# Questions tagged [aerodynamics]

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### How can a piece of paper be shaped to guarantee it falls slower than a plain sheet of paper?

My son and I are playing "MAKE" (think "HORSE") and we challenged ourselves to build the slowest falling object using only a sheet of paper. We cannot build anything that falls ...
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### Why do some high speed trains have long noses, while others do not?

Why do some high speed trains like the Shinkansen E5 and E6, have really long noses while other trains, like the Eurostar and Javelin, have shorter noses? How does the shape of the nose affect the ...
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### How to design the most hydro/aerodynamic shape for a 'vehicle' that goes back and forth (using ANSYS)?

I am interested in making a very small scraper blade that moves back and forth along a submerged surface, however I need to make it as hydrodynamic as possible so I disturb the liquid as little as ...
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### Why use non-dimensional coefficients?

Aerospace engineering textbooks make frequent use of non-dimensional coefficients like $C_L$, $C_D$ and a whole host of others. Usually, for equations of motion, it is preferred to replace variables ...
8k views

### Do all airfoils have a lift curve slope of $2\pi$?

I know that according to the thin airfoil theory all airfoils (symmetric or not) have lift curve slope of $2\pi$. I also know that finite wings should have less inclined lift curve because of the ...
• 63
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### I have a problem with my representation of roll in Simulink

I am currently an engineering student and a member of the aerospace club of my engineering school (ESILV) which is called LéoFly. We’re a team of 12 students and are building a Fusex (...
653 views

### Should Engineers Understand Equations without Relying on Derivations?

As I've progress through my undergraduate engineering program, I've noticed a shift away from physical intuition - understanding why certain phenomena or equations make sense because of basic patterns ...
112 views

### Why don't propeller designers use multiple profiles?

I'm designing a ducted fan, and I'm deciding on the airfoil profile. NACA 16-series profiles are well-suited to M > .5 or .6, but they're not particularly efficient at lower Mach numbers. On the other ...
3k views

### Can air suction be increased by consecutive pc fans in small air tunnel?

I want to make a small air filter using standard axial pc fans in order to suck smoke like that have been produced in soldering process. But I assume filtering will make it difficult. Am i wrong? ...
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### What is "Bernoulli-Lift", and why does it only account for 20% of an airplane's lift?

Whenever the question "Why do airplanes fly?" is asked (e.g. »What really allows airplanes to fly?«, »How an airfoil works?«) at a certain point the following is cited: Bernoulli's principle ...
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### Questions about the level flight lift equation

In level unaccelerated flight we have relation $$W=L=\frac{1}{2}\rho\cdot V_{stall}^2\cdot S\cdot C_{l,max}$$ taken from book Daniel P Raymer "Aircraft Design: A Conceptual Approach" equation (5.5) ...
934 views

### How does a helicopter hover

I am wondering how a helicopter manages to stay balanced and stay in one spot while it is in the air. I understand that there is a second rotor that is used to counteract the angular momentum and also ...
• 59
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### Will the airflow inside a vacuum hose keep a sphere centered inside of it?

Suppose you were to fasten a string to a ping pong ball, then fasten the string to a stationary object, and then use a vacuum cleaner with a strong vacuum to suck the ball partially into the vacuum ...
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### How to Find Drag Force from Skin Friction

Just wondering if someone can please can give me some idea, as to how I can solve this question that is not related to current study. I haven't been able to work out where to start with it just yet. ...
49 views

### Scanning and modeling my personal vehicle for aerodynamic simulation

I have this pickup truck that I love dearly. I often change the aerodynamic configuration of the truck when I use my camper shell, or roof top tent, etc. Is there a reasonably easy way to create a ...
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### What is the area when calculating the drag coefficient for a race car wing?

The drag coefficient is given by the following expression $$C_d = \frac{2F_d}{\rho v^2 A}$$ For a race car wing (which is simply an airplane wing upside down to generate downforce), what should we ...
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### Compressing the air thrusted by an aircraft's propeller through a cone like tube

If I had an aircraft that used propellers for movement and took the air from the front running it through a tube that gets very small towards the end, would it have any impact on the speed? Would the ...
43 views

### Finding Source of Heating Rate Equation

I am currently working on creating a tool to calculate the maximum heating rate on a re-entry vehicle given starting conditions and coefficients. I am using Re-Entry Aerodynamics by Wilbur L. Hankey ...
83 views

### Air velocity through a tunnel 5,000 feet long and 30 feet in diameter?

I am an architect in need help with an aerodynamics problem for a design that I am developing. I need to know the the potential velocity of air moving from one end of a pipe to the other if any ...
48 views

### How does NASA's QueSST X-59 jet work?

The QueSST (Quiet Supersonic Transport) is a project to create a more diffuse sonic boom in order to use supersonic flight commercially without the usual abrupt 1~2 psf pressure spike damaging the ...
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### Mathematical transformation of a heading angle to a roll angle

I'm trying to understand a function in a SIMULINK example of a path following UAV simulation. The gist is that, the UAV Waypoint Follower block provides a required heading from a list of waypoints and ...
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### Is the main goal for wind turbines to take maximum energy for a given diameter?

If you increase the number of blades, that will increase torque, for the same RPM you get more power,...simple logic So why only three blades, is main goal for wind turbine take maximum energy for ...
• 175
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### Why wind turbine dont use high lift coefficient airfoils?

All wind turibne use low lift coefficent airfoils from 1.0 to 1.5. Why not use high CL airfoils to get maximum torque? http://airfoiltools.com/airfoil/details?airfoil=s812-nr
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### How do those "dipole-shaped" weights attached to sections of electrical power lines work?

I see these frequently on tall power lines like the one in the image below, sometimes a single one at each end, sometimes pairs as are shown here. Sometimes on one side of the tower but not the other. ...
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### How to scale airfoil coordinates to achieve the required size?

I'm using airfoil data that is generated by a program. The generated airfoil has a chord length of 1 unit. I want to know how to scale up this airfoil to required chord length. My airfoil series ...
• 175
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### Questions about helicopter rotors - conservation of angular momentum

I have two basic questions about helicopters. Let's say the z-axis is the vertical axis from ground to sky. I know the tail rotor is there to counteract the angular momentum effects of the main rotor, ...
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### Guiding a parachute via anchor: Possible?

Here's my situation: I'm trying to drop a payload via parachute with some accuracy. I'm worried that in the above setup, the line will interfere with parachute deployment or - if not deployment - ...
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### Why is it when taking the moment coefficient relative to c.o.p., the weight is ignored?

I have been working on a question, and my lecturer has hinted me with this equation that doesn't include forces due to weight? $C_{M_x}=C_{M_{ac}}+C_L(x/c−x_{ac}/c)$ What he told us was that due to ...
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### Fluid dynamics right angle air duct

I am designing a printed piece that will deflect air from an exhaust fan on a computer 90 degrees. My question is, what would be most efficient, a circular radius, parabolic radius, or hyperbolic ...
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### Hydrofoil for skeg-hung rudder with forward centre-of-effort

I am trying to see how much I can reduce the torque on a rudder post by changing the foil shape. I think I need a rudder with a centre-of-effort further ahead than average but I don't know what rudder ...
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### Why do (some) high-speed trains have curved (convex) walls?

Comparing the cross-section of modern high-speed trains to old train waggons, which had straight walls and were limited to speeds around 200 km/h, I notice that most of them have curved outer walls. ...
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### Why do some cars have flow channels in their bodies to decrease drag?

From my understanding, the more surface area the flow passes, the more drag happens due to skin friction. An example of this is the new Ford GT, which has a converging cockpit and separated side body ...
311 views

### What's the slowest airflow speed a ramjet could work?

Thinking experiment about a flying device having the fewest moving parts, whats the slowest cruise speed achievable using a ramjet, no matter the scale of this device. Working altitude is troposphere. ...
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### What happens when the surface ends at the laminar zone of the boundary layer?

When a body travels through any fluid(like aircrafts and cars), due to viscosity of the fluid a boundary layer is formed around the surface of the body which separates the velocity of the fluid inside ...
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### How do water tunnel experiments compare to wind tunnel experiments?

I recently stumbled across the water tunnel videos by this guy: https://youtu.be/quDLzxmJl5I?t=838 He states that for his "high flow" experiments the water speed is at 0.668 m/s. The car ...
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### Closed loop guidance and control: how to tune a system with multiple feedback controllers?

I'm trying to design a closed-loop guidance system for rockets - something that can be implemented in Kerbal Space Program, for example. To do this, I'm following the design process described in ...
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### Is it possible to extract mechanical energy using Turbines behind PulseJet engine?

Pulsejet expels pulse of hot gas (unlike turbojet engine) which create some thrust(Not good enough for ). These gases are hot, fast and pulsed. Is it possible to convert kinetic energy of these gases ...
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### How can I generate smoke (or mist) that leaves no residue?

I have to visualize flow over some designs in my wind tunnel. However, my advisor has stated that previous students have wrecked the machine when they have used oils and I think Dry Ice might ...
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### How does a stator convert velocity into pressure?

I'm looking for, hopefully, a qualitative answer to how a compressor increases pressure. I understand the equations that predict this result but I can't picture it in my head. A rotor spins, ...
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### Whats the difference between leading edge and slat?

According to this figure whats the difference between leading edge flap and slat and why the slat come with plain wing and TE flap come alone? thanks.
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### Convergence problem in RANS simulation of unsteady flow

I am simulating an air flow through a two dimensional rectangular channel. The channel splits into two channels, one of them is followed by a 90 degree bend downwards and leads into a cylindrical ...
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### Calculating mass flow rate of a scramjet engine?

First post here. I'm an undergraduate ME interested in fluid mechanics. I came across scramjets and I was interested about the engine. I want to calculate the mass flow rate of the engine and I made ...
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### In horizontal axis wind turbines, why does axial component of absolute velocity stay constant (wake rotation theory)

I am having hard time understanding how does the axial component stay constant through the rotor. Every resource i look just says it is due to mass conservation but never gives the actual conservation ...
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### Formula for "ram rise" that works all the way to orbit

True Airspeed (TAS) is the vehicle speed relative to the surrounding air. My assumption is that if I am in orbit say at 120 km altitude with an instantaneous velocity of 8 km/s my TAS would be fairly ...
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### A Question of Coaxial Rotors and Lift

I'm only a HS physics student, so please bear with my lack of jargon. My question goes like this: In the scenario of two coaxial rotors spinning independently in two different directions, each with ...
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### Wing as cantilever beam (beam-rod) model for aeroelasticity fluttering analysis

I recently bumbped into a rather basic but interesting question on aeroelasticity. I've learned to derive the fluttering critical speed from Pines's theory but it involves some spring stiffness like ...
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### what is the actual meaning, role and aim of $p_0$, $V_{a_0}$ and $V_c$ for Mach-meter?

Roskam, book "Airplane Aerodynamichs and Performance" at subparagraph: "2.5.2 HIGH-SPEED AIRSPEED INDICATORS (COMPRESSIBLE FLOW)" uses the following three equations: a) \$\left(\frac{\gamma}{\gamma-1}\...
1 vote
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### Is the drag coefficient/velocity of of a vehicle based on frontal area?

Does the frontal area of a vehicle determine the velocity/drag coefficient of a car? A Ferrari 458 has a Cd of 0.33 while a Corvette C6 has a Cd of 0.29. Does this mean the Corvette will have less ...
1 vote