1. Executive Summary
September was the first flight-test month for PT1. The aircraft completed its first VTOL flight on September 6 and four more flights on September 19, when it also flew with the wings fitted for the first time. The flight data drove the next steps: the airframe was stiffened, and work started on PT1.5, the transition configuration of the current aircraft. PT2 development started on the electrical side with a custom PCB set, and a Spearhead battery was sized together with customized Project Longshot. Transition flights are planned for October.
2. Project Progress
Team Formation
| Member | Experience Level | Team | Weekly Commitment (hrs) | Areas of Expertise / Championed |
|---|---|---|---|---|
| alperenag | Level 5 | Core | 32 | Project Lead |
| Erick | Level 4 | Core | 15 | Electrical Layout & Avionics |
| Zeynep | Level 4 | Core | 30 | Flight Mechanics |
Progress Overview
PT1 is now a flying VTOL testbed. Transition was not part of the PT1 scope, so the converted aircraft is designated PT1.5. This allows transition risks to be taken on an aircraft that can be replaced. PT2 runs in parallel. Its electrical system and battery started in September for the upcoming US build. The PT2 airframe redesign starts after the transition flights, so it can use the measured flight characteristics.
3. Major Studies
Initial VTOL Flight Testing
PT1 flew five VTOL flights in September: the first flight on September 6 and four flights on September 19. Testing covered takeoff, hover, altitude hold, loiter and landing, and all flights landed safely. The aircraft was controllable from the first flight and vibration levels were low. The September 19 session also tested the aircraft with the wings fitted. Fitting the wings took about one minute, which meets one of the main field-assembly requirements of the design. With the wings on, the aircraft held position steadily in loiter.
Yaw Control and Airframe Stiffening
The first flight showed a lift-motor output imbalance of about 400 µs PWM, with one diagonal motor pair working harder than the other. In the H layout, small motor tilts from torsional airframe flex create a yaw moment that the autopilot counters with differential throttle. The airframe was stiffened before the September 19 flights, and the motor output spread was roughly halved. The remaining imbalance varied with heading, so heading-step tests were flown to separate wind load on the tail from structural effects.
PT1.5 Transition Preparation
PT1.5 adds an electric pusher and control-surface actuation to the current aircraft. The pusher runs from a separate battery, as the PT1 power distribution board has no spare output. Pusher motor and propeller options were assessed for the transition flights. The remaining integration covers skin panels, wing servos, tail servo electronics, a secondary GPS and servo power rewiring. An aerodynamic database with aileron, elevator and rudder deflections was set up for the transition simulation. Transition flights are planned for the October meetup in Turkey.
PT2 Electrical Design
PT1 flies with a minimal off-the-shelf electrical layout that has no current or voltage sensing. PT2 moves to custom PCBs based on the Quiver architecture. The set consists of a flight-controller board, a main board, a battery connector board and a tail board for servo regulation and CAN-to-PWM conversion. The tail board layout was about half complete by the end of the month. Each servo has its own regulator, so a single regulator failure cannot disable more than one control surface.
The main board is being designed so the pusher configuration can be changed without swapping the board. To do this, it carries ports for both the electric and the gasoline pusher. In the electric configuration, a secondary battery replaces the fuel tank in the same bay and feeds the pusher directly. This keeps the CG unchanged and keeps the pusher’s high current off the main battery board. A Raspberry Pi is included for a future Starlink link and onboard processing.
Battery Development with Project Longshot
PT1 uses a 3.7 kg, 12S 22 Ah semi-solid pack. For PT2, a scaled-down Longshot battery was sized together with Project Longshot: 14S3P, 19.5 Ah, about 4 kg, with energy equal to the current pack at a similar cost. The ESCs and motors were confirmed for 14S, so the PT2 power system moves from 12S to 14S. The battery uses an AS150U connector. It will be built first with external balance charging, and the BMS will be added later on a swappable board. The BMS is planned as a shared design for other Arrow vehicles.
Supply
The MAD motor, ESC and propeller order was declined at EU customs and returned to MAD. It will be shipped within the EU to the Arrow hub in Germany and held there until the next build.
4. Goals for Next Month
- Advance the PT2 PCB designs.
- Continue battery development with Longshot.
- Conduct initial transition-flight tests.
- Develop the aerodynamic database and transition simulation.
- Begin the PT2 airframe design.
5. Budget & Resource Allocation
Project Expenses
September reimbursements totaled $326.79, covering a RadioMaster RP4TD ELRS receiver with shipping and a MAD Components transfer, including bank fees and taxes.
Team Members Compensation
Team compensation for September totaled $21120.00.
Total
The total September expense of Project Spearhead is $21446.79, consisting of $326.79 in reimbursements and $21120.00 in team compensation.