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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15
votes
5answers
6k views

Why are 3- or 4-seat gliders so rare?

Sailplanes capable of climbing in rising air (not troop transports, which can only descend after the towrope releases) have one or two seats. I know of only one type with more, the Schweizer SGS 2-32 ...
0
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1answer
100 views

How do I determine the diameter of my propeller at high altitudes? [duplicate]

I'm designing a electrically propulsed HALE UAS and I need to find the diameter of my propeller to find my thrust. Is there an equation for propeller diameter that doesn't rely on knowing my thrust or ...
42
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3answers
8k views

Is it dangerous for a supersonic aircraft to fly at exactly Mach 1?

If a plane that is designed for supersonic flight, say the Concorde, kept flying at exactly the speed of sound, would there be any danger in that? If so, what could get dangerous at constant Mach 1 ...
0
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1answer
111 views

What are the difficulties in building transonic airliners?

If the sonic boom is an issue, why don't we build airliners that are capable of flying just below Mach 1? Big airliners fly at Mach 0.85 at most, and the record for current sub-/transonic civilian ...
1
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1answer
384 views

What is the difference between aircraft integration and assembly?

I have never had a clear understanding of the difference between aircraft assembly and integration. My understanding is that putting together the airframe alone is assembly and putting together the ...
0
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1answer
99 views

What thrust is used for thrust to weight ratio?

Performing some preliminary calculations for an aircraft design I have and was wondering what thrust I should use to calculate thrust to weight? The thrust calculations I have, vary due to speed (...
2
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2answers
239 views

Where is the center of gravity on a tiltrotor?

From what I understand, the CG of full-sized fixed-wing airplanes need to be forward of the wing's center of lift for stability. But the CG of a helicopter must be directly below the rotors since it ...
0
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2answers
229 views

Why do privater jets often fly at or above FL 400, but large commercial aircraft are usually in the range of FL 300 to FL 400? [duplicate]

With rare exceptions (like the Embraer business jet, which is simply their commercial jet with a different interior), almost all private jets fly in the more rarified air above FL 400. But, if its ...
2
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1answer
271 views

Why are some modern military trainer aircraft so bulky?

Modern military trainer aircraft are a lot wider and bulkier than the previous generation. Especially the canopy looks oversized. You can see this in the Boeing/Saab T-7 Red Hawk, Alenia Aermacchi M-...
1
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1answer
243 views

In wing design, how is factor of safety related to G-limits?

What does factor of safety mean with regard to the maximum G force an aircraft is rated for? Does a rating of 3Gs mean the same as a safety factor of 3? Or is there some extra margin?
3
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2answers
184 views

Optimizing the airplane for best cruising altitude and velocity

In the conceptual phase of the design, I am optimizing various entities of an airplane for the best cruising altitude and speed to reduce the cost, which also includes MTOW and fuel weight. Consider a ...
4
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2answers
405 views

What made Concorde so heavy?

The Concorde burnt five times more fuel per passenger mile than the 747. A huge contributor must have been the immense empty weight per seat, three times that of the B747. B747-300 Concorde Empty ...
24
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2answers
6k views

How exactly did engineers come to the final design of jets like the F-16 or SR-71?

I ask this question because I read somewhere that SR-71 was designed in 60's with hand calculations and drafters and when engineers later tried to improve the design with modern computers they found ...
1
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2answers
274 views

What justifies a biplane over a braced monoplane?

Biplanes became the first airplanes to enter service due to their structurally efficient design being more suitable for the weak materials then. This efficiency comes from the two wings acting as the ...
2
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1answer
183 views

Is a flying wing optimal for high altitude craft?

One of the biggest problems with flying wings is their sheer thickness, which creates excessive drag. However, since high altitude craft need bigger (and thus thicker) wings anyway, and since weight ...
1
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1answer
258 views

What surface materials do airplanes use to reduce friction?

Full swimming body suits were banned from Olympic Games a few years ago because some materials have less friction than skin and contestants that could not afford gear to increase their performance ...
-3
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1answer
162 views

What should be the thrust weight ratio for takeoff? [closed]

I am doing some calculations for preliminary design of an airplane and I was wondering how I would go about determining the minimum thrust to weight ratio needed for the aircraft to takeoff. Which ...
6
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1answer
2k views

Why do propellors have white markings on their tips? [duplicate]

Why do propellors have white markings on their tips? Here are a couple of examples:
56
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8answers
11k views

Why don’t airplanes use turn signals?

Why don’t airplanes use turn signals like cars do? Would this improve safety for ground operations at uncontrolled airports? Could a similar concept be used to indicate in air maneuvers? For example: ...
19
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4answers
7k views

Why don't modern fighter aircraft hide their engine exhaust?

In many photographs, the F-4's unique geometry hides one or both engines. I've been told that this is one of the terrific accidental features of the F-4, as it would help shield the hot exhaust from ...
2
votes
1answer
138 views

How do I find the shear center of an unsymmetrical airfoil?

I'm quite a newbie of these systems and I am designing the wing box of a drone. I know where I want my shear centre. However, I have been trying to determine the shear centre of my idealized airfoil. ...
0
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0answers
105 views

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 ...
9
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2answers
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 ...
0
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1answer
215 views

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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0answers
102 views

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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2answers
230 views

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 ...
4
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1answer
163 views

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 ...
2
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0answers
168 views

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?...
1
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1answer
168 views

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 ...
0
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3answers
272 views

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 ...
5
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2answers
594 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 ...
-2
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3answers
379 views

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 ...
2
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1answer
113 views

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, ...
5
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3answers
2k views

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?
1
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0answers
156 views

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 ...
0
votes
2answers
108 views

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 ...
5
votes
2answers
474 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 ...
4
votes
2answers
186 views

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 ...
3
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0answers
65 views

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, ...
0
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1answer
216 views

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 ...
14
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4answers
3k views

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 ...
1
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3answers
220 views

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, ...
9
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2answers
2k views

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:
0
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1answer
106 views

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 ...
2
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4answers
229 views

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 ...
4
votes
1answer
935 views

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 ...
1
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4answers
395 views

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 ...
0
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1answer
117 views

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 ...
4
votes
1answer
409 views

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 ...
1
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1answer
142 views

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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