While the 8-minute clip at the link below doesn't really include any substantive flight test maneuvers, it does give a few clues regarding the vehicle's flight characteristics. Rotation for takeoff was extremely crisp, with the plane leaving the ground after only a few degrees of pitch change. There appeared to be a significant amount of crosswind, because the plane weathercocked perhaps 8-10 degrees immediately upon liftoff. Once airborne, roll rates appeared to be crisp, and no obvious adverse yaw was apparent, although that could be because of well-coordinated rudder. Rotation for landing, like for takeoff, was minimal. It was almost flown onto the runway. It may have simply been a slightly incomplete flare that time around, but if that is the normal method of touchdown, it could imply a sensitivity to gusty winds, since the airspeed would have to fall within a very narrow band to do that consistently. (Does it come with an AOA gage?) It might also mean that the plane is touching down with a lot of residual flying speed, perhaps making pitch control in the flare subject to PIO. Neat plane guys, but I'd sure be nervous about leaving it in the restaurant parking lot without having a substantial tip for the security guard when I came out.
http://www.motortorque.com/car-news/the-new-178000-flying-car-23105.aspx
Mark,
ReplyDeleteYou have a good eye! A lot of folks wouldn’t have seen the things you did and overall you saw things correctly. Your blog was good, but I have a few insights from being in the seat that will modify some of your conclusions.
1. You are absolutely correct that the plane leaves the ground with only a few degrees of pitch change. Here’s what’s going on. Stall speed is ~45. But the rear wheels are far aft of the c.g.—think of your car. With these physical mechanics, the plane won’t rotate until ~60 knots. So I already have 15 knots of flying speed when I rotate…that’s 15 knots of safety margin to prevent post-takeoff over rotations and stalls. Essentially the vehicle is near best rate climb upon rotating. The disadvantage is a longer takeoff roll…designed for 1700’ over a 50’ obstacle. But I think that price is worth the simplicity and stall safety margin.
2. I had to smile at your observation about crosswind and weather cocking immediately upon liftoff. I can see how you would come to that conclusion. Here’s what really happened. My biggest artistic challenge in the demonstration was to get lateral spacing from the runway after takeoff so I could tear-drop to a low approach. That tear-drop turn started our pass #1 out of 4. On the first demo I was eager and checked right immediately after takeoff. Since I had plenty of airspeed margin (see #1), it is easy to do. But when I saw the video, I realized people aren’t used to seeing an airplane that is already at climb speed on rotation and would miss-interpret my maneuver as wind or gust response. If you watch the 2nd demonstration, I intentionally climbed to ~ 30 feet straight ahead and then did the check turn to the right. Just so people wouldn’t miss-interpret what was going on with the aircraft.
3.Your observation that the aircraft “was almost flown onto the runway” was also accurate. Remember from #1 above, we have 15 knots between stall speed and when I can put the aircraft on the ground. All you have to do is let the back wheels settle onto the runway at any speed below 60 knots and the vehicle mechanics bring the front wheels down positively. Think about the safety and ease of landing that brings—a general aviation aircraft that can be landed positively at any speed between stall and stall + 15. And once you are down, you are positively down—again, because of the wheel configuration. So you can do a stall landing with the front wheels in the air. Or you can fly it on to the ground—even with with power--at higher airspeeds. For the demo, I was more concerned with landing at the right spot with relationship to show-center. So all that I had to do was start the round-out, check the airspeed decreasing below 60 and fly it onto the runway at the right spot. So your observation was correct (“almost flown onto the runway”), but your implication (“airspeed…very narrow band”) is the opposite of the situation. By the way, stopping distance from 60 knots in a car with front and rear automotive disk brakes is no issue.
4. In your final thought about the residual airspeed on landing making it subject to PIO. We haven’t seen that. Perhaps the expectation of PIO comes from experience with conventional gear aircraft where the pilot has to “hold it off” in the flare to bleed off the residual airspeed. And if he has to avoid touching down too soon, he is subject to a PIO as he “feels” for the runway. That dynamic changes when you can simply fly the back wheels onto the runway over a wide range of airspeeds and the wheel configuration brings the vehicle down positively.
Keep up the sharp eye. But, there is a lot more to this car that flies than meets the eye!
My regards,
Phil Meteer
Philip C. Meteer, Colonel (Retired), USAFR
Chief Test Pilot
Terrafugia, Inc.
23 Rainin Road, Wobun MA 01801