ALPHA Electro
www.pipistrel-aircraft.com
REV.0
POH-167-00-40-150
Cruise
Aircraft at MTOM, recommended cruise power of 20-30 kW in international standard atmosphere
(ISA), sea level altitude, flaps retracted (0°):
ALPHA Electro ALPHA Electro
Cruise airspeed 85 kts (157 km/h)
Cruise energy calculation
When flying the ALPHA Electro outside the circuit pattern, it is important to estimate when the re-
maining energy is sufficient for a safe return to home base. The PNR (Point of No Return) in flight is
when we have just sufficient %SOC to return to base (and arrive there with 30%). This PNR is calculated
for flights from point A to point A (A-A). Most ALPHA Electro flights are A-A.
NO WIND CONDITION - EXAMPLE
When flying in no wind conditions along a straight track, calculating our PNR is not particularly dif-
ficult. We have enough %SOC available to take off and fly toward our destination along our track
knowing, as long as we do not proceed beyond the halfway point, we should be able to make it back
to home airfield safely.
If we start with 100% SOC. We have to be back with 30%. Therefore we have a usable SOC of 70%. Half
of this useable SOC is 35%. So, we have to turn back towards the home base - mission accomplished
or not - at 65% of SOC. The halfway point is 65% of SOC. This is only true if we start with a full charge.
WINDY CONDITIONS - EXAMPLE
Cruise speed 85 kts IAS, and we have an outbound tailwind of 15 kts (from GPS ground speed reading).
The difference between the IAS and TAS at ALPHA Electro altitudes are negligible and we can take the
IAS as TAS.
Therefore:
GS outbound: 85 kts + 15 kts (tailwind) = 100 kts
GS inbound: 85 kts - 15 kts (headwind) = 70 kts
The %SOC to PNR is calculated with the PNR equation:
%PNR SOC = useable SOC x GS homebound / (GS homebound + GS outbound).
In our example, this is: 70% x 70 kts / (100 kt + 70 kts) = 28%, that is the %SOC used to reach PNR.
So our PNR is 100% - 28% = 72%, where 100% is the initial SOC in this example.
This is very important. If we are flying with a tailwind we have to turn back to the point of origin
much sooner.
Performance
5-7
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