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Thread: Building an Experimental PA11

  1. #241

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    I then need to rig the wings before putting the aileron cables on. Almost to the end. Getting very excited. Vern stopped by today in his Cessna too! Had a nice visit. His Cessna 165 is a Beauty.
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  2. #242

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    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

  3. #243
    Southern Aero's Avatar
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    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!
    ......... It doesn't cost any more to go first class! You just can't stay as long.

  4. #244
    Crash, Jr.'s Avatar
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    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.
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  5. #245
    Steve Pierce's Avatar
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    .7 degrees
    Steve Pierce

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  6. #246
    Crash, Jr.'s Avatar
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    Is that .7 degrees between each panel or .7 degrees total dihedral? Just curious because I've heard higher numbers thrown around for total dihedral.

  7. #247

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    Quote Originally Posted by Crash, Jr. View Post
    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.
    Smart levels are also super handy for setting washout and taking the trial and error out of finding what you prefer.

  8. #248
    Crash, Jr.'s Avatar
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    Quote Originally Posted by motosix View Post
    Smart levels are also super handy for setting washout and taking the trial and error out of finding what you prefer.
    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".
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  9. #249
    BC12D-4-85's Avatar
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    Quote Originally Posted by Crash, Jr. View Post
    Is that .7 degrees between each panel or .7 degrees total dihedral? Just curious because I've heard higher numbers thrown around for total dihedral.
    Here: https://www.manualslib.com/manual/11...ft.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
    Last edited by BC12D-4-85; 04-28-2021 at 09:18 PM.
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  10. #250
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    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.
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  11. #251

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    I too prefer an abacus.
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  12. #252
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    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)
    Cessna Skywagon-- accept no substitute!
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  13. #253

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    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.
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  14. #254
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    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.
    Steve Pierce

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  15. #255
    Southern Aero's Avatar
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    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 .............
    Last edited by Southern Aero; 04-29-2021 at 03:19 PM.
    ......... It doesn't cost any more to go first class! You just can't stay as long.
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  16. #256
    Crash, Jr.'s Avatar
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    Quote Originally Posted by bcone1381 View Post
    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.
    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.

  17. #257

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    Quote Originally Posted by Crash, Jr. View Post
    the bubble level was still off by .2 of a degree.
    Or........ the bubble level was dead nuts on, and the digital level was off by .2......

  18. #258
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    Quote Originally Posted by Crash, Jr. View Post
    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.
    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.
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  19. #259
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    Quote Originally Posted by mam90 View Post
    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
    ......... It doesn't cost any more to go first class! You just can't stay as long.
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  20. #260
    cubdriver2's Avatar
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    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
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  21. #261

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    And remember, it’s a Cub. Not much else on it is probably within .2 anything..
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  22. #262

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    I’ve got a Starrett precision level that is advertised to be within .005 over 10”.


    Sent from my iPad using Tapatalk

  23. #263
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    Quote Originally Posted by Southern Aero View Post
    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 .............
    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.
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  24. #264

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    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...

  25. #265
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    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.

  26. #266

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    I officially have an airplane. Thanks Joe Norris DAR. Time to start phase 1. Thanks to all sc.org family who shared invaluable knowledge. It feels wonderful to have this behind me. Time for fun!
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  27. #267

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    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

  28. #268
    Southern Aero's Avatar
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    Congrats Dan! I've been following your build from the start.
    ......... It doesn't cost any more to go first class! You just can't stay as long.
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  29. #269
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    Congrats, Dan! Looking forward to seeing it in Cornucopia.


    Sent from my iPad using SuperCub.Org
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  30. #270
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    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!
    Jim Parker
    2007 Rans S-6ES
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  31. #271

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    After flying some more hours and doing some manuvers, takeoffs, landings, etc....here is where I'm at....
    Overview: Experimental PA11 w/J3 (zero thrust) Mount and O-200A
    Prop:Catto 76-36
    Trim: elevator Tab type
    Tail: Balanced typ
    Empty Weight 842
    Fuel: dual 36 Gallon wing tanks
    TK1 Monster Shocks and 26" ABWs

    I get 2550-2600 rpms on take off @60mph which is lower than I'd hoped for, but feels pretty solid. I could use a little flatter pitch when I go on floats...The Catto is nice, but I'm jonesing for a ground adjustable Sensenich....I'll fly awhile before I get too crazy.....another 100 or so Rpm might be nice.
    I get consistanly 93 MPH cruise once trimmed for cruise @2500RPMs
    Stall: 38 MPH indicated (no surprises)
    I rigged it the old fashion way with string and bubble and it came out perfect (no adjustment required)
    I have both right and left upper swing up doors and I bought the Piper Cub upper door latches from Univair, and they don't hold the door up very well.
    This thing is a joy to fly, and I'm having a blast....Phase 1 @ 25 miles from home base kinda stinks (only one other airport in the box)
    Standard Scott masters with Cleveland single puck brakes are a little on the weak side....It gets better as pads wear in though. Probably need boosters when I go to 29s
    My aluminum struts turned out nice....they only ended up a few pounds lighter than the supercub struts I have but I really like them..I made cable fairleads out of 1/2" PVC conduit /and drilled the flat on the trailing edge of the extrusion and tapped with a #4 to attach. I'll let you know how they hold up. ...on a J3 or an 11 you could get away with all 4 struts being the smaller profile to save some weight, but I like the bigger front struts that I have just fine. I'll keep it as is.
    Nothing earth shattering here in the STOL department, but I have a nice honest, sweet flying Cub that I'm proud as heck to have built myself. Those who have said an 11 is a great flying plane were right. I can imangine what it would be like if I would have shed 50 lbs or so. It's really nice to fly now though, and I'm happy with most of my decisions made throughout the build.
    The rubber windsheild strip is really nice and seals right up....widsheild is very solid and I love the look....I've read threads on here about it and I hesitated at first....but it's all good. I like it.

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  32. #272

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    My Catto 76-36 won’t spin up enough....2300 static, not quite 2400 @60mph on takeoff . I’m going to try my Sensenich 76AK-2-40 on for size so I can send my Catto for a re-pitch. I saw some time back that Roger Peterson used 76AK on his O200 with good results...I think it will still be too much prop to get past 2600 rpms. I’ll let y’all know.

  33. #273
    BC12D-4-85's Avatar
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    Dan you might check out TCDS 1P2 for the 76AK-2-40. Sensenich didn't approve that model vibration wise for the O-200. Stated limits are, if I read it right, 135 HP and 2600 RPM Max Continuous. I'm not saying it will blow up but you may be in little known territory when exceeding 2600 or with that particular engine. I've used that same prop and dimensions to success on two C-90's (the current one is a C-85 Stroker with C-90 cam and lifter bodies). If you want more torque at current rpms you might consider installing a C-90 cam. The O-200 likes to rev up more I assume driven by camshaft lift and timing.

    Edit: I looked it up and mine will static 2440 and exceed 2600 if allowed. I'm careful to maintain limits.

    Gary
    Last edited by BC12D-4-85; 06-08-2021 at 02:30 PM.

  34. #274

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    Thanks....This is the prop I currently have on my C90 Taylorcraft...it’s in for some maintenance so I thought I’d try it out. I will see what I get for static and if I fly it, and it happens to look like it could exceed 2600 rpms, I’ll back off. It’s THE prop for my C90-12F on my Tcraft though...I’ve tried others and this is the one. Thanks for this info Gary!

  35. #275
    BC12D-4-85's Avatar
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    Yes it's installed on my Taylorcraft now as well (PA-11 w/C90 previously). If not already done try static rpm with your current air filter and then without. I find a Donaldson P10-7150 does better than any others (Challenger or Brackett) ~20+ or more than the latter.

    Gary

  36. #276
    skywagon8a's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    Dan you might check out TCDS 1P2 for the 76AK-2-40. Sensenich didn't approve that model vibration wise for the O-200.

    Gary
    Gary,
    Just because the 0-200 isn't listed doesn't mean anything. It only means the prop wasn't tested for vibration purposes on the 0-200. It may be just fine.
    N1PA

  37. #277
    BC12D-4-85's Avatar
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    Quote Originally Posted by skywagon8a View Post
    Gary,
    Just because the 0-200 isn't listed doesn't mean anything. It only means the prop wasn't tested for vibration purposes on the 0-200. It may be just fine.
    Sure. Let's flip a coin. Winner flys the prop?

    Gary

  38. #278
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    Quote Originally Posted by BC12D-4-85 View Post
    Sure. Let's flip a coin. Winner flys the prop?

    Gary
    Not that at all. They just never did the testing. That doesn't mean it's unsafe. If they had done some testing and found a discrepancy, it would be noted on the TC.
    N1PA

  39. #279

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    Actually now that we are talking about this, my Catto has a strange harmonic at about 2375 as I’m just transitioning from liftoff to climb out ...only for a few seconds then it goes away. Anyone have that before?

  40. #280
    BC12D-4-85's Avatar
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    I'd fly the AK76 within the specified HP and RPM limits noted on an Experimental aircraft. The major changes between the C-90, C-85 Stroker, and O-200 are the cam...timing, duration, and lift, plus ignition timing. Carbs vary by P/N. The rest like displacement, compression, major components is similar as far as I know. The Stroker uses O-200 components like crank, rods, and cylinders.

    Dan's thread.......back to it.

    Rough spot with Catto? Might see if it happens with RPM deceleration too then contact Catto? Might be airspeed-rpm related as well.

    Gary

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