I'm curious if anyone can tell me what Piper's reasoning was behind the nose ribs that go in between every full rib on the Super Cub wing. The PA-12 didn't have them, yet the 13 rib sc does, and both have the same Vne at 138 mph. The -12's is actually higher when in utility category at 148 mph. So my question is, how necessary are these nose ribs? Did the -12 have thicker LE skins to compensate? I'm planning to build up some wings for an experimental project in the future, and I'm just wondering if I should leave them out, or do they serve a purpose that necessitates them being there? Thanks in advance...
Nose ribs, or not?
- Thread starter ak49flyer
- Start date
bob turner
Registered User
What a great question. Even the lowly J-3 has them.
skywagon8a
MEMBER
SE Mass MA6
I'll let you make the decision. Consider this, the leading edge of the wing needs to maintain it's shape at Vd in order to prevent any sudden and unexpected change in airfoil shape which could have catastrophic results. Vne = 90% of Vd. Vd is design dive speed, the difference between Vd and Vne is the margin of safety. Ask yourself if the leading edge is strong enough between the nose ribs to maintain it's shape. The shape of the leading edge generally controls the bulk of the air flow over the remainder of the wing.
The leading edge can be stiffened in several ways. A few examples are: increased thickness of the leading edge skin, more nose ribs, span wise stringers spaced under the leading edge skin, leading edge made of a different type of material. Let your imagination roam, there are many ways to solve this issue. Just remember you want the leading edge to maintain it's shape.
mike mcs repair
Registered User
chugiak AK
makes it stiffer wing
the -12 had less leading edge that didn't even go all the way to or attach to spar, its a VERY soft/flexible wing
the -12 had less leading edge that didn't even go all the way to or attach to spar, its a VERY soft/flexible wing
Thanks guys, that's kind of what I figured- I'm not advocating for omitting the nose ribs, just was curious. The weight savings of leaving them out would be minimal, but just guessing, I'd bet if you made your LE skins from 2024t3 and maybe go the next thickness up, you'd have a sufficiently strong wing, but I'm no engineer. Hadn't seen it discussed before and was just interested in the various opinions out there.
bob turner
Registered User
I think most go to .020 leading edge skin anyway. When you bend your own you will find out just how strong those skins are.
skywagon8a
MEMBER
SE Mass MA6
Bob, That's an open statement which could mislead ak49flyer and others. Do both the certified PA-18 and PA-12 have .020" thick LE skins? What alloy did Piper use? There is a big difference between 3003-0, 5052-0 and 2024-T3 or 7075-T3 all of which can be .020" thick. With the underlying structure being the same, the 3003 could collapse during a Vd dive while the 7075 could hold up at a much higher speed.
Steve Pierce
BENEFACTOR
Graham, TX
The earlier PA18S used 3003 .020" and a stiffener under the outboard leading edge skins.
Steve Pierce
BENEFACTOR
Graham, TX
Looking in the parts manual and drawings you can see where they switched. Same with the Short Wing series.
bob turner
Registered User
Sorry about misleading. My original J-3 leading edges were .016, and maybe T3 max. I did not know the 3003 alloy was around in the 1950s. .025 sounds like over-doing it.
Opinion, for chrissakes.
Opinion, for chrissakes.
Steve's Aircraft (Brian)
FRIEND
White City, Oregon
I'll join you... Give him a good beating... God I hate Martin clips, worse thing invented IMO...
Brian
bob turner
Registered User
Me too. I was caring for a 108 Sc with PK screws damaging those ribs. Been that way for three decades - a kindly fed gave me a field approval with the proviso - inserted by me - that the ribs would be replaced at the next cover.
supercrow
FRIEND
Smith Pond near Millinocket, Me
I saved a set of PK drilled cub ribs on my experimental by bonding .020 2024 strips right onto the top and bottom of ribs, full length. If you use .020 leading edge full length to the spar you now have a nice even transition from leading edge to ribs and can use rib lacing. I did still use the false ribs. Using this method to cap the ribs also allowed me to straighten the ribs and end up with a nice looking finished product. For an experimental, I found it an easy and strong fix that took about 5 hours per wing.
supercrow
FRIEND
Smith Pond near Millinocket, Me
Ref. above I did the caps with the leading edge in place so that the seam almost disappears.
