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15

Feathering isn't really an issue, if you can feather a prop on an engine further inboard you can do it on the tip too. There are 3 major drawbacks that come to mind: The wing structure has to be stronger: engines are heavy, the further out they are the beefier the structure has to be to hold them. Stronger wings mean more weight and possibly a thicker cross ...

13

How exactly does acceleration of air occur just by having a convex underside Just like the curved forward surface of a wing does it. Imagine for a moment that the air flows along a straight path: Now it would "see" that the surface below it curves away from its path of travel, and if that path would remain unchanged, a vacuum between the wing and the air ...

10

If we're talking about large aircraft the answer is Powerful enough that you want to stay out of them. I refer you to this delightful FAA video in which a Cessna (looks like a 172) was flown into the wake of a C-5 Galaxy. The Cessna was rolled through 360 degrees by the vortex. NASA research has shown that the rotational speed of wake vortices can exceed ...

9

The wingtip vortices create both upwash and downwash; The downwash lies within the wingspan and affects the wing angle of attack while the upwash region lies outside the wingspan and can be utilized by another aircraft (or bird) flying behind and above the wing. The flow induced by the downwash reduces the effective angle of attack of the (finite) wing and ...

9

The wing tip vortices cause significant problems for (small) aircraft taking off after a large aircraft. the FAA Advisory circular 90-23G deals with this. As an aircraft takes off, the the vortices sink behind the aircraft and move laterally over the ground. Source: FAA Advisory Circular 90-23G In case of no crosswind, the vortices simply move laterally ...

9

According to the FAA's Pilot and Air Traffic Controller Guide to Wake Turbulence (section 2.4.5) it's because: Light: in light winds the vortices stay around longer; if the wind is greater than 5 knots then the vortices move out of the way quickly and break up Quartering: crosswinds blow the vortices across the aircraft's flight path, which means that if ...

8

Yes. From an aerodynamic standpoint it makes some sense to use the wingtip vortex in combination with a propeller. In this article by Sinnige et al., the researchers modeled and tested a propeller in various positions along a semispan, concluding that there were real gains to be had due to the increased span efficiency. Up to 15% less drag was measured when ...

8

Although your explanation isn't entirely wrong, It isn't necessarily the backward tilt of the wing, but the backward tilt of the aerodynamic force. I look at it from two different perspectives. The airfoil is designed to accelerate air thus creating the pressure differentials that make the plane fly. The higher pressure areas will try to push the wing ...

8

I would actually assume the opposite to be true. Let us assume the vortex intensity and the induced drag are directly correlated. The induced drag coefficient can be expressed as: $c_{Di}=\frac{c_L^2}{\pi\cdot AR \cdot e}$ $c_L$: Lift coefficient $AR$: Wing aspect ratio $e$: The so-called Oswald factor, a number which equals one for elliptic lift ...

6

The swept-back wingtip has been successfully employed by water fowl for many millennia. The use of composite structures has made the three-dimensional shaping of wingtips much easier, and the first airplanes to use increased sweep at the wingtip were indeed composite gliders such as the Schempp-Hirth Discus. Seagull (left) Schempp-Hirth Discus 2 (right, ...

6

Depending on the size of the aircraft, very powerful. One way of thinking about his would be that the velocities in the wake are directly related to the lift produced. So, heavier the aircraft, larger the lift and greater the velocities. A human being inside a vortex of a large would feel like he's inside a tornado. For all practical purposes, it is a mini-...

6

Eliminate, no. The wingtip vortices are inherent part of lift generation. There is no lift without wingtip vortices. The wake vortices are carrying the momentum that was given to the air to produce the lift, and to cancel them, you'd have to give the air the opposite momentum, which would negate the produced lift. See How does an aircraft form wake ...

6

I've certainly run into my own wake turbulence when doing steep turns in a Cessna 172. In fact, it's the mark of a well-executed 360 degree steep turn that you do feel the bump of running over your own wake after coming full around. :-)

6

Helicopters are not easy to fly - whether full-scale manned aircraft or RC models. I would bet that your issues are more related to pilot error than any fault of the machine (other than the fact that it is a helicopter, and inherently unstable). That said, almost any aircraft can be maneuvered in such a way as to encounter its own wake, and the helicopter ...

6

Slotted wingtips provide torsional flexibility. A bird’s wingtip feathers must twist in one direction during the upstroke of the wings and in the other direction during the downstroke to keep the local wind striking the wing at an appropriate angle to generate lift and thrust... The turning could be done at the base, with a completely inflexible feather; ...

5

In general, the vertical stabilizer and rudder create a symmetric airfoil. As there is no pressure difference between the two surfaces of the vertical stabilizer, vortices doesn't form, unlike the wing, which is designed to produce lift at normal angles of attack (it is usually cambered, producing lift at zero angle of attack). You're correct that the ...

5

Please stop following the cult of the wingtip vortex and start to gain a better understanding of the flow around a wing. Stop reading if you encounter any of those myths: Pressure differences at the tip produce a flow around the tip, starting the vortex. Oversimplification! The tip vortex causes drag. Wrong! Unfortunately, the web and much of unscientific ...

5

Winglets do not change the laws of physics. In particular, they do not change the flow around a wing such that there is no up- or downwash. All they do is to involve a little more air into the creation of lift such that the vortex strength is slightly reduced. With winglets, wingtip vortices now form at the tip of the winglet instead of at the wingtip. The ...

5

You are absolutely right. The vortices form whenever the wings produce lift. Even if the lift is not enough to let the aircraft fly. Of course it is necessary to have a flow across the wing, and with very low speeds (like taxiing) the vortex is likely to be very small. But, it seems your textbook is trying to establish a save way to avoid the vortices of ...

5

There is no magical switch that gets flipped once you cross a specific sweep angle. Things are gradually changing with the cosine of the local sweep angle. Now let's look at your questions one by one: What happens to the wingtip wake on a forward-swept wing? Nothing special. It is part of the full wake system and behaves like in any other aircraft of ...

5

They function like an array of winglets. Each feather is aligned to optimize its angle of attack in the local flow, which is circulating from the bottom to the top around the tip, to extract energy from the circulating flow, weakening the circulation (by redirecting it the other way - a wing deflects air to make lift) and providing a beneficial lift/thrust ...

5

You are not interested in wingtip vortices. For now you are barking up the wrong tree. For that tug idea to work, you need to focus on the trailing vortex which is a result of the whole wing, not the wingtip. How to maximize trailing vortex intensity? Fly slow, use a small aspect ratio and create lots of lift. This means a heavy airplane with a high span ...

4

Doug MacLean has a great synopsis of wingtip devices that is worth reading, and gives a good intuition as to why propellers could reduce, but likely not eliminate, the wingtip vortex. To summarize: the wingtip vortex (really, the rolled-up vortex wake sheet), creates a downwash at the wing which effectively reduces the angle of attack of the wing relative ...

4

The picture in your question is an oversimplification. Maybe this photo of an MD-11 on a moist day will help to illustrate the point: I also think you should not call the wake vortices "tip vortices". The tip vortices are an insignificant part of the whole wake system and can be seen in the picture above on both the winglets and the horizontal tail as thin ...

4

You are correct, but your textbook is more correct. Here's why: Your reasoning is that lift is a function of airspeed, which is true. However lift is also a function of angle of attack. This is why large aircrafts take off the way they do: they accelerate on the ground with a very small AoA, hence little lift. Since lift increases with drag, by accelerating ...

4

Moving the thrust (and additional weight) to the wingtips creates more drawbacks than benefits. Yaw - because of the increased moment of inertia (compared to having the engines be closer to the fuselage - the center line of the mass), it would be harder to initiate yaw changes as well as harder to stop or reverse them. Left/right thrust differentials could ...

4

Another non-flying attribute that having a wingtip-mounted propeller can drive is landing gear length. Since there are minimum clearance distances for propeller tip to ground during taxiing, and the wings may sag or dip during a turn while taxiing, you may end up having to change your gear length (which can cause other issues in turn).

4

So it can fit into standard size airport gates and taxiways. One reason the A380 didn't see wider adoption was it exceeded the maximum wingspan that most airports are set up for, requiring airports to build special gates and widen taxiways to accommodate it... which is expensive so very few did that. Even the airports that did make the A380 mods found ...

3

The wingtip vortices carry some energy, and not leaving it behind seems like a good idea. That's why winglets are a thing, after all. So, what if you put a propeller at the wingtip, aligning the axis with the vortex core? The propeller would "see" the incoming vorticity, and the blades would get accordingly larger local incidences, thus generate more ...

3

Near the wing the bound circulation due to lift leads to an up-wash ahead of the wing and downwash behind the wing similar to the flow produced by a two-dimensional lifting wing of infinite span. A very important effect is generated by the flow due to the vortex pair that comprises the wake (at wing tips). The semi-infinite sheet of vorticity distributed in ...

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