Terry,

Thanks. I will mail John Lynch. Apparently that a motorglider is a
"powered aircraft" for purposes of 91.205 (aircraft certification) is
best stated in the ACS-100 bulletin in 1993:

-----------------------
Date: 2/10/93

Initiated By: ACE-100

AC No: 21.17-2A

Change:

1=2E PURPOSE. This advisory circular (AC) provides information and
guidance
concerning acceptable

means, but not the only means, of showing compliance with =A7 21.17(b) of
part
21 of the Federal Aviation

Regulations (FAR) for type certification of gliders and powered
gliders.
Accordingly, this material is

neither mandatory nor regulatory in nature and does not constitute a
regulation. General guidance

relative to glider type certification is also provided.

It also includes the following:

b=2E Additional Criteria for Powered Gliders.

(1) Powered fixed-wing gliders may be type certificated under Section
21.17(b) if:

(i) The number of occupants does not exceed two;

(ii) Maximum weight does not exceed 850 kg (1874 pounds); and

(iii) The maximum weight to wing span squared (w/b2) does not exceed
3=2E0
kg/m2 (0.62

lb./ft.2).

NOTE: These criteria originated from JAR-22.

h=2E Section 91.205 of the FAR. Powered gliders are considered to be
powered=20
aircraft for the=20

purpose of complying with =A7 91.205.