Seagull 540 version 2: flight and structural integrity
 

1. How does it fly?
2. Can I fly it fast and not lose the airplane? Need good structural integrity.
3. How is the "fun Factor"
4. What size 2 stroke engine. I have a ST 90.
5. What do I need to look out for?

RE: Seagull 540 version 2: flight and structural integrity
 

Flies well
It will comfortably fly as fast as the ST90 will allow it.
Fun Factor is excellent
ST90 will work OK in it (not perfect for 3D but good for most requirements) (I currently have a Saito 1.25 in mine).

Make sure that the braces are on the hoizontal stabiliser properly.
I strengthened my Landing gear block to the fuselage (I do this with most ARFs) with some triangular stock and epoxy.
I discarded the stock pushrods and clevises (I do this with most ARFs) and replaced them with 4-40 threaded rod over which I epoxied some carbon fibre tube.
Start with the recommended CofG - Mine is currently set about 10mm back from that and I find it suit me for fun flying.

RE: Seagull 540 version 2: flight and structural integrity
 

This plane is not intended to fly fast, it's an aerobat. The elevators are huge, and the ailerons are quite big for this size plane, and I guaruntee if you use the stock 3mm hardward that comes with it, you will flutter it right into the ground. If you want fast, buy a Midget Mustang or a Shoestring. I have a Webra 1.20 in mine, but I use a 4 pitch prop, so my speed is way down. The ST 90 will fly it just fine. Watch out for the stock tail gear, and weak stock hardware. Do yourself a favor and buy some 4-40 hardware and a Sullivan tailwheel.