Is the flight speed determine by the size of the avatar?

[Innula Zenovka]

Nope.  If you're not using a flight assist, you should be flying at 16.00 metres a second, whatever your size.  See the wiki article on Voluntary Movement Speeds.  

It may well look as if a smaller avatar is travelling faster, because you're covering a greater distance, relative to your size, than is a larger avatar in the same time, but it's going to take you and the larger avatar the same time to fly from one point to another.

[Innula Zenovka]

Nope.  If you're not using a flight assist, you should be flying at 16.00 metres a second, whatever your size.  See the wiki article on Voluntary Movement Speeds.  

It may well look as if a smaller avatar is travelling faster, because you're covering a greater distance, relative to your size, than is a larger avatar in the same time, but it's going to take you and the larger avatar the same time to fly from one point to another.

[Marigold Devin]

Welcome to Second Life Answers, Rioghnach

If you do not use flight assist, then your avatar, regardless of it's size, will only fly at the default speed.  It may be that others have bought small avatars that have some kind of flight aid with them.  I have a small cockatiel avatar, but this does not have any flight aid with it, just an animation overrider (AO), and aside from having little wings that flap, there is no difference in the speed at which my avatar travels as it flies.

[Lindal Kidd]

A six foot faery is not small!!!

But anyway, it only APPEARS that small avatars fly faster.  Let's say you have a 2 meter (6 foot) tall avatar.  At the flight speed of 16 m/sec, you can cross a region in 256/16 = 16 seconds.  In that time, you traverse 128 body lengths.

Now let's put on a tiny avatar, 0.5 meters tall.  The tiny also travels at 16 m/sec, and crosses the region in 16 seconds.  BUT, the tiny traverses 512 body lengths.  In terms of its apparent size, it has covered four times the distance in the same time.

Tiny aviators and sailors can get as much real fun out of sailing or flying inside a single region as a full size avatar can experience in a 16-region (4x4) grid, and with no tricky sim crossings.