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PA-12 wings on a PA-18 fuselage

D

Dnh98221

MEMBER
Anacortes, WA
Will PA-12 wings bolt on to a PA-18 fuselage? I know the angle of incidence is different, but is the difference in the wing or in the mounting points on the fuse. I’m contemplating an experimental project and have access to a set of PA-12 wings with flaps.

Thanks,

Dan
 
Here we go again- Crash Jr is probably getting tired of this question. I just had a customer inquiring about the same thing. Short version is they’ll bolt right up but you’ll have to figure out what to do with the aileron cables- totally different routing on a -12 vs -18. Hopefully he’ll give a few more details, as he was involved in modifying at least one -18 fuselage to accommodate -12 routing.
 
Yes they will bolt on. The buss cable will probably work on either. But you need to modify fuselage (add pulleys) to route main aileron cables as in a -12 or better yet -14


Sent from my iPhone using SuperCub.Org
 
So, does that mean I get the angle of incidence of the -18 or the -12? I’m not wanting to have to change the tail plane angle and/or give up the short field performance if I can help it. Sounds like a good case for going with ball bearing pulleys as well.
 
AOI is a product of the airframe.

FWIW? The best performing PA-12 I've observed belongs to Trail Ridge Air in Anchorage. Modified AOI and PA-18 wings.
 
I put 18 wings on a 12. The wing root attach points bolt on. The fuselage requires significant work to make everything else work. Even if you have free wings and are doing all the work yourself, it’s going to cost you too much.

And if you do this dispose of the 12 tanks before you even contemplate this conversion.

And if you have 12 tanks in your 12 throw them away before your next flight.
 
Sorry, guys, I don’t know where you are getting your data, but it’s wrong.

12 wings CANNOT just be bolted onto an 18 fuselage.

The angle of the lift strut attachment brackets on both the fuselage and the wing are not the same on 12s and 18s.
 
Having put 18 wings on and experimental 12 and 14, the lift struts do present a problem. The length of the struts is not the same and the forward strut has a different width lug that enters attach fitting at the wing. The 12 wings have a different design strut attach fitting. 18 wings on a 14 fuselage worked using 12/14 length struts and removing the washer shaped reinforcement on one side of forward lift strut fitting on the 18 wing. Not sure if the opposite would work in your case, maybe using 18 struts would work adding a washer at the forward attach fitting.
 
I know everyone wants to improve performance while also saving money, but sometimes reinventing the wheel comes at too great a cost.

Piper probably had dozens, if not hundreds, of trained aerodynamic engineers working on the design and development of these airplanes. I’m pretty sure they didn’t just say, “Let’s sell airplanes made up of disparate spare parts,” hoping that the finished product “might“ be airworthy enough that they didn’t crash and kill all of their customers.

I suppose if you’re an engineer and know enough to think all these things out, you can get away with it. But I doubt few, if any, of the members here have the knowledge base necessary to do that type of analysis. I’m certainly not.
 
I wanted to put -12 wings on an -18 airframe to get the -18 AOI and the -12 ailerons. As it turns out that's pretty much what I have with the backcountry. Internal cables, -12 style ailerons, and increased AOI. If a guy's got the will to make the changes on a plane? Why not?
 
If you were to take a detailed look at all of Piper's tube and fabric airplanes, you would be surprised at how much alike they are with interchangeability of parts.
 
Adding horsepower and bigger control surfaces is one thing. Guessing at changes that might be caused by changing the aoi to the overall flight envelope and parameters is another. Stewart could have just been lucky that the changes he did worked.

Where would he have been if the changes didn’t work out so well? A lot of money, time, and effort would have been down the drain. Who can afford that?

just saying....if you want SuberCub performance, buy or build a SuperCub.
 
stewartb said:
I wanted to put -12 wings on an -18 airframe to get the -18 AOI and the -12 ailerons. As it turns out that's pretty much what I have with the backcountry. Internal cables, -12 style ailerons, and increased AOI. If a guy's got the will to make the changes on a plane? Why not?
Click to expand...
J4E wings, 16 rib also

Glenn
 
Paul Heinrich said:
I’m pretty sure they didn’t just say, “Let’s sell airplanes made up of disparate spare parts,” hoping that the finished product “might“ be airworthy enough that they didn’t crash and kill all of their customers.
Click to expand...
That's exactly what happened in 1947/48 with the small airplane market in the toilet. Bill Piper and Dave Long Designed the " ninety day wonder" from napkin drawing to first flight from material scraps at Piper. Pa15 Vagabond, my first plane and a delight to fly. Under 650 lbsBe thankful for what they did, because the small sales that the Vag generated kept the bankers from closing Piper and allowed them to survive to play another day. Or....... none of you would have a Super Cub or maybe even all the clones. The lowly Vagabond is the working Mom that made the rest possible

Glenn
 
Last edited:
stewartb said:
I wanted to put -12 wings on an -18 airframe to get the -18 AOI and the -12 ailerons. As it turns out that's pretty much what I have with the backcountry. Internal cables, -12 style ailerons, and increased AOI. If a guy's got the will to make the changes on a plane? Why not?
Click to expand...


I don’t know about the clone kits but the angle of incidence difference between a
12 and an 18 is arrived at by different locations of the wing root fittings. I suppose and I’ve heard that the aoi can be changed by changing the location of the wing root spar attach fittings. That is only part of the equation. The angle of the tail plane must be changed to correspond to the angle of incidence change. That tail plain change is required to keep the proper trim range. The wing and the tail fly the plane. The rest of the fuselage is just along for the ride.
 
Paul Heinrich said:
Sorry, guys, I don’t know where you are getting your data, but it’s wrong.

12 wings CANNOT just be bolted onto an 18 fuselage.

The angle of the lift strut attachment brackets on both the fuselage and the wing are not the same on 12s and 18s.
Click to expand...

Jury struts are also problematic.
 
Dnh98221 said:
Will PA-12 wings bolt on to a PA-18 fuselage? I know the angle of incidence is different, but is the difference in the wing or in the mounting points on the fuse. I’m contemplating an experimental project and have access to a set of PA-12 wings with flaps.

Thanks,

Dan
Click to expand...
If you have skills to make the changes, your labor and the wings are free. it is worth it. It all depends on the mission!! Do you fly heavy, big winds, floats, or just on clear days. Yes it can be done and should be a good flying plane. IS IT WORTH IT. is the question and only you can give the answer.
DENNY
 
Paul Heinrich said:
Sorry, guys, I don’t know where you are getting your data, but it’s wrong.

12 wings CANNOT just be bolted onto an 18 fuselage.

The angle of the lift strut attachment brackets on both the fuselage and the wing are not the same on 12s and 18s.
Click to expand...
The strut brackets are parallel to the spar brackets in both cases, so I don't think that would be an issue.
 
Dnh98221 said:
So, does that mean I get the angle of incidence of the -18 or the -12? I’m not wanting to have to change the tail plane angle and/or give up the short field performance if I can help it. Sounds like a good case for going with ball bearing pulleys as well.
Click to expand...

You can’t change the angle of incidence without changing the tail plain angle if you want any reasonable range of trim. The tail needs to be in the proper relationship to the wing for the system to function properly.

I don’t know how bad it would be if you increased or decreased angle of attack of the wing without changing the angle of the tail to correspond appropriately but it could range from minimal to no trim at least in one direction to uncontrollable.

The primary reason the 12 is faster than the 18 is that as the wing flys through the air based on the tails control, the fuselage moves through the air at less of an angle with less drag. The reason that the 18 gets off shorter is more angle of incidence which due to the tails control of the wing, The fuselage moves through the air at more of an angle creating more drag, hence less speed but shorter takeoff.
 
Looking at a -12 vs -18 in flight I'd say the -18 has less airframe drag. Mod a -12 to include Cub gear, Cub tail, etc and the cruise speed is pretty equal to a Cub.

I know three guys who've changed -12/-14 AOI to match a Cub. None ever mentioned modifying the tail. That doesn't mean they didn't but I'd think they'd have mentioned it to me. Where's Dace Caulkins? He had adjustable spar attach fittings on a plane and moved the AOI with it. I don't recall any chatter about the tail.
 
Every discussion I've followed about increasing AOA on a 12 did include raising the jackscrew. Regardless, it seems like too much hassle. For mine I installed 31"ABW's, 3" extended gear and took out half the wash (at rebuild/ pre-fuel tank installation) and called it good. Kept it light (1095) and it flys great.
 
PerryB said:
Every discussion I've followed about increasing AOA on a 12 did include raising the jackscrew. Regardless, it seems like too much hassle. For mine I installed 31"ABW's, 3" extended gear and took out half the wash (at rebuild/ pre-fuel tank installation) and called it good. Kept it light (1095) and it flys great.
Click to expand...
Yup - been about 2 years now since riding with you, and your plane is a dandy.

Now then, about that Ford pickup .... Oh wait, that's politics.
 
Last edited:
Good point - I've been wondering that also. I guess just raise the jackscrew tower. A comparison of TCDS stab limits between 12 and 18 might be revealing, but I haven't made the comparison.
 
Gordon Misch said:
Good point - I've been wondering that also. I guess just raise the jackscrew tower. A comparison of TCDS stab limits between 12 and 18 might be revealing, but I haven't made the comparison.
Click to expand...

Approximately 1 degree positive up over wing angle.
 
stewartb said:
Do tell. My -12's yoke travel up and down was restricted by tubes, not screw threads. How do you move the jackscrew?
Click to expand...


You change the whole angle of the tail section of the fuselage. Look down the top longeron of an 18 from the front and you will see a downward turn of the longeron at the back of the fuselage in the area of the jack screw. Not a simple change to make and knowing how much to droop the aft end of the fuselage is the real challenge.
 
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