Shifting CG In-Flight

[Duster[_2_]]

A friend has installed a system in his home-built glider that enables shifting the CG position forward during higher cruise speeds (e.g., between lift, final glide, etc.). It uses two water reservoirs whose content can be transferred using a 12v pump. This is done, ostensibly, to reduce elevator-induced drag. Does anyone know of other gliders outfitted similarly and is there a demonstrated utility?

[JS[_5_]]

On Saturday, December 14, 2019 at 8:57:57 PM UTC-8, Duster wrote:
> A friend has installed a system in his home-built glider that enables shifting the CG position forward during higher cruise speeds (e.g., between lift, final glide, etc.). It uses two water reservoirs whose content can be transferred using a 12v pump. This is done, ostensibly, to reduce elevator-induced drag. Does anyone know of other gliders outfitted similarly and is there a demonstrated utility?

There was one prototype Schweizer with a trolley that could be cranked forward/aft.
Dick Brandt's Nimbus 3 had a Mercury weight shift ststem for a while. Believe George Moffatt wrote about it in Winning 2.
Jim

[Peter Purdie[_3_]]

Ralph Jones (UK Schempp-Hirth agent and father of 3 World Gold
Medal glider pilots) fitted a water shift system controlled by
microswitches on the flap drive on one of his Nimbus 2s he owned.
On one Nationals flight the electrics failed resulting in a CofG aft of
the aft limit, making it almost uncontrollable in pitch, and an early
landout. Quickly modified to fit an emergency water dump to the
aft ballast bag.

Before EASA, you could do that sort of thing....

At 05:10 15 December 2019, JS wrote:
>On Saturday, December 14, 2019 at 8:57:57 PM UTC-8, Duster
wrote:
>> A friend has installed a system in his home-built glider that
enables
>shi=
>fting the CG position forward during higher cruise speeds (e.g.,
between
>li=
>ft, final glide, etc.). It uses two water reservoirs whose content can
be
>t=
>ransferred using a 12v pump. This is done, ostensibly, to reduce
>elevator-i=
>nduced drag. Does anyone know of other gliders outfitted similarly
and is
>t=
>here a demonstrated utility?
>
>There was one prototype Schweizer with a trolley that could be
cranked
>forw=
>ard/aft.
>Dick Brandt's Nimbus 3 had a Mercury weight shift ststem for a
while.
>Belie=
>ve George Moffatt wrote about it in Winning 2.
>Jim
>
>
>

[[email protected]]

Shifting weight works great in hang gliding, not so much with modern airfoils used in our glass slippers. Pegasus had a weight shifting system in their D model, never heard anyone say it was worth the effort. 7V told me he pumped the mercury aft in Dick Brants Nimbus-3 and left it there! I rigged up a 10# lead weight that slid inside a 3” plastic pipe to see how the Genesis-2 handled with the CG near the aft limit. I flew with it for a year, couldn’t see any noticeable benefit by shifting the weight forward in the run. An aeronautical engineer who’s also a glider pilot told me it’s best to put your CG at about 85% (or more) and leave it there!
Hope this helps,
JJ