Vertical Stab attachment bolt holes

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PoconoJohn
Posts: 165
Joined: Tue Jan 14, 2020 9:07 pm

Vertical Stab attachment bolt holes

Post by PoconoJohn »

I'm positioning the horizontal stabilizer onto the back end in preparation to drill holes to attach it to the fuselage. I already drilled the holes to attach the vertical stabilizer to the HS. My plan was to offset 1/2" for the Corvair engine.

I noticed right away that one of the VS holes will mostly miss the longeron due due the offset.

I did make sure the HS was square to the fuselage using my marks (checked several times), a large square ruler and running a string from both back outer corners of the HS to the top front where the engine will mount.

I'm wondering if I should stay with the offset idea and glue a block of wood under the plate (a 1/8" gusset glued on top of fuselage in the area) and glue another 1/8" plate under it, OR mount the VS straight, glue a dowel in the existing HS hole and drill a new hole next to it.

Here's a couple of photos. One shows the offset. The other shows the existing hole and where the new hole would be if I did not offset. The hole on the other side is on center with the offset and will be near the edge without offset similar to what you see in the photo. I would have to glue a dowel in that hole also and drill a new hole if I remove the offset.

John C
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piet9996.jpg
Last edited by PoconoJohn on Thu Apr 22, 2021 2:28 am, edited 1 time in total.
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taildrags
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Joined: Tue Mar 07, 2017 10:39 pm

Re: Vertical Stab attachment bolt holes

Post by taildrags »

My suggestion? It's easy to measure, cut, and glue in a cross-block between the longerons so you can bolt through that. The epoxy will be dry in the morning and you can carry on ;o)

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power
PoconoJohn
Posts: 165
Joined: Tue Jan 14, 2020 9:07 pm

Re: Vertical Stab attachment bolt holes

Post by PoconoJohn »

Thank you Oscar.

Here it is 3:23 in the AM. I think I have an idea. I can put a dowel in that one hole and drill a new hole where the pencil mark is. I can use spacers on the two bolts going through the VS. I won't have to touch the hole on the other side of the VS.

OR

I can also make a new bracket there to get the hole lined up with the pencil mark

I really would like to go through the longeron since it's the main beam and seems like that's where the load is.

John C
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taildrags
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Re: Vertical Stab attachment bolt holes

Post by taildrags »

John; either way works. I was trying to keep you from making a hole in the longeron, you're trying to get the hole to land there. It's your airplane, you pick ;o)

-Oscar
PoconoJohn
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Joined: Tue Jan 14, 2020 9:07 pm

Re: Vertical Stab attachment bolt holes

Post by PoconoJohn »

Thanks! I'm heading out to look at it and make a decision.

John C
PoconoJohn
Posts: 165
Joined: Tue Jan 14, 2020 9:07 pm

Re: Vertical Stab attachment bolt holes

Post by PoconoJohn »

I'm now thinking of plugging the two holes and using the 1" screws and 1 3/4" screws as shown on the plans.

John C
danoliver
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Joined: Sat Feb 25, 2017 7:58 am
Location: Cincinnati

Re: Vertical Stab attachment bolt holes

Post by danoliver »

Looking at the pictures of the last original on West Coast Piet it looks like Bernard didn't offset the fiin at all. Maybe someone who has seen it in person can verify that. The camera angle makes it hard to say for sure. It also looks like he used a combination of screws and bolts in that area. Not trying to muddy the waters here just pointing out what influenced me to leave mine straight (not yet flying myself).
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taildrags
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Re: Vertical Stab attachment bolt holes

Post by taildrags »

The only experience I have is with my airplane, A75, wood fuselage. The first couple of years I owned the plane I flew it with one foot always holding a little pressure on one side of the rudder bar but I thought that's just the way it was with this Air Camper and most others flying in this configuration. That was when I had the original A65 on it. When I swapped the 65 for the 75, I got to messing with the rubber donuts on the engine mount and discarded the AN970 wood washers that the original builder had used at the mount points because they were not designed for use in this application and had become dished. I got to looking at the mount and the resulting engine geometry and deduced that the builder had fabricated the mount with a bit of downthrust and then had stacked washers to offset the engine slightly to starboard. My hangar mate, who is a test pilot, suggested that if we were going to replace the washers, that we get some good stout steel ones so I got a package of 10 black-oxide, oversize steel washers from McMaster-Carr, about a buck apiece if I remember correctly. Compare to $15.55 apiece for genuine Continental part no. 21530 engine mount washers. We did that and then took a first cut at adjusting the washer stacks to add some more side-thrust to the engine and maybe correct the yaw tendency in cruise. We did that and test flew it, and it was better. Added one more washer strategically to also relieve the need to hold back stick in cruise with anything more than half fuel, but didn't want to add anymore washers or the prop hub would start rubbing on the opening in the front of the cowl. Test flew, it was better but still needed a bit of foot on the rudder bar.

Moved back to the tail and we offset the leading edge of the VS about 1/2", test flew, and it was very close but would still creep off of heading with feet flat on the floor. Got lazy and installed a bent tab on the trailing edge of the rudder to take out the last of the yaw and now it will hold heading with feet flat on the floor. So here you see that there are several ways to get the plane rigged to stay on heading... engine thrust offset, vertical stabilizer offset, or trim tab. If you don't like the look of the offset VS, you have other options and you'll most likely need to use one method or the other. Corvaircraft will of course offset opposite of Cont/Lyc flyers, and I don't know what Ford A flyers might need or what the experience has been with those because it's not really practical to offset the engine thrust to one side with the Ford engine bearers being arranged the way they are.

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power
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KenBickers
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Re: Vertical Stab attachment bolt holes

Post by KenBickers »

PoconoJohn,

I've attached a photo of how I did mine. The vertical bolts are centered through the longerons. I made each bracket different lengths to sandwich the rudder with the desired offset. Actually I originally had a Corvair on my Piet, later swapping that out for a Continental O-200. When I did, I just swapped the two brackets to shift the offset from the right to the left.

I've seen some super-slick ways of doing this with small brackets on both sides and stacks of washers used to create the desired offset. I didn't see that approach until mine was already done. The advantage of that is the amount of offset can be dialed in by shifting washers from one side to the other until you have exactly the amount you want.

Cheers, Ken
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PoconoJohn
Posts: 165
Joined: Tue Jan 14, 2020 9:07 pm

Re: Vertical Stab attachment bolt holes

Post by PoconoJohn »

Thank you Oscar for explaining the engine mount concept. That's new to me.

Thank you Ken for the photo and explaining the washers to adjust the VS offset. I've seen that one one plane so far.

I'm going to continue thinking about this. I'm not too thrilled drilling holes to run bolts through the longerons, especially since it seems Bernard didn't do that. Just using screws (and what's #7?) doesn't seem so swift either because if I have to remove them, I'm not sure how good it'll be re-using the hole unless I put a dowel/plug in. With the offset, not sure how to attach the starboard side.

John C
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