Building more crash-worthy composite planes and cockpits

Discussion in 'Composites' started by RSD, Sep 29, 2019.

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  1. Nov 10, 2019 #61

    litespeed

    litespeed

    litespeed

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    Winginitt,

    I think others have made it abundantly clear-

    This is about secondary safety, not primary. Primary safety is a given for this conversation.

    If you have nothing to add about making a aircraft safer in a actual crash- please desist.

    You are only going over rehashed ideas and stopping others from contributing and gaining some useful knowledge.

    Forum members often stay back from commenting, when they feel others are pushing a agenda that is not on topic.

    This is beyond thread drift.

    If you wish to push your view - start a thread on your topic.

    This is a community forum- not a platform to shout your ideas.

    This is a friendly reminder, please accept it.

    Moderators /staff may be less polite.
     
  2. Nov 10, 2019 #62

    BJC

    BJC

    BJC

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    I had the exact, same, recurring dream for several months ... trapped in the airplane under water, unable to release the restraint system.


    BJC
     
  3. Nov 11, 2019 #63

    Winginitt

    Winginitt

    Winginitt

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    ( If the OP feels that the information I have posted is not helpful or of any interest to him, he needs to PM me and I will gladly respect his wishes. I don't think its your place to decide what may/may not be useful to him or other builders.)


    Exerpts from " Small Airplane Crashworthiness Design Guide"
    6.5.1.5 Energy-Absorbing Capacity of Forward Fuselage In consideration of the conservation of energy, the initial kinetic energy of an impacting aircraft must be accounted for in energy dissipated during the deformation of both soil and structure. The designer will realize that energy not absorbed by the ground will be absorbed by the aircraft’s crush zone, other areas of the aircraft structure, or in the cabin (occupied space). The goal is to avoid absorbing energy in the cabin (Uc in the following equation) and dissipate it or absorb it all in the crush zone and other parts of the fuselage. As a simplified model, the energy absorbed by the cabin can be expressed as: (6-15) where: UC = energy to be absorbed in cabin deformation. MA = mass of the aircraft vo & vf = initial and final velocity of the aircraft UG = energy absorbed in ground friction and earth plowing Pav = average force developed in the collapse of crush zone ahead of the cabin S = linear deformation (reduction in length) of the crush zone U’S = deformation energy in structure other than in the cabin or the crush zone.


    Formula 001.jpg


    where: UC = energy to be absorbed in cabin deformation. MA = mass of the aircraft vo & vf = initial and final velocity of the aircraft UG = energy absorbed in ground friction and earth plowing Pav = average force developed in the collapse of crush zone ahead of the cabin S = linear deformation (reduction in length) of the crush zone U’S = deformation energy in structure other than in the cabin or the crush zone

    For the following reasons, several ACG members believed that 71 kts was too high for a design and test impact condition. (OP is proposing 90 mph)

    Finally, there was a precedence of using stall speed (my suggestion is to design for mitigating stall speed as much as feasible)

    noted that the impact speed range checked in the NTSB accident report contained or was just above the airplane’s published stall speed. As a consequence, the ACG chose Vso (stall speed) at the MTOW. (NTSB says stall speed and accident speed are usually close unless plane actually stalls, then forces become uncalcuble)

    Winginitt: If you notice, all calculations originate from the speed/velocity of the airplane and its occupants .


    (which is the result of the velocity)

    (To me, that says he is open to any suggestions, not just encapusulating )

    If you check back you will find that I have offered suggestions about restraints, fuel tanks,air bags,seat dampening and foam support,fuel shut off, quick release belts, as well as suggestions about keeping the airplane controllable to a slower stall speed by employing fences, spoilers, and Hoerner wing tips. If you read any of the "Small Airplane Crashworthiness Design Guide" you will quickly see that they say a major problem with any safety design is that loss of control results in a subsequent change in the angle of attack......and all calculations become moot !
    In simple terms, it doesn't matter how much calculation and technology a builder uses if they can't keep control of the angle of attack....ie; stall/spin.

    So since the OP is designing a new airplane from scratch and says he wants to incorporate as many safety features into the design as possible, I don't think its redundant to say that I think the singular most important thing he can do is find the best way to retain control of the airplane until it is flying as slow as possible and as near to the ground as possible. Those two things will be the starting point for all other calculations. The "Small Airplane Crashworthiness Design Guide" says:
    in the 1967 Crash Survival Design Guide (Reference 3-7) required calculating the longitudinal and vertical changes in velocities from the average impact conditions of 71 kts and 31 deg.

    The OP says he is thinking 90mph . My suggestion is that he attempt to build features that are effective at 90mph but try to design for scrubbing speed to a lesser standard.


    Having said all that, if the OP feels that what I have been posting is not relevent or helpful to him, he should PM me and let me know. I will respect his wishes..........
     
  4. Nov 11, 2019 #64

    RSD

    RSD

    RSD

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    Winginitt - I'm the OP and unfortunately you are broadening this topic more than what I was wanting which means that we are losing the focussed detail that I was wanting. If we can now get back to the original topic that would be appreciated.
     
    BoKu likes this.
  5. Nov 11, 2019 #65

    Winginitt

    Winginitt

    Winginitt

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    Ok, sorry my info wasn't what you wanted.
     

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