014182-1-T THE UNIVERSITY OF MICHIGAN COLLEGE OF ENGINEERING DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING Radiation Laboratory FREE SPACE EC-135 SCALE MODEL MEASUREMENTS by V.V. Liepa and D. L. Dusette Task Report No. 1, Contract F29601-76-C-0004 (5 August 1975 - 31 January 1976) Prepared for: z< Air Force Weapons Laboratory ^ Kirtland Air Force Base f/ / New Mexico 14182-1-T = RL-2266 Ann Arbor, Michigan

1 1. INTRODUCTION This is the first of the series of Task Reports on Contract F2 9601-76-0004 entitled "Aircraft Scale Model Measurements and Scaling Verifications" and presents the measured surface current and charges on model EC-135 aircraft simulated in the free space. For these measurements, topside incidence was always used and the incident wave had, depending upon a particular measurement, either symmetric (incident electric field parallel to the fuselage) or anti-symmetric polarization. The laboratory measurements were made in 1.0 to 4.0 GHZ frequency range which for 1/447 to 1/114 scale model aircraft used correspond to 2.3 MHz to 35 MHZ (full scale) frequencies. However, in this report data is presented only up to 20 MHz. Measurements are presented for models with and without attached HF wire antennas connected between the top of the fuselage (near cockpit) and the vertical stabilizer. 2. MEASUREMENTS 2.1 Facility and Equipment The data presented herein was measured in our surface field measurement facility. The equipment and procedures used were essentially those described in AFWL-TR-75-217.' Figure 1 shows the basic block diagram of the facility, which, in turn, can be generalized in three basic groups, i. e.: 1. The anechoic chamber 2. The sweep r. f. source (sweep generator, power amplifier, isolator, and antenna), and 3. The receiving and recording equipment (sensors, preamplifier, phase shifter, network analyzer, analog X-Y recorder, and CRT display). 2.2 Models For measurements presented here, seven models ranging in scale from 1/114 to 1/447 were used. They all were purchased as some versions of Boeing 707 models and when related to EC-135 dimensions they do not generally have the same length and Valdis V. Liepa, "Sweep Frequency Surface Field Measurements", University of Michigan Radiation Laboratory Report 013378-1-F. AFWL-TR75-217, 1975.

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3 wingspan scale. In translating the measurement frequencies to full scale frequencies the length scale factors were used for case of symmetric excitation and the wingspan scale factor used for the anti-symmetric excitation. The refueling booms, cut out of wood, were added on all models; the booms as well as the entire non-metallic plane models were then spray painted with a conductive silver paint. Cockpit and fuselage windows were also painted and the landing gear doors and fuselage-wing joints (for metal models) were taped with conductive aluminum or copper tape. Table 1 presents relevant dimensions and other description of the models used. On some models HF wire antennas were installed. These were made of No. 30 wire and installed per specifications as given in Figure 2. Note, both wires are electrically shorted at front but on the vertical stabilizer the upper one is shorted and the lower one is open. (The open circuit condition was obtained by using a section of string, approximately 1/16 inch long.) 2.3 Sensors The measurements were made with so-called hard lead probes: the surface currents were measured using a bent 3.2 mm diameter shielded loop probe (c. f. Figure 18 of TR-75-217) and the charge measurements were made using an extension of the center conductor of a 0. 020 inch diameter coax. This extension or monopole was typically 0. 060 inches and the cable was always brought to the surface from within the model. For the charge measurements on the nose of the aircraft, a hole in a model was drilled from nose (STA: F130i into the front landing gear cavity. The sensor lead was then brought out from there and taped along the belly of the plane up to STA: F800B from where it was removed in a direction normal to fuselage and parallel to the direction of propagation of the incident wave. In the case of the wingtip charge measurements at STA: W940T the cable again joined the model at STA: F800B from where it was taped along the und the deri f th ing and passed to the top through a 0. 025 inch diameter hole drilled through the wing. The locations of body station numbers are given in Figure 3. The letter F (or W) in front of the number refers to fuselage (or wing) location, while the T (or B) after the number designates the top (or the botton) of the aircraft.

TABLE 1: EC-135 Models Used Wing Wing With Without EC-135 Fuselage Span Material Fuselage Height at Stationing Wth Wihout d 1 Span Thicknessi HF HF Model Scale cale 400 800 1200 at W600 Wires Wires 447 1/447 j 1/466 metal 0.93 cm 0.94 cm 0.86 cm.17 cm X X 325 1/325 1/341 metal 1.15 1.19 1.15.23 X X 224 1/224 1/225 metal 1.80 1.77 1.76.28 X 129 1/129 1/134 plastic 3.01 3.03 3.02.59 X 114 1/114 1/117 plastic 3.50 3.44 3.35.30 X

Liaison #1 Probe?.adc.r Beacon WL582.75 AS-52/A \ Fin STA 174 en ARN-72 ANT #lat 741/A STA 4 30 A-19-y51 /ARC-96 Liaison #2 Probe ARR-71 #1-4 Left Wing BL740 AT-1076A/A Liaison #3 Probe STA 450 Right Wing BL740 Figure 2: EC-135 HF Wire Antenna Installations

Itoo I. 1600 1400 WING STATIONS 1200 STATiON S BODY STATIONS 400 200 BODY BUTTOCK LINES 0 Note: Stations W600 and W940 are at midsections of the wing. Station W940 is located at the center of a circle tangent to the three wing edger. Figure 3: EC-135 Aircraft Body Stations; X Designates Measurement Locations

7 For current measurements an external B-dot sensor or current loop probe was used. It touched the model only at the point of measurement and even there it was separated by a small dielectric epoxy bead. Since the incident field was always horizontally polarized, the incident electric vector was always perpendicular to the sensor lead thus providing minimal interactions with the incident field. 2.4 Reduction of data When current or charge data for a given frequency scan is recorded on graph paper by X-Y recorder, it shows only very slight resemblance to what one would expect for the given case. Due to non-uniform frequency response of the measurement facility the raw data must first be normalized to the incident field which is obtained by measuring the corresponding field with the same sensor on a 3. 133 inch and/or 6. 0 inch diameter sphere(s). Data is read off from these curves typically at 100 MHz intervals (recall measurements are made in 1 - 4 GHz range) and reduced manually using an electronic pocket calculator and a sharp pencil. Where applicable, corrections for probe integration effects for current and charge measurements are applied. These corrections have maximum effect on the smaller scale models where, in certain cases, current amplitude is increased by as much as 33 percent and charge by 60 percent. 3. DATA The measured surface current and charge data normalized to full scale frequencies are presented in figures 4 through 27. When amplitude and phase data are presented, Figure XXa contains amplitude data whileFigure XXb contains corresponding phase data. This data is relative to the phase of the incident field at the particular measurement stations. Also it will be helpful to note that the even figure numbers contain data for models without HF wire antennas, while the odd figures contain data for models with HF wire antennas. Table 2 summarizes the data presented. Its main purpose is to provide a selection guide to find quickly a particular data. For example, if neecded a current

8 amplitude on top of the fuselage, with HF wires, station 800, anti-symmetric excitation - go to line designated F800T (Fuselage, 800, Top) and then across the table to select the appropriate case. In this case it would be Figure 23a. The graphs presented should be self-explanatory. The sketch insert in the upper hand corner gives immediate information on incidence, incident polarization, and the measurement location. The field values are relative to the incident field and are plotted on a linear scale. Many figures have two or even three curves over the same frequency range. Such data overlapping resulted when different scale models were measured over extended frequency range, and since each represents a different and independent measurement, the spread of data values should be indicative of the measurement accuracy for the particular body station and frequency.

TABLE 2: Data Selection Chart Station EC-135 without HF wires EC-135 with HF wires Number Symmetric Anti-Symmetric Symmetric Anti- Symmetric J Q J Q J Q I Q F400T 4a, b 5a, b F800T 6a, b 22a, b 7a, b 23a, b F1200T 8a, b 9a, b F400B3 10 11 F800B 12 24 13 25 F1200B 14 15 W600T 18a,b 19a,b W600B 20 21 F130 16 17 W940T 26 27 Note: When Figures a and b are specified, a designates amplitude and b designates phase. Otherwise, only amplitude is presented.

I Ii l I.......l I II I I I Ei STA:F400T 10 Without HF Wires Amplitude 1/224 H/Hj 1/447 1/114 d-/ '! 5 1 \/ \. / 0 5 10 15 20 Frequency (MHz) 0' Figure 4a: Current Density at STA:F400T, Symmetric Excitation, without HF Wires

I I 0 I I I 1001 Im- Ei A k STA:F400T Without HF Wires Phase (degrees) 0 -100 1/447 1/224 1/114 N OA oz -, %\ N.y,>z% N ll 14 0 I I a a 0 5 10 Frequency 15 20 (MHz) Figure 4b: Current Phase at STA:F400T, Symmetric Excitation, without HIF Wires

15 -,- --- - - ---- a I I 1 - E ^ k STA:F400T With HF Wires 10 - Amplitude |H/HI 1/447 1/224 r I 1/114 51L \\-. \ \ -.N. A N - AO I I II I I I 0 5 10 Frequency (MHz) 15 20 Figure 5a: Current Density at STA:F400T, Symmetric Excitation,with HF Wires

I a I I I 100 i -— E iTT hI Phase (degrees) STA:F400T With HF Wires 1/447 O k 1/114 / / / X,.l,! **.. %%6 -N,_ -- -. N -100 - I I I I,,.a.I...., u 5 10 Frequency (MHz) 15 20 Figure 5b: Current Phase at STA:F400T, Symmetric Excitation,with HF Wires

_ I __ __ __ _ _ I __ 15 I I I Ei k STA:FbOOT 10 1 1/447 Without HF Wires Amplitude IH/H'1 1/224 5 \ 1/114 \ s'\ / ~; l, \1..1 I..0 - I l I 0 5 10 15 20 Frequency (MHz) P —A 4-. 0 Figure 6a: Current Density at STA:F800T, Symmetric Excitationwithout HF Wires

!!! Ei A k 100 Phase (degrees) - -— C STA:F00T Without HF Wires 1/447 1/114 / 01 - C.n N^ / / '^/ 1/224 -100 M I I I 0 5 10 Frequency (MHz) 15 20 Figure 6b: Current Phase at STA:F800T, Symmetric Excitation without HF Wires

15 I, - a a I I I E A k STA:F800T 10 With HF Wires Amplitude I H/Hi f A 1/447 I V 1/224 121/114 \ \\ I I 0 5 10 15 20 Frequency (MHz) Figure 7a: Current Density at STA:F800T, Symmetric Excitation,with HF Wires

100 EF1 k ~ STA:F800T With HF Wires 1o/1I14 Phase (degrees) -1/447 oI.~ 24 (17.000-leN.-4 -- N' \\ I -100 1 - I I I I I -0 0 5 10 Frequency 15 20 (MHz) Figure 7b: Current Phase at STA:F800T, Symmetric Excitation with HF Wires

30 - - I I I i rk k 20 1 1/447 Amplitude H/Hi STA:F 1200T Without HF Wires 1/114 /' 0O 10 r 1/224 A i I I L t' |,i r! * ~~I I II U ~, lk1 - 0 5 10 Frequency (MHz) z) Figure 8a: Current Density at STA:F1200T, Symmetric Excitation,without IIF Wires

__ ___ __ _ _ __ I _I I I l Ei A 100 k Phase STA:F1200T (degrees) r Without HF Wires 1/447 1/224 o. 1/114 % I\ -. \ 0\ / -100 0 5 10 15 20 Frequency ( MHz) Figure 8b: Current Phase at STA:F1200T, Symmetric Excitation,without HF Wires

_ __ _ _ I _ _I 15 I I I E1. 1/447 STA:F1200T 0 With HF Wires Amplitude jH/H1 5 1/224 \ 114 _/ \ / 0 5 10 15 20 Frequency (MHz) Figure 9a: Current Density at STA:F1200T, Symmetric Excitation,with HF Wires

a a I I I 100 Phase (degrees) 1/447 E 'Fk STA:F1200T With HF Wires I I I I I ' i /\ \ 0 O 1/224 - / / 1/114.J 9'4 '4 a.41% 4 ft1 I I -100 I I I / / x I I....I I u 5 10 Frequency Figure 9b: Current Phase at STA:F1200T, Symmetric 15 (MHz) Excitation,with HF Wires - - -A 20

_ _1 __ I I I E 6 A k STA: F1400B 1/325 Without HF Wires 4 Amplitude/ I"i/ / 1/129 0 I I 0 5 10 15 20 Frequency (MHz) to3 Figure 10: Current Density at STA: F400B, Without HF Wires, Symmetric Excitation

15 10 a..... I I I r E ^1 —\ k STA:F400B With HF Wires Amplitude H/H1 5 - n 1/447 / 1/224 / N\\ K.\. \ j '3-.. ro4 1/114 \UA- \ X -/ \SL0.00 \-~%W I.I..... u( 5 10 15 Frequency (MHz) Figure 11: Current Density at STA:F400B, Symmetric Excitation,with HF Wires 20

m --- - - I I E A 6 k STA: F800B p.. Without Wires Am plitude |H/H1 4 1/325 2 0 5 10 15 20 Frequency (MHz) Figure 12: Current Density at STA: F800B, Without HF Wires, Symmetric Excitation

15 v I- - - - - -- - - -- --,- - - -- I I I A STA: F800B With HF Wires 10 Amplitude IH/Hi 5 1/447 1/224 /0 \\r 5 CI 1/114 - / I I _- _- '- I ~L-' _- _ -- ~_ _ --- -. - _ -_- -. 0 0 5 10 Frequency 15 20 (MHz) Figure 13: Current Density at STA:FbOOB, Symmetric Excitation,writh HF Wires

I I I I.E k 20 ^ STA: F1200B Without HF Wires Amplitude il/Hi 10 1/325 I/:129 0 L --- —-'I -- 0 5 10 15 20 Frequency (MIIz) Figure 14: Current Density at STA: F1200B, Without IIF Vires, Symmetric Excitation t)

uV I. - I I 1 I I,, --- Ei STA:F1200B With HF Wires Amplitude H/HM I n i, 1/447 10 \ 1/224 1/114 0 5 10 15 20 Frequency (MHz) Figure 15: Current Density at STA:F1200B, Symmetric Excitation,with HF Wires

- --- I I I I sensor E 60 A STA.:F130 1/325 'Without HF Wires 40 Am plitude E /Ei l 1/129 20 o \.- 00 5 10 15 20 Frequency (MHz) Figure 16: Charge Density at STA:F130, Symmetric Excitation,without HF Wires

I -- I E sensor A k S100 "STA:F130 With HF Wires Am plitude En/Ei 1/325 50 1/114 N /0 0 5 10 15 20 Frequency (MHz) Figure 17: Charge Density at STA:F130, Symmetric Excitation, With HF Wires CD

I I I I I Ei 10 STA: W600T Without IIF Wires Amplitude IH/H1 1/3 1 5 1/134 I\ '/ 0 5 10 15 20 Frequency (MIIz) C.) Figure 18a: Current Density At STA: W600T, Without II F Wires, Anti-symmetric Excitation

I I I I I I A k 50 Phase (degrees) 1/341 STA: W600T Without HF Wires 1/134 0 - I / -_/ N #01N 01 N%," %.-0 / / -50 1 I I I I I I 0 5 10 15 20 Frequency (MHz) Figure 18b: Current Phase at STA: W600T, Without HF Wires, Anti-symmetric Excitation

I- I - - - - -I I I I I E 1/466 STA: W600T W Vith HF Wires Amplitude 4 |H/Hi 1/225 1/117 1' 2 (/,-, I -. - 0 05 10 15 20 Frequency (MHz) Figure 19a: Current Density at STA: W600T, With HF Wires, Anti-symmetric excitation

-- 5- -- I l i E 50 Phase (degrees) 0 -50 0, k 1/466 STA: W600T With HF Wires 1/225 c.A I 1^\ / 9 I I I I \ /A / 1/117 / I "I I I,..a I. i., 0 5 10 15 20 Frequency (MHz) Figure 191b Current Phase At STA: WA600T, With HF Wires, Anti-symmetric Excitation

A ` -- - - I —~ I I 6 - i A k STA:W600 B Without HF Wires 4 Amplitude H/Hi 1/341 2 1/134 %. t -, - opm O %/.. 1-...-. N%., %0./ I I 0 I I I ---- --- -- I --- -- 0 5 10 Frequency 15 20 (MHz) Figure 20: Current Density at STA:W600B, Anti-symmetric Excitation, Without HF Wires

_ 1 __ ___ __ I! 6 F i A k STA: W600 B With HF Wires 1/466 4 Amplitude IH/H1I 2 0 cn en 1/225 1/117 _ x - -"~-% I I I,, -,. 6-, 0 5 10 Frequency (MHz) 15 Z Figure 21: Current Density at STA:W600B, With HF Wires, Anti-symmetric Excitation

I I I I I I E 6 k STA: F800T Without tHF Wires 4 Amplitude IH/H1 - I \ 1/341. 2 0..I --— I --- I 0 5 10 15 20 Frequency (MIz) Figure 22a: Current Density at STA: F80(T, Without HF Wires, Anti-symmetric Excitation CAD

50 Phase (degrees) 1/341. 1/134 0 5 10 15 20 Frequency (MHz) w~ Figure 22b: Current Phase at STA: F800T, Without HF Wires, Anti-symmetric Excitation

aI I I _ I I k STA: F800T F With HF Wires 4 - 1/466 Amplitude H/H1 2 - / 1/225 - 0 0 0 5 10 15 20 Frequency (MHz) Figure 23a: Current Density at STA:F8OOT, Anti-symmetric Excitation,with HF Wires

- --- — I I — ~ -- I I 50 Phase (degrees) 1/466 0 -50 i so- E STA: F00T With HF Wires /.1/117 I 1/225 -- / I '00. I q*-/ I -— ` -- - ---- —- - -` -- - ---- - - --- - -` --- 0 5 10 Frequency (MHIz) 15 20 Figure 23b: Current Phase at STA:F800T, Anti-symmetric Excitation,with HF Wires

I I l 6k i A k STA:F800B Without IIF Wires 41 Amplitude IH/Hi 1/341 2 0 1/134 -/- -... -r - - -Of ot I I -- - 0 5 10 Frequency 15 20 (MHz) Figure 24: Current Density at STA:F800B, Anti-symmetric Excitation, Without HF Wires

I IT l E1 6 4 A k STA:F8OOB With HF Wires Amplitude IH/!HI 1/466 1/117 1/225 #0 <,c- - / / \ './ I I- I I 5 10 Frequency (MIIz) 15 20 Figure 25: Current Density at STA:F800B, Anti-symmetric Excitation,-with HF Wires

60 40 -Amplitude En/E'I 20 0 5 10 15 Frequency (MHz) Figure 26: Charge Density at STA:W940, Anti-symmetric Excitation,without HF Wires 20

on a I I __ __. i u I I I, - Ei sensor k 20 STA:W940T /With HF Wires Amplitude / /6 II/HiI 10 \1/117 1/225 \// 0 5 10 15 20 Frequency (MHz) Figure 27: Charge Density at STA:W940T, Anti-symmetric Excitation, with HF Wires