Almost lost prop
 

On 12 May 2011, I was out practicing acro for the upcoming IAC contest in Grenada, MS 20-22 May. On several previous flights I had noticed a very slight vibration and had thought it was a fouled plug, but the vibration change was not consistent when switching mags. The vibrations seemed to increase on this date during the practice between 2400 and 2600 rpm so I throttled back and returned to the airport. I also had noted some dark gray smudges coming from the front and sides of the cowling on previous flights. We had replaced a broken front cowling bracket two months prior. When I first saw the smudges, The A&P and I had noticed that the rubber baffling around the cowling bracket and starter ring was touching and worn through, and thought this was the source of the small amount of residue.

After this flight, as we were about to remove and check the spark plugs, the A&P noticed more of the powdery residue and stated this was not rubber, but metal powder. On further investigation we found the prop could be moved perpendicular to the crank. When the spinner was removed, this is exactly what we saw. Two bolts had stripped and all the safety wire had broken. Tach time 608 hours.



Wooden prop (manufacturer will not be named), 70 x 78 inch was installed December 2007 with approximately 400 hours on the tach from installation to this incident 12 May 2011. This prop replaced the original 68 X 74 prop by the same manufacturer after engine was overhauled Conditional inspection with torque of prop bolts checked at 22 ft-lbs, on 28 Feb 2011. Tach time 570 hours.

My A&P mechanic thinks that the long prop bolts may have bottomed out, and created a false torque value when the bolts were retorqued on the conditional inspection. The previous engine overhaul company thinks the 8 ? inch bolts through the spacer were a contributing factor when the aircraft is used extensively for aerobatics. He recommends shorter prop bolts and using a spacer that is bolted to the engine flange and the prop bolted to the spacer. The prop and all the components on the hub were damaged and are being replaced. The engine will be torn down, inspected, and damaged parts replaced.

:eek: I think that calls for a drink ... or twelve! Finding that would scare the bejeebus out of me. Glad nothing worse happened. The lesson I take from this is to pay attention to what my aircraft is telling me. I think I'll go listen to the -6A some more.

Safe on the ground
 

Thanks for sharing and glad you are safe on the gound!

Hi Willy,

Many thanks for sharing this with us in you very well written, concise and to the point post. I too am glad you are safe on the ground. One thing I will check when I get there, is the space between the bolt head and the flange when the bolt is fully bottomed out.

My father lost a prop on a champ years ago and landed safe in a cow pasture. They found the prop a couple years later on a pond dam. Still have the prop. He had nine lives broke a crankshaft on a agwagon on take off went into a cotton field and flipped knocked him unconscious when he woke up said he smelled fuel knocked side window out crawled out got about 100 yards with broke ribs plane exploded burnt to a crisp. He died in 2006 of a heart attack he had a log aviation career as chief pilot for forest service flying T34s I would love to here some of that old hanger flying again.If you know a old timer strike up some old tails before its to late.

I can't see your pictures because I'm at work and they have the site blocked so I am responding somewhat in the dark. When I flew a Long-EZ with a wooden prop, it was mandatory to re-check the torque every month or so, especially as the seasons changed due to variations in humidity. Sometimes, the bolts would be close to loose. Also overtightening is a constant concern due to the eventual crushing of the prop core.

I'm so glad you made it on the ground safe. Wood props have their place but they require constant care and feeding.

Torque
 

As Randy noted, a wooden prop requires frequent inspections. I used to fly a YMF-5 Waco that required a torque check on the prop every 25 hours.

John Clark ATP, CFI
FAA FAAST Team Member
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA

Bill, too bad this couldn't wait until after Grenada so you could use all that prize money to help fix your plane! But seriously, sorry about the situation, and glad nothing catastophic happened in flight. My RV had the spacer bolted to the flange, and shorter bolts through the prop and spacer only. My front crush plate also had a circular channel milled to the width of the propellor bolt heads so that the bolt heads would recess in the channel, and keep them from rotating. No safety wire needed, and none to break.

I retorque my Catto prop three - four times a year. On a trip to the east coast, I retorqued the prop on the ramp at Crystal River (humidity concern or perhaps ignorance)

Yup....all need to add to your condition inspection form....check propeller torque regardless of the manufacturer or material........I know it is a PITA for some to do this but well worth the $$$ and safety to do so.....