Hi all

I'm a new member and have some basic questions about the Google earth flight simulator. Please be kind!

As you know, the displayed speed decreases as altitude increases. Isn't this the opposite of what happens in real flying?

Next question. When I'm doing a really long flight using my laptop I often lose my internet connection if I leave the laptop idle for a period. This stops google earth from updating mid flight and I'm left with the blury imagery. Is there a way to correct this mid flight?

Thank you and much obliged.

Hi Rod,

WELCOME to AVSIM!

I know nothing about the Google Earth flight sim (only that it exists). 

However, I believe that the displayed airspeed in knots would decrease with altitude IF you are keeping the Mach number the same.. i.e. Mach 0.8 at 25000 feet will display a higher knot reading say this is guessing 310 knots, but Mach 0.8 at 35000 feet may say 260 knots or so.. The Mach airspeed would be constant.

No doubt other AVSIM members will come along to help out.

1 hour ago, Rod_NR93 said:

As you know, the displayed speed decreases as altitude increases. Isn't this the opposite of what happens in real flying?

Nope, that is what happens with a real airspeed indicator as well. It happens for exactly the same reason that an altimeter also works. To explain...

Atmospheric air pressure is 14.7 pounds per square inch (psi) at sea level, but it decreases to 10.1 psi when you get up to 10,000 feet and it keeps on decreasing as you get ever higher until eventually you are in the vacuum of space. The reduction in pressure as you get higher up is caused by gravity; the weight of air molecules up high pushes down on the air molecules below them, which in turn push down on the molecules below them and so on, so the air molecules down near the surface of the earth have loads of air molecules above them pushing down on them, the ones up high have less pushing down on them. This compacts the air molecules closer together lower down in our atmosphere and makes them thin out up higher. It is why it is harder to breathe when you go up a mountain and also hard to breathe when you get up to above 10,000 feet or so in an aeroplane, because the air is thinner up there.

Because the air is thinner when you get up high, there is less air up there to act upon the air speed indicator's sensor on an aeroplane. The air speed indicator's sensor is called a 'pitot tube' and is mounted on the nose of an aeroplane. You can think of it as functioning like this:

Imagine a small open-ended tube with its open end pointing forwards, inside the tube is a piston which is spring loaded. This gizmo is mounted on the nose of your aeroplane. As your aeroplane flies through the air, the air molecules are forced down the tube and they press on the spring-loaded piston. The faster your aeroplane goes, the more the piston is pressed down against the spring as more air presses against it in the same way that you feel the wind press your hand back harder when you hold it out of the window of a speeding car if the car goes even faster. If you rig your pitot tube up to a device with a scale which can measure how much the piston is being pushed down the tube against the spring, you have the makings of an air speed indicator.

But of course since when we go up higher, we know the air gets thinner, there are less air molecules to push on that piston, so as your aeroplane climbs, even if it is going at the same speed throughout the climb, the fact that it is climbing into thinner air means your airspeed indication will drop.

That's the principle, but in actual fact there is a bit more to airspeed indicators than this: They also usually have an open port on the side of the aeroplane which can measure the air pressure without it being affected by the onrush of the slipstream. Since we know the rate at which the air thins out as we get up higher, this 'static' air pressure reading can be used to determine altitude, but it can also be used as a baseline measurement to compare against the pressure detected by the pitot tube in order to automatically calibrate the air speed indicator to some extent, so airspeed indicators are fairly accurate, but there is a limit to how well this can work, which is why they tend to under-read when you get in thinner air.

That air pressure reading hole in the side of the aeroplane is called the 'static port', for obvious reasons. How that works is similar to a barometer: Basically, a small flimsy sealed tin box with a vacuum inside it is rigged up to a mechanism which can measure its size; since air pressure decreases with altitude, how much air presses on the tin box will vary with height, and so the box will either increase or decrease in size based on the air pressure acting on it. If we measure that, and create a scale, we have an altimeter.

Welcome to Avsim by the way.  🙂

Edited April 30, 20206 yr by Chock