Raptor Composite Aircraft

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

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  1. Jul 1, 2019 #921

    Billrsv4

    Billrsv4

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    Ross is right on the money about this. Does anyone on here now remember Moller? Since I have been involved with rotary engine projects I looked him up. I even went so far as to look for a job there. He was so far off on his "estimates" that the SEC got involved for fraud. I interviewed with the man himself and wouldn't have taken the job there because, and this is just my OPNION, the guy deluded himself to further his project. The Raptor project seems more realistic than that, but the people building the thing need to adhere to the factual. Getting the weight right is at once the hardest and most important task in your design performance goals. Miss that and the rest is a snowball rolling downhill. One of the reasons Van's kits are so successful is that the average builder, following the instructions, can put the kit together and be very close to the advertized weight and performance figures. This is vital. An overweight airframe will have poorer performance in every aspect of the flight envelope. I hope this team delivers a finished product, not yet another case of vaporware.
    T. O. Bill
     
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  2. Jul 1, 2019 #922

    BJC

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    If it isn’t destroyed in testing, the prototype, with a slick paint job, and strategically placed LED illumination, will make a really nice static display.


    BJC
     
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  3. Jul 1, 2019 #923

    Victor Bravo

    Victor Bravo

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    Some day there will be the Homebuilt Aircraft version of Davis-Monthan AFB, with all of the blunders and frauds and investor-ware mock-ups on display.
     
  4. Jul 1, 2019 #924

    bmcj

    bmcj

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    Now that would make a great museum!
     
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  5. Jul 1, 2019 #925

    Victor Bravo

    Victor Bravo

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    "Right this way to the Moller Pavilion, ladies and gentlemen..."
     
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  6. Jul 1, 2019 #926

    Victor Bravo

    Victor Bravo

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    We actually have a prime candidate at my home field, the FoxJet light jet "prototype". Presented as the first article for testing, it features a plywood and MDF pressure vessel, both blue and "aerospace white" foam flight surfaces, and plush tuck & roll automotive vinyl executive cabin appointments. Although the results of the flight testing is still classified, and available only to investors, I believe that some of it's extraordinary performance came from the flight control surfaces being made from striping tape.
     
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  7. Jul 1, 2019 #927

    pictsidhe

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    Hmmm, numbers, let's see.

    230ktas = 118m/s

    132hp through a 75% efficient prop would give 629N thrust at 118m/s,

    L/D for a 2400lb (1086kg) aircraft would be 1086*9.8/629 = 16.9 That seems optmistic, it's also one person and 1/4 fuel.
    Well, it was before the aircraft went hugely overweight...

    0.35 BSFC is correct for current car turbodiesels.

    Area ruling does nothing below around M0.7

    3600nm = 6667km

    Breguet gives R= (np/(g*SFC)) * (L/D) * ln(W1/W2)

    R, range,
    V, velocity
    np, propulsive efficiency
    SFC, specifc fuel consumption, kg/KJ-s
    L/D, lift to drag ratio
    W1 inital weight
    W2 final weight

    with a BSFC of 0.35 lb/hp.hr and 75% propeller efficiency, this works out as range in km of

    R (km) = 1306*(L/D)*ln(W1/W2)

    or in nm

    R(nm) = 705*(L/D)*ln(W1/W2)

    rearranging Breguet,

    L/D = R(nm)* 0.00142 / ln (W1/W2)



    feeding in original spec weight figures for a 200lb pilot, no bags W2=2200lb, 999kg , W1=3011lb, 1367kg

    we need a L/D of 16.27, seems optimistic to me.

    Now, lets see what happens with reality, which is that annoying thing that won't go away even if you stop believing in it:

    W1, = 3000lb empty + 400lb pilot + passenger + small bag, 810lb fuel = 4210lb
    W2 = 3400lb

    rquired L/D for 3600nm range is

    drumroll,

    24

    Good luck with that. May I suggest taking a long, hard look at the successful flying contraptions that Boku builds to get there. There may some slight design compromises required.

    If the L/D is actually 14, which may still be rather generous with the size of that cabin, you can expect a range with 400lb of crew of 2109nm.
    Load it up with crew, passengers and bags of 800lb, you now have a range of 1907nm.

    Of course, this assumes that it can actually fly and someone has the sense to bolt on a redrive that will survive not only taxi, but flight.

    Anvegger, I don't give a monkey's how well the Raptor team can group hug, the numbers just don't work.

    You cannae change the laws of physics, Jim!
     
    Last edited: Jul 1, 2019
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  8. Jul 1, 2019 #928

    Deuelly

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    And it will probably be run by some corrupt 501c that gives most of the donated money to its directors. Ah, I can see it now.

    Brandon
     
  9. Jul 1, 2019 #929

    mcrae0104

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    Douglas A-4: Under weight, under budget, and it set a world speed record.

    Of course, the Raptor project does not have the resources of Douglas, but predicting weight and performance is not rocket science and even lowly homebuilders like us are capable if we are honest with ourselves about engine performance and structural weights. There is little reason that the weight of an aircraft couldn't be known to within a few percent before any materials are cut. The Raptor is an interesting counterpoint to the relentless weight-cutting philosophy of the A-4.
     
    Last edited: Jul 2, 2019
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  10. Jul 1, 2019 #930

    anvegger

    anvegger

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    I am sorry but it seams to me even Wright Brothers did not know about such a simple solution. May be they did not know what would be their design goals?
     
  11. Jul 1, 2019 #931

    anvegger

    anvegger

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    My example even better: The Spruce Goose Aircraft

     
  12. Jul 1, 2019 #932

    Victor Bravo

    Victor Bravo

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    I am a charity 'grant writer" for a living, you know . Maybe I can get the museum funded by the Bede Family Foundation (a real entity) !
     
    Last edited: Jul 1, 2019
  13. Jul 1, 2019 #933

    pictsidhe

    pictsidhe

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    What are you talking about?
     
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  14. Jul 1, 2019 #934

    TarDevil

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    I'm old enough to remember that saga. I was rooting for that little jet!
     
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  15. Jul 1, 2019 #935

    TarDevil

    TarDevil

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    Please translate for the rest of us, if you figure him out. Maybe he's cross-posting??
     
  16. Jul 1, 2019 #936

    Victor Bravo

    Victor Bravo

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    The Chief Huckster and Vice President of Fertilizer these days is not Tony Fox anymore. It's a guy named Barry Marshall. Same shpiel, far less substance, all wrapped in a delightful British accent.
     
  17. Jul 1, 2019 #937

    TarDevil

    TarDevil

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    I couldn't suppress an audible giggle when I read this.
    Shouldn't be funny. Shame on me!
     
  18. Jul 2, 2019 #938

    BBerson

    BBerson

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    I think the Wrights sent a telegram home asking their father to notify the press after the first powered flight. But no publicity prior to first flight, I think. And of course, it was self-financed entirely.
     
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  19. Jul 2, 2019 #939

    BJC

    BJC

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    Jim Bede certainly did things that were not good, adversely impacted thousands of potential homebuilders, and rightly earned the ire of many others. I make no excuses for his behavior.

    About 20 or 25 years ago, my curiosity eclipsed my disdain and I initiated several conversations with Jim. I found him to be a nice, pleasant person. That surprised me; I thought that he would be bitter and defensive. His design series, presented in Sport Aviation and available in printed copy for free, is an excellent starting place for budding designers.


    BJC
     
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  20. Jul 2, 2019 #940

    lvaero

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    No audience = No pressure
     
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