# Tag Info

30

Your friend is wrong. The Tu-154 is one of the safest Soviet designs and certainly was not about to fall out of the sky when departing Frankfurt. However, it is indeed a noisy airplane and in order to minimize its noise impact would try to climb more steeply. The flight speeds for steepest climb is only three quarters of the speed for best climb, so it might ...

14

— Sakurai, Seiya, and Matthew D. Fevergeon. "Door assembly for laminar flow control system." U.S. Patent No. 8,245,976. 21 Aug. 2012. [Current Assignee: Boeing Co.] Each door is actually one door inside another, so they can open as a scoop, or an outlet (opening fore or aft). During takeoff the door scoops in air, so higher pressure is created in ...

13

I'm having a difficult time understanding why the center of gravity is translated along this circular arc, when the turning force that pulls the airplane through the turn is acting upon the airplane's center of lift, aft of the CG. It makes intuitive sense to me why the airplane rotates about the CG on all of its axes, but all translation / movement being ...

11

This is quite common for many larger aircraft with spoilers on the wing. Using the spoilers in this asymmetric way is called roll spoilers or spoilerons. They are usually hydraulically actuated and sometimes fly-by-wire controlled. The Bronco, however, has them mechanically linked to the ailerons: The lateral system consists of spring and gear tab-boosted ...

6

None The effect of the glider is purely drag, which the tow plane must compensate for with more thrust. Both aircraft lift themselves. The tow plane thrust counteracts the induced and parasitic drag of the entire flying unit. The effect on aerodynamic performance would be comparable to a twin with one engine out, or trying to fly with speed brakes open, ...

5

Looking at this question from a fundamentals of flight perspective. The airplane towing the glider would have its forces in balance as they usually would, however there is a glider in the back that is causing quite a bit of drag. Since airplanes climb due to an excess of thrust, the airplane will climb at a much lower rate. The pitch attitude would be ...

5

Well again, a glider would have zero effect on a stall speed of the tow plane, because the tow plane technically does not have a stall speed (remember wings only stall if they exceed the critical AoA - this can happen at any airspeed and/or at any flight attitude). Now most tow planes use a release hook mounted under the fuselage just aft of the tailwheel. ...

5

I think I have a partial answer that I have found in a paper [1]: The following is a quote from the introduction: It is too narrow a view to use vanishing surface shearing stress or flow reversal as the criterion for separation. Only in steady two-dimensional flow do these conditions usually accompany separation. In unsteady two-dimensional flow the surface ...

5

To make a comparison I would set the condition. So the question would be: "Considering two airfoil with the same geometry and at the same Reynolds number, how would change the BL thickness with increasing AoA?" Another thing that would make the question more clear would be to consider a definition of the boundary layer thickness, and here I would ...

5

$C_D$ is a form factor variable, constructed to be as independent as possible of all the factors that contribute to aerodynamic forces. Two dimensionless flow parameters do influence outcomes of aerodynamic measurements: The Mach number, which quantifies compressibility of air. The Reynolds number, which accounts for viscosity/inertia effects in the ...

5

What about in a continuous pitch-wise rotation? In this case, there is only one control, and that's the elevator. In the controls domain this is known as an underactuated system, and it is both theoretically and practically impossible to stabilize two system outputs with only one control input. Not if the two outputs are connected. They are not independent ...

4

Convair worked very hard to develop a light multiservice aircraft with STOL capabilities. The short wingspan does not appear "normal" in proportion because prop wash and high lift devices were used extensively to improve lift. Power on, the wing lived in a higher airspeed environment than the tail (lift is proportional to V$^2$). The model 48 ...

4

As drag decreases as AR increases & lift also decreases as AR increases, so the Aerodynamic Performance (L/D) decreases. Why should lift also decrease? You should keep wing area constant, so lift should also stay constant. This translates into increased L/D. Generally, an aspect ratio increase has these consequences: More wingspan, so induced drag will ...

3

If the glider is being towed in perfect alignment with the longitudinal axis of the tow plane and the thrust, then no - the stall speed will be the same. In reality the tow would never be perfectly aligned like that and there would be some effect on the stall speed. For instance, if the glider is low i.e. below the plane axis, there would be a downward ...

3

Given the speculative nature of this question I dare to speculate myself :) With DC-9s part of the solution to reduce noise during approach was to ban use of full flaps. This was done to reduce drag which in turn reduces required engine power and noise. The result of lower flap setting is that higher nose-up attitude is required. If similar procedure was ...

3

Well, are you forgetting to use the tail? The "center of gravity" model can take some time to fully fathom, but it works well to describe rotation on all three axes. Let's try pitch. Since CG is ahead of wing CP (center of pressure), CP will try to pitch the nose down. So how do we "rotate" to take off? More up elevator!. Flying a ...

3

For this answer I have to speculate since I do not have the wind tunnel data which would be needed for a more substantial answer. Why should adding the spoiler reduce drag at lower speed? The most likely reason is a changed flow separation over the car's rear area. I would expect that flow separates already at some point along the rear window if no spoiler ...

3

So is the plane skidding[*] through the pitch change? Yes, absolutely. In fact, if we define skidding in pitch as a difference in pitch angle and heading vector angle, the aeroplane is always skidding when Angle-of-Attack ≄ 0. My hunch is that the wings have such an incredibly strong tendency to align themselves with the airflow that the skidding action is ...

2

The larger aspect ratio means the span of the wing increases and hence so does the weight of the structure. So, to carry the same load you need a heavier wing, which will decrease the benefit of the lower drag, or you need to choose different materials (metal -> composite) or construction technique (lightening holes in ribs, for example) for the wing to ...

2

Fixed slats are called slots. They are not in the position shown in your picture, as this produces high drag at low angles of attack. Slots are normally aligned with the wing so that drag is lower in cruise. The gap is kept fairly constant through the slot so the shape approximates the airfoil leading edge, and there is no recirculation zone.

2

Simply using the generic drag equation will get you within the ballpark required for FlightGear. $$D = C_D \cdot \frac{1}{2} \rho V^2 \cdot A$$ with $C_D$ the flat plate drag coefficient and A being a reference area of your cowl flaps. The data for the correct Reynolds number is best used, with $$Re = \frac{\rho V \bar{c}}{\mu}$$ with $\bar{c}$ = mean ...

1

The centre of gravity is the reference point of the rigid body. The six degrees of freedom are modeled as three linear translations of the CoG, and three rotations around the CoG. You’re right in that the centre of lift could be taken as the reference point as well, or any other point for that matter. It’s just that rotations of a body suspended in air take ...

1

The airplane follows an arc in the turn because of the vertical fin. When you bank, it introduces a lateral vector to the wing's lift force. The lateral vector makes it displace sideways as it's moving forward. Without the fin to provide a weathervaning effect, it would simply continue more or less pointed on its original heading, but on a slewed track, ...

1

You can still use the panel method and implement along with it an integral method for the boundary layer (like it is done in the xfoil software). The lift will be modified with the theory of displacement while for the drag the viscous drag will be computed directly by considering the friction coefficient found thanks to the integral method. One of the most ...

1

The underside of the horizontal stablizer is (generally) the suction side, as it is producing downwards lift to keep the plane stable. The HLFC panels shown in the video (screeshot below) are too small to make any meaningful difference to the flow, so they are most likely some sort of access doors or measuring devices. These can be see, at least on vertical ...

1

It's important to distinguish between longitudinal stability forces and trim forces, and I find that the literature in general does a very poor job of explaining it for the quasi-layperson. I use this concept to make it easier to picture what is going on in your mind. Longitudinal stability is simply the airplane weathervaning about the C of G into the ...

1

The drag coefficient is designed to be a coefficient - and hence be as independent from the flow state as possible. Yet, the simple cd definition $c_d = D / (1/2 \rho u^2 \times S)$ just uses the (incompressible) dynamic head of the incoming airflow as reference pressure. This way effects of viscosity are neglected, as are effects of compressibility. As ...

1

How do aircraft establish a pitch rate which corresponds to the centripetal acceleration. It is a combination of throttle and elevator, with gravity and aerodynamic forces considered. If your loop is flown at constant speed, AoA would have to be changed as well as throttle because of the changing position of the gravity vector. Mathematically, we have the ...

1

Frontal drag increase, which is not very important on low speeds, but increases dramatically on higher speeds. Construction weight and resillience - the longer wing, the lower strenghts it can carry. So the long wing is good choice for relatively slow glider (low induced drag - low strenghts and little resillience required), but for higher speeds the cost ...

1

If you take the pictured wing, the same wing blunt side forward, and something in between you start to see what was explored in the 1940s by North American aviation as "laminar flow", attempting to reduce drag by delaying flow separation as much as possible. Moving the thickest part of the wing back to around 30% and greatest camber to around 40% ...

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