Document
Comparison of RTA Vibratory Loading in the 40 - by 80 - Foot Wind Tunnel and 80 - by 120 -
Foot Wind Tunnel at the National Full - Scale Aerodynamics Complex
* Robert B. LaRue Aeromechanics Branch, NASA Ames Research Center, Moffet Field, CA 94035 .
Th is paper presents data taken in the 80 - by 120 - Foot Wind Tunnel in 1992 to data taken in the 40 - by 80 - Foot Wind Tunnel in 2016 at the NFAC. In both sets of data, the RTA was equipped with an identical set of S - 76 helicopter blades. These data sets were compared to determine the repeatability of the RTA as a testing device, and to quantify differences in 40 - by 80 - Foot Wind Tunnel vs. 80 - by 120 - Foot Wind Tunnel re sults. The contents include an overview of the RTA and test facility, as well as a discussion of the methodology used. Vibratory load data is presented for a variety of wind and RPM conditions in various test section configurations . Data presented in this report quantifies the repeatability of the RTA.
Nomenclature A = Rotor Disc Area b = Number of Rotor Blades c = Mean Airfoil Chord CTOS = Rotor Thrust Coefficient Divided by Rotor Solidity HPP = Half Peak - to - Peak NFAC = National Full - Scale Aerodynamics Complex R = Rotor Radius rev = Revolution RPM = Revolutions per Minute RTA = Rotor Test Apparatus T = Thrust ρ = Free - Stream Air Density Ω = Rotor Rotational Velocity I. Introduction ULL - Scale aircraft wind tunnel testing is a unique service provided by the National Full - Scale Aerodynamics Complex (NFAC). The Rotor Test Apparatus (RTA) is one of the Air Force’s primary
F
testbeds for helicopter rotors. Wind tunnels are used to validate theoretical predictions and ma ke improvements in designs. Given the significance of the NFAC as a test facility and the RTA as a testbed, it is imperative t o quantify the reliability of test data. The nature of this test allows it to identify the repeatability of the RTA across a variety of test environments, while also identifying differences between 40 - by 80 - Foot Wind Tunnel and 80 - by 120 - Foot Wind Tunnel configurations . The Sikorsky S - 76 is a thoroughly vetted rot or system that provides a r eliable baseline for data comparison. Loads data was collected over a wide range of RPMs and wind speeds for the full envelope of the rotor . The purpose of this report is to (1) d etermine the repeatability of data in the 40 - by 80 - Foot Wind Tunnel configuration, (2) q uantify differences between 40 - by 80 - Foot Wind Tunnel vs. 80 - by 120 - Foot Wind Tunnel configurations ,
o
and (3) q uantify differences in the 40 - by - 80 - Foot Wind Tunnel between an “ on wind tunnel external scales ” configuration, and a “ locked ” configuration.
II. Overview of Facilities & Hardware The S - 76 b lades and hub were instrumented with strain gauges and accelerometers. In an “on wind tunnel external scales” configuration, the RTA load path goes through the tunnel external scale measurement system. In an “off scales” or “on corbels” configuration, the tunnel external scales are locked .
* Rotorcraft Aeromechanics Intern, Aeromechanics Branch , NASA Ames Research Center.
In this “ locked ” configuration, t he RTA is rigidly mounted to the wind tunnel structure and restrained in the lateral plane through mechanical locking devices. It is important to make distinction with these two tunnel configurations because the difference in stand modes affects the rotor operational envelope . For example, the S - 76 rotor can be spun at 293 RPM on the wind tunnel external scales, but not in a locked configuration due to ground resonance concerns.
Thrust sweeps were performed on tunnel external scales at RPMs of 273 and 293 , with for ward flight conditions of 60 kt, 80 kt , and 100 kt. On corbels in a locked configuration, thrust sweeps were performed at RPMs of 253 and 273, with for ward flight conditions of 60 kt, 80 kt, and 100 kt . These conditions were chosen so that the rotor inplane vibratory shear forces (side and axial forces ) i n different tunnel configurations could be compared, and to match conditions tested in the 80 - by 120 - Foot Wind Tunnel in 1992. Forces were measured by an internal rotor balance in the RTA. The RTA steady/dynamic rotor balance is a five - compone nt balance that measures rotor lift , axial, and side forces, as well as rotor pitch and roll moments. The steady/dynamic rotor balance uses statically determined calibration coefficients .
Table 1 lists some general ch aracteristics of the S - 76 rotor.
Table 1 S - 76 Rotor Characteristics Parameter Value Radius 22 ft Nominal Chord 15.5 in Nominal Twist - 10 deg Blade Reference Area 113.67 ft Solidity Ratio 0.0748 Number of Blades 4 Airfoils SC1095 84% outboard SC1095R8 80% inboard Flapping Hinge offset 3.70% radius Lock No. 11.6 100% RPM 293 100% tip speed 675 ft/s Figure 1 RTA Con fi gurations (Left: 40 - by 80 - Foot Wind Tunnel mode, Right: 80 - by 120 - Foot Wind Tunnel mode ) Figure 1 shows the RTA in the 40 - by 80 - Foot Wind Tunnel and 80 - by 120 - Foot Wind Tunnel . The RTA is mounted in the wind tunnel using three struts, as shown. The model angle of attack is modified by changing the height of the tail strut. Rotor collective and cyclic control is managed through the swashplate via three electromechanical/hydraulic actuators.
The 40 - by 80 - Foot Wind Tunnel and 80 - by 120 - Foot Wind Tunnel at the National Full - Scale Aerodynamics complex are shown in Figure 2 . The 40 - by 80 - Foot Wind Tunnel is a closed - loop wind tunnel, meaning that the tunnel airflow is a closed system and contained within the tunnel circuit. However, the 80 - by 120 - Foot Wind Tunnel is an open - loop system, the airflow passes through the inlet and exits the tunnel downstream. The maximum test section velocity in the 80 - by 120 - Foot Wind Tunnel is 100 kt, while the maximum test section velocity in the 40 - by 80 - Foot Wind Tunnel is 300 kt. Both tunnels share a single drive system. The NFAC drive system is comprised of six fans with 135,000 combined horsepower (approx. 10 6 MW). Vanes and louvers are positioned w hen opera ting in 80 - by 120 - Foot Wind Tunnel mode so that the 40 - by 80 - Foot Wind Tunnel is closed off and the 80 - by 120 - Foot Wind Tunnel leg forms an open - loop wind tunnel (Fig. 2 ). For bot h wind tunnels, the first given dimension is the test section height, while the second dimension is the test section width. i.e. the 80 - by 120 - Foot Wind Tunnel is 80 ft high and 120 ft wide.
Figure 2 National Full - Scale Aerodynamics Comp lex III. Methodology All figures in the results section were plotted as a function of thrust coefficient divided by rotor solidity (CTOS). The equation for CTOS is provided below: π T CTOS = bcA ρ Ω R Where A = Rotor Disc Area b = Number of Rotor Blades c = Mean Airfoil Chord R = Rotor Radius T = Thrust ρ = Free - Stream Air Density Ω = Rotor Rotational Velocity CTOS was chosen as a good parameter for comparison because it is a non - dimensional performance parameter , unlike thrust, which is largely dependent on rotor size . Using CTOS allow s the data to be compared across different rotor systems.
Much of the data presented in the results section are the vibratory half peak - to - peak (HPP) loads. HPP for any parameter is defined as follows: | | | | Max + Min HPP = Other data is presented in the form of “per revolution” vibratory loads, i.e. 4/rev or 8/rev. P er rev vibratory loads are loads that are induced on the RTA at the specified frequency. For example, a 4/rev vibratory load occurs four times in one rotor revolution. The expected dominant vibratory loading in the inertial frame for any rotor set is b/rev, where b is the number of rotor blades. It is typical for n*b/rev vibratory loads to be significant (where n is a positive integer) , hence 8/rev loads are also pr ovided .
Vibratory a xial & side force s , as well as pitch and roll moments are presented. These parameters were chosen b ecause they show how the rotor loads influence the vehicle in the inertial plane. Axial force is in the longitudinal direction while side force is in the lateral direction.
IV. Results Figures 3 - 14 examine the repeatability of the RTA in the 40 - by 80 - Foot Wind Tunnel configuration.
The data was taken at test conditions o f 293 RPM at 60, 80, and 100 kt are compared to see how repeatable the RTA is the 40 - by 80 - Foot Wind Tunnel . In both sets of data presented in these figures, the RTA is in an “on wind tunnel external scales” configuration. The data sets were taken two days apart, one on 5/24/2016 and the other on 5/26/2016. The RTA was tested in a locked configuration between these data sets, on 5/25/2016.
Figur es 15 - 26 compare the results taken in the 40 - by 80 - Foot Wind Tunnel in 2016 with data from 1992 in the 80 - by 120 - Foot Wind Tunnel . The goal was to quantify the loading difference in the two tunnel configurations. The repeatability of the RTA over time can also b e examined from this comparison.
Figures 27 - 34 compare the results of the data taken in the 40 - by 80 - Foot Wind Tunnel with different model support configurations. O ne set of data was taken with the RTA on wind tunnel external scales, while the second set was taken with the RTA off external scales (on corbels). This was done in order to quantify the difference between boundary conditions of model supports for the two configurations, and to examine how repeatable the RTA is in the two configurations.
Blue – HPP Red – 4/rev Green – 8/rev White markers are from data taken on 5/24/2016, dark markers are for data taken on 5/26/2016.
Vibratory Axial Force (lbf) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 CTOS Figure 3 Comparison of S - 76 Axial Force in 40 - by 80 - Foot Wind Tunnel at 60 kt , 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev White markers are from data taken on 5/24/2016, dark markers are for data taken on 5/26/2016.
Vibratory Axial Force (lbf) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 CTOS Figure 4 Comparison of S - 76 Axial Force in 40 - by 80 - Foot Wind Tunnel at 80 kt , 293 RPM Condition Bl ue – HPP Red – 4/rev 1400 Green – 8/rev White markers are from data taken on 5/24/2016, dark markers are for data taken on 5/26/2016.
Vibratory Axial Force (lbf) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 CTOS Figure 5 Comparison of S - 76 Axial Force in 40 - by 80 - Foot Wind Tunnel at 100 kt , 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev White markers are from data taken on 5/24/2016, dark markers are for data taken on 5/26/2016.
Vibratory Side Force (lbf) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 CTOS Figure 6 Comparison of S - 76 Side Force in 40 - by 80 - Foot Wind Tunnel at 60 kt , 293 RPM Condition Blu e – HPP Red – 4/rev Green – 8/rev White markers are from data taken on 5/24/2016, dark markers are for data taken on 5/26/2016.
Vibratory Side Force (lbf) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 CTOS Figure 7 Comparison of S - 76 Side Force in 40 - by 80 - Foot Wind Tunnel at 80 kt , 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev White markers are from data taken on 5/24/2016, dark markers are for data taken on 5/26/2016.
Vibratory Side Force (lbf) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 CTOS Figure 8 Comparison of S - 76 Side Force in 40 - by 80 - Foot Wind Tunnel at 10 0 kt , 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev White markers are from data taken on 5/24/2016, dark markers are for data taken on 5/26/2016.
lbf) - Vibratory Pitch Moment (ft 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 CTOS Figure 9 Comparison of S - 76 Pitch Moment i n 40 - by 80 - Foot Wind Tunnel at 60 kt , 293 RPM Condition Blue – HPP Red – 4/rev 6000 Green – 8/rev White markers are from data taken on 5/24/2016, dark markers are for data taken on 5/26/2016.
lbf) 5000 - Vibratory Pitch Moment (ft 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 CTOS Figure 10 Comparison of S - 76 Pitch Moment in 40 - by 80 - Foot Wind Tunnel at 80 kt, 293 RPM Blue – HPP Red – 4/rev Green – 8/rev White markers are from data taken on 5/24/2016, dark markers are for data taken on 5/26/2016.
lbf) - Vibratory Pitch Moment (ft 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 CTOS Figure 11 Comparison of S - 76 Pitch Moment in 40 - by 80 - Foot Wind Tunnel at 100 kt, 293 RPM Blue – HPP Red – 4/rev Green – 8/rev White markers are from data taken on 5/24/2016, dark markers are for data taken on 5/26/2016.
lbf) - Vibratory Roll Moment (ft 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 CTOS Figure 12 Comparison of S - 76 Roll Moment in 40 - by 80 - Foot Wind Tunnel at 60 kt, 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev White markers are from data taken on 5/24/2016, dark markers are for data taken on 5/26/2016.
lbf) - Vibratory Roll Moment (ft 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 CTOS Figure 13 Comparison of S - 76 Roll Moment in 40 - by 80 - Foot Wind Tunnel at 80 kt, 293 RPM Condition Blue – HPP Red – 4/rev G reen – 8/rev White markers are from data taken on 5/24/2016, dark markers are for data taken on 5/26/2016.
lbf) - Vibratory Roll Moment (ft 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 CTOS Figure 14 Comparison of S - 76 Roll Moment in 40 - by 80 - Foot Wind Tunnel at 100 kt, 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev Dark markers are for 80’ x 120’ data, white markers are for 40’ x 80’ data.
Vibratory Axial Force (lbf) 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 CTOS Figure 15 Comparison of S - 76 Axial Force at 60 kt, 293 RPM condition Blue – HPP Red – 4/rev Green – 8/rev Dark markers are for 80’ x 120’ data, white markers are for 40’ x 80’ data.
Vibratory Axial Force (lbf) 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 CTOS Figure 16 Comparison of S - 76 Axial Force at 80 kt, 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev Dark markers are for 80’ x 120’ data, white markers are for 40’ x 80’ d ata.
Vibratory Axial Force (lbf) 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 CTOS Figure 17 Comparison of S - 76 Axial Force at 100 kt, 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev Dark markers are for 80’ x 120’ data, white markers are for 40’ x 80’ data.
Vibratory Side Force (lbf) 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 CTOS Figure 18 Comparison S - 76 Side force at 60 k t , 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev Dark markers are for 80’ x 120’ data, white markers are for 40’ x 80’ data.
Vibratory Side Force (lbf) 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 CTOS Figure 19 Comparison of S - 76 Side Force at 80 kt, 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev Dark markers are for 80’ x 120’ data, white markers are for 40’ x 80’ data.
Vibratory Side Force (lbf) 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 CTOS Figure 20 Comparison of S - 76 Side Force at 100 kt, 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev Dark markers are for 80’ x 120’ data, white markers are for 40’ x 80’ data.
lbf) - Vibratory Pitch Moment (ft 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 CTOS Figure 21 Comparison of S - 76 Pitch Moment at 60 kt, 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev 5000 Dark markers are for 80’ x 120’ data, white markers are for 40’ x 80’ data.
lbf) - Vibratory Pitch Moment (ft 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 CTOS Figure 22 Comparison of S - 76 Pitch Moment at 80 kt, 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev Dark markers are for 80’ x 120’ data, white markers are for 40’ x 80’ data.
lbf) - Vibratory Pitch Moment (ft 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 CTOS Figure 23 Comparison of S - 76 Pitch Moment at 100 kt, 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev Dark markers are for 80’ x 120’ data, white markers are for 40’ x 80’ data.
lbf) - Vibratory Roll Moment (ft 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 CTOS Figure 24 Comparison of S - 76 Roll Moment at 60 kt, 293 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev Dark markers are for 80’ x 120’ data, white markers are for 40’ x 80’ data.
lbf) - Vibratory Roll Moment (ft 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 CTOS Figure 25 Comparison of S - 76 Roll Moment at 80 kt, 29 3 RPM Condition Blue – HPP Red – 4/rev Green – 8/rev Dark markers are for 80’ x 120’ data, white markers are for 40’ x 80’ data.
lbf) - Vibratory Roll Moment (ft 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 CTOS Figure 26 Comparison of S - 76 Roll Moment at 100 kt , 293 RPM Condition Aqua – 100 k t , 273 RPM Green – 8 0 kt, 273 RPM Red – 60 k t , 273 RPM White markers are on wind tunnel external 2000 scales, dark markers are off scales (on corbels).
Vibratory HPP Axial Force (lbf) 0.00 0.02 0.04 0.06 0.08 0.10 CTOS Figure 27 Comparison of S - 76 Half Peak - to - Peak Axial Force On/Off Scales in 40 - by 80 - Foot Wind Tunnel Aqua – 100 k t , 273 RPM Green – 80 kt, 273 RPM Red – 60 k t , 273 RPM White markers are on wind tunnel external scales, dark markers are off scales (on corbels).
Vibratory 4/rev Axial Force (lbf) 0.00 0.02 0.04 0.06 0.08 0.10 CTOS Fig ure 28 Comparison of S - 76 4/rev Axial Force On/Off Scales in 40 - by 80 - Foot Wind Tunnel Aqua – 100 k t , 273 RPM Green – 80 kt, 273 RPM Red – 60 k t , 273 RPM White markers are on wind tunnel external scales, dark markers are off scales (on corbels).
Vibratory HPP Side Force (lbf) 0.00 0.02 0.04 0.06 0.08 0.10 CTOS Figure 29 Comparison of S - 76 Half Peak - to - Peak Side Force On/Off Scales in 40 - by 80 - Foot Wind Tunnel Aqua – 100 k t , 273 RPM Green – 80 kt, 273 RPM Red – 60 k t , 273 RPM 500 White markers are on wind tunnel external scales, dark markers are off scales (on corbels).
Vibratory 4/rev Side Force (lbf) 0.00 0.02 0.04 0.06 0.08 0.10 CTOS Figure 30 Comparison of S - 76 4/rev Side Force On/Off Scales in 40 - by 80 - Foot Wind Tunnel Aqua – 100 k t , 273 RPM Green – 80 kt, 273 RPM Red – 60 k t , 273 RPM White markers are on wind tunnel external scales, dark markers are off scales (on corbels).
lbf) - Vibratory HPP Pitch Moment (ft 0.00 0.02 0.04 0.06 0.08 0.10 CTOS Figure 31 Comparison of S - 76 Half Peak - to - Peak Pitch Moment On/Off Scales in 40 - by 80 - Foot Wind Tunnel Aqua – 100 k t , 273 RPM Green – 80 kt, 273 RPM Red – 60 k t , 273 RPM White markers are on wind tunnel external 2000 scales, dark markers are off scales (on corbels).
lbf) - Vibratory 4/rev Pitch Moment (ft 0.00 0.02 0.04 0.06 0.08 0.10 CTOS Figure 32 Comparison of S - 76 4/rev Pitch Moment On/Off Scales in 40 - by 80 - Foot Wind Tunnel Aqua – 100 k t , 273 RPM Green – 80 kt, 273 RPM Red – 60 k t , 273 RPM White markers are on wind tunnel external scales, dark markers are off scales (on corbels).
lbf) - Vibratory HPP Roll Moment (ft 0.00 0.02 0.04 0.06 0.08 0.10 CTOS Figure 33 Comparison of S - 76 Half Peak - to - Peak Roll Moment On/Off Scales in 40 - by 80 - Foot Wind Tunnel Aqua – 100 k t , 273 RPM Green – 80 kt, 273 RPM Red – 60 k t , 273 RPM White markers are on wind tunnel external scales, dark markers are off scales (on corbels).
lbf) - Vibratory 4/rev Roll Moment (ft 0.00 0.02 0.04 0.06 0.08 0.10 CTOS Fig ure 34 Comparison of S - 76 4/rev Roll Moment On/Off Scales in 40 - by 80 - Foot Wind Tunnel V. Discussion of Results The data in Figures 3 - 14 show that the RTA is repeatable in the 40 - by 80 - Foot Wind Tunnel . This result was expected, since the two tests runs were done a few days apart from each other and there were no significant changes in the RTA configuration between the two tests. While the HPP values show some discrepancy in a few of the figures (notably Figure 5 and Figure 9 ) , the 4/rev and 8/rev contributions match closely for these figures . This indicates that the rotor is inducing similar loads in both cases.
Figures 15 - 26 yield similar results to Figures 3 - 14 , showing that the 4/rev and 8/rev contributions generally match between the 40 - by 80 - Foot Wind Tunnel and 80 - by 120 - Foot Wind Tunnel configurations . However, the HPP values for the 40 - by 80 - Foot Wind Tunnel configuration are significantly higher for most parameters . One possible explanation for this would be greater flow re - circulation in the 40 - by 80 - Foot Wind Tunnel due to geometric constraints. Another possible explanation could be a difference in stand modes between the two configurations due to a difference in strut length .
Interestingly, the 4/rev and 8/rev contributions for pitch moment in the 40 - by 80 - Foot Wind Tunnel seem to make up a small percentage of the total HPP values . It is important to note a difference in the RTA drive system between the 80 - by 120 - Foot Wind Tunnel tests in 1992 and the 40 - by 80 - Foot Wind Tunnel tests in 2016. I n 1992, the RTA had two 1,500 - hp motors installed. In 2016, the RTA had one 1,500 - hp motor and an in termediate gearbox between the installed rear mo tor and the right angle gearbox.
The on/off tunnel balance scales data shown in Figures 27 - 34 indicates that there is some difference in the vibratory loading of the two configurations, particularly in the longitudinal axis (axial force & pitch moment). The 4/rev axial force data (Figure 28 ) shows significant differences in the two configurations, more so than the other parameters. Across all the data in Figures 27 - 34 , the vibratory loading is generally higher with the RTA on balance scales for a given CTOS. With the exception of Figure 28 , the 4/rev vibratory loading matches closely and the trend s are similar for the 4/rev data.
Interestingly, the 8/rev contribution to pitching moment at 293 RPM, 100kts overtakes the 4/rev contribution at a CTOS of about 0.06 (Figures 11 & 23 ). It is also at this CTOS that many of the figures comparing 40’ x 80’ and 80’ x 120’ results have an elbow (Figures 16, 17, 21, 22 & 23 ). For the 4/rev contributions at 273 RPM, 60kts (Figures 28, 30, 32 & 34 ) there is a sharp increase in slope at a CTOS o f roughly 0.05, and this condition seems to have higher loads at high CTOS than the 80kt and 100kt wind speed conditions.
VI. Acknowledgements The author thanks Christopher Nykamp and William Bartow for their mentorship and guidance throughout the course of t he project. The author would also like to thank Christopher Hartley and Christopher Northrup for their professional and technical feedback. Finally, the author thanks Dr. William Warmbrodt and Scott Waltermire for the opportunity to work at the NFAC and pe rform important aeronautics research.
VII. References [1] Shinoda, P., “Full - Scale S - 76 Rotor Performance and Loads at Low Speeds in the NASA Ames 80 - by 120 - Foot Wind Tunnel ,” National Aeronautics and Space Administration, Technical Memorandum 110379, April 19 96.
[2] Yamuchi, G., Signor, D., Watts, M., Hernandez, F., LeMasurier, P., “Flight Measurements of Blade - Vortex Interaction Noise Including Comparisons With Full - Scale Wind Tunnel Data,” National Aeronautics and Space Administration, Technical Memorandum 112385, May 1993.