http://popsci.typepad.com/popsci/200...car_on_sk.html

 

yeah that's a new one to me

 

did anybody else cringe with their explaination of lift? Its flat out 100% wrong. They made the same mistake Newton made when he tried to determine if flight was possible (Newton btw, concluded that flight was impossible, he wasn't wrong on many things, but he was WAY wrong on that one. . .) Lift IS casued by the pressure differential, the momentum effects (what they describe) are minimal by comparison in flight. In the case of a ski jumper, there is no pressure differential generated b/c ski does not equal air foil, so momentum effects are the only ones involved, but to say "lift is generated only by turning effects" is flat out WRONG.

(sorry for the engineering rant)

I laughed my *** off watching that video though. . .

 

I thought lift was what the "WonderBra" did!!!!

 

I have seen that video a while ago. Classic.

 

There is no pressure differential without movement through the air, so with no momentum, there would be no lift.

Ski jumpers absolutely produce lift via the positioning of their bodies and skis. If the ski jumper didn't produce lift, then they would not go as far as a ball of equal mass rolled of the jump at the same speed, when in fact they jump much further.

 

Technically true I guess, but its not the momentum of the air molecules hitting the wings that causes a plane to fly, its the resulting pressure differential.

And the skier creates lift, you're correct I made a mistake there, and they do so through the same means as an airfoil, albeit a fairly inefficient airfoil. The momentum effects help to, but account for maybe 5% of the generated lift force at most. Fact is, the momentum effects of the air changing direction are only really of a relevant magnitude when you're talking about flight through rarified air (low air pressure) or at hypersonic speeds (Mach number>2.5, and for very different reasons in this regime). In all other regimes, the pressure effects dominate.

If momentum effects (momentum effects as I've described them) were all we had, then as Newton predicted (incorrectly b/c he was unaware of the pressure effects), flight would be impossible as we'd never be able to go fast enough to generate sufficient lift to fly. It was this conclusion that greatly retarded the developement of the field of aerodynamics, until a pair of experimentalists (The Wright Brothers) came along and said "I don't give a **** about theory, lets see if we can fly" and proved them all wrong, which sent the theorists scrambling to explain it, and started the field of aerodynamics as we know it today. The real explaination as to why Newton was wrong is this: Lift from momentum effects is proportional to velocity, lift from pressure effects is proportional to velocity SQUARED, hence a much lower velocity is required for flight than Newton thought.

Its a shame to see popular science make the same mistake, b/c although it seems a reasonable explaination at first, we've moved far past it in the last 100 years.

 

it does, in many ways...


that is a great clip though

 

great clip!

 

I was SO afraid it would land on its snoot. Glad to see it was graceful stop.. sort of.

 

Same here... I guess we in the US occasionally forget that in England sending an old Mini down a ski jump would be the same as sending an old Ford Escort down a jump here...