"C J Campbell" wrote

§ 91.319 Aircraft having experimental certificates: Operating
limitations. (a) No person may operate an aircraft that has an
experimental certificate—
(1) For other than the purpose for which the certificate was issued;

And then......

Section 21.191: Experimental certificates.
Experimental certificates are issued for the FOLLOWING PURPOSES:

(a) Research and development. Testing new aircraft design concepts,
new aircraft equipment, new aircraft installations, new aircraft
operating techniques, or new uses for aircraft.

(b) Showing compliance with regulations. Conducting flight tests
and other operations to show compliance with the airworthiness
regulations including flights to show compliance for issuance of
type and supplemental type certificates, flights to substantiate
major design changes, and flights to show compliance with the
function and reliability requirements of the regulations.
(c) Crew training. Training of the applicant's flight crews.

(d) Exhibition. Exhibiting the aircraft's flight capabilities,
performance, or unusual characteristics at air shows, motion
picture, television, and similar productions, and the maintenance
of exhibition flight proficiency, including (for persons exhibiting
aircraft) flying to and from such air shows and productions.

(e) Air racing. Participating in air races, including (for such
participants) practicing for such air races and flying to and from
racing events.

(f) Market surveys. Use of aircraft for purposes of conducting
market surveys, sales demonstrations, and customer crew training
only as provided in Sec. 21.195.

(g) Operating amateur-built aircraft. Operating an aircraft the
major portion of which has been fabricated and assembled by persons
who undertook the construction project SOLELY for their own education
or recreation.

(h) Operating kit-built aircraft. Operating a primary category
aircraft that meets the criteria of Sec. 21.24(a)(1) that was
assembled by a person from a kit manufactured by the holder of
a production certificate for that kit, without the supervision
and quality control of the production certificate holder under
Sec. 21.184(a).