An interesting trial flight attempt...

Ramy wrote:
Actually, I may try to convince wife it may be cheaper on the long run
to buy a motorglider (or electric glider) then pay for aerotows, but I
need numbers...

And here they are!

If you already own a glider, then YOU may be able to afford a high
performance, self-launching sailplane (SLS)! Let me show you how:

The first thing to realize is the motor is about a $20,000-25,000
premium over a similar used unpowered glider (more if you are buying a
new one). Check the ads for gliders that are available both ways, such
as the PIK20E, Ventus CM, DG-400, and so on. Here's an example of what
it might cost an active pilot living in Seattle, WA, and driving the 150
miles to fly at Ephrata, WA:

Additional costs:

$1250 interest cost on the $25,000 motor purchase @ 5%
100 annual on the motor
300 extra insurance due to higher value with the motor
100 fuel and oil for 40 launches
------
$1750 Total additional costs

Avoided costs:

$1400 40 regular tows at $35/tow
300 3 aero-retrieves at $100 each
100 2 car retrieves plus dinner for crew
-----
$1800 Total avoided costs

Net cost: approximately $Zero

The analysis assumes you fly the exactly same way with the SLS as you
did before it, but as you adapt to the SLS, you will find yourself using
the extra soaring opportunities it provides: flying from airports
without a towplane, or when a towpilot isn't available; flying
cross-country when you otherwise wouldn't, because the conditions are
weak, unpredictable or the lift is beyond an easy tow. So let's include
some of this potential as another "avoided cost":

$450

three weekends flying from or near where you live (Seattle in this
case), avoiding travel to Ephrata ($60), motel ($40/night), and food
($50 for two days). Of course, you don't actually have to fly on a
weekend, if you can get afternoons off during the week.

Net cost: $1750 - $1800 - 420= $500 cheaper to fly a SLS!

The above analysis ignores repair costs (routine maintenance is small)
on the engine, which are difficult to quantify because they don't occur
predictably and vary considerably with the age and type of the motor.
Factoring in these costs might show a SLS is more expensive to fly. Even
so, for an active pilot, the additional cost of the SLS may be easily
outweighed by the advantages, providing the pilot can afford the extra
purchase price due to the motor. If not, or if the pilot is not so
active, a partnership can make the costs attractive, while the
versatility of the SLS ensures that both pilots get most, perhaps all,
the flying they wish. As in any glider partnership, each partner is now
responsible for only half the costs.

My point is that the SLS is not as expensive as it seems, if a good
accounting of the avoided costs and the effect of its versatility is
fully considered. A similar analysis can be made for sustainer type
(e.g., Ventus BT) and "touring" style (e.g., Grob 109, Ximango)
motorgliders. For example, someone that flies airplanes and gliders
might discover the touring motorglider does both well enough that only
one aircraft is required.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State USA

www.motorglider.org - Download "A Guide to Self-launching Sailplane
Operation"