You can freely build on Igor Sikorsky's Early Design for a Vertical Takeoff Aircraft
This patent expired in 1952. Every claim — 0 independent, 0 dependent — is now unenforceable. Anyone can use, reproduce, manufacture, sell, or offer for sale this technology without a license.
Original assignee
Sikorsky Aircraft Corp
Patent granted
1935
Expired
1952
Forward citations
16
What this patent covers
The patent describes a structural arrangement for an aircraft designed to achieve vertical flight through direct lift mechanisms. It focuses on the mechanical integration of rotors or lifting surfaces that allow an aircraft to ascend without a traditional horizontal runway takeoff. By positioning the lifting components to provide upward thrust directly, the design enables the craft to hover or climb vertically.
What is now free to use
All 0 claims of US 1994488 are in the public domain. Specifically:
The 0 dependent claims add narrowing limitations and are also free.
What is NOT covered
Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.
Does not cover modern fly-by-wire electronic flight control systems.
Does not cover turbine-powered propulsion systems, as it predates their aviation use.
Does not cover multi-rotor drone configurations common in modern consumer electronics.
Who is building on this today
Sikorsky Aircraft, now a subsidiary of Lockheed Martin, continues to build on these foundational vertical lift concepts. Modern aerospace companies like Bell Flight and Airbus Helicopters also iterate on the core physics of rotor-driven lift established in this era.
Products built on expired version of this technology
Early Sikorsky VS-300 prototypes
Piston-engine utility helicopters
How to cite this patent in your documentation
Sikorsky Aircraft Corp. US Patent 1994488. Direct lift aircraft. Granted 1935, expired 1952. Now in the public domain.
Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.
PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.