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  #1  
Old 04-06-2012, 06:57 PM
Pmerems's Avatar
Pmerems Pmerems is offline
 
Join Date: Jan 2006
Location: Tucson, AZ
Posts: 828
Exclamation 1 inch away from a very bad day-Cowl Horizontal Piano Pins

Gents,

I know you would never try this but I wanted to pass on a warning to all who use the horizontal hinges on your cowl .

Today I had my prop balanced. For those are not familiar with the procedure for prop balancing, it is fairly simple. Mount an accelerometer to the engine and a photo detector to detect when the prop blade passes (reflective tape is applied to one prop blade). You run the engine at cruise RPM and take a reading. Then you add weight to the "flywheel" and run it back up to cruise RPM. So it is an iterative process.

The A&P wanted to balance with the cowl on and fortunately I didn't need to remove the lower cowl (it is a bit of a pain on RV-7A with vertical induction), just the top cowl. My cowl is attached with all hinges (which except for near the cowl inlets (screws) and I have a medallion that covers the horizontal hinge pin access in the side of the cowl (2 screws).

So after removing the cowl and installing the accelerometer I thought that I really didn't need to secure the medallion covering the horizontal hinge pin access. So we continued and secured the photo detector and I started the engine. Not too long after a low idle I ran the engine up to 2450 RPM. The A&P started waving his hands and giving the cut engine hand signal. After the engine stopped I asked what was wrong. It turns out the the horizontal hinge pins were backing out. An inch more of backing out and I would have had a really bad day.

I thought I was a smart guy , just like all the other builders. I really didn't think the pins would back out like they did. I just wanted to make installing and removing the cowl a bit easier during the iterative process of prop balancing.

The moral I wish to pass on is make sure the cowl horizontal hinge pins are secured and cannot back out whenever the engine is run or you might really have a bad day. I think I dodged a bullet today .
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Paul Merems (EAA Tech Counselor, EAA Sheetmetal Workshop Instructor/Volunteer 18 yrs)
ExperimentalAero-HANGAR BANNERS
www.experimentalaero.com
RV-7A (Flying since 2010)/RV-4 (sold 1990)
Tucson, Arizona 85749
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  #2  
Old 04-06-2012, 07:01 PM
Mike S's Avatar
Mike S Mike S is offline
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
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Quote:
Originally Posted by Pmerems View Post
I think I dodged a bullet today .
Yep, I think you did for sure.
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Mike Starkey
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Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

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  #3  
Old 04-06-2012, 07:53 PM
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Ironflight Ironflight is offline
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Location: Dayton, NV
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I have seen RV's parked at shows where the pins were inserted from the front (per plans) but NOT SECURED at all - just bare ends sticking out. That's a definite increase in risk to your prop, for sure.

On the topic of horizontal hinge pins, we had a neighbor take off after rushing to put the cowl back on his Glassair that used the same attachment method. He was on an IFR clearance - ceilings reported at 400', but entered the clouds at 100'....the top cowl departed the aircraft at 200' - he had missed all the hinge loops in his haste. Had to shoot an ILS to a neighboring airport with CHT's and Oil Temp shooting through the roof - no go-around, he didn't think the engine would keep running that long. Cowl nicked the prop on the way off - prop strike, top end damage from heat.....bad day.

Moral? Haste makes waste, and make sure the cowl pins are secure....

Paul
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Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
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Dayton Valley Airpark (A34)
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  #4  
Old 04-07-2012, 06:41 AM
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panhandler1956 panhandler1956 is offline
 
Join Date: Jun 2006
Location: Ohio
Posts: 1,686
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Quote:
Originally Posted by Ironflight View Post
I have seen RV's parked at shows where the pins were inserted from the front (per plans) but NOT SECURED at all - just bare ends sticking out. That's a definite increase in risk to your prop, for sure.

On the topic of horizontal hinge pins, we had a neighbor take off after rushing to put the cowl back on his Glassair that used the same attachment method. He was on an IFR clearance - ceilings reported at 400', but entered the clouds at 100'....the top cowl departed the aircraft at 200' - he had missed all the hinge loops in his haste. Had to shoot an ILS to a neighboring airport with CHT's and Oil Temp shooting through the roof - no go-around, he didn't think the engine would keep running that long. Cowl nicked the prop on the way off - prop strike, top end damage from heat.....bad day.

Moral? Haste makes waste, and make sure the cowl pins are secure....

Paul

Wow that is scary! I like my cowl pins, but there certainly room for operator errror...
Good topic all!
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