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I'm preparing a wall force analysis from an aircraft at different angles of attack that resulted from a cfd simulation, so I can plot the lift & drag polars. For the lift coefficient, should I only pick the wing surfaces to obtain the lift and drag forces or all the airplane's surfaces for the net forces? The fuselage and the wing fairings have positive lift, so I'm a bit confused if I need take them into account.

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  • $\begingroup$ It highly depends on the size of the fuselage relative to the wings. Like if you are working a missile then there is a noticeable chance that the majority if not all of the lift is generated by the fuselage. $\endgroup$ – user3528438 Jan 21 '18 at 20:37
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    $\begingroup$ Welcome to Av.SE! $\endgroup$ – Ralph J Jan 21 '18 at 20:59
  • $\begingroup$ Why not make multiple analyses? I mean, if you already have the data, presumably you have a working algorithm you can plug in to say matlab, you might as well. One for the fuselage, one for the wing fairings, one for the wings, one for the entire aircraft. Should give a nice spread of data to go over, figure out which parts are causing the most drag and re-design them to produce less drag, etc. Ideally you would write software to do all this for you and test a range of shapes/sizes for different parts like the fuselage/fairings, nose cone, etc. $\endgroup$ – Noah Wood Jan 22 '18 at 3:43
  • $\begingroup$ The lift coefficient tables from wind tunnels are mathematically adjusted for tunnel peculiarities and based on above average surface smoothness, a 2-3ft chord, and an infinite wingspan. So, they are more efficient than the real world. However, the use of these numbers ends up being a very close approximation to the real world because the fuselage and power plant add additional lift. So, use the CL for the wind tunnel and you will have a very close real world approximation. I wrote a MS Small basic program for stall speed estimates using published CL. The result was within 2% of real planes. $\endgroup$ – jwzumwalt Jan 22 '18 at 3:43
  • $\begingroup$ Well, it depends on what you want the lift coefficient for, the entire aircraft,. or just the wings? It sounds like you want it for the entire aircraft. As to whether it's worth the additional effort, that would depend on how much lift is being generated by the rest of the aircraft surfaces. Again, form your question, it sounds like, at best, you are unsure about this, so the only way to find out is to include the aircraft surfaces in the calculation, right? $\endgroup$ – Charles Bretana Jan 23 '18 at 16:52
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If you want the lift for the whole airplane, of course you add the contributions for each part. While the fuselage might indeed contribute a positive lift, its presence will lower the lift of the wing. In the end, all parts of the aircraft will stick together when it flies and need to create just enough lift to keep its mass airborne, so it makes sense to look at the sum of all parts.

Since the wing will dominate lift, it is common for first-order calculations to consider the wing only. However, if you have data for all parts, you should include all their contributions, too, for a more precise result.

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$S_{Ref}$ could be any arbitrary area you choose .Only requirement is that it needs to be consistent for all calculations. Most commonly used $S_{Ref}$ is the wing area.

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