Hermeus CEO AJ Piplica on building a Mach 5 aircraft in 15 months — fastest jet development in 50 years

Summary

AJ Piplica, CEO of Hermeus, is building Mach 5 hypersonic aircraft out of Atlanta — and doing it at a pace that has no modern precedent. The company developed its first aircraft, Quarter Horse Mark 1, from requirements to flight-ready in 15 months, which Piplica says is the fastest jet aircraft development in roughly 50 years, back to the era of Kelly Johnson's Skunk Works.

The engineering philosophy is deliberately reductive. The Mark 1 doesn't need to do much — take off and land. That's it. Piplica's point is that you can't hit a timeline like that without stripping the problem down to its physics and refusing to over-engineer. Components are sourced from the supply chain where possible; what can't be bought is built from first principles. The iterative cadence is borrowed directly from SpaceX's playbook: build many prototypes, build them fast, and apply what you learn immediately. Quarter Horse Mark 2, a supersonic variant, was being assembled on the factory floor behind him during the conversation and is targeting a first flight in Q4 2025.

Propulsion

Hermeus uses ramjets, not scramjets. A ramjet is the simplest air-breathing engine concept — no moving parts, just compression, fuel, combustion, and a nozzle — but it can't run efficiently below roughly Mach 2.5 to Mach 3. To bridge that gap, Hermeus has combined a pre-cooled afterburning turbojet with a pure ramjet in a single engine, and has demonstrated the transition between the two modes on the ground.

Regulatory constraint

The FAA is the binding bottleneck — the hat Piplica has been wearing for six months stays on until the first flight. Moving the aircraft offshore doesn't solve this: Hermeus is a U.S. company, so FAA jurisdiction follows it regardless of where it tests. The agency's global influence in aviation means other countries' regulators largely defer to whatever the FAA decides anyway.

Defense and the F-47

On Boeing's $20 billion F-47 contract for the sixth-generation fighter, Piplica is candid that he has no inside knowledge, but his read from the outside is that the Air Force is solving a range problem. Current fourth- and fifth-generation fighters don't have the legs to maintain air superiority across the Pacific at the distances required, so a significantly larger, longer-range aircraft makes strategic sense.

The broader defence industrial base diagnosis is sharper. Between 1945 and 1975, the average time from program start to initial operational capability for a new U.S. military aircraft was five years. Since 1975, that figure has climbed linearly. The F-35 ran to roughly 20 years; the Next Generation Air Dominance program is already a decade in with a prototype that flew five years ago. Piplica traces the inflection point to a single event: Kelly Johnson retired from Skunk Works in 1975. The primes' advanced development groups — Lockheed's Skunk Works, Boeing's Phantom Works, Northrop's equivalent — have in his view grown sclerotic, and cost-plus contracting structures reinforce the drift. The absence of founder-led companies building fighter jets is, he argues, a direct consequence.

Hermeus's commercial thesis runs parallel: hypersonic passenger travel shrinks what economists call economic distance — a composite of actual distance, cost, and time — and historical evidence suggests that compressing economic distance between two economies increases trade between them proportionally, in the same way that gravitational force scales with proximity. Piplica frames Mach 5 passenger aircraft as potentially adding several percentage points to global GDP over the long run, with near-term defence contracts providing the financial foundation to get there.

On the competitive landscape, Boom Supersonic — led by Blake Scholl — flew supersonic this year. Hermeus is building the aircraft behind Piplica that it hopes will do the same.