You can use whatever you want on a homebuilt. Day, VFR is pretty much up
to what the builder wants to install

However, I would recommend against using GPS as a sole source for the
uses you are envisioning.

The heading information provided by GPS is track along the ground, not
the magnetic heading that you are pointing. Your ground speed and
airspeed are two separate and distinct animals. Your airplane will fly
with respect to indicated airspeed... regardless of what the groundspeed
reads. Winds aloft will cause differences between indicated airspeed and
what the GPS groundspeed is.

Dave

Dick wrote:
Can a GPS with compass, heading & groundspeed capability be used legally in
lieu of a separate compass and airspeed instruments on an experimental
homebuilt airplane? Or at least in lieu of the separate compass?
Thanks