Scott Ol' Ironsides in Carbon

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by stanislavz, Dec 3, 2019.

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  1. Dec 5, 2019 #41

    Victor Bravo

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    Yes, all true, but Hollmann was also known for overbuilding and over-complicating things... some distance past the point of most other successful homebuilt aircraft.

    stanislavz, if you have accepted the concept that you want a steel tube cage around the pilot, then (like it or not) you have accepted 2/3 of a full steel tube fuselage (plans-built Tailwind). Be careful, you may be expending a tremendous amount of energy (and accepting a lot of additional complexity) by going on a "holy quest" simply to prevent the other 1/3 of the fuselage from being made of steel tubes :)

    I speak from experience, I have made that same mistake many times and looked back with great regret!

    Although this does differ somewhat from your original intention with this thread, what if you built a composite wing and tail to "modernize" the Tailwind, and accepted the standard steel tube fuselage? Wittman's hand-drawn airfoil for the Tailwind wing was good, but there have likely been more recent airfoils that would offer some amount of improvement for this use.

    You could increase aspect ratio slightly, and even use the advantages of composites to eliminate the wing struts. These slight improvements could easily yield an aircraft with a 200 MPH cruise speed on 140-150HP. The very best Tailwinds here in the USA will achieve 200 MPH, but this is with 160+ HP and an extraordinary amount of fine tuning, aerodynamic improvement, etc.
     
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  2. Dec 5, 2019 #42

    stanislavz

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    Where should I send The beer ? I do agree with you. and do not agree :) Top wing with struts, have most of load on "plate" where motor, landing gear, struts, and seats is mounted. Low wing, needs a kind of rollcage still. Strut-less top wing - to much stress on corners around windows..

    And - just an imagination. You can build an full fuse in no time. But - much more times with doors, glassing, controls, panel fairing, turtle deck fairing etc.. The small things being 20% of whole, taking 80% of time. And it still will be kind of crude.

    But - go on kind of different way. Cage with only structural mounting points - 4 for wings, 2 for struts, 2 for legs, 4 for motor and 2 for legs. And some smaller for seats. All are kind of "invisible". And cover all this with nice finish, cnc cutted panels, full size with external finish in place. And any need for support of panels. All door and windows recesses are already in. Even tab and slots for instrument panel cut to. Add instrument panel, one former after seat plus - some kind of nice covering for flat panels inside - and you are good to go. All wet epoxy job - 4 corners on tail + all panel junctions. Kind of imagination - yes. Kind of Fantasy - too. But - going flat is the-way-to-go. If one wants a minimum of sanding..

    An article received. and stumbled to see, Ironside in itself was an wooden airplane cover with fiberglass panels.
     
  3. Dec 5, 2019 #43

    BJC

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    GlaStar cage removed from shell.
    upload_2019-12-5_12-42-42.jpeg
     

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  4. Dec 5, 2019 #44

    stanislavz

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    The birth of fk-9 mk3.

    15591230_1222956044460505_8838215600860618809_o.jpg 15625988_1222954967793946_8005486150232992105_o.jpg 15626510_1222955614460548_5269316270690963626_o.jpg 15723327_1222955431127233_1066752541050311424_o.jpg 15723565_1222955217793921_5067830999889600581_o.jpg 1483614785_2_FT52761_fk-lightplanes-12_.jpg 1484414326_2_FT52761_db_fk9_03_boden_xl31.jpg 1484414326_2_FT52761_db_fk9_03_gepaeck_xl31.jpg 1484414326_2_FT52761_db_fk9_03_seats_xl31.jpg 1484414326_2_FT52761_fact_szelle5701.jpg
     
  5. Dec 5, 2019 #45

    stanislavz

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    Back to Ol ironsclad. Per article, all skins were made from 2 layers of 10 oz fiberglass.

    According to this calculator (for woven glass and hand lamination )

    [​IMG]

    Just by kind of rule of thumb - (14 sqm2 wings, 2 sqm2 tail, 10sqm2 fuselage) gives only 31.2 kg per whole airplane.. ~10 % of total empty weight. Not bad at all. This belongs to modern plywood thread..
     
  6. Dec 5, 2019 #46

    stanislavz

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    I have just calculated an ch-701-alumnium technology rear fuselage weight included skins with all longerons/reinforcements, less rivets. Its come close to ~10 kg (0.025 skin, and 0.04 for longerons) With 7.2 skins area. Skin do weight only 7.8 kg..

    Going to ironsides technology - only skins thems-self would weight 8.64 kg. It is not that bad. No ideas on wooden frame weight.

    But - using knowledge, and splitting composite into two layers separated by foam - only skin is needed.
     
  7. Dec 5, 2019 #47

    Vigilant1

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    So, the Ironsides is 20 oz/sq yd fiberglass, no foam? If you want to use fiberglass in 2 layers with foam core between (for more stiffness), then it is going to weigh more unless you make the skins lighter. I think the issue might be with the damage tolerance of that outside layer. The ol Irinside skin might not have been very stiff, but all 20oz were on the outside to take the abuse (hangar bumps, pebbles tossed up by the landing gear, etc).
    One advantage of the "strings" or "waffle" approaches discussed in the "black plywood" thread is that the rear stiffening skin is also bonded frequently to the outside skin (with the Vigi-ply (TM) unidirectional string riblets, the backing later would be bonded to the front layer over nearly 100% of the area, so the glass/CF stiffening layer is more likely to help with the bumps vs. being on the other side of some soft foam).
    P.S. I like that you give the weights in kg, everything seems so much lighter that way! We should start using "stones".;)
     
    Last edited: Dec 6, 2019
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  8. Dec 6, 2019 #48

    Dillpickle

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  9. Dec 6, 2019 #49

    stanislavz

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    Ok. Sorry for mine - non imperial measuring. It is still easier for me..

    Ch-701 is taken as an example, due to be designed on light side as possible to mine afaik. Ch-750 is done sturdier in some places. But 701 have proven to be adequate.

    Back on topic. 0.5mm / 0.02" fiberglass is sturdy enough. 0.75 mm / 0.03" is even more. But - it is flexible. and will not tolerate any buckling load on it. Same is for 0.4mm / 0.016" aluminum. It is just a foil.

    But - reinforcements and longerons used in 701 are only ~2.5 kg in total.. Kind of guessing - but in 750, some bracing was added. Due to thin skin "play" then loaded.

    So - just going from thin skin, to sandwich with stability under load on a margin higher, than 0.4 skin with some angles - shows me to be ok without any formers at all. Only some uni fiber at corners in place of longerons.

    But - going to a proper composite fuselage, which is round in cross section, do allow to have ~ 30-40% less skin. And 5 layers of 7 oz fiberglass is "standard" in eu ul airplanes. Foam less of course. But needs a perfect mold.

    This a kind of classical, albeit cartoonish shape [​IMG]
     
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  10. Dec 6, 2019 #50

    Vigilant1

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    Sorry, I was joking a bit. Metric is fine and easier. But the "low" weights just caught my eye.
     
  11. Dec 6, 2019 #51

    stanislavz

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    Ha ha :) I know, no hard feelings.
     
  12. Dec 6, 2019 #52

    BBerson

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    Dacron fabric is almost ideal for flat sides like a Tailwind. Many models have flat plywood sides. Most also cut out large holes because the flat panels are not ideal for structure except at the corners. And plywood needs covering anyway.
    So a composite side panel with big cutouts would be light. Also makes assembly of internal parts and repair easy.
     
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  13. Dec 7, 2019 #53

    wsimpso1

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    I have not posted on this yet because I have many thoughts on the topic and have been busy... So here goes.

    The Tailwind is great and may be my next airplane build. If I do, it will be to plans. By the way, we should all face Oskosh and thank the soul of Steve Wittman for all he has done for our beloved homebuilt airplane obssession.

    Most homebuilts stay within some boundaries. Wooden wing structures on wooden or steel tube fuselages. Aluminum most everywhere or composite most everywhere. But then we have mixed structure designs. Sportsman and its derivatives with metal wings, steel tube through the cockpit, composite structure aft and composite shell forward. The AT-6 has steel tube fuselage through the cockpit with aluminum monocoque aft. Go with factory built airplanes and we find steel tube fuselages with metal covering (Mooney, many ag planes). And the aerobatic market is certainly loaded with steel tube fuselages and composite wings and tails. So, you can certainly build mixed structures if you want.

    Most of us have preferred material sets and that makes staying in love with the build long enough to complete the airplane more likely. Others find mixed construction to be great as it causes the builder to learn all of these different processes. Whatever floats your boat...

    Me, I tend to keep going back to WEIGHT IS THE ENEMY and the idea that you should build in a material and processes you love working in. So I will urge that you understand the design and limitations of each type, then be smart. So what is smart? Well, I always encourage folks to run numbers on everything they scheme out.

    For a sampling, some folks are talking about the steel tube fuselage. Cover it with fabric and you have the very definition of light and strong. The only reason I can come up with to put metal or composite panels on the outside is to allow frequent washdowns and inspections. Do you really need more than a few inspection ports? Because (run your own numbers) non-structural metal or non-structural composite panels will usually be almost as heavy as just making the fuselage a sheet metal or composite monocoque, at least from the cockpit back. For instance, my fiberglass panels for a structural outside (Vdive of 268 knots) are 0.68 lb/ft^2. In graphite fiber and you can cut that to about 0.30 lb/ft^2. Just try building your nonstructural panels significantly lighter than that and see how long they stand "The Real World". Post a guard when at fly-ins and do not throw away the molds for those pieces. I think that it is way better to have sturdy skins, then if they can let me leave some steel tubes in the rack, so be it.

    Now if you work out the details of the composite shell needed for the back end of the fuselage and carry it forward as a light shell around a steel tube cockpit, you might find it heavier than a fabric covered forward fuselage, but a better overall compromise on a sturdy survivable cockpit with reasonable weight and a nice shape. That is voting for looks over light. Your choice if you want to. Since our minds have been opened up on using whatever material suits in wings and tails, you can scheme out all sorts of things.

    Another path that I love is going the route of the moldless composite fuselage, but by the time you make it crashworthy and try to keep it light, you will build a mold or three for the fuselage and build it with a bunch of graphite fiber around the cockpit. It can be sturdy and reasonably light that way. And in graphite fiber, it can be lighter than any other at same levels of crash survivability.

    Me? I do not think I will self design any more airplanes. The Tailwind looks like a great airplane, built with processes I like and understand. I would build the Tailwind to plans. And the Sportsman airplanes look like a great option if I decide I must have an airplane sooner.

    Billski
     
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  14. Dec 7, 2019 #54

    Toobuilder

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    Thread drift alert: It's been said that the Piper Cherokee is essentially an aluminum Tri Pacer. The Cherokee was FAR cheaper to produce in a factory environment than its older tube and rag sibling. I wonder what a CNC punch and folded sheet metal Tailwind would be like? I'll opine that if you throw a kit together like Van does (and CR is doing) I'd bet one could knock one together pretty quick.
     
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  15. Dec 7, 2019 #55

    Dillpickle

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    A BD4?
     
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  16. Dec 7, 2019 #56

    BBerson

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    I think that's true if you are talking non structural sandwich composite panels. Because a sandwich panel cannot yield, it crunches or gets a hole in thin skins. But a solid ply panel would simply flex if someone leans on it. Much like fabric.
    I can see the compelling benefits of a non-structural skin. As Toobuilder said, the industry switched to aluminum for labor savings. I think the Cherokee is heavier but they ignored "weight is the enemy"

    So, I would like a single ply sheet. Still looking.
    My Grob has a single ply bottom aileron skin. Over time it has warped with big buckles. That's the big issue, as I see it. Not ground damage.
    Of course, the weight is still more than fabric but labor could be less.
     
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  17. Dec 7, 2019 #57

    stanislavz

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    You read my mind..

    Standard male plug/Rutan method ? Or something more exotic ?
     
  18. Dec 7, 2019 #58

    BBerson

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    Several steel tube planes have used foam and glass instead of fabric:
    El'Gringo (foam with glass outside only)
    Beachner Buick Special (foam with glass outside only, I think)
    Chris Christianson built a one off with solid fiberglass, I think.

    Regarding foam with no inside skin, Jim Bede was contracted to design a foam and glass ultralight single seater called NAC Dreamer. Glass skins in molds then foamed with liquid foam. Wasn't quite ultralight weight.
     
  19. Dec 7, 2019 #59

    stanislavz

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    Loud thinking. Is here any "aerodynamic clean fabric covered aircraft" Or fabric is always a kind of rough surface/stitches etc ? . Not polished like a glider, but kind of flush riveted aluminium..
     
  20. Dec 7, 2019 #60

    BBerson

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    The metal wings on the Schweizer 1-35 sailplane were covered with fabric, filled and sanded smooth.
     

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