Maximizing Aircraft Performance: Understanding Oswald Efficiency Factor

[ank_gl]

i googled a lot, the best hit i got was
" 'e' is a parameter which expresses the total variation of drag with lift. It is sometimes called the span efficiency factor or Oswald efficiency factor after Dr. W.B. Oswald who first used it. It would be 1.0 for an elliptically-loaded wing with no lift-dependent viscous drag, but for practical aircraft 'e' varies from about 0.75 to 0.90."

i couldn't make much of it, can anyone elaborate a lil bit

 

[kach22i]

This "Proposal" refers to "Mises 1945".

Link-1:
http://www-scf.usc.edu/~tchklovs/Proposal.htm



Some interesting stuff here but nothing on shape of wing tip.

Link-2:
--- Link Removed ----

NOTE: Link-2 is somewhat a radical view and out of mainsteam but interesting.

 

[ank_gl]

We know how to increase the velocity and the area of the wing, but how to increase the coefficient of lift? (The coefficient of lift is merely a measure of how much the estimated lift the wing will develop v/s the experimentally tested lift as measured. Since this is how far off the computations are as to the real lift produced an increase in the coefficient only indicates more error in the guesstimate!)

Secondly, adding power to increase the velocity increases lift to the square of the velocity but why? The pilot can also increase the angle of attack and produce more lift but this factor is no where in the formula!

Thirdly, increase in wing area will sometimes produce more lift but the question is which way are we to increase the wing area? For instance a wing with 40 ft. wingtip to wingtip (wingspan) and 8 ft. average leading edge to trailing edge of the wing (chord) will produce an airfoil area of 320 sq. ft. but an average wingtip to wingtip (wingspan) airfoil of 8 ft. and a 40 ft. (average) chord will also produce an airfoil of 320 sq. ft. but produce practically 0 lift!

--- LInk removed ----
dont know about the first part, 2nd and 3rd part are complete crap.
2.increasing angle of attack => increased Cl
3.8ft span and 40 ft chord wing also ll produce same lift, but would be very unstable.
right

 

[russ_watters]

We don't give crackpots free advertising even if just via debunking here, kach. That link was utter crap. Rediculously absurd. It is breathtaking how much energy they have put into something so utterly devoid of any basis in reality. In fact, many of the key points were so far off that they don't even provide a starting place for debunking. Ie, the complaint about the Venturi effect described a process that bore little resemblence to the Venturi effect. So there was nothing to debunk. The line about Burt Rutan's Voyager having it's wing on upside-down was a real chuckler though. Yah, it produced negative lift while on it's takeoff roll. That's done on purpose so they don't spontaneously take off before the pilot rotates. They sit on their landing gear with a negative angle of attack.

 

[ank_gl]

ok now anyone for my question?

 

[caslav.ilic]

Oswald efficiency factor of the wing at a given lift coefficient is defined as ratio of the wing's induced drag coefficient and induced drag coefficient of the equal aspect ratio elliptic wing at that same lift coefficient. Since the elliptic planform will have the lowest induced drag among all planar forms of same aspect ratio at any given lift coefficient, then this ratio somehow reminds of an efficiency meassure, hence the name.

Oswald efficiency factor in general depends on the lift coefficient (i.e. angle of attack). For example, a trapezoidal wing can be optimally twisted for some given angle of attack to produce induced drag near to that of an elliptic wing (near unity Oswald efficiency), but will become worse as the angle of attack shifts away from that optimized for.

The importance of wing's Oswald efficiency depends on how large is the part of wing's induced drag in the total drag for designed for performance types. For example, in range-efficient cruise of an airliner I've read that the induced drag is like 20% of total, whereas it can be more than 50% for time-efficient high-altitude loiter of a surveillance UAV.

But this is all textbook stuff, so sorry if I'm wasting your time by stating the obvious :)

--
Chusslove Illich (Часлав Илић)

 

[kach22i]

ok now anyone for my question?

It seems one of my links hi-jacked your thread, I'm sorry about that.

I can do a Google search as well as anyone else, but have little idea how to help you.

This is what I found::

Formulas and charts;
http://www.desktopaero.com/appliedaero/potential3d/induceddrag.html

Note that e simply depends on the shape of the lift distribution. It is called the span efficiency factor or Oswald's efficiency factor. Note also that the induced drag force depends principally on the lift per unit span, L/b.

Pictures and text:
http://selair.selkirk.bc.ca/aerodynamics1/Drag/Page8.html

From this equation we can see that the most powerful design feature for reducing induced drag is a long wingspan (b). Thus, any aircraft, which will be flown at relatively large angles of attack (small V), should have the longest possible wingspan. This would include aircraft such as gliders, as well as high altitude spy planes such as the U2. It also includes to a lesser degree modern jet airliners.

I trust this will help to keep things on topic.

 

[ank_gl]

But this is all textbook stuff, so sorry if I'm wasting your time by stating the obvious :)

--
Chusslove Illich (Часлав Илић)

well guess what! that didnt waste my time.

Oswald efficiency factor of the wing at a given lift coefficient is defined as ratio of the wing's induced drag coefficient and induced drag coefficient of the equal aspect ratio elliptic wing at that same lift coefficient.

that helps to understand it completely. i didnt knew what to compare it with first. making the elliptical lift distribution as the standard is a good definition

 

[ank_gl]

This is what I found::

Formulas and charts;
http://www.desktopaero.com/appliedaero/potential3d/induceddrag.html


Pictures and text:
http://selair.selkirk.bc.ca/aerodynamics1/Drag/Page8.html


I trust this will help to keep things on topic.

thanks for the help kach, but i have bookmarked both of these links for years now. they are a good help. anyways chuss solved my problem

 

[kach22i]

Now that the question has been answered.....Can the Oswald efficiency factor be applied to propellers?

The reason I ask is that some of them are rather elliptically shaped.

Sample:
http://www.whirlwindpropellers.com/html/airboat/airboat_stump_puller.shtml