"Teacherjh" wrote in message
...

if upon
reaching MDA, still in IMC, you cancel IFR (very quickly!)
then you would still be legal.


No.

In uncontrolled airspace, I believe you still must be on an IFR flight
plan to
operate IFR. You just don't need a "clearance" since no separation is
provided.


No flight plan is required to operate IFR in Class G airspace. You can't do
what is suggested here, but not for lack of a flight plan.


§ 91.173 ATC clearance and flight plan required.

No person may operate an aircraft in controlled airspace under IFR unless
that person has --

(a) Filed an IFR flight plan; and

(b) Received an appropriate ATC clearance.