Vertical Stab offset

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Vertical Stab offset

Postby HC85 » Fri Sep 08, 2017 8:12 pm

Okay, I've welded up my vertical stabilizer with the offset of 1 inch to the left as the plans show......and after I was finished , after looking at it, I thought it seemed like a LOT of offset.

I have a set of CB-1 plans and it shows 1/2 inch offset at a position further aft form the leading edge of the stab than the classic dimension position....

And, I have a set of Acro Sport II plans, and it also has a 1/2 inch off set to the left.

Is 1 inch too much, or are the plans correct for a change? I hope I didn't pull a big boo boo here by going with the plans before my gut caused me to question what I've built.

Anyone flying a classic out there with the 1 inch vertical stab offset, I'd really like to hear for you!

Rick
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Re: Vertical Stab offset

Postby mtaylor » Sat Sep 09, 2017 10:34 am

Rick,
Not sure what mine measures, I'm at work and not with the airplane. From memory I'd bet its at least 3/4" if not 1". And I still have some decent bend in my rudder tab. 1/2" seems slight to me. Just my thoughts, though.

Mark T
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Re: Vertical Stab offset

Postby dougm » Sat Sep 09, 2017 1:08 pm

There are numerous differences between the CB-1 and the Classic. I finally got my hands on a set of CB-1 plans last year and it has been an eye opening experience to compare them. You can compare the two and incorporate parts of one on the other, but you need to have a FULL understanding of the differences before doing so.

I would NOT change the Classic rudder offset. Here are three reasons:
1. The CB-1 was built for the O-200 and updated for the O-290... smaller, less HP than the O-320. You would need a larger offset to deal with the larger engine/HP.

2. The Classic fuselage is SHORTER than the CB-1. Yup, that's right, shorter. A plans built CB-1 fuselage is 15 feet (180 inches). A plans built Classic fuselage is 177.25 inches... 2.75 inches shorter. So a shorter fuselage with more HP will need more of an offset to compensate. It's an issue of leverage.

3. Every (or almost every) CB-1 I've seen or flown in has a rudder tab which tells me the plans offset of 1/2" is not sufficient... at least for the O-290. I've never seen a rudder tab on a Classic.
Doug
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Re: Vertical Stab offset

Postby HC85 » Sat Sep 09, 2017 6:53 pm

Well, I will stick with the 1" offset because It is kinda late to change now anyway, and I agree with you're statements Doug. I was just hoping for a "warm and fuzzy " from someone who is flying a classic with the 1" off set just to see how it flys. I was aware of the fuse being shorter and all the other differences already, but good to bring those points up for others to see here for sure.

Thanks Mark for your input, that's good to know.

I will be using the Verner 9. It will swing a huge prop and have gobs of torque. 372 cubes, 150-160 HP. Looking forward to hanging that beast on! So, maybe the 1" offset will keep my right leg from getting the "burn" lol!

Rick
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Re: Vertical Stab offset

Postby dougm » Sun Sep 10, 2017 3:46 pm

I'm sure several folks can comment on flying a Classic with the 1" offset. There are several completed including ones who used a fuselage from Makelan which, I assume, has the 1" offset. Maybe Hans & Sam can comment? Or others?
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Re: Vertical Stab offset

Postby mtaylor » Fri Sep 15, 2017 12:31 pm

Failed to mention I'm a CB1 with 150hp 0-320. My fuselage was built by Richard Lauzon and I'm positive that he increased the stab incindence for the 0-320.
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Re: Vertical Stab offset

Postby dougm » Sat Sep 16, 2017 9:24 am

Mark, could you measure the Vertical stab. offset? I'm curious to know what it is given that you are also using a rudder trim tab. on a CB1 with a 150hp O320. I would think that if you are running a trim tab then you don't have a 1" offset, but who knows? I've never come across a Classic with a rudder tab.
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