Report No. RD.64-157

FINAL REPORTProject No. 320-205-02X

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PMITED SURVEY OF COMMERCIAL JET AIRCRAFTALTIMETER SYSTEM POSITION ERROR

BY PACER WITH TRAILING CONECOPY '- F O

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FEDERAL AVIATION AGENCYSystems Research & Development Service

Atlantic City, New Jersey

FINAL REPORT

LIMITED SURVEY OF C(•MMERCIAL JET AIRCRAFT ALTIMETERSYSTE4 POSITION ERROR BY PACER WITH TRAILING CONE

PROJECT NO. 320-205-02X

REPORT NO. RD-64-157

Prepared by:

Jack J. Shrager

December 1964

This report has been approved for general availability. It doesnot necessarily reflect FAA policy in all respects and it doesnot, in itself, constitute a standard, specification or regulation.

jJose tD. BlattDi r, Systems Research

-and Development ServiceFederal Aviation Agency

Experimentation DivisionNational Aviation Facilities Experimental Center

Atlantic City, New Jersey

TABLE OF CONITENTS

Page

ABSTRACT .... . . . . . . . . . iv

INTRODUCTIONE . . . . . . . . . . . . . . . . . . . . . . . . 1TEST PROCEDURE .. .. .. .. .. .. .. .. .. .. . . .

TEST EWJIPMENT . . . . . . . . . . . . . . . . . . . . . . . 3

Pacer Aircraft . . . . . . . . . . . . . . . . . . . . 3

Test Aircraft . . . . . . . . 5

Ground Test Site . . . . . . 5METHOD OF ANALYSIS . . . . . . . . . . . . . . . . . . . . . 5

TEST RESULTS . . . . . . . . ........ 7

CONCLUSIONS & RECOMMENDATIONS ........ ...... 8

S.... .i

LIST OF ILUJSTRATIONS

:Lgure Page

i Pacer Aircraft's Photopanel ...... ........... 2

2 Fixed Geometry Trailing Cone Assembly .... ...... 4

3 Sea Level Calibration of Trailing ConeSystem ........... ..... .................... 6

4 Apparent Position Error Versus IndicatedAirspeed - 727 Aircraft (a) ...... .......... 9

5 Apparent Position Error Versus IndicatedAirspeed - 727 Aircraft (b) ...... ......... 10

6 Apparent Position Error Versus IndicatedAirspeed - 727 Aircraft (c) ...... .......... 11

7 Apparent Position Error Versus IndicatedAirspeed - 720 Aircraft (a) . .......... 12

8 Apparent Position Error Versus IndicatedAirspeed - 720 Aircraft (b) ...... ......... 13

9 Apparent Position Error Versus IndicatedAirspeed - 720 Aircraft (c) ...... .......... 14

10 Apparent Position Error Versus IndicatedAirspeed - 720 Aircraft (d) ...... .......... 15

11 Apparent Position Error Versus IndicatedAirspeed - 720 Aircraft FAA (N113) ...... ... 16

12 Apparent Position Error Versus IndicatedAirspeed - Caravelle Aircraft (a) ......... ... 17

13 Apparent Position Error Versus IndicatedAirspeed - Caravelle Aircraft (b) ..... ..... 18

14 Apparent Position Error Versus IndicatedAirspeed - 990 Aircraft (a) ... .......... ... 19

15 Apparent Position Error Versus IndicatedAirspeed - 990 Aircraft (b) ...... .......... 20

ii

LIST OF ILLUSTRATIONS (continued)

F igure Page

16 Apparent Position Error Versus IndicatedAirspeed - 880 Aircraft. . ......... . 21

17 Apparent Position Error Versus IndicatedAirspeed - 70T Aircraft .... .............. 22

18 Comparison of Statistically-DerivedPosition Error Versus Indicated Airspeed-727 Aircraft . . . . . . . . . . . . . . . . . 23

19 Comparison of Statistically-DerivedPosition Error Versus Indicated Airspeed-Aircraft Pilot's System . . . . . . . . . . . . 22

20 Comparison of Statistically-DerivedPosi'tion Error Versus Indicated Airspeed-720 Aircraft Copilot's System . . . . . . . . . 25

21 Comparison of Statistically-DerivedPosition Error Versus Indicated Airspeed-Caravelle Aircraft . .......... . . .0 26

22' Comparison of Statistically-DerivedPosition Error Versus Indicated Airspeed-990 Aircraft ........................... . 27

23 Composite of Maximum Statistically-DerivedPosition Error Versus Indicated Airspeed-All Aircraft .... ............ . . . . .. . 28

iii

Federal Avi.ation Agency, Systems Research and Development Service,National Aviation Facilities Experimental Center, ExperimentationDivision, Atlantic City, N. J.LIMITED SURVEY OF COMMERCIAL JET AIRCRAFT ALTIMETER SYSTEM POSITIONERROR BY PACER WITH TRAILING CONE by Jack J. Shrager, Final Report,December 1964, 33 PP. including 23 illus.(Project No. 320-205-02X, Report No. RD-64-157)

ABSTRACT

Limited flight tests were conducted using the trailing conestatic pressure measuring technique to determine the repeatabilityof commercial jet aircraft altimeter systems. The maximumdifference between the six types tested at 30,000 feet was 500feet.

iv

INTROIDCTION

report is concerned with limited tests conducted by SRDSto determine the apparent repeatability of the static pressureportion of a commercial Jet aircraft's airspeed system,

The purpose of these tests was to establish the differencebetween the indicated pressure altitude and true ambient pressurealtitude at nominal cruise altitude. The tests were to include 3aircraft of 13 different operational and commercial type Jets, a"total of 39 airplanes.

The tests were conducted in the vicinity of the FAA's NationalAviation Facility Experimental Center (NAFEC), Atlantic City, NewJersey, Aeronautical Center, Oklahoma City, Oklahoma, and MiamiInternational Airport, Miami, Florida.

TEST PROCEDURE

The procedure employed for these tests was a tower pass and amodified pacer method.

'The tower pass technique involved the test aircraft making lowaltitude passes over a vertically aimed aerial camera set up on theground. The differences between indicated and computed altitudewere determined as described in'detail in SRDS Report No. RD-64-3T.This procedure was also used to verify the sea-level calibrationcharacteristics of the calibrated TV-2 pacer and trailing cone.

The modified pacer technique with trailing cone was as follows:

1. The pacer aircraft flew in close formation but out of theaircraft generated turbulence with the commercial Jet during thelow-level tower passes. At the instant of passing over the groundcamera, a reading of the pilot's and copilot's airspeed and alti-meter, using the primary static source was made. At this instant,upon radio command, a picture of the photopanel shown in Fig. 1was made.

2. At the completion of the low-level phase of the tests,the large Jet and the pacer climbed to the test altitude underpositive air traffic control.

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3. Readings of the pilot's and copilot's instruments andphotographs of the TV-2 photopanel were taken at severel differentspeeds from minimum controllable in the clean configuration of thecommercial jet transport to maximum continuous speed of the TV-2pacer.

4. To obtain data above the limiting speed of the pacer, thelarger jet would reduce speed to allow sufficient horizontal dis-tance between the pacer and the slower moving large jet foracceleration. At all times during these procedures, visual contactbacked up by positive radar control was maintained. When sufficienthorizontal separation was attained, the commercial jet aircraftaccelerated to the fIrst test speed which was in excess of the TV-2capability. Upon attaining the desired test speed, the large jetsteadied out in straight, level, unaccelerating flight at the japparent visual altitude of the TV-2 pacer. Upon overtaking thepacer In very close horizontal and vertical proximity, the pilot'sand copilot's airspeed, altitude readings, and TV-2 photopanel wererecorded.

5. Tfnis procedure was repeated for several different flightspeeds up to the maximum coutinuous speed of the larger aircraft.

6. These runs were made in ascending and descending speedintcrements after which the aircraft returned to the airport foradditional low-level tests and landing.

In the tests involving the FAA's Boeing 720, a trailing conesimilex to that ased with the W_-2 pacer was mounted in the tailconp of the .lrLSig 720. The length of trail waz approximately12C) feet.

TEST EQUIPMENT

Pacer Aircraft

A light-weight, high-drag fiberglas cone, Fig. 2, was attachedto a hollow nylon tube. Inserted in the nylon tube approximately10 feet foar--ard of the cone was a stalinless steel tube with threesets of perpendicularly drilled static ports. A 1/32-inch pianowire was threaded through the nylon tubing to carry the drag loadsof the cone and tubing assembly. The anchor point for the tubingassembly waa i :otor-diven reel installed internally on the under-side of the fuselage cf the 1-V-2. Through cockpit-located controls,it was possible to extend or retract the cone assembly up tod.istances of 40 feet behind the 1J-2 Ihile in flight.

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The aircraft end of the tubing was led to a high-precision,servo-driven pressure transducer and a selected low-hysteresisaneroid altimeter. These instruments along with the others shownin Fig. 1 were mounted on a rack which replaced the rear seat ofthe TV-2. All the instruments were photographed by a high-speedmotion picture camera operated by the pilot.

In the case of the trailing cone installation on the Boeing720, the cone trailed approximately 120 feet behind the FAA's 720and was not retractable. In this particular case, the aircrafttook off and landed with the cone assembly extended.

Test Aircraft

The individual carriers selected standard aircraft altimetersand airspeed indicators which exhibited good repeatability and lowhysteresis and replaced the aircraft's normal instruments with thesetest instruments. The airspeed system was then checked to assurepressure integrity. During all flight tests, the altimeter settingregardless of altitude was 29.92" Hg.

Ground Test Site

The equipment at the ground test site included the following:

1. Precision aerial camera Type T-11.

2. Aneroid barometer of the weather bureau type.

3. Aspirating wet and dry bulb thermometers.

4. Portable transceiver.

This equipment is described at greater length in the SIDSReport No. RD-64-3T.

METHOD OF ANALYSIS

The methods employed to determine the difference betweenindicated pressure altitude and computed pressure altitude for thelow-level tests are described in &DS Report No. RD-64-37.

The method employed for determining this at altitude was thedifference between the calibrated trailing cone static syst~m andthat indicated by the test aircraft pilot's and copilot'sinstruments. The performance and calibration of the trailing conesystem are discussed in SRDS Report No. RD-64-156. Figures 3a and3b indicate the nominal position error of the trail cone system asalso noted in the above referenced report. The repeatability of

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bration method which, in the case of NAFEC, was + 0.004" lfg.(+ 0.125mb) and the equivalent of + 0.005" hg. (T O.169rb),respectively. Tbe resultant differences were statisticallyanilyzed through a least squares and linear regression analysisto establish the best fit straight line for the actual datapoints.

The method of analysis noted above\ncorporates the followingassumptions: 1, j

1. The instrument errors of the selected carrier instrumentswere of small enough magnitude to be disregarded.

2. The geometric difference in height between the test Jaircraft and pacer during the overtake portion of the tests weresmall enough to disregard.

3. The atmospheric conditions at altitude during the testperiod were constant.

The calibration of the pacer - trail cone - specialinstrumentation system was validated during the low-level flightswhich immediately preceded and followed the altitude tests.

TEST RESULTS

Figures 4 through 17 indicate the differences between theindicated altitude of the test aircraft pilot's and copilot'saltimeter reading, and the calibrating pacer's trailing cone-sensed pressure altitude expressed in feet versus the pilot'suncorrected indicated air speed for each test point. Thealtitude at which the data was obtained is indicated in thelegend of each figure in terms of thousands of feet representedby the letter I"V, such as 31K - 31,000 feet. The differencebetween the pilot's and copilot's altimeter calibration, whereknown, was applied as a correction to the copilot's altimeterreading. The straight line drawn through these points is theleast squared derived first degree fit of all data points shown.

In most cases, the pilot's and copilot's systems exhibitedsimilar slopes which could differ by as much as 100 feet, asnoted on Fig. 5. This difference can be due only to "positionerror" by the defined method of analysis.

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Figures 18 through 23 indicate the differences in the slopesfor each of the aircraft types tested. The maximum differencebetween aircraft of a given type at 30,000 feet was 450 feet, asnoted in Fig. 18.

Figure 23 is a composite noting the maximum differencebetween all aircraft types tested incorporating both the pilot'sand copilot's systems. The maximum difference between the severalsystems was 500 feet.

CONCLUSIONS & RECOMM ENDATIONS

It is noted that only 15 of the desired 39 aircraft weretested due to the non availability of the commercial jet aircraf+.

Due to the limited nature of the data, therefore, no technicalconcluloion can be drawn and, accordingly, no recommendationsbased on present data can be made.

REFERENCES

1. Shrager, Jack J., "Calibration Static Pressure Systems at LowAltitudes", March 1964, Project No. 115-22N, Report No. RD-64-37Experimentation Division, Systems Research and DevelopmentService, Federal Aviation Agency, Atlantic City, New Jersey

2. Shrager, Jack J., "Test of Trail Cone System to Calibrate StaticPorts for Barometric Altimeters", Project 320-205-02X, Report No.RD-64-156, Experimentation Division, Systems Research andDevelopment Service, Federal Aviation Agency, Atlantic City, N. J.

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