Does anyone know what the wing incidence (at the root) of a super cub is in relation to the waterline or centerline of the fuselage? The reason I ask is we are in that stage of building a Breezy fuselage and it calls for 0 incidence at the wing root and I had thought that a cub had 1.5 degrees... but I can't remember. Thanks Joe
Wing Incidence
- Thread starter joecub
- Start date
incidence
Joe, From the horizontal reference line on the fuselage to the bottom of the wing at the first rib the magic number is 1.84 degrees. Most seem to measure somewhere between 1.2 and 1.7 unless they have been rebuilt in a jig recently that puts it all in. You might want to check with Mark E from Thrustline on all this. He has all these numbers in his head.
Dave
Joe, From the horizontal reference line on the fuselage to the bottom of the wing at the first rib the magic number is 1.84 degrees. Most seem to measure somewhere between 1.2 and 1.7 unless they have been rebuilt in a jig recently that puts it all in. You might want to check with Mark E from Thrustline on all this. He has all these numbers in his head.
Dave
skywagon8a
MEMBER
SE Mass MA6
The L-21 maintenance and erection manual says that the angle of incidence is 2 degrees 2". at the root. This corresponds closely with the bottom of the wing being level.
If you can find a copy of 'Handbook of Airfoil Sections for Light Aircraft' by M.S. Rice you will find on page 74 all of the specs for the U.S.A. 35B airfoil which is on the Cub. That should accurately answer your question.
If you can find a copy of 'Handbook of Airfoil Sections for Light Aircraft' by M.S. Rice you will find on page 74 all of the specs for the U.S.A. 35B airfoil which is on the Cub. That should accurately answer your question.
S2D
MEMBER
Montana
Has anyone come up with the angle between the bottom of the rib and the chord line of the supercub rib yet?
I measured the straightest butt rib I had and came up with 1.9 deg.
that measures closely with what skywagon says about the botton of the rib should be level when the plane is level.
I measured the straightest butt rib I had and came up with 1.9 deg.
that measures closely with what skywagon says about the botton of the rib should be level when the plane is level.
cubflier
MEMBER
Palmer, AK
There should be 2.5 inch difference between the front and rear attach fitting. After you attach the wings the incidence at the root is the 1.84 degrees. The best measure of this is using the bottom spar caps and not the ribs since things can vary.
At least this is how the great one (that is currently chasing Kipper Snacks) told me how to do it.
Here is another thread on the subject.
http://www.supercub.org/phpbb2/viewtopic.php?t=6464&highlight=wing+incidence
A link to rigging instructions.
http://www.faa.gov/aircraft/safety/alerts/aviation_maintenance/media/1997/1997_08_Alert.pdf
Here is the drawing of the attach points. Note the attach points are not at 1.84 degrees and I forgot the angle. You can use the drawing to solve the math if you need that figure.
[/url]
Jerry
At least this is how the great one (that is currently chasing Kipper Snacks) told me how to do it.
Here is another thread on the subject.
http://www.supercub.org/phpbb2/viewtopic.php?t=6464&highlight=wing+incidence
A link to rigging instructions.
http://www.faa.gov/aircraft/safety/alerts/aviation_maintenance/media/1997/1997_08_Alert.pdf
Here is the drawing of the attach points. Note the attach points are not at 1.84 degrees and I forgot the angle. You can use the drawing to solve the math if you need that figure.
Jerry
S2D
MEMBER
Montana
thanks Jerry. I've got those figures from the same source.
that figure is great for determining the proper alignment of the fuselage , but it doesn't give me the angle if incidence of the wing at the butt rib. The actual rib determines that.
I just want to know what my true angle of incidence is.
both my butt ribs are new dakota cub ribs and both measure exactly the same at the bottom, so the angle of incidence should be that figure plus the difference between the rib and the chord.
X + 1.9 = AOI (if 1.9 is the correct angle between the bottom of the rib and the chordline)
that figure is great for determining the proper alignment of the fuselage , but it doesn't give me the angle if incidence of the wing at the butt rib. The actual rib determines that.
I just want to know what my true angle of incidence is.
both my butt ribs are new dakota cub ribs and both measure exactly the same at the bottom, so the angle of incidence should be that figure plus the difference between the rib and the chord.
X + 1.9 = AOI (if 1.9 is the correct angle between the bottom of the rib and the chordline)
S2D
MEMBER
Montana
cubflier said:
Kinda just pontificating, but if it was 3.743 (which I didn't say it was) , that would be quite a bit over factory specs
Plus I want to know the relative angle compared to the trim range of the horizontal stabilizer before I have it covered.
incidently, both my ribs measured .3 deg less than the bottom of the spar measurement.
skywagon8a
MEMBER
SE Mass MA6
I checked on the Northland CD. Piper drawing 13814 is the rib outline which gives all of the coordinates. If my math is correct the angle of incidence to a straight edge along the lower surface is 1.54 degrees.
skywagon8a
MEMBER
SE Mass MA6
S2D
You got me thinking about our different answers of .07 degrees. I found it. Dwg. 13814 shows that the trailing edge is 0.164" thick. The chord line goes through the center of the trailing edge. If you use my center line the answer is 1.54 degrees. If you have the trailing edge come to a point then the answer is 1.61 degrees.
You got me thinking about our different answers of .07 degrees. I found it. Dwg. 13814 shows that the trailing edge is 0.164" thick. The chord line goes through the center of the trailing edge. If you use my center line the answer is 1.54 degrees. If you have the trailing edge come to a point then the answer is 1.61 degrees.
S2D
MEMBER
Montana
Re: incidence
Dave can you tell me how that number was arrived at?
Seems too exact to be a figure that Mark just decided works best.
(I could understand 1.8 or 1.85 but to come up with 1.84, he must have calculated the difference between the bottom of the spars and the true chord)
If it is the measurement at the bottom of the spars, what is the true AOI of the wing on a supercub.
ag-pilot said:
Dave can you tell me how that number was arrived at?
Seems too exact to be a figure that Mark just decided works best.
(I could understand 1.8 or 1.85 but to come up with 1.84, he must have calculated the difference between the bottom of the spars and the true chord)
If it is the measurement at the bottom of the spars, what is the true AOI of the wing on a supercub.
SuperCub MD
Registered User
Collins, Wisconsin
Brian,
Airworthiness Alerts
Service memo #19
The numbers are all in there, if you do the math and cook it all down it comes to this.
PA18
Level at door bottom
Butt rib incidence +1.843
Last full rib incidence -.717
Wing washout 2.56
PA12
Level at floor between gear fittings +1.665
Butt rib incidence -.060
Last full rib incidence -2.627
Wing washout 2.567
Tolerance is +/- 1/4 degree.
Use a 30" straight edge on the rib bottoms between the spars to account for the curve in the ribs. I've got the numbers written on the shop wall so I don't have to keep looking them up.
Airworthiness Alerts
Service memo #19
The numbers are all in there, if you do the math and cook it all down it comes to this.
PA18
Level at door bottom
Butt rib incidence +1.843
Last full rib incidence -.717
Wing washout 2.56
PA12
Level at floor between gear fittings +1.665
Butt rib incidence -.060
Last full rib incidence -2.627
Wing washout 2.567
Tolerance is +/- 1/4 degree.
Use a 30" straight edge on the rib bottoms between the spars to account for the curve in the ribs. I've got the numbers written on the shop wall so I don't have to keep looking them up.
S2D
MEMBER
Montana
SuperCub MD said:
Thanks Mark, I'll look up that Service memo,
but for posterity's sake (pun intended)
please define "Butt rib incidence".
So far I've seen it measured three different ways, none of which give the same reading.
1. Bottom of spars
2. Bottom of rib
3. Actual cord of wing
4. None of the above
(all compared to the longitudinal plane of the A/C)
only one is correct.
Edited to include 4. none of the above
SuperCub MD
Registered User
Collins, Wisconsin
SuperCub MD said:
This should be the same as the bottom of the spars. Everyones favorite fish watcher likes to use the spar bottoms to check the frame, and I agree this is more accurate for the frame, ribs can be tweaked. I use the 30" straight edge between the spars when rigging. Can't check the spar bottoms on the outboard rib with fabric on.
I'd say 1 and 2 are both correct. The cord line wouldn't even be close.
Here is the AC. Read it and work it out. I'd bet a beer or 2 that my numbers are right....
http://www.faa.gov/aircraft/safety/alerts/aviation_maintenance/media/1997/1997_08_Alert.pdf
cubflier
MEMBER
Palmer, AK
SuperCub MD said:
I was in agreement with your numbers until (very recently) I broke out the plans and did the math. I also measured the spars on a set of wings I have in my hangar and came up with an angle substantially less than 1.843 and very similar to my math calculations using the plans.
Then I looked at the methodology behind the 1.843 number. The man (Gordon Mandell) that wrote the AC did not use the bottom of the spars in his calculation of the 1.843 number. It's an average of two methods taking the angular difference in the horizontal reference line of the wing bottom and the horizontal reference line of the fuselage. At least this is my interpretation of his notes.
I have his notes and methodology and would be glad to send them via email if you like. I'm interested to see if you draw the same conclusions that I have and if I'm wrong will be happy to buy you that beer or two.
Jerry
SuperCub MD
Registered User
Collins, Wisconsin
Jerry,
I'd like to read the info you have. My e-mail hasn't been working well lately, but give it a try if you want to,
drath@lakefield.net
If it takes much more than elementary math, I'll probably just drink beer.
I'd like to read the info you have. My e-mail hasn't been working well lately, but give it a try if you want to,
drath@lakefield.net
If it takes much more than elementary math, I'll probably just drink beer.
Crash
GONE WEST
Nikiski Alaska
cubflier said:
Jerry; you're now seeing and maybe fighting the same problem I had with the numbers last year when you and I went round and round over this.
They're less in actual practice and I don't know why. I pulled my hair out over this!
Did the measurements on a set of un-covered wings and a fuselage with wings mounted. The math on the fuselage was right on the money but that is where everything ended.....
Crash
cubflier
MEMBER
Palmer, AK
SuperCub MD said:Jerry,
I'd like to read the info you have. My e-mail hasn't been working well lately, but give it a try if you want to,
drath@lakefield.net
If it takes much more than elementary math, I'll probably just drink beer.
Mark,
I emailed the document to you last night so let me know if you did not receive it. I look forward to your opinion on this.
Jerry
S2D
MEMBER
Montana
to further muddy the waters:
in the Alerts Mr Mandell states that the measurement of washout should be -.7 deg at the outer aileron rib when the aft point of the level is under the rear spar.
using that calculation and assuming he got the 2.5 deg washout from some Piper source, not his own calculations, the bottom of the spars should read 1.8 (or thereabouts)
however, he says the angle of incidence measured at the centerline of the spar hing bolts should be 1.84 deg I just don't get that statement.
thirdly in his calculations that cubflier sent, he uses the full length bottom of the rib for his final figure to get 1.84 and says that the rear spar is .28 above this line. He admits there is a .2+ discrepancy and this is the more accurate measurement.
so even he uses three different lines he calls AOI, and only the one referring to the centerline of the bolt is close to the true AOI, but nowhere close to 1.84.
all I do know , is that when I measure an airplane that has 1.8 deg at the bottom of the spars, I get 2.75 inch diff between the heigth of the front and rear spar bolt C/L (Max allowed by Piper), and when I measure an airplane that has 1.5 deg at the bottom of the spars I get the factory spec 2.5" measurement
in the Alerts Mr Mandell states that the measurement of washout should be -.7 deg at the outer aileron rib when the aft point of the level is under the rear spar.
using that calculation and assuming he got the 2.5 deg washout from some Piper source, not his own calculations, the bottom of the spars should read 1.8 (or thereabouts)
however, he says the angle of incidence measured at the centerline of the spar hing bolts should be 1.84 deg
I just don't get that statement.thirdly in his calculations that cubflier sent, he uses the full length bottom of the rib for his final figure to get 1.84 and says that the rear spar is .28 above this line. He admits there is a .2+ discrepancy and this is the more accurate measurement.
so even he uses three different lines he calls AOI, and only the one referring to the centerline of the bolt is close to the true AOI, but nowhere close to 1.84.
all I do know , is that when I measure an airplane that has 1.8 deg at the bottom of the spars, I get 2.75 inch diff between the heigth of the front and rear spar bolt C/L (Max allowed by Piper), and when I measure an airplane that has 1.5 deg at the bottom of the spars I get the factory spec 2.5" measurement
SuperCub MD
Registered User
Collins, Wisconsin
S2D said:however, he says the angle of incidence measured at the centerline of the spar hing bolts should be 1.84 deg
so even he uses three different lines he calls AOI, and only the one referring to the centerline of the bolt is close to the true AOI, but nowhere close to 1.84.
I'm sure I'm stating something you all ready know, but this gave me some confusion when I first looked at this. Maybe it will help someone trying to measure a bear frame.
The AOI line is parallel to each individual front and rear spar attach bolt hole, not a line between the front and rear spar attach fitting bolt holes.
I haven't gotten the e-mail yet, but my computer has been very constipated. I'll give it a while to see if anything develops.
Glad I only bet some beers and not a bottle of Jack. It seems there has been evidence withheld, and the question altered after I answered it? I think I have grounds for a mistrial, certainly an appeal to a higher Court. I'd hate to think I can't even measure my own butt. And I will not divulge the measurements of my own butt. I'll plead ignorance, most times I can't even find it with both hands and a flashlight.
S2D
MEMBER
Montana
Can anyone verify or refute these figures
distance from center of spar attach bolt to top of spar:
Front spar: .531"
Rear Spar .614"
I got the front one from the Northland drawing and had to figure the rear one using the Piper drawing and trig.
If these are correct, I come up with the same figures cubflier does, but not positive they are correct.
distance from center of spar attach bolt to top of spar:
Front spar: .531"
Rear Spar .614"
I got the front one from the Northland drawing and had to figure the rear one using the Piper drawing and trig.
If these are correct, I come up with the same figures cubflier does, but not positive they are correct.
cubflier
MEMBER
Palmer, AK
I solved from the bottom but if I subtract from the spar heights I get
Bolt CL diff from top of spar
Front = .531
Rear = .618
Bolt CL diff from bottom of spar
Front = 5.156
Rear = 3.382
These measurements are in agreement with Gordon's calculation #2 and very close to what you have.
I could not find enough information to solve the equation from the top of spar so I had to work my way up from the bottom and subtract the spar height.
Jerry
Bolt CL diff from top of spar
Front = .531
Rear = .618
Bolt CL diff from bottom of spar
Front = 5.156
Rear = 3.382
These measurements are in agreement with Gordon's calculation #2 and very close to what you have.
I could not find enough information to solve the equation from the top of spar so I had to work my way up from the bottom and subtract the spar height.
Jerry
S2D
MEMBER
Montana
SuperCub MD said:
Guess you won't have to bring the beer Mark. Your numbers are close enough to count. Just not for the reason Gordon Mandell gave.
(as long as you define rib incidence as the measurement taken directly under the spars) on an airplane with maximum tolerance at the spar hinge fittings
