Anyone astonished at the brilliant short-field performance of the Electra Aero Goldfinch from a paved runway a few weeks ago will be equally surprised at its agility from a grass runway. This eSTOL (electric Short Take Off and Landing) airplane seems to perform well even from unimproved runways.
In its own press release, the company reports on the small craft’s ability to take off and land on “austere fields smaller than 300 feet that are minimally prepared.” Citing its work with “Agile Combat Employment and expeditionary missions” for the military, explains the economy of such craft. “Small, affordable, runway-independent eSTOL aircraft could also alleviate demand on larger, few-in-number, high performance fixed wing and rotorcraft platforms in a contested logistics environment.”
That’s a 32-degree angle of climb, by the way, according to the AOPA Pilot report.
More Usable Runways
Aircraft like the Goldfinch and its larger commuter liner coming from Electra would open up otherwise unusable “airports” which might be nothing more than short grass fields. Expanding the utility of such aircraft would mean faster transporting of casualties from accidents or natural disasters, while flying in aid workers and supplies for such occurrences.
The Aircraft Owners and Pilots Association (AOPA) reports there are 1,628 unpaved runways at public-use airports in the United States. It’s difficult to get a number on unpaved runways on private strips, but Statista says there are 13,000 such landing spots in the country, most probably unpaved.
One Diamond DA-40NG owner checked his pilot operating handbook and obtained the following distances for grass and hard-surfaced runways. Distances are compared those for hard-surfaced runways. Taking off from tall grass is apparently not a good option, wet or dry.
— Grass runway, dry, (2″) long: Increase the ground roll by 10% [ 2170 + 217 = 2387]
— Grass runway, dry, (2″) to (3.9″): Increase ground roll by 30% [ 2170 + 651 = 2831]
— Grass runway, dry, (9.8″): Increase ground roll by 45% [ 2170 + 976.5 = 3146]
— Grass runway, longer than (9.8″): A takeoff should not be attempted
— Grass runway, wet: Increase the dry grass runway distance calculation by 20%
— Grass runway, wet, (2″) long: Increase the ground roll by 10% [ 2170 + 217 = 2387 + 477.4 = 2864.4]
— Grass runway, wet, (2″) to (3.9″): Increase ground roll by 30% [ 2170 + 651 = 2831 + 566.2 = 2947.2]
— Grass runway, wet, (9.8″): Increase ground roll by 45% [ 2170 + 976.5 = 3146 + 629.2 = 3775.2]
His conclusions:
Fly when grass is dry
Keep grass cut short
Get more runway
The DA40 is not an STOL aircraft, but the percentages shown would work for Piper Cubs or Cessna’s, none of which approach the distances or climb angle achieved by the Goldfinch.
Goldfinch overflies Norman-Brittan Islander, a nine-passenger commuter liner that is a role model for Electra
Testing Everything
Electra’s flights from a field in Manassas, Virginia demonstrate not only the airplane’s short-field capabilities but its ability to operate independent of airport services. Since the craft’s batteries are re-charged in flight by the hybrid propulsion system, the only services required might be an occasional topping up of the fuel tank.
JP Stewart, Electra’s Vice President and General Manager explained the significance of Electra’s design philosophy. “The Electra eSTOL technologies increase the number of available landing sites by orders of magnitude relative to traditional fixed wing aircraft while providing for higher cruise speeds, lower costs, and lower noise than vertical lift solutions. These first flights from a field demonstrate the beginnings of this strong capability that we will continue to develop.”
Testing “included acoustic data collection to validate the low-acoustic capabilities of the eSTOL technologies.” Readings showed noise levels under 55 decibels at 500 feet overflight, “comparable to human conversation.” At typical cruise altitudes, the aircraft will be inaudible over background noise.
Flying magazine expanded on the story, explaining the technology behind blown-lift propulsion. “Electra’s eSTOL achieves its incredibly short runway requirement through the use of blown lift propulsion. Airflows are guided over the wing into flaps and ailerons that redirect them toward the ground, adding to thrust from the aircraft’s eight electric motors. This allows the vehicle to take off at what Electra describes as neighborhood driving speeds.”
Future Plans
Electra’s Goldfinch demonstrator with nine-passenger future craft
The Goldfinch as a test bed for the Electra’s technology is showing the way for the production aircraft “which will carry 9 passengers or 2,500 pounds of cargo up to 500 miles while still providing the STOL, austere operations, and low-noise capabilities. Aircraft certification and entry into commercial service under FAA Part 23 regulations is targeted for 2028.”
Historical Side Note
The Shuttleworth Trust, near Cambridge, England, houses a splendid collection of historic aircraft, including an ultralight craft designed by Neville Shute Norway, author of On the Beach and other works of fiction. The English Electric Wren is powered by a 398 cc Douglas motorcycle engine of a rated 3 horsepower (2.25 kilowatts). Rated power was probably based on an English taxable horsepower calculation that favored long strokes and small cylinder bores. Apropos of the advice from the Diamond DA40 owner, the Wren’s flights at the Trust require groundskeepers to mow the grass runway to near putting green levels.
The Wren overflies the supersonic P1A (made by the same company decades later) at Warton, England. The Wren did manage a ceiling of 2,350 feet on a good day and cruised at 52 mph. Its main selling point was fuel economy – 87.5 mpg.