Transformative Aircraft

and 

Green Flight Challenge II

ABSTRACT

The aeronautical, environmental and societal benefits of the transformation to Green 

aviation are described along with the urgencies that compel it. A proposal is presented to 

bring about these benefits by extending NASA’s Centennial Challenge for Aeronautics. 

Performance goals are set for future Green, Quiet, V/ESTOL aircraft that can transform 

transportation.

ABBREVIATIONS:

CAFE: The Comparative Aircraft Flight Efficiency Foundation

C.A.F.E.: Corporate Average Fuel Economy, the U.S. MPG standard for cars

CTOL: Conventional take-off and landing

DOD: Department of Defense

DOT 500: Dept. of Transportation Federal Motor Vehicle Safety Standard No. 500 (49 CFR 571.500), 

for slow speed 4 wheel residential vehicles of ≤ 25 mph.

DtD: “Door-to-door”, referring to a trip’s complete path

G: The acceleration due to gravity

GA: General aviation

GFC: Green Flight Challenge, NASA’s Centennial Challenge for aeronautics

GFC I: The CAFE Green Flight Challenge of 2011, fore GQ CTOL aircraft

GFC II: A proposed GFC for GQ V/STOL aircraft

GQ: Green and quiet, as applied to aircraft with those attributes

Green: Environmentally-friendly in terms of emissions and energy use

IC: Internal combustion, referring to engines

pMPG: Passenger miles per gallon, i.e., vehicle MPG x # of seats

RC: Radio-controlled, as in hobbyists’ models

SF: San Francisco, California

STOL: Short take-off and landing

TSA: Transportation Security Administration

UCSF: University of California at San Francisco

U.S.: United States of America

Vc: Cruise velocity

VMT: Vehicle miles traveled

VTOL: Vertical take-off and landing

V/STOL: Either vertical or short take-off and landing
2

Transformative Aircraft

and 

Green Flight Challenge II

by 

 Brien A. Seeley M.D., President, CAFE Foundation

May 17, 2009

INTRODUCTION

The most basic purpose of aviation is to travel fast without need of roads. Yet, 

after America’s first Century of Flight, our hub and spoke air transportation 

system fails to fulfill that purpose for the very trips that people most often make--

trips of less than 200 miles. By converging current technologies, we can remedy 

this failure by drastically reducing the distance between airport and destination 

doorstep. In our current built environment, the only feasible way to effect this 

transformation is by bringing forth a new class of Green, Quiet V/ESTOL 

aircraft—the “GQ aircraft”.

NASA articulated the vision of this transformation in 2003.1,2 Due to the continued 

worsening of surface gridlock, along with global warming and the need for Green, 

that vision has become even more urgent and compelling today. Since the firstever CAFE Electric Aircraft Symposium in 2007, it has become clear that the 

missing ingredient necessary for this transformation, i.e., ultra-quiet operation, is 

finally within reach thanks to electric propulsion.

NASA’s current quest to make aviation Green and Quiet, the 2011 CAFE Green 

Flight Challenge (GFC), is an important first step in the transformation to a future 

of sustainable mobility freedom. To maximize the benefits of the GFC, a followon “GFC II” needs to be created. Like the inaugural GFC, GFC II should demand 

GQ aircraft. But for GFC II, the aircraft must also have vertical or extremely short 

take-off and landing capability (V/ESTOL). These are the only type of aircraft that 

will have both the capability and the consent to land at “pocket airports”, very 

close to destination, eliminating the onerous delays of surface gridlock. This, 

along with enhanced computerized flight decks that make them safe and easy to 

fly, is what will make them useful and popular.

The popularization of GQ V/ESTOL aircraft can revitalize aviation, transform our 

transportation system and bring many other societal benefits. Harnessing the 
3

resource of talented citizen innovators and universities to bring forth such aircraft 

would be the most practical, efficient and valuable of any NASA Challenge. 

Ironically, after aviation has conquered the sound barrier and soared high above 

the stratosphere, its most promising new frontier turns out to be that of mastering 

the ability to fly slowly, quietly, safely over our own backyards, like birds.

NASA GOES GREEN

Fortunately, on July 31, 2009, visionary leaders at NASA launched a technology prize 

squarely aimed at Greening aviation. It is the 2011 CAFE Green Flight Challenge (GFC), 

the largest monetary prize ever offered in aviation. Aviation’s lack of Greenness has not 

been a concern of military aviation. It needed a civilian solution. No single entity, 

program, funding or leadership had emerged to make aviation Green, until now. NASA’s 

GFC will provide both the means and the opportunity to make it happen.

In summer, 2011, NASA will award $1.5M cash to the highest scoring “Prius of the 

Sky”. These will be aircraft that are Green and Quiet—GQ aircraft.

The GQ aircraft in the GFC must demonstrate 100+ mph while achieving at least 200 

passenger MPG. They must take off over a 50 foot obstacle in less than 2000 feet while 

emitting no more than 78 dBA, as measured 250 feet to the side of the runway. They 

must be capable of maintaining level flight at or below 52 mph.

Indications are that the GFC-winning aircraft will sensationally surpass the 100 mph/200 

pMPG threshold by combining the best of today’s technology. That achievement will 

attract consumers as well as global media attention. But this inaugural GFC—GFC I—is 

just the beginning of the needed Green transformation of aviation.

Imagine the GFC I-winning “Prius of the Sky” becoming able to take off and land within 

walking distance of nearly any destination, immune to surface gridlock. This is the ideal 

goal for GFC II—quiet, fast Green Flight with vertical or extremely short take-off and 

landing (V/ESTOL) capability. V/ESTOL capability can be defined as being able to take 

off or land over a 50 foot obstacle in no more than 400 feet. Achieving V/ESTOL with 

little or no reduction in cruise velocity (Vc), quietness or “Greenness” is an 

unprecedented challenge. It would produce a truly game-changing aircraft. 

GFC I, in keeping with NASA’s mission, is designed to advance aviation for the benefit 

of all. GFC II would further leverage these benefits. It would build upon GFC I’s media 

attention and could extend and solidify the value of its name sponsor’s “Green branding”. 

The top GFC I aircraft could return with ESTOL modifications to compete against totally 

new GFC II V/ESTOL designs to rapidly bring forth the best possible combined 

performance. This mix would advance several technologies concurrently:

• High-lift devices, long overdue in GA

• Circulation control
4

• Inflatable Coanda flow guides

• Multi-deployable fabric lift surfaces

• Morphing wings

• Channel-wing technology

• Electric motors with tilt-rotor capability

• Vectored thrust technology

• Powered lift

• Quiet propellers and ducted fans

• Goldschmied propulsion

• Alternative and hybrid energy sources

• High Power density of both motors and batteries

• Distributed propulsion

• Motor-in-wheel propulsion and braking

• Computerized stability and low-speed control

• V/STOL safety and reliability

• Nano-materials

• Drag reduction

Aircraft that combined the aeronautical advances demanded by such a challenge could 

not only revitalize aviation, they could transform our transportation system and bring 

many other societal benefits. This is a lofty goal that is powerfully Green in several ways 

that will be explained below.

This goal would be best achieved by setting required performance thresholds and then 

rewarding the GFC II competitor that surpasses them by the largest margin. This “Best of 

Breed” approach increases participation compared to a “First-to-Demonstrate” format. A

Best of Breed competition is more attractive to the media and hence more valuable to its 

sponsor. It can be repeated to win further incremental gains, if desired.

WHY V/ESTOL IS NOT ENOUGH

The game-changing new GQ V/ESTOL aircraft must overcome the deficiencies that have 

prevented existing V/ESTOL aircraft from becoming popular. These deficiencies are:
5

• Unacceptably high cost

• Poor fuel economy, i.e., NOT Green

• High noise emissions

• Safety concerns

• Poor reliability

• High maintenance

• Low cruise speeds

• Resentment of perceived privilege

• The obstacle of flight training

• Lack of time savings

The new breed of GQ V/ESTOL aircraft must correspondingly be very quiet, Green, 

ultra-efficient, accessible to most people and affordable. They must offer trip speeds that 

are substantially better than cars and must be easy to learn to fly. Their safety and runway 

requirements must be “neighborhood-compatible” for them to gain the crucially 

important close-in access to destinations. Global warming, peak-oil and our dependence 

upon foreign oil will increasingly demand that such future vehicles be Green.

This combination of vehicle capabilities are achievable with today’s technology. 

However, creating GQ V/ESTOL aircraft is beyond the means and market risk of small 

aircraft manufacturers. It is a highly challenging, breakthrough achievement that is ideal

for a substantial, well-focused technology prize.

“Neighborhood-compatible” runway requirements mean ESTOL aircraft that can operate 

from airstrips that are ≤ 400-feet long, and VTOL aircraft that require less than 100-foot 

diameter landing sites. Mainly because of noise issues, small diameter VTOL landing 

sites have often been forbidden in residential areas. Due to local opposition, downtown 

San Francisco now has no active helipads. It has a few unused and former rooftop 

helipads that can only be used in emergencies.3

The opposition to VTOL landing sites means that, until VTOLs become much quieter, 

ESTOL and VTOL landing sites will continue to generally coincide and thus share equal 

proximity to destination. In addition, clearing a 50’ obstacle at 250’ and landing on a 

100’ pad is essentially how helicopters operate today in order to stay out of the “deadman’s zone” of engine failure. Accordingly, in the near-term future, it follows that VTOL 

capability be should accorded only slightly greater GFC II scoring value than ESTOL 

capability. See Graph III.

SMALL HYBRID V/ESTOLs
6

GQ V/ESTOL aircraft must be very lightweight and efficient. They must move a large 

mass of air downward at velocities that do not produce much noise. These demands for 

low thrust loading and light weight favor small, 1-2 seat electric-powered aircraft with 

transient high power density for take-off and low continuous power use during cruise 

flight. Since ground commuter vehicles typically carry only 1.3 persons, a 1-2 seat 

aircraft can offer significant utility. Because of their suitability as “air taxis”, heavier 4-6 

seat V/ESTOL aircraft should be encouraged as well. These might deserve some 

allowance for greater noise due to the greater power needed for their increased gross 

weight.

As DOD’s study has recently found4, the quest for speed and being constrained to low 

thrust loading to limit noise means that future V/ESTOL aircraft are likely to need to 

employ a hybrid design of fixed-wing plus some rotor lift. See Appendix. Such hybrids 

need a short runway rather than a helipad. The hybrid’s fixed wing is needed to smoothly 

accelerate a large mass of air downward at a relatively low velocity, i.e., quietly, and its 

forward speed on the short runway provides the dynamic pressure necessary to move that 

air mass. Ideally, that short runway can be built on a very small land parcel, such as 2 

acres. Such a 2-acre “pocket airport” could provide a short runway that is 418 feet long, 

along with several spaces for aircraft parking.

To use very short runways, aircraft must be able to accelerate quickly during take-off and 

then climb out at a steep angle. They must be capable of controlled flight during a slowspeed, steep glideslope on final approach to landing. To use a pocket airport, the landing 

touchdown must be precise without overshoot or undershoot. The hybrid of fixed-wing 

plus rotor, using wing spoilers, can achieve such performance. Small, unoccupied, RC 

models have demonstrated this5. Full-scale versions of such hybrids would almost 

certainly require computer-aided stability and control in order to handle strong gusts and 

crosswinds that can rival dynamic pressure in magnitude. Such computer-aided control 

would give a valuable head-start toward precise, autonomous flight for these vehicles, 

another feature that they will need in order to become popular.

Electric motors are favored in GQ V/ESTOL hybrid aircraft because of their highefficiency, high reliability, high power to weight ratios, smooth running (more suitable 

for tilt-rotor), quiet, emission-free power and installation simplicity compared to internal 

combustion (IC) engines. However, the IC engine, if it can be quiet and Green enough, 

offers a clear advantage in range, re-fueling time and extant support infrastructure.

“SPEED IS WHAT SELLS AIRPLANES”

—Roy LoPresti

Time is a non-renewable resource. For members of the multi-tasking “X Generation” and 

“Texting Generation” time is likely to be the scarcest commodity in the 21st Century. 

Busy people tend to exhibit a disproportionate hunger for speed in their choice of vehicle. 

In order to attract a mass market, GQ V/ESTOL aircraft must provide DtD trip speeds 

that are at least twice that of any other form of transportation, and the faster the better. To 
7

accomplish this, V/ESTOL aircraft will need cruise speeds of over 100 mph on trips of 

under 100 miles and speeds of near 150 mph on trips of under 200 miles. See Graph II. 

Accordingly, GFC II must reward Cruise Velocity (Vc) as one of its key metrics, with the 

other scoring metric being Take-off Distance. See Graph III. The high speeds demanded 

in GFC II will demand aircraft with minimal drag and this may be more achievable in 

hybrid fixed-wing/rotor GQ V/ESTOL aircraft than in traditional VTOL rotor-craft.

The unavoidably long delays of single file surface travel to and from conventional 

airports by car or bus make the speed and range of CTOL aircraft almost irrelevant for 

the trips most people want to make—trips of 200 miles or less. These ground travel 

delays are now endemic in our built environment and, along with other factors, have 

severely depressed the market for CTOL aircraft today. With all due respect to the great 

Roy LoPresti, we must recognize that in the 21st Century, it will be the DtD trip speed

that sells airplanes.

The only feasible way to enhance DtD trip speed is for aircraft to become fast, GQ 

V/ESTOLs and the best way to bring that about will be with a technology prize.

WHAT ABOUT FLYING CARS?

For decades, the dream of the flying car has attracted interest and yet failed to win a 

market. The criticism usually leveled has been that flying cars have been mediocre cars 

and mediocre aircraft. Sadly, just when technology might enable a CTOL flying car to 

achieve satisfactory flight performance, the worsening gridlock that reigns between 

CTOL airport and destination robs its value as a time-saver. Ultimately, the flying car 

needs to become a GQ V/ESTOL aircraft and that could be the basis for a follow-on 

challenge to the GFC II. However, becoming Green, Quiet and V/ESTOL imposes very 

difficult demands upon a self-contained flying car that is already burdened with the 

weight and performance penalties that attend automotive use. The GQ V/ESTOL function 

is what counts most because the “last mile connectivity” for such aircraft can be achieved 

by walking, bicycle, golf cart, etc. rather than by car. Compromising the GQ V/ESTOL 

aircraft’s performance in order for it to become a flying car is probably not necessary and 

should not be the primary technology goal.

WHY NOT ANOTHER CTOL PRIZE?

High fuel costs, high prices for new certificated aircraft, a global recession and increasing 

airspace/TSA restrictions have all added to the depressed market for CTOL aircraft. 

Cessna, Cirrus, Beech and Mooney have laid off thousands of workers. General aviation 

(GA) flight operations are down nearly 50% compared to the 1990s and there are nearly 

50% fewer student pilots today than in the 1980s. The GA market is nearly moribund.

A report by Thomas Frank in USA Today on September 17, 2009, entitled “Feds keep 

little-used airports in business” cited the large expenditures being made with tax funding 

to support under-utilized GA airports. GA advocacy groups had to defend our small 
8

airports against Frank’s attack, which in effect argued that such airports were no longer 

needed.

To make matters worse, the public has recently expressed outrage at the use of private 

jets by CEOs of large companies that received government rescue funding. These jets are 

resented by the public as symbolic of a non-Green, privileged excess of luxury, expense 

and pollution. The public’s sense of fairness expects everyone should have to suffer the 

grind of gridlock like they do. If fast travel by air were affordably available to the public, 

their resentment would likely subside.

In the last 5 years, the emergence of CTOL Light Sport Aircraft (LSAs) and Very Light 

Jets (VLJs) have both failed to produce the hoped-for transformation of aviation. Despite 

expensive advertising hype for beautiful new small jets and innovative new LSAs, the 

sales of these aircraft number in the dozens instead of in the thousands. No matter how 

glitzy, these aircraft will never be able to avoid the time wasted on ground travel to and 

from CTOL airports.

The adverse environmental footprint of CTOL aviation today is unsustainable. Its 

inefficient land-use, poor proximity to destination, toxic fuels, lack of pollution controls, 

high noise emissions, vulnerability to terrorism and poor fuel efficiency all need to be 

remedied. The remedies need to come soon in order to avert loss of our CTOL airports.

SURFACE GRIDLOCK: BOUND TO GET WORSE

Experts predict that ground travel delays due to surface gridlock will get substantially 

worse in the next 20 years. Door-to-door trip speeds in the Los Angeles Basin, for 

example, are predicted to be just 22 mph in the next 10 years.1,9 This worsening is adverse 

to air travel because large CTOL and air carrier airports are usually relegated to locations 

several miles outside metro or town centers. This forces most air travelers to suffer the 

delays of gridlocked commuter highways to reach their destinations.

The trend to gridlock appears inexorable. The growth in surface vehicles and VMT 

outstrips the growth in population (See Figure 2.5). Planners find that the public is very 

resistant to giving up the privacy, security, autonomy and personal space of their cars. 

Even when cars become electric vehicles, the gridlock will remain.

The public resists using public transit. Buses and trains are inherently constrained to the 

limitations of two-dimensional, single-file surface travel. People deem the waiting, 

transfer maze, delays and limited distribution of transit stations to be unacceptably 

daunting.
9

Figure 2.5, above6.
10

These factors cast doubt on the likelihood that public transit solutions to gridlock will 

succeed. Indeed, public transit ridership is declining. A study by the Madison Institute of 

the future impact of high speed rail on reducing road use has made a similar, pessimistic 

forecast.7 See Figure 2.7 below.

Figure 2.7, above

Unlike surface transportation, flying can provide highways in the sky with unlimited 

numbers of lanes and overpasses, off-ramps and merges. A highway in the sky can be 

reconfigured instantly and does not require public purchase of expensive land that must 

be permanently removed from open-space or any other use. Unlike paving with asphalt, 

building aeronautical highways does not require millions of barrels of crude oil.
11

IF WE BUILD IT, THEY WILL COME

The transformation of aviation enabled by GQ V/ESTOL aircraft is predicated upon the 

concept of “pocket airports”, affordable 2-4 acre parcels that can be situated within 2 or 3 

miles from one’s destination doorstep.

Figure 2.9, above

Pocket airports are designed exclusively for GQ V/ESTOL aircraft and will be built only 

after such future aircraft are created, proven safe and popularized. The popularization of 

GQ V/ESTOL aircraft will most likely begin with air taxi services demonstrating their 

great utility. Later, as flight deck automation and NextGen air traffic control matures and 

makes flying easier, large numbers of non-professional pilots will personally adopt 

ownership and routine use of GQ V/ESTOL aircraft.

As shown in Figure 2.9, above, the pocket airport is only slightly larger than a football 

playing field. The 236 foot ground roll shown would give a 0.2 G deceleration to full stop 

from a touchdown speed of 38 mph. That ground roll would require a 15° glide-slope in 

order to clear a 50 foot obstacle situated at the end of the runway.

The pocket airport is analogous to the “pocket park” concept of new urbanism, where 

several small, walk-accessible neighborhood parks save having to drive to a more distant 

regional park. Pocket airports are likely to initially be built as exclusive new residential 

airparks and business campus amenities. These will prove the value of the concept. Once 
12

proven, these can sprout within walking distance of town centers. They will become the 

beacons of their neighborhoods, from which one could imagine “from here, I could go 

anywhere”.

Such opportunity will help regional cities to preserve their urban growth boundaries by 

encouraging infill development and the sprouting of new, self-sufficient exurbs with 

greater reach. Pocket airports will also invite Green surface transportation such as lowspeed, DOT 500-compliant electric vehicles, co-located mass transit stations, rentable 

bicycles as well as walking.8, 10

Walking and its cousin, bicycling, epitomize “Green”. They afford transportation, 

healthful exercise, and enjoyment while conserving fossil fuels, reducing toxic waste 

outputs, improving mind-body connection and physical vitality, and engaging people 

more fully in the experience of places. While human-powered travel modes are much 

slower than motorized travel, they are much more energy efficient, and their social, 

health, and especially environmental benefits make them now - more than ever – major 

Green.

Pocket airports not only would solve the problem of “ground leg connectivity” in air 

transportation, they could be reached by walking. Walkable communities can address 

many of the nation's greatest current public health concerns, including obesity, 

cardiovascular disease, diabetes, asthma, injury, depression, road rage, violence and 

social inequities. Walkability to bus/train transit, airport, market, shopping and job needs 

to become a priority. Land costs, existing development, tight government budgets, 

limited open space and underutilization preclude building more large airports for 

conventional take-off and landing aircraft (CTOL). But 2-acre parcels can be found 

within 2 miles of most town centers where pocket airports could be affordably built.

In the built environment of major metropolitan cities such as New York, Chicago, San 

Francisco and others, pocket airports could be implemented on large barges in the nearby 

bodies of water. This concept obviously will demand that the GQ V/ESTOL aircraft be 

extremely reliable and capable of precise spot landings.

In San Francisco, as shown in Figure 3 below, the several sites at which pocket airports 

could be built would provide excellent walkable access to the city’s major attractions.
13

Figure 3.

10 Potential Pocket Airports in San Francisco

1. Crissy Field, Exploratorium, Presidio 6. Fillmore, Western Addition

2. Ghirardelli Square, Fisherman’s Wharf 7. Kezar Stadium, UCSF Med Center

3. Ferry Building, Financial District 8. Sloat Blvd, SF Zoo

4. SF Giants Stadium, China Basin 9. Ocean Beach, Cliff House

5. Cesar Chavez Street Wharf, Shipyard 10. Baker Beach

Note that most destinations on the above map of San Francisco lie within just 1 mile 

of a potential pocket airport and virtually no point lies more than 3 miles from a 

potential pocket airport.

Converting communities to pocket airports will in itself be powerfully Green. Eliminating 

nearly 2 hours and 60 miles of surface travel to metro airports, often involving fuelwasting gridlock, could spare the need for more lanes on highways. It has been reported 

that in one year, Americans wasted 2.9 Billion gallons of gasoline while stuck in 

gridlock11, much of it in metro areas near large hub airports. The rate of increase in the 

number of cars outpaces our ability to build more lanes onto highways. (See Figure 2.5, 
14

below). The value of the time wasted in traffic is incalculable but enormous. Pocket 

airports can improve all of the above.

High energy efficiency and emission-free or bio-fueled aircraft will reduce carbon 

emissions a great deal. Distributed air travel, i.e., flying ‘as the crow flies’, shaves about 

10% off of the trip miles a car or mass transit would entail. These aspects of Greenness 

are independent of the actual MPG of the aircraft and some might say that fact justifies 

allowing GQ V/ESTOL aircraft to achieve less than the 200 pMPG demanded by GFC I. 

Pocket airports offer a degree of immunity to terrorism, a redundancy for airborne 

disaster relief and a more distributed system for Med-evac air ambulance. They are an 

ideal fit with Peter Calthorpe’s12 new urbanism and its “transit-oriented development”. 

The future of transportation is not more single file surface byways. It is not more cars or 

more lanes on the freeway.

SOCIETAL BENEFITS

Transforming our transportation system will produce many societal benefits, including 

growth in airspace capacity, mobility, safety, Green technology, jobs and manufacturing, 

along with inspiration for our next generation of young scientists, engineers and 

technology leaders. Pocket airports can make us more energy independent and that means 

both our nation and others become more self-sufficient. GQ V/ESTOL aircraft are 

unprecedented and could open a new market whose potential was predicted to approach

$1 trillion2. These benefits align with our nation’s goals and NASA’s mission.

Landing site cost tends to be proportional to the square of the runway length. An airport 

with 5000 foot runways, though 10 times longer than one with 500 foot runways, can cost 

100 times more.

It is reported that in one year, 1995, the U.S. spent $95 billion on road building. Reducing 

the cost of road-building is a societal benefit that could enormously reduces the use of 

and dependency on fossil fuels. In 2004, NASA Chief Scientist Dennis Bushnell2 cited 

Arthur Clarke’s 1984 quote that “The roads to support Autos cost as much as a small War 

and the casualties are on the same scale” as a reason to support future personal air travel. 

In that same presentation, he pointed to William Seifert’s 1968 prediction that “Any form 

of transportation that offers the lowest door-to-door travel time will always drive out 

lower speed competing modes unless the economics of the higher speed system are 

grossly unfavorable”.

V/ESTOL capability translates into safe aircraft that can land at slower speeds in smaller 

spaces in the event of loss of power. This means lower impact forces that should result in 

fewer fatalities and less property damage from off-airport landings. These benefits may 

lead to better consumer acceptance of these vehicles.

V/STOL BEATS CTOL

Graph I: (below) The Time Savings of V/STOL
15

Graph I shows the surprisingly large amount of time that can be saved by 

ESTOL/VTOL vehicles. The “ground travel time” is based upon the number of

miles out to the airport from one’s destination doorstep. Note that STOL/VTOL is 

the only aviation modality with substantial time savings relative to car travel on 

trips of less than 200 miles. 

-4

-2

0

2

4

6

8

0 100 200 300 400 500 600

Time Saved Relative to Car, in hours

Trip Length, miles

Airliner 550 mph

CTOL 200 mph

STOL/VTOL 100 mph

STOL/VTOL 150 mph

STOL/VTOL 200 mph

Car 30 or 60 mph

NOTES:

Car in urban use @ 30 mph

Car in rural use @ 60 mph

Neglecting time spent on pre-flight, taxiing

and car rental desk.

Includes 45 minutes for airliner park ’n fly

plus baggage and security check in.

Assumptions:

30 miles to CTOL or airliner airports

3 miles to STOL airport

0.3 miles to VTOL heli-pad

30 mph car to/from CTOL

18 mph golf-cart to/from STOL port

3 mph walk to/from VTOL heli-pad

Time saved with STOL/VTOL at 150 mph surpasses all

other modalities on trips from 50 to 500 miles

The time savings depicted in Graph I varies from typical conventional large airports 

(airliners and general aviation’s conventional take-off and landing (CTOL), 30 miles out) 

to future STOL airstrips (< 3 miles out) to VTOL landing pads that are < 0.3 miles out 

from destination doorstep. Assuming a 30 mph car for CTOL, an 18 mph golf cart for 

STOL and walking at 3 mph for VTOL, the ground travel times will be 60 minutes for 

CTOL and 6 minutes for both STOL and VTOL.

In Graphs I and II, the ground travel times are doubled to account for the bidirectional 

travel to/from the airports involved in any trip by air. This gives ground travel time of 

2:45 hours for airliners, 2 hours for CTOL and 12 minutes each for STOL and VTOL. 

The additional 45 minutes is added for commercial airliner travel is due to baggage-check 

and shoes-off security check-in.
16

The Graphs show that, for trip lengths ranging from 40 to 300+ miles, fast V/ESTOL 

aircraft offer significant time savings over both cars and conventional air travel. That 

range will be increasingly important as the public curtails its VMT to meet the needs of 

climate change and rising energy costs.

Graph II: (below) The Speed Advantage of V/ESTOL. Note that V/ESTOL is the only 

aviation modality that achieves significantly faster travel than a car on trips of less than 

200 miles. The fast, 200 mph V/STOL aircraft is unrivaled in trip speed until trip length 

is more than 500 miles. And 90% of all single and twin engine GA flights today are of 

under 500 miles.

0

20

40

60

80

100

120

140

160

180

200

0 50 100 150 200 250 300 350 400 450 500

Door-to-Door Trip Speed, mph

Range, statute miles

Airliner 550 mph

CTOL 200 mph

STOL/VTOL 100 mph

STOL/VTOL 150 mph

STOL/VTOL 200 mph

Car 30 or 60 mph

NOTES:

Car in urban use @ 30 mph

Car in rural use @ 60 mph

Neglecting time spent on pre-flight, taxiing

and car rental desk.

Includes 45 minutes for airliner park ’n fly

plus baggage and security check in.

Assumptions:

30 miles to CTOL or airliner airports

3 miles to STOL airport

0.3 miles to VTOL heli-pad

30 mph car to/from CTOL

18 mph golf-cart to/from STOL port

3 mph walk to/from VTOL heli-pad

STOL/VTOL Speed Advantage

Graph III: (below) A potential GFC II Scoring Formula

The formula for the simultaneous optimization of Speed and Take-off Distance 

needs to appropriately reward performance that is of practical value. Shortening 

the Take-off Distance to less than 100 feet offers very little practical advantage. 

Likewise, aircraft whose Take-off Distance exceeds 418 feet forfeit the benefit of 

pocket airports. A vertical double-tipped arrow marks the 418 foot take-off 

scores. These formula attributes are demonstrated in the Graph III below. Note 

that all of these aircraft are required to achieve a very high passenger-MPG in 
17

order to qualify for GFC II, and this will make speeds above 160 mph very 

difficult to achieve.

0

50

100

150

200

250

300

0 100 200 300 400 500 600 700 800 9001000

Score

Takeoff Distance (TD) over a 50 foot obstacle, feet

Vc = 100 mph

Vc = 120 mph

Vc = 140 mph

Vc = 160 mph

Vc = 180 mph

Vc = 200 mph

Vc = 250 mph

Vc = 300 mph

1/((0.001*((TD/Vc)^3))+(1/Vc))

Lines of constant Vc

Notes:

Helipads are 50-100 ft diam.

Soccer fields are 350-400 ft long

STOL equivalent scores:

200 mph/900 feet

160 mph/700 feet

120 mph/500 feet

100 mph/400 feet

GFC II Proposed Scoring Formula:

Score rewards Cruise Speed (Vc) and Takeoff Distance (TD)

VTOL equivalent scores:

250 mph/400 feet

200 mph/300 feet

160 mph/200 feet

125 mph/100 feet

120 mph/50 feet

V/STOL IS VERY HIGH TECH

ESTOL capability exacts a high price in the form of drag due to large wing area or, 

alternatively, the cost and weight penalty that accompanies having complex high lift 

devices embedded in the wing. VTOL capability has similar penalties in terms of 

potentially high noise and weight from its high power requirements. Today, advances in 

drag reduction, motors, batteries, actuators, high lift technologies, thrust vectoring, 

computerized stability and control and nano-material composites make the challenge of 

V/ESTOL more feasible. The suitability of smooth, power-dense, reversible electric 

motors available today for vectored thrust is particularly promising: See: 

http://www.youtube.com/watch?v=iyTKwTx_VdQ
18

GFC II REQUIREMENTS

GFC II can remove the 52 mph stall requirement of the 2011 GFC I. It still must impose 

the 100 mph performance threshold and demand a high level of passenger MPG in order 

to rival future cars. Since 35.5 MPG for ostensibly 4 seat cars is the newest automotive 

U.S. C.A.F.E. Fleet Goal for 2016, GFC II could demand that all aircraft achieve at least 

142 passenger MPG (4 x 35.5). Ideally, GFC II should require that all entrants achieve a 

take-off distance over a 50 foot obstacle of ≤ 1000 feet. This would be just half of the 

2000 foot take-off required in GFC I and could allow some GFC I aircraft to compete.

If desired, the GFC II take-off distance requirement could be more stringent, shortened to 

just 418 feet to fit the pocket airport. This would likely decrease participation and 

diversity in the competition and might demand a longer lead time and larger prize purse.

The CAFE Foundation can measure Take-off Distance accurately and considers it a 

reasonably valid indicator of whether an aircraft can fulfill V/ESTOL requirements. 

Demonstrating and measuring Landing Distance is much more difficult and is not 

necessary for GFC II. The particular technologies necessary to shorten landing distance 

and make landings ultra-precise and automatic may be worthy as the subject of a future 

challenge. That future challenge could further enhance the GQ V/ESTOL aircraft from 

GFC II.

Winning GFC II will be more challenging, more expensive and more transformative than 

winning GFC I. Consequently, the cash prize for GFC II should be at least $2M. This size 

of award along with its “Best of Breed” format (as contrasted with “First to 

Demonstrate”) incentivizes participation by a large number of teams, both private and 

from universities. In Best of Breed, all teams will get their chance to demonstrate, rather 

than becoming abortive efforts after a “First-to-Demonstrate” wins all. This increases the 

leverage and yield of the prize money invested as well as the diversity of innovations. 

History teaches us that in technology prizes it is often the aspiring “amateur”, noncorporate teams that make the most passionate and innovative efforts to win.

To maximize the benefits of GFC II, it should be formulated and announced as soon as 

possible. By continuing the name Green Flight Challenge, GFC II will increase the 

likelihood of major sponsorship support for both events, a key factor in their success. The 

lead time for GFC II should be at least 2-3 years in order to enable both GFC I and GFC 

II teams more time to modify, design and build ideal GQ V/ESTOL aircraft.

OTHER AERONAUTICAL CHALLENGES

The next aeronautical challenge should be for Green Quiet V/STOL aircraft. Other 

potential aeronautical technology prizes that aim to demonstrate autonomous flight, autolanding capability, longer range, faster refueling or recharging or quieter operation, while 

adding value, are not as important as first bringing forth GQ V/ESTOL aircraft. 

Autonomous flight and auto-landing already exist. Longer range (> 200 miles) for 
19

affordable Green aircraft will evolve naturally. Quiet operation is already sufficiently 

addressed by GFC I, which requires noise levels twice as stringent as the FAA demands.

Ground travel delays, combined with the high cost, high noise emissions, high carbon 

emissions and poor MPG of LSAs, VLJs and flying cars make these CTOL aircraft very 

unlikely to reach production volumes necessary to achieve affordability. This makes it 

inappropriate to aim prize money toward either of those domains at this time.

The crucial importance of making GQ V/ESTOL aircraft safer and easier to use by 

adding robust computer-aided safety, reliability, pilot-assistance and precision landing 

capability should be the subject of a follow-on GFC III. 

POLITICS

The great promise of GQ V/ESTOL aircraft as a transportation solution is that they can 

complement commercial air travel by restoring its door-to-door trip speeds, by 

eliminating the enormous ground travel delays. Large manufacturing companies should 

be sponsoring and promoting such transformative aircraft as a path toward a potentially 

enormous new market. That market was estimated by NASA’s Bushnell2 to be potentially 

as large as $1 Trillion.

Cynicism expressed by uninformed, unimaginative or vested interests regarding the

likelihood of such aircraft winning a large market is understandable in present day 

perspectives. However, the very purpose of a technology prize is to induce the most 

promising, urgent and transformative achievement that a risk-averse, capital-poor free 

market cannot otherwise produce. Best of all, a technology prize helps prevent industrial 

secrecy from wasting effort in isolation when networking with others in a more broadly 

shared knowledge and perspective yields better progress.

CONCLUSION

NASA’s quest to make aviation Quiet and Green, the Green Flight Challenge (GFC), is 

an important beginning toward a future of mobility freedom. To maximize its benefits, a 

follow-on GFC II should require fast GQ V/ESTOL aircraft. These are the only aircraft 

that will have both the capability and the consent to land in small spaces, very close to 

destination, eliminating the onerous delays of surface gridlock. This, along with enhanced 

computerized flight decks that make them easy to fly, is what will make them useful and 

popular.

The popularization of GQ V/ESTOL aircraft can revitalize aviation, transform our 

transportation system and bring many other societal benefits. Harnessing the frontier 

spirit of citizen innovators and universities to bring forth such aircraft would be the most 

practical and valuable of any NASA Challenge. Ironically, after aviation has conquered 

the sound barrier and soared high above the stratosphere, its most promising new frontier 
20

turns out to be that of mastering the ability to fly slowly, quietly, safely and close to the 

ground, like birds.

Footnotes and References:

1

AIAA paper 2003-264, entitled “PERSONAL AIR VEHICLES: A RURAL/ REGIONAL AND INTRA-URBAN ONDEMAND TRANSPORTATION SYSTEM (available at: http://cafefoundation.org/v2/tech_lib.php then click on 

Title # 3 under the topic “NEXTGEN PAVs AND SATS”)

2

See: http://cafefoundation.org/v2/tech_lib.php Item # 11 under NextGen: PAVs and SATS

3

http://stophelipad.org/helipads.shtml

4

DOD study on V/STOL: http://www.acq.osd.mil/dsb/reports/2007-07-Future_Need_for_VTOL_STOL_Aircraft.pdf 

page ix.

5

http://www.youtube.com/watch?v=4hZc-LVhsw8 and

http://technorati.com/videos/youtube.com%2Fwatch%3Fv=w68WRWBeWzU and

http://technorati.com/videos/youtube.com%2Fwatch%3Fv=PTbkwgvxNDw and

http://technorati.com/videos/youtube.com%2Fwatch%3Fv=PTbkwgvxNDw

6

Sperling, Daniel, et al, Two Billion Cars, Oxford Press (2009).

7

http://www.publicpurpose.com/21st-fl.htm

8

http://www.emich.edu/public/geo/557book/d373.calthorpe.html

9

In metropolitan areas, cars typically average < 35 mph trip speeds.

10DOT 500 definitions: http://www.nhtsa.dot.gov/cars/rules/rulings/lsv/lsv.html

11http://www.rita.dot.gov/publications/transportation_vision_2030/html/passenger_transportation.html

12Calthorpe, Peter, The Regional City, Island Press (2001).

http://books.google.com/books?id=qcwvvI0gfpoC&pg=PA53&lpg=PA53&dq=Peter+Calthorpe+walkability&source=

bl&ots=dFBmoeGumf&sig=rNAZHqVJAYIMETxHV2KIquSdIvA&hl=en&ei=kL3MSohrhY60A8qzsaEB&sa=X&oi

=book_result&ct=result&resnum=3 - v=onepage&q=&f=false

^Air Miles are typically 10% shorter than car miles due to curves in roads. This 10% air travel advantage is included in 

the graphs above.