Nyctosaurus rami, or can I make a wind powered airplane?

[neutrino_cannon]

http://www.bridgeport.edu/~cbennett/...yctosaurs.html

Nyctosaurus is a late creatceous pterosaur. Hitherto it was thought to be crestless, and then bam! I see this. No, it's not a hoax, I've seen about checking that. I'm pretty sure that this crested type is a different specias than non crested ones.

The beast in question was essentially a smaller version of the more familiar pteronodon, except the crest morphology is clearly different. Also, nyctosaurus has no other manual digits aside from it's wing finger, an oddity among pterosaurs.

Anyway, the theory comes along that maybe this crest and ramus supported a membrane, similar to the wing membranes, that could be used as a sail while the animal flew in ground effect.

Would that work?

[ceptimus]

In theory, if the animal is flying low enough, then the wind gradient (different airspeeds at different altitudes) does allow some energy to be extracted. I am skeptical about whether enough energy could be extracted by this 'sail' to sustain flight though.

Whenever two fluids (in this case different 'layers' of air) move differentially, there is the opportunity for energy extraction. This is most commonly seen with a sail boat, which extracts energy from the differential movement of air and water.

[arcticpenguin]

I notice this from the web page you linked:
College of Chiropractic
University of Bridgeport
Bridgeport, CT 06601-2449

[ceptimus]

Part of the painting by Conway.

[Bikewer]

If accurate, looks like it would provide the same sort of wind-powered thrust that sailboards do.

Looks an awfully lot like a sailboard, though.

[espritch]

Every time I think I've seen it all, something comes along to prove that I haven't. That critter's just weird.

[xouper]

Quote:

neutrino_cannon: Anyway, the theory comes along that maybe this crest and ramus supported a membrane, similar to the wing membranes, that could be used as a sail while the animal flew in ground effect. Would that work?

Nope. An airplane with a sail instead of an engine won't sustain level flight, even in ground effect.

[Bikewer]

Sailboards, with highly unaerodynamic humans aboard in a even-more-unaerodynamic standing position, nonetheless achieve speeds of what, 20 + knots?

Stick such a membrane onto an already flight (gliding, at any rate) capable critter and have it skim the ocean as pictured with the favoring wind.... Might give it a bit of a boost, so as to favor longer, speedier glides, or get enough above it's stall speed to gain altitude easily, where we'd presume it'd fold back down again.

Thing would need good neck muscles, though.

[JSFolk]

A. I've not seen any speed listings, but I highly doubt a sailboard reaches 20 knots. I'd say maybe 10. It just looks a lot faster when you're basically standing on the water.

B. A sailboard, or iceboat, or what have you has a keel (or daggerboard, or skates) to keep it from being pushed along by the wind. An airborne creature would have no such resistance, so it would just be blown with the wind.

C. On a more practical note, don't you think that if this would work that glider pilots would have already done it?

[Terry]

Quote:

Originally posted by ceptimus
In theory, if the animal is flying low enough, then the ground effect (different airspeeds at different altitudes) does allow some energy to be extracted.

Albatrosses are believed to do this. They extract energy from the vorticity in the flow by flying a sinusoidal path with a downwind turn in the faster part of the flow and an upwind turn in the slower part. [Yes, I know that there's no difference between an upwind and a downwind turn in a flow with no vorticity. This is a different case.]

Radio-controlled model gliders can also do this on the downwind side of a sharp ridge. Some gliders have been clocked by radar at 180mph while "dynamic soaring" (the model-airplane term for this practice). The sharp ridge causes a separation of the airflow, so in this case, the difference in wind speed between the slow and fast parts is much greater than the normal wind gradient.

Quote:

I am skeptical about whether enough energy could be extracted by this 'sail' to sustain flight though.

Me too! Looks highly improbable.

--Terry.

[diddidit]

Quote:

Originally posted by JSFolk
A. I've not seen any speed listings, but I highly doubt a sailboard reaches 20 knots. I'd say maybe 10.

Just for the record, sailboards held the sailing speed record for some time, before special-purpose craft were developed. They've exceeded 40 knots. The currect "wet water" sailing speed record is 46.52 knots (on land it's about 115 miles per hour; on ice, about 140). http://www.sailspeedrecords.com/500.html for the water records...

As for the dinosaur, I'd have to guess that the "sailhead" wouldn't do much, at least over a long distance. Over a short distance, it could provide a boost, but sails are very sensitive to wind direction - get it wrong by more than a few degrees and the thing is only causing greatly increased drag.

I'd guess it was for display more than anything, like a peacock's tail.

did

[neutrino_cannon]

Quote:

Originally posted by xouper
Nope. An airplane with a sail instead of an engine won't sustain level flight, even in ground effect.

Could you explain why? This intruges me. I'm thinking of a catameran. The analogy is pretty close. A catameran uses thrust from the wind, and converts part of that thrust into lift to keep the hulls out of the water more.

I'm seeing this critter (pterosaur, not a dinosaur, but close achosaur kin) as an albatross sort of critter that uses updraft from waves and maybe a little flapping to genrate lift, as well as getting thrust from the wind via the huge jib on it's head.

Azhdarchid pterosaurs are known to have very stiff necks, so It might have been able to keepit's head straight. Of course, nyctosaurus isn't an Azhdarchid, azhdarchids are quetzacoatlus and kin, nyctosaurus is in it's own group, and not even that close to pteranodon and kin.

There are crests on other nyctosaurus specimines, they're just a whole lot smaller and stubbier. The transition between a sailing species and a non-sailing one must have been tremendous, since the crests on most nyctosaurus would have had no aerodynamic properties (very small).

[Bikewer]

C. On a more practical note, don't you think that if this would work that glider pilots would have already done it?


You may have a point, I think that aircraft designers have tried nearly every concievable configuration.

The point about the rudder or keel is well-taken also. Thrust applied so far above the longitudinal axis would be rather unstable, tending to thrust the critter nose-first into the water.

Unless he had a suitable elevator (er, tail)

Anyone wanna build one?

[ceptimus]

Quote:

Originally posted by Terry
Radio-controlled model gliders can also do this on the downwind side of a sharp ridge. Some gliders have been clocked by radar at 180mph while "dynamic soaring" (the model-airplane term for this practice).

Current record is 229 mph. Scary video at this site.

[ceptimus]

Quote:

Originally posted by Bikewer
The point about the rudder or keel is well-taken also. Thrust applied so far above the longitudinal axis would be rather unstable, tending to thrust the critter nose-first into the water.

If there were enough energy in the wind gradient for this to work, then the creature would have to fly roughly crosswind. Flying directly downwind or into wind could not work. So the force on the creature's sail would tend to cause a rolling, rather than a pitching disturbance, and this would have to be compensated for by generating extra lift on the downwind wing, with a corresponding reduction of lift on the upwind side.

I am beginning to rethink my initial skepticism to this idea. As has already been pointed out, the albertross extracts enough energy from the wind gradient to remain airborne, though it does this using a dynamic technique. The 'sail' method is superior in one respect - that it allows the creature to remain at all times in the more efficient 'ground effect' region. The wing experiences a significant increase in l/d performance when flying at half a wingspan or less above a ground or water surface.

[JSFolk]

Quote:

Originally posted by diddidit


Just for the record, sailboards held the sailing speed record for some time, before special-purpose craft were developed. They've exceeded 40 knots. The currect "wet water" sailing speed record is 46.52 knots (on land it's about 115 miles per hour; on ice, about 140). http://www.sailspeedrecords.com/500.html for the water records...

did

I'm going to take the creationist strategy and just deny the existence of any contrary data.

SO... 10 knots it is!

Damn, and I thought I was a badass for getting a Westsail 32 up to 8 knots once.

I still don't think that birds could gain energy from having a sail... imagine putting a sail on a flat, smooth raft with no keel. All it would do is blow you downwind.

[Rocky]

I was skeptical at first.... But…

Imagine a wide catamaran that was a wing between the hulls. A long centerboard down and a sail up on each hull (sort of an “H” shape). With enough speed and control it should work. There have been hydrofoil sailboats , the only difference is getting the lift from the air.

[wayrad]

Quote:

Originally posted by neutrino_cannon
[
Anyway, the theory comes along that maybe this crest and ramus supported a membrane, similar to the wing membranes, that could be used as a sail while the animal flew in ground effect.

Darn, it'd be cool to see it jibe.

[espritch]

Just a thougt. I don't see how a sail would work if the creature was flying above the water. But what happens if the bill is in the water skimming for fish? Couldn't this act as a kind of dagger board? The dagger board on a sail boat isn't nearly as big as the sail since the water is a lot denser. This might also solve the problem of the sail being too far forward since it would be countered by the bill which is also in front.

So basically, in normal flight with the head forward, the sail would be laid back and not effect flight much. When skimming, the head tilts down, the bill enters the water, and the sail comes up to provide propulsion to maintain glide speed despite the drag from the bill.

[neutrino_cannon]

Quote:

Originally posted by espritch
Just a thougt. I don't see how a sail would work if the creature was flying above the water. But what happens if the bill is in the water skimming for fish? Couldn't this act as a kind of dagger board? The dagger board on a sail boat isn't nearly as big as the sail since the water is a lot denser. This might also solve the problem of the sail being too far forward since it would be countered by the bill which is also in front.

So basically, in normal flight with the head forward, the sail wiuld be laid back and not effect flight much. When skimming, the head tilts down, the bill enters the water, and the sail comes up to provide propulsion to keep it skimming above the water despite the drag from the bill.

The rami are stiff, there's not a whole lot that can be done about laying them flatter. I'm actually skeptical about the skimming beak. There are birds today, aptly named skimmers, that fish with this technique, but they have highly modified bills, the lower mandable being longer than the upper one and the whole beak being rather compressed. I can see from the various drawings that nyctosaurus did not have an underbite, but i'm not sure about the lateral compression, which is what's important as far as drag is concerned.

Interesting idea though.

[RCNelson]

The crest could have been part of a flashy display to impress the females of the species - like the peacock's tail impresses the peahen.

[rockoon]

I figure that thing had to have something to do with eating or screwing.

[diddidit]

Quote:

Originally posted by JSFolk

Damn, and I thought I was a badass for getting a Westsail 32 up to 8 knots once.

I was gonna call you a piker, as we surfed a wave on my uncle's C+C 35 to 12.95 knots (this on a fairly heavy (13,000 lbs including toaster and water heater), 17 year old displacement boat - our bow wave was breaking higher than the side of the boat) and shortly thereafter crash-jibed and broke a guy's arm, but then I Googled and found a pic of a full-keel, double-ended Westsail 32 at 20,000 pounds.

You did better than us. What was it, downwind in a hurricane?

Oh, to stay on topic, I don't see the crest working well as a sail without a foil in the water providing lateral resistance.

did

[diddidit]

Quote:

Originally posted by Rocky
I was skeptical at first.... But…

Imagine a wide catamaran that was a wing between the hulls. A long centerboard down and a sail up on each hull (sort of an “H” shape). With enough speed and control it should work. There have been hydrofoil sailboats , the only difference is getting the lift from the air.

In extremely controlled conditions, I think that's kinda been done. The special-purpose speed sailing boats have vertical hard wings and then an airfoil-shaped spar that supports and partially lifts the crew pod. These things only work in one direction on smooth water in honking wind, though, and they don't lift entirely out of the water.

In real-world conditions, an airfoil-lifted boat would have trouble in any waves, while the hydrofoil boat can (to some extent) ride up and down waves. Wind speed would play havoc with either. The birdosaur has the advantage of being able to flap its wings, but still, without a lateral foil in the water, the sail-head will only push it sideways.

Check this out:



From here.

did

[xouper]

Quote:

xouper: Nope. An airplane with a sail instead of an engine won't sustain level flight, even in ground effect.

neutrino_cannon: Could you explain why? ... getting thrust from the wind via the huge jib on it's head.

I notice the answer has been already been posted, but I'll respond too. A jib can only generate "thrust" if there is an appropriate friction between the vehicle and the surface (ground, water, or ice). Without such contact with the surface (as in the case of an airplane in level flight) the jib will simply act like a parachute, pulling the vehicle in the direction of the wind.

Here's a trick question. Assume you are flying an airplane in level fight and have absolutely no outside points of reference (no way to determine your ground track or distance to known landmarks), how would you go about determining the direction and speed of the wind? (Just to clarify, you can use any instruments that measure the air immediately within the vicinity of the airplane, such as altitude, airspeed, angle of attack, etc.)

• Disclaimer: On the off-chance I have failed to cover all loop-holes in the way I posed the question, I reserve the right to close said loopholes as they become known.

The answer to that question is related to why a sail on an airplane won't provide any thrust that can be used to keep the airplane in level flight.

An experiment was already mentioned, but here's another. Using an airhockey table (to provide a frictionless surface) and a flat bottomed "sailboat" (no keel or wheels, and that floats on the cushion of air from the table), and see if you can get it to sail at any angle into the wind (from a large fan nearby), or even cross-wind. The results of this experiment will show why it is not possible to use a sail on an airplane.

Does any of this help? Or if I've left some things unclear, please ask.

[MRC_Hans]

Interesting. A sail vehicle works by generating force vectors at an angle to each other. For a boat: The lift generated by the wind passing over the sail is one force vector, the lift generated by water flowing over the keel or hull generated the other. The resultant force vector moves the boat.

An aircraft (or flying animal) will normally miss one of this vectors. What keeps it up and enables it to soar on upwinds is the downward vector supplied by gravity combined with the upwards/forwards vector generated by the lift of the wings.

However, if the plane/animal can somehow lower a keel into the water, it just might be possible to "sail" on the wind. There are a lot of resultant torques and forces that would have to be managed, of course, but the possibility exists.

Interestingly, we know if no animal (other than possibly this pterosaur) extinct or extant, that uses a sail except for very crude downwind sails. Actually, sea-birds have the potential; all they would need to do is raise one wing into the air and put their feet down sideways, but none do.

This leads me to think that the extinct creature might have used the sail, not while flying but while swimming. But then it might as well have used a wing.

Hans

[ceptimus]

The posts saying, 'A sail can't work on an aircraft' are ignoring the wind gradient.

The wind near the ground/sea is slowed down by dint of friction with the surface. On a windy day, there could easily be a 10 knot difference in the speed of the wind hitting the top of the creature's sail, and the wind just a few inches above the sea where the creature is soaring.

This difference in windspeed does allow the theoretical possibility of extracting enough energy from the wind to maintain flight.

A sailboat's keel gives the wind something to react against, but the main body of the creature, flying in a slower moving airmass than the sail could do much the same thing.

Instead of air moving over (almost) stationary water, you have air moving over a lower, more slowly moving, mass of air.

[diddidit]

Quote:

Originally posted by ceptimus

A sailboat's keel gives the wind something to react against, but the main body of the creature, flying in a slower moving airmass than the sail could do much the same thing.

I'm definitely well aware of wind gradients, having seen boats with 70' masts scooting along when the 35' sticks are spitting in the water to see if they are moving at all. It's certainly possible that the critters body would be in still air while the crest would be in a bit of breeze. But I don't think that the effect from that would equal that of a keel - water is what, 600 times denser than air? Also, a keel doesn't provide lateral resistance much - when the boat isn't actually moving, the wind just pushes the boat along. When moving, the keel (and rudder) provide lift, which is what really allows sailing upwind. Without that lift, I can't see this creature doing anything but sliding along with the wind.

did

[daver]

Quote:

Originally posted by diddidit


I'm definitely well aware of wind gradients, having seen boats with 70' masts scooting along when the 35' sticks are spitting in the water to see if they are moving at all. It's certainly possible that the critters body would be in still air while the crest would be in a bit of breeze. But I don't think that the effect from that would equal that of a keel - water is what, 600 times denser than air? Also, a keel doesn't provide lateral resistance much - when the boat isn't actually moving, the wind just pushes the boat along. When moving, the keel (and rudder) provide lift, which is what really allows sailing upwind. Without that lift, I can't see this creature doing anything but sliding along with the wind.

did

I agree, the sail would function more as a kite or a parachute. Ideally, the sail would be narrow at the bottom and wide at the top, capable of being oriented perpendicular to the direction of travel at the top and aligned at the bottom. That doesn't seem to match the skeleton.

[xouper]

Quote:

ceptimus: The posts saying, 'A sail can't work on an aircraft' are ignoring the wind gradient.

True, I have been ignoring that. Having piloted both airplanes and sailboats, I think it's safe to say I know a thing or two about wind gradients. However ...

Quote:

... On a windy day, there could easily be a 10 knot difference in the speed of the wind hitting the top of the creature's sail, and the wind just a few inches above the sea where the creature is soaring. This difference in windspeed does allow the theoretical possibility of extracting enough energy from the wind to maintain flight.

I disagree with that last statement. But if you really think a sail can generate enough thrust to maintain level flight (in a wind gradient), then let's see the numbers behind this "theory". I'm always willing to be shown wrong, but not without some numbers.

[baggie]

you are all assuming that thing was for flying. It is clearly meant to be used to help it sail through the water very fast, like a rocket propelled duck

[Leif Roar]

Quote:

Originally posted by baggie
you are all assuming that thing was for flying. It is clearly meant to be used to help it sail through the water very fast, like a rocket propelled duck

Actually, the purpose of the feature was to serve as space for marketing. That's right, living dinosaur billboards. Now, that's what I call message exposure.

[JSFolk]

Quote:

Originally posted by diddidit


I was gonna call you a piker, as we surfed a wave on my uncle's C+C 35 to 12.95 knots (this on a fairly heavy (13,000 lbs including toaster and water heater), 17 year old displacement boat - our bow wave was breaking higher than the side of the boat) and shortly thereafter crash-jibed and broke a guy's arm, but then I Googled and found a pic of a full-keel, double-ended Westsail 32 at 20,000 pounds.

You did better than us. What was it, downwind in a hurricane?

I was just very lucky, I think. The boat had recently spent several months out of the water getting bunches of new stuff, and had a very clean bottom. We had pretty good wind and flat water, but it was January and 45 degrees (F... 7 degrees C) at the time, so I might have hallucinated the 8 knots part. I was at the helm while the rest of the "crew" (including the captain) was down below fiddling with the radar and making hot chocolate. Admittedly, the speed reading was from a GPS, so I might have had some current assistance.

[neutrino_cannon]

[pirate]

Aharr, methinks the timbers upon the (airlubbers?) head be not covered in sails. Methinks that they be bare, like the antlers of elk and deer. Perhaps they even be grown every year in simmilar fashion. Arrrr.

[/pirate]

[ceptimus]

Quote:

Originally posted by xouper
I disagree with that last statement. But if you really think a sail can generate enough thrust to maintain level flight (in a wind gradient), then let's see the numbers behind this "theory". I'm always willing to be shown wrong, but not without some numbers.

OK

To keep the analysis relatively simple, my design is like a conventional sailplane with vertical sails/wings extending above and below the fuselage. The MAC of the sails is in line with that of the main (horizontal) wings, so viewed along the fuselage axis from the front or rear, the wings and sails would be arranged in a + configuration. The sails will have roughly half the area of the main lifting wings. A larger than usual fin and rudder will be required to maintain yaw stability, due to increased side area of the craft.

I will assume the following arbitrary figures to keep the math simple:

Weight of craft: 10 lbs
Wingspan: 10 feet
Sail ‘span’ (top to bottom) 6 feet
Wind gradient over this (6 foot) height 8 knots
Cruise airspeed 20 knots

Assuming an L/D of 20:1 for the main glider (ignoring the sails for the moment) we require half a pound of (net) forward thrust from the sails to maintain level flight, that is to say a quarter of a pound of thrust from each sail.

Each sail has a local (averaged across its ‘span’) side flow of 2 knots, and is moving forward, with the glider at 20 knots. If it were operating at an L/D of 10:1 it would produce no net thrust or drag. Assume however that it operates at a 20:1 L/D, then to produce the required quarter pound of thrust requires it to generate a (roughly sideways) ‘lift’ force of two and a half pounds.

The sideways ‘lift’ of the two sails will cause a rolling moment on the glider, which must be compensated by one main (horizontal) wing generating more lift than the other. As the span ratio of the main wing to sail is 5:3, it turns out that the ‘downwind’ horizontal wing would be required to generate 3 lbs more lift than the upwind one.

The diagram below shows a view of the lift forces acting on the craft, as viewed from behind the tail:

 
          |
    6.5   |<--2.5
     ^    |
     |    |
----------O----------
          |    ^
          |    |
    2.5-->|   3.5
          |
          
          |
          V
      Weight = 10

I have tried to keep the figures simple, so the design is far from optimum. However, I hope it makes the theoretical possibility of such sail powered, ’in the wind gradient’ flight apparent. Please let me know whether I’ve made myself clear. I can provide further explanation or diagrams if necessary.

Should you consider an 8 knot wind gradient over a 6 foot height to be too optimistic, simply scale the glider up by a factor of two, or whatever you think appropriate.

By the way, if anyone manufactures my design, and makes money from it, I'd like 10% of the profits please

[Terry]

Quote:

Originally posted by ceptimus
OK

To keep the analysis relatively simple, my design is like a conventional sailplane with vertical sails/wings extending above and below the fuselage. [ snip analysis]

I think L/D of 20 is very optimistic, given how skewed the lift distribution will be. But I'm afraid I still dcn't see what provides the thrust here. If the lift on the top and bottom sails are equal and oposite, then don't their thrust components cancel? Or is it that you have them twisted relative to each other, and the wind gradient causes their respective 2m/s side flow to be from opposite directions?

--Terry

[ceptimus]

Quote:

Originally posted by Terry


I think L/D of 20 is very optimistic, given how skewed the lift distribution will be. But I'm afraid I still dcn't see what provides the thrust here. If the lift on the top and bottom sails are equal and oposite, then don't their thrust components cancel? Or is it that you have them twisted relative to each other, and the wind gradient causes their respective 2m/s side flow to be from opposite directions?

--Terry

Modern sailplanes have L/D figures of 50:1 or more. 20:1 is quite conservative. The skewed flow distribution is accomodated by washing out the sails towards the tips, so that the angle of attack to the local airflow remains constant over the whole span (height). As regards the side flow, yes, it is from opposite directions. Assume the wind gradient looks like this:

 20 kts <-----------------------
   18 kts <---------------------
     16 kts <-------------------
       14 kts <-----------------
         12 kts <---------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Then to my glider, which is drifting to the left at the 'average' windspeed of 16 kts, the effective wind, impinging on its sails looks like this:

                |<----4 kts
                |  <--2 kts
    ------------O------------
      2 kts-->  |
      4 kts---->|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The sails produce forward thrust from the side flow in exactly the same way as a regular yacht's sails do. Or (if you like) in the same way that a glider's wing produces forward thrust from the upward relative flow past it.

[Terry]

Quote:

Originally posted by ceptimus
Modern sailplanes have L/D figures of 50:1 or more. 20:1 is quite conservative.

Modern silplanes aren't 10' span. Model gliders, on the other hand, are. L/D of 20-25 is high performance for a 120" model.

Never the less, I think you have demonstrated that it is possible to extract energy from the wind gradient with a fixed flight path. Nice!

--Terry.

[ceptimus]

Quote:

Originally posted by Terry
Never the less, I think you have demonstrated that it is possible to extract energy from the wind gradient with a fixed flight path. Nice!

Hey! a convert
Also remember the point I made a few posts back - the main horizontal lifting wing is operating in the ground effect region, so would have a higher L/D than when flying at height.

However, I am still skeptical that Nyctosaurus rami used this method; Conway's painting shows it using the lower part of its 'beak' as a water keel, and I am skeptical about that too; but this is a skeptic's forum, so I'm entitled to be so

[ceptimus]

Bump.

Is xouper ever going to look at this again?