# Tag Info

## Hot answers tagged theory

40

Yes. The wing doesn't care what is causing air to flow past it. Headwind, propwash, 747 wake, gopher sneezes. If the airplane is restrained from forward motion, and the propwash over most of the wing is fast enough, let's say more than the airplane's stall speed, then the wing must generate enough lift to support the airplane, causing it to take off. It's ...

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 ...

12

In principle yes, but why would you do it? For vertical take-off this would be grossly inefficient. Lift is produced by deflecting air downwards. This becomes easier as more air is available for deflection since the amount of deflection needed for a given lift can be reduced. However, when all air movement is provided by the propeller, why reduce efficiency ...

9

Restricting the question to approximately horizontal airflow ... it's been tried. The Custer Channel Wing was one that tried ... it didn't quite make it, but was claimed to be able to fly at 8 to 11 mph. That may have been optimistic but the CCW5 (pictured : image from linked Wiki) apparently flew as slow as 35mph. And it keeps being tried... this time in ...

6

It has to do with the Birnbaum distribution. The center of its area is at one quarter. In potential flow theory, lift can be calculated as the linear superposition of a contribution from camber and one from angle of attack. While the camber-related part of lift is constant, the angle-of-attack related part varies linearly with this parameter. This means that ...

5

There's one thing that will forever prevent an unpowered aircraft from entering commercial passenger service: the inability to make a second attempt at a landing. Airliners, with all their instrumentation, very experienced pilots, and such don't make go-arounds frequently -- but especially during weather, they do make go-arounds. A passenger sailplane ...

4

Absolutely. Here's what it looks like: It's a turbojet here (this is an F-35 engine) but from a physics standpoint there's no reason you couldn't do it with a propeller. So long as you have some means of directing a sufficient portion of the thrust downward, you can lift off. An airfoil would also redirect the thrust slightly downward, but far less ...

4

Yes, rounded wings have been tested in the past. Probably the most famous example is the Vought XF5U "Flying Flapjack". They work perfectly fine. However, the design as pictured does have some flaws. Efficiency The lower the aspect ratio (i.e. wider front-to-back in comparison to their length left-to-right), the more inefficient the wing. This is ...

4

Presumably you are referring to using wings fixed to the airframe with props driving air over them. If instead you move the wing through the air to create airflow over it you "cut out the middleman" and end up with a helicopter or typical multirotor craft. Similarly an ornithopter moves the wing through the air to attain lift.

3

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 ...

3

You forgot to take pressure into account. This formula works assuming your nozzle is well adapted and the exit flow is at atmospheric pressure. In your case the velocity is increased but the pressure drops as stated in Bernoulli's equation. $$P_0+ 0.5\rho V_0^2 = P_1+ 0.5\rho V_1^2$$ This means that the pressure force on your nozzle will counteract the ...

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 ...

2

Theoretically, yes. Practically, no. Day to day weather is a huge factor in powered aviation. It is an even larger factor for non-powered aviation. You would not be able to satisfy the predictability and consistency needed to be a commercial scheduled carrier. At best, you may be a charter or sightseeing tour carrier. No lift means no flight. Days of no or ...

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 ...

1

Well new twin engines airliners are already some impressive gliders... The glide ratio (GR) of the A320 is around 17 and the new 787 GR is above 20. Those numbers are quite impresive considering the two big engines shut down adding a lot of drag. Without engines they could probably reach the lower limit of aerobatic gliders with a GR of around 25 to 30. I ...

1

You'll have to look up what the technology level can bring you these days. Usually, cycle design is s joint effort of what is needed and what can be done. Engine manufacturers have an aerodynamic department that is in close contact with the engine cylce designers and marketing. An OPR (overall pressure ratio) of a design is based on the maximum turbine inlet ...

1

First, let's transform the coordinates to polar coordinates for simplicity by introducing a variable $\theta$ such that: $$z=-s\cos{\theta}$$ In this coordinate, the chord distribution is then: $$c(\theta)=c_C\sin{\theta}$$ Let's write the unknown lift distribution of the bound vortex as a Fourier sine series, again in the $\theta$ coordinate: \Gamma(\...

Only top voted, non community-wiki answers of a minimum length are eligible