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Bruce,
I installed an MT 4 blade reversing (beta) prop on my IV-P because I
operate out of a 2200' field at 2,700 AGL, frequently with a tailwind.
I wanted the reversing function for supplemental / emergency use. The
MT prop uses a proprietary (custom) governor that has a solenoid to
actuate the high pressure Beta circuit. There is a mechanical interlock
in the prop hub that prevents the beta from being actuated above 1500
RPM.
For prop control I used a standard control cable. I put a
momentary contact (beta) switch at the base of the throttle control
that I can push with my index finger while simultaneously advancing the
throttle. This works very well and eliminated the complexity of an
intricate mechanism.
The biggest downside of a reversing prop is FOD. During landing, after
slowing enough so that the prop is >1,500 RPM, when Beta is actuated
it blows dust and small rocks up in front of the airplane, which the
plane then rolls through. Ouch. I have rock chips on the front surface
of the blades. These are better, however, than an off runway
excursion and not nearly embarrassing as a bird strike on the tail.
I had originally anticipated that beta would also be used on a semi
regular basis, reducing brake wear and maintenance costs. In practice I
rarely use it, usually only during practicing emergency procedures.
Beta would be useful in the event of a brake failure, poor traction or
a botched short field landing.
I would absolutely recommend a counterweighted feathering prop
configured such that a loss of engine oil pressure does NOT result in
an engine over-speed. I know of one illustrative case that started with
a cracked turbo oil supply fitting. The pilot noted fluctuating oil
pressure and wisely elected to reduce power and perform a precautionary
landing. When the nose was lowered the oil pickup was un-ported and the
oil pressure dropped below the minimum required by the governor. The
engine over-speeded, requiring a prop and engine tear down. A problem
that could have been fixed with a $10 fitting and a case of oil turned
into a $20,000 repair and 8 weeks of AOG.
I would only recommend Beta if you frequent short or slippery runways
or are prone to land long and fast. It is a nice safety net to have if
you ever need it.
Regards
Brent Regan
Bruce Ryan wrote:
Brent
I have gotten to the point where I
have to zero in on a prop configuration for my IVP (TSIO550)
I definitely will go feathering for
better glide ratio, but have been thinking about a reversible (BETA)
prop after listening to a few IVPT folks comment on the usefulness. I
probably will not do a lot of short field work, but here in the NE
runways are often covered with snow and additional drag/breaking would
offer a good safety margin.
I think someone mentioned that you
had a reversing prop and if so I wonder if I could ask a few question
- What mfg (MT?)
- Reliability/mfg support?
- What prop governor is required?
- Did you also install an
accumulator?
- What type of prop control/lockout
did you use?
- Would you do it again?
- Which feathering only ( non
reversal) prop seems to be the best match for the IVP/TSIO550
- Any important thing I forgot to
ask?!
Many thanks
Regards
Bruce
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