Seeley Aircraft Service
What is dynamic propeller balancing?
Dynamic propeller balancing is the process whereby an electronic
balancer is used to measure the vibration produced by the aircraft
powerplant. Small trim balance weights are added to the
propeller/crankshaft assembly to correct for errors and reduce the
measured vibration to the lowest level practical. On average, 19 out
of 20 fixed-wing aircraft can benefit from Dynamic Prop Balancing.
The engine/propeller combination is balanced right on the aircraft, in a flight ready where vibration
due to mass imbalance is maximum. A small tach pickup (photo-tach) is also mounted to the cowl or
engine to produce a propeller tach signal. The engine is
The balancer produces a vibration level (magnitude) which corresponds to the amount of mass
imbalance which exists. The balancer also provides a "phase angle" which corresponds to the
location of the mass imbalance on the propeller disk. The vibration level and phase angle are used
to compute a balance solution (weight amount and location). The balance solution is added to the
propeller and the measurement is repeated until the vibration level is found to be acceptable.
Using ACES digital vibration analyzer equipment.
Performed by a ACES trained A&P mechanic with over 50 years of experience in maintenance and
operation, and is also an owner and pilot.
Tachometer reading to 0.01% accuracy.
Service averages 2-3 hours~while you wait.
Service is mobile and performed at your location.
The engine and propeller combination is balanced
in concert with each other.
Why be concerned with vibration?
crew and passengers. The service life of expensive avionics and instruments is shortened
considerably when the equipment is operated in a high vibration environment. Excess vibration can
also shorten the life of expensive engine.
My aircraft runs fine. Why should I have my prop dynamically balanced?
By all means, have your propeller balance checked. The average airplane which has not had a
Dynamic Prop Balance has a vibration level due to propeller/crankshaft mass imbalance of about
.450 inches per second (IN/S) velocity. This level is more than four times higher than what is
considered to be an acceptable vibration level for propellers and represents a significantly higher
level of wear and fatigue on engine components and accessories. This average level is usually very
noticeable to the pilot and occupants. Yours may be higher or lower than the average but only a
mechanic with a vibration analyzer can tell for sure. On the average, 19 out of 20 fixed-wing aircraft
can benefit from Dynamic Prop Balancing yet many will never have it done.
My engine and prop were overhauled recently. Should I have my prop dynamically
Both new and used components need to be dynamically balanced. In fact, the best time to
dynamically balance a propeller/engine combination is right after overhaul when components are
fresh. In the DSS study, no appreciable difference was found between the vibration levels of
recently overhauled and longer time propeller/engine combinations. Even brand-new aircraft with
zero time engines and propellers need to be dynamically balanced.
What level of propeller vibration is acceptable?
In most cases, the vibration level due to mass imbalance can be brought down to under .100 IN/S
very easily. In the DSS study, the average level seen post-propeller balance was .039 IN/S. When
propeller vibration levels are this low, the operator will generally see a significant reduction in
component wear and fatigue and will find that the aircraft "feels" like a completely different machine.
In addition to that the mechanic now knows what all of the other engine vibration levels are
(Prop/crankshaft mass imbalance usually dominates them) and can utilize that information if
additional work is needed.
But won't having my propeller dynamically balanced "mask" other engine problems?
NO! An engine with an internal problem which results in unusual vibration will not respond to
balancing in the same way that an engine which only suffers from mass imbalance will. A qualified
mechanic will use ALL of the information available to make a judgment about your engine, including
the vibration response.
|Here are some frequently
asked questions about
propeller and rotor balancing.
4825 Janes Rd
Saginaw, MI 48601