aboutFalse Heavy. As far back as 1987 an
issue ofBalloon Life contained anarticle
titledFalse Drop (Hangar Flying),the
“FalseHeavy.”TheHangar Flying ar-
lowlevelwind shear thatsomehowseemed
What we are going to look at here are
situations thatcan cause aballoon to “drop”
caused by low level wind shears. It should
be notedthat these situations canhappen
hittingtheground, are most pronounced
near the surface.
are going to look at are; False Lift, dimin-
air out ofthe balloon, and air flowoverthe
lower portionof ballooncreatingdown-
First thing that we want to state is that
there is nothing false about lift. Lift is lift
differential between the air inside the bal-
loonandthe air outside or by the flow of
air over the topof the balloon.
In your training youwere told about
theeffectsof air flowing over the top of
theenvelope. While the balloonis static
theflow ofair tocompressoverthetop
creating a lowpressure area (seefigure 1).
same wayanairplane wing does.
As the balloon takes off and acceler-
ates to the speedof the air massthis flow
of air over the top diminishes. Thusany
lift createdby it is no longer available. If
and havenot changed the density ofthe air
you have lostpartof your lift.
Let’s take a look at why this happens.
While you are static onthegroundthere
are two lift forces at work. The first is the
heating of the air inside the envelope. The
second is the flow of air over the top. The
lift from each of these two elements com-
bines tocreatethelift necessarytobe at
are able torise.
What you have been taught is that the
air flow over the top is false lift because it
envelope. Thisis correcttoa point. The
lift is real and aslong asthe speedof the
ciently different the lift will continue to be
arises, it’s like going to a Chinese restau-
rantfor dinner, the foodisgreat andfills
again. The same thing happens here only
sooner. As you accelerate you lose the air
flow lift and must add more heat to main-
holdstrue at equilibrium or in a constant
about this lift, it is real, it just doesn’t stay
downward lift as well as take away the lift you
generate with heat.
Nowlet’s take alook at what happens
witha low level jet stream (see figure 2).
As you are flying along and the top of the
balloon is in a faster movinglayer of air.
You are at equilibrium withtwo compo-
nents of lift, heat and air flow. You would
liketolandsoyouallow the balloonto
cool or vent to begin a descent. As the top
components. This combined with the de-
scent. Youarenow movingmuchfaster
than planned.You apply heat but the close
doesn’t have to happen closeto theground,
itcan just as easilyhappen at 3,000 feet,
onlyyou recover before hitting the dirt.
shear can increase your rate of descent is
by diminishing the capacity of your enve-
lope. Our topic ofdiscussion here is about
gettingpulled down, but againthis situa-
tioncan happengoingup just as easily.
spot and begin to descend. Below is a low
surface movingmuchfasterthanthe air
mass you are in. As you enter the lower air
punch(figure 3). Itknocks inthe side of
theenvelope andpushingthe air out the
mouth. The bigger the differencebetween
the winds of the two airmasses the greater
Nowyou no longer havethe lift capa-
bility that you had a few seconds ago. You
cienttimebefore yousmackthe ground
and recoilback into the air, a–swing’n.
from a faster moving air mass to a slower
moving air. The effect is the same. Again
thiscanhappen at any altitude.
A 1991article,Landing Flight Path
Through Low Level Shears,byFrank
Hines,expanded on this topic.Hines com-
and heavily loadedballoons.
If a balloon descends abruptly from a
30 mphwind into a 15mphwind, it will
wind across its surface from no wind to a
15 mph wind.This will remove thebound-
cussion below), while causing distortion
inthe form of a “dish.” Thisconditionis
very dangerous to the low level flight of a
fullyloadedballoon. Itshouldbe noted
that as the envelope lowers into the slower
top of an envelope produces false lift and
there could be no worse time for this to be
flight pathof a lightlyloadedballoon as
thedistorted envelope. Heatlossisonly
by conduction and won’t be too large but
must be replaced quickly. Since a lightly
the envelope in a faster
moving layer of air adds a
second component of lift.
This is caused by the ven-
turi effect over the top of
loose and non-taught, momentary closing
of the throat happens easily.
To understandwhata “dish” can do
“heat line”fluctuates under different load-
ture, maximum altitude desired, and maxi-
mance curves and interpolate their maxi-
mum lift. They subtract the fueled system
gross weight. This is done to increase the
profit margin ofthe flight. This is legal but
not wise. Responsiveness has been turned
reaching its maximum sustained internal
temperature andneedingmostof its vol-
ume filledwith less dense hotair togen-
lighter-than-airballoon rises consequently
from heavy materials. The ship floats be-
the air because the hot air inside it weighs
less than the volume of air it displaces.
The bottom of the heated air is down close
to its mouth. We all experience this in
summer if we put two passengers in an
AX-7 and hit a shear. You can feel the
envelope “belch” warm air into your face
adds a small percentage of heat compared
sameburn in a lightly loaded balloon adds
a muchlarger percentageof liftingheat
comparedto itstotal needed hotair vol-
responsiveness. See figure 4.
If a heavily loadedenvelope experi-
heat can be squeezed out and heat lost by
heat dumping will be at the throat but also
could be at the cap seal on parachute tops.
My experience has been that the dumping
is quick and momentary.” This condition
isextremely serious if youare on a final
approach to landing because you will not
have enough altitude to add enoughheat.
loss be replaced to make the balloon neu-
trally buoyant, but more must be added to
stop any downward momentum. As stated
figure 5, but will still lose heat by conduc-
reasonable amount of heat will need to be
added. When you feel agood shearin your
face, always check the throat opening and
add some heat immediately. (Hines found
firmed by a balloon with a scoop tethered
insome wind. The scoop pressurizes the
internalvolume slightlybut the burn ca-
dence increases greatly compared to free
flight. This is to replace heat lost onlyby
one burn is a smaller
volume of heat.
Therefore balloon is
one burn is a larger
per centage of total
Therefore balloon is
fully loaded balloon
in a lightly loaded
your approachandunknowinglymake it
Knowledge of this andof the importance
cessivelyhard landingor an accident.
Some signs of shears to watch for are
lines,throatropes, or skirt; windin your
face;or evenbasket movement.It isim-
portant to realize that as the balloon low-
and starts slowing, the effect of heat loss
canbe maskedbyfalselift.Evenif the
shear is a mild one, false lift will momen-
enough and gets out of the faster moving
air, the hidden false lift and dishing disap-
pear and downyou golackingheat.
To understand what is or what could
happen to the envelope, we need to look at
what the envelope experiences in terms of
“effective wind” over its surface that re-
understandwhat a “dish” in the envelope
could doto its lift, discussedabove. The
above two effects of descending through
ashearcould happen together, in theworst
situation, or oneof them alone. Severity
porosity, speed of descent, and last but not
the mechanisms of heat loss are called
heat loss by conduction and heat loss by
volume dumping, respectfully. Heat loss
by conduction is actual h eat passing
through a media that in our case is the thin
envelope fabric and the fabric coating.
Due to the complexities of heat loss in a
porous envelope, our discussion will be
limited to relatively new envelopes with
negligible porosity. The amount of heat
loss by conduction, therefore, is largely
dependent on envelope surface area, the
difference of inside temperature and am-
bient temperature, and the speed of the
wind blowing across the envelope’s sur-
face. Since we are looking at wind shear
effects to a landing balloon, then wind
Tostart, we needtolookatwhatis
happening to the heat inside the envelope
during normal level flight. A balloon fly-
flowacross its surfaceand thereforeexpe-
The envelope has a thin boundary layer of
that actsas a blanket and helps keep heat
physics. Human skin alsohas a warm air
boundary layer on it when it is in a colder
environment. In both cases, the layer can
temporari ly masked by
speedof the fluid increases. Known
as Bernoulli’s Principle, discovered
more than200 yearsagoby the sci-
entistBernoulli, this law ofphysics
createdas air flows over and around
WhatBernoulli discovered was that
within the same fluid, in this case air,
changes in the pressure of fluid flow-
ingwithinapipe whose cross-sec-
tional area varied (venturi tube). The
wide sectionofthe pipe,butasthe
pipe narrows it must contain thesame
amount of fluid. In this narrow sec-
tion,thefluid moves at highspeed,
producinglow pressure (the venturi
The airfoil ofa wingisdesignedto
decreasingpressure. The same phe-
nomenon takes placewith the curved
surface ofthe balloon. Asthe air is
compressed to go around the surface
it speeds up and pressure is decreased.
the direction of the low pressure.
feelcolder. Thisis whatthe term “wind
chill factor” means that the weatherman is
alwaystalkingabout. Wealso cover our
heated fuel tanks to add insulation to their
boundary layer. This is to prevent the heat
we addedfrom being lost byconduction.
layersonthe inside panelstomaximize
theirinsulation efficiency to keep thecold
outside andthe warmthinside.
Changingair massescreatesa rela-
tive wind over the surface of the balloon.
Thatwindremov esthe“insu lati ng”
The next element that we will take a
look at is fast moving air across the mouth
of the balloon(figure 8).
If we were to take a balloon and place
itin a windtunnel and blow smoke byit
we would notice that the airis compressed
occurs at the top of theballoon, lift with an
are taking place over the entire surface of
the balloon. What happensif this wind is
onlyover the bottomportionof the bal-
loon, below the equator (figure 9)? Lift is
downward component to the lift.
The lower half of the balloonenters
the faster moving airmass and the surface
of the balloon causesthe air flow to gen-
erate lift. This lift is tangent to the surface
of the balloon and because it is below the
equator, where the tangent line points in a
downward direction, the lifthas a down-
ponent of lift pulls the balloondown.
Again, the effect is going tobe more
tension. Alightly loaded balloon will have
portion oftheballoon. On a heavily loaded
balloon the fabric below the equator will
have greater tensionproviding asurface
where a low pressure can develop.
These elements can allcontribute to
the balloonaccelerating downward from
an equilibrium state. The first, false lift, is
a lossof anupwardlift component. The
othersare basicallythe oppositeof false
liftandmaybeforlackof abetter term
have been described as false heavy.
In reality there is nothing false about
any of these situations. They are real and
create real flightdynamics. Whatisim-
fects,andconsider what actionsare nec-
essary when you encounter each. In many
Be aware of the elements around you
and how they can affect the performance
of your balloon.
Whathappens if youare caught in a
low level jet? Keep calm. Waiting until a
low level jet raises or taking your time and
using a very gentle slope through a shear
to get below it before landing appear to be
safe considerations.Lookfor abigfield
andexpect ahighwindlanding. Staying
on the ground initially should be your first
and best consideration.
which can cause the air to be sucked out of
capacity that was discussed above. As the
air moves over the mouth of the balloon it
createsthe dynamiclow pressure which
pulls the static air inside the envelope out.
Againwith diminishedcapacitythe bal-
loonwill accelerate down.
Ofall the possibilities discussed here,
this point will have the least impact on the
liftingcapability of the balloon.
Similar to false lift discussed earlier,
only now it is happening at another part of
lower portionof the enve-
lopeli ftvector sar e
gfenerated tangent to the
way that thye are gener -