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 ...
Tiger Guy's user avatar
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14 votes
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In case a plane stalls, what should stall first, the tip or the root of the Wing? Why?

It is preferable for the wing root to stall first. If the wingtip stalls before the root, the disrupted airflow near the wingtip can reduce aileron effectiveness to such a extent that it may be ...
Satya's user avatar
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12 votes
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Why do rockets not fly straight up after launching; wouldn’t that be less atmosphere to traverse?

Since orbiting isn't about altitude, but is instead about velocity (orbiting is the art of throwing yourself at the ground, and missing because you're going sideways so fast), the final goal is to ...
William Walker III's user avatar
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 ...
NMech's user avatar
  • 24.3k
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 ...
david's user avatar
  • 741
8 votes
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What filter is this?

It might be written that way because the transfer function of a second order system is written as: $$ h(s) = \frac{\omega_n^2}{s^2 + 2\zeta \omega_n s + \omega_n^2} $$ where $\zeta$ is the relative ...
Mika Sundland's user avatar
8 votes

Why does the upper wing skin fail in buckling and lower wing skin does not?

In a wing the normal situation is that the aerodynamic force is upwards (resisting gravity). You are right that there is some shear and a fair amount of torsion, but the result is that: the top side ...
NMech's user avatar
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7 votes
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Does every engineering design needs to have a complete theoretical backing or may experimental data suffice?

Are any designs based solely on data from trial and error used in critical mainstream engineering? Usually not. And the reason is that trial and error is expensive and time consuming. As engineers, ...
Daniel K's user avatar
  • 2,646
6 votes

How to make smoke for a small wind tunnel?

In automotive testing we use baby oil. When heated it produces a thick white smoke that is non toxic in low volumes and doesn't stick to surfaces. I built my own smoke tester using a metal pressure ...
Newbie Noob's user avatar
6 votes
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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 ...
TRF's user avatar
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6 votes
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What is the difference between shaft power and brake power?

The short answer is these terms are defined by standards organizations based on specific test methods. These methods specify the engine condition, environmental factors, fuel chemistry, inlet and ...
Phil Sweet's user avatar
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6 votes
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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 ...
mustang's user avatar
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6 votes
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What does it mean that the mass of a propellant tank is at premium?

The rocket equation says that every bit of mass you carry on your rocket is very expensive, especially if that mass is not fuel. Designers of rockets are willing to spend lots of time and effort ...
BobTheAverage's user avatar
6 votes

In case a plane stalls, what should stall first, the tip or the root of the Wing? Why?

It depends on wing geometry. You need to look at the aerodynamic center of the wing, which is the center of effort for perturbation forces. The center of lift (unstalled) will usually be well forward ...
Phil Sweet's user avatar
  • 4,755
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 ...
rghome's user avatar
  • 161
5 votes

How do I cut a crack into a polymer/plastic?

Since you used some specific words in your question, I will respond a certain way. Cracks are generated by mechanical action, and cannot be machined in. They may, in certain brittle materials, be a ...
tillmas's user avatar
  • 241
5 votes

Can a blimp enter Mar's atmosphere as a glider?

I assume that the person you are referring to is Felix Baumgartner, who achieved a maximum speed of Mach 1.25. While this speed is very fast, this is nowhere near the speeds achieved by meteorites, ...
MountainClimberi's user avatar
5 votes
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What prevents the use of electric engines to assist with spacecraft launches? (Space Shuttle Booster Supplement)

Electric turbine engines First off, "electric turbine engines" don't really exist. What you're probably thinking of is an electric version of the jet turbine engine, which is a type of ...
BarbalatsDilemma's user avatar
5 votes
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Can Voyager 1 or 2, theoretically, return to earth if given instructions before their electronic instruments shut down in 2025?

...could either one (or both) of the Voyagers be directed back to Earth at all before electronic shut down? No. It would be impossible since these satellites do not carry any type of course changing ...
Drew_J's user avatar
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5 votes
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the speed of the exhaust

He refers to Tsiolkovsky's Rocket Equation: $$ \Delta v=v_e \ln {\frac {m_0}{m_f}} $$ where: $v_e$ is the exhaust velocity; ${\frac {m_0}{m_f}}$ is the fraction of mass; $m_f$ - the "dry mass"/"...
SF.'s user avatar
  • 6,135
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 ...
niels nielsen's user avatar
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 ...
kamran's user avatar
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4 votes
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Can you postcure epoxy composites outside the mold?

Yes it can be post cured - however, without support there is a risk of sagging or warping, particularly if it is a large and heavy part. Thermal curing is simply a way of speeding up the chemical ...
Donald Gibson's user avatar
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 ...
ConjuringFrictionForces's user avatar
4 votes
Accepted

3D Transformation Between Two Cartesian Coordinate Systems Using Euler Angles

Suppose Frame 1 is a world coordinate frame and Frame 2 local robot frame. The thing that's a little confusing here is that when you transform from Frame 1 to Frame 2, you are saying that you want ...
Chuck's user avatar
  • 3,565
4 votes

How do jets/airplane cold start?

The basic method of starting jet engines designed for this sort of temperature range is to windmill the engine by blowing air into it. All the power for fuel pumping etc comes from mechanical drives ...
alephzero's user avatar
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4 votes
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What is the purpose of building multistage rockets, rather then packing more fuel into a single stage?

As the rocket is propelled upwards, it expends fuel. So there is no need to carry half empty fuel tanks. By splitting it up into separate stages, you can simply drop off unneeded mass.
Andy's user avatar
  • 110
4 votes

Resonance vs flutter

In flutter, the force applied to the structure depends on the deformation and velocity of the structure. Therefore, the force is necessarily at exactly the same frequency as the motion, though it may ...
alephzero's user avatar
  • 12.5k
4 votes
Accepted

Strange simulink error. Professor & TA don't know. Any Ideas?

Your results are correct. I have solved the differential equations in Octave using the ode solver and I get the same results: ...
am304's user avatar
  • 1,831

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