16 votes

How to make smoke for a small wind tunnel?

The testing of ventilation systems and of building air-tightness is done using smoke sticks or similar - non-toxic smoke generators that produce no ash residue. One of these may be suitable for your ...
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  • 3,701
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 ...
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  • 432
12 votes

Would a "lifting body" design be useful for a train car?

I won't say it's not possible to make a noticeable difference. But I would say that it's pretty darn unlikely. The lift and drag forces on any body generally depend on the velocity of the body ($v$),...
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  • 1,966
11 votes
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Could air-launched space planes reach escape velocities?

Believe it or not, we could have done this 50 years ago, if government funding hadn't been pulled from a project at the last minute. Frustratingly, after years of work by scientists, engineers and ...
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  • 2,485
10 votes
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Is interference between aircraft an issue for fly-by-wireless technology?

Cross-interference between aircraft is a high unlikely event because all commercial aircraft designs have to pass DO-160 environmental testing requirements. Among the DO-160 testing specification is ...
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10 votes
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How is lift related to airspeed?

Quadratically. NASA page #1 says that, as an approximation, $$\text{Lift}\propto v^2$$ where $v$ is the airspeed. NASA page #2 says that, for a better calculation, $$\text{Lift}=av^2+bv+c$$ where $a$, ...
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  • 2,485
9 votes

Could air-launched space planes reach escape velocities?

Now, I wonder if an air-launched spacecraft in the next 20 years realistically could really fly us to the moon - that is, could they reach escape velocities? Air launch to LEO: Done now Air launch ...
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9 votes

Would a "lifting body" design be useful for a train car?

You don't want to decrease the downward force on the wheels because that is your primary means of slowing down in an emergency. It already takes a while to stop a train, don't make it any longer. ...
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9 votes

Is interference between aircraft an issue for fly-by-wireless technology?

To add to what Russell said, it would take a very stupidly designed protocol to allow the comands from one aircraft to control the other, even assuming that cross-reception is good. As a everyday ...
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  • 11.2k
9 votes
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Convergent-Divergent Nozzle Design from Exhaust Velocity

You're not that far off. In your analysis, you've just neglected the fact that the gas will accelerate as it passes through the converging nozzle. This is basically converting potential energy, in ...
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  • 1,966
9 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 ...
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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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  • 22.6k
8 votes

Is interference between aircraft an issue for fly-by-wireless technology?

Modern communications systems are able to achieve essentially any desired data rate and degree of message integrity in any well-enough-defined environment. It's "just a matter" of the degree of effort,...
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8 votes

How is lift related to airspeed?

As has already been mentioned, the primary relationship is that lift goes with the square of the airspeed. To give you some intuition as to why this is, consider what a wing does. As it moves along, ...
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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 ...
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7 votes

What is the difference between aeronautical and aerospace engineering?

A space engineer deals with objects in space: from satellites, space stations, space vehicles and space probes to space debris. Space means high launch vibrations, vacuum, radiation concerns, high ...
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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, ...
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  • 2,511
7 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 ...
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  • 22.6k
6 votes

How are wind tunnel models used when designing supersonic aircraft?

In the Fluid Dynamics community about 40 years ago, the group was primarily divided into experimentalists and theorists. However, at that time CFD was quite new, had to be run on expensive ...
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  • 493
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 ...
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6 votes
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Aircraft force in g's experienced by pilot

The acceleration is given. However, the upward force is $6mg = F_{up} - mg$ $F_{up} = 7\cdot mg$ In case of no acceleration: $0 = F_{up,normally} - mg ==> F_{up,normally} = mg$ If we neglect ...
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6 votes
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Logic behind location of shear centre

why is it logical to have the position of shear center at the location of intersection of line of action of shear force and x axis? That statement isn't logical. I think you have misunderstood how ...
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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 ...
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  • 251
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 ...
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  • 3,425
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 ...
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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
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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 ...
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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 ...
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  • 3,425
5 votes
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Did Otto Lilienthal ever experiment with non-human-powered aircraft?

I'm going to answer my own question because just before posting it I found an answer. The Otto Lilienthal Museum has a comprehensive list of Lilienthal's designs. One is listed as the "small wing-...
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