Does It Take a Physicist To Explain This? – IOTW Report

Does It Take a Physicist To Explain This?

Saturday, 22 July 2023, 20:00 BFH Uncategorized 60

60 Comments on Does It Take a Physicist To Explain This?

  3. The pilot rolled the airplane (rotation along the front-to-back axis) carefully maintaining a lift force of approximately one G throughout the manoever by careful elevator control with just a touch of rudder and aileron.

    It take a fair amount of skill, especially with the engine stopped, and is very impressive to those who haven’t seen it before (and quite rightly so!).

    p.s. The rudder is on the vertical part of the tail, the elevators are control surfaces at the trailing edges of the wings and both sides operate in unison, and ailerons are also on the trailing edges but act opposite to each other.

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  11. “A weight on a string will explain it.”

    That’s Centrifugal force. Gravitates away from the center of rotation.
    Centripetal force gravitates toward the center of rotation.

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  13. Here’s something cool I learned today. Might require further investigation, but I was told buy a store manger at Home Depot, that when you “Tap” your credit card, that purchase can’t be traced. That’s why Home Depot does not offer the Tap option on any of it CC processing equipment. If I owned a guns store—–.

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  16. To elaborate a bit on Uncle Al (BTW, I have both a degree in Physics and flying experience).

    Looks like a twin engine plane. The pilot throttles back both engines to idle, then pulls the nose up (gaining altitude initially but losing airspeed). There is then a stall (an aerodynamic stall, not an engine stall) where the plane speed reduces to the point that the air flowing over the wing becomes turbulent, losing lift, and the plane starts to drop like a rock.

    Pilots practice stall recovery as part of their training. The preferred method is to keep the nose pointed in the same direction, go into a shallow dive to gain airspeed, then pull out of the dive. If you have engine power you throttle up the engine(s) to continue flying. If your engine(s) are out you go into “sailplane mode” and look for a golf course or farmer’s field to land in.

    One other possible outcome of a stall, if the pilot is not careful, is to go into a spin (the aircraft rotates about its vertical axis while descending in a dive of varying steepness). This sometimes ends poorly, but pilots also train how to recover from spins (apply opposite rudder to cancel the rotation then pull out of the dive once airspeed is re-established).

    It looks like the pilot in the video recovers without going into a spin, but does perform a barrel roll in the process of recovering from the stall. There are two types of roll–aileron rolls, where the plane just rotates on its longitudinal axis, and barrel rolls, which is sort of a combination of an aileron roll and an “inside loop.” In a barrel roll, with enough airspeed going in, the pilot can maintain the effective gravity vector downward (toward the floor of the plane) even while the plane is inverted. The pilot just has to accelerate the plane toward the earth at more than 1 g while inverted.

    Two other examples of the same phenomenon: The looping roller coasters where as you get to the top of the loop, you don’t feel pressure on your shoulders but rather just a “lightening” feeling in the seat (the pressure is still toward your feet even though you are upside down). Also clothes dryers. If your dryer drum spun as fast as your washing machine on the spin cycle, the wet clothes would just stay plastered to the drum and wouldn’t dry very fast. If the dryer drum were to rotate too slowly, the wet clothes would just roll around in the bottom of the dryer, again not drying too quickly. The drum rotation speed is set so that the clothes cling to the drum wall (by centrifugal force) only until they reach a point somewhere below the top, at which point they “tumble” through the hot air closer to the center of the drum before falling back to the drum near the bottom.

    Now, aren’t you sorry you asked a Physicist (and pilot in another life)?

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  21. @Brad:

    So in other words Centripetal force. Yes or no?

    Centripetal and centrifugal forces are always equal and opposite. If you’ve got one, you’ve got the other. Centripetal force keeps the cup in the holder. Centrifugal force makes the water pour into the cup.

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  22. I USED TO THROW SPITBALLS IN HIGH SCHOOL, INSTINCTIVELY KNEW THE ACCELERATION NEEDED CONSIDERING THE DISRANCE ACROSS THE CLASSROOM, I FOUND THAT THE PEAK ALTITUDE SHOULD OCCUR ABOUT HALFWAY TO MARY’S EAR, AND WITH THE RIGHT DIRECTION, COULD IMPACT THE TARGET WITH EASE

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  24. @SS — @Outdoor you-know-who mentioned Hoover!

    I saw Hoover fly at Oshkosh in, I think 1986 or so. Heard him speak. Did you know he flew chase for Chuck Yeager’s 1947 Bell X-1 Mach 1+ flight? Heckuva man!

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  25. @Brad. Negative on gravitational pull from two directions. Near Earth surface, gravity is ALWAYS straight down.

    In straight and level flight, the lift from a plane’s wings pulling the plane up is exactly equal to the force of gravity pulling the plane down.

    What the pilot is doing here is controlling the wing’s lift as he rolls the plane over, and does so gradually and compensating for the fact that the direction gravity is pulling him, the plane, and the water, is going around in a circle. When he’s upside down, gravity is still pulling him toward the ground with a force of, as always, 1g. But the pilot is controlling airspeed and angle of attack so that his wings are generating 2gs of force in the opposite direction. 2g minus 1g = 1g, but the direction is away from the ground, so the water pours into the cup.

    Does that make sense?

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  27. Quinn, Mr PHD with 8 likes.
    Please confirm, at the apex of his barrel roll we had gravitational pull from two different directions? Yes or no. I’m a high school educated idiot that says impossible.

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  28. Well, consider coutersteering as you do on a motor bicycle. Or any bicycle, but it is more pronounced on a heavier motor bicycle with larger tires. That is pulling in many different directions at the same time.

  30. centripetal forces (plural noun)
    a force that acts on a body moving in a circular path and is directed toward the center around which the body is moving.

    The pilot has made his own center of gravity.

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  31. Quin, Unkle Al
    Don’t worry about making me look like an idiot. I’m married.
    At the apex of his barrel roll, of flat spin, we had gravitational pull from two different directions?
    Is this possible?

    1

  32. BENITO, You Crack me up!

    I used Sandwich Meat in the Cafeteria.
    I started almost EVERY FOOD FIGHT and Monsignor Percy Johnson High School in Rexdale Ont. 1984-88

    Lets see if anyone figures out my True Identity Now. Tee Hee.

    4

  34. Why is that funny? You steer a motor bicycle by countersteering. The bike wants to stay upright, and will do so as long as the rider doesn’t do something silly. Now we get into “contact patch”. You steer to the left to go to the right. You are not only overcoming the bike’s need to stay upright, which is the wheels and tires turning, you are changing the contact patch of the front tire, and eventually the contact of the rear tire. You make the bike turn by forcing the front tire onto a shorter radius of the front tire.

    So again, it’s equal and opposite forces that need to be overcome for something to change.

  35. Brad, there’s all kinds of interesting stuff about gravity and space/time curvature and the fundamental forces but all of that is completely irrelevant to what we’re dealing with about the airplane and water.

    There’s only one gravitational force that matters, and that’s the one that attracts everything straight down toward the earth’s center. The other forces are all inertial forces that arise when you make something move, or move faster or slower, or move in a different direction. (Let’s not get into magnetic or electrostatic attraction. They exist but I don’t care in this scenario.)

    Those are not gravitational, but here’s where things may get a little strange: from a local point of view, say the inside of an airplane cockpit, there’s no way to tell if a force is gravitational or inertial, not without cheating and looking outside. And that’s why it seems that gravity may be pulling in two directions at the same time. It isn’t. But you can’t tell the difference if you’re inside a closed box and can’t look outside.

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  40. I used to have a Labrador who would ride next to me in my truck. She would always lean into me on a turn. Whether the turn was right or left, she would always lean left (into me). So was that centrifugal or centripetal force?

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  43. Tony R, that has come up for tens of thousands of miles. Leaning, or kneeing, keeps the bike more upright. The more you get your corporosity off of the center of the bike means the bike has to lean less for a radius.

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  45. @Brad: There is only one gravitational force to consider, that is toward the center of the Earth. The water is actually falling toward the Earth at all times, it is just the the airplane (and therefore the bottom of the cup) is falling faster. The end result is the the water stays in the cup.

    Getting it smoothly pour into the cup at all attitudes of the airplane during the barrel roll is some skilled piloting.

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  52. I didn’t see anything that looked like a ‘stall’. Not sure why he cut the power to do this, perhaps to make it more dramatic looking. But without thrust from the engines he did have to drop the nose to maintain speed.

    The maneuver is a type of coordinated turn. When a commercial airliner changes direction and the pilot just dials that turn into the flight director (autopilot), if you look out the window you’ll see one wing dip well below the horizon in some turns, but your drink on the tray table will have the liquid perfectly level. The plan may be banked (tilted) 30 or 40 degrees but your butt in that seat is telling you the plane is straight and level. This phenomenon is what gets inexperienced pilots in trouble when visibility is low. Their butt is telling them they are straight and level, but without visual clues they can do a lazy corkscrew right into the dirt. Balancing the force of gravity against the acceleration of the plane as it changes vector (direction) and keeping the apparent direction of gravity unchanged is the definition of a coordinated turn.

    If you were behind this plane while this was happening you would see a moderate descent while the plane did a ‘corkscrew’ roll at a constant rate. All the aircraft control surfaces are employed, aileron, rudder and elevator to make this happen.

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  54. @Lowell — One additional quirk of coordinated turns is that if the plane maintains altitude, passengers will feel a bit heavier during the turn. That’s because of vector sum of the 1g force needed to stay at height, plus the force causing the plane to turn, must always be greater than either force. In geometric terms, a rectangle’s diagonal is always longer than either side.

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  55. @Lowell — And I agree that there was zero indication of a stall (much less a spin) in the video. It was a straightforward coordinated aileron roll while maintaining a 1g cabin force by losing altitude. @Quinn’s comments notwithstanding.

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  57. Hooray, everyone gets a prize.

    Gravity is a theory that you study. So you’re all correct.

    Gravity is like replacement theory, but with fewer rules. Only liberals can play replacement theory, everyone else is DEAD WRONG.

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