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The Truth About New Jet Pack Hype
An anonymous reader writes "This week a sub-$100,000 rocket belt was unveiled and will be on sale this summer, but that's the sad thing: it's still not a real jet pack. Here's a fascinating inside look at the human-flight industry, full of law-suit scandals, technical difficulties, fuel-economy woes and endless delays. The good news? It all points to the next generation of rocketeer research, with real applications for medical rescue and military technology actually coming on the horizon. From the article: 'With a little patience, and a little funding, we could actually have the pleasure of grumbling over regulatory issues we never dreamed possible. Like being limited to specific kinds of air strips, because the jet strapped to your back is classified by the FAA as an ultralight. Or being required to wear a ballistic parachute, because Amarena's Thunderjet design could reach altitudes as high as 10,000 feet (and, for the record, speeds of up to 160 mph, provided someone can solve wind-resistance issues).'"
Sounds like a jet pack to me.
If you want news from today, you have to come back tomorrow.
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Internal combustion engines can be muffled with only minor losses of power output, for the noise comes out of one place ( the exhaust manifold ) and the power comes out in a second place ( the drive shaft ). But a jet pack, the power and the noise both come from the same place, and it is difficult to cut noise without substantially cutting power.
Furthermore, the most successful noise-limiting devices on any jet - I'm thinking passby fans on turbines - adds a great deal of weight. On a jetliner this can work, but on a jetpack adding lots of weight will render it useless. ( Remember, the power-to-weight ratio for a modern jetliner is less than 10% of the power-to-weight ratio of a jetpack. )
Wait, sorry -- I found it:
all models on the verge of availability are, in fact, jet-free and called, officially, rocket belts.
OK, I guess that's technically right. But is that really a "sad thing" that makes any real difference, or just splitting hairs? I'll take any kind of personally-mounted flying device without bitching about the technical means of propulsion.
everything in moderation
A rocket belt needs to carry its own oxidizer and reaction mass. A jetpack gets the oxidizer and reaction mass from the atmosphere. The difference in fuel economy is incredible.
Another difference is that a jetpack is regulated as an aircraft (specifically, an ultralight). A rocket belt is unregulated.
"They redundantly repeated themselves over and over again incessantly without end ad infinitum" -- ibid.
Short answer -- a jet uses outside air as the oxidizer. A rocket carries an oxidizer with it. These devices carry H2O2 in a tank to use as an oxidizer. Therefore, this is a rocket pack, not a jet pack.
I suspect they are using rockets rather than jets because a jet requires a series of turbines to compress the air for combustion, but the (liquid) fuel and oxidizer are pumped into the rocket engine, making the rocket engines simpler and lighter.
MCSE? No, sir...I don't do Windows. Yes, I am an idealist. What's your point?
Decreasing jet noise is in fact very difficult, but it is also a major area of research in mechanical engineering departments across the country.
No, unfortunately this massive research thrust isn't aimed at making jet packs more practical, but rest assured, gains in reducing aircraft jet noise could be applied to jet packs.
The noise a jet makes is the result of turbulent mixing of the high speed jet with the low speed surrounding air. Some solutions are simple, like the chevron edges on the Boeing 787 others are a bit more complicated involving heating, cooling, or electrically charging the exiting jet. The goal being always to make the mixing of the jet and surrounding air less turbulent. Suffice to say you're not likely to have a picnic next to an operating jet engine anytime soon, but it is an active area of research.