Dan Gervae
FRIEND
Building an Experimental PA11
- Thread starter Dan Gervae
- Start date
Dan Gervae
FRIEND
Upper Peninsula of Michigan
Rigged everything today, the only thing I found confusing in the rigging instructions was where it said for dihedral..measure to the center section (the birdcage?). Why not to the spar attach weldment? It says on older models measure to the spar fitting?
https://www.univair.com/content/PIP_SM005.pdf
https://www.univair.com/content/PIP_SM005.pdf
Southern Aero
SPONSOR
kcco/1ga2
Dan
I use the wing attach points on the fuselage to level laterally more accurate than using the shimming the longeron method, or can use a combination of both to verify/compare. On old Cubs ........ IF the struts don't adjust with close to the same threads showing (usually from old, bad repairs) then you will have to do some of that "linear interpolation" to get the appropriate amount of thread in the struts. One wing will fly very slightly higher than the other this way but cant be noticed or felt in flight. You shouldn't have this problem tho since your Cub hasn't been repaired several times!
I use the wing attach points on the fuselage to level laterally more accurate than using the shimming the longeron method, or can use a combination of both to verify/compare. On old Cubs ........ IF the struts don't adjust with close to the same threads showing (usually from old, bad repairs) then you will have to do some of that "linear interpolation" to get the appropriate amount of thread in the struts. One wing will fly very slightly higher than the other this way but cant be noticed or felt in flight. You shouldn't have this problem tho since your Cub hasn't been repaired several times!
Crash Jr.
Registered User
Anchorage, AK
You can also use a smart level to just measure degree difference between wings to get your dihedral. More accurate than pulling a string and measuring at the birdcage as far as I can tell but the "correct" way is to do the string method despite measuring from a very imperfect surface to a string attached to imperfect surfaces.
Steve Pierce
BENEFACTOR
Graham, TX
.7 degrees
Colorado-Cub
MEMBER
Buena Vista, CO
Smart levels are also super handy for setting washout and taking the trial and error out of finding what you prefer.
Crash Jr.
Registered User
Anchorage, AK
100%. I just set my rigging with a smart level and found that the wings weren't the same angle of incidence at the root relative to one another and was able to make it up with setting the washout to make up for the difference. A whole lot better than "one wing is heavy, lets turn the rear fork out a turn on the other side".
BC12D-4-85
SPONSOR
Fairbanks, AK.
Here: https://www.manualslib.com/manual/1140313/Piper-Usaf-Model-L-21a-Aircraft.html#manual
+0*45min or +0.75 degrees per wing measured under the front spar. Fuselage laterally level of course.
Edit: Go to the link's Page 49 (not the Manual's) for rigging.
Gary
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Hardtailjohn
Registered User
Marion, MT
I know a couple of guys that were building an airplane and invited me over to see. When I got there, they were setting dihedral with a "smart" level. I shook my head and told them that it was a great way, but there was really nothing wrong with the old way, and that usually when I "improve" on a method, it bites me. A few days later, I was having lunch with them and the UPS guy came in and told them that their new struts were on the back porch.
Of course the truth had to be pried out of them.....but finally they admitted that somehow, the "dumb" level had gotten switched to % of grade from degrees...and they didn't catch it, but it sure showed up when they checked it with the string....AFTER they'd drilled the struts.
Of course the truth had to be pried out of them.....but finally they admitted that somehow, the "dumb" level had gotten switched to % of grade from degrees...and they didn't catch it, but it sure showed up when they checked it with the string....AFTER they'd drilled the struts.
Colorado-Cub
MEMBER
Buena Vista, CO
I too prefer an abacus.
hotrod180
FRIEND
Port Townsend, WA
I seem to recall reading somewhere (maybe here) once,
that the smart level was the greatest aid to rigging an airplane to come along since the plumb-bob.
The same person went on to say that the smart level was probably responsible for more mis-rigged airplanes than anything else.
Here's a pretty good discussion on rigging a cub in which smart levels are mentioned multiple times.
And not everyone's posts agree on what part is at what angle.
rigging Cub wings (supercub.org)
that the smart level was the greatest aid to rigging an airplane to come along since the plumb-bob.
The same person went on to say that the smart level was probably responsible for more mis-rigged airplanes than anything else.
Here's a pretty good discussion on rigging a cub in which smart levels are mentioned multiple times.
And not everyone's posts agree on what part is at what angle.
rigging Cub wings (supercub.org)
I'm thinking a good quality bubble level is more accurate than a digital level. They make machinist bubble level with some pretty extreme accuracy. A DIY water level made of clear plastic hose is nothing to sneeze at either. Put a bit of soap in the water to break the surface tension and some for coloring to improve visibility. I attached a millimeter scale to it. Using some magnifiers to look at the water level in the tube with the scale behind it .... using my magnifiers (very strong reading glasses)....you can really get dimensions tight....to individual millimeters.
Steve Pierce
BENEFACTOR
Graham, TX
A bubble level and a string worked for me for years. However I find it easier, quicker and have better results with a digital level. Dihedral is very subjective because of the way they skins lay on the ribs and nose ribs and the inaccuracy of them. I play with the level in multiple places and get a good average.
Southern Aero
SPONSOR
kcco/1ga2
FWIW ..... I use certain Milwaukee and Stanley bubble levels as they advertise .0005 (half thousandth) per inch accuracy ........ (there are machinist's levels even more accurate but not practical to use). That equates to .015 on a 30" spar center Piper. The digital level at .1° is .053 at 30" ........... If memory serves me correctly ....... 1° = .211 per foot, or .0527 at 30". I prefer bubbles for building and repairing and even in this case setting dihedral but prefer digitals for other not as critical measurements like control surface deflection.
Bubbles for accuracy, digital for convenience. Just sayin .............
Bubbles for accuracy, digital for convenience. Just sayin .............
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Crash Jr.
Registered User
Anchorage, AK
If you can read a bubble level to .1 of a degree I would be mighty impressed.
Not to say it is impossible. I used both a standard bubble level and then checked with a digital level to level my fuselage and while it was close, the bubble level was still off by .2 of a degree.
68Papa
FRIEND
Chugiak, Alaska
I hate to break the news to you guys, but for the last 40 years I've made a large portion of my living using levels of various sizes, conditions as well as cost. I have spent many hundreds of dollars on bubble levels over the years and maybe one out of the many dozens and dozens I've purchased is accurate. Matter of fact if I find one that is accurate, it surprises me. They are easy to check. Over the years I've managed to gather up some good bubble levels that are adjustable, so when they do get out of wack, I can fix them. Today's lazers are hard to beat. But as a contractor, they can't ride around in the back of at truck and expect those to be any good either.
Southern Aero
SPONSOR
kcco/1ga2
Or........ the bubble level was dead nuts on, and the digital level was off by .2......
If its a bubble level, flip it around 180°. If it reads the same, it's right on! If not, trash it ........................ unless it's adjustable
cubdriver2
FRIEND
upstate NY
Any time you use a bubble level you should flip it 180* and see if it reads the same both ways. Or take the average
Glenn
Glenn
RVBottomly
PATRON
Asotin County Washington (KLWS)
I'm in the same camp. I have 4 spirit levels that have passed the 180 degree test to that level of precision.
Not to get off topic, but I like my Mitutoyo Vernier caliper, too. I consistently get within 1/1000 compared to a micrometer. I can never get a digital caliper to read within 5 or 6 thousandths repeatedly. [h=1][/h]
Dan Gervae
FRIEND
Upper Peninsula of Michigan
it lives! I have some tweaking to do but....it lives! I rigged it with a string and level...I did put a screw in the wall on each side of my hangar at the appropriate height and stretched that string tight without putting any downward force on the wing tips with the string. Just like when I run string lines for concrete....tight. My motor started right up...I have a few tweaks to do at higher rpms to get it running absolutely smooth. the weather turned cruddy so I’ll run it up better tomorrow...
Attachments
courierguy
MEMBER
Inkom, Idaho
Sounds like maybe you also have a construction background, as do I. Knowing your way around a whiskey level, a chalk line, a dry line, and a plumb bob (not to mention all the new digital stuff) was a huge help in the 5 kitplanes I've built, in keeping things square and straight.
Digital, smidgital, when it comes down to setting washout I always use my 40 year old Starrett adjustable bubble protractor. You can't fool Mother Nature/gravity.
Digital, smidgital, when it comes down to setting washout I always use my 40 year old Starrett adjustable bubble protractor. You can't fool Mother Nature/gravity.
Dan Gervae
FRIEND
Upper Peninsula of Michigan
Dan Gervae
FRIEND
Upper Peninsula of Michigan
It flys great fellas, 90mph cruise @2500rpm. I really like the the way it handles. I flew it for 30 minutes on the initial flight and so far all Is A-OK
Southern Aero
SPONSOR
kcco/1ga2
Congrats Dan! I've been following your build from the start.
JimParker256
Registered User
Farmersville, TX
Very cool! You should be very proud of this accomplishment. Seems like just yesterday you were starting the build, and I've followed the entire process. Great job, and great way to document it.
Now go fly the heck out of it, and ENJOY!
Now go fly the heck out of it, and ENJOY!
