Every time I see a large plane in the sky, or even riding in one, it seems like it just flies more slowly. I wonder if it’s an illusion or do they actually fly more slowly?
In: Physics
Bigger planes tend to fly at higher altitudes. It’s like seeing a vehicle in the distance, they appear to be traveling very slow but in fact they might be going 60 MPH.
I don’t know what planes you fly in, but it is probably an illusion caused by the fact that your brain is comparing small planes closer up with large planes farther away. The illusion is compounded by the fact that the smaller plane will look much more maneuverable: it will turn, accelerate, and brake faster than a big plane, especially where you’re seeing them taxiing on the ground or on takeoff and landing, simply because it has far less mass to have to lug into position.
Depending on the decisions the airline has made, that large plane may well be flying much faster than the small plane. The typical cruising speed for a passenger jet, even a large one, is somewhere around 450-500 miles per hour. The cruising speed for a smaller prop plane used for passenger aircraft, like a Dash 8, is down closer to 300 miles per hour.
They’re usually flying higher and there are no features way up there to compare scales with. If you ever actually see another plane while you’re up there you might be able to gauge how absurdly fast you’re going.
For a passenger, they’re bigger and more stable so the ride feels smoother and slower despite being considerably faster. It’s like riding in a modern car at 70mph vs riding in a shopping cart at 40mph. One is so smooth it’ll lull you to sleep, the other is a death-defying stunt.
It is more or less an issue of parallax. When something is closer to you it appears to move faster because you are seeing a smaller distance over a larger area. Hold a yardstick in your hand a foot from your face. The yardstick will occupy almost your entire field of view. Now stretch your arm out and the yardstick appears slightly smaller. Now place it on the far side of the room and it has gotten even smaller.
Larger aircraft fly higher in the air than smaller aircraft. Hold your hand out, the section of the sky your hand covers may be several miles across at distance the large plane is flying but may only be one mile or less at the distance a small plane is flying. Your perception of this is it takes the large plane 30 seconds to cross the distance of your hand so it must be moving slow. But the small plane crosses the distance of your hand in only a few seconds so it must be moving fast. The problem is your brain thinks they are both covering the same distance, the width of your hand, instead of the actual distance they are traveling. Your brain makes sense of that the best it can by saying the closer plane must be going a lot faster than the far away plane.
The same thing happens when you sit in a plane and look out the window. You look like you are barely moving because the section of ground you are looking at is tens of miles or more wide. Watch the ground as you take off and land. It will look like you are slowing down as you take off and gain altitude and speeding up as you lose altitude to land while the exact opposite is what is really happening. But because you are seeing more and more land area in the window during take off and less and less land in the window during landing, your perspective of your speed changes to make sense with how long it takes any visible item to cross the view of the window. When you are near land a visible item may only need to move a few hundred feet to no longer be in view versus when you are at cruising altitude a visible item may need to move 50 miles to no longer be in view.
Humans pretty much use the moving object’s size as a rule stick. In other words, we measure the speed of an object relative to its size. Ants look like they’re speeding around, because they move very quickly compared to their size.
When it comes to aircraft, all passenger jets fly at a rather similar speed, regardless of their size. For example, a Boeing 737 has a take-off speed of around 250 km/h, while the MUCH larger Airbus A380 only needs to go 20km/h faster to take off. In general, this means that a larger aircraft looks like it’s flying slower because it’s much bigger but only slightly faster, so its speed relative to its size is lower.
I used to watch C-5s fly all the time over San Antonio and it always seemed like those beasts were just floating. As they got closer you could understand their speed better. I always thought that was kind of cool.
Big things can look like they move slower because it takes longer to move one full length of their body.
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