An elderly woman stepped through the cockpit door after being announced by the Flight Attendant who was dutifully guarding the door and greeting passengers. "Excuse me" the woman said speaking so softly that I almost didn't hear her. "I was wondering...how do the engines disengage from the wheels? Surely they don't keep spinning once they come up." This was NOT a typical question from someone I would describe as a rural grandmother clad in twenty year old homemade clothing. No offense intended...she just didn't look like a person who would be interested in the mechanics of a commercial jet. Engines disengaged from the wheels? I smiled and almost laughed out loud.
Don't judge a book by its cover.
I politely explained that the wheels and the engines were not actually connected in any way...that the engines just provided thrust to push the airplane. "It's a little like putting your car in neutral and making your husband get out and push, " I told her. We had a short conversation and she asked a handful of other unexpectedly insightful questions before she smiled and left the cockpit seemingly content with my explanation. The question got me thinking that maybe she was onto something. Maybe we could design a system...possibly an electric one...that would propel the aircraft from the gate to the runway where we would start the engines for takeoff. I picked up my fight plan and noticed that we were planning to burn around 450 pounds of fuel for taxi purposes on this one flight alone. With around 2400 flights every day, this one airline would burn more than one million pounds of fuel in a single day just to get jets to and from the runway. Strange thought, I know, except that someone has already thought of it. I poked around online and found an article about a December 2011 test program that installed electric motors on the main landing gear assemblies of a Lufthansa Airbus A320. The brake assemblies of the inboard MLG wheels were replaced with drive units, each one containing a liquid-cooled electrical motor powered by the aircraft's APU. "Pilots reported that the demonstrator system not only handled well, but was more responsive than the main engines normally used for the task," said project manager Christian Mutz. Too bad grandma couldn't get credit for the idea.
© Michael Gubisch/Flightglobal
© Michael Gubisch/Flightglobal
Then I remembered another application of the concept. Those of you who attended Oshkosh last year (2012) may recognize the "roadable aircraft" manufactured and presented by PlaneDriven. The PD-2 utilizes a Glasair Sportsman amateur-built airplane and adds a 50-hp “drive unit” to the rear of the craft to provide ground power. To put the vehicle into drive mode, the pilot folds the wings, starts the drive unit, and away it goes. Sounds simple enough.
I was drawn in by the display and the odd looking little machine as I meandered my way through the endless sea of aircraft at this year's show. Three grown men were in the process of morphing the contraption from airplane to car and I couldn't resist watching the process. It was a little like rubber necking at an accident scene on the highway though...and I mean that the way it sounds. The procedure looked complicated and time consuming to say the least. A fourth member of the team was standing around answering questions for a growing crowd of observers as I heard someone ask her how long it took to make the conversion from airplane to a legal and road worthy vehicle. "We'll," she said, "our goal is for one adult to complete the task in 15 minutes. We've been working very hard on this." Someone else asked how long it currently took..."We'll," she said, "right now it takes two men two hours." I lost interest at that point and moved on to another exhibit.
I'm so disappointed. I thought for sure there would be a flying car in every garage by now!
Only two more years until 2015...where are all the flying cars?!
