This build thread of the Black CINCO saucer was of my doing. I added pictures and video along the way.
Near the end I also shared pictures of a tired white CINCO that I pushed to failure using a research motor, within the TRA Research guidelines. I posted the pictures in an attempt to dissuade someone from attempting a similar flight.
If Art has in fact discontinued production of his HPR saucers, that's unfortunate. BTW, I've had no contact with Art since the build.
His saucers are a great alternative to -traditional- rockets.
Kevin did a great job on the build thread, but when it devolved into a discussion on how the kit might be used in a very dangerous way I decided that enough was enough. The comments that were being made showed a lack of understanding of rocket science and more importantly, safety. This is not a new problem and if anything, I've been too slow to react. One of my 12 inch flying saucers was flown on a motor 4 times too big (J instead of H) at NSL2004 and it predictably shredded. I told the guy it would happen and he did it anyway. The motor landed in the spectator area. Fortunately no one was hurt but the potential for disaster was made very evident to me. I should have stopped making high power kits then but I let my ego get the better of me.
That's the history, now here's some practical rocket science: Any recoverable rocket that doesn't land on retro rockets, or wings uses some form of aerobrake recovery. Parachutes, streamers, and draggy airframes can all serve this purpose. When a conventional rocket gets heavier by using a bigger motor it's easy enough to increase the size of the parachute. You can't do this with design that depends on the airframe from recovery without substantial modifications. To keep descent rate constant, when increasing the weight, for a given Cd you have to increase the frontal area. To increase the frontal area you need more materials with can increase the weight faster than the area. You have to do this without increasing the total weight faster than you increase the area, which isn't as easy as it sounds using inexpensive materials.
All rockets are a compromise between performance, durability, safety and lightness. If you improve one, it's often at the expense of the others. For example, if you "glass the crap out of" a rocket, you improve its durability, but decrease its performance, lightness and most importantly, its safety(during descent and landing). For kit makers cost of materials and easy of assembly are part of the mix but safety trumps everything.
When I design my kits, I consider safety above all else. I consider a reasonably slow descent rate an important part of a safe flight. I strive for a descent rate of between 20 fps and 30 fps when I start a design. I make a descent rate calculation based on the expected Coefficient of Drag (Cd) and the maximum weight of the motor and rocket to determine the necessary frontal area (diameter). To keep the descent rate constant, any additional weight such as a heavier motor, more fiberglass, etc has to be compensated for by an increase in diameter. Also an increase in diameter requires more motor power to keep it flying straight. This leads to a reiterate process that sometimes results in no workable solution. 90% of my prototypes don't make the cut.
In the real world, safety and liability are two sides of the same coin. I believe that any manufacturer that knowing makes an unsafe product should be held accountable. My own personal moral code does not allow me to sell kits that can be expected to injury of another person through their unsafe use.
Rather than quit making kits completely, I've decided to draw the line at 29 mm. Above that size, the impulse range of available motors is too wide for a given diameter to limit what fits into an airframe that's open at the end. Also the potential for mayhem goes up much faster above 29 mm. The recent practice of using over-sized casing and spacers in high power reloadable motors has exacerbated the issue. What would have been an acceptable descent rate with the correct casing becomes unacceptable because of the additional weight of an over-sized casing and spacers. For many conventional rockets the motor usually weights less than airframe. This is not true for most of my kits. This means a heavier motor in one of my saucers causes a disproportionately bigger increase in the total weight(and descent rate) of the rocket.
I'm not happy about any of the this but I've learned that you can't fight either "Mother" or "Human" nature.
Art Applewhite
www.artapplewhite.com
