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1

According to the wiki page the 747 has a max takeoff "weight" of about 350,000 kg (depending on the model) and a wing surface of about 500 m2. That means that a force of 3.5 MN must be carried by 5 million square cm, or 0.7 N per square cm. If you can somehow split this evenly between the top and bottom surface, then you need to come up with a paper surface ...


4

If the bearings were to be considered frictionless, then the maximum speed of the fan will not decrease, though it will take the fan longer to reach the maximum speed. Because as the moment of inertia of the impeller increases its angular acc. will decrease (for the same torque applied), therefore it will take the fan longer to reach its maximum speed. The ...


-4

Yes, the rotation speed will decrease. The reason is that the fan gets a constant power (energy per second) from the system which translates to a constant torque that rotate the fan against air resistance (and such). Greater mass density of the fan means greater value of the relevant Tensor of Inertia component of the fan. This means it takes greater force ...


3

This will depend on exactly what kind of motor you have. If your fan is a brushed DC motor, then the fan speed will be slightly lower, since the new impeller is heavier than the old, so there will be slightly greater bearing friction. The added friction will serve as a power loss, and the motor will have to run slightly slower. If the motor is a brushless ...


0

The wheels use regenerative braking drive a propeller/turbine to provide thrust not the other way around. In a typical sailboat or other wind powered craft the wind provides thrust and the resistance given by the conveying mechanism (water or wheels) is typically minimized. In this scenario however, the wheels have a little bit of regenerative braking ...


1

If gravity increases, so does air density and pressure, but also air temperature. Since density decreases with increasing temperature, the increase in density will not be sufficient to fully compensate for the increased weight of the aeroplane. The aeroplane will begin to sink, which in turn will increase its angle of attack. Consequently, it will settle at ...


0

Put very simply: An airfoil produces lift because of angle of attack; the leading edge of the wing is higher than the trailing edge. This imparts momentum to the air through which the wing passes and also changes the potential energy of that parcel of air.John Denker's website See How it Flies probably has one of the best and most straightforward explanation ...


2

You are right, the two explanations are not mutually contradictory. There are two ways of caluclation the lift on an airplane. You can look at the total mass of air being deflected downward by the wing, and equate the rate of change of momentum of the air to the upward force on the airplane. This is exactly what is going on, and for my money it is the real ...


1

For this problem we shall strict our calculations to incompressible flow, troposphere in atmosphere and standard ground temperature is independent of gravity. Please note this is not true, modelling that is difficult so this assumption is required to close this problem. This may give error in calculations but we shall get an overall picture. Here we are ...


2

If gravity changes, then so will the density of air. Air pressure at the surface is proportional to the weight of the column of air above it, so if gravity increases, the pressure would, too. That will in turn affect the lift from an airfoil. NASA says lift varies linearly with density. I suspect the two effects would pretty much balance each other.


0

It has to do with size. For small and slow-moving objects, viscous forces have more weight in comparison to inertial forces. Also, the layer of air close to the surface of an object which moves through air is differently structured. The dimples in a golf ball will make this layer resemble that of larger objects and help to make the flow resemble that around ...


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Mythbusters covered this one. They found significant fuel saving at constant speed. Assuming their findings are correct I can only guess that the technique is not used for cosmetic reasons ie few people would want to drive a car that looks like it has been in multiple accidents and covered in dents


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Major classes of drag:Two main factors of drag are friction and flow separation. This friction drag is dominant in streamlined shape and pressure drag (drag due to flow separation) is dominant in bluff body. Ways to reduce friction and pressure drag: Turbulent flow has more momentum than laminar flow so they reduces flow separation so pressure drag is ...


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Limits can be fuselage to the tip of the wings :) !! As some user mentioned its just a force in total, nothing to worry on the limits over the integration. If one take it as a line just summing all lines will give the area and of course the force. For example if xxxx Newtons force in a single line and summing it over the sampled area (each sample is ...



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