Prop load on power boats is very similar to aircraft - ie speed
and rpm are roughly cubic functions. on single engine operation
both rpm and speed would drop to about 80 percent of top
since you will be overproped for the single ongine and it will
also be lugged down on the power curve limiting it's
max power output.  Many power boats are going to counter rotating
props - using each engine for each rotation (like the South American
canard installation) will let the remaining engine develop full HP -

Vance

Could I steer this thread towards the same concept, only in a coaxial
helicopter? :)

My (shade tree mechanics degree) says two engines in a coaxial
configuration could be interesting. :) If one engine *could* provide
enough power to maintain altitude, couldn't you toss the need for
autorotation? I'm ASSUMING the reliability of the rotary built for
proper aircraft use.

I know something along this line has been tried by the Nolan brothers
(two small two strokes)...I have a different twist in my head. I need
massive help!

Thanks guys
Phil

Most coaxial helicopter designs rely on large tail fins or torqueing
the counterotating rotors against each other for yaw control.  Fins and
rudders plain do not in the unpredictable swirl of the rotor downwash.
Torqueing works fine but not if you lose one rotor and not the other,
so you would still need a transmission.

The counter-rotating concept in general has limited application.  Many
proponents forget the efficiency loss for rotor overlap, and yaw
control problems.  Tandem is a better concept.  All of sikorsky's
recent conventional helicopters tilt the rear rotor for lift, making
them a bit more of a tandem.

Hans Conser

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