Discussion in 'Aircraft & Aviation' started by Hans Christian, Apr 23, 2007.
Yep, the case of the Phantom: you can make a brick fly if it's got enough power.
Equally, if you lost all your power, a Phantom would fly EXACTLY like a brick...
The nearest equivalent I can think of are model rockets, powered by solid fuel rocket motors. They do have model rockets (often made out of card, but reincorced with glass fibre !) that go supersonic. They have quite large motors, and are very low drag designs. I.e. Thin bodies, small fins, and definitely no wings !!
All things considered, a speed at release of 100 kph for a slingshot launch of a paper airplane is entirely conceivable (how many of you remember the AJ Interceptor...might have been balsa, but wood is just card in its raw state). Since it has very little inertia with respect to drag forces, though, speed will bleed of quite rapidly. The number of factors entering the equation is horrendous, though....one needs to take into account the internal frictional forces, modulus of elasticity, drag, inertia, etc. of the rubber band as well as the airplane. It is extremely unlikely that a paper model would have enough strength to withstand the forces required to get it supersonic, though. If 100 ft of surgical tubing can develop enough force to shred a balsa glider, I shudder to think of what it would do to cardstock.
could always find a way for it to hitch a ride on a high velocity bullet...
wow... so many replies here!!! :-D
About vacuum, those measurements are actually taken "in field", meaning, I took them everytime I flew one on an open field, with mild breezes, so those results were taken with aerodynamic drag already in the conditions.
But yes, the biggest question would be whether or not it can resist being torn apart by shock waves IF it indeed reacesh Mach 1.
I construct those gliders using very stiff cardboard, and using CA glue for the entire assembly, also before it even catches air, I also squeeze CA glue to all of the edges of the plane to prevent crumpling when it dives to the ground, it was so good, in fact, that it can dart itself to the ground at over 100 kph without crumpling... This is also in part of the plane's rigid design, the nose, fiuselage and wings are at least double-layered during construction, and, in case of the nose, is 6-8 layers of very stiff cardboard, since it acts as the nose weight
also there's momentum, yup, those gliders are indeed light, but the momentum produced after leaving the catapult is so great that during some landing speeds, it can overtake a scooter going 30 kph...
and finally, there's drag. These planes, because there's no 3d shape involved in the parts, have a very thin aerodynamic profile, so basically, my catapult, if you will, can fling the glider to high speeds because it has almost zero drag to deal with...
"If you can reduce the profile and make something thin its gonna go fast"
- from a documentary from Discovery channel
well, this theory is only concerned whether a balsa or card glider can go supersonic the moment it leaves the catapult, whether or not it can sustain it in flight (or at all - after leaving the catapult) is out of the question (but that's just for me that is... :-D )...
in the end there are only 3 possibilities...
so, before I test this one for myself, is this theory worth exploring? :-D
Hmmmm.... we can do some simple calcs. Force = mass x accelleration.
Work out (estimate) the time the catapult is going to be acting on the glider. From this and the final speed of mach 1 you can work out the accelleration. Multiply this by the weight of the glider and you will find the force. Of course, this assumes zero drag, but it will give you an idea of whether the figures are plausible or busted.
You could also try downloading a trial copy of Rocksim, the rocket simulation software. Create a glider and see what engine power is needed, the burn time and height at burn out. This will give you an idea of the thrust of the catapult needed and the length of catapult. You may need to move the wings back down the fuselage, otherwise Rocksim will complain that the design is unstable and give erroneous results.
I do not doubt your measurements. My comment about the vacuum referred to your extrapolation to supersonic velocities.
and while these objects may have very low drag, as I recall, drag force increases as the 4th power of the velocity. And that does not account for what happens at trans-sonic velocities, which as I seem to recall used to regularly shred very sturdy metal aircraft, never mind paper aircraft.
100kph is 60mph, supersonic is 750mph more than 10 times as fast, drag would be 10,000 times as high.
Cardboard soaked in CA glue is no longer, in my opinion, a paper model, it is a composite material closer to fiberglass. And if you are going to do that, you'd probably be better off using an epoxy rather than CA. CA isn't really designed to set up in open air (even though it eventually does) it is really strongest as a near monolayer film between two smooth non-porous surfaces.
Model rockets: granted it has been a couple decades since I was into rocketry but back then only the tube was cardboard, nose cone and wings were balsa and solid, not hollow paper shells.
So, even with all that negativity, I'd love to be proven wrong. and I'd love to see the Mythbusters try it.
well, the gliders that I used to come up with this theory are the ones from the AS Paper Aircraft Lab (http://www.infosnow.ne.jp/~suzuki-a/) whict are designed mostly from supersonic fighter aircraft.
ok, for the estimates...
if the catapult would work on the plane for 2 seconds, I calculated it would need an acceleration rate from 0-765 mph of about 171 m/s(sq), and estimating that the weight of the glider is roughly 20-30 grams (0.02-0.03 kg), that would be around 3.42-5.13 N (newtons) of force...
please run another computation again, to verify this... :-D
Oh I see!!!
well for the CA, I usually add this on the edges only to prevent crumpling in case it lands in an "inconvenient way". But I'm really intrigued by the epoxy method... what kind of epoxy could be used for this?...
yup, with all of the facts that you posted, it seems clear that drag, and friction will be one of the biggest, if not the biggest hurdle for this theory to be confirmed correct.
and you mentioned that if I put some additives in cardboard, it could not pe considered as a plain card anaymore, but a form of composite material... Hmmm... I guess your'e right about that, since I also intend to spray some heat-resistant paint on these gliders...
I really hope the guys at M5 industries would look on this... :-D
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