Questions tagged [aircraft-design]

Questions about the different choices that aircraft designers (typically aerospace engineers) make in order to create an aircraft.

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How did the FAA decide that firewalls should resist fire for 15 minutes specifically?

I'm searching for information on where the criteria of 15 minutes come from, in which the firewall is subjected to by a flame of 2000 °F (according to the now-obsolete 14 CFR 23.1191). I know that ...
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9 votes
2 answers
3k views

Why do sailplanes have such large tails?

Since a sailplane is focused on performance - what with tricky laminar flow airfoils and all. Eo why this Instead of this It looks to me like that long tail is needed to balance the cockpit. Buy ...
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Would an airliner fly more efficiently on a fatter wing at a low altitude?

Flying at 1000 ft, would giving an airliner wing more girth but not length, allow the plane to fly more efficiently than it normally would at that height? Yes, airliners fly best around 35,000 ft, but ...
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Why aren't isentropic noses and tails used in supersonic aircraft?

An inside out paraboloid would theoretically produce isentropic compression for an inlet cone. But this question is about nose and tail cones on fuselages, and leading and trailing edges of wings. An ...
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For jetliners, how is a swept wing justified over a thin wing?

For a given speed, a swept wing is a fatter alternative to a straight, thin wing. But why? Does not the sweep lengthen the wing and make it heavier? Is the swept wing chosen for the extra fuel tank ...
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4 votes
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Induced drag reduction from tandem wing

Induced drag is proportional to the square of span loading. The normal method to decrease it would be to increase span. This, however, leads to an exponential weight increase. So, my question is, if ...
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2 votes
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Why aren't rudders automatic? [duplicate]

Why aren't rudder pedals automatic or connected with ailerons to keep the nose of the aircraft coordinated with the turn its entering? Wouldn't this make for an easier and smoother to operate aircraft?...
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1 vote
1 answer
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Difference in lift generation for a swept wing and straight wing in subsonic condition

Would there be any differences in lift for a straight wing and swept wing (front or back) with the same airfoil cross section, same chord length, same wing span, and same area when flying in subsonic ...
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Why are aircraft not equipped with nose cargo doors when being converted from passenger to cargo variant?

I'm trying to find any substantiation / design justification why none of the OEM/STC holders are able to provision nose cargo doors on A321 / B757 / B767 / B777 fleet as part of P2F (passenger to ...
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5 votes
2 answers
639 views

In a tailwheel plane, which design elements affect the propensity for a ground loop?

In comparisons between conventional gear vs. tricycle gear aircraft, it is generally explained that the CG location relative to the mains is a necessary condition for ground-looping. But there's very ...
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When the F16 is landing the AOA will be at 11 degrees, but speed modulates more. How is possible to have fixed AOA but not the speed?

The speed in landing pattern is not fixed one due to the weight/drag of the aircraft at the moment(loads of bombs and fuel). But if you speed up then you're going to go upwards don't you(if you keep ...
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What counts as the wingspan of a tandem-wing aircraft?

When calculating the wing-span of a tandem-wing aircraft, like the QAC Quickie Q2, which set of wings do we use for that value? There are two sets of wings, and they both provide lift. In the class, ...
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3 answers
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The slowest to fastest ratio plane [closed]

What fixed wing, and motor, plane or jet, has the largest range between its minimum and its maximum airspeed by which it can safely fly for prolonged periods?
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1 vote
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Why would a plane have these lights on the bottom? [duplicate]

I'm trying to convince someone this is not a UFO but probably just not a commercial plane. What would be the reasons to have the colors of the plane lights like this? The person is claiming because it ...
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2 answers
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When does root bending moment start to become important?

I guess for small aircrafts ,hangliders etc root bending moment is not important at all,because it is relativly easy to achieve sufficient strength ,so their ideal solution will be eliptic..? Does ...
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5 votes
2 answers
528 views

Why do most aircraft with variable incidence tailplane have the possibility to trim much more degrees for nose up than for nose down?

Probably the question will be a little bit confusing but I'll try my best to make it clear. Due the position of the CP with respect of the AC, symmetrical airfoils don't produce pitching moments, but ...
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Has anyone tested or flown permeable wings to increase efficiency?

See this article: Aerodynamic Performance Improvements Due to Porosity in Wings at Moderate Re Was wing porosity ever tested/used for real aircraft? source: The aerodynamic efficiency parameter ...
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3 votes
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Is there a database of aircraft 3D models that are accurately created [closed]

I was just wondering if there was such a thing as the title describes. I am trying to work on a machine learning algorithm that generates aircraft designs based on what it learns from current designs, ...
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0 votes
1 answer
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Why does the Tu-134UBL have a sharp/pointed nose cone?

Russian/Soviet aircraft design has always intrigued me, and even more so when coming across this photo of the Tupolev Tu-134UBL with its pointy nosecone. Having looked up the performance ...
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Why are/were there almost no tricycle-gear biplanes?

A friend recently asked me: are there any tricycle-gear biplanes? After hunting around, we found the Waco AVN-8, but that's all. This causes me to ask: is there an aerodynamic or other design ...
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Is there an ideal lift distribution for human-powered aircraft?

Is there an obvious, ideal lift distribution for human-powered aircraft? Elliptic or Bell (unloaded tips) distribution? For this who will tell the Bell distribution, I have a counter-question ready, ...
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9 votes
2 answers
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How is it possible for the MIG 21 to have full rudder to the left, but the nose wheel move freely to the right and then straight or to the left?

How is it possible that the MIG 21 has the rudder to the left, but the nose wheel moves freely to the right, and then straight or to the left on the runway? See timestamp 1 min 11 sec in this video:
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How do fuel tanks prevent free surface effect? [duplicate]

Free Surface Effect is a fancy term that refers to liquids changing their relative orientation within a container, whenever the container is rotated. So imagine a large plane banking very steeply, at ...
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2 votes
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Wing dihedral in a biplane

Would a biplane be able to fly if the upper and lower wings were in opposite dihedral? Imagine a wing configuration similar to the fictional "X-wing" design from StarWars. What would be the ...
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4 votes
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Why did the design of the Boeing 247's cockpit windows change for some models? [duplicate]

Have a look at this article on a famed example of the 247. The image at the top is the aircraft during its flights with the RAF, likely some time in 1944. Note the reverse-slope windows that are a ...
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1 vote
4 answers
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Are canards actually more efficient?

Another post here triggers this question; Since I was a kid I have read endless articles about how canards are more efficient because both wing-like surfaces are lifting, whereas a tail surface is ...
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0 votes
1 answer
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Was the P-82 twin Mustang better than the P-51D? [closed]

The P-82 twin Mustang was made to replace the P-51D in the escort role. It was faster, and had two engines with two pilots. It also had a better armament but wasn't as maneuverable as the P-51D. Which ...
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Why do almost all overwing exit slides open over the trailing edge of the wings, and almost none over the leading edge?

Almost all narrowbody jetliners, and many widebodies as well, use overwing exits to augment their evacuation capabilities; to escape the aircraft, a passenger or crewmember in the exit row pops the ...
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1 vote
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Does a RC glider always loop when launched?

In the below video, the guy sets "launch mode" for hand launch where he adds a little bit of elevator. Will a glider always loop up when launched horizontally, even if the tail is set to ...
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317 views

What is the manoeuvre point?

a centre of gravity position at which stick force per g becomes zero What does this mean? If the centre of gravity happened to be at the maneouvre point, would there be stick be very light in the ...
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3 votes
3 answers
851 views

Can aileron differential eliminate adverse yaw?

Can aileron differential completely eliminate adverse yaw?
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4 votes
2 answers
233 views

Calculate pitch balance of RC glider?

Today, I played with styrofoam gliders with my kids; I made an asymmetric wing, asymmetric horizontal tail, symmetric vertical tail, and attached these to one stick for the fuselage. I've had big ...
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1 vote
1 answer
142 views

Can Bell-lift distribution increase glider efficiency(L/D)?

Can a Bell-lift distribution without a rudder has higher overall efficiency (L/D) then current gliders, if the wingspan is not limited? (Is it really possible that most of aerospace engineers don't ...
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4 votes
3 answers
918 views

Why do tapered wings not stall at the root first?

Why do moderate tapered wings stall first at mid-wing section and high tapered wings stall at tip first? The effective AoA should be always higher close to the root? (considering no geometric or ...
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1 vote
0 answers
57 views

Texts on aero-engine structures

I have been scouring the web for resources on aero-engine structures and structural design (preferably civil turbofans) but unfortunately it seems like they are hard to come by. I would like dedicated ...
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1 vote
1 answer
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How do you calculate the optimal cruising speed of an airfoil?

I am working on a school project (aircraft design). I would like to know how to calculate the cruising speed of a given airfoil. For example, if I have a NACA 5613-35 airfoil (that is the NACA 4 digit ...
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1 vote
2 answers
175 views

Lift Pressure Distribution [closed]

If the pressure goes always from high to low, we should have a compression, due the lower pressure of the air stream over the upper surface, and an expansion in the airstream in the lower surface. So ...
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1 vote
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Do aircraft designers gather real data to confirm their design (CFD, wind tunnel) data?

What tools and techniques are used to get real data test to confirm the values that are obtained by computational fluid dynamics (CFD) calculations and wind tunnel testing? Is this standard procedure ...
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8 votes
1 answer
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What's this part on the wing of BAE Systems Avro 146-RJ100?

It was always a question that what's this part on the wing of BAE Systems Avro 146-RJ100: Is it kinda aerodynamic component?
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1 vote
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Is this new intake of Airbus and Boeing aircraft's NACA inlet?

Anybody knows the name of this intake? look at the bellow images: Why don't Airbus and Boeing use the conventional NACA inlet? Why did they invent this kind of intake? I can see some parts of these ...
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Why and how were "eybrow windows" helpful in tight turns?

It is written in some answers that "eybrow windows" were helping pilots in "tight turns". How did this work? These tiny windows seem located right above the head, so I would not ...
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1 vote
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What are these two circular areas on the fuslage of Fokker 100? [duplicate]

There are two circular areas on the fuslage of Fokker 100 which are shown in the bellow image. What are those? Why are the above these two areas written "do not paint"?
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1 vote
1 answer
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How to calculate the zero lift drag coefficient for a wing with data from airfoiltools.com? [closed]

I'm currently trying to write a script in python that I can use to optimalise a flying wing aircraft. I've run into a problem when trying to use data from airfoiltools.com. I've tried to calculate the ...
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2 votes
1 answer
103 views

Can any conclusions about aerodynamic efficiency be drawn on the basis of fly-by noise?

Edit: I'm beginning to think this is more suited to the physics stack exchange, but I'll keep this here for a while... Being bored mindless, surfing the interwebz, I came across this video, where a ...
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3 votes
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Why do the aircraft made by the Soviet Union have fans in their cockpits? [duplicate]

Surely the countries which were a part of the Soviet Union were not so hot then why are there fans in their cockpits? e.g. TU-134 or IL-76 or AN-124
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5 votes
2 answers
405 views

What is the benefit of a horn control surface?

Like the one above. Is it just so that you can hinge closer to the leading edge of the aileron or control surface? Why did the designers of the ATR-72 elect to use this feature?
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1 vote
1 answer
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Does ELMS inhibit cabin pressure alarms on the 777, and would the MEC Override Vent be stuck open following an electrical failure?

I found this article rather interesting, but like most things on the internet, they can be wrong. I couldn't think of a better site to address this question. This user says: when ELMS takes over ...
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1 vote
1 answer
330 views

Why aren't grid fins used as wings for low speed aircraft?

Grid fins are used "commonly" in aerospace - usually for things like control of guided bombs or spacecraft. The most obvious example is SpaceX's use on the Falcon 9, but the US and Russian ...
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2 votes
1 answer
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Why is an air intake located on the root of the tail on some aircraft?

There is a small air intake on the root of the tail of some aircraft, especially those with engines near the end of the aircraft. What is it and why is it located there?
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2 votes
1 answer
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How can I modify a fuselage to increase the payload?

I'm designing a regional turboprop for a university assignment. The design requirements are very similar to the Dash 8 Q400 in terms of passenger capacity (90 pax), speed, range, runway length ...
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