It is quite important that the airplane performance during a continuing headwind loss be understood. Lack of consideration of this characteristic can result in assuming almost twice the performance than that which the airplane actually has during severe wind shear at high descent rates. The example data relates to the Boeing 727-200, but the characteristics are applicable to any airplane

Bliss, J. H.

English

NASA Technical Reports Server

In holography, one is able to get shape information 
since you are dealing with an image of the particle 
field, and the velocity field of the particles can also 
be obtained. A big advantage of holography is that 
there has been a lot of experience with it and one 
is quite confident when employing holography that 
you will get quality data that is useful. The big 
disadvantage in one area is data reduction. If you 
get a lot of data, it is difficult to extract oat of 
that information the subset of information which 
is important to you. I might point out, however, 
that there are programs underway at a number 
of centers focusing on automating the process of 
getting the desired information out of holographic 
images. The advent of computer technology, of 
course, is making that possible. When one makes 
a hologram of an object field, he then reconstructs 
the image field for a three-dimensional image on 
which the photography work can be done. 
Recent applications of holography include spray 
characterization, coal combustion, and much work 
in wind tunnels. One of the early applications of 
holography for particle field studies was at AEDC 
here in Tullahoma, where it was used to char- 
acterize a particle environment in a tunnel that 
was laden with particulate for purposes of erosion 
studies. That was more than 10 years ago. There 
is a great deal of experience with use of this tech- 
nique in wind tunnels. Rocket engines and various 
industrial processes are other applications. 
The advantages of the single particle techniques 
are size and velocity information, good spatial res- 
olution, and a big advantage is real-time data ac- 
quisition. This is based on light scattering which 
goes into a photo-multiplier tube, then eventually 
into a computer where the data is virtually all 
handled in real-time and managed by the com- 
puter. All of these optical techniques, of course, 
are nonintrusive. It is a single particle inferred 
LWC which can be either a disadvantage or an 
advantage depending on what the real mission or 
objective is. Quantities of interest for icing studies 
like LWC have to be inferred from the measure- 
ment of particle size and velocity. 
Let me just summarize with a few words on ensem- 
ble measurements. Ensemble measurements are 
those on which one projects light into the particle 
field of interest and collect the scattered light off 
of the ensemble of particles. There are systems of 
that kind availabie and improvements are under- 
way for them. The advantage is that those systems 
are inherently quite simple; the data, however, is 
not of as high a resoIution as one can obtain by 
other means. They are very useful, though, de- 
pending upon the mission of the instrument. 
In closing, I would again say that I think we need 
to clearly establish what the measurement require- 
ments are on the various ground and flight test 
programs. Then, based on the voids that exist in 
the measurement requirements compared to what 
we are using today, some of the advanced methods 
that are underway and available may be appropri- 
ate for implementation on those programs. 
“DEVELOPMENT OF A WIND SHEAR PERFORMANCE ENVELOPE” 
John H. Bliss 
Flying into an airmass which is moving in a new di- 
rection and/or at a different velocity may produce 
a large airspeed change. An increase is inciden- 
tal. A significant loss, well below the bug speed in 
use, will severly alter the flight path and produce 
a large descent rate. 
If there is no continuing headwind loss after such 
an airspeed loss, you can apply maximum power, 
pull the nose up, and go-around. However, a con- 
tinuing headwind loss equal to or exceeding ac- 
celerative capability will prevent a successful go- 
around. 
In a simple downdraft, altitude can  be held in air 
which is descending as fast as the airplane can 
climb. Consequently, some think altitude can also 
be held when a headwind is diminishing at the 
same rate as the airplane can be accelerated. 
It is quite important that the airplane performance 
during a continuing headwind loss be understood. 
This presentation is offered in recognition of this 
importance, and to present an aspect of perfor- 
mance not normally considered. Lack of consid- 
eration of this characteristic can result in assum- 
ing almost twice the performance than that which 
62 
https://ntrs.nasa.gov/search.jsp?R=19860002279 2020-03-23T06:34:18+00:00Z
the airplane actually has during severe wind shear 
at high descent rates. The example data relates 
to the Boeing 727-200, but the characteristics are 
applicable to any airplane. Figure 1 portrays the 
characteristic of an airplane in the landing configu- 
ration, gear down, flaps 30, loo%, power, standard 
sea-level day, and 140,000 lbs. gross weight. 
F i g u r e  1 .  
We will begin with evidence of how forces are bal- 
anced during a maximum performance climb, at 
a Vref airspeed of 128 kts (see Figure 2). It is 
important to recognize that the airborne frame- 
work coincides with the inertial framework (no 
wind shear). I would like to draw your attention 
to the angles which apply. The angle, flight path 
to “G” direction, equals 97.31O. 
F i g u r e  2.  
A climb of 1650 fpm (27.5 f ps )  is achieved us- 
ing maximum performance under stable air condi- 
tions. I would like to emphasize “using maximum 
performance”. 
Now consider Figure 3. We have the level flight 
condition, where there is an acceleration of 2.5 kps 
(4.222 fps). The angle between the flight path and 
“G” direction remains at 97.31”. Notice the rota- 
tion of lift by 7.31’ results in a slight lift deficiency 
which can be ignored due to its fleeting 1-second 
existance. Altitude is then held and airspeed in- 
creases 2.5 kts/sec. 
0 
7 m 
0 - A = 4.222FPS 
F i g u r e  3 .  
Turning to Figure 4, we have the same condition 
as in Figure 3 except with a 2.5 kps constant head- 
wind loss, the airspeed does not rise. The slight 
loss of lift in Figure 4 now becomes significant. 
The loss is constantly present due to no airspeed 
increase. The maximum flight path angle is now 
a tangent to the lift l i e  represented in Figure 3, 
with the same airspeed. All is as balanced as the 
previous condition in Figure 2 as long as the 2.5 
ktfsec. headwind loss endures. 
Inspecting Figure 4 in comparison with Figure 3, 
one sees that the only difference is the 2.5 kps 
headwind loss in Figure 4. Surely, those of you 
who have observed a free-flight model in a wind 
tunnel will attest to the almost vertical pertur- 
bations caused by slight changes in wind veloc- 
ity. The movement is near vertical because of lift 
63 
change, and altitude loss has Iittle horizontal effect 
on the model’s movement. The acceleration/climb 
chart is valid in stable air where a change in flight 
path produces the effect of descending an inclined 
plane. 
9 
Figure 4. 0-A = A-B = 4.222FPS 
When a mass descends an inclined plane due to 
the influence of gravity (see Figure 5) ,  its veIocity 
will equal that acquired by a mass falling freely 
the height of the plane. All horizontal acceler- 
ation derived from descending the inclined plane 
results from the resistance to gravity provided by 
the plane. 
As simple as this sounds, there can be complica- 
tions. If you place the inclined plane on an ele- 
vator, any vertical acceleration, up or down, will 
affect the velocity imparted to the mass. Hori- 
zontal acceleration of the inclined plane will also 
affect the velocity acquired by the mass down the 
plane. 
In an airplane, the “inclined plane” is totally formed 
by the geometry of the air. When the air geome- 
n 
Figure 5. Display o f  an inclined plane 
try is unchanging, a solid “inclined plane” such as 
displayed here, and on the accelerate/climb chart 
(Figure l), exists. 
There is nothing relative to the airplane which 
gives any re!evance to horizontal except the air 
geometry and gravitational (“g”) force direction. 
When a continuing headwind loss is present, the 
airplane’s horizontal is changed to a new direc- 
tion and so is the “g”, so the inclined plane is also 
changed. The result is altitude loss without the 
resultant horizontal acceleration, just as if the in- 
clined plane were to be accelerated toward the rear 
at the same rate as the headwind is diminishing. 
I know from experience that with no wind, a 747 
can leave 39,000 feet 120 miles from destination, 
descend at idle power, and land 20 minutes later 
using power only the last 1500 feet on final. When 
you have a 150 knot headwind at 39,000 feet, it 
takes no more than 85 miles and just over 12 min- 
utes. A much larger pose-down attitude is re- 
quired to get the same airspeed during the head- 
wind loss. There is a large altitude loss without 
the speed gain. This is obviously the result of 
a large change in the “inclined plane” and these 
changes are just as valid on the approach as they 
are at altitude. If the accelerate/climb chart val- 
ues (Figure 1) were valid, at least the time for de- 
scent would be the same in either case. Obviously 
it is not. 
Essentially, safe flight path control in the new air- 
mass can only be assured by the use of a safe ac- 
tual speed relative to the new airmass before en- 
tering. The safe speed cannot be resolved by using 
airspeed alone, which disregards the environment 
ahead. 
For take-off, the best defense seems to be a pause 
in take-off position to scan the departure path, vi- 
sually and with radar, for problem cells. If present, 
taxi off the runway, don’t take-off. 
For landing approach, where the environment ahead 
is known, a safe speed can be resolved for the ap- 
proach. A method and instrumentation has been 
described here at a previous meeting. It is the 
airspeed/groundspeed method. This sytem auto- 
mates the process and the only addition1 work load 
is to insert the surface wind. 
Presently, wind shear training (a requirement for 
most airlines) is like asking a student a question 
for which there is no answer. Conversely, the air- 
64 
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 


Development of a wind shear performance envelope

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