Gotchas with the Carmichael racer

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Hephaestus, Jun 12, 2019.

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  1. Jun 12, 2019 #1

    Hephaestus

    Hephaestus

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    So there's an old PDF floating around in here of a Bruce charmichael article on a laminar aircraft design.

    I still want to build a high speed single place commuter craft. Basic design goal being get from a->b quick as possible, with fairly docile handling.

    And I still like these pod and boom pushers for no good reason.

    What are the gotchas with this layout? Did he ever get farther beyond the initial sketches?
     
  2. Jun 12, 2019 #2

    BJC

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    I’ll leave the comments on the aerodynamics to others.

    It will take extra structural weight, compared to a tractor configuration, to keep the engine from bashing in the back of your head in a crash.

    The horizontal stabilizer and vertical stabilizers will get dinged up from stuff on the runway.

    If points A and B are unfamiliar to you, taxi speeds will be slow verses a tricycle gear configuration.

    The fuel system will be complex, due to the thin wing, lack of dihedral and engine placement.

    You will need either a ladder or a big step to easily get into and out of the cockpit.

    Don’t take any of this as intending to discourage. Build the design that you want.


    BJC
     
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  3. Jun 13, 2019 #3

    FritzW

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    Access to the engine might be a challenge.
     
  4. Jun 13, 2019 #4

    wsimpso1

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    The big gotchas are there is no flight history and no builders to lean on. Did Bruce get past the three view and to a complete set of plans? If he did you might be able to do the airplane. If he did not, you would be picking up the design, and I can tell you that is no walk in the park.

    For your mission, buying a used Long Ez or building an Open Ez might be your best path. Lots of builders have beaten the path, good fast docile airplanes, and lots of baggage capacity if operating it as a single seat bird.

    Bill
     
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  5. Jun 13, 2019 #5

    Hephaestus

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    https://www.homebuiltairplanes.com/forums/attachments/1976_09_18-pdf.23915/ there finally found the link again to the original article.

    There's no general logic to build something myself other than it's something to waste time and money on. I'm retired, what else am I going to do in a cold Canadian winter without fiki capability?

    I have the Mooney, which is about as quick as an openez. I still want more speed - from something smaller. Sane quest, perhaps not. But I also just dropped the purchase value of the Mooney into a panel and interior refit. Sanity is seriously questionable at the best of times

    Yes as far as I've found its a full blank sheet design if I want to do it. I don't underestimate the work involved, probably end up hiring someone to do a larger hunk of it (not totally insane)
     
  6. Jun 13, 2019 #6

    Jay Kempf

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    I've never found any model airplane or EXP versions of this airplane or any other details other than one reference in Alex Strojnick's books.

    The engine is completely above the cockpit so as long as the failure is to shear off of a bed mount I don't think it will be a safety issue. Actually most of the seaplanes like this haven't ever really had that supposed failure issue. If you hit hard enough to get the engine off the mount and into the cabin mostly that event wasn't survivable anyway.

    Bruce Carmichael was a big proponent of drag reduction for minimum HP and weight. This was what he thought was an optimal drag reduction platform. Many of the Long EZ variants have proven that you can get a reasonable pusher platforms with the engine in the wake of everything. There is still a strong case for all the shed vortices from wings, fuselage and cooling taking away any benefits of the drag reduction of the pusher prop but the jury is out until people build many versions and fight through the details.

    The two extremes are a racer called Pushy Cat and Mike Arnold's AR-5 and -6 if you want minimalist single human transport. But scaling any of these designs up a bit to make the human and aero factors a little more conservative might be warranted unless a dedicated records or race craft.

    If you want to design from scratch based on someone else's concept it is correct to start asking if the concept is sane. Bruce was not a person without resources. He had been teaching and consulting on a lot of varied projects so he was not a person without access to test data on a lot of configurations.

    This particular design you cite was never something that I put much thought into. I think I understand why and where he was going with it but it seems a little disjoint as an overall design. But I like weirdo concepts. The U shaped tail on a single boom under the prop seems pretty clever. The engine way up and buried in the root of the wing seems like the same old Long EZ tough to fair and difficult CG issues issue that everyone has been fighting with. The tall gear and one piece sliding nose is a bit tough but it could be done, probably not the lightest config.
     
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  7. Jun 13, 2019 #7

    Himat

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    Or some sort of kneeling undercarriage.
     
  8. Jun 13, 2019 #8

    Hephaestus

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    Bruce Carmichael (there finally got autocorrect to not butcher it - sorry if anyone can fix the title, no h please) isn't an unknown. His work like Orion's stands on its own. But I find it curious it wasnt pursued at all.

    The LG he even says in the article would be better retracted - configured like drawn for simplicity and again preserve the laminar flow.
    "It will be a neat excercise in kinematics to retract the two 10-inch-diameter wheels and legs into the small space available and seal them up" he also notes that would be a turbulent flow region.

    It does look patched together, I'll give it that, I was reading up on interference drag from the decalage angle thread when I ran across it again. But it also makes sense - doesn't look pretty like an icon a5 but function over form...
     
  9. Jun 13, 2019 #9

    Himat

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    If you are not familiar with it, have a look at the Sky Arrow.

    http://www.skyarrow.it

    That is what I imagine Bruce Carmichael design do look like when “productionalized” by someone that put practical, production cost and marketing above aerodynamic efficiency. Still it performs well.

    One piece forward sliding canopy have been done at least once on a sailplane. A picture has been shown on this forum, but I do not remember the name of the airplane.

    Engine fairing can be made work. If an inline engine with all accessories at the end opposite the propeller could be had it would be easier too.
     
  10. Jun 13, 2019 #10

    BBerson

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    The OP can edit the title with tools at top left of page. Might be a 24 hour limit.
     
  11. Jun 14, 2019 #11

    Hephaestus

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    The subject was never editable, I did start with that ;)

    I'm just curious about the overall layout, if there's something inherently impossible/unsafe/unstable with the layout that I'm not seeing.

    Yeah I was thinking a bit more conservative, bit more wing bit less power (vw perhaps?)

    Strojnicks laminar magic has some bad ideas too...126mph on 30hp is no small feat either.
    http://www.google.com/url?sa=t&sour...FjAPegQIARAB&usg=AOvVaw1H35UciF_yfEeSivLmHbFt
     
  12. Jun 14, 2019 #12

    MadProfessor8138

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    I've always wanted to redesign the Ultrabat to be built with something other than composites.
    1124870-large.jpg

    afe996478114.jpg

    2551929.jpg



    Is this configuration in the ballpark of what you're looking for ?

    Kevin
     
  13. Jun 14, 2019 #13

    bmcj

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    The mods can change the thread title. Just add a post to the thread asking them to change it (tell them what you want it to say), then after you post it, hit the “report” button at the bottom of the thread to call it to their attention.
     
  14. Jun 14, 2019 #14

    Norman

    Norman

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    There's a reason that Bruce's nickname was "all charts, no parts".
     
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  15. Jun 14, 2019 #15

    Hephaestus

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    General pod and boom pusher is yes the configuration I'd like in this case.

    Plans for the janowski j1 and j2 are available and wood based.
     
  16. Jun 14, 2019 #16

    flyboy2160

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    This needs a flutter analysis. The relatively small wing attach looks problematic at first glance. The other planes shown here have the wing attached to a much wider structure.
     
  17. Jun 14, 2019 #17

    wsimpso1

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    Hmm, look hard at F1 racers. That was Bruce's starting point. 66 sq ft of wing, O200 engine, fixed gear. While some have run pusher props, Pushy Cat notably, tractor props are so much more efficient that they end up faster than other schemes. You can grow the airplane from there, but if you start with a Casutt, you can do an immense amount of drag reduction and cockpit customization and longer elliptical wings from there.

    Billski
     
  18. Jun 14, 2019 #18

    MadProfessor8138

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    Victor Bravo posted this a while back on another thread......

    Singletrainer.jpg

    JT8S7.jpg



    Kevin
     
  19. Jun 14, 2019 #19

    plncraze

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    Get a copy of Carmichael's book Personal Aircraft Drag Reduction. He discusses his ideas there. Then start reading Ed Lesher's articles and the Dave Lednicer. Norm's "all charts..." is very true. Look at the bibliography of the OP' s initial post. Everyone who talks of complications with pusher props covers the ground well. Pushers are fine if you understand what they need to succeed.
     
  20. Jun 14, 2019 #20

    BBerson

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    Last edited: Jun 14, 2019

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