27
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 ...
- 22.1k
19
votes
Can we add treadmill-like structures over the airplane surfaces to reduce friction, decrease drag and producing energy?
You can't reduce friction with machines.
The nature of machines is that everything you do adds inefficiency. A moveable wing surface adds weight, complexity, and additional losses. Even if you did it ...
- 6,534
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 ...
- 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 ...
- 14.3k
11
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 ...
- 24.3k
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 ...
- 136
9
votes
Can we add treadmill-like structures over the airplane surfaces to reduce friction, decrease drag and producing energy?
Can you reduce friction by making a surface frictionless? Yes.
Will that reduce drag? Most of the drag comes from lift. Without lift, the airplane falls out of the sky. Most of the rest of the drag ...
- 633
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 ...
- 1,943
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 ...
- 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 ...
- 486
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 ...
- 61
6
votes
Can we add treadmill-like structures over the airplane surfaces to reduce friction, decrease drag and producing energy?
Let's be honest here...
From an engineering point of view, this is totally impractical and could never work with anything like current technology.
Consider that the surface of an aircraft is not a ...
- 161
5
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 ...
- 14.3k
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, ...
- 6,920
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 ...
- 24.3k
5
votes
Can we add treadmill-like structures over the airplane surfaces to reduce friction, decrease drag and producing energy?
Air on a wing or aileron or any airfoil does not slide on the surface of these, a very thin layer of air (boundary layer's contact surface) sticks to the surface and moves at the same speed as the ...
- 22.1k
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 ...
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 ...
- 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 ...
- 6,920
4
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 ...
- 2,878
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 ...
- 1,901
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 ...
- 14.3k
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 ...
- 22.1k
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 ...
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 ...
- 8,109
4
votes
Accepted
Why wind turbine dont use high lift coefficient airfoils?
I've finally got a few minutes to try to answer this.
Torque is bad. It's necessary, but it is bad. Ideally, you want the turbine to spin infinitely fast at almost zero torque, not slowly at high ...
- 4,597
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 ...
- 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 ...
- 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 ...
- 166
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 ...
- 1,076
Only top scored, non community-wiki answers of a minimum length are eligible