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Of hump-back whale tubercles, V1 Prandtl equasions and the long ignored V2 Prandtl equasions and birds wings.

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Of hump-back whale tubercles, V1 Prandtl equasions and the long ignored V2 Prandtl equasions and birds wings.

Postby fluidity » Sun May 09, 2021 10:15 am

It seems as humans that too many of us have been guilty of accepting established theory.
Some fascinating newer looks at Ludwig Prandtl's later and until recently ignored equasions are forcing a major re-think for wing design for efficiency.
An American Albion Bowers has dredged up this little known later equasion of Prandtl's and has been figuring out how to use it.

Quick summary:
A bird's wings have their angle of incidence vary throughout their length, typically there is no winglet as per aircraft.
It seems that designer's use of winglets is only a small part of the story. In bird's wings, there is very substantially lower angle of incidence over a large portion of the outer wing, providing a function similiar to the winglet over a much wider span.
Instead of wingTIP vorticies, the vorticies are approx 3/4 of the way from centre to wing tip and coincide with the specific overlap birds use flying in formation. According to Albion Bowers, this makes for massive lift vs drag improvements.

Not having been through aeronautical design training I don't have much of a vested interest in claiming that the eliptical wings favoured by Prandtl's first famous equasion are the be-all-end-all and I'm really fascinated to see if this is something that we can (likely) utilise for improved hydrofoil lift to drag ratios.

http://www.nestofdragons.net/weird-airp ... l-project/

Don't you just love the hectic pace of innovation in new sports? :D Or in this case... Cribbing on thousands of milions of years of evolution :)

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Re: Of hump-back whale tubercles, V1 Prandtl equasions and the long ignored V2 Prandtl equasions and birds wings.

Postby Herman » Sun May 09, 2021 10:52 am

I loved the link, I can blame a whole lot more on adverse yaw instead of my ageing balance sensors. It staggers me to think how good Ludwig would have been if he had access to modern computer modelling etc. I think the WW2 Spitfire was famous for its elliptical wings.

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Re: Of hump-back whale tubercles, V1 Prandtl equasions and the long ignored V2 Prandtl equasions and birds wings.

Postby Gestalt » Sun May 09, 2021 1:35 pm

This is pretty cool, thanks for sharing.

I'm also surprised shark skin inspired designs have not made it to our hydrofoils and kites yet.

"In this study, we have taken inspiration from shark denticles to design a set of profiles that significantly improve the aerodynamics of aerofoils. In contrast to previous studies on shark skin that have mostly focused on drag reduction/thrust improvement [21–27], we showed that the denticles also generate lift, resulting in high lift-to-drag ratio improvements. Specifically, we found comparable results to those of the best previously reported low-profile vortex generators at higher angles of attack near stall, and even much higher improvements at low angles of attack (α < 4°) [8,11,12]. The remarkable results shown here were achieved by using two mechanisms. First, the shark-inspired profiles trip the boundary layer and generate a short (reattaching) separation bubble that provides extra suction along the chord and thereby enhances lift. Second, the spanwise curvature of the denticles helps to generate streamwise vortices that can lead to drag reduction and prevent lift losses at higher angles of attack. While in this study we have considered the ideal case of the denticles' ridges perfectly parallel to the flow, future work will investigate how sensitive the aerodynamic response of the aerofoils is to the orientation of the denticles with respect to the flow." https://royalsocietypublishing.org/doi/ ... .2017.0828
rsif20170828f01.jpg
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Re: Of hump-back whale tubercles, V1 Prandtl equasions and the long ignored V2 Prandtl equasions and birds wings.

Postby Matteo V » Sun May 09, 2021 4:07 pm

Love the revisitation of the same old questions. And the tackling old research with new advanced methods is awesome.


BUT......

60% gain in efficiency??? Ummmm.... so now we need to expand all of our airport terminals to 3 times thier current size to account for the additional wingspan? And how are you going to design an aircraft carrier for just one of those flying wings?

Innovation is great, but practicality trumps all. Our current aeoronauticical designs are tradeoffs dictated by practicality. "Research for research's sake" is how humanity advances. But very little of "research for research's sake" turns into actual advancement. 'Keep that in mind at all times' when you see a good documentary with beautiful scenery and elevating music.

I think this could be another entry into my " Museum of Solutions to Things That Were Never a Problem in the First Place".

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Re: Of hump-back whale tubercles, V1 Prandtl equasions and the long ignored V2 Prandtl equasions and birds wings.

Postby fluidity » Sun May 09, 2021 7:18 pm

Matteo V wrote:
Sun May 09, 2021 4:07 pm
Love the revisitation of the same old questions. And the tackling old research with new advanced methods is awesome.
BUT......
60% gain in efficiency??? Ummmm.... so now we need to expand all of our airport terminals to 3 times thier current size to account for the additional wingspan? And how are you going to design an aircraft carrier for just one of those flying wings?
On the surface the efficiency gain does seem suspiscious. However if you look further into it, you'll note that the claim is not unreasonable when you consider drag reduction in removing a tail, fuselage even and factor in some increases in efficiency from Ludwig's forgotten second set of equasions.

Birds do it!
Regarding aircraft carriers :lol: I think that's a bit too far yet. How often do you see birds flying upside down? For fighter planes the reduced lift angle of the outer wing sections is not ideal when flying upside down, the adverse yaw issue returns with a vengence. You would neen computerisation, wing tip spoilers and to consider keeping the tail.

Airport terminals 3 times their current size?? Not sure that's a thing here ?
To summarise again, a part I missed:
Prandtl's first equasion derived the eliptical shape as a max lift/drag form for a wingspan constrained form.
Prandtl's second paper detailed a shape with "bell curve shaped lift" as a max lift/drag shape for a form without constrained wingspan.

You can look at aspect ratio as being yet another constraint but to guide us, we have birds. They are shaped more in keeping with Prandtl's second paper with non eliptical wings, reduced wing end lift and they manage in general to fly quite well indeed without vertical tail sections or adverse yaw. It's adverse yaw that is the major hangup for landing large Delta planes on runways with adverse cross winds. Whether this is the sole answer, I don't know. Aligning the under carriage direction with the runway in high crosswinds is not easy- You'll see many youtubes showing the issues and that's with traditional tailed planes which have big rudders for intentional yaw control.

Anyway... HYDROfoil forum! I'm really curious to see if this can work for a good range above board takeoff speed too. There's a lot of wing warp in this and we don't have dynamic control of the twist like a bird would for higher speeds...

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Re: Of hump-back whale tubercles, V1 Prandtl equasions and the long ignored V2 Prandtl equasions and birds wings.

Postby fluidity » Sun May 09, 2021 7:18 pm

Herman wrote:
Sun May 09, 2021 10:52 am
I loved the link, I can blame a whole lot more on adverse yaw instead of my ageing balance sensors. It staggers me to think how good Ludwig would have been if he had access to modern computer modelling etc. I think the WW2 Spitfire was famous for its elliptical wings.
I agree! The adverse yaw though, I don't think I've hydrofoiled fast enough for it to be an issue.. I steer with the hand wing too.
Gestalt wrote:
Sun May 09, 2021 1:35 pm
This is pretty cool, thanks for sharing.
I'm also surprised shark skin inspired designs have not made it to our hydrofoils and kites yet.
Thanks Gestalt, Humpback tubercles like Takuma are copying seem to be a larger scale more manufacturable solution. Wings with waves from the centre to the tips might be another solution, I've been working on my own software to produce this sort of effect like my current icon on here.

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Re: Of hump-back whale tubercles, V1 Prandtl equasions and the long ignored V2 Prandtl equasions and birds wings.

Postby Matteo V » Mon May 10, 2021 3:25 am

fluidity wrote:
Sun May 09, 2021 7:18 pm
Airport terminals 3 times their current size?? Not sure that's a thing here ?
If you squish a 747 down to a highly efficient wing with the same passenger capacity, what is its wingspan?

Look at those models gaining 60% efficiency and let me know where you think the passenger compartment is going to go, and how wide a runway you will need to accommodate that width for landing gear support.

Again, practicality is the reason we have 747's that look the way we do - it's not because we are missing something in aeronautical engineering.

As for vertical winglets being inefficient.... how about the problems with increasing wingspan for horizontal winglets, in regards to increased load/leverage in turbulence at high angles of attack? Vertical winglets have the benefit of not adding to wingspan, and not increasing load with a sudden increase in angle of attack - because they are vertical.


I'm amazed at how people get caught up in "new and improved" hype only to see it fall flat on its face. This is truly the "solar roadways" of aeronautics.

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Re: Of hump-back whale tubercles, V1 Prandtl equasions and the long ignored V2 Prandtl equasions and birds wings.

Postby fluidity » Mon May 10, 2021 7:28 am

Matteo V wrote:
Mon May 10, 2021 3:25 am
fluidity wrote:
Sun May 09, 2021 7:18 pm
Airport terminals 3 times their current size?? Not sure that's a thing here ?
If you squish a 747 down to a highly efficient wing with the same passenger capacity, what is its wingspan?
Look at those models gaining 60% efficiency and let me know where you think the passenger compartment is going to go, and how wide a runway you will need to accommodate that width for landing gear support.
Again, practicality is the reason we have 747's that look the way we do - it's not because we are missing something in aeronautical engineering.
As for vertical winglets being inefficient.... how about the problems with increasing wingspan for horizontal winglets, in regards to increased load/leverage in turbulence at high angles of attack? Vertical winglets have the benefit of not adding to wingspan, and not increasing load with a sudden increase in angle of attack - because they are vertical.
I'm amazed at how people get caught up in "new and improved" hype only to see it fall flat on its face. This is truly the "solar roadways" of aeronautics.
Hmm.
Mateo, fair or not you remind me of an argument I used to have with a hobby shop owner about jet units for small radio controlled boats.
He played your part, asserting that if it could have been done it would have been done already, that it was a waste of time trying and that the surface area to volume ratio in a small jet unit was prohibitive to performance.
I played the inventor role, taking offense at the idea that everything workable had already been tried and the guy has since been proven wrong by hundreds of DIY modellers. Perhaps he forgot to consider the ant-effect? where the smaller the moving thing is, the less of a column of material needs to be supported by each unit of area lifting it.

Anyway, back to your assertion that it's likely to fall flat on it's face.( A Prandtl wing)
I think we both see that when you remove the fuselage and change to a delta, you need to replace the people and cargo carrying volume with in wing volume? Agreed? (and this is completely ignoring that it's the tail and rudder that can be most conveniently dropped, dropping the fuselage depends on providing an alternate high utility space within the wing volume)

So in a conventional plane, the fuselage plays only a small part in lift. It's designed for high volume to surface area ratio and streamlining, minimum length for airport parking convenience and structural integrity, long for reducing the displacement motion of air it passes through, fairly constant length to provide a tidy architectural home for the nosy window-gawping payload, rounded in cross section to reduce total area etc. These are compromises that have been refined over the decades and that are still subject to minor improvements. Passengers tolerate side windows :D

We both also agree that an airport provides constraints. Constraints on wing span, on taxiing wheel base span, on take off length in the most unfavourable conditions and landing constraints dependant on cross winds and time for the aircraft to slow to a taxiing speed. Within constraints of a maximum wingspan, Ludwig's first formulae for eliptical wings makes sense.
Sizing the aircraft smaller than max lift for the total permissable wingspan the bell shaped curve pointier wings of Ludwig's later theory makes more sense as it's only in max lift for a constrained span that the eliptical shape excels.

We've both seen the open V variants of deltas that are being trialed at large model size at the moment by Bower's team. I think it remains to be seen whether they can safely deal with high cross wind landings. I think enough of a filled in delta or fuselage pod is required to allow for rear wheels to lift the plane behind it's centre of gravity. For small Prandtl wings with no fuselage this is not an issue. However, cargo volume in a normal fuselage would of necessity be relocated into the wings and I don't think any of us have quite got our heads around the best re-packaging for that. Within the constraints of an undercarriage that can fit with safety allowance on a runway speed surface, max wing span and undercarriage to suit, there is potential to redo the whole delta concept utilising the advantages of a proverse yaw design. It may well not be at 747 capacity! However I think it would be foolish to write off the possibility of very successful passenger and cargo carrying Prandtl wings on the basis that non Prandtl delta wings had some major issues. In my opinion the biggest problem is still going to be active yaw control in high cross winds.

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Re: Of hump-back whale tubercles, V1 Prandtl equasions and the long ignored V2 Prandtl equasions and birds wings.

Postby Matteo V » Mon May 10, 2021 1:31 pm

fluidity wrote:
Mon May 10, 2021 7:28 am
Hmm.
Mateo, fair or not you remind me of an argument I used to have with a hobby shop owner about jet units for small radio controlled boats.
He played your part, asserting that if it could have been done it would have been done already, that it was a waste of time trying and that the surface area to volume ratio in a small jet unit was prohibitive to performance.
I played the inventor role, taking offense at the idea that everything workable had already been tried and the guy has since been proven wrong by hundreds of DIY modellers. Perhaps he forgot to consider the ant-effect? where the smaller the moving thing is, the less of a column of material needs to be supported by each unit of area lifting it.

Anyway, back to your assertion that it's likely to fall flat on it's face.( A Prandtl wing)
I think we both see that when you remove the fuselage and change to a delta, you need to replace the people and cargo carrying volume with in wing volume? Agreed? (and this is completely ignoring that it's the tail and rudder that can be most conveniently dropped, dropping the fuselage depends on providing an alternate high utility space within the wing volume)

So in a conventional plane, the fuselage plays only a small part in lift. It's designed for high volume to surface area ratio and streamlining, minimum length for airport parking convenience and structural integrity, long for reducing the displacement motion of air it passes through, fairly constant length to provide a tidy architectural home for the nosy window-gawping payload, rounded in cross section to reduce total area etc. These are compromises that have been refined over the decades and that are still subject to minor improvements. Passengers tolerate side windows :D

We both also agree that an airport provides constraints. Constraints on wing span, on taxiing wheel base span, on take off length in the most unfavourable conditions and landing constraints dependant on cross winds and time for the aircraft to slow to a taxiing speed. Within constraints of a maximum wingspan, Ludwig's first formulae for eliptical wings makes sense.
Sizing the aircraft smaller than max lift for the total permissable wingspan the bell shaped curve pointier wings of Ludwig's later theory makes more sense as it's only in max lift for a constrained span that the eliptical shape excels.

We've both seen the open V variants of deltas that are being trialed at large model size at the moment by Bower's team. I think it remains to be seen whether they can safely deal with high cross wind landings. I think enough of a filled in delta or fuselage pod is required to allow for rear wheels to lift the plane behind it's centre of gravity. For small Prandtl wings with no fuselage this is not an issue. However, cargo volume in a normal fuselage would of necessity be relocated into the wings and I don't think any of us have quite got our heads around the best re-packaging for that. Within the constraints of an undercarriage that can fit with safety allowance on a runway speed surface, max wing span and undercarriage to suit, there is potential to redo the whole delta concept utilising the advantages of a proverse yaw design. It may well not be at 747 capacity! However I think it would be foolish to write off the possibility of very successful passenger and cargo carrying Prandtl wings on the basis that non Prandtl delta wings had some major issues. In my opinion the biggest problem is still going to be active yaw control in high cross winds.
I skimmed this..... so what you are saying (picture me in a Cathy Newman wig) is that this innovation is not practically applicapable..... making it unfortunately.... IMPRACTICAL? Just like "solar frickin roadways"!

And let me just say that it gives me no pleasure in being right in repeatedly pointing out a destructive psychological characteristic in the vast majority of the human population. Especially when I cant seem to even fathom a possible solution for our clamoring blindly toward new flashy innovation that creates more problems than it solves. Welcome to environmentalism, politics, 20 years of chicken loop design, and....... humanities future.

Sincere apologies for the harsh tone, we all have something that gets us worked up.

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Re: Of hump-back whale tubercles, V1 Prandtl equasions and the long ignored V2 Prandtl equasions and birds wings.

Postby fluidity » Mon May 10, 2021 7:24 pm

Matteo V wrote:
Mon May 10, 2021 1:31 pm
I skimmed this..... so what you are saying (picture me in a Cathy Newman wig) is that this innovation is not practically applicapable..... making it unfortunately.... IMPRACTICAL? Just like "solar frickin roadways"!
And let me just say that it gives me no pleasure in being right in repeatedly pointing out a destructive psychological characteristic in the vast majority of the human population. Especially when I cant seem to even fathom a possible solution for our clamoring blindly toward new flashy innovation that creates more problems than it solves. Welcome to environmentalism, politics, 20 years of chicken loop design, and....... humanities future.
Sincere apologies for the harsh tone, we all have something that gets us worked up.
I don't agree but that comes down not to the data, but to different ways we look at things. If you were to look up your own Myers Briggs type and compare it with mine of ENTP it would make perfect sense, we have skills and talents in quite different areas.
Rudders on aircraft are only designed for pointing the aircraft somewhere else, apart from that they are pretty much a waste of time except for compensating for the natural adverse yaw of a poor wing design. In air you can skip the rudder and fly with combo elevator/ailerons. Elevons we call them and I've slope soared gliders with them. On any delta shape they make a lot of sense.
Rudders are there to tackle adverse yaw of simple wings like the Wright brothers had and needed a fix for.
Since then, we've assumed we needed them so rudders are also used on landings to reduce side loads on wheels to (partially)compensate for cross winds.

So you can see I also have been guilty of judging Prandtl and other DELTA wings by a "need" to use a rudder to reduce cross wind landing side loads on wheels.

However it's actually a fallacy, "it's just the way things have always been done around here"

I think the advantages of a more efficient wing justify a modern reassessment of the landing carriage which is the real problem, not yaw of the aircraft.
And there's actually a solution!

I'll call it "Constrained castors for big stuff"

Let the wheels swivel for minimum rubber loss on landing and then deal with straightening the aircraft through steering as it slows down. Crabs walk sideways!

In current times we are a bit past the Wright brothers, we have computers, hydraulics, pnumatics, stepper motors, servo motors etc. If the Wright brothers had started with Prandtl wings this problem would have been solved too, it's just easier now.

Often what we "know" only holds us back. I see the Prandtl wiki is still out of date with it's subject, a new generation is coming through with the same half-story even now :lol:
The Prandtl based teachings and their missing components are going to go down in the history books, much like Luca Turin's brilliant overturning of the establishment to discover how scent really works and to use his discovery as a much more stable foundation for scent creation than previous beliefs.


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