posted 06-09- 04:13 AM               

And I need a bit of FM advice: after mucho reading between the lines, and a bit of guessing, I think the D.520 has a NACA 23016 at wing tip and NACA 23020 at wing root (the 1.0 version uses the spit's airfoil, which is horribly incorrect). The 23016 is available (P-38), but what should I use for the wing root? In real life, the Fw-190, Lancaster and F4U also used some kind if NACA 23000 airfoil.

Right now my main problem with the FM is the stall speed is *much* too high. This is a weird thing with the real life D.520, it has a high wing loading (highter than the Bf.109E4), but its stall speed is supposed to be somewhat low, about 120 km/h. This is probably balanced by its stall characteristics, some pilots (probably inexperienced) finding them "brutal" and "unpredictable", whereas others found there were plenty of warning signs!

posted 06-09- 07:30 AM               

I am not sure what you are asking, but I hope this link helps. It is a great source of information on airfolis.

posted 06-09- 08:07 AM               

Also there is wash-out, the AOA of the wing tips is set to be a little less than the root section... this is set up so the tip stalls after the root, avoiding "tip stall". Tip stall cause more loss of control in a stall, meaning harder recover and more likelyhood of a resultant spin.

One could also say that the aspect ratio of the tip section is greater, but OpenPlane models aspect ratio for the over-all wing, not each section combined. But the correct average cord length can be used for each section.

The MOST critical thing about airFoils is the airPt, the location where OpenPlane calculates the patch of the wing through the air from, and the point where the forces will be aplied. The further out the airPt is, the more it will accentuate instability when one wing approaches stall before another... so much of what causes loss of control is because one wing is flying differnt than another, different airspeed, different AOA, etc. The further out the airPt, the more this differnce is magnified...

posted 06-09- 04:44 PM               

Sv, I think that, as long as relative thickness is different (being thickness/chord, here 0.2 at root vs. 0.16 at tip) then the airfoil is different, even if the profile type is the same. Now, I may be totally wrong about NACA profiles designations... This is completely new to me.

posted 06-09- 09:22 PM               

As I remember, both the Ki-43(Oscar) and Ki-44(Tojo) had differing root and tip airfoils, so they were certainly known and used during WW2. As you describe the way it is modeled, is this moot, or are you setting the airPt to average the lift/stall/drag/etc. for the wing through this single point?

posted 06-09- 10:04 PM               

If you do, just use the correct airfoil for the correct section. Most of the WW2 planes currently have 2 airPts per wing, or 4 total (that is the minimum OpenPlane allows). You could add more if need be, it is not a problem. You can also model wash-out by using airInc to give the wing tip section and slight negative incedence angle, thus giving the wing tip a slightly less AOA - all without altering the mesh (LOD).

It is indeed an "averaging"... but always more than one air section per wing must be modeled so that certain flight phenomenum are simulated. The biggest is AOA variation... in a spin for example, the inner wing will have a higher AOA than the outer wing- this is what causes a spin, not the airspeed differnce of the wings as is sometimes imagined.

The key is to note that each section of the wing has its own path through the air, much like two card tires make their own tracks... and when turning, they can be very different!

posted 06-13- 10:11 AM               

Some aircraft actually do use 2 profiles, the P-40 uses a NACA 2215 at the root, and a NACA 2209 at the tip.

Pachy, I found out MH & company used Xfoils to generate the airfoil data for the original planes. There's both a Windows and Linux version.

I've downloaded it but haven't had a chance to try it out yet. NVfoils looked hopeful, but it only lets you change the AOT to a max of +/- 20 degrees, and you need to go to +/-90