26 votes

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

For regular paper weight and size A6, roughly a card postal size one can tear from the middle vertically the top half and bend the two flaps 90 degrees in opposite directions like a helicopter's ...
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  • 21.1k
17 votes

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

I really love this game idea! I think a flat piece of paper falling face-down is probably the least aerodynamic thing you could possibly drop if it maintained its shape and orientation, but naturally ...
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  • 171
15 votes
Accepted

How does a helicopter hover

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 ...
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10 votes
Accepted

Why do some high speed trains have long noses, while others do not?

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 ...
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9 votes

Is the main goal for wind turbines to take maximum energy for a given diameter?

The function of the wind turbine is to extract as much as possible energy from the moving mass of air. The energy of a mass $m$ of air is $$KE = \frac{1}{2}m v^2$$ and the power is (because the mass ...
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  • 22.7k
8 votes

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

What a fun challenge! We had a good time trying out various designs :) I did eventually come up with a helicopter-style design that falls about 50% slower quite consistently. Build instructions: Cut ...
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  • 1,835
6 votes
Accepted

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

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 ...
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  • 251
6 votes
Accepted

Why don't propeller designers use multiple profiles?

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 ...
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  • 486
6 votes

Should Engineers Understand Equations without Relying on Derivations?

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 ...
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6 votes

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

Extrapolating from the Gyrocopter idea for A4 paper size, I arrived at following conclusions: Bending (i.e. not creasing a fold) part of the helicopter blade along its length provides ample ...
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5 votes
Accepted

Should Engineers Understand Equations without Relying on Derivations?

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 ...
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5 votes
Accepted

How do those "dipole-shaped" weights attached to sections of electrical power lines work?

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, ...
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  • 6,337
5 votes

What affects a car's overall top speed?

The factors that affect a car's top speed - IMHO - can be grouped to the power train factors : engine power gear box and differential ratios size of the wheel and to the losses: overall aerodynamic ...
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  • 22.7k
4 votes

Why use non-dimensional coefficients?

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 ...
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4 votes

Ceiling or table fan better

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 ...
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  • 561
4 votes
Accepted

Scanning and modeling my personal vehicle for aerodynamic simulation

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 ...
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  • 6,337
4 votes

How to Find Drag Force from Skin Friction

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 ...
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4 votes

Rocket vs aeroplane? Difference in take off?

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 ...
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  • 1,608
4 votes
Accepted

Would this air amplifier attachment increase a leaf blower's effectiveness?

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 ...
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4 votes

why do centrifugal compressors have curved blades?

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 ...
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  • 21.1k
4 votes
Accepted

Will a lift force be created by the Coanda effect if high velocity air flows under a half-toroid shaped saucer?

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 ...
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4 votes

Is the drag coefficient/velocity of of a vehicle based on frontal area?

The drag coefficient $C_d$ is defined as: $C_d = \dfrac{2F_d}{\rho u^2A}$ where: $F_d$ is the drag force, which is by definition the force component in the direction of the flow velocity; $\rho$ is ...
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  • 7,666
3 votes
Accepted

Deceptional Pitot Tube

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 ...
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  • 632
3 votes

Why use non-dimensional coefficients?

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 ...
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  • 12.5k
3 votes
Accepted

How to scale airfoil coordinates to achieve the required size?

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 ...
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3 votes
Accepted

Hydrofoil for skeg-hung rudder with forward centre-of-effort

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 ...
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3 votes
Accepted

Guiding a parachute via anchor: Possible?

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 ...
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3 votes

What does “tempered water” exactly mean and how does it help cool the air?

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 ...
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  • 561
3 votes

Fluid dynamics right angle air duct

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 ...
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  • 7,489
3 votes
Accepted

What is the optimal streamlined shape?

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, ...
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  • 3,590

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