Removing "useless" struts between the fore and aft wing spar of a goat4 ultralight.

Discussion in 'Tube and Fabric' started by David Teahay, Mar 19, 2019.

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  1. Mar 19, 2019 #1

    David Teahay

    David Teahay

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  2. Mar 19, 2019 #2

    Hot Wings

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    They do look a little redundant. But 'looks' is not a substitute for properly designed structure and can get you killed.
    They may be required to shorten the column length of the spars enough that they won't fail from compression loads. IMHO, the weight saved is not work the risk without knowing exactly why the are there.

    Keep in mind that these things are so weight critical that the designer isn't going to add anything they don't consider to be required.
     
  3. Mar 19, 2019 #3

    BoKu

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    I'll be polite: Assuming that an experienced developer or designer puts unneeded structural elements into their aircraft is nothing less than an act of hubris.

    You might be right that they aren't needed, but you also might only be right under certain circumstances. Finding out the circumstances under which you're wrong probably involves plummeting. Plummeting often ends badly.

    In the case at hand, the compression struts likely stiffen the two spars in the plane of the wing, so they don't bow towards or away from each other under the compression forces of thrust, wingtip drag, or while reacting the tension forces in the struts or flying and landing wires. Looking at the drawing, I'd guess that they are there largely for the benefit of the smaller and more limber aft spar.

    It might be that the foam ribs have enough aggregated stiffness to serve the function performed by those struts. But maybe not. And it also might be that uncertainties in the properties and condition of the foam, and the integrity of the joints between the spars and the foam make them necessary.

    --Bob K.

    ETA: Basically what Hot Wings wrote while I was bloviating.
     
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  4. Mar 19, 2019 #4

    Topaz

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    Dogs and cats, living together! Mass hysteria! :rolleyes:

    The struts are there for a reason. I don't personally know what the reason is, but I'd be very reluctant to remove any parts at all on a structure that basic. The best person to ask would be Sandlin on the GOAT web page.

    Any particular reason you want to pull them out?

    EDIT: Apparently I type a lot slower even than Bob. :gig:
     
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  5. Mar 19, 2019 #5

    FritzW

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    There will absolutely be consequences but that picture doesn't show enough information to even guess what all of them might be (I'm not being snarky, just saying why your not getting more specific answers).
     
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  6. Mar 19, 2019 #6

    Riggerrob

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    Those struts carry compression loads some of the time, while other times they carry tension. They hold spare in correct alignment.
    Maybe they prevent spars from twisting away from vertical.
    The only other way - I can see - is installing foam ribs (compression). wth steel cables (tension).
     
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  7. Mar 20, 2019 #7

    wsimpso1

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    Well, I am known for a number of standard pieces of advice:

    Does this design have history? Find out and make decisions based upon its history;

    If the design has a good history, stick to the plans;

    If the design has known issues with known fixes, stick to the plans except where you have known fixes, then stick to the plans except where you stick to the plans for the known good fixes;

    If the design has known issues that make for a bad airplane and no known good fixes, avoid that design.

    I make these recommendations because most of us are not qualified to be airplane designers, even the ones among us who are qualified to be airplane designers will have to do an immense amount of work to design, fabricate, test, test fly, and find out what else is not good enough in the new design. UGH.

    So, are you trained in the engineering and experienced in the art of wing design? Are you ready to take on the responsibility for design, analysis, fabrication, bench test, flight test that redesigning the wing entails? If you have to ask us about it, I suspect you should stick to the plans...

    On this specific topic, another post...

    Billski
     
    Last edited: Mar 20, 2019
  8. Mar 20, 2019 #8

    wsimpso1

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    On to the specifics of deleting the ribs between the compression ribs.

    First off, let's get into what those ribs in the print do. Each bay of fabric has aiirload pulling it away from the wing, or in some cases, there might be some pushing on the fabric toward the center of the wing. In any case, the load is dumped from the fabric into the ribs and spars forming the periphery of each bay. Rib spacing is selected based upon, among other things, the load per unit area of fabric, and thus the load fed into the ribs and spars per bay. Then, some of the ribs are beefed up and these beefed up ribs carry the loads in the diagonal bracing wires and the fore and aft loads that can be generated, as well as the airloads. Then, if the wing is externally braced with struts or wires, the spars see significant compression (2 to 3 times the lifting loads) and are subject to buckling, which the ribs help to brace against and restrict the buckling exposures to the width of the bays.

    So, presuming the designer knew what he or she was doing, they selected bay sizes that kept the loads within what the fabric, ribs, and spars could stand. Omitting every other rib will roughly double the loads between fabric and ribs, and will double the free lengths between ribs for buckling, which will reduce the critical load at buckling to one-quarter of what it could be with all ribs present.

    Now what makes any of us think that the designer built in twice as much strength as was needed in the structures for distributing airloads and four times as much buckling resistance than was needed in the spars?

    Any builder who thinks that omitting half of the ribs is OK and builds that way will be nominated for a Darwin Award. I expect that such a ship will either develop problems with keeping the fabric attached, or will have problems with ribs cracking and breaking, or will have problems with spar buckling. Perhaps all will be seen. If we are lucky, they will be caught prior to outright failure, and the craft grounded until the wings are rebuilt with all of the ribs this time. If we are not so lucky, at least one of these modes will be seen in a post-crash investigation.

    Billski
     
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  9. Mar 20, 2019 #9

    BBerson

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    Without struts A and B, just simply tightening the wires would cause the spars to bow out or in. (like an archers bow)
    And then those bowed spars would not support forward and aft (anti-drag, drag) wing loads as well.
     
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  10. Mar 20, 2019 #10

    choppergirl

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    I'm thinking the aircraft designer added this superfluous in-flight movie VHS and Laserdisc projector on my 767... amazing what you can buy at a boneyard, if you just show up at the front gate with a suitcase full of unmarked bills.

    I'm chucking this junk out the side door to lose some weight, come what hell may. I got the need for speed, climb rate, and glide ratio.

    Demonstrating... one size answer does not always fit all... and designers, are not omniscient.

    Who could predict Lasardisc wasn't the future be all end all of all time...? Or that I would come along, buy this as scrap, and want to fly this puppy with only me onboard at the controls and one or two professional bowlers.

    Wait, this VOR system gets chunked out too... man, I'm on a rampage! What next? Toilet? Minibar? Microwave? Inflatable Bouncy Passenger Escape Slides? Drop down oxygen masks? All these passenger... seats? And carpet? And overhead compartments? PA system?

    I bet if I strip off the outside paint, I could save another 500-1,000 lbs...

    Dang, 10,000 pounds lighter, this thing flies like a fighter jet now!

    Well, sort of. I only shed 3% overall empty unfueled weight (330,000 -> 320,000 lbs).

    Where did they hide the bricks on this thing?

    At least now I got room though to install my 2 lane bowling alley... bowling gets a whole lot more interesting when the pitch/yaw/roll of the lanes could be anything at any instantaneous moment.

    ~

    Calculate what percentage weight overall are you saving by losing the struts.

    Is it even significant? Or is it 0.x%? Is it worth that?


    One of these days I'm going to win the Best Post Eva Award...

    Dogs, cats, bowling alleys, mass hysteria... how is this even topical :p The man was talking about goats...
     
    Last edited: Mar 20, 2019
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  11. Mar 20, 2019 #11

    rotax618

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    The struts are there to shorten the unsupported span of the front and rear spars as “non concentric slender struts”, just as jury struts are used to stabilise the lift struts when they are in compression. The internal drag bracing introduces compressive loads on the spars when the wing subjected to drag and thrust loads. Normally wing ribs stabilise the spars, without knowing how the ribs are attached and if they are able to resist buckling I can only assume the designer has used these “redundant” struts as a substitute.
     
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  12. Mar 20, 2019 #12

    Victor Bravo

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    Today I told my wife that I am the smartest man in the world, and (unlike all the other days) she did not take a frying pan and hit me in the head. So using the scientific principle of Calculatus Eliminatus, today for a very brief instant I must be the smartest man in the world, and I will kindly share some of my astronomical brilliance with you:

    Don't f*** with it.

    Mike Sandlin, or someone else who he knows, has very likely examined the structure of this glider in some detail. I don't know Mike personally very well but I have met one or two of the people who he flies hang gliders with on weekends, and I have a fair idea of who those people are between Monday and Friday. I feel confident in saying there are no "useless" parts in the GOAT wing.

    Useless parts cost money, time, and weight. The GOAT was specifically built to not waste any of those things. There are more brain cells in the GOAT design than you can see looking from the outside. It's not the first time that has happened on a DIY low performance glider:

    The Volmer Jensen VJ-23, the first "rigid wing" hang glider that was advertised in Popular Mechanics and every DIY magazine for amateur hobbyists... was actually designed by the same guy who designed the wing on the SR-71, Irv Culver.

    The Prue Primary glider, which looked like (and was as sexy as) the Brooklyn Bridge, was designed by the guy who built much of the U-2's and SR-71s, Irv Prue.

    The "Hippie", an early rigid wing primary glider with a fuselage that that looked like a bundle of bamboo poles and a nose that looked like a goldfish, was designed by one of the world's best competition sailplane designers of the day, Eugen Hanle.

    The Sail-Wing glider of 1923, which looked for all the world like the illegitimate (and ungainly) child of an umbrella and a kite, was designed by the same man who designed the most successful and capable combat aircraft of World War 1, Reinhold Platz.

    There are many many more examples that I can't think of right now, both powered and unpowered aircraft. The big point I'm making is that you (and I, and most everyone else here on HBA) would be in way over their head adding or removing structural parts from even a simple-looking glider like the GOAT.

    Don't f*** with it :)

    OK, my wife just walked in and reminded me I'm not the smartest guy in the world. I have a painful, frying pan sized lump on my head. My moment of genius has passed. But for one shining moment I was smart enough to save a guy's life. You're welcome.

    (edit) The Hippie was designed by Frau Ursula Hanle, Eugen's wife or widow.
     
    Last edited: Mar 20, 2019
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  13. Mar 20, 2019 #13

    BJC

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    Interesting trivia, VB.

    Makes me curious as to which, if any, professional engineers / designers had a role in other E-AB aircraft.


    BJC
     
  14. Mar 20, 2019 #14

    Victor Bravo

    Victor Bravo

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    Steve Wood, Cessna Aircraft engineer, did the Sky Pup.
    The Sonex and some other Monnett aircraft were designed by Pete Buck, from Lockheed Skunk Works.
    The Owl Racer Formula One aircraft were designed by George Owl, a professional aircraft designer.
    The Hollman Stallion E-AB was designed by Martin Hollman, a professional aircraft designer.
    The Cri-Cri, Luciole, and BanBi were designed by Michel Colomban who was one of the designers or engineers on Concorde IIRC.
    I seem to remember Chris Heintz of Zenair was also on the Concorde??? (can anyone authenticate?)
    The Cosmic Wind Goodyear racers were designed by engineer and test pilot Tony LeVier, with "help" from a bunch of WW2 vintage Lockheed engineers.
    The Wee Bee and Honey Bee were designed by a team of WW2 vintage Convair engineers
    The Volksplane was designed by Bud Evans, who I believe was a Convair engineer (Fritz, authentiicate?)
    The Backstrom Plank gliders were from Al Backstrom, who was an FAA aircraft engineer.
    The Salvay Skyhopper (E-AB grandfather of the Varga Kachina) was designed by Gene Salvay, one of the designers on the B-25 and later the initial concept designer of the OV-10 for North American.
    The Thorp T-18 was from John Thorp, who designed the Piper Cherokee (with Fred Weick)
    The Questair Venture was designed by the guy who designed the Malibu for Piper.

    Anyone and everyone else, chime in. This list could get interesting!
     
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  15. Mar 20, 2019 #15

    BJC

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    Thanks, VB.

    I knew of several of those. Van also is an engineer.

    Anyone know of others?

    Thanks,


    BJC
     
  16. Mar 20, 2019 #16

    Wanttaja

    Wanttaja

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    Pete Bowers was an engineer, too. However, he got his degree on a shortened wartime program (two years) that included technical training for an A&P ticket.

    He worked for Boeing after the war, as an engineer, but I don't know what specialty area he was in. I know towards the end of his career that he was used more as a technical writer.

    Ron Wanttaja
     
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  17. Mar 20, 2019 #17

    blane.c

    blane.c

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    delete
     
  18. Mar 20, 2019 #18

    BJC

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    Wasn’t it Pete who drew the cutaway views of aircraft for Air Progressback when they printed four issues per year?


    BJC
     
  19. Mar 20, 2019 #19

    Wanttaja

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    Re: Removing "useless" struts between the fore and aft wing spar of a goat4 ultralig

    I doubt it. Pete almost never illustrated articles or books with his own drawings. The original Fly Baby articles in Sport Aviation were accompanied by drawings by Jim Morrow. You might be remembering this illustration...it was done by Douglas Rolfe. Perhaps he was responsible for the other cutaways you remember.
    [​IMG]

    There's only one verified location for Pete Bowers's own illustrations: The biplane plans for the Fly Baby. Pete had a row with Morrow about halfway through, and ended up doing a lot of the drawings himself. Pete obviously had the drafting skills imparted by a good engineering education, but I doubt he could tackle an illustration like above.

    Many of you might be familiar with the artist Jim Dietz, who has painted a lot of legendary aircraft. A few years ago, I came across a partial Fly Baby cutaway done by him...I suspect it was early in his career.

    Ron Wanttaja
     
  20. Mar 21, 2019 #20

    ultralajt

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    Didnt have time to read all comments...sorry... so here is my opinion about these "useless struts":
    As wing ribs give some stabilization of distance between wing spars, they are not suppose to do that alone. Shrinking the wing skin at assembly and air loads in flight compress wing spars one toward another in horizontal plane, so these wing members are very necessary in this kind of ultralight wing structure. DONT remove them. Of course, you can always ask the designer Mike himself via email address on his website.
     

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