Documentation of Atmospheric Conditions During Observed ...€¦ · NASA Contractor Report 4767...

NASA Contractor Report 4767

Documentation of Atmospheric ConditionsDuring Observed Rising Aircraft Wakes

j. Allen Zak

ViGYAN, Inc. • Hampton, Virginia

William G. Rodgers, Jr.

Lockheed Martin Engineering and Sciences • Hampton, Virginia

Prepared for Langley Research Centerunder Contract NAS1-96014

April 1997

https://ntrs.nasa.gov/search.jsp?R=19970018786 2020-05-02T20:57:53+00:00Z

Available electronically at the following URL address:

Printed copies available from the following:

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Springfield, VA 22161-2171

(703) 487-4650

Table of Contents

1. Introduction and Background ........................................................................................... 1

2. Potential Rising Vortex Causes ........................................................................................ 2

3. Flight Experiments ........................................................................................................... 2

4. Data Collection ................................................................................................................ 3

4.1. Aircraft Data ........................................................................................................... 3

4.2. Other Meteorological Data ...................................................................................... 4

5. Data Processing ............................................................................................................... 5

5.1. Altitude data ........................................................................................................... 5

5.2. OV-10 Flight and Meteorological Parameters .......................................................... 5

5.3. Radiosonde data ...................................................................................................... 5

6. Results ............................................................................................................................. 6

6.1. Meteorology for Flight Days ................................................................................... 6

6.2. Wake Behavior ........................................................................................................ 7

6.2.1. Sinking Vortices .......................................................................................... 8

6.2.2. Level or Rising Vortices .............................................................................. 8

6.2.3. Oscillating Vortices ..................................................................................... 9

7. Conclusions ..................................................................................................................... 9

References ................................................................................................................................. 10

List of Tables

Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6.

Table 7.

Table 8.

Flight Summary ..................................................................................................... 11

Data Available ....................................................................................................... 11

OV-10 Parameters ................................................................................................. 11

Other Meteorological Data Available ..................................................................... 11

Data Summary for Rising Vortex Research ............................................................ 12

Data Summary for Sinking Vortices ...................................................................... 14

Data Summary for Rising Vortices ........................................................................ 15

Data Summary for Wakes with Large Oscillations ................................................. 16

iii

Figure 1.Figure2.

Figure3.Figure4a.Figure4b.

Figure4c.Figure5.Figure6a.

Figure6b.Figure6c.Figure6d.

Figure6e.Figure7a.Figure7b.

Figure7c.Figure8a.Figure8b.

Figure8c.Figure9a.Figure9b.Figure9c.

Figure 10a.Figure 10b.Figure 10c.

Figure 11.Figure 12.Figure 13.

Figure 14.Figure 15.Figure 16.Figure 17.

List of Figures

WakeVortexFlowField.......................................................................................17WakeVortex DescentRates.................................................................................17

Video Frameof OV-10Drifting BehindtheC130.................................................18Video Frameof OV-10Levelwith theStarboardVortex......................................18

Video Frameof OV-10PenetratingStarboardVortex...........................................18Video Frameof OV-10BelowthePortVortex.....................................................18

OV-10ExperimentalConfiguration.......................................................................19SurfaceWeatherMap for October19,1995,1200GMT.......................................20

850HectopascalWeatherMap for October19,1995,1200..................................20Balloon Soundingfor October19,1995,1400GMT.............................................20Balloon Soundingfor October19,1995,1750GMT.............................................21Balloon Soundingfor October19,1995,2046GMT.............................................21

SurfaceWeatherMap for October26, 1995,1200GMT.......................................22850HectopascalWeatherMap for October26, 1995,1200..................................22Balloon Soundingfor October26,1995,1131GMT.............................................22

SurfaceWeatherMap for November6, 1995,1200GMT .....................................23850HectopascalWeatherMap for November6, 1995,1200.................................23Balloon Soundingfor November6, 1995,1730GMT ...........................................23

SurfaceWeatherMap for November8, 1995,1200GMT .....................................24850HectopascalWeatherMapfor November8, 1995,1200.................................24Balloon Soundingfor November8, 1995,1600GMT ...........................................24SurfaceWeatherMap for November9, 1995,1200GMT.....................................25

850HectopascalWeatherMapfor November9,1995,1200.................................25BalloonSoundingfor November9, 1995,1843GMT...........................................25

C130andOV-10GPSAltitude for Flight551at RunTimesShown......................26C130andOV-10GPSAltitude for Flight 552at RunTimesShown.....................27C130andOV-10GPSAltitude for Flight 553atRunTimesShown......................29

C130andOV-10GPSAltitude for Flight555atRunTimesShown......................30C130andOV-10GPSAltitude for Flight 556atRunTimesShown......................31C130andOV-10GPSAltitude for Flight 557atRunTimesShown......................33

VideoFramesFromDifferentTimesof theC130WakeVortex SmokeSignature.34

iv

Appendices

Appendix A - Balloon Sounding Data For Wake Decay Flight Days

Because of the extensive data contained in this appendix, it has not been included

in the printed copy of this report but is available from the Langley Technical

Report Server (LTRS). Open the files with the following Uniform Resource

Locator (URL):

ftp ://techreports.larc.nasa.gov /pub/techreports/larc/1997 /cr/N AS A-97-

cr4767appA.txt

Appendix B - Altitude Comparison Data

Because of the extensive data contained in this appendix, it has not been included

in the printed copy of this report but is available from the Langley Technical

Report Server (LTRS). Open the files with the following Uniform Resource

Locator (URL):

ftp://techreports.larc .nasa.gov/pub/techreports/larc/1997/cr/NASA-97-

cr4767appB.txt

V

Abstract

Flight tests were conducted in the fall of 1995 off the coast of Wallops Island, Virginia in order to determinecharacteristics of wake vortices at flight altitudes. A NASA Wallops Flight Facility C130 aircraft equipped withsmoke generators produced visible wakes at altitudes ranging from 775 to 2225 m in a variety of atmosphericconditions, orientations (head wind, cross wind), and airspeeds. Meteorological and aircraft parameters werecollected continuously from a Langley Research Center OV-10A aircraft as it flew alongside and through the wakevortices at varying distances behind the C130. Meteorological data were also obtained from special balloonobservations made at Wallops. Differential GPS capabilities were on each aircraft from which accurate altitudeprofiles were obtained. Vortices were observed to rise at distances beyond a mile behind the C130. The maximumaltitude was 150 m above the C130 in a near neutral atmosphere with significant turbulence. This occurred fromlarge vertical oscillations in the wakes. There were several cases when vortices did not descend after a very shortinitial period and remained near generation altitude in a variety of moderately stable atmospheres and wind shears.

1. Introduction and Background

This research is a continuing effort on the part

-of the NASA Langley Research Center

(LaRC), the Federal Aviation Administration

(FAA) and other government agencies to

understand the complex behavior of wake

vortices in a variety of atmospheric conditions.

A significant effort is now underway at LaRC

as part of a NASA Terminal Area Productivity

Program to determine safe operating spacing

between arriving aircraft. Such spacing is now

conservatively determined _by aircraft

size/weight classes between lead and following

aircraft pairs. If this spacing can be safely

reduced under certain atmospheric conditions,

then capacity can be increased at many

airports throughout the world. The Aircraft

Vortex Spacing System (AVOSS) (ref. 1) is

striving to determine this safe spacing based

on observed and predicted atmospheric

conditions. Understanding atmospheric wake

vortex interaction is, therefore, on a critical

path in this endeavor.

Wake vortices are manifestations of flight.

Two areas of large pressure gradients are

created at the wings. Counter rotating air

flows develop behind the wing tips as shown

in figure 1. These present a hazard to aviation

in that the rolling moment induced by the

inadvertent penetration of a vortex can exceed

the roll control authority of the penetrating

aircraft. Vortex strength initially depends on

three factors: the weight, wing span and

airspeed of the generating aircraft. Other

factors involved are wing configuration and

flight attitude. Vortices descend after initial

formation. Current training material statesthat this descent continues for the first 5 nm

then levels off (ref. 2). Initial descent rates are

stated to be typically 300 to 500 feet perminute for the first 30 seconds. As shown in

figure 2, vortices then are expected tocontinue to descend at a slower rate and

eventually stop descending at between 500 to

900 ft below the generating aircraft. Pilots are

taught, therefore, to fly "at or above the

preceding aircraft's flight path altering course

as necessary to avoid the area behind and

below the generating aircraft." (ref. 3).

The NASA Langley Research Center

embarked on a series of wake vortex flight

tests during the fall of 1995 off the coast of

Wallops Island, VA. The purpose of thesetests was to collect data on wake vortex

decay, on vortex-aircraft interaction, and for

in-flight wake detection. During some on

these flights, pilots reported rising wakes.

Understanding conditions that can lead to

rising vortices is essential to the success of

AVOSS. Therefore, the purpose of thisresearch was to confirm if wake vortices

generated by a C130 NASA aircraft rise at

flight altitudes and to document the

meteorology associated with theseoccurrences. Other characteristics of the

vortices such as strength and decay will becandidates for future research.

The atmosphere plays a significant role in the

movement and decay as well as in the general

behavior of the vortex pair following initialdescent. This research documents some of

these atmospheric effects and identifies some

cases where the vortex actually rises to an

altitude above the generating aircraft in level

flight outside of ground effects.

2. Potential Rising Vortex Causes

The effects of atmospheric stratification on

aircraft wake vortices have been investigated

in the past (ref. 4, 5, 6). The vortex pair

descends and warms adiabatically owing to

compression. The vortices can then achieve a

temperature warmer than the environment,

and upward buoyancy forces can theoretically

counteract and eventually exceed thedownward momentum if the stable

stratification is very strong. The magnitude of

the buoyancy force can be measured by the

Brundt-Vais_iRi (B-V) frequency (ref. 6)

squared, which is the numerator in the

Richardson Number, a frequently used

measure of atmospheric turbulence:

Vortices can be imbedded in strong vertical

currents, especially during the afternoon on

convectively active days. Such "thermals" can

exceed 1 m/s (several hundred feet per minute)

on thermally active days as any soaringenthusiast can confirm. These conditions can

be inferred from measures of atmospheric

stability (ref. 8) from balloon soundings.

Rising motion can be imparted to the vortex

pair due to mountain waves or gravity waves

propagating along atmospheric discontinuities

such as inversions. Gravity waves from

mountains in NW Montana have been reportedto affect the initiation of thunderstorms as far

as several hundred kilometers downstream

(ref. 9).

Finally, atmospheric turbulence can enhancevortex instabilities that can be manifest in

oscillatory motions (ref. 10). Such features as

vortex bursting, Crow instability, and linking

have been observed and described in the past

(see ref. 11 for a summary). Vertical sinusoids

can be a potential source of vortices ascending

above flight generation altitude.

The above is a simplification for discussion

purposes. It is likely on any given day that

several of these effects and others, perhaps not

yet identified, can act on the vortices at any

given time and place in very complex ways.Some of these effects will be discussed in the

context of results found in this research.

where g is the acceleration of gravity, theta

the potential temperature, and Z the altitude. 3. Flight Experiments

Wind shear also plays a role. Most recently,

Proctor, et. al., have shown in vortex

simulations that nonlinear cross wind profiles

can arrest the descent of vortex pairs and that

this nonlinearity was more important than the

shear itself (ref. 7).

The NASA Langley Research Center with the

cooperation of the NASA Wallops Flight

Facility conducted a series of wake decay

flights off the coast of Wallops Island, VA. ANASA C130 aircraft acted as the wake-

generation aircraft. It was equipped with wing

tip smoke generators to make the vortices

visible to the Vailing aircraft, a NASA OV-10A. The OV-10 was instrumented to

measure and record atmospheric temperature,

dew point, winds and turbulence as well as

aircraft motion and fundamental aircraft

parameters. More details will be providedunder Data Collection.

There were six wake decay missions flown in

October and November 1995. Table 1 fists

the date, times, flight altitudes, general

weather conditions, and vortex characteristics

for each. Fright altitudes ranged from 800 m

to 2200 m (about 2500 to 7000 ft) and were

planned to coincide with meteorological

events such as inversions whenever possible.

The OV-10 collected a vertical sample of

meteorological data at the beginning of each

mission in order to determine gross

atmospheric features such as inversion heights

and strengths. This then led to selection of

working altitudes such as below, in, or abovethe inversion. Horizontal and vertical

atmospheric sampling continued in selected

atmospheric regions near the workingaltitudes. A mission consisted of a series of

runs where the C130 and OV-10 would fly

level and parallel at a chosen airspeed,

heading, and altitude. The OV-10 would

reduce airspeed to drift behind the C130 and

would start penetrating the vortices fromabout 1 mile behind to as far as 7 miles behind

if the vortices remained visible that long.

Figure 3 is a frame from the tail camera video

showing the OV-10 just beginning to driftbehind the C130. As the OV-10 entered the

vortex from either the port or starboard side,

the aircraft would descend below the track of

the opposite vortex due to the vortex

circulation (downward between the vortices).

Figure 4 is a sequence showing the OV-10

level with the starboard vortex just before

penetration (4a), in the starboard vortex (4b),

then falling down under the port vortex (4c).

The OV-10 would continue a series of

penetrations at varying times (distances)behind the C130 to accumulate data on vortex

and atmospheric characteristics at different

vortex ages. This sequence would then be

repeated for a different flight altitude, different

orientation (head wind (HW), tail wind (TW),

cross wind (CW)), or different airspeed, ff

both smoke generators were operating, the

penetration would be sequenced between the

port and starboard side: starboard vortex

penetrated then below the port vortex

followed by level with and penetration of the

port vortex then below the starboard vortex.

If only one smoke generator were operating,

the OV-10 would penetrate just the visible

vortex, but from either side. The pilots

reported the strongest roll upsets when

penetrating from the inside (between the

vortices) out. Needless to say, in the wake

turbulence behind the C130, the pilot had a

challenging task to find the center of the

vortex when air at the vortex boundary was

always moving up or down as he approachedthe vortex.

4. Data Collection

Data for this study were collected from the

C130, and OV-10 aircraft and crew, synoptic

weather charts, routine upper air soundings,

and special balloon soundings taken for these

tests by NASA Wallops Fright Facility, Flight

Ops personnel.

4.1. Aircraft Data

The experimental configuration of the OV-

10A is shown in figure 5. A discussion of

each sensor system and its output can befound in reference 12.

Of special significance was a custom-built data

acquisition system capable of recording about

two hours of data for one mission at a rate

sufficiently high to characterize high-frequency

atmospheric turbulence. Also critical to this

study were Ashtech differential Global

Positioning System (GPS) receivers on both

the C130 and OV-10 with associated ground

stations at NASA Langley and NASA Wallops

from which highly accurate positions

(longitudinal, lateral and vertical) could be

obtained. On these flights the data rate for the

Rosemount probe on the graphite-epoxy nose

boom from which wind components were

calculated was 128 samples per second.Measurement rates from the other sensors

ranged from 4 to 32 samples per second.

Temperature and dew point were recorded at

8 samples per second. The tail camera

provided video tape documentation of each

mission along with audio tracks of pilot and/or

researcher comments as well as an IRIG time

code at the top of each frame. Pilot logs were

also available from the C130 and OV-10 flight

crews. The C130 has a wing span of 40.2 m

(132 ft) and its weight ranged from 44,452 kg

to 47,627 kg (98,000 lb to 105,000 lb) during

these missions.

For this study the temperature, dew point,

wind components, GPS positions, especially

altitude, and turbulent wind components were

used in conjunction with the OV-10 video

tapes, and pilot logs to characterize the height

of the vortex encounters as well as pertinent

atmospheric conditions and vortex behavior. A

summary of major aircraft data sources

available is presented in Table 2, and Table 3

shows the parameters collected on the OV-10.

Note that in Table 2 the Ashtech differential

GPS was not available on the C 130 for Flights

552 and 553. Also note that there was no

Ashtech GPS on the OV-10 until Flight 555.

There was excellent agreement in comparisons

of pressure altitude, Ashtech GPS, and

Honeywell GPS when they were all available.

Therefore, for the earlier flights, the

Honeywell non-differential GPS was used for

the OV-10 flight altitude. Finally, there was

little or no video available for Flights 552 and

555.

4.2. Other Meteorological Data

It is important in any study of wake vortex

phenomena in the atmosphere that the ambient

meteorological conditions be determined. It

was stated earlier that atmospheric

stratification or vertical temperature and

moisture gradients, vertical wind shear, and

turbulence can play significant roles in wake

vortex behavior. Special upper air balloon

radiosonde observations were taken during

each flight to provide ambient vertical

temperature, moisture and wind profiles.

Radiosonde packages (VIZ W-9000 MK-2)

with cross-chain Loran were used with a 300

gm balloon. Ascent rate was 305 m/min for

the special soundings. In addition, Wallops

personnel take upper-air radiosonde

observations twice daily at 0000 and 1200

GMT for the National Weather Service as part

of the National Network. These were 600 grn

balloons with an ascent rate of 366 m/min.

The special data for Flights 551 and 552 wereavailable at either 2 second or 5 second

resolution corresponding to 10 and 25 meter

vertical resolution respectively; but for the

other flights (and for the network soundings)

the vertical resolution was about 750 m for

temperature and dew point and 300 m for

winds. If there were significant temperature

features, more resolution was available. The

wind information output at the 2 or 5 second

rate was a running 6 second average.

The meteorological measurements from theballoon as well as from the OV-10 must be

understood in the context of the larger scale

features of the atmosphere. Therefore, the

surface and 850 hectopascal weather maps

were obtained for each flight day. A summary

of other meteorological data available for this

study is shown in Table 4.

5. Data Processing

Processing of altitude data, aircraft speed and

heading, OV-10 meteorological data, and

radiosonde balloon data provided the basis for

this study.

5.1. Altitude data

It was possible to obtain the flight altitudes ofthe C130 and its wakes as a function of time

or distance. Software written by the LaRC

Vehicle Dynamics Branch was modified to

calculate range of the OV-10 from the C130

as a function of time. Output was altitude vs.

time for both the C130 when it generated the

vortices and the OV-10 when it penetratedthem at various distances behind. In other

words, altitude is shown as a function of time

for the OV-10, but altitude for the C130 is

shown for a time which was adjusted for the

age of the vortex encountered.

5.2. OV-10 Flight and MeteorologicalParameters

One second averages for all parameters were

computed from their original measurement

rates. Aircraft position (x, y, and z

representing the E-W, N-S and height

components respectively) was plotted as a

function of time for all runs. Heading,

pressure, temperature, dew point, and winds

were also plotted as a function of time. Wind

was shown as direction (from true north),

speed, and the three orthogonal components,

u, v, and w corresponding to x, y, and z

respectively, all as a function of time. The data

were separated into "abeam" when the OV-10

was flying parallel to the C130 at the

beginning of each run, "penetration", when the

OV-10 began to enter the wakes, and level

weather segments. Further processing wasdone for the abeam and level weather

segments to provide statistics such as

minimum, maximum, means and variances.

Altitude and all the meteorological parameters

were included in the statistics. In addition,

cross correlations were computed among

temperature, dew point, and u, v, and w

fluctuations of the high frequency

measurements from the mean value during the

time of the level flight segment. One

correlation combination was computed to

represent the turbulent kinetic energy (TKE)of the environment as follows:

TKE =U"I.tP+ V" V"+ W" W'

2

where the primes indicate deviation from the 2

minute mean.

5.3. Radiosonde data

Standard pre-processing was done at the

Wallops Flight Facility to provide

temperature, dew point, wind direction, and

speed for each pressure (altitude). The

potential temperature was calculated for

visualization of stability. All parameters

(potential temperature, temperature, dew

point, and wind) were plotted as a function of

altitude for each balloon sounding time. The

mean lapse rates (potential temperature

change with altitude), where positive is

increasing temperature with height, and cross

wind shear from about 50 meters above the

vortex altitude to 75 meters below were

calculated for every run. This is opposite to

the usual meteorological terminology for

positive and negative lapse rates where the

lapse rate is defined with a negative sign.

When the potential temperature increases with

height, the atmosphereis stable1 . B-Vfrequencywas also calculatedfor eachrun.Finally, the bottom and top of temperatureinversions and maximum strength wereidentified from the changing lapse ratestructurefor eachsounding. The data for allthe balloon soundings are included inAppendixA.

6. Results

A discussion of the most important

characteristics of vortex behavior and

associated meteorology will be the focus of

this section. First, the meteorology for each

flight day will be discussed. Next will be the

discussion of the combined vortex generation

altitude and altitude of penetration at various

vortex ages and distances behind the

generating aircraft. Finally, the meteorology

and vortex behavior will be presented for

times of sinking vortices, steady or rising

vortices, and disturbed vortices. Cause-effect

mechanisms will be included when possible.

6.1. Meteorology for Flight Days

There were no extraordinary meteorological

events occurring on any wake encounter day.

Flight tests were planned and executed when

no adverse weather was threatening the test

region. Figure 6 shows the surface weather

map (6a) and 850 hectopascal analysis (6b) for

October 19, 1995 whereas Figure 6c, d, and e

show plots of the balloon soundings at the

times indicated. There were two flights on

this day. High pressure dominated the region

with clear skies in the morning and scattered

cumulus clouds in the afternoon. The high

pressure aloft created subsiding air which was

indicated as a weak inversion and generally

stable conditions in the balloon soundings.

1or more precisely, conditionally unstable until itexceeds the moist adiabatic lapse rate

Stability at flight altitudes generally decreased

in the afternoon except for Flight 552, runs 8

and 9, which were in the top of a rather weak

inversion layer. All the other runs were above

the inversion but still in stable air. Winds at

flight altitudes were generally SW 5-8 m/s.

There was little turbulence with some cross

wind shear on some runs. The next flight day,

October 26, was very similar (Fig. 7a, b) with

even higher pressure dominating the region.

The sounding (Fig. 7c) reflects a stronger

inversion. Three of the runs (11, 12, and 13)

were at the top of the inversion where there

was a very stable atmosphere. Flight level

winds were Westerly 5-12 m/s with stronger

cross wind shears at the inversion top. There

were scattered clouds and haze trapped below

the inversion. High pressure at the surface

was the major feature on the next flight day,

November 6 (Fig. 8a, b). Again, the sounding

(Fig. 8c) shows the characteristic inversion

and stability. Lapse rates for all flight altitudes

were closer to neutral than on any prior

flights, however, skies remained clear. Winds

aloft and shears remained light, but turbulence

levels increased from the earlier flights. There

was a significant difference for the next two

flight days. A strong cold front moved

through the region early on November 8 with

a strong NW flow from the surface to 3 km

altitude and strong cold air advection (Fig. 9

a, b). This combination produced a well

mixed lower atmosphere with neutral stability

and significant turbulence. The sounding

shown in Figure 9c reflects the neutral stabilitybelow 1300 m. All the runs were in this well-

mixed, turbulent layer. Winds were 12 rn/s at

flight altitude with a trajectory perpendicular

to the mountains in Western Maryland. There

were clouds slightly above the flight altitude of

900 m (3,000 ft), some of which had vertical

development and looked like toweringcumulus in the video. Conditions on the last

flight day, November 9, 1995, were similar at

flight level, but there was increased stability

aloft from a building surface high pressure

system that moved into the area from the West

(Fig. lOa, b, and c).

The above meteorological conditions will be

called upon to help explain somecharacteristics of the wakes discussed next.

6.2. Wake Behavior

Results for every flight and run are

summarized in Table 5. All the important

information from the processing and analyses

of all the data are presented in this table. In the

discussion that follows, it is not necessary

(except to confirm a table entry) to refer to

either the weather maps or soundings. A

series of plots was generated for superimposedC130 altitude and OV-10 altitude. The C130

altitude was plotted at the time of vortex

generation. The OV-10 distance (in nautical

miles) behind the C 130 is shown in each plot.

These plots for all flights and runs for which

data were available are shown in Figures 11-

16, one sequence of runs for each flight. The

altitude data for these flights are included in

Appendix B. OV-10 vortex penetrations and

basic vortex behavior (sink, rise, or steady)

can be seen by visual inspection. One can see

the change in altitude of the OV-10 as it is

penetrating the vortices after about one mile

behind the C130: descent upon penetration,

then climb for the next penetration. Figure

lla (run 06), for example, shows the altitude

changes for the OV-10 after it started vortex

penetrations at about 1 1/4 miles behind the

C130 at 1332 GMT. The plot shows a steadydescent to the vortices until about 4 1/2 miles

behind the C130. In Figure llc (run 13) one

can see the altitude of the C130 changing (top

curve) so that the behavior of the vortex,

showing to be steady at 1500 m between 1442

and 1443 GMT, would have actually been

descending because the C130 was rising as it

was generating the vortices. The altitude

scales are the same for all plots, but the time

scales (abscissa) change depending on how

long the vortices could be seen. Unfortunately,

for Flights 553 and 555 there was no altitude

available for the C130 so we can only assume

it was level in interpreting vortex ascent or

descent. There was evidence from pilot

comments that the autopilot on the C130 was

not working properly for portions of Flights551 and 552 as can be seen in the altitude

plots for some of these runs.

There were some limitations, however, that

could affect the results. The lack of video

confirmation and pilot comments for Flights

552 and 555 prevented confmnation of wake

behavior, and the absence of altitude

information for the wake generating C130makes the determination of vortex behavior

(sinking, steady, or rising) speculative. There

were also some inconsistencies noted in pilotaltitude calls from his altimeter with the GPS

altitude plots. The GPS data are assumed tobe correct. Vertical wind measurements

appear to have a positive bias of 0.5 m/s, a

large number for atmospheric vertical motion,

so this information is only used in a relative

sense. There were some differences in

horizontal wind measurements between the

OV-10, C130, and balloons, but none beyond

that reasonably expected in the atmosphere.

The only corrections made in the data

presented in Table 5 were for differences in

Earth Geoid references for the GPS systems,

constants in both cases. Change in potential

temperature with height was also graphically

determined from balloon potential temperature

plots. The wind shear information presented

in Table 5 was calculated from the soundingtaken at a different time and location from the

wake encounter flights. When there were two

soundings bracketing a flight, some

interpolation was performed. Furthermore,

there was considerable smoothing in the

vertical winds, so that shears are not very

7

representative of those that may have

contributed to vortex behavior for any of the

runs. For this reason other parameters such as

Richardson Number used by many to assess

atmospheric turbulence is not calculated since

it includes the wind components squared in thedenominator.

Since a major goal of this study was to

determine whether or not wakes rise at flight

altitudes, the sequence of plots in Figure 11

through 16 is critical to the outcome.

During _ghts on October 19 (551 and 552)

there are only small differences between

generation altitude and vortex altitude among

the runs. For 553 and 555 there was no C130

altitude so the C130 was assumed to be in

level flight. Nevertheless, those runs in which

the vortices predominantly descended and

those where there was very little or no descent

beyond an initial period were identified and

separated for discussion purposes. Because

vortices on the last two days underwent

significant vertical and horizontal undulations,

they were also separated. Each group will bediscussed below.

6.2.1. Sinking Vortices. Vortices appeared

to be predominantly sinking during their

lifetime (represented by their smoke trail) for

551 run 06, 552 runs 05 and 10, 553 run 8,

and 555 run 03 and 04. These cases are

extracted from Table 5 and summarized in

Table 6. Note that the average potential

temperature lapse rate was 0.48 degrees

C/100 m and B-V frequency was 0.0127/s for

the sinking cases. The lower lapse rate

represents fewer upward motion forces, as

would be expected, than for the level to rising

cases presented next. Also of interest are the

two runs separated by 45 minutes in Flight

551 (runs 06 and 10). Both were head wind

cases and at the same altitude. The former

sank significantly, whereas the latter remained

nearly level. Notwithstanding wind shear

effects which may not be adequately

represented, the biggest difference was that

the airspeed of the C130 was 90 m/s for run

10 and 60 m/s for run 06. The other difference

is a slight increase in stability, therefore

buoyancy, for this later flight as interpolated

between the two closest balloon soundings.

For Flight 552 there also was a sinking vortex

followed by a steady vortex. The only

difference here was that run 05 was in a tail

wind configuration and run 06 was a cross

wind. Therefore, the cross wind shear for run

06 was three times the value of the first run

(run 05), or 0.3 compared to 0.1 m/s per 100

m. There did not seem to be any other

correlations with orientation (head wind, tail

wind, cross wind) or anything else separating

these sinking vortex cases from the others.

6.2.2. Level or Rising Vortices These cases

are spread throughout the flights as shown in

Table 7. The average lapse rate increased to

1.03 degrees C/100 m and the corresponding

average B-V frequency (0.0177) was higher.

There are individual exceptions, however.

Flight 551 run 10 and 552 run 6 were already

discussed. There may be other factorsinvolved such as wind shear and/or

interactions of all the effects, some of which

cannot be adequately determined. The

assumption that the C130 was steady for

Flight 553 may also be incorrect. It is

interesting to note that the one case

documented from the GPS plots, 552 run 9,

when the vortices rose above the generating

altitude, involved a flight near the top of the

inversion in the region of maximum positive

lapse rate. There were other cases when

vortices rose above the wake generation

altitude, but these involved large sinusoidaloscillations to be discussed next.

6.2.3. Oscillating Vortices Strong horizontal

and vertical oscillations began to appear in the

vortices on the last two flight days as close asone-fourth mile behind the C130. Some of

these oscillations are shown in Figure 17 as

the OV-10 is drifting behind the C130.

Oscillating vortex cases are shown in Table 8.

There was little discussion of the TKE

parameter up to this point because there did

not seem to be any correlation with vortex

behavior. However, it can now be seen that

all these runs are associated with high values

of TKE (average value: 1.31). It appears that

ambient turbulence was enhancing vortex pair

interaction and precipitating the oscillatory

motion. Ambient winds were perpendicular to

mountains about 300 km upwind, but the

atmosphere did not appear to be favorable for

mountain wave propagation. Normally these

would travel along a discontinuity in the fluid

such as an inversion top, but the atmosphere

at flight altitude was near neutral and well

mixed. Also, there did not seem to be much

difference in oscillation wave length fromcross wind to head-tail wind orientation as one

would expect for a mountain wave. The

vertical motion measured from the OV-10 was

higher and changed significantly during the

course of the runs. There could be more

organized vertical motion fields in the

atmosphere caused by the turbulent

overturning associated with strong cold air

advection at flight altitudes. Note that in

Flight 556 run 26, some of these oscillations

reached altitudes of 150 meters above the

generation height. The low points in thevertical sinusoids were 100 meters below

C 130 flight altitude. The degree of hazard has

not yet been determined. The C130

maintained a very steady altitude during these

flights.

Vortices remained at or below generation

height for all the runs of Flight 557 despite the

vertical oscillations. The increased

atmospheric stability may have played a role

different from buoyancy effects on that day.

Increased stability above flight altitude and

reduced cold air advection below may have

suppressed larger scale vertical motion than

might have been active on the previous day.

7. Conclusions

Aircraft wakes produced in level flight well

above the ground have been shown in severalcases to remain near the altitude of their

generation and to rise above their generated

altitude in a few cases. This is in sharp

contrast to wake vortex training material

available to the aviation community which

depicts wakes descending 500 to 901)feet

below their generation altitude. On one

occasion the OV-10 was penetrating vortices

confirmed by GPS altitude to be above the

C130 generation altitude by as much as 150

m. These large excursions were associated

with vertical oscillations in the vortex pair

most likely triggered by atmospheric

turbulence and instability. Turbulence, as

measured by the TKE parameter, and neutral

stability were highly correlated to the earlyoccurrence of these oscillations. The one

documented case (Flight 552, run 9) with nooscillations and where the vortex was above

the C130, occurred near the top of an

inversion where both buoyancy and wind shear

may have played a role. However, the wind

shear could not be resolved to a scale

sufficient to allow correlation.

9

References

1. Hinton, D.A., "Aircraft Vortex Spacing System (AVOSS) Conceptual Design," NASA Tech

Memo No 110184, Aug, 1995.

. Hay, George C. and Robert H. Passman, Wake Turbulence Training Aid, US Department of

Transportation, Volpe National Transportation Systems Center, Cambridge, MA, DOT-

VNTSC-FAA-95-4, Apr, 1995, page 2.14.

3. Aeronautical Information Manual, US Department of Transportation, Federal Aviation

Administration, Nov. 9, 1995, page 7-3-2.

4. Tombach, I., "Observations of Atmospheric Effects on Vortex Wake Behavior," J. Aircraft,

Vol 10, 1973, pp. 641-647.

5. Sarpkaya, T., "Trailing Vortices in Homogeneous and Density-Stratified Media," J. Fluid

Mech., Vol 136, 1983, pp. 85-109.

6. Greene, G. C., "An Approximate Model of Vortex Decay in the Atmosphere," J. Aircraft, Vol

23, 1986, pp. 566-573.

. Proctor, F. H., D. A. Hinton, J. Han, D.G. Schowalter, and Y. L. Lin., "Two Dimensional

Wake Vortex Simulations in the Atmosphere: Preliminary Sensitivity Studies," AIAA 97-0056, Jan 1997.

8. Higgens, Harry C. "The Thermal Index," Soaring Magazine, Vol. 27, No. 1, 1963, pp. 8-11.

. Koch, Steven E. et. al., "A Mesoscale Gravity-Wave Event during CCOPE, Part IV: Stability

Analysis and Doppler-derived Wave Vertical Structure," Monthly Weather Review, Vol 121,

Sep 1993, pp. 2483-2510.

10. Sarpkaya,T. and J. J. Daly, "Effect of Ambient Turbulence on Trailing Vortices," J. Aircraft,

Vol. 24, No. 6, Jun 1987, pp. 399-404.

11. Hallock, J. N., "Aircraft Wake Vortices: An Assessment of the Current Situation," DOT-

FAA-RD-90-29, Jan, 1991, US Department of Transportation, John A. Volpe National

Transportation Systems Center, Cambridge, MA.

12. Stuever, Robert A. Eric C. Stewart, and Robert A. Rivers, "Overview of the Preparation and

Use of an OV-10 Aircraft for Wake Vortex Hazards Flight Experiments," AIAA 95-3935,

Sep 1995.

10

Table 1. Flight Summary

Flight # Time # Wake Altitude

& Date (GMT) Encounters (m)

SynopticWeather

Wake

Behavior

551 1243-1532 4 1550

19 Oct

552 1805-2013 6 1550

19 Oct 1150

800

553 1043-1326 5 2200

26 Oct 1600

555 1608-1857 5 1600

6 Nov 1450

556 1441-1630 9 900

8 Nov

557 1647-1903 4 1100

9 Nov

Clear; High Pressure; Stable;Inv. 1100-1400 m

Sctd Cu; High Pressure; Stable;Inv. 1000-1200 m

Clear to Sctd Cu; High

Pressure; Haze; Stable; Inv.1700-2300 m

Clear; Cold High Pressure;Weak Inv. 1050-1200

Sctd-Brkn Cu; strong cold

advection; neutral; windy; turbc

Sctd Cu; High Pressure; Neutralto Sable; Inv 2000-2100; 2500-2600

Descends then steady

Descends then steadyto rise

Steady to slow sink;some rise

Slow sink

Large oscillation;some above C130

Large oscillations; allbelow C130

Table 2. Data Available

Flight-Date C130 DGPS OV-10 DGPS OV-10 GPS & PA Tail Camera551-Oct 19 Yes No Yes Yes

552-Oct 19 Yes No Yes No

553-Oct26 No No Yes Yes

555-Nov 6 No Yes Yes No

556-Nov 8 Yes Yes Yes Yes

557-Nov 9 Yes Yes Yes Yes

Table 3. OV-10 Parameters

Aircraft Parameters f(time) Met Parameters f(time)

X,Y,Z

Heading

True Air Speed

Pitch, roll, yaw and deviations

U,V,W wind

Direction/Speed

TemperaturePressure-Altitude

Dew Point

Table 4. Other Meteorological Data Available

Flight date Routine and Special Upper-Air TimesOct 19 AM

Oct 19 PM

Oct 26

Nov 6

Nov 8

Nov 9

Surface and Upper-Air1200, 1400 GMT

1750, 2046 GMT

1131, 1200 GMT

1200, 1730 GMT

1200, 1600 GMT

1200, 1843 GMT

1200Z

1200Z

1200Z

1200Z

1200Z

1200Z

Surface, 850 Hectopascal






11

Table 5. Data Summary for Rising Vortex Research

Flight No.

551

Date Run No.

19-Oct-95

6 132743 133000

10 141645 141818

13 144047 144200

14 145100 145359

19-Oct-95

5 183433 183650

6 184956 185200

7 190044 190150

8 190758 190900

9 191735 191900

10 192808 192940

26-Oct-95

8 115324 115530

9 120725 120900

11 123420 123530

12 124600 124734

13 125925 130115

6-Nov

2 164315 164420

3 165540 165730

4 170630 170730

5 173500 173600

6 175122 175330

8-Nov-95

22 153450 153550

23 154743 154918

24 155650 155750

25 160750 160844

26 162145 162245

27 163230 163323

28 165213 165320

9-Nov-95

Abeam Penetration

Beg. Time End Time Beg. Time End Time

HMS-GMT HMS-GM'I HMS-GMT HMS-GMT

Nom Fit Lvl Fit Level IAS Heading

Feet meters m/s deg

133154 134238 5000 1540 60 220

141821 142100 5000 1575 90 220

144216 144358 5000 1560 90 310

145405 150000 5000 1560 60 310

552

553

555

183707 184200 5000 1540 95 20

185310 185650 5000 1530 95 300

190210 190600 3700 1150 95 120

190957 191200 3300 1025 95 310

191910 192250 3300 1025 95 50

192949 193350 2500 775 95 220

115550 115750 5200 1600 65 290

120912 121322 5200 1650 100 100

123549 123919 7000 2225 100 80

124736 125007 7000 2225 100 170

130133 130400 7000 2225 100 350

Orientation Wake Character

556

TKE

mZ/s2

557

22 1_1_ 1_200

23 1_925 1_040

24 1_730 1_843

25 1866_ 186725

HW sinking 0.12HW slow sink -level 0.213

XW 0.222

XW 0.215

AVG 0.214

TW sinkingXW slow sink - level

XW level

XW slow sink-level

TW sink-rise-sink

HW slow sink

HW *slow sink

TW *steady

XW *slow sink

XW *slow sink-level

XW *steady-rise

164423 164800 5000 1450 70 360 XW *slow sink

165810 165940 5000 1450 70 90 TW *sink

170755 171355 5000 1450 100 270 HW *sink

173605 173750 5000 1600 70 350 XW *slow sink

175520 175834 5000 1575 70 70 TW *sink-rise

1_6_ 1543_ 3000 900 70 300

154925 155335 3000 900 70 120

155755 1_9_ 3000 900 100 300

100900 161316 3000 900 100 120

1_2_ 162750 3000 900 100 210

163330 1636_ 3000 900 100 30

165330 1657_ 3000 900 100 210

174245 174603 3800

1_0_ 1_300 38OO

175847 180055 3800

180732 181019 3800

* C130 altitude was not available and was assumed constant

HW large oscillations

TW large oscillations



XW i large oscillations

XW large oscillations!

XW large oscillations

0.142

0.222

0.17

0.083

0.187

0.356

AVG 0.249

0.156

0.209

0.041

0.348

0.115

AVG 0.136

0.866

0.176

0.743

0.386

0.386

AVG 0.626

I1100 70 145

1100 70 325

1100 70 65

1100 70 245

0.774

1.2

2.16

0.97

1.27

2.86

0.574

AVG 1.40

TW large oscillations 1.29

HW large oscillations 0.873

XW large oscillations 0.956

XW large osdllations 1.47AVG 1.3[

OV-10 C130

Mean Wind Mean Wina

deg/m/s deg/m/s

230105 224103

220107 200103

210106 N/A

220107 200105

195/09 190103

200106 190103

240104 240105

225102 240105

200104 N/A

200102 220105

315106 386103

28615.5 305/07

255/12 260116

260/11 260/10

260/11.5 250/10

270/02 270/05

270/04 270/03

300/03 270/03

230/2.5 270/03

260/04 270/03

308/12 300/08

290/10 290/12

300/10 300/09

290/11 300/13

300/10 300/10

300/10 281/11

312/15 300/11

300/10 315/08

325/07 300/10

300/08 305/20

320/10 320/08

Table 5. (continued

Mean Temp Pot Temp Mean Dew Point Mean W DTh/DZ DDir/DZ DS/DZ B-V

C K C m/s degK/100m deg/100m [ m/s/100m per sec

11.2 297.9 0.7 20 1 0.0151749

11 298 1 20 1 0.0181345

10.6 298 20 0.0181345

10.5 298 1 20 1 0.0181345

11.3 298 0.5

0.511

0.3

0.3298

0.012823

0.012823

13.4 295.5 0.8 20 0.3 0.0162884

13.2 295 1.1 20

1.1

0.3

0.313.5 20295

0.0191161

0.0191161

13.5 291 0.5 2 0.3 0.0129763

3.4 0.4 0.3292 0.0115865

4 292 0.6 10 0.3 0.0141905

6 301 2.4 15 1.3 0.0279534

288 0.4 8 0.8 0.0116667

6 301 2.4 5 13 0.0279534

6.5 301 2.4 5 1.3 0.0279534

-1.5 285 0.4 12 0.8 0.0117279

-1.5 285 0.4 12 0.8 0.0117279

-1 285 0.4 12 0.8 0.0117279

-2 289 0.4 7 0.8 0.0116465

-2

1.9 285 0 1 0.5 0

1.5 285 0 1 0.5 0

-27.3 0.5

-10 0.5

-7 0.5

-6 0.5

1 0.5

4 0.5

-21 0.5

-10 0.2

-10 1

3 0.2

-0.5 0.6

-2 0.4

-15 0.4

-13.6 0.5

-15 0.2

-7.8 0.5

-8.3 0.5

-8.6 0.5

-8.8 0.5

-9.3 0.5

-2 1

-1 1

-1 1.5

-1 1

-1 1.5

-2 2

-2 2

-8 1

-10 0.8

-10 0.8

-9 0.8

1.5

1.5

1.5

1.5

0.5

-7

-6.7

1.5

1.5

1.5

1.5

-7

-6.8

285

285

285

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

285

285

275.5

275.5

275.5

275.5

Crosswind Shr Inversionbse.

nds/100m meters

1100

1

1

0.5

0.5

900

0.1

0.3

1

1

1

0.1

1700

1.5

1.5

0.3

0.3

0.3

1100

0.4

0

0

0.4

0

1300

0

0

0

0

0.5

0.5

0.5

1280

0

0.2

1

1

Inversion top Strength

meters deg/100m

1200 2

1100 2

2300 2.4

1300 2

1500 1

1500 1

=

Table 6. Data Summary for Sinking VorticesAl:eam Pen_xati_

FlightNo. Date R_No. NomFltLvl FltLevel IAS _g Orientation WakeOmmaer

Feet rr_ters m/s deg

551 19-Oct-95

6

552 19-Oct-95

Beg. Time End T11m

HMS-GMT HMS-GMT

132743 133000

183433 183650

192808 19294O

115324 115530

165540 165730

170630 170730

Beg. Tn'ne End Turn

HMS-GMI HMS-GMr

133154 134238

183707 184200

192949 193350

115550 115750

165810 165940

170755 171355

5OO0 1540 60 22O I-1W sinldng

5 5000 1540 95 20 TW sink- level

10 2500 775 95 220 HW slow sink

553 26-Oct-95

8 5200 1600 65 290 HW *slow sink

555 6-Nov-95

3 ND0 1450 70 90 TW *sink

4 5000 1450 100 270 HW *sink


OV-10 C130

TKE _WmdMmnWmd MemTernp PotTerrp _Pan_wR/nt MmnW DIh/DZ DDir/I3E _ B-V Cross_indShr

rn2/s3 deg/n-/s deg/m/s C K C rn/s C/100m deg/100m m/s/100m per sec w/gl00m

I

N/A 230/05 Z24/03 11.2 24.9 -27.3 0.5 0.7 20 1 0.015175 1

0.142 195/09 190/03 11.3 25 1 0.5 0.5 1 0.3 0.012823 0.1

0.356 200/02 220/05 13.5 18 3 0.2 0.5 2 0.3 0.012976 0.1

0.156 315/06 300/03 3.4 19 -0.5 0.6 0.4 7 0.3 0.011586 1.5

0.176 270/04 270/03 -1.5 12 -8.3 0.5 0.4 12 0.8 0.011728 0

0.743 3(D/03 270/03 -1 12 -8.6 0.5 0.4 12 0.8 0.011728 0

AVG0.315 AVG 0.47 AVG 0.48 [ AVG0.01267r

Table 7. Data Surnmary for Rising VorticesAbeam

Flight No. Date Run No. Beg. Time End Time

HMS-GMT HMS-GMT551 19-Oct-95

10 141645 141818

552 19-Oct-95

6 184956 185200

7 190044 190150

9 191735 191900

553 26-Oct-95

13 125925 130115

555 6-N3v-95

6 175122 175330


Penetration

Beg. Time End Tir_

HMS-GMT HMS-GMT

141821 142100

185310 185650

190210 190600

191910 192250

130133 130400

175520 175834

INomFlt Lv] Fit Level IAS

Feet n'e_,ters m/s

I5000 1575 90

5000 1530 95

3700 1150 95

3300 1025 95

7000 2225 100

5000 1575 70

Heading Orientation Wake Gaaracter

deg

220 HW slow sink- level

300 XW slow sink- level

120 XW slow sink-rise

50 TW sink-rise-sink

350 XW *steady-rise

70 TW *sink-rise

OV-10

TKE Mean Wind

m2/# aegn4s

0.213 220/07

0.222 200/06

0.17 240/04

0.187 200/04

0.115 260/11.5

0.386 260/04

AVG0.216

C130

MmnV_rd M_aTetrp! PctTearp _E_vPdnt lVlx_W

_/ii1/s c K C m/s

2_03 11 25 -10 0.5

1_0/03 11 25 4 0.5

2A0/05 13.4 22.5 -21 0.5

N1A 13.5 295 -10 1

250/10 6.5 28 -15 0.2

270/03 -2 15 -9.3 0.5

AVG0.533

DINDZ DDir/I3Ei 13f213E B-V

C/103m deg/lOOm rffs/100m _ sec

1 20 1 0.018134

0.5 1 0.3 0.012823

0.8 20 0.3 0.016288

1.1 20 0.3 0.019116

Z4 5 1.3 0.027953

0.4 8 0.8 0.011(67

AVG 1.0331 AVG0.01fi

Sir Inm'simlre. Inx_sicntop _'engthn/gl00m nxters

11oo 1230

deg/100m

21

1100 2

0.3

1

1

1700 2300 Z4

0.3

1100 1300 2

0

Table 8. Data Summary for Wakes with Large OscillationsI Abeam Penetration

Flight No. Date Run No. Beg. Time End Time

HMS-GMT HMS-GMT

556 8-Nov-95

557 9-Nov-95

22

23

24

25

26

27

28

22

23

24

25

Beg. Time End Time

HMS-GMT HMS-GMT

Nora Fit Lvl Fit Level IAS Heading

Feet meters m/s deg

153450 153550 153650 154317 3000

154743 154918 154925 155335 3000

155650 155750 155755 155953 3000

160750 160844 160900 161316 3000

162145 162245 162255 162750 3000

163230 163323 163330 163650 3000

165213 165320 165330 165755 3000

I174103 174200 174245 174603 3800

174925 175040 175045 175300 3800

175730 175843 175847 180055 3800

180642 180725 180732 181019 3800

900 70 300

900 70 120

900 100: 300

900 100 120

900 100 210

900 100 30

900 100 210

1100

1100

1100

1100

70

70

70

70

145

325

65

245

Orientation Wake Character


TW large oscillationsHW large oscillations







XW large oscillationsXW large oscillations

TKE

m2/s 2

0.774

1.2

2.16

0.97

1.27

2.86

0.574

1.29

0.873

0.956

1.47

AVG 1.31

OV-lO

Mean Wind

deg/m/s

308/12

290/10

300/10

290/11

300/10

300/10

312/15

300/10

325/07

300/08

320/10

C130

Mean Wind Mean Temp Pot Temp

deg/m/s C

300/08 1.9

290/12 1.5

300/09 1.5

300/13 1.5

300/10 1.5

281/11 1.5

300/11 0.5

315/08 -7

300/10 -6.7

305/20 -7

320/08 -6.8

K

Mean Dew Point Mean W DTh/DZ DDir/DZ

C m/s C/100m deg/100m

12 -2

12 -1

12 -1

12 -1

12 -1

12 -2

12 -2

1 0

1 0

1.5 0

1 0

1.5 0

2 0

2 0

2.5 -8 1

2.5 -10 0.8

2.5 -10 0.8

2.5 -9 I 0.8AVG 1.22

0

0

0

0

DS/DZ

m/s/100m

1 0.5

1 0.5

1 0.5

t 0.5

1 0.5

1 0.5

1 0.5

1.5 0.5

1.5 0.5

1.5 0.5

1.5 0.5

B-V

per sec

Crosswind Shr

m/s/100m

Inversion bse.

0.5

0.5

0.5

Inver_on top Strength

1280 1500 10

0.2

1

1

meters meters deg/100m

1300 1500 1

0

0

0

Counter

conlroi

Figure l. Wake Vortex Flow Field (from ref. 2)

Flightpath

Levels off in approximately

5 nm in approach configuration

500 to 900 feet

Figure 2. Wake Vortex Descent Rates (from ref. 2)

17

CO

Figure 3. Video Frame of OV-10 Drifting

Behind the C130Figure 4a. Video Frame of OV-10 Level with the

Starboard Vortex

iiiiiii!iiii_iiiiiiii_i

Figure 4b. Video Frame of OV-10 PenetratingStarboard Vortex

Figure 4c. Video Frame of OV-10 Below the Port

Vortex

Cockpit Displays

5-holeProbe

NACA o_,13& Pitot-static

Dew-PointSensor

• Air Data Computers• INU / GPS

/

Air Temp.Sensor

VideoCamera

Stereo WingVideo Cameras

(left & right)

Figure 5. OV-10 Experimental Configuration

19

mWf ZJ:

Figure 6a. Surface Weather Map for October 19,

1995, 1200 GMT

_,_ _. • _.- , -_. _ z_-=_..._,,,

, ,_',_._..,.. ......_,-.-,,ff¢'_.• . !_<_ .,,,,.:_<

_.,:t_ _,/_I,L£'I,._/;I_.._'_"f"s.-"_. ;_.%-:,7"'_,<,Nz".-"..'\.,

I ,)_'" _ ', _ ,7+ 'l>z" '

Figure 6b. 850 Hectopascal Weather Map for

October 19, 1995, 1200 GMT

Bate: 10119195

Time: 1402Z

5000 F _ .:.., ,

_ ..

"°°i"! ..._ •

... SOOOF .........

i ,. .... -

:"

_ P :......

< 2000_ :

"".,..,

tOOO_

-40

¢) •nbw2,.83.asc

lemperature

............ Bee point

.......... Potentlal Iemperature

\k

'\\,

\,%k\

%%

--20

' i

"....

i

0

\\

\

/t

\f /i /\ i

i _o.,

i

#

• i\ t

\k',

',..... :, , < <i ,

20

' 4-4

"i"!"!.-!,

'44-4.-4

, i

4

-4• -I

---t_I

.--4q

40

Temperature (C)

m/s

<'1

1.0-2,5

2,5-5.0

5.0-7.5

\.,

7.5-10.0

10.0-12.5

..._ 12.5-15.0

_ _& .......

15.0.--17.5

1.7.5-20.0

20.0-22.5

22.5.--25.0

>25.0

Figure 6c. Balloon Sounding for October 19, 1995, 1400 GMT

20

•.c 2000 !--- :

i ..

.1.oooF

I,-

Date : I0/19/9_

Time : 1750Z

5000 i.- iI-

I-1-

4000 b

i-3000 _:-.............

_, -_. ..,

'.,.

.... ....

\\\\.

\\

.......... PotentJ.al

I

\

\\

}

k

\\ :

i ;''J(

Tem _erature

Oew point

Tern _erat.ure

t

0 k....t.................................J..................................L....::...................£_ .................................t......

---40 -20 0 20 40

Temperature (C)

nbu2284.1ua

Figure 6d. Balloon Sounding for October 19, 1995, 1750 GMT

E

.qE

Date : 1011gl95 ................... Temperature

............ Dew pointTime: 2046Z................. Potential Temperature

5000 ;....... "r....... ,........ ,........ ,....... _ ....... ,"....... :"'_'" ....... _ ....... :........ "....... _ ....... 1........ r........ r....... ,-....... r,"......,- .:: . \E ...... . ' i_L '_ ,-- ': k

4000 F'" "'" \": \

r- - \3000 F- "

...................... . \

F : \2ooo_ :. t

\

::::::/ --}..... ........

i-

F

I000 k

-40r i I I r i , I ; i

-2O 0

|emper-_ L_re (C)

nbu_tf3._ua

/

t

i

!

i)

.t

/

/

./

/-

i

./

"_-4 , ,

2Oi

40

Figure 6e. Balloon Sounding for October 19, 1995, 2046 GMT

|

7.:"

<

.

<'.I.

1.0-2 ._

2.5-=5.0

5.0--7.5

7.5--'10.0

3.0.0-12.

1.2.5-1.5. o

15.0-17._

17.5--20.0

20.0-22.5

22.5-25. o

"_-.._ .......

> 25.0

m/s

<'I

1.0-2.5;

2.5-5.0

sio--_7.s

7.5-10.0

",,%..........I0.0-12.5

I._. S-.'LS .0

15.0-17. S

17.5-20.0

_\._ .....20.0-22.

22. S-_S. O

._...__...__> 25.0

21

Figure 7a. Surface Weather Map for October 26, Figure 7b. 850 Hectopascal Weather Map for

1995, 1200 GMT October 26, 1995, 1200 GMT

E

It)

::)

Bate: t0126/95

Time: _._31Z

5000_ ......... I ......... I ......... _......... I ......... _......... _........FbF

4000_0.

3000

L

2000 k

k

i000o.

................... Temperature

......... Dew point

.......... PoLen'ti_I Temperaturei

"" _ //

".. \. ."

/"

i \ /

_" J _/

• ! /

....\.,, /

• \ .,.

), ,/: ),

,'-- _. /

p - _ ;.

i , , ..___12"0.......... ......... ........ , i, ; =_j,_.¢ ......... I ......... I ........

-30 -20 --10 0 .10 20 30

Temperature ((')

nb,.,8Ola,usm/sum

i

40

Figure 7c. Balloon Sounding for October 26, 1995, 1131 GMT

\.

\

I

mls

<'1

1.0-2.5

x ......._

2.5-5.O

5.0--7.5

"k2,._._

7.5-10.¢

XX

10.0-12.5

,.,,_____._

12.5-15.0

.15.0--.17.5

\:_ .....

17.5-20.0

20.0-22.5

22.5-25.0

>25.0

22

. • _ ._.,,_.- ._...._ z_?_`'_zx..-_`_--_7_?_?-°_.._::._._°7`._`.._¢?._`_.-_.._._.-_.°:_..._-.?_,_.-.._.._¢_ -

_'"............":-:"::,':;':-._iii _"/ .... _;_""-.:"":'-",':7 -: .......

Figure 8a. Surface Weather Map for November 6,

1995, 1200 GMT

A

Z}

Figure 8c.

Date : 11106/95

T.i.me : .1.7307.

5000

4000

3000

2000

I000

.0

I

:_:. .... @

_..._

!

\\

\k

@[

'. !

\\

4:c" " }_.......,.........:o., z¢

i i i r I

-40 -20

nbu623a.usm/sum

I

TempeY-ature

De,-, point

Potential Temperature

.I

//

/

!

!

/"

/"

/"

/

/

ii

@i

P•. \

X• \

0

il

Z

I , , i ......

20 40

Temperature (C)

Balloon Sounding for November 6, 1995, 1730 GMT

mls

"_ 1.0--2,5

,... 2.5-5.0L,_ %____, 5.0-7.5

:"" 7.5-10.0,--.....

10.0-12.5

"_ I2.5-15.0

.___ _.x .......

___ 15.0-17.5

"_ 17,5-20,0

_" 20.0-22.5

/ 22,5-25.0

-_,.._.......""_ > 25.0

23

_ES_A_;i_MBER 8_ "1995

'_ . K':_.....K ,.. .:.: " '; _-.", \ '_i_,N_.._";a';_.M _-.-......("J:"%;'\"_ ,'_...... •_.. " '._- -':-" ' ,..k ': _ ". _\'X' >.- ; ...... .: " '. l ' :--_' ." _'

_. ._.._ _. • ' _.. _ ,, ",,_,_,",_._• •N. ..-,.. =,..-;,t,, {-• . W. _;.., -... _:

•, _ _ _ ..... , .... .-..:_,., ...!_,...... .,_..,.._...... _,. _, , .,. _.._ ..... .,.

; _%_i.-'.-" .... _ 7i>.'"_'_#{L4"_' ._' ".'.-.'_-:.__-"-- .... ' ,_ " _-:_> _ '_: 4 - ,...... _<o_ :, . _---/. "_--." .......... _: a_ .... ", '.--.+_g ' . 1. ,.,<-,,:............. w .... .... 19 ..5g;_...... _. --,_ __,

• x.:+,,_..x.- {......._!_!_ ;_ eaE -.... _:.,. < -, -. , x.- .......i':.:.:._.:._.?:'_@... _.. 7L. _, '_....... .}'_ "'... _:_.';_:" ,'" . "L_" ',Li g.",'. ".', "_., "

_"<:_.,-%__.,- --..-..'"_ .<*g"-':, .i_'<'_ ..... ,_ , .._-,-.."_L',_i_'_'*"::_ig_i_ - " _:_:"":% "" g _{_"-.2,.......>" ........"_o/ '"',_...'_" =".,>_i":"'+__,_-5._ ....... <,., < , "'-_-_, ._,_;,., ._. ,. ",_:x... ,, :::::.u:..aa,v,.:.'.a....... .... ::2 ....... , , _ , \


1995, 1200 GMTFigure 9b. 850 Hectopascal Weather Map for

November 8, 1995, 1200 GMT

..,-.,.

v

Figure 9c.

5000

4000

3000

2000

1000

0

Date:

Time:

-40

11108195

1600Z

f

\

nbu627a. _sm/sum

.......... Potential!

\%

\\

\\

\ /"-._> t V,

\ ik i

i

I +

, , I:,C,:_;., ._._> ,-20 0

Temperature (C)


Temperature

Oe_ point

Temperature

./

/

2"

_ -

i

' r

2O

m/s

"_'- <'i

1.0-2,5

"_'_ 2.5.--5.0\-%._°.

5.0---7.5

x._.. 7.5-.'[.0.0

_- ...... 10.0-12.5

\4,-- o--. ,.N_

L 12.5-15.0

, --- 15,0-17,5

_-- a7.5-20.0_"'" _-;_C._.....

_. 20,0-22.5

Q-. 22.5-25.0%'. _

> 25.0

24

"' #.

__..:....


1995, 1200 GMT

Figure 10b. 850 Hectopascal Weather Map for

November 9,1995, 1200 GMT

5OOO

4000

3000

v

< 2000

tO00

Figure lOc.

Date : 11/09195 ................... Temperature

Tlme: i843Z ............ De= point.......... PoLen'L.i.BI Temperature

[2.......l.........:.........r.........r........1........._........."........._........"I.........".........:.........:......... f.........' ........_.........

l--

g

-- _ /..... _ > ..'>_

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/.

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.-. _ _, .I'- ":

_. : _ i_- . _-.i

.......,......................................,.................................. .......................................................-40 -20 0 20

Te_per-ature (C.)

nbuG29a, usa/_um


7--.%

'-..

%:"--."-.....

m/.'_

<':1

1.0--2.5

2.5-5.0

5.0-7.5

7.5---I0.0

lO .0-12.5

1.2.. 5-I.5.0

,,_15,. 0.--17.5

"-_-_.,......17.5-20.0

20.0-22. ,_

22.5-25.0

> 25.0

25

16001550

_ _ 1500_ 1450_ 1400

13501300

13:28:00

16001550

_ 1500= • 1450

14oo13501300

14:16:00

16001550

_ 1500

1450"- _ 140013501300

14:40:00

16001550

_ 15oo: • 1450

14oo13501300

14:52:00

551 run 06OV-lO thick C130 thin

1600

._ 1550

150014501400

n,m, 135o....... "" 1300

13:30:00 13:32:00 13:34:00 13:36:00 13:38:00 13:40:00 13:42:00 13:44:00

time of day

551 run 10OV-IO thick C130 thin

I I1 I 2 13 i I _ 4 I , ' I,4"9,

14:18:00 14:20:00

time of day

,nm ,

16oo

1550

15001450140013501300

14:22:00


1600

_- 1550

1500145014001350

i i 1 nm 1.851 T 1300

14:42:00 14:44:00

time of day


1600

_ 1550

15001450140013501300

14:54:00 14:56:00 14:58:00 15:00:00

time of day

Figure 1 l. C130 and OV-10 GPS Altitude for Flight 551 at Run Times Shown

26

b

1600

1550

1500

• 1450

"_ E 1400

1350

1300

18:34:00

552 run 05OV-1- thick C130 thin

1600

I I 1 i, 2 ii 3 Ir4 I 5 I 6 L6:7, nn

18:36:00 18:38:00 18:40:00

time of day

16OO

1550

1500

1450

1400

1350

1300

18:42:00

t550

1500

1450

1400

1350

1300

18:50:00


, , ,I 1 , , ,12 , , , ],3l 14 ..... I 5' / nm

18:52:00 18:54:00 18:56:00time of day

13OO

1250

1200

1150

1100

1050

1000

19:00:00

::3

T 1600

+ 1550

+ 1500

÷ 1450

÷ 1400

÷ 1350

i 1300


, ,I 1 12 ,i3, , , 1,4, ,nrn

19:02:00 19:04:00time of day

552 run 08

1200 OV-lO thick C130 thin1150

1100

1050

1000

1300

1250

1200

1150

1100

1050

.... 1000

19:06:00

95O

900 [1 _ 12 i 3 nm 4

19:08:00 19:10:o0d time of day

1200

1150

1100

1050

1000

95O

9OO

19:12:00

Figure 12. C130 and OV-10 GPS Altitude for Flight 552 at Run Times Shown

27

e

12oo

115o

_ 1100

1050

lOOO.m

950

900

19:17:00


11 i 2 13 14.... is nm19:19:00

1200

1150

1100

1050

1000

95O

9OO

19:21:00 19:23:00time of day

f

900

85O

_ 800

750"- _ 700

650

600

19:28:00

552 run 10

OV-IO thick C130 thin -- 90o

85O

- 800

__"" _ 750- 700

_ 650

I ' I1 j2 13 ,I4 nm 4.8 I l 600

19:30:00 time of day 19:32:00 19:34:00

Figure 12. (continued) C130 and OV-10 GPS Altitude for Flight 552 at Run Times Shown

28

17001650

-8 _ 16oo"_ • 1550

=E 150014501400

11:53:00

a

1700

1650 I

1600

E 15oo14501400

12:07:00

b

2300

2250 I

2200

_ E 21oo20502000

12: 34:O0

C

23OO

2250 1--

2200

21oo2050

2000

12:46:00d

23002250

-8 _ 2200

m 2150"- _ 210020502000

12:59:00

e

__ m

OV-10 553 run 08

I I

1700

1650

16001550150014501400

11:55:00 11:57:00

Time of Day

OV-IO 553 run 09

I I I

1700

1650

16001550150014501400

12:09:00 12:11:00 12:13:00

Time of Day

OV-IO 553 run 11

I I

23OO

2250

2200

2150210020502000

12:36:00 12:38:00 12:40:00

Time of Day

OV-10 553 run 12T 2300

2250.."_.,.._,,,,,'_2200

-_2150

_2100

_2050r _2000

12:48:00 12:50:00Time of Day

OV-IO 553 run 13 2300

2250

22002150210020502O00

13:01:00

Time of Day

13:03:00


29

.8`=

.,e,=_

a

.8`=

.9,=.=.

b

.8.=

.9,=_

C

d

e

1500

1450 I

14001350130012501200

OV-10 555 run 021500

_v______ 1450

1400135013001250

I i 120016:43:00 16:45:00

Time of Day

16:47:00

1500145014001350130012501200

OV-lO 555 run 03

i i I

150O

1450

14001350130012501200

16:55:00 16:57:00 16:59:00 17:01:00

Time of Day

1500145014001350130012501200

17:06:00

OV-10 555 run 04

i i r

17:08:00 17:10:00 17:12:00

Time of Day

1500145014001350130012501200

17:14:00

1700

165o

1600

"._ 1500E 1450

1400

OV-10 555 run 05 1700165016001550150014501400

17:35:00 17:37:00

Time of Day

1700 OV-10 555 run 06

1650

1600_ 1550 "-""-'-----"_'_--__-"•_ 1500

E 14501400 I i I

1700165016001550150014501400

17:50:00 17:52:00 17:54:00 17:56:00 17:58:00 18:00:00

Time of Day


30

L

"t G,

::3 _,

b

c

d

C

1000

900 I800

700

15:12:00

1000

900

800

700

15:24:00

1000

900

800

700

15:34:00

1000

9OO

8OO

70O

15:46:00

1000

9OO

8OO

70O

15:56:00

556 run 20

OV-IO thick C130 thin lOOO

600

700

15:14:00 15:16:00 15:18:00 15:20:00time of day


i l 1 ,I 2 , , i 13 I ,I4 , ,rim , ,

15:26:00 15:28:00 15:30:00time of day

1000

900

800

, , , 700

15:32:00


i i1, t 12 i I 3[ i 4

15:36:00 15:38:00 15:40:00 15:42:00time of day

lOO0

9OO

800

nm 7oo

15:44:oo

556 run 23


9oo800

Ir1 I 700omE15:48:00 15:50:00 15:52:00 15:54:00

time of day

556 run 24


800

i1 C ' ,r2, , , 13 , , , q4, nm 700

15:58:00 16:00:00

time of day


31

1000

900

80O

7OO

16:06:00

556 run 25

OV-IO thick C130 thin

, , , 1,1.... 12 , , _t3, , ,p4 , , ,F5 , ,li6, , I, 7 , ,I8 .....

16:08:00 16:10:00 16:12:00time of day

1000

I90080O

nm 700

16:14:00

g

1000

900 I800

700

16:20:00

556 run 26

OV-lO thick C130 thin /_ t lOOO

_ _ 900

r ],1 p2 , i ' ,i3 , , i,4 .... i5 _ , , _6 , ,nm, ,_ 7,_._ , 700

16:22:00 16:24:00 16:26:00 16:28:00time of day

h

1000

900

556 run 27

OV-IO thick C130 thin

8OO

700 I 1, , _I 2 , , ,I 3 , 14 , , ,I § , 1,6 , ,nm

16:32:00 16:34:00 16:36:00time of day

1000

9OO

80O

7OO

16:38:00

556 run 28

lOOO OV-IO thick C130 thin lOOO

°° ooI i oo-_ _ 800 800

700 1,1 Hi2 , , b3 p4 4,5 _ , , I 6, , J7 ,nm , _,8 700

16:52:00 16:54:00 16:56:00 16:58:00i time of day

Figure 15. (continued) C130 and OV-10 GPS Altitude for Flight 556 at Run Times Shown

32

b

C

d

557 run 22

OV-IO thick C130 thin1200

1150 I'-- __

1 lOO ---_-_

N _ 1000950900 lil I

17:41:00 17:43:00 17:45:00

time of day

12001150110010501000

nm 950900

17:47:00

557 run 23

OV-lO thick C130 thin

1150 115011oo -- ,-, 11oo:} 1050 1050"_ _ 1000 1000

950 950900 900

17:49:00 17:51:00 17:53:00

time of day

"_ E

12001150110010501000

950900

17:57:00

-- i

557 run 24

OV-lO thick C130 thin1200

I150

__ 1100

_ lO5O1000950

,I 1 12 nm 900

17:59:00 18:01:00

time of day

12001150110010501000

95O9OO

18:06:00

557 run 25

OV-lO thick C130 thin

i I 1 ,I 2 i nm

18:08:00 18:10:00

time of day

1200115011001050100095O9OO

Figure 16. Cl30 and OV-10 GPS Altitude for Flight 557 at Run Times Shown

33

I.O

Figure 17. Video Frames From Different Times of the C130 Wake Vortex Smoke Signature

REPORT DOCUMENTATION PAGE Form ApprovedOMB No. 0704-0188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,

gathering and maintaining the data needed and completing and reviewing the collect on of nformat on Send comments regard ng th s burden est mate or any other aspect of thiscollection of information, including suggestions for reducing this burden to Washington Headquarters Services, D rec orate for nformat on Operat ons and Reports, 1215 Jefferson Davis

Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of _l'anagement and Budget, Paperwork Reduction Project (0704-0188). Washington, DC 20503.

1. AGENCY USE ONLY ( Leave blank) 2. REPORT DATE 3. REPORTTYPE AND DATES COVERED

April 1997 Contractor Report4. TITLE AND SUBTITLE

Documentation of AtmosphericConditionsDuringObserved Rising AircraftWakes

6. AUTHOR(S)

J. Allen Zak, Vigyan, Inc.William G. Rodgers, Jr., Lockheed Martin Engineering and Sciences

!7. PERFORMINGORGANIZATIONNAME(S)ANDADDRESS(ES)

Lockheed Martin Engineering & Sciences

Langley Program Office

Langley Research Center, Mail Stop 371Hampton, VA 23681-0001

9. SPONSORING/ MONITORINGAGENCYNAME(S)ANDADDRESS(ES)

National Aeronautics and Space AdministrationLangley Research CenterHampton, VA 23681-0001

5. FUNDING NUMBERS

C NAS1-96014

538-04-11-11

8. PERFORMING ORGANIZATION

REPORT NUMBER

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA CR-4767

11. SUPPLEMENTARY NOTES

Langley Technical Monitor: BurnellT. McKissick

12a. DISTRIBUTION / AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Category 47

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

Flight tests were conducted in the fall of 1995 off the coast of Wallops Island, Virginia in order to determinecharacteristics of wake vortices at flight altitudes. A NASA Wallops Flight Facility C130 aircraft equipped withsmoke generators produced visible wakes at altitudes ranging from 775 to 2225m in a variety of atmosphericconditions, orientations (head wind, cross wind), and airspeeds. Meteorological and aircraft parameters werecollected continuously from a Langley Research Center OV-10A aircraft as it flew alongside and through thewake vortices at varying distances behind the C130. Meteorological data were also obtained from specialballoon observations made at Wallops. Differential GPS capabilities were on each aircraft from which accuratealtitude profiles were obtained. Vortices were observed to rise at distances beyond a mile behind the C130.The maximum altitude was 150m above the C130 in a near neutral atmosphere with significant turbulence. Thisoccurred from large vertical oscillations in the wakes. There were several cases when vortices did not descendafter a very short initial period and remained near generation altitude in a variety of moderately stableatmospheres and wind shears.

14. SUBJECT TERMS

Aircraft wakes; Wake vortex; Flighttests; Wake decay research flights;Rising vortices;Atmospheric conditions;Wind shear

17. SECURITY CLASSIFICATIONOF REPORT

UnclassifiedNSN7540-01-280-5500

18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION

OF THIS PAGE OF ABSTRACT

Unclassified

15. NUMBER OFPAGES

40

16. PRICE CODE

A03

20. LIMITATION OF ABSTRACT

Standard Form 298 (Rev. 2-89)

Prescribed t_y ANSI Std. Z39-18

298-102

36

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