8,597 reputation
1730
bio website en.wikipedia.org/wiki/…
location United States
age 71
visits member for 3 years, 10 months
seen 7 hours ago

BS Mechanical Engr.
PhD CS(AI)
CS Prof (4yr)
Numerous consulting jobs.
15 yr at http://www.pharsight.com
Published book on CS & several articles
4 kids, 2 grand
Pilot(student)

P.S. The picture is a Beta-prime distribution. It shows the program speedup factors you can get if you see a problem twice in 2, 3, 4, and 5 samples.


May
13
answered Numerical modelling of a step function in time in a hydrodynamic system. (Runge Kutta fourth order)
May
13
comment Why don't we build helicopter based space shuttles?
Can airplanes fly in no atmosphere? Of course not. There's nothing for the wing to react against. A helicopter rotor is just a wing that goes in a circle. (They are called "rotary wing aircraft".)
May
13
answered Resistors in parallel: How do I make this rigorous?
May
12
comment If atoms are mostly empty space, why doesn't light pass through everything?
True, if you keep in mind that where an electron "is" is uncertain - it is a wave function that is spread out. So is a photon.
May
11
comment Why is paper (or any tailless) airplane pitch stable?
If you see it nosing up and stalling, that means move the weight further toward the front. It needs to be forward of the center of lift, wherever that is (but not too far forward).
May
11
comment Why is paper (or any tailless) airplane pitch stable?
@Cleric: Actually you can choose any point you like as the fulcrum, it doesn't matter. If you choose the CG, the lift of the main wing produces an up torque, and the tail a down torque. (In a vacuum there is no lift.) Go back to the simple aircraft. Now lengthen the back of the main wing until it touches the horizontal stabilizer. Now you have a single-wing aircraft, but it still works, because at the back there is less lift than at the front (or negative lift). The differential lift between front and back produces the torque. A simple paper airplane can illustrate this perfectly.
May
11
comment Why is paper (or any tailless) airplane pitch stable?
@Cleric: The speed-dependent torque due to differential lift doesn't go to zero. The weight in the nose produces its own torque that counteracts the speed-dependent torque, so it's stable when the total torque is zero.
May
10
comment Control surface effect
What you're asking is really basic aircraft controls. There's no calculation required. Center of mass should be forward of center of lift. Ailerons control rate of bank, and bank controls rate of turn. Elevators control speed, and throttle controls rate of ascent or descent.
May
10
revised Why is paper (or any tailless) airplane pitch stable?
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May
10
revised Why is paper (or any tailless) airplane pitch stable?
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May
10
comment Why is paper (or any tailless) airplane pitch stable?
@Wet: Thanks for edits, and yes, quaternions are basic "rocket science".
May
10
revised Why is paper (or any tailless) airplane pitch stable?
edited body
May
10
revised Why is paper (or any tailless) airplane pitch stable?
edited body
May
10
revised Why is paper (or any tailless) airplane pitch stable?
added 134 characters in body
May
10
answered Why is paper (or any tailless) airplane pitch stable?
May
8
comment Why is paper (or any tailless) airplane pitch stable?
You're seeing "decalage" in action. Here's some basic stuff to read.
May
6
comment Does my (too low) tire pressure, affect the speedometer of my car?
I agree with this answer, on the assumption that the steel belts determine the outer circumference of the tire. If the tire is very flat, the tread gets squeezed tangentially as it moves through the contact patch, because it it taking a shorter path. This is not like a caterpillar tractor tread, unless the tire is allowed to slip tangentially along the rim, which I assume it is not. It will experience tangential stress, which might cause some slipping. Evidence of this would be the filler tube departing from being perpendicular to the rim.
May
4
comment Is a Super-luminal Laser spot possible?
Why fool with seconds? Suppose you see a supernova at one point in the sky, and one year later you see another at a different point. They are separated by millions of light years. Nothing "traveled" between them, except maybe our imagination.
May
3
revised Passively moving air
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May
3
comment How does a hovercraft hover, if it has low pressure underneath it?
I suppose they call it "low pressure" because it's lower than "high pressure".