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Personal Jet Pack for X-mas!
teamhasnoi writes "This guy has spent mucho time and money building a ducted fan 'jet pack'. No faking for this guy, it looks like there is some real technology there. Now he just needs a sponsor."
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Here's the Google cache link in case this gets /.'ed.
It seemed like from the design that the heat goes out the back, not down. The turbine is used to drive a fan. The turbine will fire out around the bottom perimeter of the fan, and the fan blows just air downward.
Note that this is on a passenger-mile basis. The plane itself is obviously not getting 40 mpg.
But then again, I could be wrong.
I visited the Smithsonian Air & Space museum about 2 years ago, and noticed a cool device that was, I believe, based on an engine built by the Williams company.
(Williams makes some very small turbojet engines, famously for use in cruise missiles)
If I remember correctly, the Jetpack was a very Buck Rogers-looking device, with considerably greater endurance than the Bell Rocketbelt. Unlike the Rocketbelt with its' flight time of ~30 seconds (depending on which model you get your hands on); the Jetpack had a flight time of about 7 minutes, and featured a helmet shaker that would get your attention when you were about to run out of fuel.
(I want to say the Smithsonian display claimed a flight time of 30 minutes...)
So there's the problem... we can easily build an engine -- turbofan or rocket -- that'll lift itself, some fuel, and a person -- it just can't lift very much fuel, and these engines (or rockets) are thirsty!!
I can't seem to find much mention of the Jetpack on the Air & Space site, so here's what I can find:
- www.flying-contraptions.com
- "The WASP (Williams Aerial Survey Platform) had a jet engine on the bottom; a single occupant essentially stood on the fuel tank. Williams International, in Walled Lake, Michigan, makes little fanjet engines for cruise missiles, which were ideal for one-man jet belts. Bell worked with them on a jet belt with 7-minute endurance, which first flew on 7 April 1969. Later Williams developed the WASP, later renamed the "X-JET", which looked like a pilot standing in a garbage can. The 600-pound turbofan was mounted in front of the pilot, and the WASP could stay airborne for 30 minutes, reach speeds of 60 mph, and land in a four-square-foot area. It is unknown where the project stands today. It was a contract with the Army Tank Automotive Command. "
- Smithsonian Air & Space Museum page about the Bell Rocketbelt
- "However, despite the belt's apparent popularity, it turned out to be a commercial failure, mainly due to its limited use because of its short duration use. The Army's higher priority of missile development also contributed toward the loss of Army interest. The Army, and also Marine Corps which had considered the belt, did not adopt it and Bell no longer became sought its further development. In January, 1970, a license to sell and manufacture the Bell Jet Belt was granted by Bell Aerospace Textron to Williams International (formerly Williams Research Corp.) of Walled Lake, Michigan. Williams went onto to develop an improved, longer-duration jet-powered version of the belt."
- Page mostly about the Bell Rocketbelt, but attributes a turbojet-based belt to them as well
- This site seems to confirm my "30 minute flight time" recollection -- but the quote is "...an endurance of up to 26 minutes was anticipated", which would seem to say it was never achieved.
- Here's another (similar) picture, but the site it links to is a 404.
All that said, this thing looks interesting. High-bypass turbofan, ducting similar to an AV-8(A|B) Harrier, carbon fiber for light weight... I want to see video of it flying!"...America's great minds of today, teaching America's great minds of tomorrow. Poor bastards." -- A Beautiful Min
The funny curve at the inlet of the compressor means that it is a hybrid between an axial and a centifugal compressor. Centrifugal compressors work better for low flow rates and can operate with a zero flow rate (that is with the inlet blocked) without a huge increase in the amount of torque required to drive it. Axial flow compressors can handle higher flow rates (like the turbofans on airliners) but are susceptible to compressor surge (try google) where the blades of the compressor stall at the wrong combination of flow rate and rpm.
Maybe a simpler way of explaining is to compare the compressor vanes to the leading edge of an airplane wing. The blades are cambered so that the leading edges are aligned with the oncoming air at the flow rates and rotor rpm that the engineers designed the compressor for. This will minimise separation on the thin compressor blades to keep the efficiency of the compressor as high as possible.
As for your hybrid car, the generator on your turbine might have (for the sake of argument), say, 80% efficiency, and the electric motors will convert electric power to mechanical power at about the same efficiency. This gives you about 64% of the power at the road that you would get from a direct driveshaft. That's why you don't see that arrangement too often.
One other thing, IIRC, Noel Penny Turbines, or someone associated with them, made some gas turbine powered cars, and I seem to remember something about Rover being involved too. As the saying goes, Google is your friend.