and Gauges
not cause any problems. This article explains what you can and
cannotdo in case one of them fails, and some steps to prevent such
failures.
A balloonis a simple aircraft, having noelectrical system or
propulsion system. As a result of its simplicity, a balloon pilot
needs only a limited set of measurement devices. The measure-
ment devices can be grouped into two categories—gauges and
instruments. Gauges measure fuel quantity, fuel pressure, and
envelope temperature. Instruments measure the results of flight
operations, such as altitude and rate of ascent or descent. The
earlyinstruments andgaugesweresimpleand requiredno
batteries.
If you fly a balloon system that was manufactured under a
type certificate, the FAA issued the type certificate under FAR
Part 31—Airworthiness Standards: Manned Free Balloons. A
hotair balloonis required tohave the following four instruments
and gauges: an altimeter, a rateof climb indicator, a fuel quantity
gauge, and an envelope temperature indicator.
Amechanical altimeter isa barometer witha dial face that is
calibratedinaltitudeinsteadof barometricpressure.Whenitgoes
higher, the barometric pressure drops, and the sealed bellows
insidetheinstrumentcase willexpand. The expansiondrivesaset
of gearstocause the indicator needle toindicate a higher altitude.
As it descends, the barometric pressure increases, compressing
the bellows and causing the needle to indicate a lower altitude.
Amechanicalrateofclimb indicatororverticalspeed
indicator is a barometer whose bellows have a tiny hole. When
theinstrument stays atthe same elevation,no air leaksinto or out
of thebellows, sothe indicator needle showsa 0 rate of climb. As
the instrument is taken higher or lower, the bellows expand or
contractwhile theairleaksintoor outof the bellows. The bellows
drive an indicator needle showing the rate of climb or descent.
The mechanical altimeter andverticalspeed indicator were both
designed foruse in airplanes where vibration is common. A
balloon has no vibration, so the needles may stick, causing an
erroneous reading. Tap the instrument’sface witha finger tofree
Another rate of climb indicator is a variometer, a sensitive
electronic instrument that measures the volume of air flowing
intoor outof a thermosbottle to determine the descent or ascent
rate. (Requires batteries).
Many balloons were equipped witha mechanical thermom-
eter to measure the envelope’s air temperature. It is commonly
called a “hanging meat thermometer” as it looks like a meat
thermometer with a large dial face. It is installed near the top of
the envelope during inflation, and removed during deflation.
The firstremoteelectrical temperature gauge used a thermo-
couple and a current meter (galvanometer). A thermocouple is a
junctionof two dissimilar metalsthat generate electrical current
when heated. The meter needle indicates the temperature of the
thermocouple junction inside the envelope.
Fuelpressure gauges use a curved metaltube to move a dial
indicator aspressure increases. Variousmanufacturersplace the
gauge on the fuel cylinders, inthe fuelmanifold, or inthe burner,
either before or after the blast valve. If the gauge isconnected to
the manifold or between the manifold and the blast valve in the
burner, itcan be damagedif fuel isleftin themanifoldafter flight.
Heat will cause the liquid propane to expand and destroy either
the gauge or a fuel line.
Fuellevelgauges use a float thatturnsa magnetatthe end of
a shaft as the fuellevelchanges. The magnetmovesthe indicator
needle. If the fuel level gauge stops working, a repair station or
propane dealer candrain the fuelandrepair or replace the gauge.
Newer balloons may have an electronic instrument pack,
combining analtimeter,variometer,temperaturegauge,and
possibly otheritemssuchas adatarecorderandaGlobal
PositioningSatellite (GPS) receiver. Such an instrument pack
may connect to an envelope temperature sensor using a wire, or
awirelessinfrared orradiotransmitter packinthe envelope. Such
apack providesa convenientdisplay of muchusefulinformation.
Unlike the mechanical instruments, it requires fresh batteries to
operate properly. The remote infrared or radio transmitter also
requires fresh batteries. If the batteries are allowed to run down,
your expensive instrument pack may fail to operate.
