Airframe types
The Airframe type dropdown at the top of the Builder console is the authoritative picker for the flight model. Choosing a type sets the flight regime (multirotor, VTOL transition, fixed wing, quadplane, or tiltrotor), a default motor count, and the coaxial flag, and the console shows or hides the type-specific input groups accordingly.
Picking a type is a starting point, not a lock: motor count, the coaxial switch, and everything else stay editable afterward. The same dropdown appears in the Setup Wizard's first step.
Supported types#
| Airframe type | Flight model | Motors | Coaxial |
|---|---|---|---|
| Quad X | Multirotor | 4 | No |
| Quad H | Multirotor | 4 | No |
| Tricopter | Multirotor | 3 | No |
| Hexa | Multirotor | 6 | No |
| Y6 (coaxial) | Multirotor | 6 | Yes |
| Octo | Multirotor | 8 | No |
| Octo X8 (coaxial) | Multirotor | 8 | Yes |
| Dodeca ring (12) | Multirotor | 12 | No |
| Hexadeca ring (16) | Multirotor | 16 | No |
| VTOL transition | VTOL transition | 4 | No |
| Fixed wing (tractor) | Fixed wing | 1 | No |
| Fixed wing (pusher) | Fixed wing | 1 | No |
| Fixed wing (twin) | Fixed wing | 2 | No |
| Quadplane (lift + tractor) | Quadplane | 1 cruise + 4 lift | No |
| Quadplane (lift + pusher) | Quadplane | 1 cruise + 4 lift | No |
| Quadplane (lift + twin) | Quadplane | 2 cruise + 4 lift | No |
| Lift + cruise (open rotors) | Quadplane | 2 cruise + 8 lift | No |
| Lift + cruise (ducted fans) | Quadplane | 2 cruise + 8 lift, ducted | No |
| Tiltrotor (tricopter) | Tiltrotor | 2 tilting + 1 fixed lift | No |
| Tiltrotor (tilt-quad) | Tiltrotor | 4 tilting | No |
The two ring layouts and the two lift-plus-cruise types are the shapes of aircraft that carry people. See Large airframes and people on board for occupants, ducted rotors, drive losses and how the checks change with scale.
All multirotor types share the same momentum-theory hover core and differ by motor count, coaxial flag, and layout. Quad H sizes identically to Quad X; the layout distinction is informational. The coaxial flag adds a hover-power penalty and halves the disc count, which is why Y6 and Octo X8 hover less efficiently than their flat six- and eight-motor counterparts.
On a coaxial layout the lower rotor of each pair works in the upper one's wake, so each rotor counts at a share of its isolated thrust in max thrust, thrust-to-weight, hover throttle and the motor-out check. The share is worked out from the Coaxial power penalty: 0.83 at the default 0.943, the measured value (a stacked pair needs about 1.334 times the hover power of two rotors flying apart, Cameron et al.), and 0.70 at 1.20. A build saved with 1.20 keeps it, and the Builder offers the measured value above its checks. Hover power and endurance carry the power penalty only. If you measured max thrust on the stacked pair rather than on one rotor, enter 1 in Coaxial thrust factor under Advanced model factors; any other value from 0 to 1 sets the share yourself, and 0 works it out. A max thrust inferred by Live Calibration from the aircraft's own hover already includes the effect and is not reduced again.
The motor-out check assumes a layout for each type: a ring of evenly spaced rotors with alternating spin, or coaxial arm pairs that spin opposite ways. See The Builder for how it is judged.
Frame presets#
Start from a frame on the Balance and CG page loads a dimensioned frame (a 5 inch freestyle quad up to an X8 heavy lifter, two fixed wings, a quadplane, a tiltrotor and two eVTOL classes). A preset sets its airframe type, dimensions and masses. Every preset except the two eVTOL classes also sets a motor Kv, an ESC rating, a main connector, a main lead and a flight pack that suit the class, so the build reads as a coherent aircraft straight away. The flight pack replaces the pack on the motor bus and keeps its position, or is added when the bus has none; packs on other buses, such as an avionics pack, are left alone. Applying a preset clears the previous motor's measured max thrust, measured loaded RPM, resistance, no-load current, continuous rating and propeller RPM limits, and the parts library chips, because those figures belong to another frame. Everything stays editable afterwards.
What each regime changes#
- Multirotor: the props carry the weight in every phase. Forward flight uses the induced-plus-profile-plus-parasite power curve when you set a flat-plate drag area.
- VTOL transition: a tailsitter-style craft whose airfoil arms become a wing in cruise while the props become pushers. Selecting it reveals the VTOL transition (wing) group (airfoil arm chord, wing CL max, wing Cd0, span efficiency, cruise prop efficiency) and fills a starting arm chord if none is set. The readout adds stall and transition speed, wing loading, and a transition-feasibility check. See Forward flight and VTOL.
- Fixed wing: a plane with no hover. Selecting it reveals the Fixed wing (wing) group (wing span, wing area, wing chord, CL max, Cd0, span efficiency, cruise prop efficiency) and fills starting wing dimensions and a starting drag area you can edit. The hero cards switch to stall speed, cruise endurance, and range.
- Quadplane: dedicated lift rotors for vertical flight plus a wing and cruise motors for forward flight. Selecting it reveals the wing group, the Lift rotors (dead in cruise) group, and the Lift rotor motors group (lift motor Kv, lift prop diameter and pitch, lift ESC current), with starting values filled in.
- Tiltrotor: motors that tilt to hover and rotate forward for cruise, optionally with fixed lift rotors that are dead weight in cruise. Selecting it reveals the wing group and the Lift rotors (dead in cruise) group.
The motor count column above is the default the type sets. On quadplane and tiltrotor types the Motors field counts the cruise or tilting motors, and the Lift rotor count field in the Lift rotors group counts the rotors that lift in hover and are dead weight in cruise.