As part of the Grassroots Mapping Curriculum series.
United States. Size: Unregulated Balloons
We try to design our equipment to be non-hazardous, but also unregulated. It is important for everyone doing these activities in the U.S. for safety reasons as well as the information about regulations and stipulations on size and materials. “Section 101.1 Applicability” of the regulations outlines the requirements for exemption.
FAA guidelines Federal Aviation Regulation 101(FAR101) provide exemptions for the type of small balloons used by the grassroots mapping community:
"101.1a(1)Except as provided for in §101.7, any balloon that is moored to the surface of the earth or an object thereon and that has a diameter of more than 6 feet or a gas capacity of more than 115 cubic feet. (2) Except as provided for in §101.7, any kite that weighs more than 5 pounds and is intended to be flown at the end of a rope or cable."
Our size limit is therefore 6ft or 115 cubic feet of gas. At sea level, helium provides 7.5lbs of lift for 115cu ft (based on 65.5/1000 cu ft, from pg 68, “A History of Flying” C.H. Gibbs-Smith), 5lbs is therefore a realistic payload limit for a moored balloon as well. Currently, the point and shoot camera with gps grassroots mapping payloads are at around 1 pound. Expansion is possible towards additional sensors, stereo pair data collection, larger consumer SLR cameras, heavier duty line, etc.
In separating safety from U.S. law, the following represents responsible use of unregulated balloons and kites.
When you fly your balloon, check for any local regulations such as restricted airspace. Washington DC is restricted airspace. Purchase a sectional chart from the nearest general aviation airport to locate restricted air spaces. If the flight area is withing 5 miles of any airport and above altitudes of several hundred feet, contact the local airport or FAA Flight Service Station(FSS) in order to report a Notice To Airmen (NOTAM).
FSS contact and hotline (pdf)
Part of the preflight mission planning will include surveying the flight area for hazards. During the flight tall buildings and trees are also avoided as a precaution to wind currents and turbulence on the imaging platform.
Another interpretation of FAR 101 from a high altitude untethered balloon project.