Engine "squeal" at cruise

[Mike Buettgenbach]

~ 350 Hrs on engine
Carbs are well sync'd
No apparent noise on shutdown
I have to "soft start" kit on the engine

Over the last 40-50 hrs of flying, there has been a squeak/squeal/screech during taxi. It happens a bit above idle and stops about 3500 RPM. Nothing noteworthy on t/o roll or climb-out. Upon landing, no noise at any rpm.

Today-- On climbout, a similar noise happened, I turned back to the airport...then it stopped. Continued to the destination. Enroute (about 30 min at this point), a similar noise started at a similar tone frequency and ramp'd up in frequency over about a 20 sec period, stayed for 10-15 sec and stopped. [4500 ft, 5360 RPM, no indication of change in instr]
I won't go thru all the details, but it happened 2 more times in a similar fashion before I got back to home base.

No gear box problems (that I know of). Just finished annual condition insp, all is good.

I don't want to lead the witness, but it "feels" like a gear box problem...

Suggestions welcome!
Thx

 

[Jesse]

I would recommend a call to Lockwood Aviation and talk to Dean, their expert, and ask what he thinks.

 

[roger lee]

A few guys had this complaint in other aircraft. I ended up as wind coming through cracks or gaps in the cowl or wing attachment points. It only happened at certain speeds and angles of attack. They taped the gaps and the noise quit. They thought it was the engine too.


The gearbox can squeal, especially at shut down. What oil do you use? What is the gearbox friction torque? (this should have been checked at annual)

Try to duplicate the noise then change angle of attack or speed on the ground.

 

[Mike Buettgenbach]

I use Aeroshell Plus 4. Oil chg every 50 hrs. I prob use 20% 100LL
Friction torque was within spec. (don't have the cklist just now)
During one of the cruise events, I pitched up slightly and the pitch (of the squeal) did change. The other events were on AP and constant pwr, pitch and attitude.

Thx for the comments!

 

[J.Coles]

Also check your Pito spinner hole. I have to use some grease there once in a while as that can make a whine to wake you up real quick.

Cheer
Julian

 

[rvbuilder2002]

Also check your Pito spinner hole. I have to use some grease there once in a while as that can make a whine to wake you up real quick.

Lubricating the pitot tube bearing in the spinner is not called for in the maint. manual, and it should not ever need to be done.

The bearing is made of Rulon, a self lubricating Fluoropolymer.

Use of any lube that might tend to attract and collect dirt (abrasive material) is likely to greatly shorten the life of the bearing and the pitot tube. If the pitot tube bearing is causing a noise, something is likely wrong that should be investigated more beyond just lubricating it

 

[AJSWA]

Engine squeal at Cruise?

Mike ,
Are you sure it is engine?
Do you have a viking shield on the front of your canopy by chance?
I had a similar nasty experince sunday a week agon on my first flight just after lift off a loud buzz started and turned to a screech noise, like a dry or failing bearing. I Leveled off at 500' and changed engine speeds to check if it was mechanical which it wasn't so re-checked temps and all good so kept going. After recalling reading about a loud buzz on another thread of the forum, I pulled down on the canopy bow to reduce the clearance of the fiberglass and the instrument cowl and thankfully shut the noise up.
May not have anything to do with your problem but certainly worth considering.

 

[BigJohn]

Had a similar problem early on in flight testing. Turned out to be a fiberglass cowling edge that was too close to fuselage. It would vibrate at certain harmonics. Nearly drove me crazy finding it! Two minutes with a piece of sandpaper and it was fixed. Hope your problem is just as simple.

 

[Shedman]

I to have had this noise during run-up and taxi. We isolated the squeal to the spinner bearing, sprayed on lube whilst idling and it shut up instantly.