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Thread: Therapy Project

  1. #81
    www.SkupTech.com mike mcs repair's Avatar
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    my laser printer prints different sizes, like if you do 3 separate prints or try to rerun a sheet through it might be 1/4" different size.....

  2. #82
    RVBottomly's Avatar
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    Wing Planning

    As I wait for my fuselage materials order to come in, I started thinking about wings.

    Plans call for a wood wing, but state that a PA-18 wing is suitable. I'm drawn to a wood wing after looking at Marty's work on his 2+2, but I'm also intrigued by the possibilities offered by Keller flaps.

    I contacted Performance STOL and they pretty much said they don't know if the Keller flaps would be compatible with wood spars and ribs. Pretty much discouraged me from trying.

    And, just to add to the mix, I have a friend who owns a commercial forest and mill. He told me he has some extremely nice 20 foot vertical grained douglas fir, no knots, straight grain, 14 rings per inch, etc. He knows I love this kind of wood and would give me first dibs for boats, airplanes, whatever.

    I guess the first question is, does anyone know what the weight of a standard aluminum PA-18 spar is so I can compare it to this doug fir?

    Second question, should I abandon the Keller flap idea, or go with an aluminum wing?

    I'm not really asking you all to decide for me--just laying out the latest swirling thoughts.

  3. #83
    RVBottomly's Avatar
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    Quote Originally Posted by mike mcs repair View Post
    my laser printer prints different sizes, like if you do 3 separate prints or try to rerun a sheet through it might be 1/4" different size.....
    I ran into that, too. Somewhere I found a scale setting for my Officejet printer to match the scale shown on the screen. It always takes me a little bit to remember how to do it.

    Now I remember, I ended up taking a copy of an image and putting it into a Word document, and then adjusting the scale of the image to the inches shown in the MSWord program. I made a couple templates that were accurate to 1/64". Not machinist quality, to be sure, but helpful.

  4. #84
    skywagon8a's Avatar
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    Quote Originally Posted by RVBottomly View Post
    Plans call for a wood wing, but state that a PA-18 wing is suitable. I'm drawn to a wood wing after looking at Marty's work on his 2+2, but I'm also intrigued by the possibilities offered by Keller flaps.

    I contacted Performance STOL and they pretty much said they don't know if the Keller flaps would be compatible with wood spars and ribs. Pretty much discouraged me from trying.

    Second question, should I abandon the Keller flap idea, or go with an aluminum wing?
    Years ago I helped a friend get an STC to install flaps on his wooden spar J-3/PA-11. This was approved at the Birchwood Airport by Gordon Mandel of the Anchorage FAA engineering. I don't recall if there were any differences from the metal spar PA-18. I would suggest that as long as the spar is properly supported at each hinge location that it would be satisfactory.

    If you want to get the airplane records from the FAA, I think that I may be able to find the N number. The plane has since been destroyed.
    N1PA

  5. #85
    RVBottomly's Avatar
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    Quote Originally Posted by skywagon8a View Post
    Years ago I helped a friend get an STC to install flaps on his wooden spar J-3/PA-11. This was approved at the Birchwood Airport by Gordon Mandel of the Anchorage FAA engineering. I don't recall if there were any differences from the metal spar PA-18. I would suggest that as long as the spar is properly supported at each hinge location that it would be satisfactory.

    If you want to get the airplane records from the FAA, I think that I may be able to find the N number. The plane has since been destroyed.
    Thanks for the info. The plans allow for an optional set of flaps, so I don't think you need to track down the STC info. I think the Performance STOL concern was that the Keller flaps apply more twisting force than standard flaps.

  6. #86
    skywagon8a's Avatar
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    Quote Originally Posted by RVBottomly View Post
    I think the Performance STOL concern was that the Keller flaps apply more twisting force than standard flaps.
    So just beef up the area a little bit. I would do whatever is necessary to install those flaps.
    N1PA
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  7. #87
    Cub junkie's Avatar
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    The 2+2 plans show a picture of a flap. Thats all. If you want to see how it can be done check out how Marty did it on his wood spar. The Wag Aero prototype 2+2 was built with PA12 wings.
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  8. #88

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    if your not totaly set on making your own wings, this caught my eye.http://alaskaslist.com/1/posts/10_Tr..._Tip_Wing.html
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  9. #89

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    I like wood, I like aluminum too. They both have their merits. I also see no problem with the added load of BIG flaps on the wood spar, just add the needed structure to transfer the twisting load forward to the front spar. I can understand being cautious about adding the flap loads to a factory with that is not designed for the added load, but that is not where you are at.

    One note about the Keller flap design, it is optimized to replace the stock Piper flaps which do not go all the way up the the rear spar.
    I would keep researching and choose a flap system that utilizes most all the space aft of the spar. If nothing else jumps out then go with the Keller system.

  10. #90
    RVBottomly's Avatar
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    Quote Originally Posted by tempdoug View Post
    if your not totaly set on making your own wings, this caught my eye.http://alaskaslist.com/1/posts/10_Tr..._Tip_Wing.html

    Tempting for sure. But I think I'll press on.


    Quote Originally Posted by CharlieN View Post
    I like wood, I like aluminum too. They both have their merits. I also see no problem with the added load of BIG flaps on the wood spar, just add the needed structure to transfer the twisting load forward to the front spar. I can understand being cautious about adding the flap loads to a factory with that is not designed for the added load, but that is not where you are at.

    One note about the Keller flap design, it is optimized to replace the stock Piper flaps which do not go all the way up the the rear spar.
    I would keep researching and choose a flap system that utilizes most all the space aft of the spar. If nothing else jumps out then go with the Keller system.
    Well, that sets the wheels turning. I guess I'm going to dig in a bit more on flap design and wing "beefing up."

    One idea I've seen is to have compression members bracing top and bottom of spars instead of just the middle.

  11. #91

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    Quote Originally Posted by RVBottomly View Post

    Well, that sets the wheels turning. I guess I'm going to dig in a bit more on flap design and wing "beefing up."

    One idea I've seen is to have compression members bracing top and bottom of spars instead of just the middle.
    Correct, similar to the N brace at the lift struts but primarily you need to transfer the upper and lower flap attachment loads forward to the front spar. If the flap has a greater cord the mounting loads are actually reduced at the spar since they have a shorter moment arm back from the structure. Higher loads yet less moment arm.

    A year ago my project was to use a wood structured wing. I was going to use Vee braces to carry to control loads forward though the structure. I have evolved from there to achieve my design goal but am still not fully locked down on details yet. I do not need to be yet.

    You are scratch building so you are open to many options to achieve your desired goals. As with me on my project, you are building the fuselage structure first. This is very good since once the main fuselage is built there is still a massive amount to do to build out the systems prior to covering.
    It is during the main structural work on the fuselage that you do your final design and planning for the wings. There is no need to be stuck with what was provided 70+ years ago when you can benefit from the decades of what has been learned since.

  12. #92
    Gordon Misch's Avatar
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    primarily you need to transfer the upper and lower flap attachment loads forward to the front spar.
    I think triangulation, like with the N-strut you mentioned or another method such as with the ribs, also matters in order to prevent twisting the spars.
    Gordon

    N4328M KTDO
    My SPOT: tinyurl.com/N4328M (case sensitive)
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  13. #93
    Southern Aero's Avatar
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    RV

    FWIW, if you look at Pipers design flaps and aileron hinge points are mounted to the spars but fairly lightly. The "false spars" are closest to the hinge points and carry most of the loads thru the false spars into the ribs...... that spreads the loads. If there were no false spars there would be greater need to stabilize the spars.
    ......... it doesn't cost any more to go first class! you just can't stay as long.
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  14. #94
    RVBottomly's Avatar
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    Materials arrived

    So I finally got my fuselage materials. Had the 24 foot long box delivered to the local depot to save shipping costs.

    But the driver called me and said I ought to check it over for damage:

    as dropped off.jpg

    I talked to Wicks and was told to accept and inventory the damage. They'll make it right. Happily, when I got it home, I found only 1 six foot section of 1" X .035 and 3 six foot channels damaged beyond usability. Everything else looks sound.

    I've got my jig table set up and a bunch of steel. The only thing I don't have at the moment is time. But I hope to be scratching some of that up shortly.
    Attached Images Attached Images
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    Damage sucks, luckily they are just shorts which are easy to ship the replacements.

  16. #96
    RVBottomly's Avatar
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    Yesterday I had a pleasant enough time cutting up tubes, profiling ends by grinder, file, and snips, and laying things out for the upper section of the fuselage.

    Of course, once it was there, I had to tack it. I love the new Smith AW1A torch, but didn't think to take pictures of it.



    Over on CharlieN's thread I mentioned the Vagabond. The responses there almost had me switching to building a Wagabond (I have the plans in the shop). I was thinking of lengthening it and putting on bigger wings, etc.

    Then I remembered I went through all this before. I'm sticking with the original plan unless I get persuasively derailed. I'm looking forward to fitting the lower fuselage section together this week and then jigging the frame for joining. It really is nice to spend some time just working with material.
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  17. #97

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    It's a good feeling when each sub-assembly comes together.

    My gas rig that has been my mainstay has been a Purox 200 which I believe is the same size torch your Smith's is. Great size to work with.
    If you get tired fingers or hand cramps you might consider some friction tape or similar on the body of the torch so it will stay in your hand without gripping it. This will allow more finesse while working.

    My father gave me the Purox torch I have back in the late '60s, it was a used hand me down and has seen allot of use over the decades. That was the first "real" tool I had.

  18. #98
    Dave Calkins's Avatar
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    RV. save the Doug Fir for your boating hobby. Weight of it will be more than the aircraft standard Sitka Spruce.

    As to transferring flap loads to the tear spar and beyond. Doubling the ribs at the flap hangers or making a truss rib with an additional plywood web will transfer the loads to the front spar an ameliorate rear spar twisting more elegantly than doubling compression members or having "N" struts.

    imho
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  19. #99
    RVBottomly's Avatar
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    Quote Originally Posted by Dave Calkins View Post
    RV. save the Doug Fir for your boating hobby. Weight of it will be more than the aircraft standard Sitka Spruce.

    As to transferring flap loads to the tear spar and beyond. Doubling the ribs at the flap hangers or making a truss rib with an additional plywood web will transfer the loads to the front spar an ameliorate rear spar twisting more elegantly than doubling compression members or having "N" struts.

    imho
    Good points. I did check out the fir more closely. It's really solid, hard, old-growth stuff from the Blue Mountains of WA/OR. Really tight rings and really dense. I weighed a rough cut 2X6X16 and it came out to 48 pounds or so. That's more than 36 pounds per cubic feet. In boatbuilding we always rule-of-thumbed doug fir at 34 pounds/cu ft. Just now I see them using 32-33 pounds, but that must be the lighter new-growth stuff.

    I'm pretty much sold on some kind of truss rib instead of additional compression members. Mike MCS mentioned something like that in an older thread and that started the gears moving.

  20. #100
    RVBottomly's Avatar
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    Quote Originally Posted by CharlieN View Post


    My gas rig that has been my mainstay has been a Purox 200 which I believe is the same size torch your Smith's is. Great size to work with.
    If you get tired fingers or hand cramps you might consider some friction tape or similar on the body of the torch so it will stay in your hand without gripping it. This will allow more finesse while working.


    My father gave me the Purox torch I have back in the late '60s, it was a used hand me down and has seen allot of use over the decades. That was the first "real" tool I had.

    I passed on a Purox torch in an auction 2 decades ago because I didn't know anything about them. I think it was a "Presto" model. I now wish I had grabbed it.


    So far the grip feels pretty nice. I don't grip it very hard. The next improvement will be to get some lightweight hoses.

  21. #101
    Gordon Misch's Avatar
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    I'm pretty much sold on some kind of truss rib instead of additional compression members.
    Yes. You'll be resisting moments with the truss rather than torsional stiffness of the spars.
    Gordon

    N4328M KTDO
    My SPOT: tinyurl.com/N4328M (case sensitive)

  22. #102
    RVBottomly's Avatar
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    Another week, and most of that week was spent doodling and planning. I spent a lot of time laying out the jig for the lower fuselage frame. I didn't like how the plans depicted the jig.


    The lower fuselage bends up at the rear gear attach point. The jig drawing is set up to more or less accomodate it, but I wanted a precise X-Y-Z coordinate for each station. That is not in any one place on the plans.


    Bouncing among various drawings, I was able to finally locate all the points I wanted. It turns out that the plans for the jig look to be fairly accurate, but I wanted to see for myself.


    Last Friday, I visited the new Harbor Freight that opened in Lewiston, ID, last month. Before that, the nearest one was 135 miles north. I saw an "open-box-scratch-and dent" mini-lathe for $350. I looked it over and it followed me home. I actually had been scouring the local Craigslist for something I could use to turn down liner tubes. This ended up being a decent enough solution.





    On the lower fuselage frame, there are two splices at the gear attach points, just as there are on the super cub. The plans have 3/4" .035 longerons joined by 5/8" liner tubes. I didn't like that much gap--the longerons' ID is around .680 and the 5/8 OD is, of course, .625. The standards apparently allow that much gap with several rosette welds, but I wanted tighter. I had ordered a length of 11/16 X .090 from Univair and had it ready. It just needed to be made a little smaller.








    My first try on the lathe was a little rough. After shimming the tool height and getting familiar with its operation, I ended up with some decent pieces.


    Prebent the liners and dry-fitted joints.







    Then I started tacking tubes.






    I mentioned doodling and planning. I've spent a surprising amount of time reading aerodynamic books and articles. The focus has been trying to calculate flap and aileron forces on a spar, of all things. So far, I think I have a handle on it using the drag and lift equations and estimating various coefficients. I'm surprised there doesn't seem to be a lot of information on such things. I know people put big slotted flaps and move ailerons outboard, but I've never actually seen any calculations to support it. I'm sort of obsessed with seeing the numbers.

    Anyway, another thrill-filled day and a half in the shop. A cold front and strong winds kept outdoor activity at a minimum--and made me appreciate the heater I put in the shop last year. Plugging along.
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