8,034 reputation
1728
bio website en.wikipedia.org/wiki/…
location United States
age 70
visits member for 3 years, 6 months
seen 9 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.


Jan
22
comment Transformators (primary and secondary windings)
@Ylyk: You'd have to read the placard on the transformer. I think it's typical to be rated in terms of peak voltage, not rms.
Jan
22
comment Why aren't gas planets and stars fuzzy?
Since you're asking this to make people think, and I bet you could make a good answer, why don't you answer it yourself?
Jan
18
comment How much effect does the Bernoulli effect have on lift?
@Alyosha: Pretend you're a wing. You can only be lifting if the pressure underneath exceeds the pressure above. Then pretend you're a slug of air. This wing comes along, cuts you in half, then pulls/pushes you downward. Same thing.
Jan
18
comment How much effect does the Bernoulli effect have on lift?
@Marty: I just think John S. Denker's book is terrific. He's a flight instructor, world-class physicist, and great teacher. I can read his stuff over and over and keep getting more out of it.
Jan
18
comment How much effect does the Bernoulli effect have on lift?
@Alyosha: There really isn't a larger thing. If you really want basics, you can go back to Newton's laws. Bernoulli's principle is just a consequence of Newton's laws.
Jan
18
comment How much effect does the Bernoulli effect have on lift?
@Marty: Yes. There is more than one way to analyze it.
Jan
18
comment Why are magnetic lines of force invisible?
You can only see things if they generate, absorb, reflect, or refract light. BTW, you can see magnetic fields by using iron filings.
Jan
16
comment Turboshaft Turbine Mathematical Model
Good question. I'm sure it depends on the resistive and inertial load of the driven turbine.
Jan
14
comment thought experiment involving water pressure
+ @Hapjake: Amount (volume) of water can be divided, but not pressure. Pressure depends purely on the height of water above the point at which the pressure is measured. An easy way to think of it is, suppose you have a tube with cross section 1 square cm, and you insert it into the water. Then the pressure at the bottom is just the weight of the water above the bottom (in the tube).
Jan
14
comment What causes an aircraft to roll when rudder is applied
@Rory: I'd been debating this with Larian, and then investigated. Pipers (low wing) have pronounced dihedral, but Cessnas (high wing) have practically none, so I was wrong about that. I claimed both have no noticeable sweep, but I was wrong about that too. They both have a little sweep on the outboard wing sections. Enough to produce roll? hard to tell. OTOH planes designed for aerobatics tend to have symmetric airfoil, zero dihedral, and some sweep. So I have to say, I'm less sure than I was.
Jan
14
comment What causes an aircraft to roll when rudder is applied
@Rory: But when you put in n degrees of rudder, the plane quickly equilibrates to a certain yaw angle wrt the airflow, at which point both wingtips are at equal speed, though one is forward of the other. Then wing sweep and dihedral produce roll moment, in ways depending on specific aircraft design.
Jan
12
comment What causes an aircraft to roll when rudder is applied
I'll grant you it's a bigger and really interesting subject. Every time these issues come up I learn something new. Cheers.
Jan
12
comment What causes an aircraft to roll when rudder is applied
Hey @Larian, I guess we're going to disagree here :) My understanding is any rudder displacement, regardless of bank, is going to produce a roll moment in an aircraft with dihedral. I was taught, and it was definitely handy for hands-off flying, that I could hold course with just my feet, in a 172 (that seems to have no sweep).
Jan
12
comment What causes an aircraft to roll when rudder is applied
In fact, Wikipedia says fighters have exactly that, so they trade off dihedral effect in favor of maneuverability.
Jan
12
comment What causes an aircraft to roll when rudder is applied
The small Cessnas I know have dihedral, but not any sweep, that I'm aware of. Diagram C is really confusing. I'm sure the sweep of the forward wing increases roll moment just because it sticks out further, but it says the trailing wing has more AOA and the leading wing has less. How can that be (assuming there is upward dihedral angle)? My sense of geometry says the opposite. If the dihedral angle were negative (anhedral) then I could see it. Maybe that's how your fighters are made.
Jan
11
comment Simple elastic collision
On top of all these good answers, remember that momentum is a vector, not a scalar quantity. So change in momentum is also a vector.
Jan
8
comment How to calculate uncertainties of a natural exponential function?
Just report your results as graphs on semi-log paper, with T on the log axis. Then you've just got two straight lines for your fit, one low, and one high.
Jan
8
comment How to calculate uncertainties of a natural exponential function?
1. Because it doesn't affect the gradient. 2. What do you mean "do with"?
Jan
8
comment Estimating drag due to wind - ribbon-shaped sail
Good question. I can imagine there could be technical solutions along the lines of how oscillations are addressed in airfoils and tall buildings.
Jan
2
comment Control cable failure and critical flutter speed margin?
Check this link. Flutter is a dynamic feedback condition that depends on a number of things.