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# Questions tagged [aerodynamics]

Aerodynamics is the study of how air moves and interacts with solid objects. It is an essential part of aircraft design.

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### Why will the max lift point not be at the center of a swept but constant chord wing?

(In this question when I say "swept wing" it means the blue wing seen at the bottom. So no fuselage or anything) If you look at this graph from this answer, you'll see the max lift point of ...
2 votes
1 answer
103 views

### Why will the pressure distribution of a swept wing promote stall?

Here it explains how the bound vortex will change the lift distribution of a wing. What is meant by the lift distribution changing is that there is less lift at the tip, meaning the pressure ...
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### Understanding the constant speed prop and 2-4 degrees optimum

I've read through some answers on here and just wanted to write my own description of how this works and let someone check for me. Currently I've just started to fly an King air 100 with PT6A We ...
1 vote
1 answer
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### What happens in order to make a shock when the flow first turns?

Imagine you have a really zoomed in view of a 2d ramp, which is at 20 degrees. Zoom in on the exact point the ramp turns from horizontal to 20 degrees. When the first supersonic air molecules reach ...
1 vote
1 answer
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### How does the downwash behind a swept wing differ from a normal wing?

How does the downwash behind a swept wing differ from a normal wing? (I know you can’t trust everything you see on the internet, but this seemed legitimate) Here it said: The downwash pattern on a ...
1 vote
1 answer
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### Can a sound wave travel through a shockwave?

Say you have a scenario where there is a shockwave, and you sent a normal sound wave towards it. Could the sound wave travel through that shockwave? If so/not, why? Would it depend on the strength of ...
22 votes
8 answers
8k views

### Why do airplanes usually pitch nose-down in a stall?

Why do airplanes usually pitch nose-down in a fully-developed stall? I've seen this seemingly-simple question discussed on other aviation forums, but there doesn't seem to be a single agreed-upon ...
0 votes
1 answer
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### Why are shockwaves allowed different angles at different distances from a body?

It's been (well) established that a shockwave can only be at the angle of the Mach cone. (I now understand this part). However, in this picture: you can see that the shock is at 2 angles. I also ...
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2 answers
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### Why will a slower moving parcel of air above a wing create drag in non-inviscid flow?

This answer explains why a thicker boundary layer will cause a type of form drag. It uses inviscid flow to explain this. It is a great answer, but I can't seem to see how this applies in a real world ...
2 votes
1 answer
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### How does a thickening boundary layer create form drag?

Imagine a normal wing with flow over it, and to simplify things it's at 0 AoA. Drag is being made mainly because of form drag and skin friction drag. I'm not sure on this, but I don't think there ...
4 votes
2 answers
124 views

### How does ground effect work with a banked wing?

How would an explanation of ground effect such as this one from Peter Kämpf be modified to account for a highly banked wing? A paraglider and HP canopy pilot told me that when he banks a wing to touch ...
-2 votes
1 answer
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### What is the speed and temperature profile of the boundary layer at the stagnation point?

At the statgnation point where the air velocity is zero, what is the shape of the velocity and temperature profile of the boundary layer? Is the velocity profile of the boundary layer in the form of a ...
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1 answer
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### What's gonna be the physics behind building 'futuristic' airplanes? Use physics formulas or even theories to answer this question [closed]

After thinking about these 'futuristic' airplanes, I wonder if there's any special physics theory or law behind them. I wonder how faster they can be, persevere more and fulfill the aviation's lover ...
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3 answers
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### VTOL Propeller Sizing and Executing a transition from VTOL to Forward Flight mission profile

Hi I am an engineering student, currently in the process of designing a compound UAV drone capable of both vertical and forward flight. I've made significant progress, having completed initial gross ...
0 votes
5 answers
617 views

### Forward Slip - Which speed to maintain?

Which is the proper speed to be maintained during a Forward Slip? Near Vfe or Vref? Which one will let you lower with the shorter ground distance and why?
1 vote
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### Why don’t closed wings eliminate tip vortices?

It’s clear that tip vortices never really can be prevented, but why doesn’t a closed wing do that? There is no ‘tip’ on a closed wing so where does the air go to make a vortex? On a normal plane the ...
5 votes
1 answer
155 views

### Could a propeller system for airplanes with automatic, cyclic blade-pitch control that is designed to counter p-factor be practical?

Considering that P-factor is a result of differing angles of attack of the blades on an airplane's propeller, I would imagine that if there was a design that could control the pitch of each individual ...
3 votes
2 answers
93 views

### Lateral Stability- Why aircraft will not return of its own accord to the original heading after a sideway gust?

I am reading the Stability section of FAA it says: If an aircraft is flying in a straight line, and a sideward gust of air gives the aircraft a slight rotation about its vertical axis (i.e., the ...
7 votes
1 answer
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### Gap between F22 ailerons and flaperons

You can see in the below picture that there's an F22 on approach (I think) and this is almost a perfect bottom view of the plane while it's going straight, it isn't banking. There's gaps between the ...
2 votes
1 answer
1k views

### How does airfoil affect the coefficient of lift vs. AOA slope?

I'm trying to understand whether the airfoil shape can affect the slope of Cl vs. AOA (coefficient of lift vs. angle of attack) in the "linear" portion, e.g., from a few degrees negative to ...
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1 answer
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### Why will the flow turning angle be 0 (or close to) inside of the Mach cone?

(Disclaimer : This probably seems like my 56th question on the same topic, but this will be my last relating to Mach cone angle and shock angles, as I think I understand most of the topic) So the ...
1 vote
1 answer
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### F15 Startup Intake drop

So I’m aware that the F15 has intake Ramps that adjust to airspeed and AOA, in order to ensure that the airflow is entering the engine smoothly and not too fast. But why does the system drop the first ...
1 vote
4 answers
182 views

### Can smaller wing area improve the aircraft experience during turbulence?

Amid the recent incident of Singapore Airlines flight 321, leaving one dead after a severe turbulence, I ask myself if having an aircraft with smaller total area, there is less turbulent air that ...
11 votes
1 answer
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### What are those little pieces for on the C27J?

Here is a picture I took. You can see some pieces on the vertical stabilizer, but only on one side. I imagine this is for an aerodynamic purpose, but I am not sure. What do you think about its purpose?...
0 votes
1 answer
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### Range, Endurance and Fuel Cost Savings of an Aircraft

I have recently carried out CFD simulations on the A320 fuselage and modified its fuselage. I did this by matching the Reynold's number of the cruising altitude. The reference values were taken at ...
4 votes
1 answer
954 views

### Can weight reduce a plane's glide ratio?

The FAA says glide ratio doesn't change, regardless of weight, here on page 5-7. Glide ratio is not affected by weight because, while a heavier glider sinks faster, it does so at a greater airspeed. ...
17 votes
3 answers
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### What happens in a stall during a slip?

In flight training we're warned against skidding turns since they have a higher potential for a stall/spin (the classic example being the stall/spin on the base to final turn). However, how does the ...
0 votes
1 answer
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### Why would there be a drag discrepency when simulating transonic flow over scaled CRM geometry?

I have a discrepancy when simulating a wind tunnel experiment of a 2.7% scaled NASA CRM geometry as used in the wind tunnel. I am trying to replicate exactly the wind tunnel model and flow conditions ...
-1 votes
1 answer
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### Can a shock in certain circumstances be at a lesser angle than the Mach cone?

(Excuse the drawing quality) What will happen if a shockwave has an angle less than that of the Mach cone? In this picture, the black line represents the Mach cone. The orange line represents the ...
0 votes
1 answer
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### Does the flow turning amount change as you get further away from an object?

Will the flow turning amount change as you get further away from an object? This answer explains why shockwaves will extend past the body that made them (good starting point). This question is asking ...
3 votes
2 answers
186 views

### Engineless Blimp Navigation System

I understand wind direction can vary in a column of air? With only altitude control on a blimp to navigate for long flights, a blimp in theory could navigate without engines. In order to take real ...
1 vote
1 answer
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### Why does the angle of a shock change when the flow leaves the influence area of an object?

In this (great) answer, it says: "far enough" from the Concorde's nose, the path followed by the airflow is not affected by its presence and it's just a straight line. Close to the nose we ...
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3 answers
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### Why do stealth aircraft generally lose in maneuverability?

Whilst stealthy built aircraft have (or claim to have) many anti-detection systems, they seem to have to compromise on less maneuverability features, and even have to keep their missiles inside, not ...
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1 answer
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### Lift without aerofoil? [duplicate]

I have seen some RC planes flying without any form of airfoil, the wing is literally a flat board. What I want to understand is how lift is generated under these conditions. I understand kinetic ...
13 votes
2 answers
44k views

### What is the method to calculate a finite wing's lift from its sectional airfoil shape?

I am struggling to get my head around a concept that I believe should be fairly simple to understand. Lift versus drag and AoA data of many airfoils are freely available, for instance the NACA 4-...
2 votes
1 answer
143 views

### Is a stream of air / jet exhaust low pressure?

Inspired by this answer, is a moving stream of air (Jet exhaust, rocket plume, etc) low pressure? I’ve always thought that a higher pressure area (say the combustion chamber of a rocket engine) will ...
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3 answers
146 views

### How do I choose Cl during cruise flight with a given MTOM and variable S?

Currently I'm challenging myself to build an airplane from scratch. I have a background in aeronautical engineering but I have no experience in actually designing an aircraft from the ground up. (FYI: ...
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### Why doesn't the Coanda effect also pull air from inside the jet / streamline?

As explained nicely in this answer, the Coanda effect will make a streamline of air draw from the surrounding air outside of the streamline. This picture shows it nicely : So my question is what ...
18 votes
0 answers
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### What causes the "dead band" phenomenon during takeoff on the Boeing 737?

During takeoff, the Boeing 737 encounters a distinctive "dead band" phenomenon after the initial pitch reaches approximately 10 degrees. Essentially, a slight increase in back pressure is ...
0 votes
3 answers
286 views

### Why does the shock angle always seem to equal the "sound cone" angle?

(I'm going to use the term "sound cone" for the area you can hear an aircraft when it's at Mach ≥ 1, illustrated by this picture. Not considering the shockwave.) So as explained in this ...
1 vote
1 answer
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### Can I reduce drag with channeling freestream air at the backward facing surface?

Idea is to increase static pressure at backward facing surface to reduce drag. Can I reduce drag with channeling freestream air at the backward facing surface, like picture suggest?
3 votes
1 answer
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### Angle of bank affects on descent rate

I’m attempting to do some maths regarding the ‘impossible turn’ (engine failure after takeoff, followed by a 180+ deg turn back to the field to land). I understand how to determine radius, rate of ...
0 votes
1 answer
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### What is the main reason raked wingtips are more efficient than winglets? [duplicate]

What is the main reason that these: Are more efficient than these?: My main guess is that they improve L/D compared to winglets, as they provide more upwards lift making them more efficient. It ...
4 votes
3 answers
259 views

### Can a wind gust below the rotor affect the lift force in a helicopter?

If a helicopter is hovering and a very strong, narrow and focused wind gust comes from the front and passes few feet below the rotor blade without touching the fuselage or any part of the aircraft for ...
1 vote
2 answers
108 views

### Why does adding heat to the subsonic flow increase the speed of the flow?

In Rayleigh flow, adding heat to the subsonic flow increases the speed and adding heat to the supersonic flow decreases the speed. But what is its physical cause?
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### induced drag at supersonic speed [duplicate]

for a delta wing with supersonic leading edge at small angle of attack there is no stagnation point on leading edge so There is no connection between the top and bottom of the wing. Therefore, the air ...
4 votes
1 answer
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### Why Cessna 152 has different airfoils at the root versus at the tip of the wing?

I recently read that C152 have two different airfoils on its wing. NACA 2412 at the wing root and NACA 0012 the wingtip. Why? And why are those particular airfoils (with their inherent aerodynamic ...
1 vote
1 answer
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### Lift Coefficient question

I am making a RC Airplane, it has a wing profile as shown above. What might be the approx. lift coefficient of this? The wingspan is 80cm, what will the lift provided be by this wing at 65kmph ?
1 vote
2 answers
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### Does separation happen easier with less dense air?

Does less dense air affect when separation happens? So if you have a cylinder traveling in a straight path like the one above, there is separation happening at a given speed. If you were to change ...
12 votes
2 answers
2k views

### What is the meaning of "Docile pitch behavior" in the context of Pugachev's Cobra?

In another answer on SE Aviation it is mentioned that the ability to perform Pugachev's Cobra in a non-thrust-vectored aircraft needs "docile pitch behavior of the airframe up to approx. 110° angle ...