FES (Front Electric Sustainer)

On Nov 5, 5:10*am, LimaZulu wrote:
On 4 nov., 18:10, Herbert kilian wrote:

Here is a video of a composite launch of a LAK 17 by means of auto-tow
followed by using the electric sustainer that is installed in front of
the pilot. *Looks like a promising new launch method provided the car
gets the glider high enough for a dealing with any launch
interruptions.http://blog.cafefoundation.org/?p=4759
It says nothing about the time it takes to get to around 1,500' AGL,
the altitude I usually release from tow. *The remaining charge in the
Li-Po batteries may not be sufficient for a normal stustainer
operation (20-30 min) at the end of the day but you can always throw
in more batteries, I suppose.
Herb, J7

You can download igc file of this flight, where you can see climb rate
data.
At end of flight was another climb for about 1000m (17-20kW of power)

http://www.onlinecontest.org/olc-2.0....html?dsId=213....

As there is adjustable throttle, pilot can fly horizontaly on low
power (4kW only due to very clean aerodinamic) for more than one hour
with fully charged batteries (4,2kWh of energy in 30kg of batteries).
Total climb available with 4,2kWh is about 1500m, at 400kg take-off
weight.
So with initial 450m (1,500' AGL) of climb to catch thermal, there is
still about 2/3 energy left. This is enough for another 65 km of
horizontal flight to get home!

Regards,

Luka

Thank you Luka, very interesting.
Since you seem to a member of the development team, there are other
questions I have. Of utmost interest is of course the amount of drag
that the folded propeller creates and how it typically affects the
glider's polar. As time goes on, you will most likely offer
conversion kits for a number of gliders and I hope, my LS8-18 might be
one of them.
Also, what is the min height you must have for the shaft center of the
prop from the ground, is that a restriction?(nobody should be tempted
to ground launch or land with the prop running) Are gliders with 4
inch wheels OK?
This would be a great kit to put on our experimental certified gliders
here in the US!
You probably heard this before but I had this idea about 5 years ago
and made some sketches but never took the steps to verify the
concept. Congratulations on making it work! You should try to get an
article into 'Segelfliegen'.

Herb

On 11/5/2011 1:44 PM, Herbert kilian wrote:


Thank you Luka, very interesting.
Since you seem to a member of the development team, there are other
questions I have. Of utmost interest is of course the amount of drag
that the folded propeller creates and how it typically affects the
glider's polar. As time goes on, you will most likely offer
conversion kits for a number of gliders and I hope, my LS8-18 might be
one of them.
Also, what is the min height you must have for the shaft center of the
prop from the ground, is that a restriction?(nobody should be tempted
to ground launch or land with the prop running) Are gliders with 4
inch wheels OK?
This would be a great kit to put on our experimental certified gliders
here in the US!
You probably heard this before but I had this idea about 5 years ago
and made some sketches but never took the steps to verify the
concept. Congratulations on making it work! You should try to get an
article into 'Segelfliegen'.

Herb


If I understand correctly, you need a glider with a circular fuselage
cross section at the transition between the spinner and the nose.
However, most glider noses have an oval cross section. So a conversion
kit would not work for many gliders (without modifying the shape of the
nose).

Luka is the original developer of the FES, together with his father
who is the Lak agent for Slovenia. The Lak factory has adopted the
design and you can order new gliders from the factory with FES
installed. They have a comparison with another glider suggesting that
the drag of the folded propeller is negligible. I certainly can’t
tell any difference with mine – being able to use the best lines of
energy is far more important, and saving retrieves is a huge
convenience.

As well as Lak 17s, Luka has modified a Silent which had a non-
circular nose. He had to develop a new shape, which was more cut back
and redesigned/remade along the fuselage to arrive at a circular cross
section at the point that the spinner/nose cone joined on.

(I have a Lak 17a which Luka converted to FES – it was the 6th, AIUI,
and he has done a few more since. The Silent was in his workshop with
work commenced when I took mine there in late 2010.)

He developed the FES sustainer first on his own glider, then modified
it before doing the Silent and mine, and meanwhile developed the more
powerful motor and larger battery version for self launching, with
which he won an award – see his website.

There is about 2 ½ inch clearance from propeller to level ground on
the basic Lak 17 with a 1 meter (39 inch) diameter propeller. I would
not risk running the FES while moving on the ground except on smooth
tarmac. In emergency, if it failed to stop running before landing, I
would expect damage. I don’t know if a modified undercarriage is
planned for self launch with more clearance.

I understand that Luka will consider retrofits to other gliders if
they have suitable fuselages, but I would have thought that each
different type is a major development effort, and the economics might
be difficult for a one-off. If interested, you could always write and
ask him.

(I am not an agent for Luka, just a satisfied customer via the UK
agents, Baltic Sailplanes, but I have written a couple of articles for
the BGA magazine, Sailplane and Gliding, about the FES – why I went
for it, and how I have found it – to sum up, very pleasing.)

Chris N.