# Tag Info

57

Banners have a lead pole to keep the leading edge straight. This pole is weighted at the bottom, which ensures that the top and bottom of the banner remain in the correct place. By itself, this would ensure the banner remain perfectly vertical. To achieve the proper angle for viewing on the ground, a tab is attached to the top of the lead pole, adjusted to ...

8

Yes, it does make sense. However, the angle of attack increase of the tailwheel airplane would only be possible if it touches down on the main wheels while there still is much clearance of the tail wheel or skid. Normally, the ground attitude of tailwheel airplanes should be very close to their landing attitude, so all three wheels touch down almost ...

8

Yes. With a tailwheel airplane, if you are trying to make a "wheel landing" (on the main wheels only) rather than a 3-point landing, it is critical that the sink rate be very low at the moment of touchdown, or else the plane will tend to pitch nose-up (tail-down) which will make it bounce back into the air. A plane with tricycle gear doesn't have ...

4

Stalling speed increases with altitude. Maximum altitude is the point at which stalling speed rises to meet maximum airspeed. To get higher, the options are to; increase thrust, increase wing area, reduce weight, or improve aerodynamic efficiency. These principles apply to all aircraft using aerodynamic lift. In the case of the paraglider, its aerodynamic ...

4

They can be, as on the An-72/74, which has the engines mounted above and forward of the wings in part to increase lift, utilizing the Coanda effect. One downside is that this makes access for maintenance more difficult, which is a large factor in operation costs. https://en.wikipedia.org/wiki/Antonov_An-72 https://en.wikipedia.org/wiki/Coand%C4%83_effect

3

Short version of (by now) two other answers: a sailing vessel needs a sail in one medium and a keel in another: a foil in the water, conventionally; ropes dragging on the ground; electromagnets in the storm wall of Jupiter's Great Red Spot, in a science fiction story; reaction wheels in inertia, in a solar sail.

3

In addition to the Antonov 72/74's, Boeing worked on the YC-14 concept as a replacement for the C-130's. Also, many seaplanes have to place the engines as far up as possible, to keep the engines and propellers out of seaspray. This has the secondary effect of accelerating airflow over the wing and increasing its effectiveness. The engine wash is also used ...

3

Agreed. Tail wheel aircraft generally have the required angle of attack on touchdown (for a given landing speed) very close to the angle achieved when all three wheels are in contact with the ground. Hence, if the aircraft is landed at too higher speed the tail will be high, and without care, the touchdown can cause the aircraft to rotate around the main ...

3

In the SI system the weight is measured in Newtons [N = kg*m/s^2], while the mass is measured in kilograms [kg]. To convert kilograms in Newtons, i.e. a mass measurement in a weight, you multiply by the acceleration of gravity g. In this case you're converting a change in mass to a change in weight, the conversion is the same, but both sides have an ...

3

From a quick Google search, you can find that Sikorsky Firefly and Tier One R44 are two examples of eHelos, conventional helicopters converted to electric propulsion. They both fly around 20-30 minutes (though the Firefly never flew). As for building an electric helicopter, I believe off-the-shelf components (such as Tesla motors and batteries, available ...

2

Let us assume level flight. Then the forces acting on the aircraft are shown in the following sketch (not necessarily to scale): The forces are : the total aerodynamic force $F_A$, which is split into two components: lift $L$ (perpendicular to direction of motion) and drag $D$ (parallel to direction of motion) the weight $W$ the thrust $T$, here acting ...

2

If a taildragger is configured and flown properly, actually the result is the same as for a tri-gear. If you land 3-point, a "full stall" landing, the ideal is for the tailwheel to make contact just before the mains, so that ground contact has the result of reducing AOA (a tiny amount). If you contact mains first you are likely to skip or bounce ...

2

It's not so simple. For swept wings it is essential whether the leading edge is sub- or supersonic. What does that mean? If the leading edge is within the Mach cone emanating from the tip of the wing, it is called subsonic. The approaching air will "sense" what is coming and behave much like in subsonic flow. This avoids wave drag and keeps nose ...

2

Generally, you are right. Reducing wing area is reducing overall drag. Within limits. Induced drag depends on speed and span loading. If the reduced wetted surface allows you to fly faster, reduced drag will be lower, leaving more of the power budget to overcome viscous drag. However, if wing span is reduced, induced drag will be higher at the same speed, so ...

2

The relation between tip vortex strength and induced drag is not a simple one and the suggested advantage is not realised in practice. Meanwhile, a pointed tip has other problems. Some that occur to me: If the wing has a constant aerofoil profile then a pointed tip will tend to stall first at high angles of attack. This creates turbulence over the ailerons ...

2

One of the approaches to reducing this drag is taper the wing No, not at all. The vortex strength depends on the lift at the center wing. This strength invariably tapers to zero towards the wingtip, regardless of the wing's geometric taper ratio. The taper ratio will only change the local gradient, not the absolute decline in vortex strength. In the end, ...

2

High performance sailboats can sail faster than wind speed in certain conditions. Therefore, your question is not as absurd as it might seem at first glance. However, the technique that enables sailboats to do so is not available to airplanes, at least not in flight. Sailboats use the speed difference between water and wind. Their keel keeps them from being ...

2

For a glider to move forward using vertical sails, you would have to fix it to the ground somehow, as if it was on tracks, to provide the lateral resistance that allows the reaction force between lateral air movement and the vertical sail to occur. Something like a kite surfer. Replace the kite with a regular glider, with a tether line running from the ...

2

Sail-powered vehicles cannot be faster than the wind they travel in (along the wind direction) and need another medium (ground or water) that offers resistance. An airplane, to be in flight, needs to move forward w.r.t. the air sorrounding it and cannot be in contact with another medium. The two are mutually exclusive. A similar question got a similar answer....

2

Positive or negative here depends on the coordinate system you have used. An airfoil producing positive lift (up) will invoke a positive circulation, and that will require a counter-acting torque, which is then negative (pitch-down). Some more detailed explanation can be found on wikipedia. https://en.wikipedia.org/wiki/Pitching_moment https://en.wikipedia....

2

It is not so hard, actually. You need to know the speeds ahead and inside the intake. You can deduce their ratio from the pressure recovery factor, and normally the Mach number inside the intake is between 0.4 and 0.5, so this, combined with your design flight speed, is a good starting point. In supersonic flow the air is rammed into the intake face, ...

2

There's less drag at the same speed (and other things being equal, aside from altitude). This is due to lower air density at higher altitude, which linearly affects drag. But just the same, it affects lift! You get less drag, but less lift too. If you want to fly level, you can't afford that: lift must be equal weight. So what do you do to restore lift? You ...

1

The direct answer to the question as it is ("What´s the relationship between AOA and Airspeed?") is simple: none whatsoever -- that is, until you introduce context and some conditions. Your context is: we want an airplane to fly. And not just 'fly' but to keep level, at least. For that, you need a certain amount of lift. Lift is used to counteract ...

1

A practical answer to help you understand critical angle of attack and stall speeds would be the operation of fast jets. The quickest way to land a jet is to join for a ‘run-in and break’ this could be at any speed but typically 350kts. A high-g turn would be used from overhead the runway at circuit height to the downwind position. The aircraft would be ...

1

"Can we get into a stall without reaching the critical AOA?" -- no. "We know that any aircraft will stall at its stall speed (for a specific weight, CG position, etc.)"-- we need to add "G-loading" to this list of parameters. The "stall speed" we usually talk about is the 1-G stall speed. Change the weight or the G-...

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You might have heard of the "coffin corner" the U-2 pilots flew in. The U-2, at 90,000 feet, had only 9 knots between stall speed and Vmo. Airliners fly in a similar, but wider corner, with circa 15-30 knots between stall and Vmo. Vmo is where shockwaves start appearing on the upper wing surface, buffeting, engine surge and all kinds of bad stuff ...

1

Ignore the part of the diagram above the blue line. Assuming that the trailing edge at the wing root is at right angles to the fuselage, then 6.5 and 23.5 and trigonometry tell you everything about the triangle that is like a delta wing whose root lies on the midline of the fuselage. Now you know the length of the delta wing's trailing edge. So use similar ...

1

As others have stated, tandem cockpits have advantages in that they create more slender bodies and require minimal modifications from single seat variants. The twin-seat modification is not always an issue, as many airplanes are designed from the get-go as two seaters, such as the F-4, F-14 and F-15. F-15 single and twin seaters share the same canopy, the ...

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