# Tag Info

## Hot answers tagged aerodynamics

17

Clearly the plane must enter and exit through the belly of the larger plane Why so? If you drop this condition, things become much easier, because you could attach the smaller planes externally and avoid folding the wings. And this was indeed tried and even used operationally. The concept is generally termed as Airborne aircraft carrier. The first (?) and ...

15

You ask the right question. Given the amount of misinformation out there, I can understand why you are confused. First the tip vortices: They are neither a source of downward force not do they cause drag. They are only a consequence of lift creation by wings of limited span. This answer tries to explain this in more detail. If, however, you mean the wake ...

11

Referring to one manufacturer's nomenclature and systems: The "AIRSPEED LOW" caution occurs shortly after the speed drops below the Minimum maneuver speed. The Min Maneuv spd is ~30% above stalling speed for slat/flap config. Even if the auto-throttle is not engaged in any mode, as long as the auto-throttle is armed, this is the speed at which &...

8

Yes, thrust force vector must have a force equal to (but opposite) the combined gravitational force and aerodynamic drag force (from velocity) to climb at constant speed. In horizontal flight, thrust equals drag to fly at constant speed. But some of the drag comes from the wing creating lift. Since the larger wing moves "a lot of air a little", ...

5

Putting vertical surfaces at the front is pretty much trying to make the plane fly backwards in the yaw axis. Remember that it is just a weathervane. It will want to switch ends same as a weathervane would if you reverse it to the wind direction and let it go. If you tried to fly a plane configured like that, you'd crash as soon as you got airborne, unless ...

4

Sometimes a thick airfoil trailing edge can even reduce drag - witness US Patent 4858852A by McDonnell Douglas Corp. However, this applies to a supercritical airfoil flying at much higher Reynolds and (most likely) Mach numbers than what you have in mind. A similar experience was already made 40 years earlier by Northrop when they could improve the flight ...

3

Back to the basics: with credit to @jamesqf for the comment about soft/rough field takeoff ... "get weight off the wheels as soon as possible". With a cross-wind take off, we leave weight on the wheels as much as possible, then rotate. "Since you can't crab before becoming airborne" Rudder and ailerons become effective as speed ...

3

It's a double Gurney flap, but I'm not sure how it helps, here. Another example: The Eurocopter AS355 TwinStar helicopter uses a double Gurney flap that projects from both surfaces of the vertical stabilizer. This is used to correct a problem with lift reversal in thick airfoil sections at low angles of attack. The double gurney flap reduces the control ...

3

It's a convoluted way to think about it, but yes, the "fictitious force" commonly called centrifugal force is merely the effect of inertia, which is offset by centripetal force to create a curved path.

3

It was actually done post-WW2 as part of the USAF FICON and Tip Tow projects which thought to extend the service life of the B-36 by giving it some escort fighters and photo reconnaiscance aircraft for damage assessment. It ultimately wasn't put into production as it was rather dangerous and seriously degraded the performance of the carrier aircraft, meaning ...

3

Would it even work properly? Depends on your definition of "properly". Would it steer the aircraft like a tail one would? In principle yes. Would it be as easy to use as a tail one? Not by a long shot. Putting the vertical fin in the front will not make it act as a stabilizer any longer: any small deviation in sideslip angle will get amplified by ...

3

No. Total vertical force implies the sum of all vertical forces. In a steady climb, the sum of all vertical forces must be zero, or it wouldn't be a steady climb. I think what you really want to ask is whether all upwards-pointing forces are higher than weight, and then the answer is yes, because drag adds a downwards pointing component which also needs to ...

3

Yes. Vertical forces are forces in the earth axes reference frame. So remaining in this reference frame: the aircraft is climbing steadily; it has a vertical speed component, which causes a vertical component of aerodynamic drag $D*sin \gamma$; and since F=m*a, at constant velocity there must be an equal opposite force pointing upwards. Notes: Upwards ...

3

Washout can be geometric (angle of incidence changes over span) or aerodynamic (airfoil changes over span), or a combination of both. The wing station where that washout starts or ends can be freely chosen, so the airfoil and incidence might stay constant over the inner wing and only start at mid-span. The goal is always to shape the lift distribution over ...

2

An 'appreciable amount of lift' is subjective, but with thanks to @RobertDiGiovanni's answer above, I was able to work out some example values, shown below. (I used the link to airfoiltools.com to get CL data to approximately solve the lift equation for a B737 - exact type not specified - at various speeds during the ground roll). At an assumed constant (...

2

No, especially not for the conditions you stated. Even if we consider that "same exact ariplane" will not melt away at Mach 2 or 5, different phenomena start to appear at such speeds. Let's restrict speeds to below about Mach 0.5 for now. At such speeds, compressibility of air does not affect characteristics significantly, and things become easier. ...

2

See what the L/D curve for NACA 0012 is at 15 degrees AoA, and calculate the Reynolds number for that chord and airspeed. That estimates the maximum lift, i.e., force at right angles to the duct. Then you know, by leverage, the max force exerted by the servo on the vane, and from the servo arm's length, the max servo torque. But that estimate of lift will ...

2

Sure, it's possible. There have been several experiments with so-called "parasite aircraft" over the years, some of which even managed some success before inevitably being canned for reasons of practicality and cost. Docking them together is going to be the hard part. A hydraulic claw won't work; aside from the sheer weight of such a device, planes ...

2

Consider a C-5 Galaxy and a T-38. Big and little. The C-5 cargo compartment is 19 feet (5.76m), The T-38 wingspan is 25 feet (7.7m). So not going to fit. Weight capacity of the C-5 is 291,000 lbs, and the little T-38 onl weighs 12,000 lbs or so. So THAT isn't the problem. Now...if you were to park the little jet on a platform extended from the back, and then ...

2

With increased weight, the descent rate will indeed increase at the same collective input (the same main rotor blade pitch angle). The rotor speed will increase as well as the upflow through the rotor increases. I think your intuition is good with this, right? Now, let's say you want to reduce the rotor speed back to what it was at the lower weight. You'...

2

Turbofan and propeller thrust is known from the manufacturer and does not normally need to be included in wind tunnel testing. Models usually represent solid structure, so they have: hollow nacelles propellers left off However, Cessna included props with electric motors on their Sky Courier tests. In CFD models can exclude engines as well, but there is ...

2

What seems be the case here is that a truncated trailing edge has a flat plate riveted on (called a double Gurney flap). This places the plate perpendicular to airflow (more or less). This, in turn, has the effect of increasing air pressure on whichever surface of the rudder is deflected into the airstream, giving a similar effect to increasing rudder area -...

1

I'm wondering if the 'prolonged' effect of using yaw causes a spiral dive. I understand that a spiral dive is caused by an excessive angle of bank, but can it also be created by an excessive amount of yaw? If by "yaw" you mean the aircraft's yaw rate, then we can observe the following-- In a low-airspeed constant-altitude turn where the bank ...

1

Here is another consideration. At the aft end of an aerodynamic body, we taper the body so the streamlines in the air flow over it do not separate, because of the flow separation drag penalty. But in doing so, we increase the length of the body's tail end, which increases wetted area drag. There then comes a point where truncating the fuselage profile (so as ...

1

From a physics point of view (which may or may not agree with manufacturers’ terminology) a stall is when the angle of attack is steep enough that the airflow breaks away from the upper surface of the wing. Low airspeed is just what you would expect. In level flight at a known air pressure the relation between these two is well understood, but in other ...

1

Positioning of the engine can severely affect the aircraft's CoP and CoG, having it directly at wing level must move CoP or CoG in abrupt ways. Also, if an aircraft engine were to be creating fluctuations of exhaust gas, then the lift of the aircraft will also fluctuate. Throttle of the engine would not only affect how much thrust the aircraft produces, but ...

1

This is not a hypothetical question since Cessna did manufacture versions of the 172 that included constant speed props. These included: The FR172, aka "The Reims Rocket", produced in France from the late 1960s to the mid 1970s. The R172K Hawk XP, produced in both France and the US from 1977 to 1981. The Cessna Cutlass 172RG, produced from 1980 ...

1

Interesting example. MY INTERPRETATION OF THE QUESTION [NEW] Here is an image from GlobalSecurity.org which I have modified to illustrate my interpretation of the question. The angle of attack of the wing is exaggerated in the original image. My interpretation is that the question involves only vertical movement of the wing - e.g. along the vertical red ...

1

It's funny how many people misunderstand such a fundamental principle of flight like how an aircraft wing creates lift. Most misunderstandings stem from incorrect textbooks written by unqualified people who know about flying, but not about physics. This incorrect information is often passed on at flight training schools by flight instructors who were ...

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