Cubdriver

Correct, when the frame of reference or air parcel (cockpit) accelerates, all bets are off on the motion of the contents of the air. For that matter, even the air itself has mass and will move to one side. But an aircraft in cruise is assumed to be in force-vs-drag equilibrium, at a constant forward speed, and there is no acceleration. Nothing in the cockpit feels any force at all, besides gravity.

Considering only the still parcel of air for the meantime, the helicopter is in equilibrium on the forward-backward axes, both forces are zero. But as we agreed earlier, all bets are off when the frame of reference (cockpit air parcel) starts accelerating one way or the other. For that matter, our cockpit air parcel could even accelerate up-down or to the side, and the bug or toy would have to move accordingly depending on the magnitude of the cockpit parcel acceleration.

An example. When the astronauts take off in a rocket from Cape Canaveral, they weigh much more than they do before the launch starts. This is the force exerted on them by the acceleration of the rocket. But when they are in space, they do not even weigh a single g despite a constant linear (actually orbital) motion of over 18,000 mph. Of course by that time the earth's gravity is greatly reduced by the extra distance from the earth's core, but still, they are going 18,000 mph in perfect forward/backward equilibrium. No acceleration= no force acting on them. They play around in the air with nothing holding them to anything. Same with our helo-toy and the fly, except they still have earth's gravity to deal with. Life is easy and there is no random (or constant) acceleration acting on either one.

[edit] I went back and reread the original post, and in our example the airplane does accelerate in the question, so of course the fly and helo-toy feel additional forces acting on them. In that case, if they are already airborne, how much extra force they will have to exert to stay put depends on the ability of the air to support their mass as the air parcel (airplane) accelerates. In other words, the air itself has a certain viscosity which may be enough to support them if they are light enough. Probably not- but a shred of tissue paper for example would probably be light enough not to feel any force that is not in equilibrium forward backward. Low viscosity air is not sufficient to support the heavier objects and they would have to accelerate at a rate proportional to the airplane acceleration in order to stay in hover or forward flight.

Winged Wheeler

Cubdriver:

The astronauts are in equilibrium, as you said, but there is a force acting on them. Gravity exerts a constant pull on the astronauts--the velocity at which they are moving allows them to fall around the Earth, rather than down to it. Their weightlessness is not due to the absence of a gravitational field (it is measurably and calculably there); it's due to the fact that they are falling.

OP:

As to the helicopter, if the plane suddenly stopped wouldn't you expect the chopper to continue forward and hit the windscreen? That's why we wear lapbelts and shoulder harnesses. So why wouldn't the helicopter move back to the bulkhead as the aircraft accelerated forward?

WW

jungle

If you place your glass of water atop your ball bearing collection on your extended tray table, will it slide off the back under acceleration?

Can an accelerometer feel pain?

AirbusA320

The helicopter will move forward.

Because as the aircraft accelerates it pushes the cabin air forward.
In a recent WSJ article they posted a bunch of GOOGLE interview questions. They used an example of a helium balloon in an accelerating car. The balloon moves forward because the air is pushed forward. It has nothing to do with any of Newton's laws.

KIRK, OUT.

Cubdriver

Yep. The reduction in gravity in orbit is about 10% due to the extra distance, while the weightless effect is due to a component of acceleration towards earth as an orbit decays.

FDXLAG

The helicopter will move forward with the air in the cabin. If your helicopter is hovering and the wind gradually increases at the same rate of acceleration of your hypothetical aircraft; what happens if the pilot does not compensate? How is this wind any different from the relative wind created by the air in the cabin of the aircraft moving forward with the aircraft as it acceperates.

We all agree that the pilots not wearing oxygen mask dont suffocate dont we? The air in the cabin moves forward at roughly the same acceleration as the ACFT.

Winged Wheeler

1st and 2nd laws, at least, apply to this discussion. Your statement to the contrary is incorrect.

The helium ballon is lighter than air. Thus, the mass of the air is more significant (relative to the mass of the balloon) than in the case of the helicopter. While I have an open mind and I have not done the math, I hypothesize that the inertia of the helicopter (1st law) would be greater than the force applied to the helicopter by the mass and acceleration of the air (2nd law) and the helicopter would move aft to the bulkhead.

WW

alarkyokie

Also, in the mentioned scenario,when you go around a left curve, the balloon
travels left, to the inside of the arc...(with the windows rolled up)
Seen it, can't explain it.

FDXLAG

Why does the balloon go up?

Would you expect the air pressure inside the car to be higher on the inside or the outside of the turn?

AZFlyer

uh oh....

You were right there!

Only to let it slip away....

Well, Cubby, for a guy who knows so much about Physics, I think you could have studied harder in English class.