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US35b Full size print out

Longwinglover said:
OK 25 posts of people giving their best guess. Let's go to "the" source, Clyde Smith, Jr. - The Cub Doctor. Quoting from the Sept/Oct 2005 Cub Clues newsletter A Study of Piper Ribs Clyde says in part:

"All fabric Piper ribs employed one airfoil design, the USA 35B, but were modified by increasing the upper coordinates by 4%. Thus the terminology "USA 35B Modified" was the typical description of the Piper rib and the chord was 63 inches. All the ribs were similar from the J2 through the PA-25 Pawnee.
...
In my weekend siminars, I divide the wings into two classes, the "Cruiser Wing" and the "Cub Wing". The Cruiser wing was used on the J4, J5, PA-12 and PA-14. The Cub wing was used on the J3, PA-11, PA-18, PA-25 and all the short wingers. The differences here were that the Cruiser wing had the "S" or "Sloped" type of false spar and had a stamped nose plate rivited into the leading edge or nose section of each rib, rather than the individual truss type bracing.
...
The Cruiser wing panels did not have the short nose rib sections between each main rib either
...
The Cub type wing had the concave type false spar and the nose of each rib had the individual brace members. These wings also utilized the short nose rib sections, forward of the main spar, between tha main ribs."

John Scott
Click to expand...

John, missed your post, looking for that quote now. Thank you!

If it weren't for the fact that I have two J3 cub ribs and a 12 and 14 rib, I would have never considered this, however the two j3 line up pretty good as do the 12 and 14, but the 14 and 12 are slightly larger at the cord that the j3, however they don´t perfectly line up to the original piper drawing as the j3 is slightly small and the 14 is slightly larger cord. Only the 12 lines up the closes to the drawing... I guess this is all has to do because of the jig differences... 4% is very subtle expect at stations where the cord is thickest at station 18.9... right now from my notes, j3 is 7.53 and 7.56 inches and the 12 is 7.68 inches and the 14 is 7.74 inches... :/
 
By cord, are you referring to the chord (the distance between the leading edge and the trailing edge)?
Is it different between the 3 and 12 ?
 
Hi JimC, By cord thickens I was referring to camber thickness on the airfoil. Aerodynamic_camber.jpg
To answer your question, yes there are differences hence my questioning if the j3 and the 12/14 weren't different, the old USB 35B and USB 35B Modified, it's hard for me to gestimate as the difference is slightly more then half of what it should be in modified vs standard 35B camber thickness. 7.74 - 7.53 = 0.21 inch vs the +0.308 inch where the standard 35B should have 7.392 inches the modified is 7.7 inches, and non of the ribs measure on or the other...


Mike, these are full ribs, and their cord length is almost identical only thing that makes them different is slight bends along the entire rib and it is less than 0.067 of an inch when I convert form millimeters :p and I pace a heavy DM board on them to measure.

These are supposed to be all original Piper ribs, but been in Europe, I'm almost certain that some repairs where made that could have change the ribs all together, all airplane where wrecked at one time or another and surplus parts where used to spring them back to life. :D
 

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I overlaid an AutoCad drawing of the leading edge skin (from printed dimensions on the Piper Drawing) over the photo of the nose rib that was posted above. Both had issues and neither matched the Piper Drawing.

The PDF print of that was 153 megabytes, so I can't post it here. So, I just took a photo of the screen. It may be too large to post as well.

The three small green circles near the upper surface represent one problem area. The Piper drawing called for that ordinate to be 4.036" (the bottom circle). It should have been 5.036 (the top circle). The Piper draftsman drew it as the middle circle (and the nose rib appears to match the error in the drawing, giving a concave upper surface near that point- oops). When drawn by dimensions, the height of the nose radius point is also off by a little over a tenth of an inch.
 

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I was well aware that it is a Dakota rib. I used it because it was also used earlier in this thread and because it is wrong.
I haven't been out to the airport to pick up a Piper rib to compare it to the drawing (which contains inconsistencies as well) -- the coordinates and dimensions listed on the Piper leading edge skin drawing don't match the drawing linework and don't match the Piper rib drawing. These drawings are all typical of our drafting tolerances and shortcuts in the days before we had Cad software.

My hunch is that Piper was building to jigs, not drawings.
 
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Thanks Mike. I never seem to tire of watching that. After some new phase in building I go back and look at it again and learn something new in the details that I had missed before I tried making a part.
 
JimC said:
I was well aware that it is a Dakota rib. I used it because it was also used earlier in this thread and because it is wrong.
I haven't been out to the airport to pick up a Piper rib to compare it to the drawing (which contains inconsistencies as well) -- the coordinates and dimensions listed on the Piper leading edge skin drawing don't match the drawing linework and don't match the Piper rib drawing. These drawings are all typical of our drafting tolerances and shortcuts in the days before we had Cad software.

My hunch is that Piper was building to jigs, not drawings.
Click to expand...

The Piper ribs have the same "discrepancy" as the Dakota rib shown in Jim's picture. I am elbow deep in new Piper rib nose repair sections and second hand ribs at the moment and they are all like that with that concave appearing section along the top. I purchased a Univair nose rib and it is different again.

I have chosen not to worry about it too much: Before the internet and everyone chatting about these sorts of discoveries and the Northland CD I just used to rebuild the aeroplane with the parts to hand and go out and fly it and it flew like a Cub. A jig was made by selecting the best looking Piper rib and drawing around it with a pencil. So, I have decided not to fret too much and just get on with it.

Andrew.
 
JimC said:
My hunch is that Piper was building to jigs, not drawings.
Click to expand...
I agree with JimC,
It is not unusual, in prototype construction, to make the drawing from the first part. Then sometimes the engineers refine the drawing. Yet they still build subsequent parts from the original fixture. Thus the parts really never match the drawing. This may not be so likely to happen now in the computer age, but back then things were different.
 
MainlandCub said:
A jig was made by selecting the best looking Piper rib and drawing around it with a pencil. So, I have decided not to fret too much and just get on with it.

Andrew.
Click to expand...

My point exactly, there was debate, but when I took measurements the discrepancies where all over the map, thus the conclusion that moving from jig to jig changed some of the ribs in less than 2% of the chamber thickness all together. :D
 
I found the Piper error of 4.036 vs 5.036 at the location of the concavity to be the most interesting. That goof did actually hurt the performance of the wing.
 
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Hi Jim, are you referring to a station between station 44.100 and 50.40? I am not following the station you are referring to? changing 4.036 to 5.036 or vise versa only affects upper camber profile of the air foil, would it not? Sorry I think I need some coffee... :D
 
I'm referring to the upper surface ordinate at Station (abscissa) 3.15
The draftsman mislabeled that ordinate as 4.036 when it should have been 5.036
He drew the ordinate at 4.81, and that is what the Dakota rib is built to.

Kerri-Ann's upper surface ordinate at Sta 3.15 is 5.040 (a difference of 0.004), which is good 'nuff fer guvm't work.
 
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Cool, got it!!! What I sis when I drew it up was make ordinates according to the 104%, so I took the 35B airfoil and added the 104% to that, which is what should have been intended (I believed) and I come up with 4.92 (4.731 * 1.04.) I did not catch that on Kari-Ann's drawing. Probably why I did not have to add another ordinance to smooth the curve out, but who know. I will send you my DWG if you like... or send me the picture of the dakota rib and I can line it up. I have not been out to the hangar to get my ribs out and take some reference pictures with a ruler but I will try that ASAP and compare it using original piper ribs.
 
Check my post #35 for a photo of a photo of the Dakota Rib laid over Kerri-Ann's drawing and with my copy of the leading edge skin done from coordinates from Piper DWG # 10631 (and another drawing whose number I don't recall). For Station 3.15, the lower small green circle is where 4.036 would fall, the upper small green circle is at 5.036, and the intermediate small green circle is at 4.81 (which is what the Dakota Rib is built to).

I've also tried to attach here, a copy of part of DWG # 10631 with the bad coordinate outlined by a black rectangle. That coordinate should be 5.036 instead of 4.036. However, I couldn't do so, because the upload software won't do anything larger than 620x280, and I can't fit the bitmap drawing into that aspect ratio. I was able to attach it as a jpeg.

E-mail me at jrccea1 at gmail.com
and I will send you a copy.

I would like a copy of your drawing as well. A DXF file would probably be most likely to be compatible.
 

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I would like to edit my previous post, but can't. Piper Leading Edge Skin Drawing# 10630 has some good coordinates. Sta 3.150 upper surface is called out as 4.936", but only 4.990" will fit (this is in lieu of the 5.036 that I used instead of 4.036" as taken from another Piper drawing in my previous post). Most of the rest of 10630 looks pretty good, but the leading edge radius is 1.5436" instead of the 1.125" and 1.000" that Keri-Ann or I used previously. More to come.
 
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Here is a comparison of the Wag Aero 2+2 vs the data from JimC and myself. Jim's is in blue and the ordinates come from the image above, I took the 35B data and added 4% to that and is in yellow.

Wag-Aero-vs_JM_JIMC02_zps545b3747.png


Well, as you can see JimC's data is closer to Wag-Areo and as soon as I can get some volunteer to send in pictures of Piper Ribs or Dakotas or D&E (am I forgetting anyone) that have been take as parallel as possible to the and have a ruler in the picture, I can line them up and see how they differ. Also, if someone has their J3 drawings form Wag Areo and they care to take a picture of the nose rib drawing with a ruler under it, that would help. My set of plans is in a box I currently can get to... had a friend invade my hangar and I don´t have access to a lot of my stuff at the moment. :D
Regards,
 
The Pioer drawing doesn't specify the leading edge radius. I like yours better than mine, so changed my nose radius to match yours.
 
What do you guys with autocad plots think happens behind the Rib STA 18.900 upper ordinate? I know the Rib STA 25.200 upper ordinate is lower, but the tracing I have of a Piper rib shows and upper curve increasing past the Rib STA 18.900 upper ordinate before descending down towards the Rib STA 25.200 ordinate.

However the best fit through the known ordinates from Piper drawing 13814 with a loose piece of cap strip doesn't follow the tracing of the Piper rib. I don't think I will be following the tracing of the Piper rib, but I was curious what your plots showed.

I am looking at Piper drawing 13814 when quoting the Rib stations.

Thanks,
Andrew.
 
The digital copy of 13814 that I have is 'warped' with mid-chord being roughly 0.15 inch too high relative to the leading and trailing edge so that neither the upper or lower surface can be constructed by tracing. Consequently, it would need to be reconstructed from the printed stations and ordinates. I would do that, but not all of them are legible on my drawing. Anyone have a list of them?

For example, the ordinate at 12.600 is 7.3?0. What is the ? digit?

The ordinate at 25.200 is 7.4?0. What is the ? digit?

The ordinate at 37.880 is 5.7??. What are the last two digits?

I don't have the ordinate for Sta 50.400 or any of the stations and ordinates aft of there.

With those in hand, it would take me a couple of hours to accurately reconstruct the drawing and extract the high point.

As an aside, the station called out as 9.45 on this drawing is called out as 9.4375 on other Piper drawings.
 
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I've already measured enough of 13814 in AutoCad this morning to tell you that it is NOT accurate.

BTW, the drawing labled as 13814 on the link site is NOT 13814. It is one of Kerri-Ann's rib drawings overlaid with a leading edge skin drawn by me based on Piper Leading Edge Skin Drawing # 10630.

The high point on the link drawing is at Sta 19.019 and the ordinate is 7.852.
I wouldn't put much faith in either number.
 
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JimC said:
The digital copy of 13814 that I have is 'warped' with mid-chord being roughly 0.15 inch too high relative to the leading and trailing edge so that neither the upper or lower surface can be constructed by tracing. Consequently, it would need to be reconstructed from the printed stations and ordinates. I would do that, but not all of them are legible on my drawing. Anyone have a list of them?

For example, the ordinate at 12.600 is 7.3?0. What is the ? digit?

The ordinate at 25.200 is 7.4?0. What is the ? digit?

The ordinate at 37.880 is 5.7??. What are the last two digits?

I don't have the ordinate for Sta 50.400 or any of the stations and ordinates aft of there.

As an aside, the station called out as 9.45 on this drawing is called out as 9.4375 on other Piper drawings.
Click to expand...

This is from Piper drawing 13814 from the Northland CD.
Leading edge = 1.77
9.450 = 0.000 / 6.920
12.600 = 0.031 / 7.390
25.200 = 0.176 / 7.480
37.800 = 0.283 / 5.770
50.400 = 0.220 / 3.290
56.700 = 0.126 / 1.780
59.850 = 0.076 / 0.983
63.000 = 0.000 / 0.164
 
Thanks.

Would you confirm the Station 37.800 please?
The drawing I have seems to read 37.880.
I'll post the station and ordinate of the upper surface high point tomorrow.
 
In your list, there is a missing station and ordinate at roughly about station 44.100. Do you have that station and ordinate?

Also at either station 31.5 or 31.3. The ordinate at that point is 6.760.
 
The high point on Piper drawing 13814 appears to be at sta 19.346, ordinate 7.701.
Consider this preliminary till I double check it tomorrow.
 
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