# Tag Info

21

Most twin-engine aircraft with counter-rotating propellers have the rotation set up so that the propellers are rotating inward towards the center at the tops of the propeller arc. This configuration reduces the P-Factor effect at slow speed high angles of attack, and eliminates the "critical" engine that is present on multi-engine aircraft where both ...

9

For an aircraft designed for cruising efficiency it is important to have as little trim drag as possible. See ATR 72 link: The wing may appear unusually small, but it is made to produce the needed lift at cruising speed at its most efficient Angle of Attack, where lift to drag ratio is highest. If the wing produced too much lift for level flight at its ...

9

One function of common inner span flaps that's not often discussed is stall management. Not only does some flap lower the stall speed, but it ensures the wing root stalls while the tips are still flying; this prevents an incipient stall from turning into a low altitude stall-spin if a wind gust or unplanned maneuver pushes the aircraft from "controlled ...

8

The actual mass alone is nearly irrelevant to its a trajectory - what mostly matters is the mass/drag ratio - so if you scale the drag correctly, it feels quite the same - at least from the operational point of view. As one does not drop bombs by sight only, a small adjustment on the computer will do the other trick.

8

No, both would reach the ground at the same time, although the one with the higher airspeed would go farther before hitting the ground, assuming atmospheric conditions are invariant. On the other hand, if both aircraft have the same flight path angle, the one with the higher airspeed would have a higher sink rate.

7

There are two primary benefits of wing sweep at ultralight speeds. The first is that it acts as variable dihedral -- the higher your angle of attack, the more dihedral effect you get from sweep. Secondly, when you see ultralights (or hang gliders) with a lot of sweep, it's generally for a tailless design that needs to get the tip fins/rudders and twisted ...

7

Aside from the decreased takeoff speeds, there are a couple reasons why typical Part 25 aircraft do not allow flapless takeoff: There is usually a sweet spot at lower flap settings that generate the best climb gradient at V2, and it's usually not with flap retracted. It is typical to see several takeoff flap settings that cater to best climb and best field. ...

5

Thankfully, aerodynamics in the usual flight range is linear. Therefore, there is a gradient of lift over angle of attack and another one over the flap deflection angle. Both are constant over a range of maybe ±15° and can be combined. The angle of attack is referenced to the fixed part of the flight surface and the deflection angle to the moving part ...

5

Equating rate of climb with more lift is wrong. In order to climb the aircraft needs more thrust but a bit less lift. Therefore, the first statement is wrong: Adding more power does not create more lift. The only case where this happens is at high speed and the maximum sustainable lift coefficient: More power allows to fly at a higher load factor, but ...

5

In addition to the previous answers, you could argue that yes: provided you had a long enough runway you could theoretically perform a takeoff run that accelerates you to a speed which is sufficient for taking off and remain airborne with no flaps (and for this exercise let's assume an A320 has a flaps-up speed of 210 knots, give or take), but you'd be ...

4

There are two considerations. Two parallel vortices will tend to move upwards if the air flow between them is upwards. You can think of it as each 'blowing' the other upwards. This suggests the P-38 configuration maximises lift. I am not convinced but I don't have access to the software to know either way. Nor did they. The second consideration concerns ...

4

In straight and level flight at an airspeed V, the weight W is balanced by the lift L, and the aerodynamic drag D is balanced by the thrust T. D is much smaller than L. In a passenger liner, D may be 1/12 ... 1/20 of the weight, or so...

4

Provided the bomb has the same ballistic characteristics, the mass of the bomb would be irrelevant to this. Now the weight of the actual MK82 series 500lb bombs may have a distinct effect on the maneuvering characteristics of the attacking airplane during a bombing run as opposed to carrying a load of MK76 ‘Smurf Killers’ to a target.

4

That's because Bernoulli's principle breaks down at and above supersonic velocities. In the subsonic realm, when an atom is sped up, it doesn't have much time to spend pushing around a fixed place (it passes by that place quickly). In doing so, the static pressure drops as the speed increases. And in doing so, the neighboring atoms, who are also not doing ...

3

Source: nap.edu Not really no. The velocity off a propeller does not shoot straight back, rather in circular motion (shown above and below). Source: High-Lift Propeller System Configuration Selection for NASA's SCEPTOR Distributed Electric Propulsion Flight Demonstrator, NASA From the conclusion of that NASA report on span-wise propellers generating lift: ...

3

In reality, in a strongly- deflected stuck-rudder situation, the pilot would be best advised to forget about the doors and just land the plane, selecting a runway with a strong crosswind component if at all possible. After all, when landing with a strong crosswind, it's not that uncommon to hold the rudder at close to full deflection in the "downwind" ...

3

This is quite a flabbergasting question... As you're standing on the floor of your home, Lift equals Weight. The lift is supplied by the floorboards to your feet. That's static lift. If you tilt up a floorboard and pull a toy car across it, it will be lifted upwards and even fly up after the floorboard ends. That's dynamic lift. Note that the required ...

3

It is theoretically possible to do a flaps up take off if you have a long enough runway, but why would you want to? An airplane is designed to be most efficient in the air, so the sooner you get there, the better. The lift available to an aircraft is proportional to the area of the wings (and flaps increase that area), however, the drag those wings produce ...

3

Several other good answers, but one reason I haven't seen yet is pilot proficiency. You don't want pilots only practicing short-field takeoff and landing technique on actual short fields, which might be rare depending on 5he routes any given pilot happens to fly. If they use that technique on every takeoff and landing, though, then you know they'll always be ...

3

I do a lot of soaring and you thermal at min sink +/-, which is normally just few knots above stall, around 1.1 Vs. The slower you can go the better (smaller circle) and sometimes going below min sink is worthwhile if it lets you core the thermal better, but your ability to do this can be limited by the glider's particular stall characteristics and your own ...

2

Both the airfoil shape and inherent properties of the air contribute to the stall angle of attack. You asked for a theoretical background, but I will list the factors that influence stall because there is no simple formula for it. The most important factor is the suction peak which develops right behind the stagnation point on the upper side of the leading ...

2

Let's try to derive something. Assume the x-axis points to the right and the y-axis points up. I'm gonna use the subscripts b and s for bottom and side. The incoming velocity vector is decomposed in two components along the axes, so $v_s=v\sin\theta$. Writing the total drag force as a vector: \$\vec D=\begin{bmatrix}-D_s\\D_b\end{bmatrix}=\begin{bmatrix}-C_{...

2

You are basically describing an ejector pump. This would not be very efficient, I'm afraid (I'll try to dig up some comparative figures). The arrangement in this case would be a jet engine used to accelerate an amount of air inside a duct. With a long enough duct, the end result would be a single airmass exiting at (somewhat) uniform speed. Unfortunately, ...

2

A trailing-edge control surface, when it deflects, changes the camber of the overall airfoil. More camber means more lift, in whatever direction that airfoil is mounted. In your example, adding up elevator increases the horizontal stabilizer's camber, which increases the downward force it applies. Philosophically, "why" it does this is just, well, that's ...

2

Ground effect only comes into play within about 1 wingspan’s height above a surface and it is largely unnoticeable until approx 1/4 to 1/10 of a wingspan above the surface. While it is true that ground effect greatly increases the lift to drag ratio of the wings, it does not reduce parasite drag nor does it account for the fact that it is more efficient to ...

1

As noted in the answer linked in comments, the practical limit for ground effect is about half the wingspan over a relatively flat, impermeable surface (you'll get better effect from smooth water than from heavy swell, for instance). Flying in ground effect for either economy (reducing power needed to fly) or in an emergency (engine out prevented climbing, ...

1

What height over a fixed plain can a plane begin to take advantage of the ground effect or when air is compressed between the wing and ground? It varies, but, generally speaking, ground effect usually becomes noticeable somewhere around half the plane's wingspan above the ground. So, for a plane with a 50-foot wingspan, ground effect would only be viable ...

1

The wings don't benefit all that much. Look at a small airplane from head on - how much wing is directly behind the prop? My airplane for example, the prop is 86" diameter. The fuselage is 46" wide - so 20" of wing on either side is behind the prop. The wing itself is 35'6", or 426", so less than 1/10" is in direct prop airflow. The prop pulls the plane ...

1

Tires. Tires are under very high stress normally due to the compromise between extreme performance requirements and low weight. Tires aren't cheap. By doing a higher-speed-than-necessary takeoff, you're increasing tire wear and inviting tire problems that you just don't need to invite. It would be a very false economy to save a little in what exactly, ...

1

The answer depends on several factors: Bank angle. The minimum speed rises with the inverse of the cosine of the bank angle. A steep bank angle is preferred for best climb because it helps to fly as close to the core of the thermal as possible. Wing loading. With old designs made from wood and fabric you can get as low as 18 m/s, with modern composite ...

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