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Thread: Therapy Project

  1. #241

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    Quote Originally Posted by gdafoe View Post
    Sounds like a great idea. Pictures we need pictures.
    This is part of a roller set for 7/8 tube mounted on my older mill.
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    The rollers are machined out of HDPE bar.
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  2. #242
    gdafoe's Avatar
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    Very interesting thanks
    Gerald

  3. #243
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    Fuselage weight so far and jack screw bracket

    I ran out of materials for a while, so, being curious, I decided to weigh the fuselage as it is right now.

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    After I weighed, I noticed that the scale read about 3 pounds heavy with no load. I took it to be 97 pounds in reality.


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    I tested that weight two other ways: one using my so-called balance beam approach where you balance the object, and then move the fulcrum a known distance and add weight on one of the arms to calculate weight on the balance point. That method produced 96.8. The other method was simply a two-point weighing with a digital fish scale, yielding 96.5 pounds.


    So 97 pounds is a fair guestimate. Frankly, I was surprised because the fuselage is almost a foot longer than a PA 18, and I used some .028 stiffing tubes in the tail sections of the fuselage. I was bracing myself for something heavier. This weight includes the turtledeck arches and the superstructure formers, but no tabs to speak of and no channel for doors, etc.


    Then my UPS delivery came. I spent some time pondering how to make the jackscrew bracket assembly. The plans simply said to buy it, but I had trouble finding it online. So I went with trying to fabricate it. I couldn't have even begun without Northland drawings and Christian Sturm's drawing website.


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    Jigging the assembly


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    Tacked.


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    I've got some tweaking to do, but I was surprised how it went together after scratching my head over this for days.
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  4. #244
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    Adjusting stabilizers

    After tacking in the jack screw pedestal a couple days ago, it seemed right to put the stabilizers in place to check the alignment.

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    I didn't take photos, but I adjusted that jack screw pedestal to align with the center and had to tweak the tail to make it straight.

    Next checked how the stabilizer travel was working. At first it looked like it would bind on the pedestal legs, but I saw that it was out of alignment with the center line. A few adjustments on the rear pivot point allowed it to move up and down more freely.

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    I spent a fair amount of time getting the horizontal reference line leveled again and then measured the up and down travel. It's 2 degrees up and 6 degrees down.

    That's within PA 18 specs according to the erection manual, but I need to find some specs like that for a PA 14. Either that or spend some time noodling the difference in angles of incidence on the fuselage.

    I took some photos front and back just because, and then I dropped my camera and broke the lens. Just another day in the shop....

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  5. #245
    Gordon Misch's Avatar
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    That jack screw tower can be a stinker. If it's not aligned just right it messes up all sorts of related stuff. Don't ask how I know!
    Gordon

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  6. #246
    skywagon8a's Avatar
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    Look at page 2: You have slightly more than the spec. Leave it there, more is always better than not quite enough.
    http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/fd34b4a887cf0ab786256a61006cac5c/$FILE/a-797.pdf
    N1PA
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  7. #247
    RVBottomly's Avatar
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    Quote Originally Posted by skywagon8a View Post
    Look at page 2: You have slightly more than the spec. Leave it there, more is always better than not quite enough.
    http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/fd34b4a887cf0ab786256a61006cac5c/$FILE/a-797.pdf
    That's exactly what I was looking for. Thanks!

    Vic

  8. #248
    RVBottomly's Avatar
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    Working on bungee struts

    I'm still pondering suspension, but for the time being I figured I'd build gear struts as shown in the drawings. They are a bit different from the drawing because I extended the gear.

    I learned something, though. I first fabricated bushings to weld onto the end of the struts, welded them on, and put finger straps over them. The plans said "ream (drill) to 3/8" after welding."

    Well, welding that material ended up hardening it, and I wore out drills trying to make a slightly undersized hole for reaming.

    So I started over and drilled the bushing material first on the lathe. It worked out easier.

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    Also milled out coves for the bungee attachments

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    I'm still eyeballing things and am scheming up a dampening device. Meanwhile, I wanted to see how things traveled.

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    I need to look at my notes in the shop. My recollection is that there is 10 inches of axle travel for 4.5 inches of strut telescoping.

    A movie of it:


  9. #249
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    More landing gear work

    Time goes by, and I have the occasional hour here and there to work on things. I've sort of entered the drudge zone: fabricating the bungee strut assembly.

    I'm not fully convinced I want to use the as-designed system. But I'm interested enough in getting the fuselage on wheels to go ahead with the materials I have.

    So, a few photos of the drawn out process of making bungee struts.

    First reinforcements welded on.

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    Then drilling 1/4 inch holes for bolts to slip through a slider that is supposed to hit stops in inside the inner strut.

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    After all this welding, the outer strut no longer accepted the internal 3/4 sliding strut. So I needed to ream it out. I didn't have a 3/4 reamer, but I did have a 3/4 hole saw and an old hole saw chuck that I could weld to drill extension. After going through lots of cutting oil and wearing down the hole saw to .735", I went to lapping compound and more oil. Eventually I had a free-sliding tube. The word of advice here is to order a 3/4" hand reamer. My excuse was that they were backordered.

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    Actually, the photo is out of order, but welding on bungee attachments.

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    Testing the fit and alignment with Walmart bungees

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    The internal strut has a 1/4" slot through which a bolt goes to a slider inside the strut. So time to try to make slots.

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    The slider and stops within the internal strut were specified at a certain diameter. Of course, the inner strut material I had was thicker walled 3/4 tubing, and I didn't have a proper tube to fit the smaller diameter. But I did have some thick walled 5/8 tubing that could be turned down. Here is a testing of the fit.

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    I still need to install the stops and slider, but I wanted to eyeball the travel of the strut.

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    So, everything seems to be consistent with the plans. I still need to add caps on the bungee attachment ears and also add the internal stops. It seems strong enough, but I'd like to have rubber bumpers in front of the stops. Not enough room to put all this stuff in, though.

    I have some nice new bungees. I'm impressed with how stiff they are. As in, I'll have to review those installation videos a few times to make a decent tool for the task.

    So, I'll use this set up for now, but I still am noodling variations ranging from simple homemade oleos to some of the fancy suspension systems described on the site. I may end up with several different versions to try out. That is what is cool about experimental building. But it is SLOW, sometimes.

  10. #250
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    More landing gear strut fun

    Finally brought this phase more or less to completion.

    First had to clean up the slotted strut and fabricate a slider. I ruined one strut by letting the slot go wild before I caught it while milling.

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    The it was time to fabricate the internal stops the slide runs into.

    Used a hole saw to get some 5/8 discs.

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    I neglected to get photos for installing the stops and slider. Suffice it to say that a stop goes in first, then the slider (properly aligned to fit the holes in the lower strut), and then the other stop. The stops are welded in place.

    Next I used a 1 3/4 hole saw to cut out 1 1/2 discs for the bungee retainers. The inside diameter of the hole saw I had was exactly the 1 1/2 inch specified.

    Then welded them on.

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    After some post-welding clean-up and tweaking, the struts move up and down as advertised. I have bungees, but I don't want to put them on until I paint the assembly and...build some kind of bungee installation jig.

    In other news, the wing materials I ordered in April may or may not get shipped next week. It depends on who you talk to at Aircraft Spruce. I'm really looking forward to starting on that portion of the project.
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  11. #251
    RVBottomly's Avatar
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    Heh. Just when I was thinking I was mostly done with the bungee suspension, I ran across Bill Rusk's post on his Javron build.

    And saw this picture:

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    From post 154: https://www.supercub.org/forum/showt...l=1#post525332

    So now I think I need reinforcing gussets too....

    For the sake of curiosity, I jury-rigged up a stretch test bed to see how stiff the bungees I have were. They are stiff. Approximately 100 pounds per inch of stretch. They start out at about 10 inches at resting stretch, and have another 10 inches when installed in the retracted position. Two per side is around a ton total on those little ears. Then when you bounce, even more force. I was nervous about the set up as designed. The Javron arrangement has convinced me to add the gussets.

    All of this is connected to the self-education aspect of experimental. I had a 4 hour road trip today and spent most of the time noodling in my head acceleration rates with changing bungee forces over distance. Blah! But fun.

  12. #252
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    Gussets, now a question

    I added gussets to the bungee struts. Then, of course, had to ream out the slag again so the tubes would telescope. I feel better about it all.

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    But now a question.The old farmer in me wants to know why there are no grease fittings on the hinge points? I've looked several places and have not seen anything like that. I've seen them added to elevator hinge points, etc. Why not landing gear?

  13. #253

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    My guess would be petroleum based grease and natural rubber are not that compatible. The other reason is the old "we don't do it that way".
    DENNY
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  14. #254

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    There are plenty of lubricants available today that would not harm the rubber.

    When I make a pivoting joint, the bushing material will be an engineering plastic, Teflon, Delrin, UHPDE or such.
    The inner sleeve would be Stainless steel, chrome plated shafting, or hard anodized aluminum.

    These all make build and forget assemblies.

    Back in the mid 70s I started using chrome shafts from old shock absorbers from cars bikes or whatever, machined as needed. These were mounted around the bolt they ride on and fitted snug inside a Delrin bush. As of today every one of these joints are still in service without any need for maintenance.

    I still build this way, I have not used a bronze or any metal bushing in my life.

  15. #255
    Cub junkie's Avatar
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    Extra grease finds its way all over your aircraft courtesy of the slipstream. Non commercial airplane will be fine with a light lube each condition inspection.
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  16. #256
    RVBottomly's Avatar
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    Quote Originally Posted by Cub junkie View Post
    Extra grease finds its way all over your aircraft courtesy of the slipstream. Non commercial airplane will be fine with a light lube each condition inspection.
    I was thinking along these lines after I posted the question. It's not like your average square baler is going over 12 mph ever.

    CharlieN, your approach is light-years ahead of what I've done. I like it, but felt like doing it as drawn for the first iteration. But it's not even bronze bushings here. Steel on steel.

    All the steel on steel pivots or hinges I've seen (other than, say, door hinges)--like on swather casters or irrigation hose reels--had nice grease fittings. So I started wondering.

    That and reading about the occasional problem I've read about with landing gear suspension frozen from sitting out in the elements too long.

    So the key, as drawn, is lubrication. It just seemed grease would be convenient, instead of disassembly and lube say every annual.

  17. #257
    RVBottomly's Avatar
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    Christmas in July

    Two deliveries arrived today.

    First, I got some tires:

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    Basic 8.50 X 6

    BTW, one tire has a sticker saying "First Tire." Anybody know what that means?


    Then, after waiting since early April, my spruce spars and related materials showed up:

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    So I'll put wheels on so I can wheel the fuselage around, and then set up for building wooden ribs. I felt like a kid at Christmas, even if I had to use a sharp Buck knife to open up the presents.
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  18. #258
    skywagon8a's Avatar
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    Quote Originally Posted by RVBottomly View Post
    All the steel on steel pivots or hinges I've seen (other than, say, door hinges)--like on swather casters or irrigation hose reels--had nice grease fittings. So I started wondering.

    That and reading about the occasional problem I've read about with landing gear suspension frozen from sitting out in the elements too long.

    So the key, as drawn, is lubrication. It just seemed grease would be convenient, instead of disassembly and lube say every annual.
    Vic,
    Originally the stabilizer pivot tube passed through another steel tube welded to the tail in the fuselage (still does). The outer tube had a hole drilled into it in order to make it easy to squirt oil. How often do you think this got done on airplanes which were stored outside and not flown much? As a result there were a lot of "frozen" stabilizer hinge tubes. The trim still worked because the tube was twisted a little. The angular change for full trim travel is very small so the build up of rust didn't get noticed. This was usually found when a mechanic attempted to remove the stabilizers for periodic recovering. Now with lifetime fabrics even this doesn't get done very often. As a result some of us mechanics began welding a small tube over the oil hole in order to screw in a grease fitting positioned so as to not interfere with the control horn. I see no reason not to do the same thing for the gear fittings. No one will fault you for deviating from the plans for this.
    N1PA
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  19. #259
    RVBottomly's Avatar
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    Just for fun, I put the wheels on and rolled the fuselage out into the sun.

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    Actually, the prosaic reason was that I wanted the shop empty so I could rearrange things for rib making. Plus a little spring cleaning that was put off until July.
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  20. #260
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    Rib making

    Switching gears and having fun with wood again.

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    So far I have 4 done. 22 left to go....

    One thing I'm sort of holding off on is how I want to deal with the trailing edge coves. I'm planning to make the flaps more slotted--so I'd like a bit more of an S shape in front of the flaps. And I'm still pondering making ailerons more like the Ex cub--if I can only get a good view of them.
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  21. #261
    Gordon Misch's Avatar
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    Vic, if you haven't done so already, check in with Marty57 here. He did wood wings that are works of art. He'd be a good guy for tech reference when you're in head-scratching mode.
    Gordon

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  22. #262
    RVBottomly's Avatar
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    Quote Originally Posted by Gordon Misch View Post
    Vic, if you haven't done so already, check in with Marty57 here. He did wood wings that are works of art. He'd be a good guy for tech reference when you're in head-scratching mode.
    I have his build log site bookmarked. It's been really helpful.

    Sent from my SM-J320V using SuperCub.Org mobile app

  23. #263
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  24. #264
    RVBottomly's Avatar
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    Thanks brown bear. I was looking all over for something like that.

    Vic

  25. #265
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    Halfway point on ribs

    So a bit more than a month has gone by and I've only been able to snatch a few hours a week on the ribs. But I finally got a system down and have reached my 13th rib. Half way. They are getting quicker to build: about an hour of cutting, assembly, epoxying. I let them cure overnight and then put gussets on the other side.

    They weigh 8 ounces even before I trim gussets and sand excess epoxy off. But...I still plan to add a plywood gusset at the back end to hold a cove for ailerons and flaps.

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    I'm still pondering what I will do with the flaps. After talking to PSTOL people who were not willing recommend the Keller flaps for wooden wings, I started wanting to know what the stresses are. I'm also trying to come up with a decent way to check on spar stresses if I move the ailerons out toward the wing tips. I know everyone does it, but I still would like to see numbers on what is happening.

    That's the self-learning part of experimental, I guess.

  26. #266
    skywagon8a's Avatar
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    Vic,
    Try to find a copy of "Analysis and Design of Airplane Structures" by E.F.Bruhn. My revised copy was published in January 1952. Used book stores are full of interesting and sometimes very useful books. I found my copy in Portland Oregon. Old airplane design books are full of easy to understand basic information. Aerodynamics and structures hasn't changed in the past century, only the presentation has changed.
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    Quote Originally Posted by skywagon8a View Post
    Vic,
    Try to find a copy of "Analysis and Design of Airplane Structures" by E.F.Bruhn. My revised copy was published in January 1952. Used book stores are full of interesting and sometimes very useful books. I found my copy in Portland Oregon. Old airplane design books are full of easy to understand basic information. Aerodynamics and structures hasn't changed in the past century, only the presentation has changed.
    I think I have 3 copies of Bruhn, one is 3rd edition, forget the date, one is 1958 and then the most recent 1973 edition. Somewhere in the 40s they dropped some of the wood and wire braced information. I would also suggest ANC 18 and ANC 19. ANC18 is design of wood aircraft structures, ANC 19 is inspection and grading wood and inspection of wood structures.


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  28. #268
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    Quote Originally Posted by skywagon8a View Post
    Vic,
    Try to find a copy of "Analysis and Design of Airplane Structures" by E.F.Bruhn. My revised copy was published in January 1952. Used book stores are full of interesting and sometimes very useful books. I found my copy in Portland Oregon. Old airplane design books are full of easy to understand basic information. Aerodynamics and structures hasn't changed in the past century, only the presentation has changed.
    I found a pdf version through a subscription service. I see hard copy versions going for $198 used!

    Looking through the pdf version I see it's exactly what I was looking for. Now I have to dust off my calculus and start cranking on some of his examples so I can understand the various methods.

    I felt right at home when he was talking about Simpson's rule calculations. I was doing that on my boat design project a few years ago.
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  29. #269
    Gordon Misch's Avatar
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    I found a pdf version through a subscription service.
    Could you please post a link? Thanks!
    Gordon

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  30. #270
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    Quote Originally Posted by Gordon Misch View Post
    Could you please post a link? Thanks!
    I got one version through Sribd:

    https://www.scribd.com/doc/220947115...-E-F-Bruhn-pdf

    There is another scan of the 1949 at archive.org:

    https://archive.org/details/in.ernet...166811/page/n9
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  31. #271
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    Thanks Vic. Pages 12 and 13 refer to statically determinate and indeterminate systems. I would argue that the flap reactions at the spar are indeterminate, since both the spar and multiple ribs contribute to resisting drag and lift forces and their associated moments at each attach point. So have fun with the elasticity eqns! The analysis looks ugly to me - - -
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  32. #272
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    Quote Originally Posted by Gordon Misch View Post
    Thanks Vic. Pages 12 and 13 refer to statically determinate and indeterminate systems. I would argue that the flap reactions at the spar are indeterminate, since both the spar and multiple ribs contribute to resisting drag and lift forces and their associated moments at each attach point. So have fun with the elasticity eqns! The analysis looks ugly to me - - -
    Me too. LOL. It will give me something to try doing during down time in my 9 hour docket tomorrow.... Beats playing Candy Crush, which I've seen many do.

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    Good on ya sir!!!!!!
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    I haven't posted anything for a while mainly because it would be repetitive. I've been building ribs--one at a time--letting them cure overnight, etc. In the time available I've only been able to build 3 or 4 a week. But now I have 4 left to go.

    In the mean time, I've been contemplating flaps. The Wag Aero plans show an undetailed "optional" flap 62" long and a chord of 13.25 inches. That makes the chord around 20% of the wing chord.

    Chapter 8 of my copy of Abbott and Doenhoff talks about high-lift devices. Flaps of 30% of wing chord or more seem typical. Then I saw the discussion on a fixed vane double slotted flap and those lift coefficient numbers of 3.0 or more. So back to kicking around the idea of a fixed vane double slot:



    This template's chord is 31% of wing chord. I'm thinking the flaps could be 7.5 or 8 feet long instead of the 5 feet of the drawings. There is room to move the ailerons out. My concern has always been stress on the rear spar. I've been slogging through stress calculations--I'm very rusty. I'm almost ready to try some empirical destructive testing for fun and profit.

    As I researched things related to this I ran across compression struts for a Pitts biplane. I like that approach: plywood web over spruce capstrips snuggly wrapping around the spar. Maybe those could line up with flap hinges.

    For a cove I'm already contemplating carbon fiber laid up over a mold. I've done a lot of fiberglass stuff with boats, so that idea seems not so foreign.

    Still kicking things around. I may end up with single slot flaps to start, but design the cove to accommodate the double slotted version later, for comparison.

  35. #275
    Lowrider
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    For what it's worth I went with 8' flaps to 50* and 8' with 8 degree droop ailerons that can be pinned up with normal aileron deflection without droop.
    Somewhere along the way I have lost the ability to act politically correct. If you should find it, please feel free to keep it.

    There are no new ways to crash an airplane no matter how hard you may try!

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    The built up compression structure is a sound idea. I expect they might need to be next to the control surface fasteners utilizing an angle bracket, but I have not been in a Pitts wing in decades so I should review them.

    Flaps, if going slotted I would increase cord as much as possible.
    This could allow your double slot flaps to be sized up close to what I am building but with a simpler structure compared to mine.

    I would increase the aileron cord to probably 30% and shorten their span to suit. The further they get moved outboard allows their span to be reduced as well. Granted consideration needs to be paid to effectiveness with the reduced speed related to the flaps that will now offer substantial lift.

  37. #277
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    I have found of all the planes which I've flown, the ones which had the longest flaps and wings had the best low speed extra lift capabilities and characteristics. The ones with the shorter flaps, while they did produce lift were more effective in just drag production. Most STOL type planes have long single slotted flaps. As the deflection increases there is more need to pay attention to a leading edge slot for the flap. When the deflection increases further a second slot as you are suggesting enters the picture. My Cub is using a long 110" single slotted flap using the stock PA-18 cross section. The deflection of 56 degrees is showing with tuft testing to be satisfactory, with a smooth air flowing from the trailing edge. With this experience in mind, I would only consider your extra slot if you desire to exceed 56 degrees of deflection. One not STOL airplane which I've flown extensively (DC-9-30) had a double slotted long flap with a leading edge slat. The slow speed capabilities and advantages of the various available settings were very obvious and worthy of your consideration for your plane. The DC-9-10 had a shorter fuselage and no leading edge slat. It seemed to feel better during landings than the -30 with the LE slat.

    When increasing the lift using flaps, the center of lift of the entire wing moves aft. When increasing the flap lift further it becomes necessary to consider the authority of the horizontal tail to control the pitch moments. When you also incorporate leading edge slats which move the center of lift forward balancing the extra flap, less consideration to changing tail size is necessary.

    When in High School I made a smoke wind tunnel as a science fair project using multiple nozzles for smoke stream distribution. Initially used cigarette smoke which rapidly clogged the nozzles (imagine what it does in your lungs!). When using dry ice it worked beautifully. The air flow was generated with a vacuum cleaner drawing the air through an approximately 2" wide tunnel. I still have this tunnel in the attic.
    Perhaps you ought to consider a side therapy project of a smoke tunnel? I would like to visually see just what the airflow paths would be at different deflection angles both with a single slot and a double before I went through with building the full sized parts.

    Here are some examples.
    https://www.instructables.com/id/How...a-wind-tunnel/
    https://www.grc.nasa.gov/www/k-12/WindTunnel/build.html
    https://www.youtube.com/watch?v=9s1b50cxSK0
    https://www.youtube.com/watch?v=NIHNtjFJook

    If you wish to exceed 56 degrees of flap deflection you will need to address the geometry of the entire actuating system starting with the flap handle all the way to the flaps. The standard Cub system just will not go any further than 56 degrees. At least mine would not without a major alteration.
    Last edited by skywagon8a; 09-29-2019 at 07:24 AM.
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  38. #278

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    The idea of a smoke tunnel is an interesting idea and one I should consider for my far from simple approach.
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  39. #279
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    Quote Originally Posted by skywagon8a View Post
    Perhaps you ought to consider a side therapy project of a smoke tunnel? I would like to visually see just what the airflow paths would be at different deflection angles both with a single slot and a double before I went through with building the full sized parts.
    So much to learn! So much fun to have, and so little time!

    Sky, I like the idea....

  40. #280
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    Quote Originally Posted by CharlieN View Post
    The built up compression structure is a sound idea. I expect they might need to be next to the control surface fasteners utilizing an angle bracket, but I have not been in a Pitts wing in decades so I should review them.

    Flaps, if going slotted I would increase cord as much as possible.
    This could allow your double slot flaps to be sized up close to what I am building but with a simpler structure compared to mine.

    I would increase the aileron cord to probably 30% and shorten their span to suit. The further they get moved outboard allows their span to be reduced as well. Granted consideration needs to be paid to effectiveness with the reduced speed related to the flaps that will now offer substantial lift.
    Charlie, here is a photo I saw of the compression rib:
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    It came from this blog:

    https://mars58superstinker.wordpress...pecial/page/8/

    Vic

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