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Post by Mike Monce - HJG on Mar 27, 2013 19:57:50 GMT
Well I was wrong... about the curves for flaps in the air file....there really aren't any However, I did run across the pitch moment for the flaps that in the DC9 series has a negative value, which (according to the guru Ron Freimuth) should have a positive value... So, flap editing really comes down to the cfg values along with just the air file parameters. But those parameters also play into the lift and pitch curves in general as they change the AoA Yep... BULLNUTS AND JELLYBEANS! Mike
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Post by aerofoto - HJG Admin on Mar 27, 2013 20:04:54 GMT
It's a "KIWI-ISM" And I've got "plenty more" from where that last one came from .... SO .... stick around "ACOURT" and I might be able teach/corrupt you some more ;D Sent you a PM BTW Mark C AKL/NZ
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Post by christrott on Mar 27, 2013 21:13:36 GMT
Glad to know you're making headway on the pitch moments.
Mike - When I said "angle of incidence" I was speaking the effective AoI. Remember, flaps add lift by changing the incidence of the wing, not just by making the wing bigger. Same with slats. because of the changes in the airflow by changing the lower curvature of the wing, you effectively change the area, camber, *and* incidence of the wing, creating more lift. The change in apparent incidence (not actual) is what causes the pitch trim change as it affects the center of pressure/lift more than anything else. The change in camber and area is what creates the additional lift and/or drag.
I wish I had a good graphic showing what I'm talking about, but the book that has the image showing it is in storage so I can't scan it. My explanation using the figure was an attempt to explain it as simply as possible just so you can see how the effective angle of the wing compared to with everything retracted changes and that it happens to have a direct correlation with how the pitch trim changes as that angle changes.
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Post by acourt on Mar 28, 2013 0:05:02 GMT
Chris, I think I see what you're saying. Angle of attack is measured from the chord line of the wing, which always extends from the leading edge to the trailing edge. As the slats extend, they take the leading edge with them, down and forward. But since the trailing edge stays in place, the chord line is angled down toward the slats/leading edge, recuding the angle of attack. Likewise, as the flaps extend, they take the trailing edge with them, again changing the chord line and angle of attack, but in the opposite direction. Whew! Been a while since I've had to think about that! Is this kind of like the drawing you're looking for? flysafe.raa.asn.au/groundschool/aileron2.gif
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Post by acourt on Mar 28, 2013 0:13:44 GMT
I second that hardy Bullnuts and Jellybeans. But, I think I've got the numbers close. All I did was work with Chris's suggestion: change the slats' pitch scalar to -10.0, then add a pitch scalar to the Flaps.2 section of +8.5. I'm still not sure the trim works out right, put the pitch attitudes and power settings are still right on. But here's some things to notice...
1) When you extend the slats, a hefty nose-up trim is required. When you retract the slots, you'll need to trim nose-down quite a way.
2) Extending the flaps/slats directly to 5 degrees is the smoothest, since the pitch change from the slats is almost exactly opposite of that from the flaps. This is a common technique in the airplane.
Both these characteristics are shared with the real airplane, so I'm pretty happy. Try it, and let me know what you guys think.
I know all of you probably think I'm crazy for chasing after this seemingly inconsequential detail, but you wouldn't believe the difference it makes to me. That "slats retract, trim nose down" muscle memory is hard to break.
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Post by hornit - HJG on Mar 28, 2013 6:05:23 GMT
As a real pilot, over the years, I have done a lot of air file editing AND cfg entry editing. FS is a strange beast and as others have said, you can change a parameter like flap lift, drag scalar, control surface effectiveness, etc, but what you end up with rarely works in ALL flight regimes. You usually end up breaking something else more than you "fix" what you are focusing on.
FDE's are like this too, and its kind of an art to get things to feel right. I've come to the conclusion over the years that the best we can do, is to get some of the quirks for different aircraft to be close. FS just does not have the fidelity to make a wide range of FDE's perform in any real world fashion.
Bottom line? its fun to try, but in the end, you ALWAYS end up compromising something and never getting it completely correct for all phases of flight. I personally concentrate mostly on the slower phases of flight around landing and takeoffs. Mostly since i like to handfly these wonderful models in the sim. As long as its somewhat "close" I am really happy and no longer get wrapped up in the minutiae of perfect speeds, trim, feel, etc.
I think HJG has done a MARVELOUS overall job of making these birds FEEL darn close to what its like in the real world, within the limits FS imposes. My hat is off to ALL of you responsible. I have been particularly happy with the MD series and the DC-9's. I think they fly really well for a simulation and enjoy hand flying all of these birds a lot. This coming from someone who has 12000+ hours in the MD-88/90 aircraft.
Good luck acourt! I'd be interested to try what you come up with when its ready!
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Post by hornit - HJG on Mar 28, 2013 6:07:55 GMT
In the MD-88/90 going directly to flaps 11 from a clean wing is the same as your comment about flaps 5 acourt. The whole wing reconfigures simultaneously and its the smoothest transition we can do.
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Post by acourt on Mar 28, 2013 10:59:21 GMT
In the MD-88/90 going directly to flaps 11 from a clean wing is the same as your comment about flaps 5 acourt. The whole wing reconfigures simultaneously and its the smoothest transition we can do. In the 717, all we can do is clean directly to 13. It's close, but a little rough on the pax. I too love hand-flying the HJG DC-9s. You understand what I was saying earlier: I can't believe how close the model is. Granted I fly 717s, but don't let anyone tell you otherwise: she's physically, aerodynamically, and operationally a DC-9 with big engines, TV screens, and a little automation!
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Post by christrott on Mar 28, 2013 23:10:44 GMT
Spending a lot of time dealing with flight dynamics keeps these things close-at-hand for me. And thank you for that graphic. While not showing the slats/flaps, it does illustrate the same principle I'm trying to describe. As the control surface changes the shape of the wing, it changes the center of pressure, the lift, and the drag it has. I used the term "Angle of Incidence" instead of Chord as one of the main reasons for having slats versus just flaps is to create a reasonable deck angle during descent for passenger aircraft with "mach" wings that are designed more for cruise than slow speed. The reason for this is that the size of the flaps needed creates too much of an aft movement of the center of pressure, causing the plane to either attain too low of a deck angle (sometimes even negative pitch) on approach or the plane runs out of effective trim prior to stalling. For those who don't understand what I'm talking about, look at the BAe-146 on approach or even the B-377. Because of the large flaps, they have a nose-down or flat deck angle on approach, this leads to a very high chance of nosewheel-first contact. To reduce this and to give more favorable go-around conditions, designers added slats. The additional benefit of using slats is that you can create and even more "critical" wing design because the slats deployed by themselves can give significant additional lift saving additional weight on wing structure by reducing the wing area. This was used on the BAC 1-11 and thus why the retraction of slats at low speed during climb was such a problem. The 727-200 does this as well and is why the outer slats do not get retracted until well over 200 knots at most weights.
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