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Jet-Man Yves Rossy: Best Engine,etc?

  1. May 19, 2008 #1
    So by now, everybody's probably seen the news and videos of Yves Rossy, the Swiss pilot, jetting around over the Alps with wings strapped to his back, and 4 mini-turbojet engines attached to those wings. The entire apparatus is said to weigh 120 lbs.

    Each of his 4 engines is a JetCat P200, with specs as follows:

    Thrust at full power 50 Lbs / 220N
    Weight incl starter 4.8 Lbs / 2.2Kg
    Diameter 5.1 inches / 130mm
    RPM Range 33,000 - 110,000
    Exhaust temp 670C
    Fuel consumption 25.37 oz min at full power
    Fuel Jet Al, 1-k kerosene
    Lubrication 5% oil mixed in fuel
    Maintenance interval 50 hours


    But apparently his flight only lasted 5 - 10 minutes, due to fuel constraints.
    I was wondering how this might be improved upon.

    I was reading that turbofan engines typically offer superior fuel efficiency over turbojets, as well as quieter operation. Also, Yves had to wear thermal protection because of the heat from the jet exhaust, and hopefully turbofan exhaust is less hot. Another thing is that a turbofan could perhaps reverse thrust by flipping the blade angle, allowing aerobraking for landing without a chute.
    But how do they fare on thrust-to-weight ratio?

    I hunted around the next for the smallest turbofan engines I could find. One site I found was this one:

    http://cpl.usc.edu/eschuste/

    The other I found was this one:

    http://www.globalsecurity.org/military/systems/aircraft/systems/f107.htm

    So the smaller engine out of those two turbofans seems to have a higher thrust-to-weight ratio (granted, the first one isn't a military-certified product)

    Suppose we assume that a 2-engine setup is the most desirable, so that if one fails then you still have the remaining one to fly with.
    Then what would be the best type of engines for our winged man?

    I'm thinking that you'd want each engine to be capable of generating 100 - 120 lbs of thrust, with a max weight of 10 lbs each. Is that doable for a turbofan?
     
    Last edited: May 19, 2008
  2. jcsd
  3. May 19, 2008 #2
    It's been awhile since I've studied the subject, so don't take 100% of what I say to be valid.

    JetCats, from what I know, are reasonably popular engines for RC aircraft, and thus have lots of hours on them, and I've heard of just about every variety of engines made by them except for turbofans. They make turboprops, helicopter setups, etc. but I don't know of a turbofan in production.

    It might be possible to make an engine with that weight and thrust, but the design will have to be different. I was trying to imagine what would be so much different between the turbojet and the turbofan and why you don't see RC turbofans as much...I just realized it must be because of the vast difference in diameter of the compressor/turbine components and the fan components. If everything turns at the same RPM, your fan sections is going to have much higher stresses on it. To get around this, you'd need some kind of gearing system, which drops your efficiency a little, and adds more components and complexity. These little puppies are spinning sometimes faster than 100,000 RPM, and I'm unsure how close they are pushing the limits of the materials, and if they are using exotic stuff or not.
     
  4. May 19, 2008 #3
    To add to that, I wonder if you could take their turboprop set up, change the gearing, and drive a ducted fan with it. I don't know if you'd gain much from that modification or not.
     
  5. May 19, 2008 #4
    I was thinking that with 4 engines, it'd be best to give them a 4-cornered layout:

    x x​
    ---------------
    x x​

    whereas with 3 engines you'd give them a triangular layout:

    x​
    ----------------
    x x​


    Either of these layouts would enable the jet-wing to stably stand on end, to enable VTOL.

    But I'd imagine that the 4-cornered layout would be better, since if one fails, then at least you have the remaining 3 to keep you stable for VTOL.

    You'd of course need electronics to rapidly adjust the engine outputs to maintain balance and stability in VTOL.
     
    Last edited: May 19, 2008
  6. May 20, 2008 #5

    FredGarvin

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    Science Advisor

    The limitation is not in the engine. It's in the fuel capacity. You are talking about huge issues with making a larger bypass ratio turbofan that small (trust me, I work with small engines). To keep the size manageable, you would need to shrink the core components. You reach a ton of limiting factors very quickly, namely blade tip clearances and bearing problems. Besides, the efficiency gains you would get probably wouldn't be measurable at that scale and you will not cool the exhaust gases appreciably. There are just some aspects you can't get around.

    If you think you have fuel concerns now, you might as well forget an F107. Their 160+ pounds and we run them on JP-10. The average joe can not buy JP-10. Also, strapping two F107's to your body would probably tear you apart and they would be so heavy, the basic premise that Yves is operating under would no longer apply.

    He needs to examine better ways to carry fuel. That's where the current technology makes you look.
     
  7. May 20, 2008 #6
    Hi, I just mentioned the F107 for reference. Clearly its thrust and weight are overkill. But I'd point out that the sports industry has often used cutting-edge technology to deliver leading-edge performance that people are willing to pay a pretty penny for.

    If someone can just establish a basic platform to get the foot in the door and establish a market, then the leisure/hobbyist world will come running, and their money will drive the innovation and evolution of the platform.

    Don't underestimate the power of male teenage hormones to move massive mountains of money -- look at internet porn and GTA-IV. Think of this jet-wing thing as the next GTA-IV.
     
    Last edited: May 20, 2008
  8. May 21, 2008 #7

    NateTG

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    Science Advisor
    Homework Helper

    In the US the whole FAR 103 thing massively favors stuff that can't go more than 45 knots, which also makes for easier fuel economy and range.

    Beyond that, pulse jets may be practical for an application like that since they're light, simple, and cheap.
     
  9. May 21, 2008 #8

    minger

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    Science Advisor

    The difference between turbojets and turbofans are bypass flow. In a turbojet engine, all of the flow is directed through the combustion area. In a turbofan, a portion of the flow is directed around the combustion area.

    http://www.grc.nasa.gov/WWW/K-12/airplane/aturbf.html
    And agreed with Fred (as usual). You can get fuel economy close to a turboprop by having large bypass ratios, which is way too difficult on a small jet like that.
     
  10. May 21, 2008 #9
    Here's an article:

    http://machinedesign.com/ContentItem/61407/TomThumbturbinespowerradiocontrolledjets.aspx

    Since the F107 and PW610 are each about 12" (30cm) in diameter, then why is it outrageous to consider a turbofan with half that diameter? 6" (15cm) would be a reasonable size for personal-sized wing.
     
    Last edited: May 21, 2008
  11. May 21, 2008 #10
  12. May 21, 2008 #11
    What about a small-sized version of the geared turbofan?

    http://frontierindia.net/geared-turbofan-engine-demonstrates-alternative-fuel-capabilities

     
  13. May 21, 2008 #12
    Here's a nice article from latest May2008 edition of Mechanical Engineering Magazine:

    Just read this and drool:

     
    Last edited: May 21, 2008
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