# Search results

1. ### Airplane pulling on the earth?

Okay, folks... let's put this one to bed. Tide: Your momentum argument depends on what your reference system is... if it is the Earth, then yes, the Earth loses a small bit of angular momentum as the plane ascends, but gains it back when the plane descends. If you consider the plane to be in...
2. ### Simple homemade helicopter

Herrbeta, always glad to help... Never say that... no project is ever useless. The most informative learning in engineering comes from actually DOing something. Anyhow... psf is "pounds per square foot" [lb/ft^2] Disk loading is a measure of the amount of thrust per unit rotor disk...
3. ### Simple homemade helicopter

Okay... What you're proposing is a little ambitious, but from a very basic perspective, let's analyze hovering flight... You are going to want a relatively low disk loading... let's say 10 psf (lb*ft^-2). So in hover, thrust is equal to weight, so that makes the rotor area... DL = 10...
4. ### Contact between two rings or two cylinders

Cylinder on Cylinder contact I recommend "Mechanical Engineering Design" 7th edition by Shigley, Mischke, and Budynas. ISBN: 007-252036-1 Section 4-20 has some great preliminary analysis tools and formulae for contact stresses of spheres on spheres and cylinders on cylinders (which I think...
5. ### Calculator for Mechanical Engineering

I personally use a TI-92 Plus. I bought it 6 years ago and still argue that it was the best \$200 I ever spent. I use it for EVERYTHING! Cheers...
6. ### Motor selection

Okay, as a good standard metric, the power output of a motor is proportional to the cube of the rpm. So your engine, as described, delivers 1 hp AT 1800 rpm. Using the cube metric, the engine should deliver about 0.005 hp at 300 rpm and 0.02 hp at 500 rpm. You are correct in that the power...
7. ### Personal exteriorless 'copter

There are a few problems with this idea. 1.) Counter-torque - in order to keep the passenger from spinning opposite the rotor, the machine would need two counter-rotating sets of rotorblades. The gearing to do this would make the vehicle bulkier and heavier (thus being less practical and...
8. ### Forced Vibration of a Cantilever Beam

Ah... a subject near and dear to my heart... vibrations... The quintessential book on vibrations is "Fundamentals of Vibrations" by Leonard Meirovitch (ISBN: 0-07-041345-2) aka the 'Bible according to Meirovitch'. Exactly the problem you describe, he addresses... along with every other...
9. ### Finding facts for fight

If you go to NORAD's website (http://www.norad.mil/) they are constantly tracking and updating orbital elements on everything that they are able to track. The NORAD TLE (two line element) gives you all you need to create and propagate the orbit of any orbiting object. Here are a few...
10. ### Navigation Question

The location of the poles vary throughout the year... by a few inches. And the rotation rate changes by a few tens of milliseconds throughout the year. So, no biggie... this tsunami is not a significantly huge terrestrial event (despite what the media is saying... and the chicken-littles...
11. ### To destroy an asteroid

Excellent question. At present we have NO way of destroying or even deflecting an incoming asteriod. I know what you're thinking, "But we have TONS of nukes on missiles sitting in silos all over Montana." Well, you're right, but we do not have any nuclear equipped missiles - be it the...
12. ### Deep Impact Mission Sounds Scary?

If you look at the value of the Jacobi integral for the Sol-Earth-'comet of interest' system, that can tell you a lot. Since this value is quite large for the comet targeted by Deep Impact (being run by UMCP... GO TERPS!), the amount of energy being imparted by the impactor is insufficient to...
13. ### Jet Engines

No... you can't make a jet engine run on H2/O2... it wouldn't be a jet... it would be what we like to call a "rocket". By definition, jets run on air... dumping a fuel and oxidizer together to combust is the definition of a rocket engine.
14. ### Boot Strapped Lift

As a good friend of mine always says... "You can't lift yourself up to the ceiling by pulling on your collar." However, this analogy does not apply here. Think about it this way. All you're doing is making flow pass over a wing to generate lift. Consider three cases: 1) A plane is...
15. ### Heated Tires

While they are stickier (and that is part of the reason), the primary reason for heating the tires is to maintain a nearly constant tire pressure from when the tire goes on the car to when it comes off some hundred miles later. Pit crews have gotten so good at making control adjustments to a...
16. ### Insects depend on vortices to keep them aloft

The military (or more appropriately DARPA) has been putting a load of money into micro-air vehicle (MAV) research. A lot of money has been given to the University of Maryland to develop a micro-rotary wing vehicle and synthetic jet actuator controllers...
17. ### Increased Flow Speed

Basically, what the problem comes down to is viscosity. You're trying to minimize the surface effects of the fluid along the interior surfaces of the pipe. Since viscosity is the product of shear stress at the wall surface and the gradient of the axial velocity at the wall, that's your...
18. ### 3D Thrust-Vectoring and Supercruise

I think I know what you're talking about here... The exhaust gasses are exiting the engine nozzle at supersonic speeds and being dumped into stagnant atmosphere. So, the pressure difference causes a shock wave to form. These shock waves from the edges of the nozzle converge until they...