passed at high speed by a semi (Or even a bigger vehicle) has experienced this same effect. When the air encounters the greater curvature of the top front of the airfoil, it has to go up and around. This creates pressure (experienced as drag). Then it has to “hurry to catch up” over the top of the airfoil. Why doesn’t it simply take longer? Because the air behind it (that is, to the front of the wing) is the higher pressure - pushes it - and the air in further back along the top of the wing is lower pressure, sucking it back. Try to imagine the steady-state pressure diagram of the wing in motion. This faster flow creates some of the lift. Angle of attack creates the rest, but angle of attack also increases the low pressure area on the top of the wing. The Wright brothers figured this out in 1901 by experimentation, and determined the better choices of airfoil… incidentally contradicting the “common knowledge” of the experts at the time who relied on observation and guesswork rather than experiments. True, with enough power and angle of attack, anything can fly; presumably for supersonic, this airflow is irrelevant because the air instead of flowing forms shockwaves. ---
**Author:** ![Measure\_for\_Measure](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/measure_for_measure/32/557_2.png) [@Measure\_for\_Measure](https://boards.straightdope.com/u/Measure_for_Measure)\ **Post date:** [May 8, 2026, 7:55pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/32 "2026-05-08T19:55:21Z")
Ok, I have a very rough answer from a chart at [this wiki article](https://en.wikipedia.org/wiki/Angle_of_attack). [![](https://upload.wikimedia.org/wikipedia/commons/thumb/d/d1/Lift_curve.svg/1280px-Lift_curve.svg.png) ](https://upload.wikimedia.org/wikipedia/commons/thumb/d/d1/Lift_curve.svg/1280px-Lift_curve.svg.png) At zero angle of attack, we have a coefficient of lift of about .6. Planes cruise at an angle of attack of about 2 to 5 degrees, generating a coefficient of lift of .65 to 1.05. At takeoff the angle of attack is from 10 to 16 degrees, generating a coefficent of lift of 1.4 to 1.7. So at cruising altitute, most of the lift is generated by the shape of the wing (eg 1.05/.6 = 1.75\<2.0). During takeoff most of the lift is generated by angle of attack (eg 1.4/.6=2.33\>2.0). Either way **if we believe this chart is roughly accurate and is indeed a typical lift coefficent curve _and_ I’m applying @Dorjan’s formula correctly** , then wing shape is not a trivial or even a small factor. It matters a lot even during takeoff, if 1/3 or more of total lift is considered a lot. ---
**Author:** ![md-2000](https://avatars.discourse-cdn.com/v4/letter/m/9d8465/32.png) [@md-2000](https://boards.straightdope.com/u/md-2000)\ **Post date:** [May 9, 2026, 5:33am UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/33 "2026-05-09T05:33:23Z")
I recall reading about an accident with a Grumman Tiger (old 4-seater) long ago. It has a low wing with laminar airflow airfoil shape. Apparently the plane took off from a grass field runway that had been recently mowed and was wet with dew - the grass clippings stuck to the wing and disrupted the airflow enough the plane could not gain altitude in time. ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [May 9, 2026, 7:17am UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/34 "2026-05-09T07:17:56Z")
> [@Crafter\_Man](#): > > Wings push air down. Same with helicopters… the spinning blades push air down. Helicopters don’t fly so much as beat the air into submission. ---
**Author:** ![pjd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pjd/32/3009_2.png) [@pjd](https://boards.straightdope.com/u/pjd)\ **Post date:** [May 9, 2026, 7:57am UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/35 "2026-05-09T07:57:07Z")
> [@CalMeacham](#): > > Actually, it’s a god question. Are you saying that airplanes are held up by the power of prayer ?! ---
**Author:** ![md-2000](https://avatars.discourse-cdn.com/v4/letter/m/9d8465/32.png) [@md-2000](https://boards.straightdope.com/u/md-2000)\ **Post date:** [May 9, 2026, 7:56pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/36 "2026-05-09T19:56:33Z")
> [@pjd](#): > > Are you saying that airplanes are held up by the power of prayer ?! Much like Wiley Coyote running off a cliff, they are supported by the belief they will fly. If you lose faith, you are no longer sustained. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [May 9, 2026, 8:07pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/37 "2026-05-09T20:07:02Z")
[![Imgur](https://live.staticflickr.com/2274/1845966605_4873922c28_b.jpg "Lift!") ](https://www.flickr.com/photos/11822576@N08/1845966605/) ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [May 9, 2026, 8:17pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/38 "2026-05-09T20:17:19Z")
> [@GargoyleWB](#): > > Most of the benefit of the “Bernoulli wing” or other convex profiles isn’t the raw lift force, which as stated in posts above is rather minimal. The benefit is in its lift response profile to different angles of attack. A symmetric “barndoor” wing is going to have a very steep lift response to angle of attack and induce turbulence and stall condition much more rapidly. A curved wing is going to maintain a shallower lift response over a greater AoA, and not collapse into a stall condition from the induced turbulence until much much later. This is more of a question for the experts than any sort of informed comment, but ISTM that this is true and a very important observation. If you built a plane with flat (literally, “barndoor” wings) it might fly, but very inefficiently, as even the slightest wing inclination to produce lift would immediately generate turbulence, resulting both in drag and in a strong tendency to stall. Whereas a wing shaped like the cross-sections in my illustration in post #29, with convex shapes at both top and bottom, would tend to induce laminar air flow except at an extreme angle of attack, allowing for efficient flight with much less risk of stalling. Is this an accurate description? ---
**Author:** ![Measure\_for\_Measure](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/measure_for_measure/32/557_2.png) [@Measure\_for\_Measure](https://boards.straightdope.com/u/Measure_for_Measure)\ **Post date:** [May 9, 2026, 10:54pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/39 "2026-05-09T22:54:39Z")
Here is your barn door wing plane. It flies, though not very well. [![](https://cdn-tp6.mozu.com/24645-37138/cms/37138/files/c46ff897-7bce-49b2-89cc-405202eeceda?quality=60&_mzcb=_1778166700719) ](https://cdn-tp6.mozu.com/24645-37138/cms/37138/files/c46ff897-7bce-49b2-89cc-405202eeceda?quality=60&_mzcb=_1778166700719) I repeat that wing shape matters a lot, accounting for 1/3 to 90% of lift, depending upon the extent of the angle of attack. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [May 9, 2026, 11:06pm UTC](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890/40 "2026-05-09T23:06:49Z")
> [@Measure\_for\_Measure](#): > > Here is your barn door wing plane. It flies, though not very well. I had a few of those. They flew fine, though were undoubtedly not very energy-efficient! 😉 The only adjustment you could make was to move the wings backward or forward along the little slot that they fit in. If they were too far back, the plane would fail to take off or would dive if thrown, but too far forward, and it would stall. It was a very delicate adjustment, with those barn door wings! [Previous page](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890.md?page=1) [Next page](https://boards.straightdope.com/t/stupid-question-how-do-planes-really-fly/1029890.md?page=3)