Balloon Life,May 2000

16

With the first successfulcrossingof the
Atlantic by balloon of the Double Eagle II
in1978, anentirelynew era of longdis-
tance balloonflightbegan. Soon the Pa-
cific had beencrossed, thenboth oceans
were crossed by hot air balloons. Roziere’s
entered the scene with anAtlantic cross-
ingby the first Europeanteamfrom Bel-
giumin1986andthefamousChrysler
ChallengeRaceAcross the Atlanticin 1991.
These flights in many ways served as
test flightsfor the final challenge, a bal-
loonflight aroundthe world. As withall
test flights, theyalso servedas platforms
forrapid advancements in ballooning tech-
nology. One of the advancements born of
this era could be described as ballooning’s
blackbox—the Comstock Autopilot.
Unlike the much heralded black boxes
of commercial aviation, those flight data
recordersthatoftenrevealwhyaplane
hascrashed, ballooning’sblack boxwas
designed to keep the aircraft flying and to
do soreliably. After 20 years of develop-
ment the Comstock Autopilot has proven
itcan dojustthat.
“Itreallybeganasapurelyrecre-
ational project,” says engineer. designer,
inventorand pilot, BruceComstock. “Back
inthe late 1970’s someone else was pro-
ducing what they called a balloon autopi-
lotthatwasreallynothingmorethana
thermostatdevice thatdidn’tworkvery
well. That got me thinking about building
a realautopilotandI spentquite a lot of
timeworkingonitanda balloonflight
simulator.OfcourseIneverfeltthere
wouldbemuchmarketforanautopilot
becauseI knew thatpeopleboughtbal-
loonsforthefunof flyingthem,so they
weren’t likely to spenda lot of money on
somethingdesignedtodotheflyingfor
them.”
Afterdesigninghisfirstunit,Com-
stock did his own test flights, flying with
the autopilot “until my friends got tired of
it. We’d go out and fly with this thing and
justsitthere in the basketwithour arms

crossed and go for a ride.” But his friends
wantedthe visceral experience offlying
the balloon, not just riding in it, so the unit
wasplaced onthe shelf.
His first so-calledproductionmodel
wastheninstalledon thehot airballoon
that Don Cameron and Jim Howard hoped
to cross the Atlantic in. Unfortunately that
unitnever flew as Cameron and Howard
spent a summer in Newfoundland waiting
for a weather window that never arrived.
Enter acharacter namedSteve Fos-
sett.“Stevefirstcalledmewhenhe and
TimColewereplanningtheirAtlantic
flight,” says Comstock. His first reaction
tothiscallisnow ballooninghistory.“I
didn’t know who this guy was and here he
saysheplanstocrosstheAtlanticina
balloon, butnoone’sever heardof him
andIsurelywould have heardof him or
anyone else anywhere close to having the
experience to cross the Atlantic I thought,
soI politelyput him off.”
Ti mCo lewou ldi nt erv eneon
Fossett’s behalf and a Comstock Autopi-
lotModel1wasinstalledintheirR-77
balloon. InAugust of 1994the Model 1,
Fossett and Cole made their first success-
ful ocean crossing. (This wasthe first of
severalComstockAutopilotsusedby
Fossett.)
NextcameFossett’scalltosayhe
intended to fly the Pacificsolo and planned
tousethesameautopilot.“I foundthis
news very distressing,” recalls Comstock,
“because all of these units I had built up to
thenI consideredtobe toys.Theywere
analog devices in which all of the values,
likeratesofclimb,altitude,etc.were
determined by voltages. This proved to be
a verycumbersome waytobuildthings
and the unit was not terribly reliable. The
Model I could sometimes drift as much as
600feetupordownfromitsassigned
altitude.
Inlongdistanceballoonflyingthe
firstpurpose of anautopilotistoflythe
balloon level—very level. If you’re mak-

inga long distance balloonflight what’s
really important is flying level, for a long,
longtime.Theratiooflevelflightto
ascending and descending is very great on
flights that last several days or weeks. The
autopilothastodothisandmustdoit
reliably,especiallyonasoloflightbe-
cause this provides the pilot his only op-
portunityfor sleep.If theautopilot fails
yourflight is probably going to end within
hours because you losetheability to sleep.”
Thisfactwasdemonstratedindra-
maticfashiononKevinUliassi’smost
recentround-the-worldattemptwhena
capsule electrical system failure disabled
hisautopilotwhileat29,000feetover
India.“Itwasanabsolutepanic,”says
Comstock, “because Kevin had to imme-
diately start flyingthe balloon while also
trying to poke around with an ohms meter
to locate and correct the electrical failure.
Itbroughthometobothof usthatif an
autopilotwere to fail a solo flightwould
definitelyend withina matter of hours.”
Ifmaintaininglevelflightandpro-
viding sleep periods are the primary func-
tions of an autopilot, they are not its only
purposes.“There’snotalotofthrill,I
think,” says Comstock, “inflying one of
theseround-the-worldballoonswhen
you’re awake becauseyou’re sittingin a
closet.Youbasicallywanttobeflying
levelbut youdon’twantto be a slave to
flying the balloon all those hours.” So the
autopilotservestoprovidefree time for
even the awake and alert pilot—time that
can be used for any number of other tasks
besidesconstantlyactuatingtheburners
on and off.
Fossett went on to fly the Pacific with
the Model I, or “Vegematic” as Tim Cole
had dubbed it because it was packaged in
a Tupperware® vegetable crisper. How-
ever, when Fossett then announcedplans
toflyaroundtheworld,Comstocklaid
downthe law.He mustnotflywiththe
Model I, it simply was not reliable enough.
InfactComstocktoldFossetthe needed

Ballooning’s Black Box

by Glen Moyer

An essential tool for long distance solo balloon flight.

17

Balloon Life,May 2000

notone, buttwo good, reliable autopilots.
“The reason for two was again reli-
ability,” Comstockexplains.“Roughly
speaking if you have a unit that has a one
in one hundred chance of failing, if you
have two then the chances of both failing
is about one in ten thousand.”
What resulted was the development
andtesting ofthefirstversion ofthe
Model II, an autopilot based on a digital
computer that can fly virtually any bal-
loon that operates on a “on-off” cycle.
(There have since been seven major re-
finements to the Model II computer pro-
gram.) Its actions arebased purely on
sensing atmospheric pressure, yet it can
fly a balloon level at 10,000 feet with an
accuracy of plus/minus 10 feet! “It uses
pressure altitudebecause flying at a con-
stantpressureismore likelytokeepyou in
the samewind pattern than flying at a
constant geometric altitude,” saysCom-
stock.TheModelIIisbuilt arounda
single board,industrial control,digital
computer with an operating speed of less
than10 megahertz,chosennotforits
speed but for its own reliability.
“Atthe time I selected that computer
there were 20,000 of them that had been
used in harshindustrialenvironments for
years,” says Comstock, “and all the bugs
are out of that computer.” While itsoper-
ating speed has been questioned by some
Comstockremindsthem thatnothinghap-
pensthatfastina balloon,itsimplydoesn’t
need the speed of today’s blindingly fast
500, 600 or 750 megahertz processors.
Theprogramthat runsthe autopilot is
writteninLanguage C. The algorithm that
makes the decisionto heat and how much
is only onelineofan8 page,single-
spaced,program.Therearoftheunit
incudes five connections. Two for the 12
volt DC power supply, another for a 1/4-
inch tube thatcan be plumbed toanexter-
nal port in the event the unit is within a
pressurizedcapsule,and twoelectrical
switch contacts that can be used to turn
somethingonand off, typicallya solenoid
valve to fire the balloon’s burners. It’s all
housed in a unit that measures 4 x 12 x 8
inches and costs?? “Around $10,000” is
as specific as Comstock will say.
Each unit is also equipped with an
ear-shattering90decibel altitudealarm. It
serves asawatchdog,checking about
once per secondonthe performance ofthe
autopilotand ready to sound off if neces-

sary.The current Model II alarms at a
variance of 500 feet of altitude, above or
below the set altitude, or if the ascent/
descent rate is morethan 300 feet per
minute. Why the need for an alarm? “Re-
member these units were designed to be
used by a sleeping solo pilot that could
end up deadif they fail towake up to deal
with aproblem,” says Comstock.The
most likely cause of an alarm is running
out of fuel in the tank connected to the
burner.
The unique design of the Model II
program allows the autopilotto adapt on
the fly; since most long distance Roziere
balloons are flown only once, on the real
flight,notatestflight,this wasvery
important. The unit has to reliably adapt
toany balloon withoutthe benefitof a test
flight during which various parameters
could be preset. Most of his testing was
done in lightly loaded hot air balloons
because of their greater degree of diffi-
culty to control.
“IhavearoutineI taketheunitthrough
now,” says Comstock,“including shut-
tingoff the fuelsupplyuntilthe balloonis
ina steep descent, thenturning onthe fuel
and watching as the autopilot stops the
descent, roundsoutthe balloonandfliesit
back to the desired, presetaltitude. Foran
experienced balloon pilot thisis a simple
task, but to teach a black box to do this
reliably is another matter.”
Seven Model II autopilotshave been
built;twothatflew withSteve Fossettare

now at the bottom of the Coral Sea, and
twomorewerebuilt asreplacements.
Kevin Uliassi has two and a spare had
been on the shelf until it recently went to
ateamstaging foran upcominglong-
distance flight to the North Pole.
There isalso a ModelIII on the shelf.
That unitwas tofeature a numeric keypad
for easyinputof altitudes,rate of climbor
descent and variousother control factors.
However, when balancing the extremely
limited market for such a device against
the years of development and testing re-
quired to create a reliable design, Com-
stock says the Model III will stay right
there, on the shelf.
Currently he is at work on a Model
IV.It’s primaryadvantagewill be the
addition ofan altitude shift device. By
dialing in apreferred rate ofclimb or
descent the autopilot will be capable of
morethanjustlevelflight.Thiswillfacili-
tatealtitudechangesfrom one cruiselevel
to another.
Fornow,withthe successofBreitling
Orbiter III, the potential market for even
the Model IVcan bemeasured by less
thanthefingers ofonehand.Infact,
Comstock sayshe hasnoactive interestin
another unit. Still he takes great pride in
the fact that the Model I and II combined
have flown morethan 57,000 air miles
and achieved threeabsolute world dis-
tance records for balloons. Quite an ac-
complishment for a little black box!

Comstock Autopilot