SS  Serpent

Serpents. Tails effects on stability:

102 pink ¾ serpent head, built February 2019:  Tests:

1. With original rear keels dived over uncontrollably - wouldn't stay up even for seconds.

2. With keels removed, ribbon tails attached at centre line, flew stably to 30km/hr or so, then WI.

1. With full width tail was weaving unstable and fell off to side when wind dropped.

2. With full width tail attached by cords leaving 300mm gap, no improvement

3. With full width tail attached with bungies, no improvement.

3. With the same tail but attached to head at a single point, flew steady and didn't fall off in light wind.

4. With octopus' tails (unlinked, from octopus 1), had WI from quite low wind speed.

5. With wide tail attached for half its width; very little improvement.

6. With ribbon tails attached to sides of TE, tended to hang off to one side, had slow recovery. Check this

7. With a developed Y tail attachment (width and length) was stable thru to strong winds.  (>50km/hr)  

8. Would 102 with full width tail exhibit WI at lower wind speed than for 30m Serpents- scaling?

30m serpent weaving instability from 25km/hr:

Various different tails tried:

1. With scoops (to add drag): Falling off unstable, sometimes recovered and fell off to the opposite side.

2. Tail split into 3, 4 and 5 longitudinal sections for first 4 to 8m:  No noticeable improvement.

3. Fringes down the sides of the tail: No improvement.

4. A knot in the tail about 4m out; Considerable improvement but not as good as single point attachment.

5.The same head with 8 linked tails (Octopus) has no instabilities through to very strong winds.

In 2019 focus was on taking tail tension through the centre line at the head attachment them moving it out to the edges from a few metres out (to get the tail to fly flat). The theory in this was to allow some angular correction in the head without it having to pull the entire tail around with it.  This was thought to be a point of difference in the 6om Red (Jan 2019) which is stable in strong winds but after a few days heavy wind flying the original dimensional differences had stretched out and, the tail's edges were under tension right from the head- but it still flew well in strong winds. Wind pressure probably neutralises the tension differentials anyway.

Scaled to 60m, Serpents have no instabilities to above 50km/hr- why?

The two 60m Serpents (red original and Al farsis') are made of different fabric (by weight and stretch) and , the Al farsis' has (and needed) an extra bridle row, but they fly very similarly and are both stable through to above 50km/hr.

 If the difference is in scaling, is it because of entrained air mass, or because of different pocketing effect because fabric is proportionally stretchier?

If not scaling, what then?

All Serpents (in fact all SSSLs with serpent style heads) are very sensitive to head bridles 3, 4 and 5.  Pulling these in creates a toed-in keel effect which reduces WI dramatically.  In fact this is also noticeable on curved leading edge keelless pilot prototypes.  The 30 m Serpents appear to have proportionally around the same pull in of 3, 4 and 5 bridles as the 60m's

As of January 2022, tests, the yellow, magenta and mauve 30m Serpents, which have various differences, all show WI at around the same wind speed. 

There's clearly a solution in the tail attachment geometry, but graphical imperatives don't permit a narrower tail - which also unfortunately prevents making smaller more manageable SSSL Serpents. 

Another possible and as yet untried solution is to try heavier tail fabric- works for the SSSL Rays and it's noted that tail drag is proportional to tail weight not area for smooth tails, 

Falling off to one side in light winds (which all Serpents so far are subject to) is a function of tail length, and attachment geometry- but is it reduced or exacerbated by more weight?     

The simpler bungy, aeolian rear bridles and sliding ring automatic bridle on the Mauve 30m seems to work as well as the more complex pulley system used on the yellow and magenta 30m Serpents- check this. - appears to require lighter bungy.

LE bridles need to be set so that the LE centre collapses last; The magenta 30m at one stage had fixed centre leading edge bridles with the auto bridle rigged only to the outer LE bridles. This appeared to work satisfactorily, needs to be tried again.

23 Jan '22: changed mauve 30m tail from magenta , 1.5 kg to mauve 2.1 kg.  Looks better but seems more WU- has barely any wind range before WI onset.  Seemed little better after centre rear bridle  was let out 100mm (to same as other centre body bridles) and adjusting line putting tension on tail centre was released.  Heavier tails cause earlier onset WI?  Try shortening the tail. 

Mauve head 30m, 26 January strongish mid-range, WU shortish line.  Would fly for no more than a minute or so- wild figure eighting.  With rear 11m of tail removed (26m total) was even more WU- looped.  Suggests that there are multiple stable modes - one for Serpent heads with minimal tails and especially ribbon tails attached single point or on tuned Y, but another with a "brute force" tail - long enough and heavy enough to keep the head pointed up.  Brute force mode comes with falling off to side when the wind fails - like the 60m's.

29 Jan '22: modified magenta 30m Serpent by halving tail width from 700mm below head  and removing tail fringes.  Light mid-range wind Wakanui, flew well but probably still WU, maybe worse, definitely not better.  LE required letting out a notch to compensate for less tail drag.

Wakanui Kite day 30 Jan '22 light wind early on, quite strong easterly later in day.

30m magenta with narrow tail and small whiskers flew well under Ray 4 all day, as did  the 30m yellow.  30m mauve was quite WU even in lightish wind but then flew OK under SSP 14 with some LE through bridle buckling.