+ Reply to Thread
Page 1 of 2 12 LastLast
Results 1 to 15 of 22
Like Tree1Likes

Thread: Track distributive prop

  1. #1
    Registered User
    Join Date
    Apr 2012
    Location
    Portland, Oregon
    Posts
    5

    Track distributive prop

    Is it possible to design a propeller such that the blades follow a race track between two shafts separated by the length of a wing? In this way, the prop wash would be distributed evenly across the surface of the wing. The opposite side wing would have the same arrangement turning in the opposite direction to counter the gyro and torquing forces. This distributed prop wash could assist in low speed take off by generating lift from ground-speed zero.
    Thanks
    Gleitsma

  2. #2
    Registered User Jan Carlsson's Avatar
    Join Date
    Jan 2009
    Location
    Sweden
    Posts
    1,463

    Re: Track distributive prop

    I am not sure I understand it correclt, but it sounds complicated.
    Jan.

    A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away. Antoine de Saint-Exupery
    "Flight by machines heavier than air is unpractical and insignificant, if not utterly impossible." Simon Newcomb, 1902

  3. #3
    Registered User timberwolf8199's Avatar
    Join Date
    Sep 2011
    Location
    Grand Rapids area, MI, USA
    Posts
    210

    Re: Track distributive prop

    Like a conveyor belt mounted in the wing with a propeller blade attached to it that cycles from root to tip and back?

    If so, way too complicated to ever be feasible from either a physical or monetary standpoint. I see structural challenges, mechanical losses, aerodynamic inconsistencies,....
    Last edited by timberwolf8199; April 3rd, 2012 at 08:15 AM.

  4. #4
    Registered User Jay Kempf's Avatar
    Join Date
    Apr 2009
    Location
    Warren, VT USA
    Posts
    2,304

    Re: Track distributive prop

    The great thing about a prop shaft is that it's forces are symmetrically distributed around the shaft in 3D. Wouldn't be true with a tank track with props sticking out of it. Imagine the blades going around the end of the track. Yikes. It would have to be really wide to distribute the loads meaning very heavy and with some pretty sophisticated bearing arrangements to afix it to the track itself.

    Take a look at the shell delivery system on the the Vulcan Minigun or the A6 cannon. Those are tracked delivery systems. YIKES! the amount of money and precision machining and casting required plus the life of the components. That is probably less complex than you are talking about. The life of some of those components is measured in minutes, not hours.
    Jay K.

    VT USA

  5. #5
    Registered User
    Join Date
    Apr 2012
    Location
    Portland, Oregon
    Posts
    5

    Re: Track distributive prop

    Thanks for the reply. Let me try to describe my question a little differently. I am not appreciating the complexity. Imagine 2 engines on a wing (ie a 4 engine aircraft). Using the 2 prop shafts...connect them with a belt (one could just be passive and one powered for that matter) and mount the props on the belt. Rather than a small stream of prop wash relative to the length of the wing, you would distribute the airstream from the prop belt along a relatively large portion of the wing. So my question is, does this yield additional lift to the wing over and above just increasing airspeed? You could imagine the same idea working on a twin engine boat...
    Gleitsma

  6. #6
    Registered User timberwolf8199's Avatar
    Join Date
    Sep 2011
    Location
    Grand Rapids area, MI, USA
    Posts
    210

    Re: Track distributive prop

    the prop design for a blade that travels in a straight line would be like that of a wing. A prop blade that travels in a circle is twisted like you see in a normal prop. Efficiency in one will mean inefficiency in the other.

    The inertial forces on the belt of a blade going around at high speed would be exceedingly high and very likely impossible for a belt to handle.

    there's no point in having two engines as they would have to be synchronized in order to both contribute power.

    The structure necessary to maintain alignment and squareness of two shafts/shivs/pulleys is more than you would want to incorporate.

    Bearings (regular rotating prop) are very efficient. Belts sliding in a track (proposed translating prop) are not. So you would have excessive mechanical losses.

    These are just a few difficulties that come to mind right away. The losses here would be more than enough to offset any gain from distributed prop wash. You'd be better off putting four standard propellers.

  7. #7
    Registered User Jay Kempf's Avatar
    Join Date
    Apr 2009
    Location
    Warren, VT USA
    Posts
    2,304

    Re: Track distributive prop

    Quote Originally Posted by gleitsma View Post
    Thanks for the reply. Let me try to describe my question a little differently. I am not appreciating the complexity. Imagine 2 engines on a wing (ie a 4 engine aircraft). Using the 2 prop shafts...connect them with a belt (one could just be passive and one powered for that matter) and mount the props on the belt. Rather than a small stream of prop wash relative to the length of the wing, you would distribute the airstream from the prop belt along a relatively large portion of the wing. So my question is, does this yield additional lift to the wing over and above just increasing airspeed? You could imagine the same idea working on a twin engine boat...
    Gleitsma
    If you force the same velocity of air over both the top and bottom of the wing directly behind a air thruster you may negate any benefits of the contribution of pressure differentials that create lift. If you increase the local velocity and turbulence over the wing in most flight regimes you will just increase drag.

    In short there are no benefits to doing this. You will get worse performance and more complexity and weight. That is unless you are designing into some loophole that has yet been discovered in aviation history.

    What is your goal? Designing something novel just to design something novel without some target or goal is just swinging swords at windmills. It's an activity but it doesn't do anything. If you are looking for some increase in lift or increase in speed of the overall airframe using this new technique you describe then you are going in the wrong direction. And that is regardless of the mechanical complexity you are ignoring.

    Props are about getting the most thrust for the amount of input power. That means that blade area, disc loading or whatever math model you would like to use plus an efficiency factor are what drives the analysis comparing one setup to another. Wings are well known quantities where velocity, lift, drag, AoA, and other variables are used to compare one configuration to the other. So you could spend some time learning about those things and build yourself a spreadsheet to compare configurations. But in the end everything you suggest looking into makes worse performance to known even less than state of the art.
    Jay K.

    VT USA

  8. #8
    Registered User bmcj's Avatar
    Join Date
    Apr 2007
    Location
    Fresno, California
    Posts
    7,162

    Re: Track distributive prop

    Timberwolf nailed the major problems faced by the system as proposed. Much of a prop's efficiency comes from the high RPM at which you can run them (short of running the tips at transonic speeds). I doubt you could make a belt system that could run at those blade speeds without structural, stability, vibrational, and power loss issues.

    The beauty of a propeller is that you can simply turn it faster (up to a point), add blades, increase the diameter (which adds more blade area at that premium high velocity region), or add power and pitch.

  9. #9
    Moderator Dana's Avatar
    Join Date
    Apr 2007
    Posts
    5,273

    Re: Track distributive prop

    Mechanically, forget about it. Consider this: at the instant when the blade reaches the pulley or sprocket at the end, its angular momentum goes from zero to whatever it is going around the pulley, instantly. Infinite acceleration means infinite loading (well, really it means things bending or breaking). So now the blades have to be mounted with some kind of flex coupling, and they're whipping around all over the place... my head hurts just thinking about the problems, and I design indexing conveyors (timing belts with stuff attached to them) for a living.

    -Dana

    Drink wet cement, and get completely stoned!

  10. #10
    Registered User Jay Kempf's Avatar
    Join Date
    Apr 2009
    Location
    Warren, VT USA
    Posts
    2,304

    Re: Track distributive prop

    Quote Originally Posted by Dana View Post
    Mechanically, forget about it. Consider this: at the instant when the blade reaches the pulley or sprocket at the end, its angular momentum goes from zero to whatever it is going around the pulley, instantly. Infinite acceleration means infinite loading (well, really it means things bending or breaking). So now the blades have to be mounted with some kind of flex coupling, and they're whipping around all over the place... my head hurts just thinking about the problems, and I design indexing conveyors (timing belts with stuff attached to them) for a living.

    -Dana

    Drink wet cement, and get completely stoned!
    Yeah, sheesh, the reaction into whatever track would have to hold onto it would be, ummmm, slightly abrupt to say the least. I didn't even think of what TW brought up though that the blade travelling on the linear part of the track doesn't need twist but the part travelling around the end of the track does. There are so many opportunities to have factors of inefficiencies in this design that it would be hard to even get started.
    Jay K.

    VT USA

  11. #11
    Registered User
    Join Date
    Apr 2012
    Location
    Portland, Oregon
    Posts
    5

    Re: Track distributive prop

    Thanks for all of the good critiques...all of the issues raised make sense to me.
    As to my purpose...it is not to be novel for the sake of novelty...I am actually interested in designing a ground-effect vehicle and was interested in maximizing the air-flow beneath the "wing". There is a fan-wing design that uses a turbine-type cylinder prop which is similar to a hand push-mower blade. That novel design allegedly achieves lift at a very low take-off speed by "fanning" the prop-wash and diverting this downward. I was thinking that a linear...elongated prop-design might achieve something similar esp. for a ground-effect craft.
    Overall, I still wonder if the principle I am suggesting has been tested. That is, considering the prop as not just a device which provides thrust, but does make a contribution to lift when the prop is mounted on a wing. Of course, with most prop aircraft, the majority of wing surface area is outside of this prop effect. I was just trying to enhance this effect which would be most important at low speed (before the wing can attain much lift) and esp. in ground effect.

  12. #12
    Registered User Jay Kempf's Avatar
    Join Date
    Apr 2009
    Location
    Warren, VT USA
    Posts
    2,304

    Re: Track distributive prop

    Quote Originally Posted by gleitsma View Post
    Thanks for all of the good critiques...all of the issues raised make sense to me.
    As to my purpose...it is not to be novel for the sake of novelty...I am actually interested in designing a ground-effect vehicle and was interested in maximizing the air-flow beneath the "wing". There is a fan-wing design that uses a turbine-type cylinder prop which is similar to a hand push-mower blade. That novel design allegedly achieves lift at a very low take-off speed by "fanning" the prop-wash and diverting this downward. I was thinking that a linear...elongated prop-design might achieve something similar esp. for a ground-effect craft.
    Overall, I still wonder if the principle I am suggesting has been tested. That is, considering the prop as not just a device which provides thrust, but does make a contribution to lift when the prop is mounted on a wing. Of course, with most prop aircraft, the majority of wing surface area is outside of this prop effect. I was just trying to enhance this effect which would be most important at low speed (before the wing can attain much lift) and esp. in ground effect.
    There are other ways to skin that cat. You could put a round fan in a duct and then transition it to a wide flat flow nozzle. It is a bad way to generate thrust so lots of losses but if you need to concentrate flow it works well. The Roots type compressors like you described as a reel type lawn mower is for compressing a little flow to a larger than normal pressure in one pass and is considered a positive displacement pump. Those would never provide a large volume of flow to lift or push anything but they are useful for shoving more air into a small cylinder like in a super charger. Takes a lot of HP to drive them.

    One way to do what you are talking about it to use a large fan and pressurize a box. Then use the box to put flow around a large slot like in a hover craft. That can be made somewhat efficient as long as the flow rate through the slots is not overly restrictive and all the flows are pretty balanced fore/aft and side/side.

    Have you thought of using a large flat squirrel cage type impeller and then just putting vanes on to direct the flow where you want. That makes blades go around a cylinder not in a straight line and can generate a lot of flow and pressure if designed right. The impeller is it's own inlet in those sorts of designs. It wouldn't be too hard to make either.
    Jay K.

    VT USA

  13. #13
    Registered User Dan Thomas's Avatar
    Join Date
    Sep 2008
    Posts
    3,007

    Re: Track distributive prop

    P-factor from such a tracked arrangement would be detrimental, on top of all the other negatives. The propwash is not perpendicular to the prop blade's travel, so that the blast over the entire top of the wing would be at an angle and the opposite angle on the bottom. Can't help but create a roll.

    What we see flying is what works. Study the history of aviation to see what didn't. Very informative. Examples abound:

    Track distributive prop-strange-weird-airplanes-world-24.jpg

    Dan

  14. #14
    Registered User bmcj's Avatar
    Join Date
    Apr 2007
    Location
    Fresno, California
    Posts
    7,162

    Re: Track distributive prop

    Quote Originally Posted by Dan Thomas View Post
    Examples abound:

    Attachment 18259

    Dan
    Wow! Did they find and restore the original or did someone just build a replica (and why )?

  15. #15
    Registered User Dan Thomas's Avatar
    Join Date
    Sep 2008
    Posts
    3,007

    Re: Track distributive prop

    Quote Originally Posted by bmcj View Post
    Wow! Did they find and restore the original or did someone just build a replica (and why )?
    Don't know for sure but it looks like a replica. The picture shows what looks to be a Rotax two-stroke driving a Warp Drive prop. Those weren't around when this thing was originally built in the '30s or thereabouts.

    It probably flies, but not well. Survival of the fittest really does apply to aircraft designs. This thing was likely built by someone who either was fascinated by it, or was sure that it still had possibilities. Sure looks draggy, and where would one carry anything?

    Dan

+ Reply to Thread
Page 1 of 2 12 LastLast

Similar Threads

  1. [Wanted] Wanted a prop spinner for a MiniMax w/ Rotax 447 w/ 3 blade prop.
    By Chief Kirk in forum For Sale / Wanted
    Replies: 0
    Last Post: March 11th, 2012, 08:44 PM
  2. Naive Prop Questions (effects of prop length)
    By teknosmurf in forum General Experimental Aviation Questions
    Replies: 25
    Last Post: June 17th, 2011, 09:58 AM
  3. would you say this is the right prop?
    By billyace in forum Rotorcraft
    Replies: 1
    Last Post: December 2nd, 2010, 05:58 AM
  4. prop
    By W.M.Patrick in forum For Sale / Wanted
    Replies: 0
    Last Post: November 5th, 2003, 08:57 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts