Questions tagged [theory]

Questions about the theoretical aspects of aviation.

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What methods are used to calculate the geometry needed to obtain a bell-shaped lift distribution?

In aerodynamics, what methods do people use to calculate the geometry of a wing (and body) needed to obtain a bell shaped lift distribution? Please go into as much detail as possible for a stack ...
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Bell Shaped Lift Distribution Literature [closed]

Context: I am very interested in learning about the bell shaped lift distribution (BLSD) for the purpose of designing a flying wing with this lift distribution. This is the first academic topic I am ...
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1 vote
2 answers
271 views

Is aerodynamics science still being discoverd? [closed]

Is aerodynamics science still being discovered(like mathematics for example) or everything has already done?
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How calculate lift/drag using static pressure taps in wind tunnel test?

An airfoil section in a wind tunnel has many static taps on its upper and lower surface. These static ports can only read static pressure which acts perpendicularly to the local airfoil surface. In ...
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Help with calculate forces from pressure distribution

V=50m/s deltaPg= -981 Pa deltaPd=490,5 Pa c=1m r.com/PCshZ.png Above is calculate Fz with integrals and with average pressure. Why F3 is calculate from 0 to C/2 if pressure distribution is drawn at ...
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How long is a BAK exam valid for? (CASA Australia))

I am looking to get back into flying, and I passed my BAK theory in 2016. Is that still valid? I want to go straight to PPL so I will be doing PPL theory anyway, just would save me a step, unless I ...
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EASA PPL theory instrumental approaches rules

I am learning for EASA PPL in Czech. I noticed that in some of the books there is chapters about Instrumental Approaches Air Law rules. For example - ILS approaches Parallel approaches Simple ...
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Derivation of the axial force coefficient for an airfoil in terms of the pressure and skin friction coefficients

In chapter 1.5 of Fundamentals of Aerodynamics by Anderson, there is an expression for the axial force coefficient of an airfoil in terms of the pressure and skin friction coefficients. However, "...
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How to choose the right map projections for flight plan?

There are 2 projection of maps that I saw online. UK CAA is a transverse projection map, while ICAO maps are conical. It seems that transverse map is easier for flight planing as straight lines are ...
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1 answer
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If aircraft specific energy is a combination of kinetic and potential energy, why is altitude not a variable in the energy-maneuverability theory? [closed]

The Energy-Manueverability formula is $$ P_S = V \left( \frac{T - D}{W} \right) $$ with velocity $V$, thrust $T$, drag $D$ and weight $W$. $P_s$ represents specific energy, which is a combination of ...
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Which source(s) provides the most authorative and correct flight dynamics theory? [closed]

Just like many curious people, the question: " How airplanes actually work?" occupied my mind for a long time. Different sources gave different answers where most claimed the Bernoulli ...
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Is it possible for an airplane to enter another airplane? [duplicate]

I was making some cool fictional airplane designs and realized that most of my larger airplanes have a bay inside that stores a plane or two. But then I thought, is it even possible to make a plane ...
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2 answers
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Relation between lift force and torque produced in propeller used for vertical take-off and landing aircrafts

There are many answers for this question but none of them are specific. I need to find the exact relation between the lift force of a propeller of specific pitch, attack angle , dimensions and ...
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1 answer
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Is it incorrect to say that "passenger jets like to cruise at higher altitudes because there's less drag"?

I hear it stated quite often that aircraft like to fly high because there's less drag at higher altitudes. $$ \text{Range} = \frac{V}{g} \frac{1}{\text{SFC}} \frac{L}{D} \ln \left( \frac{W_\text{...
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2 answers
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Is the well known textbook-formula for net-thrust oversimplified or do I have a misinterpretation?

In order to understand how Jet-Engines works I came across the "famous" formula for net-thrust: https://en.wikipedia.org/wiki/Turbojet#Net_thrust $F_{thrust} = Q_{out} \cdot v_{out} - Q_{in}\...
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Why is the aerodynamic center for most airfoils located at the quarter chord location?

I've been reading several sources on the location of the aerodynamic center https://web.mit.edu/16.unified/www/FALL/fluids/Lectures/f03.pdf https://en.wikipedia.org/wiki/Aerodynamic_center John ...
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Could gliders be a clean, practical alternative to other forms of transport?

Would it be possible to use pure gliders as an eco-friendly mode of transport? From what I have read so far, gliders can travel at a speed of 100-170 km/h. That would not be able to compete with a jet ...
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12 votes
5 answers
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Could propeller wash provide sufficient lift to take off - even in theory?

I know this seems a crazy thing to ask but it is not the same as lifting oneself by the bootstraps. If you try to lift yourself that way, there are two equal and opposite forces, yet there are ...
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2 votes
2 answers
239 views

Is the Batjet Design Physically Feasible?

I realize the plane is fictional. However, in the Batman Animated Series by Warner Bros, we see this Batjet. So this got me thinking (and I'm not a physicist): is this air frame configuration even ...
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How to determine the number of compression stages given a compression ratio?

I have a personal project to design a gas turbine engine, the main problem that puzzles me is how do I determine the pressure rise in each stage of an axial compressor? Say, I'm planning on a 38:1 ...
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1 answer
535 views

Why does Vmca decrease with increasing altitude?

A question from a mock MEP class rating test: Many thanks for your help.
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1 vote
0 answers
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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 ...
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9 votes
3 answers
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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 ...
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2 votes
1 answer
434 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 ...
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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 \...
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0 votes
1 answer
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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 ...
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1 vote
0 answers
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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 ...
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0 votes
1 answer
384 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). ...
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2 answers
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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 ...
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3 votes
1 answer
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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 ...
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2 votes
4 answers
379 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 ...
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4 votes
2 answers
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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 ...
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10 votes
3 answers
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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 ...
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4 votes
1 answer
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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 ...
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2 votes
1 answer
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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 ($\alpha(z)=\alpha=\text{const}$) and constant section ($\beta(z)=\beta=\text{const}$, and $a_{2\text{D}}(z)=...
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3 votes
1 answer
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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 Airport ...
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13 votes
6 answers
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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 ...
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6 votes
2 answers
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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....
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2 votes
3 answers
979 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 ...
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37 votes
7 answers
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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. ...
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11 votes
5 answers
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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 ...
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12 votes
1 answer
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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 / ...
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7 votes
2 answers
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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 ...
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48 votes
2 answers
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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 ...
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7 votes
1 answer
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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 ...
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4 votes
1 answer
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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 ...
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1 answer
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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 ...
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15 votes
6 answers
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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 ...
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6 votes
2 answers
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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 ...
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11 votes
6 answers
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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 ...
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