The simulation of an aircraft flying through a downdraft or microburst is presented. The simulation was performed under the conditions of constant takeoff thrust. The resulting wind shear conditions were filmed and examined for possible pilot corrective action in the future

Frost, W.

English

NASA Technical Reports Server

speed/groundspeed system gives him a tool with 
quantitative information from which real answers 
are available. Judgment can be developed which 
is impossible otherwise. Actual training is then 
possible with skills develop 
a power reduction is required for stabilized speed. 
This is done, quantitatively, by using two mini- 
mum speeds. The airspeed is not allowed below 
normal, and groundspeed is never below the value 
expected over the threshold. Either speed can 
be normal or above, but neither below. The pi- 
lot then has full quantitative knowledge of what 
to expect ahead at all times, and he c m  expect 
both speeds to be normal at the threshold. If they 
are not, (groundspeed excessive) he can go-around 
“LABORATORY MODEL OF FLIGHT THROUGH WIND SHEAR” 
Walter Frost 
This address deals with the simulation of an air- 
plane flying through a downdraft, or microburst. 
This project came to pass about this time last 
year, at the time when the Pan Am accident had 
just occurred. The television company, Alan Lands- 
burg Productions, which produces the television 
show, “That’s Incredible,’ decided they would like 
to do a series on wind shear. They talked to John 
McCarthy, Bill Melvin, and a few others. Finally, 
Norm Crabill at NASA Langley Research Center 
directed them to FWG Associates, Inc. One of 
the things they were insistent upon was an actual 
model study of an airplane flying through a mi- 
croburst, and they would not be satisfied with a 
computer graphic simulation. 
We had, roughly, two weeks to design, construct, 
and carry out the simulation. We decided to use 
a large building next door to FWG Associates, 
Inc., the small research and development company 
located in the UTSI Research Park. This build- 
ing is approximately 50 feet wide, and we had to 
do some quick scaling laws to determine the best 
method of handling the project. We decided to 
show the takeoff because it is the easiest to do. 
We needed to simulate a constant take-off thrust; 
subsequently, we used, roughly, 100 feet of surgical 
tubing stretched through the door of the labora- 
tory. This gave us an essentially constant thrust of 
about 2-1/2 pounds, which is what we calculated 
as being needed for the size of aircraft being mod- 
eled. We hung a large fan in the ceiling which had 
about 16,000 cubic feet, and scaled the velocity 
coming out of that fan relative to the velocity of 
the aircraft as it passed through the microburst. 
Our tail was on the line because we had an agree- 
ment with Landsburg that if it indeed worked, 
they would pay us a relatively adequate sum of 
money. However, if it did not work, we were go- 
ing to eat it! So, we were trying very hard and 
getting very anxious near the end. Nevertheless, 
it did work very well. We actually put a control 
into one of the aircraft models and learned a lit- 
tle about the dynamics of the aircraft. We found 
that if you pitched up, as Bill Melvin and others at 
that time were saying, when you passed through 
the wind shear, often times the model would come 
out of the wind shear and not crash. However, if 
you tried to put the nose down and pick up speed 
at all, which was the other option, the aircraft in- 
variably crashed. 
A lot of people have asked whatever became of the 
results. It was supposed to go on national 
television; but it didn’t sell, because it was com- 
peting against 60 Minutes, and the second sequel 
of the series which we were supposed to be in was 
never released. I have, however, brought a short 
clip that I have put together on my l/%-inch video 
tape and I would like to show it to you. Inciden- 
tally, one of the airplanes which had a controlled 
system in it flew right into a television camera. 
Another of the models was glued back together so 
65 
https://ntrs.nasa.gov/search.jsp?R=19860002280 2020-03-23T06:34:23+00:00Z
many times it was amazing that it still flew. 
first part of the video was transcribed from high- 
speed film onto television tape, and it shows the 
aircraft coming out of the microburst, made vis- 
ible by COa fog. A series of pictures, Figure 1, 
show the aircraft as it flies into the wind shear, 
lifts, loses lift, pitches up, and hits the ground. 
Figure 1. Sequence of a i r c r a f t  t ra jectory 
through simulated microburst 
hen you study the downdraft phenomena, Fig- 
ure 2, which has been illustrated, it shows a simi- 
larity to things we have measured with radar, sug- 
gesting that a microburst is a cold outflow moving 
down towards the ground and spreading out in all 
directions. The markers on the wall indicate a 
scaling of about 100 to 200 feet, respectively. If 
you will notice, the air jet comes out and spreads 
out all over the ground. It is not, however, per- 
fectly symmetric; because we have discovered that 
microbursts are not perfectly symmetric. 
You can see from Figure 2 how relatively shallow 
the outflow is once you get out of the downdraft. 
66 
It took only about two seconds for the model to fly 
the entire length of the building, so to control it we 
had to be quick. However, interestingly enough, 
you could control it if you were on your toes. We 
simply had an elevator to give us pitch control. 
If you are interested, there was article written about 
the simulation in Aviation Week and Space Tech- 
nolo=. We have a few of the reprints of that ar- 
ticle here if you would like to have one. 
“AVIATION WEATHER OF THE 1980’S” 
Sepp Froeschl 
I would like to  thank Walt and Dennis for giving 
me the opportunity to talk to you for a few min- 
utes, because I think it is a rare, if not unique, 
occasion to have such a wide range of expertise 
to talk to. To give you a few ideas of my back- 
ground which may be the reason for some rather 
controversial things I will say later, I am a meteo- 
rologist, and I work for the Canadian Government. 
I am caIled a Chief Analyst and Prognostician of 
the Quebec Weather Center. I have been a pilot 
for over 40 years, with a wide range of experience 
from military to airline flying. Over and above 
this, I am an enthusiast in meteorology and, par- 
ticularly, aviation meteorology. As the title of my 
impromptu speech indicates, we are in a transition 
period. Our problem is that there is still a wide 
credibility gap between the user and the provider 
which is what I call the weather services. As for 
users, I am referring to the various components of 
the aviation community. 
I think we have tried for too long to do every- 
thing for everybody, and I am afraid that if we 
carry on this trend, we might end up doing noth- 
ing for anybody. We are, due to budgetary con- 
straints, having to cut down on personnel, and 
having to use more and more automation. Please 
do not get me wrong; I am not anti-modelling or 
non-automation, because my initial ideas and ed- 
ucation are in mathematics. However, I am a re- 
alist. Since I am a user as well as a producer, 
I think we need a different approach. This is, I 
think, the weather services. They should get into 
measurable, quantitative configuration and move 
away from qualitative information. In my opin- 
ion, this is our biggest handicap. Originally, when 
we moved into qualitative terminology, it was a 
way out of the situation; but, in the last 30 years, 
we have not moved too far ahead. I once wrote 
a thesis on aircraft icing; and after hearing at the 
last six workshops how much is going on in icing, 
I went back and read the thesis. I thought to my- 
self how new it all sounds to me; but remembered 
that thesis was 30 years old. In other words, we 
have not made good use of the new technology 
because it is primarily an advance in technology, 
not so much in real science. We should, however, 
make better use of this technology, especially in 
aviation meteorology. With the new high-speed 
computers we should make use of them instead of 
being used by them. If we make full use of them, 
we can really go into a quantitative description 
of the atmospheric conditions. By doing that, we 
are avoiding controversy and ambiguity. For ex- 
ample, I hate the term “VFR conditions”, because 
VFR includes many things besides meteorological 
parameters. Over and above that, we cannot mea- 
sure VFR. We can define it as something, but it 
cannot really be defmed in quantitative param- 
eters. We might say three miles, 1,000 feet, or 
whatever; but it doesn’t mean anything because 
you can’t measure or forecast that in terms of at- 
mospheric conditions. What we should do, by go- 
ing to quantitative expressions or terminology, is 
forecast a ceiling of 500 feet and a visibility of one- 
half mile and then the user can call it, or do with 
it, whatever he wants. 
One of my theoretical specialities was icing, as I 
mentioned before. If we continue to talk about 
light to moderate rime icing in clouds with a risk of 
heavy mixed conditions in build-ups, we are wast- 
ing time. Every pilot knows that if he is in build- 
ups, convective clouds, etc., there is a danger of 
icing existing there. What is light to moderate? 
We have from a Cessna 150 up to the Space Shut- 
tle. In the old days, there was about 150 kts speed 
f 30 %, and that was everything we had. So, we 
could be rather generous in using those terms for 
everybody; but now it is completely out of range. 
What I would like to say, and what I would like to 
implant into you, is the idea that we should: 
a) Aim for quantitative information; i.e., fore- 
casts, observations, etc., and move away from qual- 
itative. 
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Laboratory model of flight through wind shear

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