Torque

Helicopters display alooooot of physics. I can’t actually get my hands on real helicopter, so I used the next best thing—Microsoft Flight Simulator X. Torque is a key component of flight with helicopters. The engine applies torque to the main rotor blade shaft, which in turn causes the rotor blades to rotate and generate lift. Because of Newton’s third law, however, the helicopter also experiences torque from the rotor blades which must be countered with a rear tail rotor which is controlled by anti-torque pedals The pilot of a helicopter can directly control the torque output (displayed on a gauge in the top left as a percentage of maximum torque of a specific helicopter) with a control called the collective. I decided to do a demonstration flight in Flight Simulator in an MD-500 helicopter. If you pay attention to the torque gauge in the video below, you’ll notice that there is actually a significant amount of torque even when the helicopter is resting on the ground. This is because while the helicopter is resting, the rotor blades are still rotating and fighting air resistance. Increasing the torque will cause the rotor blades to generate more lift until finally the force from lift is greater than the force from the helicopters weight (mg), thus allowing the helicopter to accelerate upwards (notice that as I increase torque during takeoff, I must apply slight pedal inputs to keep the helicopter straight because of the increased torque). Also notice that the torque does not always stay constant throughout the flight, during hovers, and especially during landings. During landings such as the one I performed, you may actually notice an increase in torque as the helicopter nears the ground. This increase in torque increases the lift force to allow the aircraft to decelerate vertically and land smoothly on the ground instead of slamming into it.

VIDEO:


NOTE:Sorry the video quality sucks, I have to find better compression software (the original file was 900+mb =/). Its also kinda hard to see the gauge. I will reshoot and upload a higher quality video when time permits.

Oops...

This weekend was a weekend full of concerts and rehearsals for me. I started with a 2 ½ hr Youth Symphony rehearsal on Friday night, a rehearsal and concert for our school’s orchestra from 3-8:30P.M/ on Saturday, and another rehearsal/concert for Youth Symphony from 11:30A.M to about 9:00P.M. (yeah, I was pretty busy). Through all this one of my most important tools is my Getzen Custom Series 3047AFR trombone. I bought it in 10th grade and its been my main concert horn ever since, travelling with me to Kaui and Japan. When I first got it, it was nice and shiny, and although it still is fairly nice and shiny, it is now showing the signs of “heavy use.” Scratches are somewhat unavoidable, but also present on my trombone are dents both big and small. The largest dent is on the top of the main tuning slide. It dropped from the top of my trombone on a really hot day once (the hotter it is, the sharper your instrument gets. For example at ideal conditions your note A might be at 440Hz, but on a really hot day, the A played in the same position might be at 444Hz). The tuning slide had a potential energy of about (0.75kg)(9.8)(1.5m)=11.025J. When it hit the ground, all the potential energy was converted to kinetic energy. The velocity at which my slide hit the ground was thus about 5.42 m/s. When the slide hit the ground, there was an impulse between my slide and the ground. Since I did measure the velocity of the tuning slide immediately after it bounced off the ground or the time it stayed in contact with the ground (No, I did not drop and dent my slide in the name of science!), I cannot calculate the impulse, but I can conclude that the impulse was strong enough to leave a sizable dent in my brass tuning slide (brass is actually quite malleable). So I guess every time my trombone gets new “battle scars,” I’ll be thinking about physics!


My trombone doesn't look like this anymore =( (image courtesy of Getzen Co.)

Toys > Cleaning

I was cleaning up around my house the other day because it was getting to the point where I had to climb over stuff to walk through the living room, and I found a toy I received as a gift a few years ago. Since cleaning isn’t exactly fun, I decided I’d play around a bit with this toy. This toy consists of a wheel with magnetic tips that rolls along two metal rods. The wheel is held to the rods because of ferromagnetism. When you place the wheel on the rods and tilt it, the wheel will begin to roll along the path of the rods (see video 1).



Tilting is required to move the wheel because the force from the weight (mass*gravity)needed to overcome the inertia, or tendency to resist changes in motion, of the wheel. Once in motion, the wheel accelerates until it hits the bottom point of the rod. Assuming I started the roll from the top of the rod (holding the rod perpendicular to the ground), the wheel will have a potential energy equal to the mass of the wheel multiplied by the height of the rod. Because of conservation of energy, the kinetic energy of the wheel while at the bottom of the rod will therefore be equal to the potential energy of the wheel while it was at the top of the rod. In an ideal situation, the wheel would then be able to rise to the same point it started after it turns around for an upward motion. My wheel does not rise to the same level again at the second try, however (see video 2). This does not disobey the conservation of energy because energy was taken away from the system by friction (there is rotational friction between the wheel’s tips and the rods).



Because mechanical energy decreases due to friction each time wheel goes back up, the wheel reaches a progressively lower height. To keep the wheel moving, you must keep tilting the rod in a way that allows gravity to provide force to the wheel to replace the energy lost from friction. The lower you tilt the rod, the greater the y-component of force from weight, and thus the greater the speed of the wheel. As you can tell from the video, I was so blown away by the sheer awesomeness of this toy that I didn't bother to finish cleaning the house. I'll finish that...soon.

Into the Unkown

Like Joseph Kittinger, jumper for Project Excelsior, I am ready to jump into the unknown after what I have seen thus far of physics. After all, we won’t ever know the unknown until we go and see for ourselves right? Joseph Kittinger did not know what it was like to jump from over 70,000 feet above Earth, but that did not stop him from doing it, then doing it 2 more times until he reached 100,000+ feet. I feel that the groundwork has been established well for me this first quarter and hope that future concepts will become easier to learn as the year progresses. I really hope I don’t reach some sort of terminal velocity for my learning! I will strive to give it my all in physics throughout the entire year. I was lost throughout the year in chemistry. I got off to a weak start in chemistry and did not try hard enough to completely comprehend concepts, which I am sure is the reason why chemistry became progressively harder for me. I don't want to have a repeat of this this year. Although my experiences in chemistry were . . . not ideal, I am not letting that stop me from having fun in physics, and seeing and more importantly understanding all the physics I encounter in my everyday life is basically awesome. You really have to get yourself pumped for doing something like jumping from 20 miles above the Earth, and I am certainly pumped for the rest of physics!

Here’s a video with clips from the Project Excelsior jumps. The view from 20 miles up is amazing.

This Is Your Captain Speaking...

I am an avid flight simmer, with much too many hours logged in Microsoft Flight Simulator X, Falcon 4.0 Allied Force, and IL2 Sturmovik. One of the most important tools of this hobby is the joystick (I can’t afford a yoke, and you can’t fly combat with a yoke).


Yes, I like to flight sim

My primary joystick, the Saitek AV8R, uses a spring to hold the center stick in place and when I move the stick in any direction, the spring compresses like so:





Newton’s third law states that for every action, there is an equal and opposite reaction. The force of the spring is equal to the product of the spring constant and the displacement away from the rest point of the spring. So if I push the stick in a way such that the force of the spring is 10N, I would have to push on the stick with 10N of force to keep the stick in place and prevent any sudden pitch changes with my plane. The amount of force is directly proportional to the displacement (how much the spring is compressed or stretched) of the spring, so the further I push the stick, the greater the force required to hold the stick in a steady position. The throttles on my controller also display another aspect of physics. Somewhere inside the controller where the throttle is connected, there is something that is creating friction so there is a certain degree of stiffness to the movement of the throttles, allowing me to make precise adjustments to the power of my aircraft. I was surprised to find that even my game controllers demonstrated different aspects of physics!


Name that school!

Parachutes

Last year at the “Blues on the Bay” event at Kaneohe featuring the Navy’s Blue Angels, the U.S Army’s Golden Knights parachute demonstration team was one of the opening acts. They jumped from a CH-47 helicopter and drifted slowly toward the ground after deploying their parachutes. Their parachutes allowed them to have acceleration much slower than -9.80 m/s^2. If they had jumped without parachutes, they would have had acceleration closer to -9.80m/s^2 because the body of a person is much less than the surface area of a parachute. The bigger the surface area, the more drag is created. Either a small pilot chute or a static line attached to the aircraft is used to aid in the deployment on the main chute. An improperly packed parachute may not deploy, and therefore will not create the drag necessary to safely descend back to earth. Even without a parachute, however, a person will only accelerate until he or she reaches terminal velocity (about 50-60m/s for a human body), and there has been at least one case in which a skydiver survived a freefall to Earth
(See Mikey Holmes : http://www.esquire.com/dont-miss/wifl/parachutefailure0807).

Disk Brakes

Today I decided to replace the V-brakes on my bike with disk brakes from an old bike. Both brakes work by applying kinetic friction (surfaces are not completely smooth when looked at through a microscope, so when two surfaces rub together, they don’t just glide past each other, they experience friction), however the way they are applied differs. V brakes apply kinetic friction to the bike’s rim, while disk brakes apply kinetic friction to a disk mounted on the rim that passes through a slit in which two brake pads are squeezed to apply kinetic friction to both sides of the disk.

Here is a picture of the disk brake mechanism:


Because of this, disk brakes have an advantage over V-brakes because disk brakes don’t wear down a bikes rim (you can see some black marks left from the V brakes). Brakes help to decrease my bikes velocity through negative acceleration, assuming my bike is traveling in the forward direction. I can vary the amount of negative acceleration by varying the force applied to the brake cables through use of the brake handles. During installation, some oil dripped onto the brake pads, which reduced friction between the pads and the disk. Unfortunately, that was not what I wanted :(

Here's a picture of the V-Brakes on my bike...


And here's my bike with the disk brakes installed:


The finished product: