Prop Balancing

Smooth running machines last longer and with operator fatigue. Considering the cost of aircraft engines, making them operate smoothly even more important to extend engine life and performance.

An aircraft’s propeller is essential a giant flywheel bolted right to the output shaft of most single engine piston aircraft. With this “direct drive” approach, the engine and propeller are essentially one integrates unit. If the prop is out of balance, then the engine is out of balance.

The prop manufacturer statically balances the prop, meaning the prop is balanced, but only with itself. Likewise engine manufacturers balance engines to various degrees of refinement.

So why doesn’t a balanced prop mated to a balanced engine not actually balanced? The balance points of each is slightly different. And it’s this difference that causes vibration.

The remedy is to have the prop dynamically balanced. Dynamic balancing is accomplished by adding very small amounts of weight in the form of a washer tactically mounted to the prop’s mounting flange.

A special sensor is attached to a prop blade and as the prop spins, the out of balance rotation is detected by a computer program that suggests where to place the counter balance weights on the prop hub.

The proof not just in the data, but the feel of the plane. Other seasoned pilots are astonished how smooth the engine operates.

A quality dynamic prop balance costs between $200-$350 depending shop rate and part of the country. Many shops charge a flat fee to perform the service. Worth EVERY penny.

Getting a New Prop & Spinner

Installing new Hartzell Prop
Installing new Hartzell Prop

From the pre-buy process, I knew the prop had seen better days was eminently due for an overhaul.  The previous over had flow to Mexico on numerous occasions on humanitarian missions.  Unfortunately the back country gravel runways took a toll on the prop.  While flying from Alice Texas KALI to 10C Galt Field outside Chicago, the dreaded red mist appeared on the windscreen indicating the prop hub had fallen out of tolerances.

Sending the prop to Maxwell propeller in Minneapolis, they determined the prop and hub was worn beyond limits and unserviceable.  This was not a big surprise.

The dilemma came in selecting a prop.  What to do, which manufacturer, which type.  Maxwell recommended a Hartzell Top Prop and spinner kit.  At the time a traditional 2-blade bowtie unit was $8500 and a 3-blade scimitar was $10,400.  Being an excited new aircraft owner… I went for sex appeal and bought the 3-blade!

The ramp appeal of the 3-blade is off the hook great.  Worth the money for appearance alone.  While talking with a rep at Hartzell to ensure compatibility with my engine and STC’s, the rep said if they made a 5 blade prop for Cessna’s they’d sell everyone they could make.   Hilarious!

New Prop Installed
New Prop Installed At JB Aviation at 10C

Hartzell claims their latest 3-blade Top Prop design won’t reduce cruise performance, while still increasing climb performance.   This is traditionally not the case as 3-blade props are known for improved climb with a slight reduction in cruise performance.  Who knows if the Hartzell claim is actually true.  I had no baseline for measurement, as the old McCauley prop was worn out and didn’t perform to specs anyway.

Ramp appeal won, and Maxwell delivered a shinny new Hartzell PHC-G3YF-1RF/F8068 (SA02821CH).

The prop performs fantastic.  On the old airframe with a tired engine, I’m seeing cruise performance of 135kts TAS.  Pretty standard for a 182.

Quoting Eddie Albert from the Longest Yard… “The rest is hiss-tor-re”.   Yeah a movie I saw for free by climbing the fence at the local drive-in with my 2nd cousin Jeff when I was like 14.