So, are those calcs right and it would only take 1.5 horsepower to keep that
glider going in level flight at 35 mph?


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Sounds about right but... (you KNEW there was a but, right?) :-)

You want thrust, not horsepower. Reality tends to differ from the
conversion-factor solutions due to velocity and prop losses. (Remember the NSU
'Prinz'? Ever see the little ducted-fan power pod that used the tiny Wankle?
Something like 6hp and TINY. With even a whiff of green air it could keep you
up all day after a winch launch.)

And of course the weght is no longer 400 but something more (ie, engine,
controls, fuel, mounting, etc).

But you're on the right track: Lift vs Weight, Thrust vs Drag (Notice that
horsepower is not mentioned :-) Once airborne, it doesn't take much to keep a
high-lift, light weight, aerodynamically efficient airframe flying. The tricky
bit is getting airborne to begin with :-)

(Then comes those horrible inverse equations dealing with drag (square it) and
power (cube it) any time you want to get there in a hurry.)

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You did good, Bill. Your logic mirrors that of the Wright brothers which puts
you head & shoulders above 99% of the crowd.

-R.S.Hoover