Computer derived reference design of intercity VTOL aircraft and analysis of control power requirements and operating cost

Hoffman, M. A.

English

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,CONTROL POWER REQUIREMENTS OF VTOL AIRCRAFT
Quarterly Status Report No. 1
Period: I April - 301
 June, 1969
NASA Grant No. NGR-05-004-051
Principal Investigator: Myron A. Hoffman
Professor of Mechanical
and Aerospace Engineering
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Introduction
This progress report covers the first three months of effort on
NASA Grant No. NGR-05-OGN-051. During this period Mr. Gary Vanderpol,
a senior, developed the tilt-wing VTOL design program to be described.
Mr. Peter Levin, a master's candidate, will continue this work.
Mr. John Seevers, a doctoral, candidate in the controls area, has
begun to study the problems associated with control power requirements
for the hover phase of flight as part of his doctorate thesis
research.
1
Research Accomplished
Ur order to evaluate control power requirements, it is necessary
to start with a representative VTOL vehicle, in this case an it+tercity
VTOL transport. For this pu , pose a computer program was written to
permitl the rapid design of a series of VTOL aircraft of the tilt-wing
type, following the philosophy of Ref. 1. The basic program inputs
are the, design cruise speed, altitude and range and the number of
passengers. The outputs include a detailed weight breakdown, key
vehicle: dimensions, as well as fuel and time required in each phase of
the mission. In addition, a direct operating cost (DOC) program was
also written, since this is one of the better measures of the economic
usefulness of a particular design.
The: characteristics of the reference design are shown in Table I.
It grosses about 54 ,000 lbs, and can carry 80 passengers over a stage
length of 200 miles at cruise speeds of 400 mph at 20,000 ft. cruise
altitude. It is powered by four turboprop engines with large, 12 ft.
diameter propellers. The vehicle has been designed to provide a high
slipstream velocity over the entire wing to prevent wing stall during
the critical retransition-to the vertical descent phase The estimated
DOC is also shown in Table I. The values are quite reasonable and in
line with projections of other groups.
The..additional power required for control purposes in the low
speed fright regimes has been specified as a percentage increase in
the installed :power:
NE	 (TMPL V
^ P)TOT " NT-1
	 TIP ,,	
(cPF)
where MRP is the maximum rated power, NE is the number of engines,
(THP)HOV is the thrust horsepower required in hover, n P and nTh
are the propeller and transmission efficiencies, respectively and
(CPF) is the control power factor. For -the reference design this was
somewhat arbitrarily specified as 1.15 to give us a starting point for
sensitivity analyses. This simple way of expressing the control
power requirement allows us to evaluate the effect of various "control
power" levels on aircraft gross weight and DOC. (Note: this use of
the term control power here is strictly for convenience; in this context
it means only the excess installed power for control purposes.)
Initial results of such a study are shown in Tables II and III for
CPF's of 1.05 and 1.25. A new VTOL aircraft was designed for each value
or OF but with all other specifications held constant. It is interest-
ing to note that for a five-fold increase in control power (from 5%
to 25% of MRP), the vehicle gross weight increased by less than 4%.
Thus it appears that this type of tilt-wing VTOL aircraft is not as
sensitive to the level of control powerspecified as certain types of
jet-powered VTOL designs.(2)
A more meaningful measure of the penalty paid for additional
installed power fora commercial vehicle is the DOC. As shown in
Table il, the flight operations cost and depreciation costs each in-
creased about 9% for the five-fold increase in control power.
The maintenance costs appear, to decrease almost 40% as the engine
power is increaszd. This is due to the use of the multi-regression
formula for maintenance costs-developed in Ref. -3 which has a negative
icoefficient on the engine power term. The more conventional ATA
formula which predicts increasing maintenance costs with engine power
level seems more reasonable in this particular case.
In any event the total DOC will increase no more than 9% for a
five-fold increase in control power. The implications of these
results will be explored more fully, but the initial impression is
that large increases in installed power for control purposes result in
relatively small economic penalties compared to the increased safety
in the low speed flight regimes (assuming, of course, that the
added power is utilized effectively).
REFERENCES
1. M.I.T. Rpt. FT-66-1, Nov. 1966.
2. Schaeffler, J., Alscher, H. and Steinmetz, G., "Control-Power
Usage for Maneuvering in Hover of the W -101*Aircraft," J. Aircraft,
4 9 5 9 p 445-451.
3. M.I.T. Rpt. FT-66-2, Nov. 1966.
►—
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DESIGN PROJECT INPUT DATA
_	 PILOT SALARY	 35000,010DOLLARS/YEAR
COPILOT SALARY	 21000.00
_ 
:;JLLARS/YEA
_	
R	
_
PILOT AND COPILOT FLIGHT TIME	 960.00 HOURS/YEAR
FLEET SIZE	 12	 AIRCRAFT
AVERAGE A
	
36.00 MONTHS
DEPRECIATION TIM
	
12.	 YEARS
TIME BETWEEN OVERHAUL - ENGINES
	 4000.00 FLIGHT HOURS	 T
VEHICLE UTILIZATION
	 3000900 HOURS/YEAR
_	 ENGINE COST	 _	 300.00 DOLLARS/LB
ELECTRONIC EQUIPMENT COST	 150000.00 DOLLARS
NUMBER OF SEATS ABREST 	 6
TOILETS
CREW MEMBER
SPECIFIC FUEL CONSUMPTION - NRP
	 0.55 LOS OF FUEL/HP-4k
PROPELLER TIP MACH NUMBER 	 0175
PROPELLER ASPECT RATIO
	 15.00
PROPELLER EFFIENCY
	 0090
TRANSMISSION EFFIENCY 	 0.90
THICKNESS TO CHORD RATIO - WING
	 0110
OSWALD WING EFFECT FACTOR 	 0.70
AIR DENSITY - SEA LEVEL STANDARD DAY
	 0.002.3769 SLUGS/CU. FT.
AIR TEMPERATURE - SEA LEVEL STANDARD DAY
	 519.00 DEG. RANKINE
AIR TEMPERATURE - SEA LEVEL HOT DAY 	 550.00 DEG, RANKINE
KINEMATIC VISCOSITY OF AIR - S.L. HOT DAY
	 0.00015723 SQ0 FT /SEC
STRUCTURAL LOAD FACTOR 	 4.50
CRUISE VELOCITY	 4.00.00 MPH
HEAD WIND VELOCITY	 15.00 MPH
NOTES
11 AIRCRAFT ASSUMED TO BE OPERATING ON A HOT DAY
21 TOTAL GROSS WEIGHT INCLUDES FUEL
31 ENGINES ASSUMED
	
DELIVER 7.
51 RESERVE TIME NOT
	
	
LCUL
	
ED,
T.
	
CRUISE VEHICLE	 FLY AGAI	 W
REFERENCE DESIGN_
AVAILABLE CONTROL POWER z 15.0 PERCENT
OF REQUIRED THRUST HORSEPOWER
COMPONENT WEIGHTS - LBS
FUSELAGE	 6556.63
WING	 5068.45
ENPENNAGE 1351.69
ENGINES 2823.26
PROPELLERS 3339.42
NACELLES 1411963
ENGINE OIL 140.00
UNDERCARRIAGE 1622.03
TRANSMISSION 2186.50
FURNISHINGS 3750.00
AIR CONDITIONING 1540.00
HYDRALICS 571.65
ELECTRICAL EQUIPMENT 645.57
ELECTRONIC EQUIPMENT 642.00
FLIGHT CONTROLS 1081.35
FUEL TANKS 200.14
D
CREW	 600.00
TOTAL GROSS WEIGHT	 54000.07
WING DIMENSIONS
I
R
BS/SQ
Q.FT.
A
T
MENGINE SPECIFICATIONS
NORMAL RATED POWER	 17645.40 HP
MAXIMUM RATED POWER	 21174.47 HP
NUMBER OF ENGINES	 4
PROPELLER SOLIDITY	 0.25
PROPELLER DIAMETER	 11.59 FT
CLIMB PHASE
VELOCITY OF CLIMB	 7150
CRUISE PHASE
LIFTIDRAG
LIFT COEFFICIENT
10679
0197
:t	 PARASITIC DRAG COEFFICIENT
INDUCED DRAG COEFFICIENT
09045
0.045_
DESCENT PHASE
-	
RAT'E OF DESCENT 74.12	 FT/SEC
VELOCITY OF DESCENT 591.33	 FT/SEC
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f TABLE OF PERFORMANCE
LBS	 RANGE - MI	 TIME -
I•t•
1
	
0.
•77	 IL•
94
1.00
•00	 We
.88 MI	 51.44
Z
"+	 DIRECT OPERATING COSTS
STAGE LENGTHS (ST * MILES)	 200.00
CRUISE ALTITUDE (FEET) 	 20000.00
FUEL BURNED (LOS)	 3298935
BLOCK SPEED (MPH)	 381.50
FLIGHT OPERATIONS (CENTS/MILE)
IL
RANCE
IC LI ILITYa
TOTAL (CENTS/MILE)
	
48.04
MAINTENANCE (CENTS/MILE
N
TOTAL (CENTS/MILE)	 17.34
DEPRECIATION ICENTS/MILE)
AIRCRAF1	 21006
A
TOTAL (CENTS/MILE)	 34.96
riuu l%	 7 0G * 0 V
SEAT MILE
	
1157
mREFERENCE DESIGN
AVAILABLE CONTROL POWER = 5.0 PERCENT
OF REQUIRED THRUST HORSEPOWER
COMPONENT WEIGHTS - LBS
FUSELAGE
	 6537.74
7.58
2529.00
3266.29PROPELLERS
NACELLES
ENGINE OIL
UNDERCARRIAGE
TRANSMISSION
FURNISHINGS
A•IR CONDITION
4
ELECTRICAL EQUIPM	 •ffv
ELECTRONIC EQUIPM T	 .00
FLIGHT CONTROLS
	
1 .76
CREW	 600.00
TOTAL GROSS WEIGHT
	 52959.78
WING DIMENSIONS
SPAN.	 48.40 FT
RATIO
MEAN SWEEPBACK ANGLE
	 000 DEG
ASPECT RATIO
	 9050
WI:NG_LOAOLNG
	 214.75 LBS/SQ1FT.
WING AREA	 246.61 SOFT.
TOTAL LENGTH	 77913 FT
nvkmcTCo
	
	 19 G9. GT
PAS
IL
DIRECT OPERATING COS?S
STAGE LENGTHS (ST * MILES)
	 200.00
CRUISE ALTITUDE (FEET) 	 20000.1
FUEL BURNED (LBS)
	 3057.46
BLOCK SPEZU (MPH)	 d3.37
FLIGHT OPERATIONS ( CENTS/MILE)
OPIL
OIL	 0.01
INSURANCE	 3.91
PUBLIC LIABILITY	 0187
TOTAL (CENTS/MILE)
	 45987
MAINTENANCE (CENTS/MILE)
TOTAL ( CENTS/MILE)
	 23.17
DEPRECIATION (CENTS/MILE)
AIRCRAFT	 20.75
ENGINES	 4.67
L
AIRFRAME SPARES
	 2.07
curimm eftAnce	 -	 ^ ffn
TOTAL (CENTS/MILE)
	 33.61
T
ILE
vui.4grc4i oluUn nuum	 AY.1.3.1 -
CENTS/AVERAGE SEAT MILE
	 1.60
REFERENCE DESIGN
AVAILABLE CONTROL POWER = 2590 PERCENT
OF REQUIRED THRUST HORSEPOWER
COMPONENT WEIGHTS - LBS
FUSELAGE	 6575.63
KING	 5182.14
PROPELLERS 3414.63
NACELLES 1564906
ENGINE OIL 140.00
UNDERCARRIAGE 1653963
TRANSMISSION 2223.86
FURNISHINGS 3750.00
AIR CONDITIONING 1540.00
HYORALICS 585.94
ELECTRICAL EQUIPMENT 652.45
ELECTRONIC EQUIPMENT 642.00
FLIGHT CONTROLS 1102.42
.31
6,;3 0.00
TOTAL GROSS WEIGHT	 55063.48
WING DIMENSIONS
SPAN	 49.74 FT
D
	
FT
RATIO	 .50
RATIO
	
9.
_	 FUSELAGE DIMENSIONS
TOTAL
NUMBER OF PASSENGERS	 80
NUMBER OF SEATS ARREST 	 6
IG	 DIRECT OPERATING COSTS
STAGE LENGTHS (ST. MILES)
	
200.00
CRUISE ALTITUDE (FEET)	 20000.00
FUEL BURNED ILBS)
	
37,37.99
BLOCK SPEED (MPH)	 .379.83
FLIGHT OPERATIONS (GENTS/MILE)
nr nr	 a cn	 ^^
OIL	 0.01
INSURANCE	 4.02
PUBLIC LIABILITY	 0187
TOTAL (CENTS/MILE)	 50.19
_	 MAINTENANCE (GENTS/MILE)
TOTAL (CENTS/MILE) 	 13.84
DEPRECIATION (CENTS/MILE)
AIRCRAFT	 21.37
TOTAL (CENTS/MILE)	 36.35
TOTAL DIRECT OPERATING COSTS
rcwr¢iMtrc	 1Afl_3A
T MIL


Control power requirements of VTOL aircraft Quarterly status report, 1 Apr. - 30 Jun. 1969

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