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Thread: Huge R/C Jet Structural Failure

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    Registered User rv6ejguy's Avatar
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    Huge R/C Jet Structural Failure

    https://www.youtube.com/watch?v=8yf_QTbDeWM

    Amazing 1:2 scale Gripen. Wonder what engine they were using here?

    Just a little bigger and it could be man carrying but you might want that ejection seat. A real shame to see it break up but a good lesson for doing analysis and static testing on any design, especially one which will carry you aloft. TLAR engineering didn't work out so well here...
    Ross Farnham
    Racetech Inc.
    14 years and 407.3 hours on Subaru Turbo powered RV6A
    "The world is changed by your example, not by your opinion" Paul Coelho
    http://www.sdsefi.com/aircraft.html




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    Registered User BBerson's Avatar
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    Re: Huge R/C Jet Structural Failure

    How do you know that is wasn't engineered?
    Might have been assembly flaw, flutter...

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    Registered User rv6ejguy's Avatar
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    Re: Huge R/C Jet Structural Failure

    Quote Originally Posted by BBerson View Post
    How do you know that is wasn't engineered?
    Might have been assembly flaw, flutter...
    Watching at .25 speed- a bit of rudder input during the roll and the fin snapped off at the root, then the whole aircraft disintegrated into confetti. Just a guess on my part...

    What say the structure guys here?
    Last edited by rv6ejguy; January 10th, 2017 at 07:12 PM.
    Ross Farnham
    Racetech Inc.
    14 years and 407.3 hours on Subaru Turbo powered RV6A
    "The world is changed by your example, not by your opinion" Paul Coelho
    http://www.sdsefi.com/aircraft.html




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    Registered User Jay Kempf's Avatar
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    Re: Huge R/C Jet Structural Failure

    Looks like he was entering a knife edge camera pass. The fin certainly snapped off at the root. The rest has no explanation. No reason for the fuselage to come unglued. Hardly looked like it entered and perturbed divergence or any drastic attitude. So who knows what let go that let the rest let go. Most of these things are painstakingly made to "look" like the real thing. I too wonder what engine they were using. It amazes me that people have the money to waste on almost full scale models. Sheesh. If I had that kinda disposable income I wouldn't mess with a half scale fighter. I'd just put a seat in it and have at it. That's why we have an "experimental" category Have a guy stand on the ground with a transmitter while I fly it. No one would know until I died in this case of course in front of everyone... D'oh~!
    Jay K.

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    Registered User BBerson's Avatar
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    Re: Huge R/C Jet Structural Failure

    Half scale is big for a model, but still it's a model and probably balsa and foam and weighed less than 100 pounds, is my guess.
    An EA-B would be in the 2000 pound range and need 10 times the thrust.

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    Registered User Jay Kempf's Avatar
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    Re: Huge R/C Jet Structural Failure

    Not the jets. They are all just glass or carbon in a mold with just enough bulkheads to make the hardpoints work out. Been that way most of the time I have been in the hobby. That thing was way past ultralight weights with a tailcone of PBS Velka sizes so couple hundred pounds of thrust and the fuel it takes to make that happen for at least 20 minutes or so. That wasn't a 100lb model. Yeah they try to keep them light but fuel is fuel.
    Jay K.

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    Re: Huge R/C Jet Structural Failure

    I though I saw a reference to 100 kg, or approx 220#

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    Re: Huge R/C Jet Structural Failure

    Just like Airbus in 2001.

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    Registered User Himat's Avatar
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    Re: Huge R/C Jet Structural Failure

    Quote Originally Posted by Jay Kempf View Post
    Looks like he was entering a knife edge camera pass. The fin certainly snapped off at the root. The rest has no explanation. No reason for the fuselage to come unglued. Hardly looked like it entered and perturbed divergence or any drastic attitude. So who knows what let go that let the rest let go. Most of these things are painstakingly made to "look" like the real thing. I too wonder what engine they were using. It amazes me that people have the money to waste on almost full scale models. Sheesh. If I had that kinda disposable income I wouldn't mess with a half scale fighter. I'd just put a seat in it and have at it. That's why we have an "experimental" category Have a guy stand on the ground with a transmitter while I fly it. No one would know until I died in this case of course in front of everyone... D'oh~!
    A guess, the plane did break up due to the dynamic pressure when it yawed violently. Could also be a combination of dynamic pressure and inertial forces. We have discussed this video at least once before here on HBA, I’ll look and see if I find the thread

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    Re: Huge R/C Jet Structural Failure

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    Re: Huge R/C Jet Structural Failure

    I reviewed it too, and agree that the vertical fin looks like it went first. In many airframes, once the vertical fin goes, yaw stability is lost, airframe acccelerates in yaw and/pitch, and either the airplane departs controlled flight or breaks up or both. In this case, there was a lot of fuselage forward, stabilized by a lot of fin aft. When the fin departed, the now unbalanced nose forced big yaw/pitch accel, and then either the rotational accel or the nose angle or both produced failure level loads in the wings and forward fuselage. The nose may have partially failed, adding to the big pitch angle which failed the wings and canard. Spectacular. If the fuselage and wings stayed together, it likely would have spun and fell to Earth., like the XB70. Always catastrophic ...

    There are plenty of examples of both intact and breakups after loss of the fin, with the 2001 Airbus crash in New York and the XB70 crash being particularly famous. The B58 and SR71 are both noted for engine failure while supersonic being capable of causing airframe breakups.

    Billski

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    Registered User Jay Kempf's Avatar
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    Re: Huge R/C Jet Structural Failure

    Quote Originally Posted by wsimpso1 View Post
    I reviewed it too, and agree that the vertical fin looks like it went first. In many airframes, once the vertical fin goes, yaw stability is lost, airframe acccelerates in yaw and/pitch, and either the airplane departs controlled flight or breaks up or both. In this case, there was a lot of fuselage forward, stabilized by a lot of fin aft. When the fin departed, the now unbalanced nose forced big yaw/pitch accel, and then either the rotational accel or the nose angle or both produced failure level loads in the wings and forward fuselage. The nose may have partially failed, adding to the big pitch angle which failed the wings and canard. Spectacular. If the fuselage and wings stayed together, it likely would have spun and fell to Earth., like the XB70. Always catastrophic ...

    There are plenty of examples of both intact and breakups after loss of the fin, with the 2001 Airbus crash in New York and the XB70 crash being particularly famous. The B58 and SR71 are both noted for engine failure while supersonic being capable of causing airframe breakups.

    Billski
    Most model airplanes are so overbuilt for the task that they cannot be broken. This is probably a fine example of scale effects. The larger the airframe the harder it is to achieve high power to weights so the greater the attempt to save weight. This thing came literally "unglued" as it traveled forward. Certainly when the fin let go the reverse lawn dart throw came into play. Still can't believe how catastrophic, early and large chunks just breaking in half. Normally you lose a wing fold first or something and the fuselage stays intact. Still amazed that a guy would put tens of thousands into a model airplane. This one could have been approaching $100k depending on power plant and the level of servos required. It would be interesting to find a website on the construction of that plane to see if there were any fatal errors.

    Just found a basic construction photo. Shocker it is all plywood formers and looks like yards of balsa sheet. I stand completely corrected. Never seen anyone do that for 30 years on a large model. That would never survive.
    Last edited by Jay Kempf; January 11th, 2017 at 08:25 AM.
    Jay K.

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    Re: Huge R/C Jet Structural Failure

    Once the fin went, it pulled enough of the rear structure with it, that the whole tail fluttered off. Europeans love the extreme big models and are usually done by clubs over there . For a jet it flew like crap.

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    Re: Huge R/C Jet Structural Failure

    The wings appeared to flap a bit as it taxied on the grass, not too encouraging. The commentator was wittering on about an aviation certificate and how there were a lot of steps... There's no need for an ejection seat with a self dismantling plane, just a parachute needed. In fact, just attach the rip cord to the rear of the plane?

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    Re: Huge R/C Jet Structural Failure

    Quote Originally Posted by Jay Kempf View Post
    That would never survive.
    Q.E.D.

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