Efficiency factor for an Airbus A380

[Airbusboy]

I am trying to calculate Induced Drag using Cl^2/Pi*AR*e. I understand e is a value less than 1. A bit of googeling, it seems it is approximated to 0.9 for general calculations.

Is there an accurate value for the A380? Would this info be available anywhere?

[enicalyth]

Oswald's "e" was a useful concept for the times, their computational methods, airfoils, wing sweeps and so on. You can estimate it if you want but try and do too much with it and an aerodynamicist will slap you down these days. I have had the good luck to work for both company "A" and company "B" and computation is all in the fluidics school of thought that began to emerge about 1973 or so. Generally speaking the aerodynamicist of today does not use much empiricism. The analysis may compartmentalise drag under four broad headings but these are artificial conveniences. In nature things fly and pay no attention to how you might like to break things down for easier mathematics. Airbus and Boeing might talk to a client about four or more drag headings and lift coefficients and all you can say is that the sum totals agree to spooky accuracy but not the parts. If you still want to go ahead have you not discovered the Piano X website that offers you FREE a beautiful analysis of the A380 and B787 and many other aircraft? It is the brainchild of one Dr Dimitri Simos but even his lift and drag breakdown will differ in parts from companies A and B. Both companies use his software and knowing their own aircraft perfectly will use the professional version of Piano to analyse their own aircraft. This gives them a steer on how good Simos is and he is very very good. Then they can use Piano to analyse their competitors. That's my recommendation. Google Simos, Lissys, Piano X and take all the freebies you can get. You can also see the prices of items you want but make sure you are seated with a stiff drink at your elbow. Real experts do not come cheap.

PS: My gut feeling is that any value of "e" higher than 0.89 is too good to be true in a swept wing Mach 0.80 plus regular passenger transport jet.

What an interesting topic. You have enlightened my day!

Best Rgds

The "E"