Ventus 3

[[email protected]]

New pic on the SH site. First flight very soon.

[Clay[_4_]]

What is the advantage of a polyhedral(?) wing?

[Darryl Ramm]

On Thursday, December 24, 2015 at 12:57:38 PM UTC-8, Clay wrote:
> What is the advantage of a polyhedral(?) wing?

Never being mistaken for a PW-5?

[[email protected]]

On Thursday, December 24, 2015 at 3:57:38 PM UTC-5, Clay wrote:
> What is the advantage of a polyhedral(?) wing?

One benefit of the greater dihedral outboard is that it has a longer moment to apply stablizing force which increases roll stability and roll response to yaw.
It also spreads the the flow field giving the effect of more span than a "flat" wing.
It allows the tip skids or wheels to be further inboard so the tips don't see ground loads.
It also looks cool.
UH

[Jonathan St. Cloud]

One aerodynamicist explained that it is a benefit in climb but has a penalty in cruise. It does look cool though. Word on the street it is a three year wait for a new Ventus

[Clay[_4_]]

So you have 65 ft of wing in a 60 ft span (I'm exaggerating). Glider thinks it has 65 ft span. Runway lights must like it too. Not sure my 5'1" wife would.

[jfitch]

On Thursday, December 24, 2015 at 1:49:12 PM UTC-8, wrote:
<SNIP>
> It allows the tip skids or wheels to be further inboard so the tips don't see ground loads.

It also puts a lot of wing very close to the ground on roll out. Closer than some rocks, weeds, etc. From experience owning a Duo.

[JS]

Looks really cool.
Handles very nicely in the air.
More ground clearance with wings level.
(you may need to ask the wing runner to hold it higher)
With a low sun angle, there's always a reflection catching your attention.
Doesn't fit in the trailer as easily.
Pulling the tip out of the trailer, you're not on the center of gravity.
If there's any undulations or rocks, with a wing down the wing can hit outboard of the skid.
Not much to compare to a PW-5, unless V3 has a forward-hinged canopy.
Are the multiple angles easy to refinish?
Jim

[Martin Gregorie[_5_]]

On Thu, 24 Dec 2015 13:56:24 -0800, Jonathan St. Cloud wrote:

> One aerodynamicist explained that it is a benefit in climb but has a
> penalty in cruise. It does look cool though. Word on the street it is a
> three year wait for a new Ventus

Curiosity: why did he say that there's a benefit on the climb but penalty
during the cruise?

I've been told that using a multi-panel wing is better because the drag
from a dihedral break increases sharply as the angle increases: so much
so that a six panel wing performs better than a four panel wing of the
same span and area because of reduced drag from dihedral breaks. I don't
remember any speed effect being mentioned, hence my question.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[waremark]

On Thursday, 24 December 2015 17:26:24 UTC, wrote:
> New pic on the SH site. First flight very soon.

Looks quite similar to the Arcus wing. The Arcus glides well at speed, although the wing loading cannot be particularly high.

[[email protected]]

On Thursday, December 24, 2015 at 4:56:27 PM UTC-5, Jonathan St. Cloud wrote:
> One aerodynamicist explained that it is a benefit in climb but has a penalty in cruise. It does look cool though. Word on the street it is a three year wait for a new Ventus

I spoke at length with Tilo at the factory this year regarding the new V3. He had put together a crack team, with many aerodynamicists outside the direct employment of SH to design a wing whose purpose is for less time thermalling and more time in level flight. I doubt that they would purposely design such a wing that pays more of a penality in straight flight. Tilo specifically mentioned that newer models of optimal lift theory/design account for a three dimensional model that dictates the need for dihedral for straight flight optimization of lift. His words, not mine. The wing is amazing when seen in person. Photographs do not do it justice.

[J. Nieuwenhuize]

Op vrijdag 25 december 2015 02:38:04 UTC+1 schreef :
> On Thursday, December 24, 2015 at 4:56:27 PM UTC-5, Jonathan St. Cloud wrote:
> > One aerodynamicist explained that it is a benefit in climb but has a penalty in cruise. It does look cool though. Word on the street it is a three year wait for a new Ventus
>
> I spoke at length with Tilo at the factory this year regarding the new V3.. He had put together a crack team, with many aerodynamicists outside the direct employment of SH to design a wing whose purpose is for less time thermalling and more time in level flight. I doubt that they would purposely design such a wing that pays more of a penality in straight flight. Tilo specifically mentioned that newer models of optimal lift theory/design account for a three dimensional model that dictates the need for dihedral for straight flight optimization of lift. His words, not mine. The wing is amazing when seen in person. Photographs do not do it justice.


If we go back to theory, the perfect wing is a double super-ellipse (Lamé curve):
http://en.wikipedia.org/wiki/Superellipse

Both the top view and the dihedral of the wing should have the shape of a super-ellipse for lowest induced drag for a given bending moment (structural weight) and wetted area (profile drag at high speeds). Both the A350 and the Dreamliner are very close to this ideal:
wallpaperswide.com/download/boeing_787_dreamliner-wallpaper-1920x1200.jpg

Another plus compared to a wing without dihedral and winglets is that the interference drag between the winglet and the wing is much reduced since it's proportional to the radius of the fillet and how sharp the break is.

Such a gradually curved wing is impossible to build because all the control surfaces would have a bend in them. The wing with sections progressively canted more and more (polyhedral) is a good compromise.

It also helps with flutter apparantly. The Vortex shedding frequency of the various sections make the critical flutter speed for such a wing higher, allowing either a higher VNE, or a less stiff and thus lighter wing structure.

[[email protected]]

On Thursday, December 24, 2015 at 12:26:24 PM UTC-5, wrote:
> New pic on the SH site. First flight very soon.

Will it be 18M only or 15/18M or 18/21M?

[ND]

> Are the multiple angles easy to refinish?

they aren't any harder, just more involved. but that's what separates the men from the boys ;)

In some ways it actually makes a refinish easier though i think. but that deals with the finer points of the process. stuff that people wouldn't think matters that actually does. at a break in the dihedral, you can hide your spray overlaps better.

> Jim

[[email protected]]

On Monday, December 28, 2015 at 8:27:09 AM UTC-5, ND wrote:
> > Are the multiple angles easy to refinish?
>
> they aren't any harder, just more involved. but that's what separates the men from the boys ;)
>
> In some ways it actually makes a refinish easier though i think. but that deals with the finer points of the process. stuff that people wouldn't think matters that actually does. at a break in the dihedral, you can hide your spray overlaps better.
>
> > Jim

Certainly easier than repair or refinish of an elliptical contour.
UH

[krasw]

sunnuntai 27. joulukuuta 2015 16.34.34 UTC+2 kirjoitti:
> On Thursday, December 24, 2015 at 12:26:24 PM UTC-5, wrote:
> > New pic on the SH site. First flight very soon.
>
> Will it be 18M only or 15/18M or 18/21M?

18/15.

[[email protected]]

On Monday, December 28, 2015 at 10:56:28 AM UTC-5, krasw wrote:
> sunnuntai 27. joulukuuta 2015 16.34.34 UTC+2 kirjoitti:
> > On Thursday, December 24, 2015 at 12:26:24 PM UTC-5, wrote:
> > > New pic on the SH site. First flight very soon.
> >
> > Will it be 18M only or 15/18M or 18/21M?
>
> 18/15.

18/15: surprised. Side hinged or front hinged canopy?

[Andy Blackburn[_3_]]

On Sunday, December 27, 2015 at 1:56:26 AM UTC-8, J. Nieuwenhuize wrote:
>
> If we go back to theory, the perfect wing is a double super-ellipse (Lamé curve):
> http://en.wikipedia.org/wiki/Superellipse

I know we've had this discussion before and maybe something is lost in translation - but I cannot find a reference in an aerodynamics or aircraft design text anywhere to confirm use of super-elipse as a wing planform plus dihedral choice - optimal or otherwise. The only reference to super-elipse anywhere in any aircraft design text I could come up with was here:

http://www.dtic.mil/dtic/tr/fulltext/u2/a461449.pdf

It refers to the cross-section shape for a fuselage as a super-elipse is generally a rounded rectangle shape. I'm not clear how this shapes maps to an elliptical shaped wing planform with continuous polyhedral - which is what I think the post is describing. Even the included wikipedia page doesn't show that. Double-elipse refers to a wing where both the leading and trailing edges are eliptical - as in the Supermarine Spitfire of WW II. Do you have a reference to any technical papers on double super-elipse (planform AND polyhedral) as an optimal design for wings. I can't find anything and am curious about where this comes from.

http://www.militaryairshows.co.uk/must.jpg

>
> Both the top view and the dihedral of the wing should have the shape of a super-ellipse for lowest induced drag for a given bending moment (structural weight) and wetted area (profile drag at high speeds). Both the A350 and the Dreamliner are very close to this ideal:
> wallpaperswide.com/download/boeing_787_dreamliner-wallpaper-1920x1200.jpg

Here is a nice planform view of the 787.

http://i.stack.imgur.com/1OUtR.jpg

I'd be hard-pressed to describe the planform as a perfect eclipse - it seems to be the typical swept double-taper design with a higher aspect ratio outer panel than typical in earlier designs. It's a transonic wing design so you'd expect some different considerations than for a glider. The shape of the dihedral is more a function of wing flex than anything else, somewhat enhanced by the raked winglet. I've seen no claims by Boeing that the dihedral is for anything other than handling and ride qualities - that they do claim. They do make aerodynamic claims about the raked winglet, but it is a more complex rationale than simple elliptical planform and they have since introduced a double-raked winglet on the 737 Max. Flow fields at wing tips are...complicated.

https://thedesignair.files.wordpress.com/2012/05/737max-winglet-2-630-620x413.jpg

>
> Another plus compared to a wing without dihedral and winglets is that the interference drag between the winglet and the wing is much reduced since it's proportional to the radius of the fillet and how sharp the break is.

That seems to be true from published studies but for a glider Reynolds number the radius of curvature above which there is no additional benefit is less than a meter. The V3 radius of curvature is more than 10 meters for the polyhedral section and considerably tighter for the winglet transition, so I suspect more complex considerations are involved - possibly handling and ground clearance of the tips as has been previously discussed. I am skeptical of the arguments that you can sneak in more wing area or aspect ratio onto a polyhedral wing as only the wing planform component in the direction perpendicular to gravity (in level flight) matters. Any component of lifting force inward on one wing is cancelled by the opposite wing so you get net zero lift and some additional drag, which is why most aircraft don't have 45-degrees of dihedral and spans along the wing of 21 meters instead of 15.

>
> Such a gradually curved wing is impossible to build because all the control surfaces would have a bend in them. The wing with sections progressively canted more and more (polyhedral) is a good compromise.

True that.

>
> It also helps with flutter apparantly. The Vortex shedding frequency of the various sections make the critical flutter speed for such a wing higher, allowing either a higher VNE, or a less stiff and thus lighter wing structure.

Flutter is an aeroelastic effect so it's a function of stiffness, sweep, twist and bending - among other things. It's hard to say very much about polyhedral all by itself. Maybe.