Rear Bear Vs. The Russian Bear

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by pie_row, Dec 2, 2009.

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  1. Dec 28, 2009 #381

    pie_row

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    Did you factor in the 30 or 40Gs that the model is pulling? To my eye it looks like about a 1,000ft loop they are flying and in other videos I've seen them doing it in about 5~6sec. Guessing on the G loads but far higher than I could live through is what I'd say.

    If the radio weighs 4.21875 lbs and they are pulling 40G Then it is scale for me at 9G.
     
  2. Dec 28, 2009 #382

    JimCovington

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    Most R/C receivers are on the order of 1 oz, not 70 oz.

    I'm still not sure why you insist on scaling models, which we've all pointed out don't scale linearly.

    Why not use a real example of a man-carrying aircraft? The Carbon dragon is very close to what you've suggested for an airframe (carbon spar, AR 12, 300lb gross weight, tested to 5Gs) and it weighs about 140 lbs. Where are you going to shave weight from that?

    I saw the magic dragon while it was being built - Steve didn't miss many (any?) chances to save weight.

    He even left the engine out! :)


    No point in debating models & scale anymore - enough!

    Go ahead and BUILD it!

    If you succeed at the 100lb goal, it will one one fun rocketship. Even if you only come close, it should still be an entertaining plane.
     
  3. Dec 28, 2009 #383

    pie_row

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    Ran the numbers and the DS Kinetic 100 would weigh 99lbs at twice the size. That would not include space for a pilot but it would be stressed for some very high G loads. I don't know how maney G it would be stressed for but propbably enough to carry me.
     
  4. Dec 28, 2009 #384

    JimCovington

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    OK, so enlarge the fuselage from 4" diameter to 26" diameter (that's a HUGE increase!), add engine, exhaust, prop, fuel tanks, landing gear (even a single wheel setup is adding several lbs) - how much have you added? Where are you taking away weight to get back to 100lbs?
     
  5. Dec 28, 2009 #385

    pie_row

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    One thing that I've noticed playing with my design calc is that the cross section of the spar cap stays the same as you scale up and down the wing size. So cutting the wing span in half for the Carbon Dragon should make the spar ½ the weight. With ¼ of the wing area you should have ¼ or so for the minimum wing weight per sq ft wing area. The tail surfaces should be much smaller to get reasonable tail volume coefficients. Does this about cover it?
    Sounds like a plan!
    It takes mass to support wetted area. Reducing the wetted area should make it possible to reduce weight.
    At 99lbs it is stressed for going 400mph!!! stress it for 150 mph and you should have the weight to put the other stuff in.
     
  6. Dec 28, 2009 #386

    JimCovington

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    You have to lose 70lbs out of a 140lb airframe (1/2 the weight!) to allow for 30lbs of engine, exhaust, prop, fuel systems, instruments & gear and still hit your 100lb design weight - so no, I don't think it does cover it. Detailed design docs would let you know for sure.

    Ooops, now you're ignoring G loads.
    It's not just speed. Using your calculations, you demonstrated how it's stressed for 9Gs at your weight ONLY if it's carrying 70 oz of radios & batteries. Since it's not carrying that much weight, that means you can't reduce mass and keep the strength you want.

    You need rigidity&strength for both G loads and flutter resistance. You're beefing up two different areas or the airframe, and you can't ignore one just to focus on the other.

    Using your numbers & your examples, I still don't come up with a 100lb airframe.
     
  7. Dec 28, 2009 #387

    autoreply

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    8 lbs engine... well, prop, PSRU and respective fairing are all made of Helium?
    You made the wrong ones. Assumptions are usually backed-up by experience. Yours aren't. Taper for your application would ideally be between 0.4 (least induced drag) and 0 (least constructional weight)
    An aspect ratio of 12.5 is insane. If low weight is your goal, go to 3 or 4, nothing more. If low drag (or low power) is your goal, accept some more weight, despite the heavier weight it will let you climb faster.
    So your fuel weight is NULL?
    Then you're terribly wrong. Don't think, but know. Since you lack the knowledge or insight to confirm or deny it's nothing more than a vague "feeling" than you're right... ;)

    25-30% claimed laminar flow over fuselage, in real life "some" maybe half of that in the best conditions is my personal guess. I've read and discussed it quite a bit, so it might be better to stop this (interesting) conversation or continue it in private so that Pie_rows goal can be achieved in a realistic timeframe instead of us distracting him again ;)

    As for the global discussion; AR=4 wing, open cockpit (only a beam under your butt) and a monocoque streamlined rear fuselage with conventional (all-moving) surfaces, taildragger (fixed, single main wheel) and one-piece rutan-build wing with very low density foam and a very thin profile (low Reynolds!) might do the job if you ignore ailerons or flaps and go for spoilers, activated by a simple cable.

    Basically a concept like the Verhees Delta, but completely aimed towards weight, not towards real-life requirements
    [​IMG]
     
  8. Dec 28, 2009 #388

    bmcj

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    Don't forget the teardrop shaped helmet to reduce head drag and the fin on the back of the helmet to double as a rudder (turns where you look) to save the weight of hinges, rudder cables and rudder pedals. ;)
     
  9. Dec 29, 2009 #389

    Topaz

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    Have we discussed ramjets yet? After all, no moving parts!
     
  10. Dec 29, 2009 #390

    JimCovington

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    Oh, please! With the associated high-pressure fuel pumps & titanium leading edges, you're talking about AT LEAST 120lbs to get up to the necessary Mach+ speeds.

    :roll:
     
  11. Dec 29, 2009 #391

    Topaz

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    I'll bet a Weedhopper could lift it with a little reenforcement! :)
     
  12. Dec 29, 2009 #392

    Mac790

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    I don't think so, I proposed a rocket engine a few pages ago but they didn't like it (probably a rocket engine is to heavy) :). But seriously, first there was a discussion about high subsonic speeds, next about stratospheric flights, there was a short spontaneous off topic discussion about laminar shaped fuselages. Now there is a discussion about 100lbs titanium planes? I'm lost.:whistle:

    Seb
     
  13. Dec 29, 2009 #393

    Topaz

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    A good troll will do that to 'ya. ;)

    I'm expecting flying saucers to enter this discussion any time now, possibly under a "low AR" guise...
     
  14. Dec 29, 2009 #394

    Starman

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    No, a rocket engine isn't too heavy, what was amazing in that video you posted was the long duration of the fuel burn. If you notched it up to 3Gs acceleration you wold only get 1/3 the duration, but you would pass 300mph in five seconds, accelerating upwards. After a twenty second burn you would be going up so fast you wouldn't stop till you were at the edge of space.

    That was a liquid fueled rocket, but a solid fuel rocket is nothing more than a tube with a cork at one end ... and another cork at the other end ... with a hole in it. You could make a big rocket out of a steel tube that wouldn't be prohibitively heavy, and the steel tube could serve as a backbone structure.

    You could even make an ultralight version, but don't expect to reach the edges of space with that one. :uzi:

    The plane could have the usual switch blade wings that will pop open when it reaches the top of it's trajectory and turn it into a plank glider. OOPS, I gave too much away already. :computer:
    It's simple, I've worked out that design to the nth degree, and I love explosives :ban: and don't forget the cork!!
     
  15. Dec 29, 2009 #395

    Starman

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    Was that titanium leading edges for a weedhopper? or is it the 6000lb cri cri? I kind of liked that cri cri with the two V8 engines, but I would put one in front and one in back, and that sucka stole my supersonic prop idea too.

    You know, don't you, {{all huffy :mad:}} if you use solid rockets rather than ramjets you don't need the high pressure fool pumps.
     
  16. Dec 29, 2009 #396

    JimCovington

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    If anyone here decides to put a 900lb thrust rocket engine on a 100lb airframe and climb on before lighting the match, I hereby promise to not only buy tickets to the spectacle, but to bring enough popcorn for everyone.
     
  17. Dec 29, 2009 #397

    Starman

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    That's right, if you had rockets you wouldn't need a generator, which would be handy, because you wouldn't have one. You could use matches and a long fuse.

    OK, it's a deal! It's something I've always wanted to do too, I mean watch someone else do it. Just kidding ... I'M rocket maaaaan! I'll do it.

    I can't find a picture of the 6000lb cri cri with the two V8s, if anyone can find that I will be eternally gratefull. Untill then you can get an idea of what I mean by this one:

    [​IMG]

    ... and for the titanium leading edges and the rocket:

    [​IMG]

    Sorry, no UFOs yet, at least no high res fotos, at least not the ones the feds don't have.
     
  18. Dec 29, 2009 #398

    Starman

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    Just kidding, the 6000lb cr cri had the two V8s in front and counter rotating supersonic props, remember that on, what was that called?

    That one there looks like it would be pretty stable upside down, doesn't it?

    Hey, don't mind me, I just ate a pound of 85% chocolate and two slices of ginseng root .... HAHAhahaha ... . ...the night is still young,.
     
    Last edited: Dec 29, 2009
  19. Dec 29, 2009 #399

    Topaz

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    And I'll bring the video camera. I could certainly enjoy the $10k from America's Funniest Home Videos! :gig:
     
  20. Dec 29, 2009 #400

    pie_row

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    You changed what you wrote and what you quoted of me after the fact. And so this statement of yours is a lie. And in doing this you abused you moderator privileges.
     
    Last edited: Jun 22, 2011

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