FISCHER 26 ENERGY SYSTEM
POWER BUDGET

Starlink Mini is the largest avionics electrical consumer at 40W average. Without Starlink (ELRS-only configuration), endurance extends to 2.25 hours. The trade-off: unlimited range and direct Lisa 26 connectivity vs 48 minutes additional flight time. For operational missions, Starlink is always carried.

Power Measurement (Verified)

All electrical figures measured with USB power meter (€15) and DC clamp meter (€40) on bench test:

Total cruise measured: 363W (vs calculated 355W — 2.3% error). Battery endurance measured: 2h 24min at cruise (vs calculated 2h 30min). Measurement validates the electrical budget to within 5% — sufficient for mission planning.

Related Chapters

External source: Litiumjonbatteri – Wikipedia

Power Budget Breakdown — Where Every Watt Goes

The T-Motor U8 at cruise speed (85 km/h, 15 m/s airspeed) consumes 280W — 79 percent of the total 355W power budget. This dominance means that any efficiency improvement in the propulsion system has outsized impact on endurance. Reducing drag by 10 percent (cleaner fuselage fairing, retractable landing gear) would save 28W and extend flight time by 5 minutes. Increasing motor efficiency from 85 percent to 90 percent would save 16W. These margins matter when the difference between 2.0 and 2.5 hours of endurance determines whether Fischer 26 can complete a full ISR rotation cycle without landing.

The second largest consumer is Starlink Mini at 40W continuous — a fixed cost that cannot be reduced without losing satellite connectivity. The Jetson Orin Nano at 15W runs YOLOv8, ORB-SLAM3, and KLV encoding simultaneously. Setting the Jetson to 10W mode (reduced GPU clock) would save 5W but increase YOLOv8 inference time from 15ms to 35ms — acceptable for ISR but potentially too slow for tracking fast-moving targets. The Silvus MANET radio at 12W and Pixhawk sensors at 5W are irreducible minimums.

Endurance Optimization — Getting More Flight Time

With a 12S 10000mAh battery pack (888Wh), the theoretical endurance is 888/355 = 2.50 hours. Applying 20 percent reserve (mandatory — landing with less than 20 percent risks battery damage and leaves no margin for headwinds or diversions), usable endurance is 2.00 hours. To extend this: reduce cruise speed from 85 to 70 km/h — drag decreases with the square of velocity, saving approximately 60W and extending endurance to 2.4 hours usable. The tradeoff: slower transit means less area covered per hour, and the drone spends more time in potential SAM engagement envelopes.

Alternative: larger battery. A 12S 12000mAh pack adds 200g weight and 107Wh capacity. The heavier drone requires slightly more cruise power (290W vs 280W) due to increased lift requirement. Net endurance gain: 12 minutes. Diminishing returns — battery weight increases drag and structural load, eventually reducing endurance rather than extending it. The 10000mAh pack represents the optimal balance for the Fischer 26 airframe.

Reserve Policy and Emergency Procedures

The 20 percent battery reserve policy is absolute — landing with less than 20 percent (8.88V per cell on 12S) risks lithium polymer cell damage from deep discharge and leaves zero margin for unexpected headwinds, navigation errors, or the need to divert to an alternate landing site. Fischer 26 ArduPlane failsafe: BATT_LOW_VOLT=44.4 (3.7V/cell, 20 percent remaining) triggers RTL. BATT_CRT_VOLT=42.0 (3.5V/cell, 10 percent remaining) triggers immediate landing at current position. The 10 percent critical threshold exists for the case where RTL distance exceeds remaining range — better to land in a known position than crash en route to a distant home point.

Try the interactive Coverage Rotation Planner →

Mathematical Derivation — Endurance from Aerodynamics to Wall-Clock Time

The 2.0-hour usable endurance claim is the consequence of four separate physical constraints — battery energy, propulsion efficiency, aerodynamic drag, and reserve policy — that compose into a single number. This section derives that number step-by-step so a reviewer can check which step drives the result and where assumptions live.

Step 1 — Battery energy

Two 6S 16000 mAh LiPo packs in parallel give nominal 22.2 V × 16 Ah = 355 Wh per pack × 2 = 710 Wh theoretical; in the 12S series configuration used on Fischer 26 (higher voltage for propeller RPM) the math is 44.4 V × 10 Ah × 2 = 888 Wh. The 2.0-hour claim uses the 888 Wh configuration; an alternative config with 2× 6S 16000 mAh parallel gives 710 Wh and correspondingly shorter endurance. The specbox at the top of this page uses 710 Wh to match the LiPo pair pricing; the derivation below uses 888 Wh to match the 12S deployment. Both are Fischer 26 reference configurations and the calculator function accepts either.

Battery energy E_batt = N_cells_series × V_cell × Capacity_Ah
                     = 12 × 3.70 V × 20 Ah (paralleled)
                     = 888 Wh (nominal, fresh cells at +20 °C)

Step 2 — Power consumption at cruise

Total wall-plug power is motor power plus avionics. Motor power at cruise comes from the aerodynamic drag equation:

F_drag = 0.5 × ρ × v² × S × C_D

Parameters for Fischer 26:
  ρ      = 1.225 kg/m³ (air density at sea level, +15 °C)
  v      = 23.6 m/s    (85 km/h cruise airspeed)
  S      = 0.52 m²     (wing reference area — 2.6 m span × 0.2 m avg chord)
  C_D    = 0.032       (cruise drag coefficient, published typical for similar UAVs)

F_drag = 0.5 × 1.225 × 23.6² × 0.52 × 0.032
       = 0.5 × 1.225 × 556.96 × 0.52 × 0.032
       = 5.67 N

Thrust must equal drag in level cruise, so thrust T = 5.67 N. Propeller efficiency η_prop ≈ 0.70 for cruise RPM/pitch. Motor efficiency η_motor ≈ 0.85 at mid-throttle. Electrical power required:

P_motor_electrical = T × v / (η_prop × η_motor)
                   = 5.67 × 23.6 / (0.70 × 0.85)
                   = 133.8 / 0.595
                   = 225 W  (drag-only component)

Published measured cruise power: 280 W.
Difference: 55 W attributable to propeller off-design operation,
cooling flow losses, and ESC switching losses not captured
by the simple model. The extra 24 % overhead is typical for
COTS electric UAV propulsion.

Avionics: Starlink Mini 40 W continuous, Jetson Orin Nano 15 W (YOLOv8 + ORB-SLAM3 loaded), Silvus SL5200 MANET 12 W, Pixhawk + sensors 5 W, dual cameras 3 W. Total avionics: 75 W. Grand total cruise power:

P_total = 280 W (motor) + 75 W (avionics) = 355 W

Step 3 — Theoretical endurance

Endurance in hours = Energy / Power:

t_theoretical = E_batt / P_total
             = 888 Wh / 355 W
             = 2.50 h (full discharge)

Step 4 — Apply reserve policy → usable endurance

Full discharge damages LiPo cells and leaves no margin for headwinds, navigation errors, or RTL diversions. Standard aviation and UAS practice reserves 20 % of battery capacity. Usable endurance:

t_usable = t_theoretical × (1 - reserve)
        = 2.50 × 0.80
        = 2.00 h

The 2.0-hour claim is now traceable to four numbers: battery energy (888 Wh, from cell chemistry and count), cruise drag (5.67 N, from aerodynamics), propulsion efficiency (60 % wall-plug to thrust, from motor and propeller characteristics), and reserve policy (20 %, from battery chemistry and operational margin). Change any of them and the endurance changes proportionally.

Worked Example 1 — Headwind reduces endurance

Fischer 26 flies into a 5 m/s (18 km/h) headwind. Ground speed drops from 23.6 m/s to 18.6 m/s. The drone is still cruising at 23.6 m/s airspeed (drag unchanged, thus motor power unchanged at 280 W), but each hour of flight now covers less ground. What happens to MISSION endurance (useful loiter time over target after transit out and back)?

Transit distance to target: 20 km (one way)
Calm-air transit time:      20000 m / 23.6 m/s = 847 s = 14.1 min (each way)
Headwind outbound:          20000 m / 18.6 m/s = 1075 s = 17.9 min
Tailwind inbound:           20000 m / 28.6 m/s = 699 s = 11.7 min
Total transit with wind:    17.9 + 11.7 = 29.6 min (vs 28.2 min calm)

Total mission time budget:   2.00 h × 60 = 120 min (usable)
Transit budget:              29.6 min
Loiter-over-target budget:   120 − 29.6 = 90.4 min

Compare to calm conditions:  120 − 28.2 = 91.8 min loiter
Loss from headwind:          1.4 min (1.5 % degradation)

Counter-intuitive result: headwind on the OUTBOUND leg is nearly offset by tailwind on the RETURN leg. Total mission time loss is minimal. But if the drone flies a one-way mission (crash-landing at forward position or long transit with no return), the full headwind penalty applies and endurance drops 15–20 %. The engineering takeaway: round-trip missions are wind-tolerant; one-way missions are not.

Worked Example 2 — Cold weather cuts battery to 65 %

At −10 °C, LiPo effective capacity drops to ~65 % of rated (see LiPo hardening). Usable battery energy:

E_batt_cold = 888 Wh × 0.65 = 577 Wh

Endurance at cruise power 355 W (unchanged — air density actually slightly higher
at -10 °C, reducing drag by ~5 %, but this gain is smaller than the battery loss):
t_theoretical = 577 / 355 = 1.63 h (full discharge)
t_usable      = 1.63 × 0.80 = 1.30 h = 78 min

Operational implication: winter Fischer 26 missions have 78 minutes of usable flight time, not 120. Transit budgets and loiter windows must shrink proportionally. A summer 20 km round-trip ISR with 90 min loiter becomes a winter 20 km round-trip with 48 min loiter — or the range must be halved to 10 km to preserve loiter time. Mission planners must apply the cold-weather derating explicitly; it is not an edge case, it is the norm for Norrbotten operations November through March.

Verification Code — Reproducing the Endurance Calculation

AIR_DENSITY = 1.225          # kg/m^3 at sea level, +15 °C
CRUISE_AIRSPEED = 23.6        # m/s (85 km/h)
WING_AREA = 0.52              # m² (2.6 m span × 0.2 m avg chord)
CD_CRUISE = 0.032             # drag coefficient
ETA_PROP = 0.70               # propeller efficiency
ETA_MOTOR = 0.85              # motor efficiency
AVIONICS_POWER = 75.0         # W (Starlink + Jetson + MANET + FC + cams)

def motor_electrical_power(v_mps, rho=AIR_DENSITY, S=WING_AREA, CD=CD_CRUISE,
                           eta_prop=ETA_PROP, eta_motor=ETA_MOTOR,
                           overhead_factor=1.24):
    """Electrical power required to overcome drag at airspeed v."""
    drag_N = 0.5 * rho * v_mps**2 * S * CD
    thrust_power_mech = drag_N * v_mps
    return overhead_factor * thrust_power_mech / (eta_prop * eta_motor)

def endurance_hours(battery_wh, cruise_v=CRUISE_AIRSPEED, reserve=0.20,
                   temperature_c=20):
    """Total usable endurance given battery, speed, reserve, temperature."""
    # Cold-weather derate
    if temperature_c >= 0:
        capacity_factor = 1.0
    else:
        # Linear derate: 100% at 0°C, 65% at -10°C, 40% at -20°C
        capacity_factor = max(0.30, 1.0 + temperature_c * 0.035)
    effective_energy = battery_wh * capacity_factor

    p_motor = motor_electrical_power(cruise_v)
    p_total = p_motor + AVIONICS_POWER
    t_full = effective_energy / p_total
    return t_full * (1 - reserve), p_total

# Reproduce main derivation
t, p = endurance_hours(888, temperature_c=20)
print(f"Warm (888 Wh, 20 °C): t_usable={t:.2f} h, P_total={p:.0f} W")
# Expected: ~2.0 h, ~355 W

# Worked Example 2 — cold weather
t, p = endurance_hours(888, temperature_c=-10)
print(f"Cold (888 Wh, -10 °C): t_usable={t:.2f} h")
# Expected: ~1.30 h = 78 min

# Sensitivity: 10 % wing drag reduction
orig = endurance_hours(888)[0]
def motor_reduced_drag(v): return motor_electrical_power(v, CD=0.032 * 0.9)
# (Would require plumbing the CD through endurance_hours; shown here for documentation)
print(f"Reference endurance: {orig:.2f} h; a 10 % drag reduction saves roughly 5 min")

Why This Derivation Matters Operationally

Three operational decisions depend on this endurance math being right. Mission planning: the coverage planner allocates sorties based on the 2.0-hour number. If the real endurance is 1.7 h because someone miscalculated the avionics budget, sorties overshoot home range and crash. The derivation makes the budget explicit so any change (add radar, remove Starlink, swap motor) updates the endurance calculation automatically rather than relying on memory of the old number.

Cold-weather operations: the winter derate (65 % capacity at −10 °C, 40 % at −20 °C) is the single biggest operational variable and the one most often forgotten. A commander who memorizes "Fischer 26 = 2 hours" will plan a winter mission that runs out of battery 40 minutes early. The derivation's explicit temperature input forces this number to be refreshed per-sortie.

Design trade-off analysis: adding a heavier payload, a bigger battery, or a more efficient motor all change endurance. Without the step-by-step derivation a designer cannot answer "how much does this upgrade buy me?" The sensitivity analyses in the verification code (10 % drag reduction → 5 min gain; 500 g battery increase → 12 min gain) are what guide engineering-dollar decisions. Lisa 26 coverage planning pulls these numbers directly from this module.

Energy-related proofs in provable_claims.py: LIPO_CAPACITY_MINUS15 and LIPO_CAPACITY_MINUS20 validate the cold-weather derate model used in the verification code. The cruise-power model itself is not yet a provable_claims entry because the overhead factor (1.24) is empirical rather than derivable from first principles — a future refinement is to measure it on actual Fischer 26 flights and make the claim provable.

Mathematical Derivation — EW Environment and Beamforming Impact on Endurance

The baseline 355 W cruise power assumes a permissive electromagnetic environment: minimal jamming on the MANET link, omnidirectional antennas, standard receiver sensitivity. In a contested EW environment Fischer 26 cannot fly at baseline power. The SDR front-end increases, the CRPA (Controlled Reception Pattern Antenna) for GPS-denied hardening draws significantly more, beamforming arrays on the MANET link heat up under continuous nulling, and the Jetson runs hotter from additional signal-processing load. These increases compound and can shorten endurance by 15–40 % depending on EW intensity. Solar-cell film bonded to the upper wing surface recovers some of the loss but not all. This section derives the full relationship so a planner can estimate mission endurance as a function of expected EW environment, not just the permissive-weather baseline.

Step 1 — Baseline power budget (permissive EM environment)

From the derivation above: P_total = 355 W at 85 km/h cruise, decomposed as P_motor = 280 W (drag-limited) + P_avionics = 75 W (Starlink 40, Jetson 15, MANET 12, FC 5, cameras 3). This is the floor — power cannot go lower without removing avionics function.

Step 2 — EW-mode power additions

Three distinct EW-response subsystems increase power draw when the platform operates in a contested electromagnetic environment. Each has a published or datasheet-derived power draw that the endurance calculator must include as a conditional load.

SUBSYSTEM           BASELINE   EW-ACTIVE   DELTA    SOURCE
─────────────────────────────────────────────────────────────────────────────
Silvus MANET radio  12 W       28 W        +16 W    Silvus SL5200 datasheet
  (adaptive FHSS active, higher TX duty cycle to penetrate jamming)

CRPA GPS antenna    0 W        8 W         +8 W     Novatel GAJT-710
  (only active when GPS-denied mode detects jamming; beamforming nulls
  direction-finding DOA estimation runs continuously)

SDR spectrum mon.   0 W        18 W        +18 W    USRP B205mini-i datasheet
  (Silvus-built-in spectrum sweep for adaptive FHSS channel selection;
  activates when interference detected above -80 dBm on primary channel)

Jetson AI load      15 W       22 W        +7 W     NVIDIA Orin Nano datasheet
  (additional signal-classification inference for jammer identification,
  ~30 % GPU utilisation on top of YOLOv8's 30 %)

TOTAL EW OVERHEAD                         +49 W
P_total_EW = 355 + 49 = 404 W

Endurance impact at 888 Wh:
  t_theoretical_EW = 888 / 404 = 2.20 h
  t_usable_EW      = 2.20 × 0.80 = 1.76 h = 106 min
  Baseline was 2.00 h = 120 min
  Endurance loss:   14 min (11.6 % reduction)

Step 3 — Beamforming subsystem (heavy EW environments)

Step 2 covers the standard EW-active configuration. Heavy EW environments require an additional layer: directional beamforming on the MANET link. Instead of omnidirectional radiation, the Silvus SL5200 can drive a 4-element phased array to produce nulls toward identified jammer directions while maintaining link toward friendly ground stations. Power draw at the RF stage increases approximately linearly with the number of independent beams maintained.

Beamforming additional power:
  P_beam = N_beams × 6 W (RF phase-shifter chain per beam)
       + 4 W (beamforming controller FPGA)

Typical deployment:
  1 beam  (toward friendly GCS):           P_beam = 6 + 4 = 10 W
  2 beams (GCS + relay to peer Fischer):   P_beam = 12 + 4 = 16 W
  3 beams (GCS + relay + null toward jammer): P_beam = 18 + 4 = 22 W

Worst-case heavy-EW environment (3 beams active):
  P_total_heavy_EW = 355 + 49 (EW subsystems) + 22 (3-beam)
                  = 426 W
  t_theoretical = 888 / 426 = 2.08 h
  t_usable      = 2.08 × 0.80 = 1.67 h = 100 min
  Endurance loss from permissive baseline: 20 min (16.7 % reduction)

Step 4 — Solar-film compensation

Fischer 26's upper wing surface is 0.52 m² (wing area from the drag derivation above). A thin-film solar laminate bonded to the upper surface — perovskite or flexible GaAs depending on cost/efficiency trade — generates power during daylight cruise. The cell chemistry choice sets the ceiling:

Cell technology         Efficiency  Wh/kg (panel)  €/Wp   Source
─────────────────────────────────────────────────────────────────────────
Perovskite thin-film    15–18 %     120–180        0.8    NREL 2024 cell efficiency chart
Flexible mono-Si        20 %        80–100         2.0    SunPower C60 flex datasheet
Flexible GaAs           28–30 %     300–400        15.0   Alta Devices (now LeapFrog) datasheet
Multi-junction GaInP    34 %        250–350        30.0   Spectrolab XTJ Prime datasheet

Useful solar irradiance at cruise altitude (300-2000 m AGL):
  Peak (summer, clear, noon):     1000 W/m² (AM1.5 standard)
  Typical Nordic summer, 13:00:    700 W/m² (60° solar angle)
  Overcast summer:                 150 W/m²
  Winter, 12:00, 60° N latitude:   200 W/m² (clear, low sun)
  Winter, overcast:                 30 W/m²

Select mid-efficiency perovskite thin-film at 16 % for cost reasons (Fischer 26 is designed to be expendable — €30/Wp GaAs contradicts the whole expendable-platform economics). Applied to the 0.52 m² upper surface with 0.85 effective area factor (wing curvature, non-uniform sun angle during banked flight):

Effective collector area: A_eff = 0.52 × 0.85 = 0.442 m²
Cell efficiency η_cell:    0.16
Power electronics efficiency (MPPT + buck converter): 0.92

Solar power harvested at irradiance G:
  P_solar(G) = A_eff × η_cell × η_mppt × G
            = 0.442 × 0.16 × 0.92 × G
            = 0.065 × G  W  (G in W/m²)

Scenarios:
  Peak summer noon (1000 W/m²):    P_solar = 65 W
  Nordic summer 13:00 (700 W/m²):   P_solar = 46 W
  Overcast summer (150 W/m²):       P_solar = 10 W
  Winter noon clear (200 W/m²):      P_solar = 13 W
  Winter overcast (30 W/m²):          P_solar = 2 W (negligible)

Step 5 — Compose the full power model and compute compensation

Net battery drain = P_total_EW_mode − P_solar. Usable endurance is now a function of four variables: battery energy, cruise airspeed, EW mode, and solar irradiance.

P_net(mode, G) = P_total(mode) − P_solar(G)
            where P_total(mode) ∈ {355, 404, 426} W for {permissive, EW-active, heavy-EW}
            and P_solar(G) = 0.065 × G W

t_usable(E, mode, G) = (E / P_net) × (1 − reserve)
                    subject to P_net > 0

SCENARIO MATRIX — t_usable in minutes, E = 888 Wh, reserve = 20 %
════════════════════════════════════════════════════════════════════════
                     Permissive  EW-active   Heavy-EW
                     (355 W)     (404 W)     (426 W)
────────────────────────────────────────────────────────────────────────
Night / no solar      120         106          100
Winter noon (200)     126         111          104
Overcast summer (150) 125         110          104
Nordic summer (700)   138         121          113
Peak noon (1000)      146         129          119
────────────────────────────────────────────────────────────────────────
BEST CASE:  peak sun + permissive   = 146 min  (+22 % vs baseline)
WORST CASE: night + heavy EW         = 100 min (−17 % vs baseline)
BREAK-EVEN: what solar G fully cancels heavy-EW overhead?
  P_solar = 426 − 355 = 71 W  ⟹  G = 71/0.065 = 1092 W/m² > peak AM1.5
  Conclusion: solar alone CANNOT fully compensate heavy-EW — must accept
  some endurance loss OR upgrade to 25 % efficient GaAs film (break-even
  at G = 700 W/m², achievable in Nordic summer midday).

Step 6 — Battery sizing to recover baseline endurance in heavy EW

If the operational requirement is "maintain 2.0-hour endurance regardless of EW mode and darkness", solar compensation alone is insufficient. We must size the battery for the worst case (night + heavy EW = 426 W). Required energy with 20 % reserve:

E_required = (P_total_worst × t_target) / (1 − reserve)
          = (426 × 2.0) / 0.80
          = 1065 Wh

Battery upgrade: from 888 Wh to 1065 Wh
  Energy increase:        +177 Wh (+20 %)
  Typical LiPo pack scaling: 16000 mAh/pack × 2 → 19200 mAh/pack × 2
  Weight increase:        +0.4 kg (LiPo ~250 Wh/kg)
  Drag penalty at 85 km/h: ~3 W (heavier plane requires slightly more lift)
  Net endurance (night + heavy EW): 2.0 h ✓
  Net endurance (peak sun + permissive): 2.45 h (improvement)

Operational takeaway: the planner can choose between two deployment profiles — baseline-battery Fischer 26 (cheaper, €120/pair LiPo) with 100-min endurance in worst case, or heavy-battery Fischer 26 (€145/pair LiPo + 0.4 kg weight) with 120-min endurance guaranteed. The second profile costs €25 and 400 g per airframe; the first profile costs 20 min of loiter time per sortie. For sustained operations in a contested EW environment, the heavy-battery profile pays for itself after approximately 30 sorties.

Worked Example — Mission in EW-contested sector, Nordic summer afternoon

Mission: 25 km transit to sector boundary, 75 min loiter over contested zone with active Russian Krasukha-4 jamming on 300 MHz (triggers EW-active mode), 25 km return. Time of day: 14:00 on 21 June at 65°N (Arctic summer). Airframe: standard Fischer 26 with baseline 888 Wh battery.

Transit phase (permissive EM environment, below jamming influence):
  G_sun at 14:00 summer 65°N:         650 W/m²
  P_solar                           = 0.065 × 650 = 42 W
  P_net_transit                      = 355 − 42 = 313 W
  Transit duration round-trip        = 2 × (25 km / 85 km/h) = 0.59 h = 35.3 min
  Energy consumed in transit         = 313 × (35.3/60) = 184 Wh

Loiter phase (EW-active, solar still available):
  G_sun unchanged (still daylight)    = 650 W/m²
  P_total_EW                          = 404 W
  P_solar                             = 42 W
  P_net_loiter                        = 404 − 42 = 362 W
  Energy available for loiter         = 888 − 184 − 888×0.20 = 526 Wh
  Available time                      = 526 / 362 = 1.45 h = 87 min

Mission feasibility check:
  Transit budget:                     35 min ✓
  Loiter budget required:             75 min
  Loiter budget available:            87 min ✓  (12 min margin)
  → MISSION VIABLE with 12 min reserve loiter

If the same mission is flown at night (21 December, 14:00, 65°N — darkness):

P_solar = 0 W (winter darkness)
P_net_transit = 355 W
P_net_loiter  = 404 W
Transit energy = 355 × 0.59 = 209 Wh
Loiter available = 888 − 209 − 178 (reserve) = 501 Wh
Loiter time = 501 / 404 = 1.24 h = 74 min

  → MISSION MARGINAL — 1 min short of 75-min requirement.
  Either reduce loiter to 70 min, reduce transit distance, or use heavy-battery configuration.

The contrast between the two scenarios makes the solar contribution visible: 42 W of continuous solar during a summer-daylight mission adds 13 minutes of loiter time. Over 50 sorties per season, that is 10+ additional hours of ISR coverage from the €600 (Wp × €/Wp estimate) solar film investment — which corresponds to approximately 2–3 additional target engagements per week that would otherwise require a second sortie.

Verification Code — EW Power, Solar, Endurance

BASE_MOTOR_W    = 280.0
BASE_AVIONICS_W = 75.0

EW_OVERHEAD_W = {
    "permissive":    0.0,
    "ew_active":    49.0,   # Silvus high-TX + CRPA + SDR + extra Jetson
    "heavy_ew":     71.0,   # plus 3-beam beamforming (22 W)
}

SOLAR_AREA_EFFECTIVE = 0.442  # m²
SOLAR_EFFICIENCY     = 0.16    # perovskite thin-film
MPPT_EFFICIENCY      = 0.92

def p_total(ew_mode="permissive"):
    return BASE_MOTOR_W + BASE_AVIONICS_W + EW_OVERHEAD_W[ew_mode]

def p_solar(irradiance_w_per_m2):
    return SOLAR_AREA_EFFECTIVE * SOLAR_EFFICIENCY * MPPT_EFFICIENCY * irradiance_w_per_m2

def endurance_minutes(battery_wh, ew_mode="permissive", irradiance=0, reserve=0.20):
    """Usable endurance in minutes given battery, EW mode, solar irradiance."""
    p_net = p_total(ew_mode) - p_solar(irradiance)
    if p_net <= 0:
        return float("inf")  # solar covers all consumption (unlikely)
    t_full_hours = battery_wh / p_net
    t_usable_hours = t_full_hours * (1 - reserve)
    return t_usable_hours * 60

def mission_feasibility(battery_wh, transit_km, loiter_min, cruise_kmh=85,
                        ew_mode_loiter="ew_active", irradiance=0, reserve=0.20):
    """Return (viable, loiter_budget_available_min, margin_min)."""
    # Transit assumes permissive environment (below contested zone)
    p_trans = p_total("permissive") - p_solar(irradiance)
    transit_h = 2 * transit_km / cruise_kmh
    e_transit = p_trans * transit_h

    reserve_wh = battery_wh * reserve
    e_loiter_avail = battery_wh - e_transit - reserve_wh

    p_loiter = p_total(ew_mode_loiter) - p_solar(irradiance)
    loiter_avail_h = e_loiter_avail / p_loiter
    loiter_avail_min = loiter_avail_h * 60
    margin = loiter_avail_min - loiter_min
    return (margin >= 0, loiter_avail_min, margin)

# Reproduce scenario matrix
print("ENDURANCE MATRIX (minutes, 888 Wh battery):")
print(f"{'':20s}  Permissive  EW-active  Heavy-EW")
for label, G in [("Night", 0), ("Winter noon", 200),
                 ("Overcast summer", 150), ("Nordic summer", 700),
                 ("Peak noon", 1000)]:
    row = f"{label:20s}"
    for mode in ["permissive", "ew_active", "heavy_ew"]:
        t = endurance_minutes(888, mode, G)
        row += f"  {t:8.0f}"
    print(row)

# Reproduce worked example (summer EW mission)
viable, avail, margin = mission_feasibility(
    battery_wh=888, transit_km=25, loiter_min=75,
    cruise_kmh=85, ew_mode_loiter="ew_active", irradiance=650,
)
print(f"\\nSummer EW mission: viable={viable}, loiter avail={avail:.0f} min, margin={margin:.0f} min")

# Reproduce winter-night version
viable, avail, margin = mission_feasibility(
    battery_wh=888, transit_km=25, loiter_min=75,
    cruise_kmh=85, ew_mode_loiter="ew_active", irradiance=0,
)
print(f"Winter night EW mission: viable={viable}, loiter avail={avail:.0f} min, margin={margin:.0f} min")

Fischer 26E-LE Extension — Stand-off EW at 1000 m AGL

The derivations above cover the baseline Fischer 26 energy budget. The LE variant (Fischer 26E-LE) operates at the tier-3 stand-off altitude of approximately 1000 m AGL with the seven-mast antenna cluster replacing the baseline single-mast jammer. Two new energy costs matter: (1) the cluster's 74 W EMCON-2 average draw, and (2) the 207 W EMCON-3 surge demand during active 10-target engagement sequences.

The LE variant is energy-budgeted for continuous EMCON-2 operation across the full mission, with short EMCON-3 surges when multiple threats arrive in a batch. The full budget is derived on fischer26e.html; the numbers below show how engagement workload extends or compresses that budget.

Ten-target engagement — energy impact at 1 to 4 minutes per target

A realistic stand-off engagement scenario for the LE variant: ten hostile drones cross the horizon within a 30–60 minute window, and the cluster must suppress each for 1–4 minutes until the target is either destroyed by cooperating forward assets or aborts due to link denial. The time-per-target varies with target type — a Lancet-3 loitering munition typically aborts within 60–90 seconds of 2.4 GHz denial, while an Orlan-10 ISR bird may persist for several minutes under 915 MHz jamming before its operator commands RTB.

# pip install numpy
# le_engagement_energy.py — energy impact of 10-target engagement batches
CLUSTER_PEAK_W_EMCON3 = 207       # all 7 masts TX, 70 % duty during engagement
CLUSTER_AVG_W_EMCON2  = 74        # both gimbals, 30 % duty, idle baseline
TRANSIT_TIME_S        = 30        # gimbal slew + target handoff between targets
N_TARGETS             = 10

# Cruise + avionics on LE airframe at 20.6 kg MTOW, 3.5 m wing
CRUISE_W    = 354                 # from fischer26e.html derivation
AVIONICS_W  = 75

BATTERY_LE_WH     = 2500
USABLE_FRACTION   = 0.80          # 20 % reserve policy
SOLAR_SUMMER_W    = 95            # Nordic midday, perovskite on 0.86 m²
SOLAR_WINTER_W    = 17

def engagement_energy(t_per_target_s, n=N_TARGETS):
    """Energy consumed in Wh for a batch of n engagements."""
    surge_wh   = (CLUSTER_PEAK_W_EMCON3 * t_per_target_s * n) / 3600
    transit_wh = (CLUSTER_AVG_W_EMCON2 * TRANSIT_TIME_S * n) / 3600
    return surge_wh + transit_wh

def mission_endurance_h(t_per_target_s, solar_w, n=N_TARGETS):
    """Endurance in hours when one 10-target batch occurs mid-mission."""
    baseline_demand = CRUISE_W + AVIONICS_W + CLUSTER_AVG_W_EMCON2
    engage_wh = engagement_energy(t_per_target_s, n)
    remaining_wh = BATTERY_LE_WH * USABLE_FRACTION - engage_wh
    return remaining_wh / max(1, baseline_demand - solar_w)

for t_target_s in [60, 150, 240]:
    wh = engagement_energy(t_target_s)
    summer_h = mission_endurance_h(t_target_s, SOLAR_SUMMER_W)
    winter_h = mission_endurance_h(t_target_s, SOLAR_WINTER_W)
    total_batch_min = (t_target_s + TRANSIT_TIME_S) * N_TARGETS / 60
    print(f"{t_target_s}s/target, 10-target batch: "
          f"{total_batch_min:.0f} min wall-clock, "
          f"{wh:.0f} Wh consumed")
    print(f"   Summer endurance: {summer_h:.2f} h; Winter endurance: {winter_h:.2f} h")

# Output:
#  60s/target, 10-target batch: 15 min wall-clock,  41 Wh consumed
#     Summer endurance: 4.81 h; Winter endurance: 4.03 h
# 150s/target, 10-target batch: 30 min wall-clock,  92 Wh consumed
#     Summer endurance: 4.68 h; Winter endurance: 3.93 h
# 240s/target, 10-target batch: 45 min wall-clock, 144 Wh consumed
#     Summer endurance: 4.55 h; Winter endurance: 3.82 h

The critical observation: even the worst-case scenario (10 targets × 4 min of EMCON-3 surge = 45 minutes of continuous peak cluster draw) consumes only 144 Wh of the 2,000 Wh usable battery capacity — 7.2 % of usable energy for 45 minutes of active jamming against ten separate hostile drones. The LE variant is not energy-limited at 10 targets. It is limited by gimbal slew time between targets (30 s × 10 = 5 minutes of non-engagement transit), by CAN-FD bus throughput during simultaneous triplet retasking, and by operator cognitive load tracking ten parallel engagements — none of which are energy constraints.

The practical limit on engagement batch size is therefore not battery capacity but the time window during which the ten targets are simultaneously present in the cluster's 5–15 km stand-off footprint. If the ten hostile drones arrive spread over 45 minutes (the worst-case engagement duration), the LE airframe can service them sequentially at 4 minutes each and still have 3 h 49 min of endurance remaining in winter conditions to continue patrolling. If they arrive within a 10-minute burst, the cluster's 2-gimbal architecture means it can only engage two at a time, and the remaining eight either abort or pass through unopposed — which is a tactical limit, not an energy limit.

Sustained high-tempo operations — multiple 10-target batches per mission

A second-order question: how many complete 10-target batches can one Fischer 26E-LE service per mission before battery becomes the constraint?

n_batches = (usable_wh - baseline_mission_wh) / engage_wh_per_batch

For a 3-hour mission in Nordic winter with the 4 min/target scenario:
    usable_wh            = 2500 * 0.80 = 2000 Wh
    baseline_mission_wh  = (354 + 75 + 74 - 17) * 3 = 1458 Wh
    remaining_for_surge  = 2000 - 1458 = 542 Wh
    engage_wh_per_batch  = 144 Wh
    n_batches            = 542 / 144 = 3.8 batches

    So: 3 complete 10-target batches (30 engagements) with 110 Wh margin,
    or 4 batches (40 engagements) with the airframe landing 12 min early.

Three complete 10-target batches across a 3-hour winter mission represents 30 hostile engagements — which is more than most brigade-level threat estimates project for a single stand-off sortie. The LE variant's energy budget is therefore sized correctly: it can absorb realistic engagement density without hitting the 20 % reserve floor. In summer conditions the solar augmentation extends this to 4+ batches comfortably.

This is the operational justification for the Fischer 26E-LE variant's 2,500 Wh battery sizing documented on fischer26e.html. A smaller battery (e.g. 1,500 Wh) would force the airframe to choose between long patrol time and high engagement capacity. The 2,500 Wh sizing, with the cluster's 74 W EMCON-2 efficiency and the 207 W EMCON-3 surge ceiling, produces an airframe that can patrol for 4+ hours AND absorb 30+ target engagements in that window.

Why This EW/Solar Derivation Matters Operationally

Four separate planning decisions depend on this extended power model being correct. First, mission feasibility in EW environments: the baseline "2 hours endurance" number is not what Fischer 26 actually delivers when flying against active Russian Krasukha or Shipovnik systems. The planner must use the EW-active or heavy-EW figures (106 or 100 min) when sizing sorties against contested sectors. A commander who plans a 90-min loiter based on the baseline number will see his drone RTL at 75 minutes — having burned through the reserve in 15 minutes of unexpected EW contact.

Second, solar-film investment ROI: the 0.52 m² wing area is already used for lift — adding solar film costs only the film itself (€600 for perovskite at full coverage) and ~50 g of weight. The break-even is around 30 sorties in Nordic summer. Against a winter deployment (solar contributing < 15 W average), the ROI window extends to 6 months or more — the investment is harder to justify for purely arctic units. Units operating year-round or south of 65°N see faster payback. The planner can compute per-unit-cost of additional loiter-minute at each cell-technology tier: perovskite at 800 min gained per €600 = €0.75/additional-minute, GaAs at 1500 min for €12,000 = €8/additional-minute. The choice is transparent rather than handwaved.

Third, battery sizing decision: the 20 % battery upgrade required to maintain 2-hour endurance in night+heavy-EW conditions adds €25/airframe and 0.4 kg. For a force operating primarily in permissive daylight with occasional EW contact, the baseline battery is the right choice. For a force expecting sustained heavy EW (e.g. near the Estonian or Finnish border in a contested scenario), the heavy-battery profile is cheaper per mission than losing a Fischer 26 to an unexpected RTL. The derivation makes this trade-off explicit rather than buried in a specs table.

Fourth, validation of the GPS-denied claim under EW conditions: the CRPA subsystem's 8 W continuous draw is what makes GPS-denied navigation possible against jamming — but it is not free. The derivation forces this cost to be visible. A reviewer examining FSG-A's "GPS-denied in contested EW" claim can follow the math all the way from CRPA antenna gain pattern → 8 W RF power requirement → 4-minute endurance cost → operational impact. The cost of autonomy against jamming is paid in flight time, and the derivation quantifies exactly how much.

Energy proofs in provable_claims.py now include FISCHER26_EW_OVERHEAD (49 W EW-active load, verified from datasheet sum) and FISCHER26_SOLAR_NORDIC_SUMMER (46 W at 700 W/m² irradiance with 16 %-efficient perovskite, verified from multiplication), with the endurance-matrix function itself verified by executing the worked example. Claims about solar-film bonding durability against wing flex and thermal cycling are NOT validated — FSG-A has not conducted flight testing, and the cell-manufacturer's published flex-tolerance specifications are the only evidence base.

Implementation

# Fischer 26 Power Budget Calculation
import json

power_budget = {
    "battery": {"cells": 12, "capacity_mah": 10000, "voltage": 44.4,
                "energy_wh": 888},
    "consumers": {
        "motor_cruise":    {"watts": 280, "duty": 1.00, "note": "T-Motor U8 at 85km/h"},
        "starlink_mini":   {"watts": 40,  "duty": 1.00, "note": "Continuous uplink"},
        "jetson_orin_nano": {"watts": 15,  "duty": 1.00, "note": "YOLOv8 + ORB-SLAM3"},
        "silvus_manet":    {"watts": 12,  "duty": 1.00, "note": "SL5200 at 300MHz"},
        "pixhawk_sensors": {"watts": 5,   "duty": 1.00, "note": "FC + baro + OF"},
        "cameras":         {"watts": 3,   "duty": 1.00, "note": "IMX477 + Infiray T2S+"}
    }
}

total_watts = sum(c["watts"] * c["duty"] for c in power_budget["consumers"].values())
endurance_h = power_budget["battery"]["energy_wh"] / total_watts
reserve = 0.20  # 20% reserve

print(f"Total power:  {total_watts:.0f}W")
print(f"Endurance:    {endurance_h:.2f}h ({endurance_h*60:.0f} min)")
print(f"With reserve: {endurance_h*(1-reserve):.2f}h ({endurance_h*(1-reserve)*60:.0f} min)")
# Output: 355W, 2.50h, 2.00h usable

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Sources

ArduPlane documentation (ardupilot.org). Starlink Mini specifications (starlink.com). T-Motor datasheets. NATO STANAG 4671 (UAV Airworthiness). Fischer 26 design documentation (FSG-A internal).