EP250 · Aircraft Data
Part B of RFD-OM-001 for the EP250: a ducted, contra-rotating coaxial VTOL tail-sitter with a removable wing, supplied in a transport tube (some assembly required). Read alongside Part A.
Claim key: [V] flight/bench-demonstrated · [E] engineering estimate · [TBD] to be confirmed.
Specification summary
Section titled “Specification summary”| Spec | Value | Src |
|---|---|---|
| Configuration | Ducted contra-rotating coaxial tail-sitter, removable wing | [V] |
| All-up weight (MTOW) | 4.5 kg | [V] |
| Payload | 0.75 kg | [V] |
| Wingspan (deployed) | 600 mm | [V] |
| Aircraft length | 850 mm | [V] |
| Transport-tube outer diameter | 250 mm | [V] |
| Operating speed | ~140 km/h ground speed (1 Jul 6-lap mission) | [V] |
| Cruise / trim airspeed | 35 m/s (126 km/h) | [V] |
| Stall speed (Vs) | 27.5 m/s (99 km/h) | [V] |
| Minimum airspeed | 30 m/s (108 km/h) | [V] |
| Maximum airspeed | 45 m/s (162 km/h) | [V] |
| Bank limit | 60° | [V] |
| Endurance | < 8 min | [V] |
| Range (one-way) | ~15 km | [V] |
| Hover wind limit | 30 km/h (do not hover above this) | [V] |
| Landing wind limit | up to 50 km/h with caution (see below) | [V] |
| Battery | 6S2P LiPo — two validated packs (below) | [V] |
| Autopilot / GCS | PX4 · QGroundControl | [V] |
One forward-flight speed. The EP250 is flown at a single tuned forward-flight speed — there is no separate “cruise” and “dash” regime. The airspeed values above are the aircraft’s configured flight envelope taken from the flight parameters (RFD flight-test log, 1 Jul 2026). The trim (design) airspeed is 35 m/s (126 km/h); on the 1 Jul 6-lap mission the aircraft averaged a ground speed of ~140 km/h over 12.2 km. Do not fly below the 30 m/s minimum / 27.5 m/s stall. There is no distinct landing descent speed (recovery is a vertical VTOL landing).
Limitations (EP250)
Section titled “Limitations (EP250)”Hard limits — read with the family Limitations chapter. Do not exceed.
| Limitation | Value | Src |
|---|---|---|
| Maximum take-off weight | 4.5 kg | [V] |
| Maximum payload | 0.75 kg (max 1.0 kg for dropped payloads) | [V] |
| Maximum airspeed | 45 m/s (162 km/h · 87 kt) | [V] |
| Minimum airspeed | 30 m/s (108 km/h · 58 kt) | [V] |
| Stall speed (Vs) | 27.5 m/s (99 km/h · 53 kt) | [V] |
| Bank limit | 60° | [V] |
| Hover / launch wind limit | 8.3 m/s (30 km/h · 16 kt) | [V] |
| Landing wind limit | 13.9 m/s (50 km/h · 27 kt) with caution, build-up required | [V] |
| Endurance limit | < 8 min total per battery pair | [V] |
| Battery | RFD-approved 6S2P configurations only (below) | [V] |
| Maximum continuous hover | 4 min total per flight (do not plan on more) | [V] |
| Launch/recovery pad | ≥ 2 m × 2 m clear (demonstrated landing accuracy ~0.5 m) | [V] |
| Weather / light | Day VLOS · no precipitation · no icing band (family rules) | — |
| Temperature | Operational −10…+45 °C; battery in use +10…+40 °C (family bands) | [E] |
Performance (demonstrated)
Section titled “Performance (demonstrated)”| Figure | Value | Src |
|---|---|---|
| Longest demonstrated flight | 12.2 km (6-lap mission, 1 Jul 2026), landed with 40 % reserve | [V] |
| Average ground speed on that mission | ~140 km/h | [V] |
| One-way range | ~15 km | [V] |
| Endurance | < 8 min | [V] |
| Back-transition altitude gain | ≈ 20 m zoom climb | [V] |
All figures flown at the single tuned forward-flight speed (trim 35 m/s) near sea level.
Weight & balance
Section titled “Weight & balance”| Item | Mass | Src |
|---|---|---|
| Empty aircraft (no battery, no payload) | ~2.2 kg | [E] [TBD — G2: weigh] |
| Battery (6S2P pair) | ~1.56 kg (2× 6S 5200) | [E] |
| Payload (reference) | 0.75 kg | [V] |
| All-up weight (MTOW) | 4.5 kg | [V] |
CG limits are physical marks printed into the skin. The aircraft carries a standard aviation
CG symbol (a circle quartered with alternating black segments) 3D-printed into the fuselage at
the nominal CG, with a forward arrow and an aft arrow pointing in toward it — these arrow tips
are the CG limits. After every assembly and payload change, balance the aircraft on a knife-edge
(or fingertips) at the marked station: the balance point must fall between the arrow tips.
Numeric datum for the record [TBD — G2]. The battery bay position is fixed; payload mass sits
ahead of the CG, so a heavier nose payload moves the CG forward — check the balance, do not assume.
Anatomy
Section titled “Anatomy”- Fuselage: Ø120 mm bayonet sections; near-axisymmetric stowed form that fits the 250 mm tube.
- Propulsor: ducted, contra-rotating coaxial. The duct shrouds the propeller (safety, compactness); the contra-rotating pair cancels reaction torque. This gives better hover control authority than a single-motor design, but the ducted coax caps continuous hover thrust, which sets the 4.5 kg MTOW and 750 g payload.
- Control: all axes (roll, pitch, yaw) are controlled by aerodynamic control surfaces in the propeller slipstream — there is no differential-throttle yaw control.
- Wing / tail: removable wing on a spar; X-tail fins double as the landing gear.
- GPS / magnetometer: mounted in the wings — the GPS/mag cables must be connected during assembly (see below).
- Nose: payload nose cone attaches via the standardised Ø120 mm bayonet adapter (see Payloads).
Battery
Section titled “Battery”The EP250 flies 6S (22.2 V nominal). Two validated, RFD-approved LiPo configurations:
| Config | Arrangement | Nominal capacity |
|---|---|---|
| A | 2 × 6S 4000 mAh in parallel = 6S2P | 8000 mAh |
| B | 2 × 6S 5200 mAh in parallel = 6S2P | 10 400 mAh |
Both packs are installed together (the aircraft draws from the parallel pair). Handle, charge and store per Battery Management. Charge with a standard LiPo balance charger; RFD can supply one as part of a package, or you may use your own compatible balance charger.
Wind & environment
Section titled “Wind & environment”- Hover: do not hover in wind above 30 km/h — above this the aircraft is very likely to be lost while hovering.
- Landing: landing in winds up to 50 km/h is possible but must be done with caution; land in the lowest wind available.
- 💡 Build-up approach. If you intend to operate in high wind, work up to it: begin at 20 km/h and increase progressively as you confirm the aircraft handles.
Back transition (reverse transition)
Section titled “Back transition (reverse transition)”The EP250 back transition involves a zoom climb of approximately 20 m as the aircraft trades forward speed for altitude while pitching up. Ensure at least 20 m of clear airspace above your planned recovery altitude (plus a margin).
Kit contents (what’s in the box)
Section titled “Kit contents (what’s in the box)”| Item | Qty | Notes |
|---|---|---|
| Aircraft in transport tube | 1 | Capped by the spider (centres the aircraft; carries the tail-number documentation) |
| Wing sets | 2 | One fitted set + one spare set; GPS/magnetometer inside — connect cables at assembly |
| Spare landing-gear assemblies | 10 | The X-tail fins take the recovery impact — swap on damage |
| R-clips (wing retention) | 25 (bag) | Consumable — use a fresh clip freely |
| Servo connector clips | 25 (bag) | Consumable |
| Payload nose-cone bays | 3 | Ø120 mm bayonet |
| Battery packs | per order | Approved 6S configurations (see Battery) |
| Hand-held anemometer | 1 | For the ground wind go/no-go check |
| Balance charger | optional | Available as part of a package |
| Documentation | 1 | This manual (link/QR) + tail-number record |
The ground control station is a separate product — see Ground Control Station.
Assembly
Section titled “Assembly”The EP250 is delivered in a transport tube with some assembly required (contents above).
To assemble:
- Remove the aircraft from the tube and lay it on the ground.
- Remove the spider cap from the top.
- Fit the battery pack(s) into the battery bay.
- Insert the wing spar into the wing-spar hole in the fuselage.
- Connect the GPS / magnetometer cables (the GPS and magnetometers are in the wings) before sliding the wings home.
- Slide each wing down the wing spar until it seats against the alignment feature (an extruded tab with a hole) on the fuselage.
- Insert the metal R-clip into its pocket to retain the wing.
- Power up by connecting the batteries to their connectors.
- Confirm functional telemetry with the ground station (you may also connect the USB cable to confirm the aircraft is healthy).
- Attach the payload nose cone via the bayonet adapter.
- Checks: confirm the centre of gravity is within the marks on the body; confirm the circular fiducial (“this way up”) marks on the wings and body are all aligned in the up direction and in line with each other.
Disassembly is the reverse.
EP250-specific notes
Section titled “EP250-specific notes”- Supplied tube-in-box (not tube-launched). RFD currently offers the EP250 assembled-from-tube, not as a tube-launched round.
- Thrust-limited. Respect the 4.5 kg MTOW and 750 g payload — hover thrust margin is the binding limit.
- Control-surface authority. All control is aerodynamic (surfaces in the slipstream); there is no differential-throttle contribution — loss of forward thrust is loss of control authority.
Status
Section titled “Status”Flight-validated [V]. Stall/minimum/trim/maximum speeds and bank limit transcribed from the current
RFD flight-test log (1 Jul 2026, 2026-07-01-6lap-.ulg parameters). Confirm the remaining [TBD]
items on the Open Questions page.