History:
The design of a roadable aircraft presents many design challenges.
1. The craft must be small enough in its retracted or folded position to fit within (standard) garages, drive up facilities and parking facilities which limits the principle dimensions to a volume of 20 feet by 7 feet by 7 feet
2. In order to fit within the current transportation system to avoid heavy glass and all wheels breaking the craft must be below 1500-pound empty weight (curb weight) and licensed as a 3 wheeled motorcycle.
3. The folding and storing of the wings presents particular difficulty. If the wings are folded aft the aircraft may fall on its tail, if the wings are folded forward to a preferred cg location then the wing may block the visibility of the operator. If the wing is stored on top of the vehicle then gust from passing trucks may blow the vehicle over on the ground. Re-attaching the wings in less than perfect weather conditions provides difficulty even for trained personnel. Some prior roadable aircraft towed the wing and tail along in trailer fashion with its related problems. Damage to the control surfaces on the ground must be minimized so the wing needs to be where it is protected. Complex folding mechanisms are prone to failure, require maintenance and are heavy. Wings and flying surfaces dangling off the aircraft provide poor aesthetics for the vehicle.
4. In order to move the aircraft on the ground several schemes have been employed. A common method is to provide a clutch to the main engine and power is sent through a transmission that is heavy. Some designs use hydraulic motors in the main gear driven by a hydraulic pump off the main engine. Others use a totally separate engine for that purpose.
5. There are many ways others have dealt with the problem of operational controls of roadable aircraft and (flying cars). The principle problem is that there is a mix between the roll and yaw axis in the separate vehicles. One designer placed the flight controls in the left side of the cockpit and the ground controls on the right. One designer placed the controls up under the panel where the operator pulls them out when usage is desired. One designer has the control wheel designed such that the wheel is in half and then it is rotated upward to form a complete circle for road use. Another designer suggests using a steering wheel oriented such that it resembles ones used in buses to overcome this obstacle. Other have the controls located outside or mixed between existing controls. Causing possible confusion in emergency situations. Each of these has their advantages and disadvantages.
A simple lightweight solution is needed to meet each of these needs.
PAV Design philosophy
In order to break through barriers of prior designs and increases utility to the modern aircraft here is a short list of things that must be meet.
- Push button operation
- Safety:
- Propeller to remain clear of ground, people and personnel
- Cg to move forward during ground operations:
- Weight below 1500 pounds.
- Security
Push button operation for changing from road to flight mode:
It is important for the wing to be of push button operation in order to receive wide acceptance among the general population. As a designer / builder/ mechanic it is easy to imagine my self placing the wings in place and flying off. But those same tasks performed by wife or teenage daughter seem unlikely, maybe even unsafe. Additionally the ability to change the mode of operation during rain or other inclement weather reduces the desire of the operator to get outside of the vehicle and move panels around in less than desirable weather conditions. With that in mind it is also important for the system of change to be as simple as possible and still accomplish the task while having safety features that prevent flight with the wing partially engaged.
Visibility is an important consideration in any aircraft configuration. The PAV should be the same visibility on the ground and in the air.
The purpose of the control system is control the aircraft in the air and the car/motorcycle on the ground. The desire is for the controls to be most like the controls of and aircraft in the air and most like that of an automobile on the ground. This conversion should be lightweight and simple in operation. Further the operation of the pedals and controls should be such that it is not likely the feet or hands be caught in the controls during transition. The transformation should be sufficient that the operator reacts to the correct set of controls in the event of an emergency. The transformation should be such that it is not necessary to exit the vehicle during conversion in possible inclement weather.
The one barrier that is not a technical barrier but a legal barrier is that of operating an aircraft on the current road system. Current laws require heavy equipment, such as safety glass and all wheel brakes, which make the possibility of vehicles greater than 1500 pounds unfeasible. Making it necessary to license the vehicle as a 3-wheeled motorcycle.
Takeoff from roads is to be avoided and flight must be operate with in current FAA system.
Precision Design feels strongly about this. It’s current designs includes multiple safety devises to prevent extension of the wings while moving forward. This is to prevent any one from taking off on highways. Further purchasers will be bound contractually from doing so.