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Overall Length Between the J3 & PA-18 & AOI

Stinson Pilot

Registered User
North Bend, Wa
I have a few questions for the brain trust.
Looking over the Wag Aero Sport Trainer and the North Land PA-18 drawings, the overall length of the PA-18 appears to be 214.75" and the J3 is 208.78125.
It's kind of hard to compare the two lengths apples to apples because both drawings have the overall measurements depicted in different views.

Most everything else is about the same with minor exceptions. The cabin widths are the same. I'm thinking I'll just build per the North Land drawings.

Second question is the AOI between the J3 & PA-18 has a difference of 1.5". I did some searches, but the question wasn't really answered that I could find. I'm pretty sure they share the same airfoil. So the question is why did they increase the AOI in the PA-18?

Thanks
 
Just a factoid. Not confirmed. I was told by an old timer, that Piper used the same fixtures for the PA-18 as the J-3 for the basic fuselage. Other than extra braces in the rear and the overhead wing attach points, seems pretty similar.
 
I've been looking pretty hard at both drawings. Minor differences, mostly the cabin truss. I'm going to compare tube sizes next.
 
Are those length dimensions from the firewall to the tail post or are they overall lengths? If overall, the differences could be in the engine installation.

If the angle of incidence is different, it could be related to the higher horsepower on the PA-18 and flight testing differences due to the horsepower increase. Also increasing the angle of incidence also raises the tail of the fuselage at the same cruise speeds, thus reducing some drag. The wing will fly at the same angle on both airplanes if loaded the same, at the same speeds.

Keep in mind that Wag-Aero was copying Piper's airplane, so to prevent lawsuits they would have changed some things. Use the North Land drawings for accuracy.
 
If you really study the J3 fuselage drawing vs the Super Cub fuselage drawings you will figure out the firewall in further back a small amount on the J3 opposed to the Super Cub but in my experience that is not so. I have an adapter for my Super Cub fuselage jig to repair J3 and PA11 fuselages and they all fit the same at firewall, tail post, gear fittings and rear wing attach fittings.
IMG_20181201_104256.jpg
 
I have the North Land Drawings and I'm looking for dwg 13388. I can't find it on the thumb drive. I found it on https://www.supercubproject.com/drawings/main.aspx but that site will not let me save the drawing or transfer a copy of the file. I want to take some of the main drawings to have printed on larger paper. I'm limited to standard 8 1/2 x 11. Why isn't this one on the North Land drawings and where can I get it?

Update: I found a workaround to save them. Still don't know why that particular drawing isn't on the North Land thumb drive.
 
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The Northland drive has the newer fuselage drawing. Use the parts manual for the drawing/part number.

I have opened and then saved/downloaded a lot of drawings from supercubproject.com
 
Thanks guys...
Looks like the newer SC drawings added some .028 wall tubes to some of the aft bays.
 
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Looks like a good bit of 1025 behind the cockpit to the tail. Do most just substitute 4130 for it?
I've done some searches with varying answers.
 
On the wing incidence question, the Wag Aero and North Land plans clearly show a 1 1/2" difference. I'm guessing that gets the fuselage in a more level attitude in cruise flight for a little less drag.
They both share the same airfoil. So what's the real reason?
 
On the wing incidence question, the Wag Aero and North Land plans clearly show a 1 1/2" difference. I'm guessing that gets the fuselage in a more level attitude in cruise flight for a little less drag.
They both share the same airfoil. So what's the real reason?
Your going to have to post some pictures of the drawings and how you are finding the difference. Is it in the front or rear fittings that are changed? Did you take into account the spar butt hinge location? Are you finding the incidence change more or less than that of a PA 18? It could be miss labeled drawings.
 
Attached both drawings. The rear spar on both drawings are the same distance from the upper longeron.
 

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  • North Land Dwg.jpg
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  • Wag Aero Dwg.jpg
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They all look pretty close to being the same locations. I included the beefed up Clipped Wing Cub spar fittings, they look to be in the same locations as the other two.
 

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  • Clipped Wing Cub spar fittings.jpg
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  • Front Spar SC on Left, Wag on Right.jpg
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  • Rear Spar SC on Left Wag on Right.jpg
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Now look up how the butt hinge is attached to the spar. PA 18 VS J3 and you should find the 1 1/2 difference.
DENNY
 
Thanks Steve for the pics. I saw that in the drawings when Denny mentioned it. I'm building a CWC and wings will be wood. I'm building the SC to get rid of the spar inside and a little extra gross weight. One of the members posted a CWC with boosted ailerons, I'm going with that option as well.
Steve, that roll over fixture is nice! That has definitely been noted!
With what I'm doing looks like I'll be building the superstructure to the incidence of a Cub/PA11.

Thanks for all the help so far, there will be many more questions I'm sure.
 
Why would you need boosted ailerons on a Cub?
Acro!
I'm building this because I like flying Cubs, and I like acro. I had a Steen Skybolt for 9 years and a Sorrell Hiperbipe for the last 5 years. I like rolling around. I know I won't be able to do full negative with this CWC, but I'm getting older and all the positive acro will be plenty for me. My wife actually likes flying acro with me. I'm very fortunate in that regard.
The Skybolt had boosted elevators, and it was very nice when pulling G's.
 
I never would have chosen a Cub for acro, though clipped wing J-3s were popular in their day. You might compare the differences between the Champion 7GCAA or 7KCAB and the 8KCAB which was designed for acro. I believe the 8KCAB Decathlon has less wing incidence than the 7 models. While I'm not certain, they may have different airfoils also. Perhaps you could incorporate some of their differences in your Cub version? Perhaps Bob Turner could pipe in as he has a Decathlon and a Cub.
 
I never would have chosen a Cub for acro, though clipped wing J-3s were popular in their day. You might compare the differences between the Champion 7GCAA or 7KCAB and the 8KCAB which was designed for acro. I believe the 8KCAB Decathlon has less wing incidence than the 7 models. While I'm not certain, they may have different airfoils also. Perhaps you could incorporate some of their differences in your Cub version? Perhaps Bob Turner could pipe in as he has a Decathlon and a Cub.
Stock long wing Cub is just a blast to play with. I have a little Stearman, Great Lakes, Moth and Pitts time but the Cub is just more fun, maybe because you need to make it do it


Glenn
 
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