Jabiru Winglets

[kasper]

And if its pure efficiency then as noted my reading is that its a pretty close run thing between span vs tip ... but my reading is generally on wing tip devices on flying wings ... there the potential to address directional stability (or instability) adds in the bonus that means you are likely to find them useful. In general a winglet on a swept flying wing has a better/wider efficient speed range than you can achieve on one that uses either geometric or aerodynamic twist to provide directional stability.

 

On unswept wings on our speed group where we are dragging around a tail for stability purposes wing tip winglets are generally either restricted to aesthetics or aesthetics + a bit of increased aileron authority at low speed.

 

 

[Marty_d]

Life is too short to fly ugly aeroplanes!

Bugger.

 

 

 

[facthunter]

Looks beaut but fly bad no good. Style should follow function, not compromise it. (like many designs do) They are good for plastic models on a wanker's desk. Not much else. A plane can look "right" and be right (or close to it.) Winglets let the plane fit into a hangar easier. Most analysis I've seen conclude the extra wingspan as Arthur says will do the same for efficiency. Nev

 

 

[pylon500]

my reading is generally on wing tip devices on flying wings ...

Directional stability, and the need for vertical devices for said stability is dependant on wing sweep.

The more rearward sweep, the less need for vertical surfaces.

 

Swept forward to straight flying wings need vertical surfaces, by the time you get to around 30º sweep back, no vertical surfaces are really needed, especially if there is any dihedral still present.

 

Winglets on a swept flying wing would actually be counter-productive, unless they actually turned down.

 

All these variations do and have existed, as well as those that technically didn't need tip fins (or winglets).

 

 

 

 

 

 

 

 

And an example of a swept flying wing that probably didn't need tip fins,

 

 

But as some here would say, it looked cool....

 

 

[kasper]

Directional stability, and the need for vertical devices for said stability is dependant on wing sweep.The more rearward sweep, the less need for vertical surfaces.

Swept forward to straight flying wings need vertical surfaces, by the time you get to around 30º sweep back, no vertical surfaces are really needed, especially if there is any dihedral still present.

 

Winglets on a swept flying wing would actually be counter-productive, unless they actually turned down.

 

All these variations do and have existed, as well as those that technically didn't need tip fins (or winglets).

 

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And an example of a swept flying wing that probably didn't need tip fins,

 

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But as some here would say, it looked cool....

Ah but you overlooked the point on efficiency - and the SB13 with the swept wing and tip fins is the not to look cool but to provide the range of efficiency.

To explain on flying wings:

 

with straight wings twist cannot balance 1/4 chord moments of the section or variance of CofG/Coflift ... you need low moment sections (unless pendulum stability is used eg parachutes/paragliders) and use of elevons/elevators is inefficient as it needs to kill lots of lift to get a average pitch change due to the wing running on 1 span line - no tail effect

 

With rearswept wings you get the displacement of the elevons/elevators outboard are displaced behind the rest of the sing and you get effective tail ... and with use of geometric or aerodynamic twist you can balance out both the Cm from the wing section and the moment from the CofG/Coflift displacement ... and the added bonus is that the 'twist' out at the tips is behind the CofG and acts as a tail in terms of directional stability ... but it costs.

 

High twist gives solid directional stability but has drag at all angles of attack and worsening drag as you move away from the design point for the twist.

 

Use of minimal twist to aim for your design point of speed/CofG may lead to very low directional stability and use of winglets to add directional stability can provide the stability at lower drag than twist does ... and the drag increases as you move away from the design point with winglets are substantially lower than the drag from having enough twist for stability at design point and then flying away from that design point.

 

That's exactly what the SB13 (last pic) was testing - how to optimise a swept wing for a design point and have lower drag when operating away from that design point to be competitive with standard class 'normal' tallied gliders

 

 

[cooperplace]

Life is too short to fly ugly aeroplanes!My Skylark has really big winglets ( by LSA standards ), in a review on the aircraft by an American magazine their comment was "The Skylark's winglets are either an efficient aerodynamic device or a clever marketing ploy, but either way they work!"

 

I have done some research on the design and from what I can find the design is correct to reduce tip vortices. As for how much difference they make? As I have not flown a Skylark without them I couldn't tell you.

 

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that winglet seems to be there to make a signal, you know, the middle finger in traffic signal.

 

 

[Marty_d]

Use of minimal twist to aim for your design point of speed/CofG may lead to very low directional stability and use of winglets to add directional stability can provide the stability at lower drag than twist does ... and the drag increases as you move away from the design point with winglets are substantially lower than the drag from having enough twist for stability at design point and then flying away from that design point.

Wouldn't there be a point where the drag vs stability is very similar with washout vs winglets? I'm thinking a tapering sweptback like the 4th & 7th pictures where the tips are very small compared to the mean chord. I can understand your point about the SB13, looks like constant chord or very close to it, in which case the drag penalty for washout (twist) would be fairly high.

 

 

[kasper]

Wouldn't there be a point where the drag vs stability is very similar with washout vs winglets? I'm thinking a tapering sweptback like the 4th & 7th pictures where the tips are very small compared to the mean chord. I can understand your point about the SB13, looks like constant chord or very close to it, in which case the drag penalty for washout (twist) would be fairly high.

Absolutely - there is a point (the design point) where twist is sufficient to counter the Cm from the section and the Cm from CofG in front of Coflift ... and ANY flight away from that design point will require elevon to hold the pitch ... and that creates drag.

For models the lack of directional stability that usually results from this is not a problem - the fact that the wing flies sideways or wiggles/wanders its nose is immaterial so many models just do without directional stability.

 

However in human aircraft the wander/wiggles is a PITA ... or nausea inducing. The result is that you put in MORE than necessary twist for pitch ocntrol to induce directional stability ... and that increases the minimum drag quite a lot AND whenever flying away from minimum you hit lots of additional drag ... the usual result is it has a very narrow drag bucket and the low point aint that low ... don;t be fooled by claimed ld ratios of aircraft like the Horton iv and vi ... when they were actually flown at Michigan State Uni after the war in controlled testing the ld was nowhere near as 'brilliant' as claimed ... though they did have nice directional stability.

 

So the issue for human flying wings is to create minimum drag through twist to manage the Cm and CG of the aircraft and sufficient directional stability to make it nice to fly.

 

And this can be seen even in human carrying flying wings that do exist ... this wing/trike setup had absolutely neutral directional stability without the ting tip - it was a vomit comet but add the wing tips and it became like a train on rails and lost no measurable speed ... trike have enough drag to rarely see tip effects.

 

 

And these tips were made by me with two additional goals in mind:

 

1. Same tip left/right so less mold making

 

2. cranked 'seagull' setup - because its cool and unusual

 

the added bonus was that when you took the wingtip off (Velcro to the inside of the upper/lower skins onto a wedge molded into the tip) it was weighted to actually fly as a chuck glider ;-)

 

 

[pylon500]

Actually, the B2 bomber is probably a bit of a red herring, as it most likely flies tail heavy with a negative pitching (normal) section, and relies on computer stability in pitch to make it flyable.

 

It also uses drag rudders, as do most of the other 'finless' flying wings, so really they defeat their own purpose.

 

Might as well just put a long skinny fuse out the back, and stick a tail and fin on it...

 

But as for passive (no rudder) winglets, not a hell of a lot of effect.

 

 

[Mick]

I had an interesting discussion with Matt Hall at Old Station last year after he had fitted winglets to his MXS-R race plane. He said there was no increase, even a slight reduction in straight & level flight but the benefit for him was a significant reduction in bleeding speed in the high G turns. At the time of our discussion Matt said he was still re-learning the aircrafts feel & characteristics as at that stage he had not flown it alot since adding the winglets. Matt did make the comment "The potential is good and watch this space!" Based on how the season played out his comment was not out of place. I am looking forward to chatting more this year now that Matt has clearly settled with the changes.

 

 

[Downunder]

With the development of trikes into fully strutted wings, I wonder why no manufacturer has made a "solid" wing?

 

Weight?......Kasper?

 

 

[Keenaviator]

With the development of trikes into fully strutted wings, I wonder why no manufacturer has made a "solid" wing?Weight?......Kasper?

Billow shift - a characteristic of flex wings that assists with turning.

 

 

[kasper]

Weight - Nope - weight of a 'solid' wing will generally be lower than the fabric wing ... you guys who have not assembled a trike wing will not appreciate that a two seater wing with wire bracing will be in the 55-60kg range and at the upper end of that or slightly higher. A 'solid' wing will not come in higher than that.

 

Billow shift - 'ish. Whilst there was a significant amount of billow shift in the first generation of wings the new ones - esp those designed for 60-80knts - are so damn tight with trailing edges that are pushing the material limits - that they have not a lot of billow shift.

 

Where solid wings have been tried (proper solid wings, not trikes with rigid hangglider wings) the issue is one of control force - precisely the roll control forces. When a long span solid wing was flown the roll control force and response was horrible - hence the 'ish on billow shift which is what can make the turn control on a flexi wing soft. But when a lower aspect ratio wing was flown the control feel was 'normal' but the glide horrendous - you pay somewhere when you change.

 

I have the spars and ribs for a lower aspect solid wing made up and sitting in the container waiting for a chance to put it together ... but house building and work keeps getting in the way.

 

I also have designed a 'fixed' roll augmentation and trim system to go on a longer span solid wing to work elevons built into the wing but have not even started on that wing other than the calcs and drawings. On this think of the elevons working relative to the fixed point of the mast with me still controlling the wing directly ... trim being by moving the fixed points of the control rods on the mast ... the 'fun bit is that the control kinematics I have designed are to be pro-roll for the first section of wing movement relative to the mast and anti-roll thereafter to allow unload of wing force to enter normal bank angles and return to wings level if the wing goes past a set angle relative to mast ... and as its going to be an experiment its all adjustable.

 

As it is I have three factory designed wings and my own designed flexi wing to play around with on the trikes I am focusing on clearing house building stuff to allow more flying time and a bit of building time.

 

 

[pylon500]

I think I can picture what you're going to do, I was going to go a different way back in my hang gliding days, with a high aspect rigid I wanted to build.

 

I think some one else may have tried it already somewhere, where ailerons (only, as pitch is ok via weight) were connected to a floating lift cable system, that was then linked to the aileron belcranks.

 

This meant that it still had the A frame 'wiggle' modern kites have, but the wiggle drove the ailerons instead of the crossbar.

 

 

I later realised that this could run away with itself, so the ailerons needed to be mass balanced, and maybe even have anti-servo tabs.

 

 

[Keenaviator]

Just like Atos.

 

http://www.a-i-r.de/eng/air_04e.php?kat=108#

 

 

[kasper]

I think I can picture what you're going to do, I was going to go a different way back in my hang gliding days, with a high aspect rigid I wanted to build.I think some one else may have tried it already somewhere, where ailerons (only, as pitch is ok via weight) were connected to a floating lift cable system, that was then linked to the aileron belcranks.

This meant that it still had the A frame 'wiggle' modern kites have, but the wiggle drove the ailerons instead of the crossbar.

 

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I later realised that this could run away with itself, so the ailerons needed to be mass balanced, and maybe even have anti-servo tabs.

LOL - yep you figured exactly the same as me - they need to reverse throws to prevent runaway - or as you suggest have antiservo tabs to prevent runaway ... and other than having more mass further out and rearward I would have considered using antiservo tabs instead of reversing kinematics in my drawings.

On your bar wiggle running ailerons there are several rigid wing hanggliders that use bar wiggle for spoilers - easier/lighter to build than ailerons.

 

 

[kasper]

Just like Atos.http://www.a-i-r.de/eng/air_04e.php?kat=108#

except ATOS is spoilers not ailerons - similar to the older Extaccy

 

 

[Bruce Tuncks]

Anjun, the winglets make the ailerons more effective by making the airflow over them more fore and aft.

 

There is a picture of a tufted glider wing where the airflow over the aileron near the tip on the upper surface was INWARDS towards the fuse. This would have been due to a combination of the tip vortex and a flow separation.

 

Here's how to tuft that area... stick lots of short lengths of fine dark wool over the area . Stick them at the front so they trail and show the airflow.

 

Has anybody done this? I would love to see the pictures.

 

 

[Bruce Tuncks]

I was planning to stop and perhaps buy some Jabiru winglets from Mike Sharples ( Avocet) on my way past Hawker in 2 weeks.

 

But he didn't respond to a message and now I'm worried he might have gone. Does anybody know?

 

 

[Old Koreelah]

Can't help you Bruce, but his absence from the forum has been noticed here as well.

 

 

[pylon500]

If you want to align airflow past ailerons, it's better to fit fences on the end of the ailerons than hope for winglets to help (and I certainly wouldn't expect the Jabiru ones to be of any use).

 

Having said that, the Jabiru ailerons need all the help they can get, as they are very poorly designed.

 

 

[anjum_jabiru]

On a positive note, if the ailerons got jammed for any reason you know that it would not make a huge difference as long as the rudder was functional.

 

 

[pylon500]

On a positive note, if the ailerons got jammed for any reason you know that it would not make a huge difference as long as the rudder was functional.

Provided it's one of the newer Jabs, and not a 55.

 

 

[anjum_jabiru]

Why? Is it because the ailerons on a 55 are that good or the rudder is crap?

 

 

[facthunter]

Neither of them are outstandingly effective. Could do with a bit more control authority. Ex bulldozer drivers might have more difficulty than "milk the mouse " types. Nev