Cutting-edge advancements in wing design are reshaping the future of Short and Ultra-Short Takeoff and Landing (STOL/USTOL) aircraft—especially in electric aviation.
Why STOL and USTOL Matter in Electric Aviation
Electric aircraft are naturally suited for STOL missions. In fact, USTOL (Ultra Short Takeoff and Landing) performance has already been proven using distributed propulsion.
Compared to eVTOL (electric vertical takeoff and landing), which requires compromises between hovering and cruising performance, STOL aircraft offer:
- Longer range
- Simpler, more conventional design
- Easier certification (they fit existing aircraft categories)
Achieving Maximum Lift: The Key to STOL Performance
To achieve short takeoff distances, an aircraft must generate high lift at low speeds. There are two proven methods for increasing lift:
1. Aerodynamic Surfaces (Flaps and Slats)
These devices modify the wing’s shape to increase lift:
- Flaps (at the trailing edge) deflect air downward.
- Slats (at the leading edge) delay airflow separation at high angles of attack.
Examples:
- Zenith CH750 uses prominent flaps and slats for bush flying.
- Antonov AN-2 features automatic slats that deploy below 40 mph, allowing extremely slow, stall-free descent.
2. Blown Flaps via Distributed Propulsion
This method involves blowing propeller wash over the wings:
- Increases airflow speed over the wing, boosting lift.
- Works even when aircraft speed is low.
- Using multiple small propellers (distributed propulsion) ensures lift is enhanced across the entire span.
Result: Lift coefficients over 4.0 can be achieved.
For comparison: a Cessna 172 typically has a coefficient around 1.6.
Why Multi-Element Wings Are So Effective
The more air a wing can push down—without causing stall—the more lift it creates.
- Slats energize airflow, allowing the wing to operate at higher angles of attack without stalling.
- Flaps, especially slotted flaps, redirect air downward while maintaining smooth airflow.
One historic example is the Handley Page multi-flap wing, which achieved a remarkable lift coefficient of 4.33.
Nature-Inspired Innovation: Covert Flaps
Researchers at Princeton University’s BAM Lab introduced a new concept: covert flaps.
These are flaps located on the upper surface of the wing that deploy automatically at low speeds when wake regions form.
Benefits:
- 50% more lift
- 30% less drag
- Allow higher angles of attack without stalling
These results were confirmed both in wind tunnel tests and with flying models.
Toward the Ultimate eSTOL Aircraft: Combining Technologies
Currently, most electric STOL aircraft—like Electra Aero—focus only on distributed propulsion and blown lift.
But combining all high-lift technologies could lead to revolutionary performance:
- Multi-element wings (flaps + slats)
- Covert flaps
- Blown lift from distributed propulsion
Together, these could achieve lift coefficients over 4.0, reduce runway requirements to under 50 meters, and improve safety margins.
One partial demonstration of this hybrid approach is the TVS-2MS, a modified Antonov AN-2 that took off in just 6 seconds using 60 meters of runway.
Conclusion
High-lift wing design, distributed electric propulsion, and bio-inspired innovations are converging to transform flight.
The future of eSTOL and USTOL aircraft is not only efficient and quiet—it’s closer than ever.