Lift

[Tom22]

I thought I would ask a trivia question .

 

Without friction could lift be obtained?

[r22butters]

Does the Space Shuttle count?

[Tom22]

Does the Space Shuttle count?

 

The Space Shuttle counts when it is not operating in a vacuum.

Edited January 21, 2010 by Tom22

[Eric Hunt]

Yes you would get lift - you are deflecting air down, so you get a reaction up (lift) and back (drag). Even if you used simple newtonian physics, with air particles behaving like tennis balls, you would get lift. But that is over-simplifying things.

[kodoz]

If you had a frictionless surface, would you have adherence of air to the airfoil? If not, then no friction = no lift. That's my Junior College Remedial Physics 101 answer. I see me deleting this post later out of shame.

 

That won't stop me from criticizing Eric's answer, which is good, but assumes most lift is from Newton's 3rd. So you'd get at least some lift.

[arotrhd]

Just look at Eric's Avatar....lots 'o lift, NO friction. Even repeats in perpetual motion. And no criticism from me.

 

-WATCH FOR THE PATTERNS, WATCH FOR THE WIRES-

 

BTW Tom, how's the grad research going. Have you decided to further my studies into wire strike education and prevention yet? Go Eagles!

[Guest pokey]

interesting question,,,,, i dont really have an answer. Looking at the situation in reverse, if we were to increase the air friction ? i guess it would produce the same amout of lift as prior to our increase, but? take ALOT more power to spin it. I think i'll go out on limb here & say YES, still will produce lift AND? you can eliminate the tail rotor because once you spin the main rotor up to operating speed? it will never stop ! hmmm we can eliminate the engine too !

 

I think this sounds like a good project for a rainy day

[jaredsega]

Google FoilSim its pretty cool

[RockyMountainPilot]

No friction means no heat means everything is solid, even air. Nope, no lift.

[Tom22]

All right, I get some utility out of my books!

 

arotrhd,

Grad school is going well. I’m looking for a research project – I would like to research something that involves helicopters since that is where my interest lies.

 

I think kodoz has the right idea.

 

This is what I think the answer is:

 

It is easy to see why the surface pressure distribution is the dominate factor in the production of lift – it is. The surface pressure distribution normal to the airfoil is in the vertical direction (lift) and shear stress (drag) acts tangential to the surface. Drag (friction) is usually seen as having a negligible effect in the generation of lift. After all, inviscid theories can predict lift on an airfoil below stall speed with great accuracy (Anderson, 2007). However, lift is the integrated (from the calculus) distribution of pressure and sheer stress and the reality is that, “the presence of friction is the very reason why we have lift” (Anderson, p.316). Why?

 

Nature ensures that the viscous boundary layer stays attached to the airfoil all the way to the trailing edge and the boundary layer is the mechanism for which the flow adheres to the surface. The boundary layer leaves smoothly from the trailing as a result of nature choosing a particular value of circulation on a giving airfoil at a particular angle of attack. This is known in aerodynamics as the Kutta condition. M. Wilhem Kutta was a German mathematician who first observed this phenomenon of flow circulation and it is a significant aspect of the circulation theory of lift. Through friction, nature enforces the Kutta condition and without it, there would be no lifting force (Anderson, 2007). It is interesting to note that the surface pressure distribution, “is an inviscid phenomenon, that would not exist in a frictionless (inviscid) world” (Anderson, p.316).

 

Anderson (2008) states Newton’s third law is an effect of lift rather than being the cause and that the pressure distribution on the airfoil alone is the fundamental source of aerodynamic force.

 

References

Anderson, J.D. Jr. (2007). Fundamentals of aerodynamics (4th ed.). New York, NY: McGraw-Hill.

Anderson, J.D. Jr. (2008). Introduction to flight (6th ed.). New York, NY: McGraw-Hill.

Edited January 22, 2010 by Tom22

[Guest pokey]

R A A A A A Tssssssssssss !

 

i guess i'll scrap my plans on my frictionless/engineless/tailrotorless fly forever & free helicopter

 

Thanks Tom for tossing a wrench on my road to $ billions $ Care to buy a slightly used time machine?

 

[DaveKnell]

No friction means no heat means everything is solid, even air. Nope, no lift.

 

Not true, I'm afraid: there's more ways to make a fire than just by rubbing sticks together..

 

--Dave

[RockyMountainPilot]

Not true, I'm afraid: there's more ways to make a fire than just by rubbing sticks together..

 

--Dave

 

How would you create heat if there is no friction between molecules?

[DaveKnell]

How would you create heat if there is no friction between molecules?

 

I might:

- burn some gasoline;

- pass an electric current through a resistor;

- collect ~10^30 tonnes of hydrogen together and let it collapse under its own gravity. It'll heat up - I'm sure you're aware of Boyle's law - and become properly exothermic when nuclear fusion kicks off.

 

--Dave

[RockyMountainPilot]

I might:

- burn some gasoline;

- pass an electric current through a resistor;

- collect ~10^30 tonnes of hydrogen together and let it collapse under its own gravity. It'll heat up - I'm sure you're aware of Boyle's law - and become properly exothermic when nuclear fusion kicks off.

 

--Dave

 

But all of those require friction between molecules.

[kodoz]

But all of those require friction between molecules.

-- Breaking chemical bonds requires energy, but not necessarily friction

-- Electrons aren't molecules, but partial credit here

-- Fission/fusion? Subatomic particles don't know the meaning of friction.

[DaveKnell]

But all of those require friction between molecules.

 

I don't think so. Can you explain why?

 

--Dave

[Tom22]

R A A A A A Tssssssssssss !

 

i guess i'll scrap my plans on my frictionless/engineless/tailrotorless fly forever & free helicopter

 

Thanks Tom for tossing a wrench on my road to $ billions $ Care to buy a slightly used time machine?

 

 

Sorry Pokey, I didn’t mean to throw a wrench in your plans for a frictionless helicopter. Don’t scrap those plans just yet. I think another good project for a rainy day is the human-powered helicopter; after all, the prize is still up for grabs! However, there is competition so you better get started.

 

http://www.vtol.org/awards/hphregs.html

 

http://www.humanpoweredhelicopters.org/

Edited January 23, 2010 by Tom22