What's an airplane and what isn't?

[ahearn]

This is a question I've often seriously pondered, when I have nothing else of greater importance to ponder.

What is an airplane? Is it defined by it's physical characteristics (wing, tail, ect.)? Or by it's aerodynamic characteristics (lift, stability, drag, etc.)? Or something else?

If you put a big enough power plant and (optionally) some kind of control surfaces on a brick, you can make it "fly." It has little or no aerodynamic lift, but can be sustained in a "flying" attitude by shear power alone. There are many model planes (and many real planes) that are not much more than bricks or strange non-aerodynamic shapes that "fly." Are these airplanes or not?

On the other hand, there are gliders, which must minimize drag and maximize lift for good aerodynamic performance. Put a miminal power plant on it to simply overcome the drag, and you have a nice powered aerodynamic machine that is actually "flying" and is basically aerodynamically stable and controllable. Are these better definitions of airplanes? When would they cross the line (what line?) and not be airplanes anymore?

There are "airplanes" such as many modern fighter jets that are aerodynamically unstable hunks of metal and composites, with control surfaces that would be unflyable if it were not for computers for management of this instability. So maybe instability is not a good way to access whether it's a plane or not.

All planes have degrees of inherent instability, varying in different modes of flight (liftoff, landing, AoA, high speed, etc.). The Wright Brothers' plane was very unstable, but could be controlled by a human pilot with some experience.

So, is an airplane maybe defined by a combination of its lift/drag/stability/controllability characteristics?

If so, it looks like the current definition is that if it can be dragged through the air, whether it has lift or not, and is controllable, whether it's aerodynamically stable or not -- then it's an airplane.

Any thoughts?

[Karl B²]

From Merriam-Webster:

alteration of aeroplane
Date: 1907
: a powered heavier-than-air aircraft that has fixed wings from which it derives most of its lift

I know the accepted definitions do not include rotorcraft, yet they produce lift by the same manner: a planar surface (wing) lifts the craft by its passage through the air.

Karl

[ChrisP]

Yep, aeroplanes are a sub-set of 'aircraft', being those aircraft that fly by generating lift by means of wings.

If it doesn't, then it's an aircraft not an aeroplane. Balloons, for example, are aircraft but not aeroplanes. Hovercraft aren't aeroplanes either, but ekranoplans are.

As Karl suggested helicopters and autogyros do actually count as aeroplanes.

[Ollie]

Some dictionaries limit the definition of "airplane" to fixed wing, heavier than air, aircraft with a propeller, jet or rocket for propulsion and some do not. Even if the fixed wing definition were universially accepted, ornithopters, swing wing airplanes and pitcheron controlled airplanes would violate the letter of the definition while meeting the spirit of the definition. Some aerobatic airplanes derive little of their lift from fixed wings in one flight mode but almost all of their lift from wings in other flight modes.

My conclusion is that it is not possible to write a definition of "airplane" that will unambiguously define it for all possible configurations and flight modes of aircraft now and in the furure. The reason being that all possible configurations and flight modes have not been examined and in fact will never be known. Because of this specification problem, there will always be some uncertainty involved in the definition of "airplane."

It is only in the last 30 or 40 years that we have begun to understand the ways in which hummingbirds and some insects produce both lift and propulsion with their wings. Their ways are quite different from airplanes, helicopters, autogyros and larger birds. Researchers are presently trying to employ these newly discovered modes of producing lift in designing miniature UAV's.

[Danal Estes]

FAA Regs, i.e. federal regs, Title 14, Chapter 1, "Definitions":

Aircraft means a device that is used or intended to be used for flight in the air.

Seems pretty comprehensive... but, as you point out, this is "aircraft" not "airplane". So:

Airplane means an engine-driven fixed-wing aircraft heavier than air, that is supported in flight by the dynamic reaction of the air against its wings.

Interestingly narrow and broad at the same time, eh? Of course, they go on to define rotocraft, gyroplane, gyrodyne, helicopter, etc., etc. And, they can ammend if something new is developed!

Here's one place to look at the definitions (Chapter 1) or any other part of the regs:

http://www.access.gpo.gov/nara/cfr/cfrhtml_00/Title_14/14cfrv1_00.html

[Viper Pilot]

Originally posted by Danal Estes
. . . . Airplane means a(n) engine-driven fixed-wing aircraft heavier than air, that is supported in flight by the dynamic reaction of the air against its wings. . . . B]

So gliders/sailplanes are not airplanes??

VP

[Tony Oliver]

'airplane' (American) is defined as an 'aeroplane'. Which derives from the Greek 'aer'=air, and 'planos'=wandering.

Not a lot of people know that!

My two dictionaries define it as 'a powered flying vehicle with fixed wings' and ' heavier than air flying machine powered by motors or jets' - gliders and helicopters lose out again.

[ahearn]

It appears that the lexicographers know how they want to make the distinctions...

My little dictionary defines "aircraft" as any machine that flies through the air, an "airplane" as a powered aircraft that is heavier than air, and an "airship" as a powered aircraft that is lighter than air.

So, I suppose a brick with a motor and propeller is an airplane. No mention of whether or not it can be controlled. I would have to argue, however, that the brick is not "flying" any more than it would be if I attached a rope to the brick and swung in around my head or shot it out of a cannon.

[Karl B²]

I'll put my doubts up as to -plane originating as "wanderer." One definition of "plane" is to soar or glide, with origins in the French "planer," which refers to the flat position of a bird's wings while gliding/soaring. Latin "planus" means level or flat.

Karl

[Capt. Electron]

ahern,

I think the brick could be considered an aircraft, but not an airplane, as it has no wings.


Jimmy

[Jim Walker]

How about a very literal american translation.

Air = air

Plane = to make smooth or even, remove by planing.

Put the two together and you have a device that exerts force on air. In my terms I always think of air planing as redirecting air to achieve flight. So if you accept my premise, then any device that redirects air by using a plane of some sort and thus achieves flight, is an airplane.