Designs for the Future Don’t Address Today’s Safety Problems

Two workhorse airplanes of today could be replaced by radical new designs in 35 years, although there is an alternative scenario where the airline industry is a fraction of its current size. Beware of glitzy projections that the future will feature extensions of current technology and even more passenger-miles.

If in three decades oil costs $150 a barrel (or more) air travel will be a pricey commodity available only to governments and the very rich. As transport for the masses, air travel will be a memory.

This stark vision of the future has not discouraged the National Air and Space Administration (NASA) from sponsoring teams at MIT, Boeing, GE, and Northrup Grumman to come up with aircraft designs that burn 70% less fuel and create less noise than existing planes. Two designs resulted, both of which pack passengers into high-density seating in order to rationalize fuel costs of $5-$10 a gallon. Today’s jet airline industry is based on fuel costs of $1-$2 a gallon – which has led to a misery of discomfort, from cramped seating to fees for baggage and just about everything else.

The U.S. airline fleet, presently numbering about 4,000 planes, could well be 1,000 planes or fewer in 35 years – not big enough to justify investments in radical new designs. And safety might be improved more by investing in pedestrian research into improved electronics, a better interface between pilots and their increasingly automated airplanes, a more maintenance friendly aircraft (less avionics hidden behind sidewall panels), and a real advance in on-board fire detection and suppression (vast areas of current airliners are unprotected, to include the passenger cabin and main deck cargo compartments). Today’s jet, redesigned to yield a much safer airplane, might have been a more fruitful effort than for NASA to engage in a radical rethinking for a mass transportation industry that won’t be around in 35 years. The number of passengers turned off by the hassle of air travel has already declined by a couple percentage points; the economic meltdown has further depressed air travel. A tripling of ticket prices and serious limitations on stocks of jet fuel may well be enough to change air travel as it is known – from a convenience enjoyed by millions annually to a select mode for a few hundred thousand.

MIT won the NASA competition for new “green” subsonic airplane designs.

The objective was to develop concepts for quieter subsonic commercial airplanes that would burn 70% less fuel and emit 75% less nitrogen oxide (NOx) than today’s commercial jetliners. NASA also wanted aircraft that could take off from shorter runways. NASA expects air traffic to double in 35 years, necessitating rethinking the basic airplane design. There is an adage that just when you think present trends will continue into the future, they are about to change. That point may have been passed in the last couple years. The entire transportation system – air, rail, maritime, auto and truck – will be dramatically altered by the end of cheap oil.

This inexorable fact did not affect NASA, which blithely predicted a doubling of passengers in 35 years.

The MIT design team met NASA’s challenge by developing two designs: a 180-passenger “double bubble” airplane to replace B737 class aircraft, currently employed for domestic flights, and a 350-passenger “hybrid wing body” series to replace the B777 class aircraft now used for transcontinental and international flight.

According to MIT’s aeronautics professor Ed Greitzer, a “radical change” is needed. “Aircraft silhouettes have basically remained the same over the past 50 years,” he said, describing the traditional, easily recognizable “tube on a wing” arrangement of an aircraft’s wings and fuselage.

For the domestic B737 replacement, Greitzer’s team reconfigured the tube-and-wing structure. Instead of using a single passenger cylinder, two partial cylinders placed side-by-side were used to create a wider fuselage. Its cross-section resembles two soap bubbles joined together. The rear mounted engines take in slower moving air. Known as Boundary Layer Ingestion (BLI), this technique allows the engines to burn less fuel for the same amount of thrust (at a drawback of more stress on the engine).

The "double bubble" concept has an extra wide fuselage to provide some extra lift. The aircraft would carry 180 passengers, lightly more than the current B737-800.

The "double bubble" concept has an extra wide fuselage to provide some extra lift. The aircraft would carry 180 passengers, lightly more than the current B737-800.

The design mitigates some of the drawbacks of the BLI technique by travelling about 10% slower than a B737. To further reduce the drag and the amount of fuel burned, the concept airplane features longer, skinner wings and a smaller tail.

A version of the airplane built out of conventional aluminum (as opposed to weight saving composites), would burn 50% less fuel (as opposed to 70% less) and might be attractive as a lower risk, near-term alternative.

The “double bubble” concept of conjoined tubes evidently did not consider the demands of emergency evacuation. With two fuselages of passengers, and only half as many emergency exits (from the artist’s rendering), the problem of crowding and delayed evacuation at the exit doors could be a show stopper.

The “double bubble” design is particularly attractive from an airport perspective. The airplane could use the current boarding and jet bridge designs. From an airport rescue and fire fighting (ARFF) view, delayed evacuation may be a real problem.

For intercontinental travel, the MIT tam designed a triangular shaped hybrid winged body aircraft that blends a wider fuselage with the wings for improved aerodynamics. The large center body generates lift, thus overcoming a major limitation of the current tube-on-a-wing design – the conventional fuselage produces drag, not lift.

For longer range and more capacity, a blended wing body is envisioned that would carry about 350 passengers.

For longer range and more capacity, a blended wing body is envisioned that would carry about 350 passengers.

Both the domestic and the intercontinental designs feature one real safety benefit: the fuel in the wings is separated from the engines at the rear of the fuselage. The intercontinental design has the added advantage of wrapping most of its crash-absorbing structure around the passengers.

But survivability could be improved in present designs with 3-point restraints similar to that found in automobiles, and by facing the seats toward the aft end of the airplane. This would have the beneficial effect of spreading the force of a sudden deceleration across one’s entire backside, not just across the width of a 2-inch wide lap belt.

NASA might better spend its limited time and resources on a more modest but significantly better payoff research program. Specifically, NASA is the repository of the Aviation Safety Action Program (ASAP) database, the anonymous reports submitted by flight crews, mechanics and air traffic controllers. NASA is the repository to assure submitters of independence from the Federal Aviation Administration

NASA could cull through these reports, identify the 20 or so greatest threats to safety, and come up with mitigation strategies. Simple things, like radios that don’t lose a message when two persons broadcast on the same frequency. Or separating electrical power conduits from oxygen lines, so that arcing does not burn through the oxygen line, worsening the fire problem.

There is another axiom that has been forgotten in this 35-year look ahead: solve today’s problems today.