# Tag Info

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Most helicopters of modern manufacture are dynamically unstable while hovering- they require constant, "hands-on" control inputs from the pilot to keep things in balance. This task is very demanding and requires a lot of practice to master. Hiller helicopters (which have been out of production for many years) were one of the rare examples of ...

9

It all depends on the level of efficiency you seek. A train, given its size, has a ridiculously small cross section. This small frontal area footprint is being 'pushed' by the inertia of hundreds of tonnes of metal. All high speed train have aerodynamic noses, but some will tend to be pedantic about how many thousandths of a percent efficiency they can ...

6

In general, most airfoils only approximately display the $2\pi$ lift slope as predicted by thin airfoil theory. That is because airfoils are not actually infinitely thin in practice, and will deviate from thin airfoil theory by a small amount. $a_0$ is left in the above equation so one can predict the elliptical finite wing lift slope (effects of aspect ...

6

There are propellers with different aerofoil sections. For example, the propeller attached to the Rolls Royce engine kept in my graduate college had symmetric aerofoil sections roughly about 25 % and smoothly varying to bottom flat airfoil sections at the rest. The aerofoil profile selections are based on the performance requirement, structural rigidity, ...

6

Knowing the derivation is important because it usually tells you what initial assumptions were made in the derivation and what the limits of applicability of the resulting equation are. Understanding both of these things is an essential skill all engineers must master.

6

Should I, as an engineer-in-training hoping to complete research, focus on trying to understand equations to my satisfaction, or should I instead just become well acquainted the equations, their use cases, and their general behavior? Engineers apply equations to predict behavior. The critical requirement is to know the constraints of the equation. The ...

5

According to the wiki, these are called Stockbridge dampers. The design is tuned for a specific length and one might also expect a specific mass/material. The weights are mounted on flexible arms, typically a length of stiff cable, which allow the assembly to absorb energy that might otherwise be imparted to the longer power lines, or more accurately, that ...

4

There are two major benefits to dimensional analysis (non-dimensional coefficients) according to Frank M. White, Fluid Mechanics, 2nd Ed. My answer is heavily paraphrased from this source. They allow scientists/engineers to reduce the number of experiments required to explore a given phenomenon. They provide scaling laws allowing experiments to be performed ...

4

There are far too many factors involved to definitively state that a table fan cools more than a ceiling fan or vice versa. For starters, there are different styles of both. It also depends highly on what you consider "cools better". For example, if you were to come inside and are sweaty, and are looking to cool down quickly, standing in front of a small ...

4

What you seek is called 3D photogrammetry and is a relatively exciting segment of 3D modeling. You can use those terms to search with your favorite search engine and be overwhelmed with options. I found a link to a summary performed a bit more than a year ago, which might be more useful to you. https://pfalkingham.wordpress.com/2016/09/14/trying-all-the-...

4

A plane relies on aerodynamic lift to stay airborn. This is much more efficient than using raw vertical thrust like a rocket does. The downside is that planes always need to be moving perpendicular to the direction of gravity. Pretty much all planes except for fighter jets do not have enough thrust to take off vertically. For traveling from point A to B on ...

4

probably not, here is why. the coanda effect describes how a moving mass of air entrains nearby air and sets it in motion. So if we start with an extremely fast-moving but small jet of air, with it we can urge a much larger mass of air into motion. However, energy conservation dictates that the kinetic energy of the large mass of air set into motion be less ...

4

As the air moves from the center out it accelerates in a pattern similar to a hurricane. the velocity vector angle changes to reduce the rotational whirlpool and angular momentum component of the airflow but add to its pressure and centripetal momentum. The blade angle of attack to airstream follows air velocity vector more or less under 14 degrees to give ...

4

It is important to realize any airborne device will go in the direction of the sum of all force vectors (including gravity). We have our centrifugal impeller drawing air in from the bottom. The device will be pulled down. The air flow out the sides will create low pressure, pulling the device down. The device will have a better chance flying if it is ...

3

There are two speeds that the pilot is concerned about. First is airspeed, and the second is ground speed. Ground speed (speed of the aircraft relative to the ground) can and is checked by GPS. This speed tells the pilot how long the flight will be and if they are staying on track with their fuel calculations for the flight, crucial, but less critical ...

3

The qualitative behaviour of a physical system often depends on the relative size of two (or more) different effects. For example, in fluid flow, turbulence tends to develop when the force to accelerate the fluid (i.e. its inertia) is big compared with the viscous forces in the flow. In the opposite situation where the inertia forces are small relative to ...

3

This is a simple math question. Multiply your x and y coordinates by the scaling factor you want. Say your chord length is 100mm. To make it 150mm, multiply all your values by 1.5. If you have a picture of an airfoil, just scale the image by 150%.

3

As a Naval Architect, this is a question that I am often asked. The centre of effort is very close to the geometric centre of the spade as you know. Is there a fixed skeg or keel immediately in front of the rudder? That affects the hydrodynamics significantly because the hydrofoil would then have an effective length that is the skeg width (aligned with ...

3

As the diagram shows you may be able to use a standoff arm to maintain separation between the payload and the guide line. However friction between the standoff and the guide line may cause the two to tangle or jam. Given no knowledge of the payload layout or size. You could run the guide line down the center line of the paracute, not sure if it would be ...

3

I would argue that "tempered water" was the unfortunate result of a marketing department not doing their homework. Typically in plumbing design, I come across "tempered water" on emergency fixtures (emergency eyewash or emergency showers) or for things like the mixing valves on showers. OSHA has requirements for tempered water delivered ...

3

A curved elbow will be considerably better than square elbow, because it reduces turbulence. The exact mathematical shape of the curve is not really important; usually a circular radius is chosen because it is easier to fabricate. It is important to keep the cross sectional area the same as the air moves through the turn; two circular arcs that share the ...

3

There's a lot more to it than just minimum drag shape. At 200 kph, you want it to be aerodynamically stable as well. If the pipe is supporting the fairing, and you want to limit the load on the pipe, then the pipe has to be forward of the center of resistance of the fairing. The shape will depend on temperature, altitude, humidity, the size of the pipe, ...

3

The two main considerations concerning wind power generation is the speed of the air and the duration of wind (air flow). The more of both, the better. Trying to harness wind flow within a building will be difficult because the air flow will most likely be low (slow speeds) and the duration of flow may also be short, except on very windy days. Even a wind ...

3

No - the sphere would likely stick to one wall, or bounce between them. A sphere is not a very aerodynamic shape, having both a relatively blunt front, and sudden cut off at the back. This causes a lot of turbulence, such as the familiar vortex shedding shown here: This shows how the air flows around a fixed sphere in free space - in your hose, the vortex ...

3

As has been mentioned above by Eric Shain the correct answer is to take the partial with respect to y= CL and equate it to zero. Let's Call the max L/D, M. $$M = \frac{C_L}{C_D} = \frac{C_L}{C_{D_0} +K*C_L^2}, \quad C_{D_0}=0.015\ and\ K=0.05$$  \frac{\partial M}{\partial C_L} =\ \frac{\partial}{\partial C_L} [ \frac{C_L}{0.015 +0.05*C_L^2}]\ =\quad \...

3

Yes. Aircrafts, other than a few which could lift vertically, create lift by moving forward in the air and bending the stream of air flow around their wings. Airplanes create the traction forward by the thrust of their engines not by traction of their wheels, so they will start to move even on water like a sea plane or on a free treadmill, ice, even from a ...

3

As with a lot of things in engineering (and life in general), you have to weight the cost vs benefit associated with the application. Sometimes it’s enough to treat the equation like a black box, needing only to know the input output behavior. Other times, knowing the how to derive equations enables you to derive new things from new assumptions. You won’t ...

3

The problem you cite in the question is a pretty standard homework problem in a graduate fluid mechanics course (it might be also an undergraduate course but less likely). Therefore, I would be reluctant to provide the solution. What is important to remember when dealing with this problem is that it is crucial to attend the lecture at which the subject was ...

3

These are the dimensionless coefficients. The equation computes the $C_{m_x}$ at some point not at the aerodynamic center by adding the $C_{m_{ac}}$ to a (nondimensional) force times a (nondimensional) distance. Note that the $C_{m_{ac}}$ is independent of angle of attack. To the first order, it is a function of the camber line. But the $C_l$ is a function ...

3

The difference is in the drag coefficient. Typical drag coefficient of the 50's cars have been in the range of 0.38 to 0.42 or so. typical drag coefficient of modern cars even the ones not renowned for their streamlined body is ranging from 0.26 to 0.34. drag is the retarding force exerted on moving bodies by the media they are moving in. it tries to slow ...

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