New answers tagged

3

For maximum altitude, the primary distinction to be made is whether the airplane flies at subsonic or supersonic speed. Subsonic speed There are several factors for maximum altitude, but the maximum altitude of specially developed high altitude airplanes is determined by the coffin corner which in turn depends on the product of lift coefficient and Mach ...


0

"A braced monoplane has most of the structural advantages of a monoplane with less of the aerodynamic disadvantages" Very surprising statement since, in the previous paragraph it is said: "the extra wing produces 20% more lift with 100% parasitic drag increase". Actually, with spars, cantilever wing structure, and the aerodynamic ...


7

In a way, yes. By using smooth metal surfaces with countersunk rivets, modern aircraft use a surface with low friction already. In the past, wooden structures were varnished to give them a smoother surface. In the second World War, German crews would polish the normally matte paint of some of their airplanes to eke out the maximum in top speed. There have ...


4

Without knowing more about what you are designing it is impossible to come up with a specific number. But there are a number of factors that you should take into account: the lower the thrust to weight ratio, the longer it will take to accelerate, so the longer the required runway will be. During the take-off roll the lift can usually be neglected, but the ...


25

It is so you will see a circle when they are turning. Without contrasting bright tips turning propellers are invisible, and pose a grave risk for someone who is deaf, wearing heavy hearing protection, or distracted by other noises.


0

Not being in aviation, I would tend to think that the main reason that signals aren't utility for ground taxiing (which seems the most practical\potentially useful place) is that planes movement are generally setup to prevent the short reaction time we regularly have in cars. "Reasonable" car spacing, and traffic lights, are such that there is ...


6

How they were invented As @Bianfable wrote: They were first used on the Douglas DC-9. On the Douglas quad-jet DC-8, leading-edge slots are used, compared to the Krueger flaps used by Boeing for its 707:[1] A DC-8 door-operated slot next to an engine pylon (diecastaircraftforum.com) When Douglas put those slots on the DC-9 (tail-mounted engines) during ...


3

There are pretty strict rules on how planes should travel on the ground. They are generally directed by ground control in the tower, and if they come upon another plane there are guidelines to who has right of way, and unlike car drivers, pilots generally know and follow the rules.


-1

Aircraft accidents are not caused by "that plane made an unexpected turn", but by "that plane came out of nowhere". Also, cars operate on a flat surface. There are 3 choices: Left, Right, Straight. Aircraft maneuver in 3D. How would turn signals express a climbing turn? A loop?


-1

Although all of these answers are very good (and correct), they are missing an important fact: planes try to go on the most direct routes (unless mountains, or other landmarks that affect flight, are in the way). This means that most planes will be traveling in a straight path, so turns aren't applicable. That too planes are given routes that do not travel ...


9

Airplanes don't coordinate visually because they can't The other answers are correct, but they all seem to miss an important point: airplanes barely see each other! Because (and in contrast to e.g. cars): they can be anywhere in 3D, not just 2D on specific streets they are incredibly fast (think of at least 2x the speed of a car on the highway) they are ...


50

I think the points raised in other answers are good, but they miss the essential difference. Cars choose from a discrete set of options, but planes do not. When you indicate left when driving you are communicating to other traffic that either you are taking the next left turn, or that you're changing lanes (depending on context). In some situations the exact ...


1

While not capable of level-flight supersonic performance, the Korean War era F-86 Sabrejet was capable of slightly exceeding Mach 1 (I recall the figure as Mach 1.05) in a shallow dive. This was one of its performance points over the (otherwise similar) MiG-15, which was Mach-limited and became nearly uncontrollable in the transonic regime. While not ...


0

I'd like to add a small point not mentioned in the good answers already here. Piloting a different aircraft model needs training, much more so than driving a different car model. I don't know to which extent regulation demands formal retraining for general aviation. But for sure there is a real temporary cost in safety and comfort when switching with ...


0

Is it true that the F-4 was harder to target with heat-seeking missiles due to the shape of the empennage? If so, then why don't modern aircraft use a similar design? I have no comment on the ability of the tail design making the aircraft more difficult to target with heat seeking missiles but I can give a few educated guesses on why this tail design is not ...


16

Aircraft have radios with which to communicate their intent. Cars do not. Pilots should be utilizing these radios even at uncontrolled airfields. A good mantra to have is that there are no uncontrolled airfields. Just pilot-controlled airfields. I will communicate my intent on the Common Traffic Advisory Frequency before entering the movement area of any ...


3

A member of the Century Series, the F-102 was the USAF's first operational supersonic interceptor and delta-wing fighter. (Wikipedia: Convair F-102 Delta Dagger) Its innovative "coke bottle" fuselage design to lower the drag at the wing root was critical in achieving supersonic flight. Me at Saigon with my F102


76

At uncontrolled airports, there is rarely enough traffic for signals to be needed, and pilots should (though are not required to) communicate with each other on CTAF—an option that cars do not have. In the air, if you're close enough to see a turn signal, you are way too close and need to immediately follow the collision avoidance procedure. More generally, ...


33

There are a few which do (none of them in production, though) and the reason is the added weight and restrictions in varying nozzle geometry for best efficiency. The tail arrangement of the F-4 is the result of its heritage. Early McDonnell jets all had the fuselage extended past the engine exhaust in order to shift the engine mass forward, near the wings, ...


10

No. The empennage on the F-4 was never laid out in that manner to shield against IR guided missiles tracking it not could the design aid in doing so. Like the increased dihedral or the outboard sections of the wing the severe anhedral angle of the tailplane is more or less a cheap patch for poor aerodynamic design. The 23° anhedral to the tailplanes were ...


15

The heat-seeking missiles of the time when the F-4 entered service were fairly limited compared to newer designs, and had to be targeted at an angle where they had a good view of the tailpipe of an aircraft. This changed somewhere around the late 70s when all-aspect missiles were introduced, allowing aircraft to be targeted from other angles as well. I've ...


0

First, analyzing the data shows some lift and drag benefits at low AOA but much worse performance at higher AOA. Why? Because with undercambered wings, at higher AOA the concave bottom creates a higher pressure lifting "bubble" which a "permeable" area hurts. At lower AOA, a little "bleed" through the wing may enhance lift and ...


0

DH108 (DeHaviland) Powered by the 3000lb thrust DH Goblin and piloted by John Derry 6th Sept 1948 achieved Mach 1.07 in a dive.


2

Gliders spend a lot of time circling, entering thermals dodging others while ridge flying and generally performing manoeuvres designed to terrify most power pilots. Henry Ford remarked 'there is no substitute for litres'. For a glider pilot 'there is no substitute for span'. Mine is a titchy 15 meters. And even that represents a very large moment of inertia ...


21

Keep in mind that not all sailplanes are designed for extremely light weight. Decreasing the weight also decreases the minimum sink rate, but doesn't help the still-air glide ratio, and actually hurts the glide ratio against a headwind. Even in sailplanes that are designed for very light weight, designers have sometimes thought it worthwhile to employ a ...


6

Silly comments aside, "fat" wings, ones with greater camber, were all the rage 100 years ago when designers found they could eliminate draggy external bracing by building cantilever wings. Hugo Junkers was one of these pioneers. Wind tunnel testing also showed increased camber not only increased lifting efficiency, but also, combined with large, ...


2

Pressurized aircraft such as LearJets are designed to maintain sea level pressure up to a certain altitude, say 28,000 feet. Above that altitude, the cabin pressure begins to fall so that at 43,000 feet in this example, the cabin pressure is about 5,000 feet of altitude. However, air ambulances can tell the tower what altitude they will fly so that they ...


2

I have two keychains both with pieces of fuselage from Virgin Atlantic 747-400's. One is 1.6mm thick and the other is 2.8mm thick!


0

Also, you have to think that the air does not hit the wing at a 90* angle to the leading edge on a swept wing. The shape of the wing ribs is not necessarily the shape that the air is being in contact with. It is probably going to be a longer trip than the shape of the rib in certain areas of the wing, like close to the tip, where both leading and trailing ...


1

One area where geodesic airframes have seen a recent resurgence, is 3-d-printed model airplanes. I've seen an example where the fuselage and wings and tail surfaces were all of open geodesic construction, similar to the well-known Vickers "Wellington". The model was covered by a heat-shrunk plastic film such as Monokote. Here's a website featuring ...


2

As other answers already note, the major attraction of geodetic framing was to provide a lighter and stronger structure than internal framing, with the not inconsiderable bonus of leaving much more internal space for fuel and payload. The geodetic frame could directly carry a fabric skin in a streamlined shape, instead of requiring the addition of (heavy) ...


4

Yes, sweep makes a wing heavier and less efficient. But making the airfoil of a straight wing thinner runs into diminishing returns and also will drive up mass. Since a thin wing needs to create the same lift as a thicker one, only the local speed increase from thickness can be tackled by making the airfoil thinner. The speed increase necessary for lift ...


2

The downwash is about as high as wide, and angled only by a few degrees (more at slow speed). So the longitudinal distance needs to be many times longer than the wing span to make the wings independent. And it would still be less efficient than increasing the span: If you double the span, you will decrease induced drag four times. If you half the lift, you ...


2

Since both the lift curve slope and the effective angle of attack are reduced by the cosine of the sweep angle at quarter chord, the lift coefficient of a swept wing at the same geometric angle of attack is reduced by the square of the cosine of the sweep angle. Also, the pressure distribution over chord differs between straight and swept wings, especially ...


2

Addressing only why gliders, even with only one main wheel, rarely ground loop. Point by point: No toe-in/-out. No camber. Tailwheel only, and often landing on grass. Low CG. The wheel's axle may be almost as high as the CG. Mass concentrated very close to the CG, especially if still carrying ballast. Large wingspan and lightweight wings make it easier to ...


2

With all the connections between the cockpit and the rest of the aircraft, a modification which makes the cockpit swivel out of the way is way too complicated. In cases where a conventional airframe needed wide open access to its cargo hold, the tail would be made removable. The Junkers 52/1m would be one example, and the Conroy CL-44 "Skymonster" ...


1

Other than the answer of there isn't space, you would need to cut open the airframe. When 747 passenger planes are converted into freighters they don't have a nose door. There is obviously space but cutting up the airframe would make legally getting it in the air again virtually impossible.


7

CG Fore/Aft Location The further forward the main wheels are in front of the CG, the greater the propensity for ground looping. Main wheel separation The closer together the main wheels, the greater the propensity for ground looping. Main wheel Toe-in and Toe-out The following text and images come from the book "Landing Gear Design For Light Aircraft&...


8

The simple answer is there isn't the space. The problem with nose cargo doors is the cockpit. The cargo door must be high enough on the aircraft to line up with the main cargo hold to be useful. On larger aircraft designed with this in mind from the start, (747, C-5, An-124, An-225) the cockpit is placed in a location above the main deck so that the cockpit ...


0

The original question states: 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 the11 AOA) ? Because any changes in pitch increases the amount of the lifting force. This is a flawed premise. Any time that the ...


0

Because wetted aspect ratio $b^2/{S_w}$ merely improves on wing aspect ratio as an estimate of efficiency, for $b$ just choose whichever wingspan is largest. That's good enough to compare one tandem planform to another. You could get fancy and use a weighted average of the wings' spans, weighted by how much lift each one produces, with those in turn ...


6

Using AoA as reference gives a simple way to maintain a safe stall margin. If approach speed was used as reference, there would have been multiple speeds to memorize, as the weight is not the same from mission to mission. Remember, wings basically always stall a certain AoA, not certain speed. Specifying a AoA to maintain, the weight of the plane is ...


4

Correct that changes to one performance parameter will affect others, but it isn't totally clear what you are asking. If you are in the pattern at 11 deg AOA and level flight you are in equilibrium. 11 deg AOA correlates to a certain airspeed at a given weight. That airspeed will vary depending in weight, and the correct indicated airspeed must be for each ...


3

The actual answer is straightforward. The F-15 wing was originally just a swept wing with a given taper ratio which resulted in a slightly swept trailing edge. The inboard portion was straightened just to simplify the flap. Because the flap hinge was now perpendicular to the fuselage the end of the flap was effectively sealed against the "booms" ...


6

The Space Shuttle (or "Space Transportation System (STS)") reportedly re-entered the atmosphere from low Earth orbit at about 17,500 mph, and touched down as low as 214 mph, for a ratio of 81.77. https://www.nasa.gov/mission_pages/shuttle/launch/landing101.html


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