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1 vote

What are the correct Cd0 and Cdi values for a NACA 2412 airfoil?

My quandary is that if all this is true, there should be a noticeable deceleration when the aircraft is rotated at 55 knots while taking off, resulting from a doubling of drag. This is not observed. ...
sophit's user avatar
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5 votes

What are the correct Cd0 and Cdi values for a NACA 2412 airfoil?

Answering the question: Why are induced and parasite drag equal at best L/D? It is easy enough to do the math... Starting with a simple parabolic polar $C_D=C_{D,0}+K\,{C_L}^2$ Divide both sides by $...
Rob McDonald's user avatar
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2 votes

What are the correct Cd0 and Cdi values for a NACA 2412 airfoil?

Is it possible the mathematical modeling is overestimating Cdi? Maybe they used the wrong data! For the answer, below, a simple approach is taken that converges on the desired result. In completing ...
Thomas Perry's user avatar
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3 votes

What are the correct Cd0 and Cdi values for a NACA 2412 airfoil?

An airfoil does not have $c_{d,i}$. Induced drag is a 3D effect. An airfoil is a 2D entity. When you look at airfoil drag data in a book, the non-constant value (that sometimes looks like a parabola)...
Rob McDonald's user avatar
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7 votes

why does the rotor could head (Nr) "overspeed" if the collective is lowered suddenly, what is the Physics behind it

On a turbine helicopter, the engine is being managed by a governor that maintains the rotor RPM (that you trim to a specific value in the green arc). When you move the collective, you are changing the ...
John K's user avatar
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5 votes

why does the rotor could head (Nr) "overspeed" if the collective is lowered suddenly, what is the Physics behind it

The engine keeps pushing the rotors just as hard (at least at first), but the drag goes down so the rotors speed up. You've got the metaphor backwards. Imagine instead that you are removing a bolt ...
Chris's user avatar
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1 vote

Would it be practical to have missiles that can aim forward and backwards?

The M2 Browning certainly does not have a problem firing forwards or backwards owing to its Mach 2.5+ muzzle velocity. A rearward fired missile could theoretically be propelled away from the aircraft ...
Robert DiGiovanni's user avatar
4 votes
Accepted

Would it be practical to have missiles that can aim forward and backwards?

So I was wondering why they don't just design a missile capable of swiveling around and targeting a bogey behind the aircraft. They did. The AIM-9X is able of doing precisely that. The caveat is, you'...
Therac's user avatar
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2 votes

Would it be practical to have missiles that can aim forward and backwards?

Typical missiles have fins in the back that are used for steering. If the missile is launched towards the rear of the aircraft, it will have a tail wind. Then the fins will be destabilizing instead ...
Anonymous Physicist's user avatar
2 votes

Would it be practical to have missiles that can aim forward and backwards?

That is a whole lot of machinery to design a swivel missile launcher rail. Things that can fail. Then, a different missile to be launched at a starting speed of 'minus 500 mph" or so. Backwards. ...
WPNSGuy's user avatar
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1 vote

What's the efficiency between the duct and the fan blade?

Even for just a simple propulsive fan it'll be hard to find one formula incorporating the many practical input variables: blade radius, blade count, blade twist, rpm, airspeed, air density, rotor ...
Camille Goudeseune's user avatar
1 vote

Could an passenger jet perform a complete power down & up IN FLIGHT?

There would be no powering down the entire aircraft in flight. No fly-by-wire system could even do this. Computer-wise, it's possible to shut down and restart some of these mostly due to redundancy. @...
Taylor B's user avatar
20 votes

If a Cessna 172 is dropped from the sky, what minimum altitude is needed to safely land?

Not much in principle. In freefall, the 172 would reach its stall speed in a little over a hundred feet. You'd need to make sure to get the nose down as soon as possible. Then you need to gain a ...
Chris's user avatar
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21 votes

If a Cessna 172 is dropped from the sky, what minimum altitude is needed to safely land?

Minimum altitude is 0 ft: simply release the plane and let it sit pretty on the ground. Call it cheating, but it fits the scenario perfectly. If you want it high in the air, what probability of ...
Therac's user avatar
  • 25.5k
-1 votes

Is it possible to hear a sonic boom when the aircraft is exactly at Mach one?

Yes a plane at M1.0 would make a sonic boom. And yes it would be heard on the ground. @Peter Kämpf and others who say no are demonstratively incorrect. On Chuck Yeager’s first supersonic flight he ...
constructionist's user avatar

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