The pilots operating manual of our Cessna 182 contains the lift-versus-alpha and lift-versus-drag data of the airplane, so I assume this is data that should be publicly available.
Is there a trustworthy resource where I can get the polar curves of different aircraft, especially airliners? I'm looking for that of the Airbus A350 XWB in particular.
Polar curves for older airliners can be found in lecture notes or technical publications. The drag polars of the most recent ones, where no independent measurement is yet possible, are a closely guarded secret. If you see something, it will be restricted such that an important part of the puzzle is missing. For the polars to be meaningful, you need aircraft mass and flight conditions, air temperature and density and sometimes also engine thrust information to make any meaningful comparisons. Also be aware that the Airbus method to determine the reference area is different from Boeing's, but at least those methods are published. Full disclosure is only available to potential customers on the basis of an Non-Disclosure Agreement (NDA).
I know of no source for the A350.
I was moderately surprised to learn, however, that there are surprisingly well-modelled drag curves for many modern jet transport aircraft including the Boeing 777 in a book called Aerodynamic Design of Transport Aircraft by Obert. They will in all probability not be 100% accurate, but they work much better than required for your run-of-the-mill back-of-a-napkin calculation. Keep in mind that for any meaningful analysis, you need a fairly accurate engine model, too, and before going into even more detail you need to be sure whether engine nacelle drag is included in the drag curve or the engine model or (worse!!) in both or neither.
Also, if you just need some independent data to innocently play with, google "Piano X 787 sample analysis".
You may choose to download this Excel spreadsheet which contains a list of over 100 glider performance figures in the tab "Gliders" . The spreadsheet allows comparison of two aircraft **Polar Curves*.
Boeing and Airbus does not make public the figures pertaining to Drag Polar Rates.
You can find some assumptions here.
where no independent measurement was yet possible, you mean is? – Federico Aug 21 '14 at 08:39