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Author
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Topic: Compressibility
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Falck
Pilot
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posted 06-23- 02:24 AM
  
Anyone tried tinkering with the airAdvantage property to try to simulate compressibility?airAdvantage <factor> - Mechanical advantage factor that the pilot has in overcoming the control surface forces of the trailing edge device. A value > 1 makes it easier on the pilot. IP: Logged |
bjorn
Pilot
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posted 06-23- 03:26 AM
I've fiddled a bit with compressibility, but in a different way. I mounted the horizontal stabilizer on a rotational DOF around the X-axis. If the pivot point is located a bit behind the airPt, it will give you an instable behaviour. The airflow will want to rotate the stabilizer upwards, which will give it more lift, giving a nose down momentum, which will alter the airflow enough to start rotating the stabilizer downwards. It's difficult to tune to decent behaviour, though. I did get so-so results when playing with this for the Typhoon (which was plagued by a weak tail section anyway.) When pulling out from high speed dives, the oscillation starts, and you have to be very very careful to both gain altitude, lose airspeed and keep your tail where it belongs.This is not quite what you asked for, but with the DOFs you have there for damage anyway, you can simulate compressibility induced flutter, but it is a lot of work. Note: It's a 3 dimentional tuning. The pivot point location and the strengths of dofSpring and dofDamp.
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/Bjorn. IP: Logged |
Tailslide
Pilot
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posted 06-23- 03:45 AM
Falck, the current p38 and Spit1a has this adjusted as close as we can get by setting low advantage properties. Try taking them in high speed dives and see how they roll, pullup. It's not great but better than nothing. The problem is the better you get the compression happening the worse low speed handling gets when it really shouldnt be affected at all. TS IP: Logged |
juzz
Pilot
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posted 06-23- 01:02 PM
The Typhoon tail problem was actually due to elevator flutter/oscillation ripping the tail off, and it could happen at any airspeed. It wasn't that the tail was weak, but that the forces the flutter generated were very large. The local strengthing they tried had no affect at all on tail loses.Typhoons were regularly loosing their whole tail at one of the frames just before the vertical fin for no known reason and in normal flight conditions as well as dives, until they figured out the correct cause and solution - which was to adjust the elevator balance. On a similar note, how do you make the wings rip off the planes at a certain speed and/or G loading? Not many of the planes lose their wings, even at +15G(!), last time I checked. [This message has been edited by juzz (edited 06-23-2000).] IP: Logged |
bjorn
Pilot
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posted 06-23- 02:46 PM
Juzz,The answer to losing wings lies in damage DOFs. It's a pain to tune them, but it's worth the effort. As a minimum, set a DOF at the wing root that allows the wing to flex a little bit upwards and downwards. A rotational spring DOF. It should not be allowed to flex very much before breaking, but it should probably allow for some static deformation. The hard work is now that of tuning the spring strength. It is possible that some dofDamp should be there too, but I don't know how you'd go about to get a good value. To make this more advanced, add a DOF that allows the wing to swing backwards/forwards. This one will probably be the main cause for losing wings when slamming into ground objects. Again, it should not be allowed to flex much before breaking, and probably not allow for a whole lot of static deformation, but this is purely a guess from my side. An extra bonus that very few aircraft have, is a DOF allowing rotation of the wing around its centerline. A nearby explosion or ramming an object can then rotate the wing a bit. Allow for a little static deformation here, if you bump the wing tip against the runway, you should probably twist the wing a bit around this axis. Again, tuning all of these are a pain. It's hours and hours and hours of heavy G's, low G's, high speed pullouts, stunts, ramming things, dipping wingtips in water and on runways, flying through flak, being shot at, flying too close to bombs going off, rough landings, etc, before you can be satisfied with the result.
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/Bjorn. IP: Logged |
Tailslide
Pilot
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posted 06-23- 04:32 PM
Also, there is no warning in SDOE about bending wings like a creaking sound or anything. I originally had the Yak wings fold up at 9 gees and everyone was constantly ripping off the wings in testing so I had to bump it up some. The wings in the real planes did flex (some more than others) and it affects the flight models. So after you get done updating the damage model you have to retest stall handling as a flexible wing can be harder to tip stall. TS IP: Logged | |
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