Raptor Composite Aircraft

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Dexacare, Mar 28, 2016.

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  1. Jun 23, 2019 #821

    Kyle Boatright

    Kyle Boatright

    Kyle Boatright

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    Lesson 1: How to make the CG acceptable when your rear mounted propulsion system didn't meet weight goals.
     
  2. Jun 23, 2019 #822

    Marc Zeitlin

    Marc Zeitlin

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    Once again, not to defend anything going on with this project, but many side-by side canard aircraft need ballast in the nose when flying solo. In my COZY MKIV, I carry 50 lb. of ballast in the nose when solo, and take it all out when I have a front seat passenger that weighs more than 100 lb. Velocities generally don't need ballast (but also generally fly more forward within their CG range).

    It's not at all surprising that the Raptor would need nose ballast for flight testing (when solo) and to ensure that the CG is mid to forward within the CG range for the start of testing. And since it weighs approximately 2.75X what my COZY MKIV weighs empty, it's not surprising that it would need ~2X times the ballast. In fact, since the 50 lb. I use gets me exactly on the rear CG limit when solo, if I wanted to be at 1/3 of the CG range, I'd need a LOT more. So 100 lb. isn't out of line, as a reality check here.

    It would be very interesting to see the estimate of CG range for the Raptor, as well as to see what the W&B range looks like with the current engine as well as with a much lighter one. It MIGHT be the case that the empty CG would be so far forward with, say, an O-540 or O-550 that the maximum front seat weight would be minimal, and you couldn't even take 2 people in the front. But without seeing the W&B calcs (as well as the location of the AC), it's all guessing.
     
  3. Jun 23, 2019 #823

    rv6ejguy

    rv6ejguy

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    I've learned a lot about canard characteristics from your posts in this thread Marc. Thanks. Many things never even occurred to me before. I'm curious as to how wide the C of G envelope is in something like a Cozy or Velocity compared to something like an RV-10?
     
    Last edited: Jun 24, 2019
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  4. Jun 23, 2019 #824

    flyboy2160

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    We need a poll: Is this thread The Most Entertaining Thread on HBA?
     
  5. Jun 23, 2019 #825

    BJC

    BJC

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    Only if you consider watching a train wreck in slow motion entertaining. To me the whole thing is just sad.


    BJC
     
    Last edited: Jun 24, 2019
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  6. Jun 23, 2019 #826

    Marc Zeitlin

    Marc Zeitlin

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    You make the assumption that I'm not making things up as I go along :). But thanks.

    So I know diddly about RV-10's, but a perusal of this POH:


    shows a CG range of about 8" (108" to 116"). Canards tend to have smaller CG ranges than conventional aircraft. A COZY MKIV has a CG range of 97.5" to 102", or about 4.5". Long-EZ's have a range of 97" to 103" (6" total). On the other hand, a Velocity XL (similar in size to the RV-10 and Raptor):


    has a CG range of 127" to 134" - about 7", so not substantially different than the RV-10.

    The difference with canards is that the front seats are not just slightly forward of the CG range - they tend to be VERY far forward of the CG range, so an extra person in the front changes the CG position a lot (although less for the heavier canards, like the Velocity XL). With an RV-10, adding baggage or people in the rear seat will substantially move the CG aft, whereas adding baggage or people to the back of a 4-seat canard hardly moves the CG at all.

    I never worry about CG with respect to what/who I throw in the back seat - only that the person next to me in the front weighs 100 lb. or more so that I can remove my nose ballast, or that they're less than 280 lb, so I'm not forward of my forward CG limit. Happily, the largest person I can FIT in the front seat with me is about 240 lb. (without liquifying them and pouring them into the plane).

    On the COZY MKIV (and Long-EZ, and I presume the Velocity as well), rear CG limit is more limited by deep stall considerations than stability considerations - I've flown my plane at 103" (1" aft of the rear limit) and it's not even close to being only neutrally stable. But it MIGHT be susceptible to deep stall at that location.
     
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  7. Jun 23, 2019 #827

    BJC

    BJC

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    My understanding is that the liquifying part of that is an irreversible process.


    BJC
     
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  8. Jun 23, 2019 #828

    mm4440

    mm4440

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    Sometimes it takes more than magic. In engineering it is said, " All it takes is time and money, possibly in infinite amounts. Prayer couldn't hurt.
     
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  9. Jun 23, 2019 #829

    Marc Zeitlin

    Marc Zeitlin

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    Well, I can say that no-one has ever requested it in order to get a ride.
     
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  10. Jun 23, 2019 #830

    Deuelly

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    And it makes the rudder pedals very slippery.

    Brandon
     
  11. Jun 23, 2019 #831

    pictsidhe

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    So, I just need to mumble a few incantations, and anything is possible?
    Why the hell is that in none of my reference books?
     
  12. Jun 23, 2019 #832

    Marc Zeitlin

    Marc Zeitlin

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    I don't know where you went to engineering school, but at MIT, there was an engineering course (Mechanical Engineering 2.47) titled "Spells, Incantations and Sacrifices - Advanced" (strangely, there was no introductory course in this area - go figure). The textbook used (IIRC) was Hermschmitdt's "Goats, Chickens and Virgins: a Sacrificial User's Manual". The course covered all means of effecting the supernatural when designing mechanical, aeronautical, nuclear, civil, or electrical engineering systems. Since software is always supernatural and non-deterministic by nature, there was no need to cover it in this course. It was numbered 2.47 because it was, in truth, a thermodynamics course - all magic must at its core violate the laws of thermodynamics (something Hermschmidt makes abundantly clear in Chapter 3 - Basis of Events).

    Obviously, it's not as simple as just "mumble a few incantations" (I assume you were being rhetorical), else why would Hogwarts, et. al. be necessary - everyone could do it. You have to be trained. It's certainly possible to be autodidactic in this area, but it's rare.

    I would have assumed that this would be covered at all engineering schools, no? That's what happens when you get both your degrees from the same institution - you don't get a view of what goes on in the wider world... although maybe times have changed since I was graduated in 1981.
     
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  13. Jun 23, 2019 #833

    BJC

    BJC

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    At Georgia Tech, we did not sacrifice virgins.


    BJC
     
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  14. Jun 23, 2019 #834

    Marc Zeitlin

    Marc Zeitlin

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    Sure you did. You just used different techniques. At MIT, well... let's just say social ineptness was taken to the extreme.
     
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  15. Jun 23, 2019 #835

    TarDevil

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    I'm suddenly in an alternate world.

    Perhaps there is a way the Raptor will, indeed, fly
     
    Last edited: Jun 24, 2019
  16. Jun 23, 2019 #836

    Kyle Boatright

    Kyle Boatright

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    Must not respond to post... Must not respond to post...
     
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  17. Jun 24, 2019 #837

    BJC

    BJC

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    I had it all set up for you ...


    BJC
     
  18. Jun 24, 2019 #838

    Scheny

    Scheny

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    I read your book proposal and it is suggesting to use a magnetic coupling. Wow, it is working under misalignment, and has 112% efficiency, as alignment errors will recuperate into additional torque.
     
  19. Jun 24, 2019 #839

    pictsidhe

    pictsidhe

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    Hmmm, I'm drawing a google blank on Hermschmitdt. Is it only available from the MIT bookshop?
     
  20. Jun 24, 2019 #840

    bmcj

    bmcj

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    Couldn’t find any?
     
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