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Troy Thornton
Troy Thornton

I’m Spinning Backwards!



This also works when filming cars driving - if a camera is filming at 50 frames per second and the wheel is spinning such that it completes a full rotation every 1/50th of a second, the wheel will seem to be stationery. A wheel rotating reverse to the direction of travel must therefore be falling just short of a full rotation within that time slot, forcing your mind into the optical illusion.




I’m spinning backwards!



Unfortunately it behaves just like the COM is forward even while it isnt during reentry. As soon as I hit the atmosphere and the Reaction Wheel Torque fails (@ about 64km) the vessel starts tumbling backwards with the tail to the retrograde marker.


Thanks for your information and advice. It wouldn't help to test flight this craft under those conditions.The craft flipped backwards and keeps spinning during reentry up until it decends below 10 through 8km and then I can somehow fly level again. Which confirms @Plusck his explanation about drag versus lift.


Balance problems can make you feel dizzy, as if the room is spinning, unsteady, or lightheaded. You might feel as if the room is spinning or you're going to fall down. These feelings can happen whether you're lying down, sitting or standing.


"We'd turned the tape around, and I was in another room, heard the vocal melody coming backwards, and thought, 'That's miles better than the right way round', then spent the rest of the night trying to learn the melody."


Yorke was recorded singing the melody backwards; this recording was in turn reversed to create "backwards-sounding" vocals. I Will was later released in a different arrangement on Radiohead's subsequent album Hail To the Thief (2003).


Concerning the strong nose-down tendency: Changing the CG location to help this problem implies moving the CG backwards. This may not be a good idea, if the plane also seems unstable in yaw. Your description of how the plane flies indicate your problems may be that the tail surfaces, both horz. and vert., are too small. There is a calculation for how big tail surfaces should normally be, but I don't have it just here at hand. The minimum size of the tail is calculated using the areas of the wing and fuselage, of course, as these are what generate the forces which the tail must counteract. Your design seems to have a very large wing, and may need larger tail area to control it.


Dr Hugh Hunt @hughhunt For fun stuff on spinning things go to Dynamics movies page See also How does a bike stay upright - Surprisingly it's all in the mindHow do we manage to stay up on a bike? Gyroscopic forces are not important for the stability of a bicycle - as you can see if youread on below - but they help us to control the bike when riding with no hands. More important than anything is "the trail". The front wheel makes contact with the pavement at a point that lies behind the point where the steering axis intersects with the pavement - and the distance between these is called the trail. The trail is not zero because the steering axis is tilted and the front fork is bent. The trail works to stabilize a bike in much the same way as castors work on a tea trolley. When you lean to the right, say, on your bicycle force at the contact point on the pavement will push the front wheel to the right. This helps you to steer effortlessly and it allows for hands-free steering through leaning slightly left or right. The gyroscopic effect helps but the trail is the more important factor.The photos below catalogue an experiment which proves that the gyroscopic effect is small. Here I am pictured riding an ordinary bike, but with an extra wheel attached to the front axle. The tyre hasbeen removed to give a little clearance from the road and some copper cable (earthing cable with green insulation) wound around the rim in its place to replace the momentof inertia due to the tyre. The "extra" wheel can be spun up by hand, before you start riding,at any speed you like, even several times the speed of spinning of the "actual" wheel. It can be spun either forwards or backwards and what is so clear is that it really makes no differenceto the "ride" of the bike. The bike is just as easy to ride whether the extra wheel is spinning or not, forwards or backwards, fast or slow. So this makes us wonder: "How do we stay up on a bicycle"?The way we stay upright on a moving bike is by active control through steering. This is why we have to learn to ride a bike. If, as learners, we find ourselves falling over to the left then we learn to steer the bike to the left, which generates forces that tilt us back upright again, thereby putting the wheels back under our centre of gravity. Beginners are very wobbly, but as we become expert the corrections become smaller and we can ride in a straight line.The faster we ride, the smaller the steering adjustment needs to be, simply because the bike moves much further in a given time. When riding very slowly the steering adjustments required are very large. When completely at rest, active steering can do nothing for us.A good analogy is to ask, "Why is it easier to hop (or pogo-stick) along a straight path than it is to stand still on the ball of one foot?" The reason is that we use each hop to generate correcting forces and also to put our foot down in a new place that is closer to where we need it to be in order to maintain our balance. It is worth adding here that some bikes are easier to ride than others, and this is all to do with the "trail" described above, and many other parameters such as the hight and width of the handlebars, the height of the seat and the mass of the rider.Also note that a bike with no rider can stay up much more easily - as many of the bloggers responding to this article have said. This is because the bike is now much lighter and the centre of gravity is much lower. So the forces acting to cause the bike to fall over are smaller. This means now that both "trail" and gyro effects are much more significant in the overall dynamics of the bike and it stays up more easily. It is almost certain that gyro effects are important at the initial stage of steering manoeuvres. Many riders (especially motorbike riders)tell me that they notice the effect of "counter steering" above a certain speed.This is where any movement of the handle bar to the right (say) causes the bike initially to fall to the left. This is exactly as would be expected from the gyroscopic effect acting on the front (steering) wheel). The more sudden the steering manoeuvrethe more pronounced will be the effect - because the gyro effect is a couple (a moment, a torque - call it what you like) that results from the rate of change in direction of the angular momentum of the wheel. The larger the change of angular momentum, and the shorter the time over which the change takes place then the bigger the gyroscopic couple. But what happens after the initial gyroscopictransient is then no longer gyroscopic - you're then down to the effect of the trail and other steering geometry effects.The bike with the reverse-spinningwheel shown below would not exhibit any counter-steering effect because the front wheel has no net angular momentum. My point is that gyroscopic effects are not needed to keep you from falling over when you are riding in a straight line. I am not saying anything about what happens when you actively wish to steer away from straight ahead. Misconception 1:Some people think, incorrectly, that the gyroscopic effect exists because a wheel is spinning and thattwo spinning wheels must increase the gyroscopic effect - just like two heaters in a room are hotter than one. But the direction of the gyroscopic couple depends on the direction of spin and anyone who has tried this out by holding a bike wheel will know this. This meansthat two bike wheels spinning in opposite directions will produce couples in opposite directions and these will cancel. It is the purpose of the experiment described on this page to show that because this cancellation makes no difference to the ridability of the bike thengyroscopic effects can't have been important in the first place.Here is another photo that shows that it is easy riding even if the extra wheel is spinning backwards to cancel out (or even reverse) all gyroscopic effects. Let's do the math - some simple sums show clearly why the gyroscopic effect is unimportant: When riding quite fast at 12 mph, ie 6 m/s, a typical bike wheel (diameter 600 mm, circumference 2 m) rotates 3 times per second, which is a spin rate of &nbsp &nbsp &nbsp &nbsp ω = 20 radians per second.its peripheral mass, around m = 1kg, is concentrated at the rim, ie at a radius of r = 300 mm. The moment of inertia J is therefore&nbsp &nbsp &nbsp &nbsp J = m r2 = 0.1 kg m2 (near enough).Suppose I am falling over and I try to use the gyroscopic effect to help push me upright again. Consider some pretty frantic wobbling of the handlebars back and forth sinusoidally at a rate of, say, fhandle=1.6 wobbles per second (equivalent toan angular frequency of wobbling w handle= 2 p fhandle = 10 radians per second) and at an amplitude of, say, +/- 6 degrees (ie &#920 handle= 6/180* p = 0.1 radian) .The wobbling motion is therefore &nbsp &nbsp &nbsp &nbsp &#952 handle = &#920 handle sin(&#969handle t), and differentiating this gives a peak handle wobbling speed of &nbsp &nbsp &nbsp &nbsp &#937 = &#969handle &#920 handle = 10 * 0.1 = 1 rad/s . and this is the forced precession rate of the front wheel acting as a gyroscope.At its peak, the couple required to achieve this precession motion, due to gyroscopic effects, is &nbsp &nbsp &nbsp &nbsp &#920 = J &#969 &#937 = 0.1 * 20 * 1 = 2 N mThe bike and I weigh, say, 100 kg = 1000 N, so th


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