Saturday, October 27, 2018

Autogyro as flying car -- part V

Let me sum up the argument and add a few observations.

In Part I we introduced the gyro and related its history and why it was seen as the flying car of the future in the 30s.

In Part II we contrasted the gyro with the helicopter and showed why it could be substantially less expensive.

In Part III we looked at what would be needed to make a gyro easy enough to fly as a car used by a substantial number of people, and the technological innovations since the 30s that might make that possible.

In Part IV we looked at the economics again, this time from the demand side, and what a widely used airspace traffic system might look like.

In Travel Theory we went over the economics of Part IV again in great detail. By far the biggest flaw in most of the flying car proposals or prognostications we have seen over the years has been the lack of a serious cost-benefit study. Quite frankly, there has always been a gap between the value of a flying car and its cost. But now that we have some numbers, we can see that it might just be possible that it could close in the foreseeable future.

Going back over the series, I see that I have left out one of the more important issues in the argument for the gyro as flying car -- the weather. Weather is the major limiting factor for flying light aircraft.

Unless you are Home on the Range, where the skies are not cloudy all day, the most common problem is clouds. Under visual flight rules, which is what most of us think of when we imagine being in a flying car, they often form a ceiling that limits your altitude. Even if you are flying on instruments, you have to be able to pop out into clear air at least 500 feet over the airport and find the runway, which is a fairly nerve-wracking (e.g. dangerous) experience.

The rotorcraft really shines here compared to a fixed-wing aircraft. Not only can you come out going much slower, but you are enormously more maneuverable, safely, near the ground.  Add that to a high-precision GPS and peer-to-peer navigation system as in Part IV, and the cloud problem begins to clear up quite a bit. In fact, with a few more sensors and transponders between the vehicle and a well-equipped landing pad, completely automatic landings would be fairly straightforward in a heavy fog.

The number 2 weather problem is wind. There are two aspects to this: first is the added difficulty of takeoff and landing, and the second is the fact that turbulence gives you a queasy and uncomfortable flight. This turns out to be another area in which the gyro (or helicopter) shines.

The aerodynamic reason is wing loading. If you have a small wing going fast, it is less perturbed by any given wind because the wind is a smaller percentage of the airspeed it sees. This is why big airliners (wing loading 150 pounds/square foot) are much steadier than light small planes (15) in gusty winds. A Piper Cub hit by a 25-knot gust can see its lift double or nearly disappear; an airliner just gets a small bump.

The rotor on a gyro (or heli) is moving at airliner speeds and has a loading (e.g. 75) that is a lot more like the jet. This means that not only is the gyro a more comfortable ride in gusty winds, but it's a lot more controllable in crosswinds for takeoff and landing.

There are two flight schools at Bay Bridge Airport, just across the Chesapeake from Annapolis. One teaches gyros and the other fixed-wing. Usually it's very busy there, with several planes going around the pattern practicing takeoffs and landings as well as transient traffic.

One day last week, we had a blustery day of 15 gusting to 20 knot quartering crosswinds. This is not at all unusual; as I write from a different place in the Bay, the winds here now are 15 gusting to 25. Anyway, that day at Bay Bridge the gyros (and a couple of transient helicopters) had the place completely to themselves.

The implications for flying cars are left to the student as an exercise.

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