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Thred Zeppelin

Added this to [wjt]'s "a search for G.U.F.F." idea and figured it deserved its own posting.
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In the same way that nobody has ever thought of internally ballasting an Archemidian screw for underwater, they also haven't realized that the same concept carries over to all fluid mediums such as air and if Zeppelins were screw shaped and rotated above the gondola, (or better yet were torus shaped and inverted while rotating around the gondola... but that's another daydream), then the lifting body 'becomes' the propulsion system.

Did a little doodle I did.
[link]


Sorry for the blurry. https://imgur.com/gallery/cHUWiGu
[2 fries shy of a happy meal, Jul 29 2019]

Hullaballoon Hullaballoon
This idea is related to the magnificent "Hullaballoon" by epic Halfbaker [bristolz]. RIP [hippo, Jul 31 2019]

[link]






       Nice sketch, with a Flash Gordon feel. I suppose GUFF is about ways to warp spacetime very locally by altering the patterns of the constituents. This aeroscrew is one way.
wjt, Jul 29 2019
  

       I have a feeling that we've been here before, but a (admittedly, very brief) search come up nada. Or was that one in the water?
neutrinos_shadow, Jul 29 2019
  

       What I still haven't seen is any evidence that an Archimedean screw is as efficient - in water or air - as a propellor. I'm not saying it's not, but that thing in the paddling pool didn't seem to have any method of measuring power consumption as a function of distance.   

       Are you sure you're not just falling into the same "gut instinct" trap that led early propellor designers to assume (wrongly) that a multi-turn helix was more efficient than a fractional-turn helix? Or have you got measurements of actual efficiency?
MaxwellBuchanan, Jul 29 2019
  

       //Nice sketch, with a Flash Gordon feel.//   

       Thanks. "Savior of the Dirigiverse!"   

       //Or was that one in the water?//   

       Yep. A fluid is a fluid is a fluid.   

       //What I still haven't seen is any evidence that an Archimedean screw is as efficient - in water or air - as a propellor.//   

       <shrugs> You got me Hoss.
There are no numbers or measurements to back up the things I see in my head because the things don't exist yet, so I can never be sure of anything until I build them. My gut says I'm on to something or it wouldn't have dragged my ass down this path in the first place.
This one is quite beyond my humble tinkers skills to build or test I'm afraid.
  

       I searched for a very long time for any prior art or math of any kind before tackling the water version of this. All I can say is that my mental projector shows me air pressure resisting initial radial compression causing drag and an outwards traveling pressure wave. As that slightly pressurized air passes the mid-point of the... give me a sec... prolate spheroid, most of the force used to spread that air is then recaptured as the pressure equalizes behind the craft minus however much of the pressure wave escaped before reaching that mid-way point.   

       What I'd really like to see is if enough solar hot air could be used in place of a lifting gas, and whether that same lift could be attained by the use of UV light from the craft itself.
If we could make dirigibles Efficient and profitable without the use of flammable or irreplaceable gasses then we could revive Zeppelin travel.
  

       //A fluid is a fluid is a fluid//
Hmm... but a compressible fluid (air) is NOT an incompressible fluid (water).
//solar hot air//
I've never understood (modern) hot air balloons. Shirley there's a better (safer, more efficient) way to heat the air in the envelope than an open flame? They have the big burners and then complain when things catch fire and explode.
neutrinos_shadow, Jul 29 2019
  

       I remember the Hullaballoon
sninctown, Jul 30 2019
  

       // but a compressible fluid (air) is NOT an incompressible fluid (water).//   

       Good point. I wonder if undulating the fin of the screw could use that fact to add speed?   

       //I've never understood (modern) hot air balloons. Shirley there's a better (safer, more efficient) way//   

       Ditto. I love the idea of creating lift from light.   

       //Hullaballoon//   

       I miss [bris].   

       One issue I see with a full helical drive (and this may explain why multi-helical "corkscrew" propellers are inefficient) is that only the last bit of the helix can have any effect on propulsion. To find the total thrust, you just need to know the mass and velocity of whatever is being flung out the back end. That's true for a rocket, a jet or a propellor.   

       If a multi-turn helix is moving through water (or, I would bet, air at reasonable speeds), it's only the fluid leaving the final turn of the helix that is doing any work; the rest of the helix is effectively idling. So, you could remove all but the last turn of the helix and it will provide just as much thrust.   

       Now, large ship propellors, which are designed to operate at relatively low rpm, also adhere to this principle - the blades occupy most of a full circle when viewed from behind, and the reason for having 3 or more part-helix blades instead of one complete turn of a single helix is that the propellor can be made more compact (ie, shorter from front to rear).   

       So, on reflection, I'm bound to say that your Archimedean drive will be no more efficient (and I would guess less so) than either a single-turn helix or a well-designed propellor.
MaxwellBuchanan, Jul 30 2019
  

       // it's only the fluid leaving the final turn of the helix that is doing any work; the rest of the helix is effectively idling. So, you could remove all but the last turn of the helix and it will provide just as much thrust.//   

       No. Picture the same prolate spheroid trying to attain speed if only the end threads were exposed.
If the craft is accelerating from a stand still then every bit of surface area extraneous to the prolate spheroid is channeling water and providing thrust. Same with decelerating.
By 'pulling' itself, rather than being pushed, the linear drag of the hull in motion is converted to the boundary layer drag of the medium on a spinning object which, if plotted on a graph, should remain on a fairly constant gentle curve as the speed of the craft increases whereas the faster an object is 'pushed' through the water the more resistance it must overcome on a very steep curve of resistance over time.
  

       //So, on reflection, I'm bound to say that your Archimedean drive will be no more efficient (and I would guess less so) than either a single-turn helix or a well-designed propellor.//   

       Well... you could be right.
If you are right though then it's funny how there is no math out there on the subject. Should be easy enough to model.
Maybe now that someone has thought it up it will be.
  

       hmmm, is "propellor" the proper spelling there? It red-flags for me.   

       Presumably it's significant that, on the prolate spheroid (or, at least, on the back half of it), the successive turns of the screw don't overlap each other (much). Therefore, contra [MB]'s model, they can all contribute to pushing fluid "out the back end".   

       Nicht wahr?
pertinax, Jul 31 2019
  

       I guess if it's a prolate spheroid then yes, the more equatorial strakes will produce thrust that doesn't just hit the strakes nearer the back end. But then again where are the rearmost strakes getting their air (or water) from? It can only come from the layer of fluid that has passed over the equator.   

       The only way to avoid this is if you have some kind of detachment of flow, so that fluid that has passed over the equator does not (as it wants to) follow the contours and hug the body. But if you have this detachment, then you've created a vacuum behind your ship, which is not a good way to move forward.   

       I guess my point is that [2f] has argued all along that this sort of thing is super-efficient, but has no idea whether it is or isn't. And all the experience with helical thrusters suggests that it isn't. And logic also suggests that it isn't. And there was no attempt to measure efficiencies on the small model that [2f] drove for a couple of metres in a pool.
MaxwellBuchanan, Jul 31 2019
  

       Baby steps...   

       I can only relay what I see in my head when I ask it to show me physics scenarios. It isn't always right. Like that time it was 'sure' that a weighted object spinning at the end of a tether would release perpendicular to center rather than on a tangent. Took a good whack to fix that one.
That's the great thing about things that pop into your head all on their own...
...there is no shame when you're wrong, and no swelled head when you're right.
Just wonder at where it comes from.
  

       Oh, and I didn't say that this would be more efficient, the Mechanical Engineering prof I was working with said that my tweaks to the water version would make for a high 90%ish efficiency range on that concept.
No clue about the zeppelin version.
Works fine in my head, and would work even better if properly internally ballasted and I'm having a great time wrapping my head around the gizmos needed to let an internal passenger compartment function through emergencies and such.
  

       That's what I mean - I think what you see in your head is what everyone else sees in their head, and is susceptible to the same errors.
MaxwellBuchanan, Jul 31 2019
  

       It sure seems to be right a lot...   

       I still wonder where the math is? and if 'propellor' is proper English spelling?   

       Turns out "propellor" is wrong. Learn something new every day.
MaxwellBuchanan, Aug 01 2019
  

       //It can only come from the layer of fluid that has passed over the equator//   

       Good point, [MB]. So now I'm imagining ducts passing through the body of the spheroid to emerge between one strake and the next with the purpose of feeding fluid to the latter. And then I'm imagining the added drag that these ducts would probably entail. And then I'm wondering what happens if you have a skeleton of strakes, in the same configuration as before, but with no enclosed spheroid to speak of. Did we need to enclose that spheroid for buoyancy? Damn. What if the strakes themselves were tubby enough to be buoyant?
pertinax, Aug 03 2019
  

       //perpendicular to center rather than on a tangent.//   

       tangent: tan·gent /&#712;tanj&#601;nt/ A tangent to a circle is a straight line which touches the circle at only one point. This point is called the point of tangency. The tangent to a circle is perpendicular to the radius at the point of tangency.
RayfordSteele, Aug 03 2019
  

       Wait... I don't know if I can whack that back the way it used to be if I was right the first time.   

       Something weighted swinging around on a tether from an immovable center point in a vacuum gets released from the tether.
That object;
A) flies in a direct line-of-sight from the tether at the point of release.
B) moves out of line-of-sight with the tether at the point of release.
C) curves due to magic.
D) none of the above.
  

       I used to think it was A, now I think it is B. Please don't tell me it's D, because once you've whacked on, well...
...
  

       Don't think about where the weight is coming FROM; consider where it is GOING TO. At "now", it's velocity is tangential (it's not moving towards or away from the centre, therefore must be tangential). All the string does is pull it around a bend; it wants to keep going straight, but the string won't let it. Remove the string -> carries on tangentially, because there is nothing to make it "go around the bend".
neutrinos_shadow, Aug 06 2019
  

       Ah, got it. Whacks on Daniel san.   

       The enormous rotating surface area is going to cause problems. For example you will get lift (or drop) from the Magnus effect depending on direction the wind is coming from.   

       The other problem is the conservation of angular momentum. Research why a helicopter needs a tail rotor (and cannot simply have an internal counter-rotating weight). I'm not exactly sure how it's going effect the zepplin, but it's likely to cause problems with stability, steering, etc.
xaviergisz, Aug 06 2019
  

       Ah, but all of these negatives become positives when gyroscopic forces play well together.   

       The precession of one spinning body offsets the precession of other spinning bodies quite nicely once the circles within circles have been calibrated.   

       ...in my head anyway. No guarantees.   

       hmmm, one of my uses of the word precession above red-flags as misspelled while the other one doesn't. Guess they cancel out...   

       So I was daydreaming about this at work again today and I think that one of the negatives might actually make the whole concept financially viable.   

       Zeppelins are very dependent on optimal weather patterns to function well so guide-lines and towers would be needed for effective inner city travel.
Thing is though, every electric motor is also an electric generator.
This means that, first of all since the hull would remain able to spin while tethered it would withstand far greater turbulence than conventional lighter than air craft because of the energy conversion from linear to centrifugal.
Secondly each craft would be able to not only passively recharge itself during down-times but actually feed power back to the grid by filling the city skyline with what amounts to hundreds of massively powerful turbines.
  

       Also, having thought about it a bit more, I think I can indeed make a working scale model prototype to derive the non-existent math from.   
      
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