First, thank you all for the direct answers to my question. Now, regarding the 737 sample case, it should be checked which flaps-slats combinations are normally possible; it may be the case where let's say flaps 20 cannot come with retracted slats (if there is a problem with the slats deployment you are allowed to use only flaps 0).
Regarding the tables with infinite numbers of dimensions; I do not understand why this should be needed. The buildup concept used in JSBSim lets you specify delta of each coefficient for every aerodynamic surface (flaps, elevator, stabilizer, etc.) independently; JSBSim adds all that together. For the downwash, DATCOM could be executed first for the clean configuration, obtain Epsilon vs. alpha, then for certain airfoil representing one slat-flap combination, obtain the new Epsilon vs. alpha, and finally we can build a 2D table for deltaEpsilon vs. alpha vs. flaps. If the slat is another input, then 3D tables (with tableData breakpoints) are already applicable in JSBSim. We can then have one 2D table for slats 0, then another for slats 20, etc. The elevator sweeps could be done with flaps up, and then, this elevator effects included as another contribution in the aero buildup. One important issue in generating the independent contribution of each aero surface is that sometimes there are interferences between them; this can be significant for example between flaps and airbrakes. Finally, one short question: why there is no dedicated horizontal stabilizer property available in JSBSim, and we need to use for this the speedbrake property? Just curious... Fabian > A couple problems that I've been addressing lately is that Datcom doesn't > produce downwash angles when you drop flaps. Also, the elevator sweeps are a > function of free-stream angle of attack (i.e., AOA at the wing, not the > elevator). Another important omission from Datcom is that you can't drop > flaps then do elevator sweeps. > > To me, these are important factors, since most of the crashes happen near > the ground, when you have flaps and gear down. The FAA testing is heavy on > near-ground performance, because that is where you get into the most > trouble, such as losing an engine during take-off or landing. > > One approach that I've been considering is to calculate what the airfoil > looks like when you lower the flaps, and input THAT as the airfoil, then do > all of the normal calculations. For something like a 737 where you have > leading and trailing edge flaps, you could easily get into 20 cases, with > each case generating all of the coefficient tables (Cd, CL, CM, etc.). For a > twin-prop aircraft, you just have trailing edge flaps, but you really need > to run power effects at each flap setting, and you really should split the > aircraft in half, since you could be flying on one engine. Engine thrust > should be run at several settings, such as off, idle, cruise, and max, as a > minimum. Interpolation between those power settings should be fairly > accurate. > > Let me give you a good example. Twin engine prop aircraft, drop the flaps > fully, you lose the right engine, and push the left one to max in order to > climb. On the right side, you just have freestream airflow over the right > wing, flap, rudder and elevator. On the left side, you have a prop blast > hitting the wing, part of the flap, left side of the rudder, and most of the > elevator. Ignoring the engine torque issue, you are going to experience > different lift (higher on the left side) which creates a rolling moment. You > will also experience different elevator control effectiveness right versus > left. Rudder dynamic pressure might actually be different left versus right, > creating a yawing moment, which is in addition to the thrust different left > versus right. > > Now, is this a little overkill? Maybe, since most trainers that I've seen > don't go into such details. It is possible to generate data for these cases, > and I think it would yield higher fidelity trainers than anything seen > before, simply because that kind of data hasn't been available before. The > question I'm wrestling with is whether it is worth all the headaches. After > all, we could end up with 60-80 times more data than what we currently deal > with now. > > Any thoughts? > > Bill > > > > > ------------------------------------------------------------------------- > This SF.net email is sponsored by: Splunk Inc. > Still grepping through log files to find problems? Stop. > Now Search log events and configuration files using AJAX and a browser. > Download your FREE copy of Splunk now >> http://get.splunk.com/ > _______________________________________________ > Flightgear-devel mailing list > Flightgear-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/flightgear-devel > > ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
