..on Sat, 23 Feb 2002 15:42:11 +0100, "Lorenzo Scaldaferro" <[EMAIL PROTECTED]> wrote in message <[EMAIL PROTECTED]> in newsgroup: rec.aviation.simulators:
..first, I need to apologize for showing bad form in responding by separate emails too, and for posting this onto the www.flightgear.org developers mailing list. See below for justification: > Hello, > i'm an italian mechanical engineer student and i'm writing a thesis > about "landing gear vibration problems". I'm gonna finish it but i > still have some doubts and i hope you can help me to clarify. > > 1. I know how shimmy dampers work but i don't know if they are always > used on planes or if they are not, and > i'd like to understand what makes deciding that use, after > simulations, or always with planes with a certain > weight or operational speed. > 2. I found a publication about "landing gear dynamics" called: Landing > gear integration in aircraft conceptual > design, by Sonny T. Chai and William H. Mason, it's described > how to > proceed to design gear and choose wheels, > dampers, etc. but nothing is written about considering > vibrations during design, so i'd like to know why. 3. I saw > there is an intense use of F.E.A. for shimmy, brakes vibrations > and gear vibrations in general, but i > also think i understood that the problem is not fully > understand. So > what kind of future considerations can we > do? Are modern airplanes problem free? What are the new > technologies > to resolve the problem? Because from what > i found the way to proceed is use Moreland and Pacejka theories, > made simulations and FEA, test the gear (just > in two words) but from what i understand is in use that you can > really discover if the plane has shimmy or so > and sometimes we prefer to maintain a light shimmy if we > discover it > after production and there's not an easy > way to resolve. > > I know my questions could result stupid but every discussion, > document, link or else would be very appreciate. ..if you, Lorenzo, understand, as I believe, what you have read, you may be able to provide a valuable set of eyes and opinions on the below. > Thanks a lot, Lorenzo ..FlightGear 3 different flight dynamics models all share a landing gear problem, if you care to DL the FlightGear source code, you may be able to add another set of engineering eyes. Warning, DL is some 27 MB. ..FlightGear runs on linux, unix, MacOS, and the Microsoft wintendo "os"'es. It is networking capable, on limited hardware, you can farm out flight dynamics number crunching to another box on your lan, or, you may have a multi pilot environment, and fly several planes. There is also a glass cockpit project, and a moving map project going on, these can plug into Flightgear over a lan, internet, or a cluster of boxes. (No games yet, only the wee beginnings of bomb drop code, games can of course be written on this code base. ;-) ) ..open source code such as Linux, FlightGear and some Unix'es, is _potentially_ FAA Certifiable, just like AN bolts, because anyone, such as any FAA inspector, may legally inspect and reverse-engineer the code, in_excactly_ the same way they torture AN hardware thru failure. ..closed source software licenses, such as Microsoft's, usually makes reverse engineering such as "FAA" type inspections, a criminal offence, this consequently makes such software un-certifiable for aviation use, where-ever airworthiness is a requirement. ..(and, no, I'm not going to waste anyones time on an os flame war. ;-) ) ..now, FlightGear is still _far_ from airworthy. ;-) But it _is_ moving in a direction that I like a _lot_. :-) [arnt@lana FlightGear]$ ls -GAFl /usr/local/lib/FlightGear/Aircraft total 104 -r--r--r-- 1 1000 590 Feb 8 13:22 747-uiuc-set.xml -r--r--r-- 1 1000 1587 Feb 9 04:25 747-yasim-set.xml -r--r--r-- 1 1000 897 Dec 24 13:44 a4-yasim-set.xml -r--r--r-- 1 1000 692 Feb 8 13:22 beech99-uiuc-set.xml drwxr-sr-x 3 1000 4096 Feb 16 19:05 c172/ -r--r--r-- 1 1000 1523 Feb 9 04:25 c172-ifr-set.xml -r--r--r-- 1 1000 1703 Feb 9 04:25 c172-larcsim-set.xml -r--r--r-- 1 1000 1815 Feb 13 21:03 c172-set.xml -r--r--r-- 1 1000 670 Feb 8 13:22 c172-uiuc-set.xml -r--r--r-- 1 1000 1599 Feb 9 04:25 c172-yasim-set.xml drwxr-sr-x 3 1000 4096 Feb 16 19:05 c182/ -r--r--r-- 1 1000 2433 Feb 13 21:03 c182-set.xml drwxr-sr-x 2 1000 4096 Feb 16 19:05 c310/ -r--r--r-- 1 1000 2482 Feb 13 21:03 c310-set.xml -r--r--r-- 1 1000 702 Feb 8 13:22 c310-uiuc-set.xml -r--r--r-- 1 1000 978 Dec 24 13:44 c310-yasim-set.xml drwxr-sr-x 3 1000 4096 Feb 16 19:05 dc3/ -r--r--r-- 1 1000 1618 Feb 13 13:10 dc3-yasim-set.xml -r--r--r-- 1 1000 1526 Feb 9 04:25 harrier-yasim-set.xml drwxr-sr-x 3 1000 4096 Feb 16 19:04 Instruments/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 shuttle/ -r--r--r-- 1 1000 907 Dec 11 19:32 shuttle-set.xml drwxr-sr-x 5 1000 4096 Feb 16 19:05 X15/ -r--r--r-- 1 1000 1213 Dec 11 20:18 X15-set.xml drwxr-sr-x 2 1000 4096 Feb 16 19:05 x24b/ -r--r--r-- 1 1000 1029 Feb 8 00:30 x24b-set.xml ..you will find the Cessna 172 is the best modelled plane in the sim, unfortunately, most planes share the c172 gear. According to the docs, the UIUC 747 hang its nose some 70 degrees into the ground from its Cessna 172 main wheels, which again hints towards a realistic c172 nose gear performance on a 747 load. ;-) Apart from this, I understand 747 runway operations are simulated ok, they rotate nicely out of the ground and take off nicely at correct rotation speeds etc. Ditto for the Convair880. Handling of these 2 is documented as sluggish, I'm not (yet) aware of the "as compared to what" reference. [arnt@lana FlightGear]$ ls -GAFl /usr/local/lib/FlightGear/Aircraft-uiuc/ total 100 drwxr-sr-x 2 1000 4096 Feb 16 19:05 Beech99/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 Boeing747/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 Cessna172/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 Cessna172-71/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 Cessna172-73/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 Cessna310/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 Cessna620/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 Convair880/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 F104/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 F4/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 Learjet24/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 Marchetti/ drwxr-sr-x 16 1000 4096 Feb 16 19:05 models/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 Pioneer/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 Pioneer-TD/ -r--r--r-- 1 1000 8227 Oct 22 2000 README-aircraft-uiuc.html -r--r--r-- 1 1000 3280 Oct 22 2000 runfgfs.bat drwxr-sr-x 2 1000 4096 Feb 16 19:05 T37/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 TwinOtter/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 TwinOtterAllIce/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 TwinOtterTailIce/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 TwinOtterWingIce/ drwxr-sr-x 2 1000 4096 Feb 16 19:05 X15/ ...where the TwinOtters can ice down. These are products of the icing reserarch done at University of Illinois at Urbana-Champaign, urbana, IL., see http://amber.aae.uiuc.edu/~m-selig/ ..the first flight dynamics model used for the above research and in FlightGear, was LaRCsim, which was developen under NASA funding by Bruce Jackson, http://dcb.larc.nasa.gov/www/DCBstaff/ebj/ebj.html ..thenafter came JSBSim; from cat /usr/local/lib/Flightgear/Docs/README.JSBSim: "JSBSim JSBSim is an ongoing attempt at producing an OO Flight Dynamics Model (FDM) to replace LaRCsim as the default FDM for FlightGear. It can also be used standalone. JSBSim uses config files to represent aircraft, engines, propellers, etc. Also, the flight control system is described in the config file." ..Jon Berndt's JSBSim aims towards an engineering tool. Andy Ross came up Yasim, which tries to approximate JSBSim/LaRCsim style configurations from known, or guessed, aircraft performance numbers. I understand Andy wanted to play with carrier approaches, none of our sim planes was ready for this, so he threw in the A4 and the Harrier. ;-) The Yasim 747 has a problem climbing to cruise ceilings, as yasim planes still dont burn off fuel, so the 747 gets close up there, but too heavy. (Andy is fixing this now.) ..now, Jon will be fixing our landing gear code in his spare time, as soon as he finds the time, but we can still use more help, not only on the landing gear code, there is plenty more that needs to be done, see http://www.flightgear.org/ -- ..med vennlig hilsen = with Kind Regards from Arnt... ;-) Scenarios always come in sets of three: best case, worst case, and just in case. _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
