Questions tagged [lift]

The force acting on an aircraft in opposition to gravity which keeps the aircraft in the air.

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61 votes
11 answers
43k views

How do wings generate lift?

Just the basic question that every aviation enthusiast must be curious about: exactly how does a wing generate lift?
0 votes
0 answers
35 views

I need to find either the relationship between power and lift force in helicopters (RC ones if possible) [migrated]

My original goal was to investigate the relationship between voltage and lift force in toy helicopters, however i've been advised that it will be easier to find help with the relationship between ...
3 votes
2 answers
128 views

Will ice on an airfoil work as a vortex generator?

Vortex generators are little fans that generate vortex to attach flow to an airfoil and delay stall. If frost or ice are formed on an airfoil, technically they also generate turbulence and vortex,I am ...
5 votes
2 answers
113 views

2D to 3D Non-Elliptical Lift Curve Slope Correction Factor Reference

I'm working on automating some aerodynamic calculations for a particular multidisciplinary design tool and in the course of setting it up I ran across this formula from the input theory manual $$ {CL_\...
4 votes
5 answers
1k views

Explained intuitively, why does aspect ratio affect induced drag?

Over the last few hours, I've been trying to intuitively understand induced drag, and how aspect ratio affects it. I already know the equations, but while they explain the relationship, they do not ...
1 vote
3 answers
3k views

How do I calculate the center of lift?

See my other question here for the background context. Consider this simple plane. I have applied the 4 basic forces: lift, drag, weight, and thrust. My question is, where, precisely, do I apply the ...
7 votes
1 answer
698 views

What is the total lift equation of a helicopter with 3 Flettner rotors?

I'm doing research regarding the possiblity of using Flettner rotors on helicopters. I would like to derive the total lift equation for a helicopter that consist of 3 Flettner rotors. Given that: ...
2 votes
2 answers
112 views

Why does lift coefficient not change with velocity in inviscid flow?

Why exactly is lift coefficient constant with velocity in inviscid flow? (For a given angle of attack, 2D section and fluid, pre-stall etc) Does it come out in the derivation of lift coefficient or ...
0 votes
1 answer
119 views

How to choose an attack angle?

I'm writing a little piece of code for preliminary design that can calculate the ideal wing area for a given load, cruise speed and aspect ratio or span. It seemingly works well on the A380 data: <...
0 votes
2 answers
88 views

Why does the leading edge vortex accelerate the flow downward?

I know leading edge vortices over delta wings make more lift. I understood that the core of the vortex sheet is low, so there is suction flow that makes lift. But, I can't understand how a leading ...
2 votes
1 answer
78 views

What are some features of a wing, which effects its lift coefficient other than its sectional view? [duplicate]

What geometrical features of a lifting surface apart from which airfoil it has, I mean the ones visible from the top and front view of a wing (for ex: its span, AR, sweep, dihedral etc.) effects its ...
3 votes
4 answers
358 views

What causes lift?

Now this seems to be the question of the ages, and various questions on this site regards it. The often told description of lift is that it is due to air traveling faster over the wing than under it, ...
4 votes
1 answer
125 views

How does Condensation Affect Lift?

Here are two pictures of condensation happening above the wing: The condensation happens because the pressure drops above the wing which in turn causes the temperature to drop. When the temperature ...
1 vote
2 answers
111 views

What methods are used to calculate the geometry needed to obtain a bell-shaped lift distribution?

In aerodynamics, what methods do people use to calculate the geometry of a wing (and body) needed to obtain a bell shaped lift distribution? Please go into as much detail as possible for a stack ...
0 votes
1 answer
167 views

How to calculate lift and drag of commerical aircraft in different phases of flight?

What is the best way to mathematically calculate values of lift and drag forces, in different phases of flight: takeoff, climb, cruise, descent, and approach? Edit: I have the idea of calculating the ...
1 vote
2 answers
308 views

What does deploying landing flaps do to the (L/D)max and minimum drag speed of an airplane?

I thought that deploying flaps will increase both the drag and lift, thus increasing L/D ratio? But do they increase proportionately? And how exactly does that correlate with the increase/decrease of ...
2 votes
1 answer
371 views

Converting 2d Cl to 3d [closed]

I am trying to convert 2d Cl data obtained from javafoil for a NACA 4412 into 3d data to be used for analysis of the airfoil, but cant find any equations online
0 votes
2 answers
171 views

Which one produces more lift?

I have come across this question on Twitter. I have found a similar question here. The aircraft isn't flying but just doing Cobra Maneuver. Since the direction of the lift is in the same direction and ...
4 votes
2 answers
239 views

Never heard of this Aerofoil?

I just came across this aerofoil, 65-2xx? I searched this but it doesn’t come up with anything like 65-200 for example but instead SG6051 which is the closest I could find to this? Am I missing ...
2 votes
2 answers
375 views

When rearranging the lift force equation to solve for lift coefficient instead of lift force, why is the numerator often given as F not 2F?

the standard description of the Lift force affecting the lift surface is: $$ F={\dfrac{1}{2}}\rho v^{2} SC_{L} $$ the basic rearrangement gives the following definition of the lift coefficient: $$ C_{...
1 vote
1 answer
351 views

How can I estimate the coefficient of lift for take off?

For the CLto (take off lift coefficient), is there some way to estimate this? I was thinking of using CLmax but wouldn’t this be too big? I was thinking maybe CL cruise?
2 votes
2 answers
151 views

How do I calculate where a wing is most likely to break?

I want to make a delta wing out of carbon fiber, but I do not know how many carbon fiber layers would be needed to prevent the wing from breaking due to shear stress. What would be the calculations ...
10 votes
1 answer
929 views

What is the best combination of airfoil shape for flight in ground effect over water?

What is the best airfoil shape for flight in ground effect over water?
-1 votes
2 answers
155 views

Why airflow travels faster on upper wings?

I have been looking for solutions and come up with two popular explanations: Conservation of mass / Continuity For a positive-cambered wing, the streamlines would be compressed/converged at the ...
-1 votes
1 answer
196 views

The stall velocity condition: Exactly what is stall velocity? [closed]

Question: if my stall velocity is 20m/s, then... If the airplane is travelling at a velocity greater than or equal to the stall velocity, can one assume the plane will not stall? Can one assume that ...
3 votes
1 answer
171 views

Are horizontal engine pylons generally shaped to provide lift (in either direction)?

Most civil multiengine jets and some civil multiengine propeller aircraft have engines mounted in nacelles on the ends of pylons extending some distance away from the wing or fuselage. Wing-mounted ...
5 votes
4 answers
971 views

Why does lift decrease and drag increase when approaching the stall condition?

This is an ECQB-PPL question specifically asking what happens before the stall. I do understand that after the critical angle has been reached, the airfoil is no longer generating lift (so obviously ...
7 votes
6 answers
2k views

Can induced drag be negative?

For an aircraft in straight and level flight, lift-induced drag is the horizontal component of the force perpendicular to the wing chord. Positively cambered aerofoils generate lift starting at small ...
50 votes
8 answers
13k views

How complete is our understanding of lift?

I'm currently studying for my PPL and one of the accepted textbooks contains the following disclaimer at the end of the Principles of Flight section on lift: It is important to note that the forgoing ...
23 votes
8 answers
23k views

Does lift equal weight in a climb?

This subject keeps coming up in the discussions and questions such as this one, which asks if lift equals weight in level flight. Good answers there, pointing out that upwards force has many sources. ...
9 votes
4 answers
2k views

If an elliptically-shaped aerofoil gives the optimum lift distribution, why aren't propeller blades designed around this ideal?

So given an elliptical lift distribution is the most efficient, why are propellers not designed around this? Props aren't affected by the adverse stall characteristics that concern a "main", ...
1 vote
1 answer
106 views

Is it possible for the lift force unit vector to be equal to the weight force unit vector?

I know that the drag force is parallel to the direction of flow, thus equal to the unit vector of velocity. But if you consider a vehicle, when its angle of attack is below the velocity vector from a ...
9 votes
6 answers
1k views

How to recognize the horizontal winglet in the Horten design, or the experimental glider in this video?

Comments below the NASA Armstrong Flight Research Center video Proving Prandtl- With A Twist! incclude: This video is entirely a hidden jewel in youtube, it deserves much more attention than what it ...
0 votes
2 answers
187 views

Help with calculate forces from pressure distribution

V=50m/s deltaPg= -981 Pa deltaPd=490,5 Pa c=1m r.com/PCshZ.png Above is calculate Fz with integrals and with average pressure. Why F3 is calculate from 0 to C/2 if pressure distribution is drawn at ...
0 votes
1 answer
479 views

How to solve normal and axial aerodynamic force coefficients integral equation to calculate lift coefficient for an airfoil?

$$ c_n = \frac{1}{c} \left[ \int_0^c (C_{p,l} - C_{p,u}) \, dx + \int_0^c \left(c_{f, u} \frac{dy_u}{dx} + c_{f,l} \frac{dy_l}{dx} \right) dx \right] $$ $$ c_a = \frac{1}{c} \left[ \int_0^c \left(C_{p,...
31 votes
4 answers
7k views

Principle of aerodynamic lift: are misconceptions also taught in flight schools?

Describing lift as the result of "equal transit time" on both sides of an airfoil is a fallacious theory widely found in technical books and articles for general public (see below for details about ...
9 votes
2 answers
732 views

Why is ground effect greater over smooth hard surfaces?

Helicopter Flying Handbook: Ground effect is the increased efficiency of the rotor system caused by interference of the airflow when near the ground. The air pressure or density is increased, ...
3 votes
1 answer
240 views

Does an airfoil in supersonic flow have zero circulation?

In incompressible flow, the Kutta-Joukowski theorem can be used to relate the lift (per unit span) to the circulation around an airfoil. However, if we look at an airfoil or the flat plate (see below) ...
6 votes
3 answers
13k views

What is the effect of flow separation on lift, pressure distribution and drag?

Consider an airfoil (a wing) in an airflow. When angle of attack increases, at some point the flow start to separate from trailing edge. By increasing the angle of attack more, this separation area ...
3 votes
3 answers
564 views

How do thick and thin airfoils compare in lift generation?

I find myself confused when comparing the lift generation amongst Thick and Thin Airfoils. A paper to which I have added reference below claims that thin airfoils are better in generating lift because ...
0 votes
1 answer
553 views

How to calculate the takeoff speed for a hypothetical aircraft?

Given some basic information such as: aircraft weight wing load (including wingspan, and basically the whole wing configuration) airfoil profile coefficient of lift angle of attack Is it possible to ...
10 votes
2 answers
3k views

How would an airfoil react if it was flown backwards?

Out of curiosity what would happen? Would pressure on both top and bottom flip? or stay the same or act as a normal wing with less lift? I'd assume it would still take longer to travel over the top ...
1 vote
1 answer
155 views

How to turn inviscid data to viscous?

I have used Panel method to calculate Cp vs x/c graph and CL. But as panel method assumes attached flow it does not give an flow separation and thus in CL vs alpha graph I could not find any stall. My ...
3 votes
1 answer
330 views

Why is the CG assumed to be between the CP and the tail?

While discussing stability (Longitudinal, Lateral, Directional), invariably, all texts assume CG to be between CP and tail. Ex: Look at the specific image in wikipedia https://en.wikipedia.org/wiki/...
5 votes
2 answers
310 views

Will air accelerate over a wing and generate lift, if the air has zero viscosity? [duplicate]

Will air accelerate over a wing, if the air has zero viscosity? Will the wing produce any lift under these conditions?
2 votes
0 answers
98 views

Streamline Curvature Theorem applied to Airfoils?

I am new to studying aerodynamics and taking up aeromodelling and am currently learning how lift is obtained in-depth. When studying the two common explanations as to how lift is generated by an ...
0 votes
0 answers
54 views

How does a forward lifting surface affect ideal lift distribution of a main wing?

In Peter K's answer to this elliptical wing with lowest drag question the minimum induced drag lift distribution for a wing is described as one with a constant downwash angle across its span. When a ...
14 votes
8 answers
10k views

Why does a stall decrease lift, rather than increasing it?

A stall occurs when the angle of attack of a wing or other airfoil becomes so high that the airflow over the upper surface of the wing separates from the wing, rather than remaining attached to it; ...
5 votes
4 answers
3k views

Why does NASA say $v^2$ is velocity squared rather than speed squared?

Lift and drag forces scale as the square of the relative flow speed, $v$. But speed is the magnitude of the velocity vector; that is, speed is the square root of the sum of the squared velocity ...
0 votes
1 answer
78 views

How do I calculate induced drag? [closed]

How would I go about solving this problem? An aircraft has 6000lbs of total lift and a downwash angle of 6 degrees. Remember that the total lift vector is tilted aft by HALF the downwash angle. What ...

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