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Thread: Shrouded prop for static lift?

  1. #31
    Registered User BBerson's Avatar
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    Re: Shrouded prop for static lift?

    Quote Originally Posted by leviterande View Post

    but i didnt get you, you mean you want to have a central liftfan in a cruize airplane where it has a standard propeller at the front. unless you want to tilt the central lift fan it will be HUGE dead weight in cruize or maybe you could have a small sketch to show us?

    kalle
    A dead weight yes. But what is the alternative?
    A VTOL requires a 1 to 1 thrust/weight ratio or more.
    A normal airplane requires a 1 to 4 ratio while climbing and just 1 to 10 for slow cruise at best L/D.
    It would be inefficient to run the large lift engine for slow cruise.

    The high speed military VTOL airplanes need about 1 to 1 thrust for cruise, so it makes sense to use the same engine for lift and cruise.
    Transport VTOL (see Dornier DO 31) designs usually have separate lift engines for takeoff and landing and yes they are just dead weight in cruise.
    I am working on direct lift for the low speed range only, not interested in high speed.
    So there is no need to tilt the lift system for cruise. Some tilt for takeoff or landing is desirable however.

  2. #32
    Registered User leviterande's Avatar
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    Re: Shrouded prop for static lift?

    why not tilt the lift fan ? so you would have a propeller running and a lift fanthat is tilted forward to compensate the deadweight?


    Kalle

  3. #33
    Registered User BBerson's Avatar
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    Re: Shrouded prop for static lift?

    Most of the crashes with military VTOL are in the transition. A tilting device might take a minute or so to activate... too slow in a go around or some other emergency.
    Also, a prop lift system designed for static thrust is not ideal for high speed propulsion.
    BB

    p.s. I recommend the book: VTOL Military Research Aircraft by Mike Rogers 1989, used from amazon.com or other book sellers.

  4. #34
    Moderator Topaz's Avatar
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    Re: Shrouded prop for static lift?

    Another good resource is Introduction to V/STOL Airplanes by David Kohlman. Iowa State University Press, 1981.
    "If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them." - Henry David Thoreau

    Design Project: Conceptual Design of an "Inexpensive" Single-Seat Motorglider
    Discussion Thread for the Project: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

  5. #35
    Registered User leviterande's Avatar
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    Re: Shrouded prop for static lift?

    hehe, BB, is that you:
    shrouded prop for improved static thrust - PPRuNe Forums

    I was doing reasearch for bellmouth when i found that and recognize the topic!

    if we imagine a rotor inside a huge bellmouth, the thrust will be dramatic!

    Kalle

  6. #36
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    Re: Shrouded prop for static lift?

    Quote Originally Posted by leviterande View Post
    hehe, BB, is that you:
    q
    Kalle
    Yep, I sometimes stumble upon my own comments also while doing Google searches.
    Mr. Lappos and others have confirmed that increased thrust with a shroud is possible. I need to see it myself before I believe it. At this point, I am not sure if a shroud is better than a larger rotor and gear drive. Each would have advantages, and I am not sure if a shroud would help on a large rotor.
    BB

  7. #37
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    Re: Shrouded prop for static lift?

    Static lift with a shrouded or ducted prop?

    It's been done, but you may be surprised at what it looks like. I bought the videos and seeing it in flight, lifting off the ground while tied to a windsock pole, the sock hanging limp, is an eye opener.

    Custer Channelwing: The Facts

  8. #38
    Registered User leviterande's Avatar
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    Re: Shrouded prop for static lift?

    Quote Originally Posted by freedive57 View Post
    Static lift with a shrouded or ducted prop?

    It's been done, but you may be surprised at what it looks like. I bought the videos and seeing it in flight, lifting off the ground while tied to a windsock pole, the sock hanging limp, is an eye opener.

    Custer Channelwing: The Facts

    Very interesting that you saw the video of it, the whole custer channel thing is extremely controversal, one side say that it add high ift plus forward thrust as you can read in the website and other say that it only bends the airflow down which simply mean that dont get that up lift as meant by custer.
    personally , custers design and the claims are ...well too good to seem to be good cuz you deal with both thrust and lift at the same time!! something is wrong it seems

    Kalle

  9. #39
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    Re: Shrouded prop for static lift?

    I know I'm about 2 years late to jump into this thread, but I just discovered it this morning. I have designed, built, and flown numerous shrouded prop aircraft; both VTOL and conventional pusher configurations (see attached photo). Generally speaking, on a normally sized free prop you should expect to get 4-5 lb/hp of static thrust. With a similarly sized shrouded prop, you should expect to get 7-8 lb/hp. The important thing to remember is that the prop and shroud are a unit, designed to work together. The pitch distribution of a shrouded prop is unlike that of a free prop. If you just put a free prop in a shroud, you won't see the advantages you're looking for. Shrouded props I've worked with exhibit higher thrust out to over 200 knots. On top of that, they make only half the noise of a free prop (but if you screw up the lip shape, they can be twice as loud). It's not a simple task to design a good shrouded prop, that's why we've developed our own CFD code to help out.
    Attached Thumbnails Attached Thumbnails Shrouded prop for static lift?-cruise031605.jpg  

  10. #40
    Registered User BBerson's Avatar
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    Re: Shrouded prop for static lift?

    Welcome to the forum flyboy51. It's never too late.
    Is that photo the "Solotrek"?
    I don't see any expansion duct in the photo, are those ducts optimized for static thrust?

    The electric systems are getting lighter every day, I might need to get back into experimenting with liftfans.

    thanks flyboy51, please post some video or other data if you can. (we shun patents and secrets here)
    Bill

  11. #41
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    Re: Shrouded prop for static lift?

    Quote Originally Posted by flyboy51 View Post
    I know I'm about 2 years late to jump into this thread, but I just discovered it this morning. I have designed, built, and flown numerous shrouded prop aircraft; both VTOL and conventional pusher configurations (see attached photo). Generally speaking, on a normally sized free prop you should expect to get 4-5 lb/hp of static thrust. With a similarly sized shrouded prop, you should expect to get 7-8 lb/hp. The important thing to remember is that the prop and shroud are a unit, designed to work together. The pitch distribution of a shrouded prop is unlike that of a free prop. If you just put a free prop in a shroud, you won't see the advantages you're looking for. Shrouded props I've worked with exhibit higher thrust out to over 200 knots. On top of that, they make only half the noise of a free prop (but if you screw up the lip shape, they can be twice as loud). It's not a simple task to design a good shrouded prop, that's why we've developed our own CFD code to help out.
    Hi flyboy51.Great to see an actual machine in the air !You may also be familiar with Glenn Martins machine?Very similar in design to yours.He is here in New Zealand also where I am.Many years ago, I built a Benson Gyrocopter with 20 ft. rotor.I also fabricated the rotor myself.I am now considering building a VTOL similar to the VZ-8 built back in the '60s - see numerous entries on the net.What I envisage are two 8 ft. diameter props in shrouds. One in the front and one in the rear.8 ft. is very similar in diameter to the VZ-8 props.The craft would be for two people.The VZ-8 used three blade props but any further specs on the props I have been unable to obtain.Could you suggest typical rpm, horsepower and expected lift of props?I also don't know what is the best pitch.What companies could you suggest that could give me a quote on these props?I am not looking for a racing machine and would be quite happy to cruise over the countryside at 50 mph.

  12. #42
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    Re: Shrouded prop for static lift?

    Here is a video update of the Martin Jetpack.

    El Martin Jetpack volando a 5.000 pies de altura | Avión Microsiervos

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