I have a recently bought Pitts S1-C and I am trying to get its new
airworthiness certificate since the one it had became void at the change of
ownership. The FAA, however, wants a letter stating that the S1-C is an
aerobatic airplane which seems like complete bull to me. I'm wondering where
I could get such a thing and who they would accept as an authority on the
subject.

any help would be appreciated.