I have built and flown 2 Tiger 60's. Both had .91 4s's. Bashed the second one a little. Made it a taildrager and added a nose cowl. Also made my rudder and elev aa little larger. But I did not change the aileron size. I did however remove most of the dihedral. I thought I had no issues with flutter because I never heard any. But I did have a couple of hinges (ca) break on me and I do not know what caused that. I replaced the CA with du-bro nylon hinges and no more problem. Ialso had a great time flying these. They taught me alot of aerobatics. Very easy to land as well.