Hydraulic and electric constant speed props are two totally different animals.
You could say that hydraulic props are analog and that electrically adjustable props are digital, as a good analogy.
Hydraulic constant speed props are constantly adjusting as the oil pressure changes due to the output of the governor.
They are designed to have a relatively quick response and be operated continuously and therefor ideal for aerobatics.
Conversely an electrically adjustable prop only changes the pitch in increments when the power to the motor is applied.
Most electric governors have an adjustable band (dead band) of rpm in which the motor will not activate so that it is not continuously hunting to find the correct RPM.
This is necessary because the motors are not usually rated for 100% duty cycle.
If the adjustment motor is run continously it would tend to over heat and its life would be severely shortened.
The dead band is the reason for the slow response of and electric prop.
That is probably why aerobatics is not recommended with these props.
It's all about compromise.
If a large enough motor were used to provide continous operation (without the deadband) it could certainly keep up with the rigors of aerobatics, but would probably require too much current and be too heavy to mount out there on the nose.
Jim
--- On Sun, 5/3/09, Charlie England <ceengland@bellsouth.net> wrote:
Van probably says no N>acN>ro with electrics because they have much slower response
time than hydraulic props. Still not as bad as *no* response time from a fixed
pitch, & they do acro all the time. :-) The issue is over-speed if they are
in flat pitch going up & can't respond quickly enough to limit rpm going
down. The throttle can solve this, just like it would with a fixed pitch prop;
just extra work load for the pilot. A more significant question is whether MT
approves it for acro.
Charlie
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