I’m most curious to know about when the planing is gaining speed for lift off, and you can kind of feel the force of the acceleration, once it lifts off you can’t feel that so much any more. Does it maintain the speed it needs for lift off, or does it no longer require quite that force, and so actually slows down some? (Not a science person, sorry if I’ve fractured the lingo somewhat!)
And secondly, why does the wing always have “no step” printed every four feet along the wing? Are a lot of people walking on the wing, yet unaware where not to step? Because I’ve never seen anyone walking on the wing, while prepping or putting away the plane at the airport. Are they secretly dancing on the wings when no one is looking? Is it such a big problem it needs to be on every plane?
Second first: So fueling people, mechanics, won’t walk out there, it is not designed for that & important stuff under the skin may get damaged. +/- other stuff.
Secondly covering the first: There is still some acceleration bit it is smoother & less rapid. You body acclimates to it quickly so you don’t notice it as much + it feels more normal because you can see that the plane is pitched up so you expect the seat to feel that way …
Plus other stuff that will be pointed out & will show that I don’t know what I am talking about. This is just a place holder until the experts of the SDMB come to set you straight.
Right. You are feeling the rate of increase of the speed, not the speed itself. The highest rate of increase is from a standing start into the takeoff roll. By the time you reach takeoff speed the rate of acceleration has declined to the point you no longer feel it as much. You’d feel the same sensation in any fairly powerful car, if you could ignore speed limits and wind it out to maximum speed.
Second question: while wings are not commonly used as footpaths, mechanics or inspectors do need to get up there every so often and if one did happen to step on one of the ‘no step’ areas, some fairly expensive damage could occur. So a few bucks for some painted stenciling as a precautionary measure is worth the cost.
Sorry to double post, but further on the first question: another way to look at it is that the plane goes from 0 to liftoff speed (maybe 180-200 MPH) within 10 or 15 seconds. Once in the air, it continues to accelerate to its cruising speed of maybe 550 mph, but takes several minutes to do so. Slower acceleration rate = less sensation of acceleration.
Note also that as the jet accelerates along the runway, the entire power of the engines is applied towards the jet’s horizontal forward speed. As soon as the airplane lifts off, some substantial portion of that power is re-allocated, now working towards lifting the airplane vertically against gravity. At that point, essentially, much of the increase in forward speed (acceleration) is being traded away in order to raise it off the ground.
Total WAG, but I’d think you’re more aware of acceleration on the ground because you’re sitting level and being pushed back in your seat. While you’re climbing, you’re being pushed back in your seat anyway by the tilt of the plane and gravity. Separating out what portion of that sensation is due to slope and gravity, and what portion is due to acceleration, is more difficult.
One thing to note is that the wings are made to take stress from below (they carry the entire weight of the plane in the air and nearly the entire weight on the ground) but not from above. Similarly, on a propeller plane you can pull on the propeller, but you cannot push on it or lift it.
One form of it - friction drag (aka “parasitic” or “profile” drag) - definitely does.
But another important kind - induced drag - decreases with airspeed. This is the drag associated with the production of lift, and for an aircraft in flight* it is proportional to the inverse square of the airspeed.
Total drag is lowest at the airspeed where the two types are equal. This is the best glide airspeed - which is also the best rate of climb airspeed. It would be something like 240 kts for a typical airliner, and meaningfully above the airspeed at which the plane normally leaves the ground.
*That’s “unaccelerated” flight: straight and level, or a constant rate of climb or descent.
Yes they are, but not as much. An airplane does take some negative G’s at times, and has to be able to.
Sure you can. The loads go right into the crankshaft, through the engine bearings and crankcase, then the mounts, and into the airframe.
Some props, particularly on turboprops, are *designed *to have the blades be able to rotate past feather and into negative pitch, for reverse thrust after landing (beta mode).
No Step. I’ve worked on various aircraft and needed to walk on wings, fuselages, and even some flight controls to do maintenance and inspections. It can be difficult to tell where you can and can not walk on such surfaces especially when first working on a new aircraft.
When I trained other mechanics, one of the first things was to show where you could safely walk on, or even inside, the aircraft.
Thanks for all the answers, I definitely understand better now.
I have one more if you’re feeling so inclined. We were mostly in 700 series planes on a long, long journey that more than once required coming in, from over the ocean, to over land to reach the airport. Each time it seemed like the pilots were waggling the plane, sort of rocking it back and forth a little, just as we would cross from over water to over land.
What the heck? That’s a big old plane and a manoeuvre more suited to a smaller, more agile plane, to my mind. First time, I thought it was a one off, but consistently for three approaches, makes me think it’s something else. It wasn’t enough to spill drinks or anything, but easy to feel, and really visible if you had a window seat.
Air flight still seems a little like magic to me, especially with such super big planes, Yikes!
Thanks for the learning, always greatly appreciated!
There’s lot of air turbulence when flying from over water to over land and visa versa. If the land and water have different temperatures, that can cause turbulence. Also if their are hills and cliffs soon after the ocean, that can cause updrafts.
On a small plane like a Cessna Skyhawk, you’ll often see NO STEP on the wheel pants. These are fiberglass fairings that are not designed to support the weight of an adult. You’ll also see NO PUSH on many aircraft because it’s not designed to be pushed from there. NO PUSH is often seen on the elevators, for example.
The rudder adds the 3rd axis of control and acts like the rudder of a ship. It can be used to make minor corrections against the ailerons which are used to bank the aircraft and change direction. If the plane is hit with an odd crosswind it will push against the vertical tail plane causing the plane to slip sideways and is corrected with the rudder until the gust passes.
Look at the size of the vertical stabilizer and you’ll understand why a crosswind affects the movement of the plane. It’s a lot of surface to push against.
Along with the physics explained above I believe that a large amount of the decrease in acceleration you ‘feel’ is actually just your senses being tricked. Right before you lift off the runway you’re traveling in excess of 150 mph which is about the fastest most of us will ever go on the ground. Consequently things are really, really zipping past your view out the window, giving your brain a very tangible sense of high speed. Then when you take off, the ground disappears, and suddenly you have no *visual *ques of high speed (or any speed) at all. Plus the noise actually *reduces *once you’re in the air, which normally is a sign of slowing down.
I remember the first time I rode on a big airliner, this feeling was so strong I thought we were about to stall!
Not to discredit your theory Hail Ants, but let me assure you my eyes are tightly closed and my knuckles white, on take off. I’m not really taking in any visual clues, though I do take your point.
One factor that hasn’t been mentioned yet regarding the sensation of acceleration is that acceleration forward pushes you back into your seat. This is the same sensation you get if you just tilt the seat backward. In flight simulators they use this similarity in sensation to fool you into thinking you’re accelerating down the runway by just tilting the whole simulator backward.
After you take off the aeroplane’s nose is pointing up into the sky at an angle of between 10 and 20°, ie your seat has been tilted backward. From that moment on, while the aeroplane is climbing to cruising altitude, the engine thrust stays much the same and the speed is controlled by raising or lowering the nose of the plane. The result is that pointing up at an angle of say 15° and staying at the same speed feels much the same as lowering the nose to 5-7° and accelerating. In the first case you are being pushed back into your seat by the angle of the plane and in the other you’re being pushed back by the forward acceleration. Either way you don’t feel much change after you take off.
What actually happens with the speed is you take off at something like 130 - 150 knots (depending on the aeroplane type) then after liftoff you stay at the take off speed until about 600 feet at which time climb performance is traded for acceleration and you gradually accelerate to 250 knots, retracting flap as you go. From 250 knots the speed gradually increases as you climb until you eventually are cruising at about 400-450 knots.
By contrast, if you’re cruising in level flight at a moderate power setting, and push the power up to the maximum you can definitely feel the acceleration, much like you do at the start of the take off roll.
