Ill throw some advice in there (I also happen to be a pilot)

Instrument Lights: Unless you are shooting some kind of piper cub or something chances are the instrument panel is lit its self. Don't be afraid to use the instrument lights during the day to add some fill light. The type of lights vary by aircraft but you may be able to make the instruments really pop. Note the difference when the avionics are on vs when they are off.

Remove The Seats: Depending on the aircraft and what the owner allows you to do most if not all aircraft seats can be removed pretty easily. This will allow you to place the camera right where the pilot would be. The main reason for this is that the cockpit its self usually is designed to reduce glare from the pilots point of view. That is why the upper part typically over hangs the instruments a bit (note the upper black portion). In some planes you may also be able to remove the cabin seats (or bench) which will make maneuvering around in the cabin easier.

Shot from the pilots point of view (or in between both seats to get the whole panel). This is the most natural position and will yield a great image partially because its what people are expecting to see.

If you really are not getting the windshield in the shot you can try covering the windows from the outside and using interior flashes to control light more evenly.

Use a wide angle lens (note the blacked out windows and instrument lights)...

Or are really wide angle lens...

You can always take a few images and stitch them together (See Scotts excelent comments bellow).

The only piece of advice I will give you that contradicts what others have said is to not use a polarizer (if there is any digital instrumentation or potentially polarized windshields). Modern avionics with daylight readable digital displays can not be seen at certain polarization angles due to the way they are made. You may also have some strange (or potentially interesting) things happen with the windshield. Depending on how "small" you are talking about when you say aircraft you may encounter UV blocking or polarized windshields that will interact with your filter. You can read up on it here.

On a similar note depending on windshield material putting a flash on the exterior of the aircraft may take some experimentation to get right. While aircraft glass often appears "clear" most of the modern stuff is coated in various ways.

If you want some inspiration check out how the big makers are doing it. Piper seems to have all avionics on, windows blacked out. While Mooney seems to use a full light situation and is not bothered by glare in their shots. On the glare note, the digital screens are built to be easily read with some glare.

If you need to shoot the panel of a specific plane this wont be of much help but if you just need to shoot a panel you can go to an avionics shop and see if they have any panels they are about to install. its not all that uncommon for shops to upgrade the full panel of a plane and possibly do a dry assembly outside the plane. In this case you may get lucky enough to see a panel with everything in it outside of the plane. You may also get lucky and get a panel that has been installed but the rest of the plane is still apart and makes for easy access. Likewise interiors are removed for annual (or 100 hour for commercial) aircraft inspections which may make for easier access to photograph the panel however they may also remove parts of the panel during these checks.