Polystyrene Flying TARDIS Rotor Craft.
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Pretty neat til' it crashes.
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https://www.rocketryforum.com/showthread.php?61166-Polystyrene-Flying-TARDIS-Rotor-Craft
As soon as I saw the multicopter rotor unit at the very TOP, I figured out what the likiely cause of the crash would be. Well, you mentioned it crashed ("spoilers"), so I was ready to figure out why.
Extremely nose-heavy, with lots and lots of "fin" area behind the CG. As long as they kept it vertical in calm wind, it could fly. But once it got too much sideways velocity to it, there would eventually be more side force to topple it over, than the rotor thrust differential could overcome. Now maybe they got away with it tilted a little for a while, but if they let it be tilted much to develop much sideways velocity, it would run out of control authority, and "lawn dart" or extreme weathercocking effect would take over.
Seeing the last few feet where it was nose-down at an angle, it seems that is exactly what happened, and no way could the rotor dfferential thrust ever make it point back "up".
Either it needed to have some dead tailweight added (performance hit), or have the rotor unit in the middle (appearance hit), so the CG and CP would be at the center.
Well, another way it could have been flown would have been a ducted fan or simply big prop inside, and add big control surfaces to the back (hinge the last 12-18" to be able ot move back and forth to pitch, yaw, and some roll control. But it would then need to fly like a big model airplane, mostly sideways, but the Tarids usually "flies" pointed upright (most of the time when near the ground, anyway). And even then it would be tricky (many years back, someone made a flying Snoopy's Dog House, looking like a doghouse but with the front and back ends missing so the air could flow thru, and apparently flew well, flew at many R/C plane airshows).
And of course it would not look right with parts of the lower Tardis sticking outwards or inwards for control surfaces.
Maybe four internal ducted fans with differential thrust, or internal vanes to deflect thrust from a BIG prop inside (with the extra complexity of preventing roll due to engine/prop torque).
Definitely something to test out in a small-scale crude foam model first. If the guys who did this big multirotor Tardis had tried small cheap prototype first, I'm sure they would have discovered the fatal flaw. At least if they kept pushing the flight envelope enough. Heck, all they needed for a crude prototype was to use an existing multicopter, and make a suitably sized "Tardis" our of cardboard or foam that would take less than 30 minutes to glue together, then some time to secure the Tardis to the bottom of the copter, and see what happened (main issue there being to risk a smaller relatively cheaper copter).
Not knowing any more abut it, I figure those guys were really good multicopter pilots, but may not know enough about aerodynamics and extreme nose-heaviness to realize the flaws and serious limitations. Or maybe they did know, but the pilot accidentally let it tilt too far anyway.
BTW - this effect is one of the big reasons the old LLRV/LLTV was so dangerous. Too much sideways airflow could make it get out of control. The one Neil Armstrong ejected from had problem battling the wind, causing him to use up all the thruster fuel, making it go out of control so he had to eject. Another crash was also partly due to aerodynamic side force effects.
https://en.wikipedia.org/wiki/Lunar_Landing_Research_Vehicle
As soon as I saw the multicopter rotor unit at the very TOP, I figured out what the likiely cause of the crash would be. Well, you mentioned it crashed ("spoilers"), so I was ready to figure out why.
Extremely nose-heavy, with lots and lots of "fin" area behind the CG. As long as they kept it vertical in calm wind, it could fly. But once it got too much sideways velocity to it, there would eventually be more side force to topple it over, than the rotor thrust differential could overcome. Now maybe they got away with it tilted a little for a while, but if they let it be tilted much to develop much sideways velocity, it would run out of control authority, and "lawn dart" or extreme weathercocking effect would take over.
Seeing the last few feet where it was nose-down at an angle, it seems that is exactly what happened, and no way could the rotor dfferential thrust ever make it point back "up".
Either it needed to have some dead tailweight added (performance hit), or have the rotor unit in the middle (appearance hit), so the CG and CP would be at the center.
Well, another way it could have been flown would have been a ducted fan or simply big prop inside, and add big control surfaces to the back (hinge the last 12-18" to be able ot move back and forth to pitch, yaw, and some roll control. But it would then need to fly like a big model airplane, mostly sideways, but the Tarids usually "flies" pointed upright (most of the time when near the ground, anyway). And even then it would be tricky (many years back, someone made a flying Snoopy's Dog House, looking like a doghouse but with the front and back ends missing so the air could flow thru, and apparently flew well, flew at many R/C plane airshows).
And of course it would not look right with parts of the lower Tardis sticking outwards or inwards for control surfaces.
Maybe four internal ducted fans with differential thrust, or internal vanes to deflect thrust from a BIG prop inside (with the extra complexity of preventing roll due to engine/prop torque).
Definitely something to test out in a small-scale crude foam model first. If the guys who did this big multirotor Tardis had tried small cheap prototype first, I'm sure they would have discovered the fatal flaw. At least if they kept pushing the flight envelope enough. Heck, all they needed for a crude prototype was to use an existing multicopter, and make a suitably sized "Tardis" our of cardboard or foam that would take less than 30 minutes to glue together, then some time to secure the Tardis to the bottom of the copter, and see what happened (main issue there being to risk a smaller relatively cheaper copter).
Not knowing any more abut it, I figure those guys were really good multicopter pilots, but may not know enough about aerodynamics and extreme nose-heaviness to realize the flaws and serious limitations. Or maybe they did know, but the pilot accidentally let it tilt too far anyway.
BTW - this effect is one of the big reasons the old LLRV/LLTV was so dangerous. Too much sideways airflow could make it get out of control. The one Neil Armstrong ejected from had problem battling the wind, causing him to use up all the thruster fuel, making it go out of control so he had to eject. Another crash was also partly due to aerodynamic side force effects.
https://en.wikipedia.org/wiki/Lunar_Landing_Research_Vehicle
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