Questions tagged [theory]

Questions about the theoretical aspects of aviation.

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26
votes
8answers
3k views

Is there an aerofoil that gives reasonably good lift for both air flow directions: forward and backward?

Could an aerofoil be designed to give reasonably good lift for both flow directions? I was motivated by this related question on Aviation SE: Can a plane fly backward if its propeller is in reverse? ...
1
vote
0answers
51 views

Is there any bibliography for triplane aircraft design?

I've been tasked with designing an RC aircraft that has the greatest lift force for a specified wingspan, total length and takeoff velocity, and thus have been studying the different wing ...
8
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3answers
3k views

How does the bypass air provide thrust?

To my knowledge, bypass air produces 80% of total thrust. But I don't understand to how it does that. By accelerating the air, by increasing the speed or increasing the pressure of the air? Is it ...
11
votes
6answers
6k views

Why does an aircraft pitch up when the speed increases?

Can anyone please explain why aircraft pitches up when the speed increased? (please consider an aircraft, Wing AC, CG and Tail AC lies on a line.) The ideal explanation I'm looking for should have ...
15
votes
6answers
3k views

What is the optimal bank angle to accomplish a given turn in a glide?

For an aircraft in a glide, what—if any—is the optimal bank angle to make a given turn while maximizing glide distance and maintaining published best glide speed? In other words, at a constant ...
2
votes
1answer
243 views

Would adding a slat and a slotted flap increase the max CL of a multi element airfoil to 6.5?

Would adding a slat and a slotted flap increase the of a multi element foil to 6.5? I understand, as a general rule, the max $C_L$ for a classic NACA airfoil is as follows: Base: 1.5 Slat: + 0.7 ...
9
votes
3answers
3k views

What is the physical meaning of circulation found in Kutta condition?

The Kutta–Joukowski theorem is applicable for 2D lift calculation as soon as the Kutta condition is verified. When this is the case, there is a circulation $\small \Gamma$ around the airfoil. My ...
30
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4answers
6k views

Principle of aerodynamic lift: are misconceptions also taught in flight schools?

Describing lift as the result of "equal transit time" on both sides of an airfoil is a fallacious theory widely found in technical books and articles for general public (see below for details about ...
0
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1answer
119 views

Pitching moment as a pure moment and its measurement with a homemade force balance

In mechanics, we learn that a force $F$ acting at a certain application point $P$ can exert a torque (also called moment of the force) about another arbitrary point $Q$ in the plane, i.e. $\tau= F \...
2
votes
4answers
217 views

What is formula for induced drag in stalling regime?

I'm wondering what is the formula for induced drag in a stalled regime, i.e. in a regime where the $C_L$ (coef. of. lift) has started to decrease but is still nonzero. I've a feeling that the ...
0
votes
1answer
83 views

Would turbine blade twist change if all conditions except the density of the fluid remained the same?

While designing a turbine, the blade twist is apparent from the velocity triangles, and this analysis only depends on the velocity. However, would there be any difference for different media? When ...
3
votes
1answer
140 views

Vortex Lattice Method with eliptical panels

I implemented vortex lattice method (or deeper here) into my aircraft simulation program. The problem is that sometimes trailing vortex filaments from Horse Shoe Vortexes of main wing hits panels of ...
1
vote
0answers
59 views

What is the relation between solidity and lift coefficients?

I've seen this graph in a couple of places. I'm not sure what it's supposed to mean, as the formulae I've seen in the papers cannot be found in any standard book or reference. Please let me know if ...
29
votes
11answers
17k views

Why can gliders fly for so long?

When you throw a paper airplane, it flies for a couple of seconds before losing speed and stalling. With a glider, it has a very long wingspan, but you take off with another plane or winch tow pulling ...
21
votes
4answers
3k views

Would an aircraft with contra-rotating propellers longer than the plane's wingspan be able to fly?

I enjoy taking the time to try and visualize how fictional aircraft might actually work in reality. Unfortunately there are some that seem highly impractical from an engineering student's point of ...
0
votes
1answer
351 views

How to refute this geometrical method to find MH370? [closed]

A geometrical method to find MH370 has been published on the Net (see images below). I am sure it is wrong (because if it were that easy, thousands of people would have had this idea back in 2014). ...
9
votes
5answers
3k views

Are aircraft capable of sustained inverted flight at constant altitude?

Inverted flight as a part of manouveres, dogfights, acrobatics is fairly common but my question is: Are any aircraft capable of sustained inverted flight without losing altitude? e.g. Could you fly ...
0
votes
2answers
490 views

What's a typical first lesson of glider flying like?

What is a typical first lesson for glider flying like? Does it usually include a pre-flight mini lecture on basic theories at all, or if not pre-flight, do instructors usually spend some time on the ...
18
votes
2answers
2k views

When does the use of afterburners save fuel?

An afterburner uses a lot more fuel for a little more thrust (rule of thumb: 50% more thrust for 5 times the fuel flow with full dry power). Is a flight maneuver possible where using the afterburner ...
4
votes
2answers
250 views

If the the body and it's wing is mostly covered with solar panels and flies with electric motors, is it possible for that aircraft to fly?

First before I say anything else, this is indeed a stupid question. It would be most likely heavy, bulky, and expensive. But theoretically, is it possible to fly with only Solar energy? What does it ...
4
votes
1answer
9k views

How are Cd and Cl calculated from Cp data?

Given pressure coefficient data for corresponding x/c (position along chord) values on a wing, I am looking to calculate coefficients of drag and lift. Here's what I have: b, MAC, S, sweep angles at ...
2
votes
0answers
218 views

How to demonstrate that an elliptical circulation distribution can be induced by an elliptical chord distribution?

I intend to demonstrate that a wing with an elliptical chord distribution, without torsion ($\alpha(z)=\alpha=const$) and constant section ($\beta(z)=\beta=const$, and $a_{2D}(z)=a_{2D}=const$), can ...
4
votes
1answer
564 views

Where does upward momentum come from in leading edge vortex?

I believe I am beginning to understand how a leading edge vortex creates lift. Faster air creates a lower pressure above the wing making lift. But I am hoping to get another view of this in terms of ...
3
votes
1answer
927 views

Am I correctly calculating the density altitude?

I came across the following question while studying for the FAA PPL written test: Determine the density altitude for these conditions: Altimeter setting: 30.35 Runway temperature: +25°F ...
11
votes
1answer
1k views

What is the meaning of “Docile pitch behavior” in the context of Pugachev's Cobra?

In another answer on SE Aviation it is mentioned that the ability to perform Pugachev's Cobra in a non-thrust-vectored aircraft needs "docile pitch behavior of the airframe up to approx. 110° angle ...
17
votes
7answers
5k views

How to build a 2 mile long runway on a 1 mile square island?

On Puzzling.SE I found this question: You have a 1 mile long x 1 mile wide private island that you wish to turn into a resort. A plane requires a 2-miles long runway to take off. What do you do?...
38
votes
7answers
21k views

Is gravity less on an airliner at cruise altitude?

Is the force of gravity less on an airliner at cruise speed and altitude? I'm not talking about a special reduced gravity flight with a parabolic flight path, just a typical long distance flight. ...
6
votes
2answers
373 views

Would it be feasible for a typical passenger jet to carry along its own Oxidizer?

We know that many Space Shuttles / Rockets etc. carry their own oxidizer with them. This is partly because at the heights they operate the atmosphere is too rarefied to have enough oxygen to sustain ...
7
votes
2answers
3k views

How to start deriving longitudinal equations of motion for an aircraft?

I hope this is a relevant place for me to ask a math question regarding aircraft design. I am trying to understand how one would implement a controller to control the pitch angle of an airplane for a ...
12
votes
1answer
693 views

What are the relative braking contributions from wheel brakes, spoilers and thrust reversers?

What is the relative contribution to braking forces in a typical large commercial aircraft from the three different devices contributing to braking after touchdown: Wheel brakes Speed brakes / ...
10
votes
1answer
483 views

Why are the power and drag curves called polars?

See Wikipedia:Drag polar and Wikipedia:Polar curve (aviation) for example. These curves are not on a polar coordinate system. Why are they called polars?
5
votes
2answers
382 views

Can a gyro-copter soar?

If one centers the gyro-copter in a thermal and then simulates a hover facing headwind; can the gyro-copter climb up like that ? Is it technically possible or is it advisable....
2
votes
3answers
675 views

Is there any engine that doesn't use a propellant to produce thrust?

As far as I know, all engines used in aircraft produce thrust by means of some propellant: kerosene, hydrogen peroxide etc. Maybe I've missed something, but could you tell me, are there any engines ...
7
votes
1answer
627 views

Do frequency response / Bode plots for an aircraft or helicopter come from modeling or empirical testing?

I was intrigued while reading an article by this snippet: Examination of the V-22’s frequency response plots (Bode plots) in 2000 showed that the aircraft failed to meet the basic stability ...
39
votes
2answers
22k views

Why/when is the blunt nose better?

Most large aircraft and some fighters have blunt, rounded nose cone. OTOH many fighters (that don't use the nose for air intake) and notably the two supersonic airliners (Concorde, TU-144) have the ...
7
votes
2answers
1k views

Would a 90 kg object jettisoned from an aircraft create a detectable movement?

I was reading the description of an old hijacking which has this snippet of interesting information: After takeoff Cooper told Mucklow to join the rest of the crew in the cockpit and remain there ...
11
votes
6answers
21k views

Can planes take off from a treadmill?

Note that this is more of a Physics question than an Aviation one. This topic has been extensively covered on the Physics Stack Exchange site, and the answers there are recommended reading for ...
8
votes
3answers
4k views

How long would a cruising aircraft take to crash if everyone spontaneously vanished?

I recently saw a movie in which what appeared to be a Lockheed C-130 Hercules was suddenly without occupants. They did not move or exit the craft, they simply vanished. I assume that the craft ...
7
votes
1answer
1k views

Are Aircraft yokes self centering in non-auto pilot mode?

In a typical car steering wheel if you release it while the car is in motion, it will return to its center, neutral position. What's the corresponding situation in an airplane? Is a yoke self ...
6
votes
1answer
507 views

Is there an equation which allow us to perfectly match a helix propeller and an engine?

Is there an equation which allow us to perfectly match a helix propeller and an engine? I'm looking for an equation that allow me to correctly dimension an helix propeller for my engine. I mean that ...
13
votes
1answer
791 views

How can I get the velocity-power curve for a particular aircraft?

The answer for How does wind affect the airspeed that I should fly for maximum range in an airplane? refers to a velocity/power-required curve. As far as I can tell, this curve can't be deduced from ...
6
votes
2answers
3k views

Is the maximum lift-drag ratio found at minimum drag?

Figure 10-5 of the FAA's Pilot's Handbook of Aeronautical Knowledge shows: I didn't think $L/D_{MAX}$ coincided with $D_{MIN}$. Is this Figure accurate?
5
votes
2answers
8k views

What is the definition of “best L/D”?

What does "best L/D" mean? Is it meaningless without context? Do you need to know "best for what?" Or, is it synonymous with max L/D?
39
votes
4answers
4k views

Is a rotary wing craft capable of supersonic flight?

Just what the title states. Since the Wright brothers, aviation technology for fixed-wing craft has advanced by an order or more. Rotary wing craft on the other hand (I know little about aviation; ...