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wing wash

That makes sense - but I have not seen a Cub with that kind of disparity. The max I have seen is about two tenths of a degree; well within the new aircraft tolerance. Couldn't get my hands on the smart level today, but promise to get you some numbers on how my ribs go up and down. A visual sighting says they are all in alignment.
 
Just courious, what is the "new aircraft tolerance" for wing washout, on a SuperCub and where would I find that?
Thanks.
 
It is on the fuselage drawings. They are available on CD, I believe, but I cannot tell you who to send $ to. I have seen them on friends' computers, and a friend gave me a J-3 CD that I have yet to load. You won't find it in degrees; it is in the tolerances specs in inches.
 
Suppose you have to check all the blueprint measurements of an aircraft at annual and reject any that aren't in tolerance everywhere?? Wouldn't be too many still flying.

Now that you mention it, that would be a good idea. So who do I see about getting a copy of all the blueprints of the Supercub, PA-14, 12 etc.
Hell I think I'll just start grounding any airplane that flies in here till the FAA provides us with all the blueprints to all the airplanes we annual.
 
Well, if you find a wing that is a full degree off on one side, in all seriousness I would consider looking a little further. That would be mounting holes a full half-inch or more from where they ought to be. We just don't see them off that much.
 
S2D said:
Suppose you have to check all the blueprint measurements of an aircraft at annual and reject any that aren't in tolerance everywhere?? Wouldn't be too many still flying.

Now that you mention it, that would be a good idea. So who do I see about getting a copy of all the blueprints of the Supercub, PA-14, 12 etc.
Hell I think I'll just start grounding any airplane that flies in here till the FAA provides us with all the blueprints to all the airplanes we annual.
Click to expand...

Yep

You hit it out of the park.

Cheers!


Jerry
 
Bob:
You haven't worked on many old beaters from Alaska. I've got a few that have no threads showing on the strut forks on one side and the max allowed on the other side. You have to put a trim tab on the aileron to make them fly halfway straight. These things have been rode hard and put away wet many times. They are not unairworthy, just tweaked a bit. Kinda like my old 83 Chev pickup, not pretty, but it does what I want it to do.
By the way, I don't have a smart level, matter of fact, I've never even seen one. I use a carpenters level with a 3/8" block secured to one end. Just like the Piper Service Letter specifies. I have used it on more than 1 or 2 Cubs in the last 46 years. Most of them fly hands off right out of the hanger. Some need a little tweaking, if the fuselage has been twisted sometime in the last 50 years. Different strokes for different folks, I guess.
These damn things (Cubs) ain't rocket science you know. They were all hand made, and provisions were provided to compensate for the difference in planes. Adjustable strut forks, adjustable tail wires and trim tabs for example.

DSC00190.JPG
 
said:
Well, if you find a wing that is a full degree off on one side, in all seriousness I would consider looking a little further. That would be mounting holes a full half-inch or more from where they ought to be. We just don't see them off that much.
Click to expand...

best(worst?) I have seen is left front wing attach most of 1" high(have pictures somewhere in the box)(and same front gear fitting up the same, also the left top longeron/eng mnt tube behind header tank broke) when put in jig... every thing else was fine.. this was a happily flying plane, down for cover...."never wrecked" that he could remember(I'm sure there was a heat gun involved..), just an old polar bear guide plane's first trip in a jig on the way to new cover.....

.5 deg difference quite common, I can think of one flying one here that's 1 deg....

throw in one side having a univar rear spar with the attach mounting hole that an 1/8" off from an original.... :D

I quite enjoy tring to make a really bent one fly nice.. strait ones are no challenge
 
I have measured a couple low time SCs with no apparent damage nor repairs that did not meet Piper's own spec.

Brian, You can ground a lot or airplanes and I have seen some dosies but if I sign off the assembly and rigging I am going to do my best to do it per the rigging instructions.
 
Steve Pierce said:
I have measured a couple low time SCs with no apparent damage nor repairs that did not meet Piper's own spec.

Brian, You can ground a lot or airplanes and I have seen some dosies but if I sign off the assembly and rigging I am going to do my best to do it per the rigging instructions.
Click to expand...

My only point was, we are not provided with commercial access to any of that data. so how can we legally check for it. I've been trying to get a copy of a Piper report that is referenced in the Type certs to maintain an A model and I can't get it from Piper or the FAA.
But I bet if everyone started grounding those cubs or sueing piper cause they don't have the data, something would change.
 
I doubt it. They don't care. I understand what you are saying and agree. Kinda like the fabric system manufactures making us conform to their STC but a manufacturer can do what ever and doesn't have to tell us how so we can repair it.
 
We are all in pretty much agreement - but I will never recommend a purchase of a Cub that is off by a full degree at the wing attach points. The rigging procedure is not designed to check that, although it could be done with a spirit level and some trigonometry. Sure, they fly. Some fly better than others.

I do have a fuselage that was crunched. The left rear wing attach point was 3/4 of an inch low. It is being fixed. The crunch was almost not noticeable before measurements were taken.
 
I did a little experiment in the house here with the kids, not a airplane in sight. I took my Craftsman 4 foot Digital level and put it on a 4 foot straight edge. Try to follow me. Then i zeroed it. I have a 3/8 by 3/8 piece of square key. I lifted the 4 foot level and set it to .7 degrees. Then i took the keystock and slid it in the up end until it touched the level going between the level and straight edge. When it touched both it was at 29.5 inches. Then the second thing i did was to lift the level up farther to 2.5 degrees and measure at the 29.5 inches and i come up with about 1 5/16 inches. I know its confuseing but if you think about it you can see where it applies. So if im gathering this correctly a wing by using the right measuring points, which im still not 100% sure of, is twisted 1 /5/16 inches from butt rib to outer aileron rib at 29.5 inches distance between measuring points front to back. Clear as mud right? Remember this has nothing to do with leveling a airplane. So my thinking is, note i said thinking, is to level the airplane like steve says and put a 3/8 spacer on a level at 29.5 inches and the .7 degrees should be there. Is the center of the front spar where the ribs connect the place to have the front of the level? TMTOMH=to much time on my hands. doug
 
One more thing that was sortve interesting. With the four foot level sitting up on one end at 2.5 degrees, at the four foot end, its just about two inches up. I can really see now why long tanks like atlees needs to be installed with the washout in the wing.first. Anything that would be put on with the wing laying flat and then twisted like that, than to go and put the washout in afterwards, something eventually would have to give. I wonder if that would even affect the 24 gallon ones if they were put in before the washout was set. Not as long inboard to outboard though, so little less twist.
 
Does all this twisting affect the drag wire tension much? Just wondering?
Laz
 
Laz, when a wing is built on a table a spacer is usually put under the rear spar at the outer aileron rib to simulate how it will be when on the airplane. Then the leading edges and stuff are fastened on.
 
Laz said:
Does all this twisting affect the drag wire tension much? Just wondering?
Laz
Click to expand...

Here's an old post by Flapman that addresses your question.



PostPosted: 31 Jul 2005 11:54
When Piper built Super Cubs at Vero Beach they specified that the wing washout would be set up on two leveled sawhorses. One under the # 1 rib and the other under the # 15 rib. A block of wood would then be placed under the # 15 rib flange just beneath the rear spar. This block of wood measured 1 and 3/8 inches.
As an aside, this washout was put in the wing BEFORE the drag wires are tensioned. If the wires are tensioned while the wing is flat, they will be out of tension spec and out of square when the washout is added.
Regards,
Flapman
Click to expand...
 
Stewart, you made feel pretty good with my guessing a wing is twisted 1 5/16 inches. thanks Dont go shooting me out of the water now. doug
 
I'd like a little more information on that statement. I tried to trammel a wing with the wash-out block in place. It would square, starting with the tank rod. Thought I had a major problem till I removed the block and then everything fell in place.
 
I had just trammeled my wings dead flat before asking the question. I will put the 2 1/2 degs. in and see how it changes, before adjusting anything. It makes sense to tension with the twist in, as that's how the wing "sees "the wind. I wonder about trammeling it square though. Stay tuned!
 
A very smart engineer once had me stretch a string along the main spar, prior to trammeling. After all, the maximum strength of that spar is attained when it is dead-straight. Try it - you will find it helps in the setup, and may even save some time.

I realize that such a procedure is not, strictly speaking, legal - but you will find that after you get the spar straight, all the bays will be in tram. It should go without saying that at least one bay must be trammed at the outset.
 
This is in the FWIW dept. As I said, I had trammeled (and string lined) my wings with 0 deg. twist. I then put in the 2.5 deg. wash and remeasured. here's what I came up with:
First wing: @tank bay= .053" difference (set trammel point on one dimension, and check corresponding wire)
# 1 wire bay (next bay)= .053" diff.
#2 wire bay .053" diff.
#3 wire bay (tip end, long wires)=.040"
Second wing (for repeatability)
Tank bay with (strut out)= .020"
#1 bay=.069"
#2 bay=.046"
#3 bay= .065"
The wire tension was noticeably different . One side too tight, the other "about" right (by feel on each drag bay set of wires). I used a pull gauge (16 to 18 #)and 1/2" deflection on the original flat trammeling.
While the measurements don't sound like much difference, I wouldn't consider them acceptable as a trammel job? It seemed pretty far out. I guess I'll get out my little wrenches and see if I can get it adjusted with the twist in.
 
Could someone fix it so these last two posts come up, when i hit them it comes up saying, hacking attempt, hacking what? What does hacking mean?
 
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