DARPA Moves Forward on X-65: Plane with no moving control surfaces
DARPA’s X-65 experimental aircraft aims to control flight using active flow control—jets of compressed air and other techniques embedded in the wings—instead of traditional moving flaps and rudders. Commenters explore how this might improve stealth, reduce mechanical complexity, and enable new performance regimes, while raising concerns about dependence on engine bleed air, redundancy and safety in engine-out scenarios, and limited applicability to piston-powered drones. The thread also branches into broader reflections on how well online tech communities handle highly specialized aerospace topics.
Active Flow Control Concept
- X-65 explores “active flow control” (AFC): using jets of air or electrical/plasma actuators to manipulate airflow instead of traditional moving flaps/rudders.
- Techniques discussed include pneumatic bleed-air jets, synthetic jets with oscillating diaphragms, and plasma actuators that ionize air to alter flow and reduce drag.
- Aim: improve performance, reduce external moving parts, and potentially enable new planforms and high-lift or post-stall control regimes.
Air Supply and Engine Dependence
- Likely source of compressed air is engine bleed air or an auxiliary power unit; a separate compressor is possible but seen as heavy/inefficient.
- Commenters note this makes the concept naturally suited to jet/turbofan/turboprop aircraft, not small piston-prop drones where control surfaces are cheap and compressors are a large overhead.
- Some argue future designs could still justify compressors if AFC significantly boosts lift/drag performance.
Prototype vs. “No Moving Surfaces” Claim
- The demonstrator will have both conventional control surfaces and AFC effectors.
- Traditional controls provide a baseline and safety “training wheels”; tests will progressively lock them out.
- Several commenters call the “no moving control surfaces” headline misleading for this prototype.
Safety, Redundancy, and Failure Modes
- Concern: loss of engine → loss of compressed air → loss of control.
- Mitigations floated: multiple engines, APUs, ram air turbines, emergency batteries, parachutes, self-destruct, or unmanned-only use.
- Icing of tiny outlets and behavior in clouds/freezing rain flagged as open engineering questions.
Stealth, Structure, and Complexity
- Removing external actuated surfaces may reduce radar cross-section and allow metal-free wings/tails, though internal hardware still reflects radar.
- Debate over whether AFC truly reduces complexity: hydraulics vs many valves, sensors, and computation.
- Counterpoint: many small effectors can be more fault-tolerant; moving parts are smaller and easier to maintain.
Meta-Discussion and Critiques
- Some applaud DARPA’s exploration of novel control methods and tie it to earlier AFC experiments (e.g., other UAVs, Harrier reaction jets).
- Others express cynicism about defense projects or complain about low-quality, nitpicky, or domain-ignorant commentary on aerospace topics.