redhawk

redhawk

Well Known Member
Greetings out there,
The cowling on my RV8 was fitted in such a way that the pins that pull the 2 halves together via the piano hinges are very hard to install (requiring a drilling of the pins in and a bit of hammering action!). I don't want to rebuild and repaint my cowling and someone suggested trying the smaller diameter pins (.063) vs the standard .090.
I'm concerned about the strength of these smaller diameter pins and would like to hear any opinions on this, or any other suggestions...
Thanks
 
Here is the basic philosophy on piano hinge, regardless of how it is being used.
If is under very much tension, with the addition of vibration, the hinge section will fail.

Guys that get great service out of the hinges on there cowl, are guys that end up with a great cowl installation.
I.E., when they put the top cowl in place, its hinges will snap in place in such a way that it looks like it is fully installed without even installing any of the hinge pins or the fwd screws.

The guys that will always be replacing broken hinges, are the guys who have to push/pull the cowl into position and/or fight to get the hinge pins installed
There are other factors, such as degree of vibration from prop imbalance, etc., but this is the biggest factor.

To your question... Smaller pins would probably be more than strong enough (considering the strength of the hinge material by itself), but I think you would be putting a band-aid on the real problem. Not to mention that you would then have a sloppy pin in all of the areas that the standard pin would have fit fine.
 
What Scott said is the absolute truth! What Scott described is what you should strive for, sometimes tough to attain on your first cowl though!
 
Hinge pins done right

I also have to agree that cowl done right, which mine was (though I was not the builder:D), are the best...until I had actually seen one not well done I could not figure out what all the complaining and angst was about. Mine slip in and out snug, but effortlessly, and "stitch" the halves nicely together that one can barely see a seam.

Please remember that even though there is only inches of WC pressure differential, multiplied on several square feet means at least a couple hundred pounds trying to blow top and bottom apart.

JMHO.
 
Try This!

If your pins are difficult to insert, try this.

Take the top cowling off and try inserting the pin is each side of the top and each side of the bottom individually. As you insert the pin, look for restrictions. Very often you will find an "eye" that is out of alignment. Adjust that eye.

Once you can insert the pin easily in each side of the top and each side of the bottom, they should go in easily with the cowling halves together.

90% of the time this will fix it!

My pins have been removed and inserted many time in the last 19 years and I have never had a problem with them and have never experienced a broken hinge.
Good luck!
 
Do what Mel says and then... Sometimes during construction a little epoxy works its way into one of the eyes. A quick fix is to run a drill bit through all the eyes. You have to twist it by hand, and it takes a while, but its a sure fire way to clean out the eyes from leftover paint and epoxy.....
 
Cowl pin fit

After building my cowls, getting the side pins in was EXTREMELY tight. After the first engine run I didn't take the cowl off until the next day. It helped to "relax" the cowl fit. After a couple flights and letting the cowl completely cool before splitting, now the pins can be pulled and inserted by hand up to the last couple inches, yet still snug. Top and bottom lugs now snap together like a fitted glove.
 
pins

Two comments - if you need to clean the holes in the hinges, take a long length of pin and flatten slightly the end using a hammer. This is like a drill bit and can help in cleaning holes.
I had everything fitting well and then added an air intake hose and now the pins are harder. Look what may be putting pressure on the cowl as it is being installed.
 
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