Document
Tybrin Corporation Joe Pahle, Dave Berger Dryden Flight Research Center Dryden Flight Research Center Mike Venti, Jim Faber, Chris Duggan and Kyle Cardinal Air Force photo by Bobbi Zapka: http://www.edwards.af.mil/shared/media/photodb/photos/100916-F-9126Z-024.jpg A Preliminary Flight Investigation of Formation Flight for Drag Reduction on the C-17 Aircraft National Aeronautics and Space Administration
Why Investigate Formation Flight?
•
• Primary benefit is reduced drag, resulting in fuel
savings or longer range
- A 14% fuel savings demonstrated in flight for two F/A-18s in cruise
configuration (2001 NASAlOFRC)
- A 15% power reduction for two Oornier 00-28 (1995 Hummel)
• If successful, the concept may be applied to existing
Ale without external modifications
t. o J ! ,,~ Rotati on L' L /:/ effect ofW Figure from: Ray, Cobleigh, Vachon, and St.
, ' , ' John, "Flight Test Techniques Used to j /' LResultant aerodynamic Evaluate Performance Benefits During j .... force : ...j L 2 + 0 i-...: Formation Flight", NASAlTP-2002-210730.
,'-' I:' IY " AIAA AFM 2011
Background
•
• Formation Flight is a very old concept ...
- 1914 Wieselsberger - AIAA-1970-1337 FORMATION FLIGHT TECHNOLOGY - AIAA-1995-3898 AFF "A preliminary investigation into the application to civi I operations"
• With some very recent interest (particularly for transport-
class vehicles)
- AIAA-2007-4163 Formation Flying of Commercial Aircraft, Variations in Relative Size and Spacing - Induced effects and control - AIAA-2009-3615 Formation Geometries and Route Optimization for Commercial Formation Flight - 2010 DARPA - Formation Flight for Aerodynamic Benefit program - AIAA-201 0-1240 Aerodynamic Performance of Extended Formation Flight There are technical economic and regulatory issues that must l 1 be addressed before formation flight would be considered a AIAA AFM 2011 viable option
CAPFIRE
•
Cargo Aircraft Precision Formations for
Increased Range and Efficiency
• Gather qualitative flight data and pilot comments with trail
vehicle in the area of influence from the lead vehicle's vortex
• Use the C-17 FFS and auto-flight system to stabilize at pre-
determined trail locations with predicted drag reduction (non-
optimized)
• Use production fuel flow instrumentation and off-line thrust
model (driven with flight data) to estimate drag reduction
AIAA AFM 2011
Flight Test Approach
•
• NASA partnered with USAF/AFFTC as a product of the
NASA Aviation Safety Research Test and Integration
Plan
- Production C-17 aircraft used in test
- USAF AFFTC engineering staff assisted in safety assessment,
test documentation, flight preparation, and flight test
- NASA engineering staff on board for real-time data
assessment and safety monitoring during test.
- Flight data obtained through the C-17 Advanced Wireless
Open Data System (AWODS)
AIAA AFM 2011
Flight Test Approach (cont.)
•
• A similar (but simplified) flight test approach to the
NASA Autonomous Formation Flight (AFF) program
was used
- Stabilized Tare points outside of the vortex influence were
flown before and after a horizontal or vertical test sequence
- Step-wise horizontal profile co-altitude with lead vehicle
• 1000 ft in trail (flights 1 and 2) • 3000 ft in trail (flight 3)
- Step-wise vertical profile at one of the horizontal test points
near the estimated vortex location
- Automatic control of position using FFS was desired, but
much of the flight data was pilot flown
1. Ray, Cobleigh, Vachon, and St. John, "Flight Test Techniques Used to Evaluate Performance Benefits During Formation Flight", NASNTP-2002-210730.
AIAA AFM 2011
Formation Geometry
•
Lead Not to scale .:::::- .....
..... .....
..... ..........
.......... ~ .....
..... ..........
.......... .....
..........
---::.---- .... -
---
110075 Approximately to scale
1+--------- - 18 wing spans
AIAA AFM 2011
Test Point Sequence
•
• Utilize existing C-17 FFS, auto-flight system, and instrumentation
• Collect preliminary, qualitative results near estimated position of
lead's vortex on both sides of the lead
~120ft~
~t-----+-----{
20 ft Lead Longtrack separation 3000 ft Trail
...... .. .....------ 180 ft ----------I.~I
110074 AIAA AFM 2011
Test points for September flight (flight 3)
•
Cross track offset, Vertical Test Note ft offset, ft point T1 400 200 5 minute dwell after stabilized H1 240 0 3 minute dwell after stabilized H2 220 3 minute dwell after stabilized H3 200 0 3 minute dwell after stabilized H4 180 0 3 minute dwell after stabilized H5 160 0 3 minute dwell after stabilized T2 400 200 5 minute dwell after stabilized V1 180 20 3 minute dwell after stabilized V2 180 -20 3 minute dwell after stabilized V3 180 -40 3 minute dwell after stabilized V4 180 -60 3 minute dwell after stabilized T3 400 200 5 minute dwell after stabilized AIAA AFM 2011
•
Position
Surfaces
Trail
Control
NASA Real-time Display
~_ ~!.ilI!9iIm ~~ ~~ I 1 I I G N1 Nz Wf LPT 2011 2.
HPT BLD ACC ACC
Engine parameters
AIAA AFM
•
-80 ------------ -85 ------------------- -90 deg ------------------------ -95 Longitude, ------------------------- -100 ------------------ -105 ------------ -110 38 36 34 32 30 28 26 24~----~----~----~------~----~----~ Latitude, deg
Test Point Locations During Flight 3
AIAA AFM
Steady State Data Analysis
•
• Stabilizing at test point with existing pilot visual aids did not
yield sufficient steady-state data for detailed analysis
• An alternate flight data analysis technique was developed
- "steady-state" criteria over a period of 10 s
- criteria was applied across all test points with proximity to the
estimated vortex position
.
Flight Condition: 273 KCAS < V < 277 KCAS and 1 V 1< 4 knots/s
. .
Test Point: Zoffset < 4 fils and Yoffset < 4 fils
4 • % 4 •
t Wfi < 200 pph
Engine: L N2i < 2 - and L Fi < 400 Ibis and
s
i=l s i=l
i=l AIAA AFM 2011
Example of Steady-State Criteria
•
-- Total test point I "'" I.""., I I I 1+'" I """" ' "" ,., I I .. "'" I I I """ I """'" I I "'" " ..... " •• I " • Selected - - - - - - - e - - - - - - - - - - - - - - nl - - - - - - I , , , , I ! ' I , , , , I I I I ! ' , , I I I I " ! I I , I , , , , I I ! I , , , , I I I I , ~ , , I I I I , , • , !. I I I , , • 6 ~ - - - - - - :!::.
- - - - - - - - - - - - C) (1) '0 ~ c:: - ~ - - - - - - - (1) 0 " ""'" '.!.""" I "'!' I I 'I""'!"'" '" I I "" I I "'" I, I ""',., I "", •• " 't. •• " I "" - - - - :.;: , , " "": " """" ~ , , , , , , , , , , ~ , , , , , , , , , , ~ , , , , " Test point V2 on left side " ;" " """ -2 - - - - - - - - -4 1.05 - - - - - - - - ,., """ .1 ' " I "'" I J.""" I I I I.L" "'.1.' "" '"" I L "'" '" " L '" ""'" L I I "", " . L" " " I '" 1.00 ~ - - - e - - - - - - - - - 'm '0 - - ~ (1) :!::. N 0.95 '-Ml : " " " " " : " " , .-.,.
- - =='~
~ § 0.90
(1) c:: ::::J LL - - - - - - - - I '" ". ," I I I ," I I I."'" I I I I I ,'1 I •• ,' I "1"" I '" I I I ," I I •• ,' I "1"" I I. I I ," I "' " I I I. ," I I I , 0.85 - - - - - - - - - - - - - - - - - - - - - . - - - - - . . ~ . .
. . . . . . . .
0.80 L...,;"",,;._----II....-_----L __ ----L. __ ---L. __ ---'- __ ......... __ ....L... __ -'--_-----'
o 20 40 60 80 100 120 140 160 180
Time, s Red data points meet "steady state" criteria AIAA AFM 2011
Initial Data Assessment (flight 3)
•
• Engaged FFS at 3000 ft trail in flight at 275 knots
- Most test points in the area of influence of the vortex were pilot flown - Identical points repeated on the either side of the lead aircraft. Some asymmetry was noted, with H5 on the right side likely on the "downwash" side of the vortex
• Very difficult precision task for pilot to fly
- Pilot noted that effort was similar to Aerial Refueling, but somewhat easier since it was not all 3 axes. Task was "not operationally representative" for the C-17.
• A reduction in estimated thrust and fuel flow is clearly
evident
- The benefit got larger as the trail vehicle got closer to the "wingtip overlap" point. This occurred on both the left and right sides.
- Average aileron required for trim also increased as the trail vehicle moved closer to the "wingtip overlap" point AIAA AFM 2011
Comparison of Tare With Test Point
•
::::- - - - T2 C'C ...
.... -- H5
-
C) Q) 5 "C
-
£: - - - - - . '';'~ : i., ',;. ~ ' :- ' ,:. ; ,;. . ~ . ~ . ~;.. . :..;..; . ~ . ~ ' ..;..;., ' ;,:..:. ' ~.:... ' .;.. ' ~ :"; ';"~:":' " .;, . ..:.. . ...:. .~.;,. . ~ ' ~,;,. ' ;"'''; ,~ . ~\' ,. ~ .; ,''-.: .' ;.;. ' .:., . .. ; .. ...:,:.. . ...
...
Q)
-
:.a: -5 1.1
-
::::- '(6 "C 1.0 ... Q) ::"N 3:"(6 0.9 .9E ~ ...
-0 0.8 Q) s::::: ::s LL ~---------~------------~------------~------------~-T~Average 0.7 .---------r-----~---____.r___---___r_-~ d uri ng test point with 1 en <C sigma bounds () ~ '> ~_ v 0 50 100 150 200 250 300 Time,s 110077 AIAA AFM 2011
Summary of Test Points (trail)
•
c: ........ . ... .. "1' . .. .. . .................. . ..... . .. .. .. .. ... . .. . .... .
... C) ~ Q)
....... • '! ' ·1 ·········· I . :1 . ·I ··························· · ······· ···
'n; 'C .. • . =- ......... .. .. • . I .. .. .. ....• .• ........... .... • . .. ... . .. . :t . .. .
Q)"":: C)a:
........................... ........... ! . lE '1' ......... I .! . ·1·· ·····
co I -4 .......
Q)- ..... , ... , . .. .. .. .. ... , .. , , .............. , . . " . .. ...... . .." ..... .
-8 >
«
-12 1.2
i ~ 1.1
:J N ... ,- 1 0 .s:::: - • ... co
m E 0.9
... 0 ~ c: 0.8 0.7 ~~~~~~~~~~~~~~~~~~ Mean~reasafuncffonoffu~1 1.1 ---~
aircraft weight
~'C .2 Q) ~,~ 1.0 Q)- :J co ..... E
m 0 0.9
'0 c: ....
T1 H 1 H2 H3 H4 H5 T2 V1 V2 V3 V4 T3 T1 H 1 H2 H3 H4 H5 T2 V1 V2 V3 V4 T3 l Jl J v- v- Trail on left Trail on right Test point 110078 AIAA AFM 2011
Comparison of Lead and Trail Fuel Flow
•
..
Average during .. .. . , .. ... . .. .. ...... ....... .. .. . .. . , .. ... .. . .
-
~ 1.05 test point with 1 (1) --0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. sigma bounds
i ~ 1.00
0=
~ E 0.95
(1) ...
~ g 0.90
m +'" ~ 0.85 0.80 L....-.L....-..I....-~...I....-....I....-....&....- ...................... .....&.........&.........&.... ...................... ---'-----'-----L.----L.----L.----L----I~1..........j Mean tare as a 1.1 function of total ..
aircraft weight ~ 1.05 . .. . . ..... . Tare points in red ~ +'" i~ 1.00 ..
0·-
N r :r~~~~~~~~~~~~~~~~~ l- ~~ ~ ~Jl ~
~ ~ 0.95 (1) ...
~ g 0.90
m +'" ~ 0.85 .................. .
0.80 L....-.L....-..I....-...a.......- ___ ....I....-....&....- ...................... .....&.........&.........&.... ...................... ---'-----'-----L.----L.----L.----L----I----I""'-- ___ '-------...
l T1 H1 H2 H3 H4 H5 T2 V1 V2 V3 V4 T3 Jl 1 H1 H2 H3 H4 H5 T2 V1 V2 V3 V4 T3 J v V Trail on left Trail on right Test point 110079 ) --- Increasing time AIAA AFM 2011
Percent Change Corrected For Lead
2 ~~I--r- I ~I-- __ I~ I --~ I ~I~T I ~ I ~~ I --~I~ I --r- I ~I-- __ I~I--~I~I~TI~I~~I--I~~I--~I
•
•
o r· . · ··· ·· ·· ·· ·· ·· . ··· ··.·· ·· · .• . .. .. ...... .. .. ... . .. .. . ... .• .. .. - ~ Oe
• •
r' ... • .............. .. ... . ...................... ... ...............
~ '(6 -2
- '-
Q)~
• *
.2 Q) -4 r' ................... • ....... • ............ * ..... . ................ .
• • • •
+"0) t: t: Q) co
• • • r' .............. • ............................ • .................... -
CJ.c -6 ~ CJ
•
a..
-8 r' ........................................... . .. • .................
- 10 __ """'-- ____ ---il l.........! Data points with spoilers> 2 __ ~~_~ --1 2 deg have been removed I I I I I I I I I I I I I I
• •
o r' ............................................................. .. . - +"- tn-
• • •
r' .. . ... .. ... . .. ....... .. . .. .. ... . .. .. .. . .... . .. ... . .. .. . ... . • .. ..
2 '(6 - 2 .cob +"- r' ................................................................ - +" Q) -4
• • •
t: C)
• •
Q) t:
•
CJ co 6
•
r· ... . .. ...... .. ....... . .. .. ........... .. . ... . ................... .
'-.c - •
&. (.)
•
-8 r' .. . ...... • .. ~ ....... ~ ..... • ............. . . ~ ........ .. . ........... .
•
• •
-10 ~~~------I~ I --~~~~ I ~~--~--~~~----~~~~~~--~--~ l T1 H1 H2 H3 H4 H5 T2 V1 V2 V3 V4 T3 l1 H1 H2 H3 H4 H5 T2 V1 V2 V3 V4 T3 J J v- Y' Trail on left Trail on right Test point 110080 AIAA AFM 2011
Sample Pilot and Crew Comments
•
• T1 - Left side "Pilot noted that position is maintaining very well" - NASA engineer • H3 - Left side "I can hand fly this point no problem" - pilot • H4 - Left side "Pilot holding steady right stick, no rudder, 2-3 Ibs right stick" - FTE • V2 - Left side "Position right on and ride feels very stable and smooth" - NASA engineer • V3 - Left side "Rough ride with large aileron movements" - NASA engineer Comments taken from notes written by FTE • H2 - Right side "Like balancing on the head of a pin" - pilot and research engineers during test • H5 - Right side "by far the most difficult point to fly" - pilot points.
• Hard to maintain, applying hard left - FTE All comments must be taken in context of the exploratory, research • V2 - Right side "A bit bumpy" - pilot focus of the tests.
AIAA AFM 2011
Percent Change in Fuel Flow and Thrust
•
.. - .. ..
Perce~t change in fuel flow
o
.' . . . [[J : .... fr.om tar~s (corrected for lea~)· . ~ ~ ... , .....
~TT't"T"1
=
~ "-'-'-iIjIh-. •••• • ••• Cl) en -S
==
ca u -10 · . . . .. . . .
. . . .. ............ . .. . ....... . ................. .
:e -20 · . . .. ... .
Cl)
ffiHB
> -40 -15 -60 . .
r nt cha e in thrust .
o
~ : ~ '.' . . . fr:om t reeted for lea~): : : . ~f-n' : : : : • :
=
~ ~ -S en . . Some evidence that regions
% rl+t+H-!-'-t t++rf' 'tiiiI
==
• '.' • • • . '. • -'"++H t-t+TTTTT'1':' •• • .• :. . exist with benefit> 10% -10 ~ within the vortex area of . . .
...................
:e - 20 H+W-.f-H-I-+ +H-II . . . • .
. . .
~ influence > -40 L..L.L-L.W-" • • .'. . '- . - . -. - .' .- . - . -. - . ;- . - . -. - . .- '. - . -. - . .- . - '. -. --' . . • . ' . • • • • .- • • • . • , • • • • • · . . . . . . .
-15 -60----~--~--~~--~--~--~----~--~--~--~ 2S0 200 1S0 100 50
o -so -100 -1S0 -200 -2S0
Crosstrack offset, ft 110081 AIAA AFM 2011
Test Data Summary
•
• Most test points flown in the vortex showed a reduction in average
fuel flow and thrust compared to the tare test points
- Test point data averaged over a 3 min "stabilized" period, tares averaged over a 5 minute period - In general, the greater the reduction in average fuel flow and estimated thrust, the greater the average aileron trim required to hold position
• The maximum average fuel flow reduction was approximately 7-80/0
(compared to the tare points before and after). This was during test
point H4 and H5 on both the left and right side.
- Average fuel flow reduction during both vertical profiles was 4-5% - Although benefit "maps" are incomplete, data suggests that regions with fuel % flow and thrust reduction greater than 10 compared to the tare test points exist within the vortex area of influence AIAA AFM 2011
Conclusions
•
• Qualitative flight data and comments were gathered during several
two-ship, C-17 formation flights at a single flight condition (275
knots, 25,000 ft)
- The C-17 FFS and auto-flight systems were used to stabilize the aircraft at some trail locations with predicted drag reduction - The pilot was able to fly test points, but the workload was high
• Production fuel flow and inputs to an estimated thrust measurement
from the C-17 instrumentation system were of sufficient data quality
for this initial experiment
• Predicting the maximum benefit location, or "sweet spot" for the
trail aircraft was significantly hampered by the lack of knowledge
regarding the actual location, size, and velocity profile of the wake
vortex
AIAA AFM 2011
CAPFIRE - Potential Development Path
•
-Address safety concerns and technical risks early Commercial Passenger -Integrate with future airspace concept developments -Leverage partnerships Commercial Cargo Military Transports AIAA AFM 2011
•
Questions?
Joe Pahle NASADFRC Phone: 661-276-3185 Photo by Mike Venti E-mail: joe.pahle@nasa.gov Used by permission AIAA AFM 2011 2 5 Your Title Here :.
, ...
..
..• · > '.'
~ -."
..
,
~
Vertical Separation, ft.
NASA AFF Phase 2: Vortex Mapping
Test Point Matrix
•
Test Point Matrix 60% • • • • • • • 40% c
-
• • • • • • i ...
• • • • • • 1.'1:1 2 0% Co Q,) tJ) • • • • • • • Co :s, 0% c I 5( -7 % -50% -2 5% 0% 25% % s: ;~ • • • • • • ~ • " -20% I c I • • • • • • I :a VI I I • • • • • • -40% Q.
I N I • • • -60% Y Position (% Wingt ip Separation) M=0.56 & 0.86 -50% -25% 0% 25% 50% Nose to tail separation: 20, 55, 110, 190 feet (% Wingtip Separation) Note: Wingtip Separation = - Wingtip Overlap
•
4 4 8.4 8.4 10 10 X X lead trail - - ------------- ------------- 8.2 8.2 flight C-17 --------------------------- --------------------------- 8 8 for
Winds
----------------------------- ----------------------------- crosswind 7.8 7.8 and --------------------- -- ------------------------ headwind 7.6 7.6 -------- -~ --- ....
f-J" 7.4 7.4
o 0 O
20~--------~--------~--------~--------~------~ 10 30~--------~--------~--------~--------~------~ 20 10 -1 -30~--------~--------~--------~--------~------~ -20~--------~--------~--------~--------~------~ -20 -10 headwind, knts crosswind, knts AIAA AFM
Executive Summary
•
• Qualitative flight data and comments were gathered during several two-
ship, C-17 formation flights (targeted at drag reduction) at a single flight
condition (275 knots, 25,000 ft)
• The C-17 FFS and auto-flight systems were used to stabilize the aircraft at
some trail locations with predicted drag reduction
- The pilot was able to fly FFS test points, but the workload was high
• For this limited set of tests, the maximum average fuel flow reduction was
approximately 7-8% (compared to the tare points before and after).
- There is some evidence that regions with fuel flow and thrust reduction greater than 10% compared to the tare test points exist within the vortex area of influence AIAA AFM 2011