page 45 - American Bonanza Society

Tech Tips
Tech Tips are answers to questions about a specific airplane,
system or operation presented by an ABS member, and are
the opinion of the Technical Advisor. Answers are the best
information available based on indications presented by the
ABS member asking the question. Actual inspection of the
aircraft or system in question may change an initial Tech Tips
opinion. Aircraft owners, pilots and readers are advised to
physically present airplanes and indications to a qualified
mechanic before choosing a course of action.
Bob Ripley
retired from Delta Airlines as
a manager of line mainte nance
(Atlanta) and has run an
FBO focusing on Beech
maintenance for 20+ years.
Curtis Boulware has managed
a Bonanza, Baron, and T-34
Mentor-specific shop for 13
years, winning numerous national
awards for T-34 restorations.
He earned his Private in a T-34
and enjoys flying all models of
the Beech piston family.
John Collins
has previously owned an
FBO and avionics shops, and
for several years has been
ABS’s Avionics columnist.
He owns a Bonanza and is
a CFI/CFII.
Dan Honeycutt
is an A&P/IA with over 20 years
experience. He owns a
California-based FBO
specializing in Bonanzas
and Barons.
Arthur Miller
has won numerous FAA
awards as a mechanic,
and runs a Beech specialty
shop in central Florida.
Tom Turner,
ABS-ASF Executive Director,
holds a Master’s degree in
Aviation Safety. He has
specialized in Beech pilot
instruction for over 20 years.
Q:
Prop vibration in cruise
Skip Bakos, Crown Point, Indiana
I own a 1998 B36TC with the Tornado Alley turbonormalized conversion.
The plane sat idle for a little more than two years due to some “life issues.”
During that time, there was a humidity problem in my hangar that caused
considerable rust damage on the cam, lifters and other rotables. These problems
were repaired by two very well known and trusted Bonanza airframe and engine
shops. We’ve been flying the aircraft often now for the last four months, having
logged some 35 or 40 hours during this time.
During start-up, run-up, taxi, and take-off the plane is amazing. It performs as
expected and provides all of the required power to climb away safely. During
the climb, the plane is smooth as can be and all engine gauges are within
their desired ranges. The major problem we had before the required engine
maintenance was that TIT would exceed the maximum 899 degrees Celsius on
the takeoff roll and would not be achieving the appropriate power. During the
climb-out we are at full power, full prop, mixture set to 35 gph, cowl flaps open,
gear up, and climbing at about 120 knots with the remaining engine gauges all
in the green (normal) operating range.
The issue we are having is when we climb to the desired altitude (doesn’t
matter if it’s 4000 feet or 10,000 feet) and start to level off and accelerate towards
our desired 160-ish knots indicated. Following the checklist step by step, we
close the cowl flaps (while maintaining close eye on CHT not to exceed 380°F),
maintain full throttle (which is about 30.1" MP), smoothly bring the prop back
to the desired 2500 rpm, and then in the 3-5 seconds (as the checklist states)
lean the mixture to between 16.0-17.5 gph while maintaining a close eye on the
TIT peak and also CHT. Leaning the mixture to LOP and about 17.5 gph gives us
about 1540°F TIT based on the JPI and all CHT below the specified 380°F.
Once we are fully configured for cruise, we begin to feel a vibration in the
seats, floor, and rudder pedals. In my opinion it feels like the prop is not in
sync with the engine. This feeling does not happen every time, and when it
does it only lasts for a couple of minutes at the most. During the vibration, all
of the engine gauges remain right where we put them. We have made sure that
the cowl flaps were fully closed (in case it was vibration from them) and even
opened them a little in case they were hitting the cowling, but didn’t change
the feeling at all. The one thing that has made the vibration go away (based on
a recommendation) was to change the pitch of the prop by any amount. We
have reduced it to 2490 rpm and the sensation went away. We would then bring
it back to the specified 2500 rpm and the vibration sometimes happens again.
We have been asked multiple times about making sure we aren’t flying
between 2350-2450 rpm at or above 24" MP and we definitely are not! We
also have felt the vibration when we start our descent without changing any
power settings yet. When we receive a lower altitude we first get the plane
pitching over at least 100-200 fpm and with the desired altitude armed before
decreasing to the 23-25" MP, 2300 rpm, and while maintaining the cruise
mixture setting. While maintaining these specified settings throughout the
58 AMERICAN BONANZA SOCIETY MAY 2013