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 .
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 .