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Produced by the NASA Center for Aerospace Information (CASI)
NASA
Technical Memorandum 82932
(NASA-TM-8233,2) A REMOTE
AUGMENTCR LIFT
N83-12087
SYSTEM VITH
A TURBINE 5UASS ENGINE
(NASA)
p HC A02/MF
A^1 ,1
csci 21E
U11 Ci as
G3/07
00841
A
Remote Augmentor Lift
System With a Turbine
Bypass Engine-
1"T
A'k7 \k"
Alp, Laurence H. Fishbach and Leo C. Franciscus ^?^,
No V 19
V% 14
CY)
Lewis Research Center
R
#1 V CD IN
Cleveland, Ohio
ACC,,Qr
ESS DEPT
Prepared for the
Thirtoc!nth Congress of the International Council of Aeronautical Sciences
and Al ycraft Systems and Technology Meeting
sponsored
by the American Institute of Aeronautics and Astronautics
Seattle, Washington, August 22-27, 1982 OD
NASA
A REMOTE AUGMENTS LIFT SYSTEM WITH A TURBINE BYPASS ENGINE Laurence H. Fishbach and Leo C. Franciscus National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 44135 I. INTtODUCTION ABSTRACT Providing a vertical takeoff or landing A study of supersonic vertical takeoff or (VTOL) capability to high speed aircraft pos- landing (VTOL) fiahter aircraft employing two ses many challanges in aircraft/propulsion engine types, a conventional medium bypass system integration. This is especially true ratio turbofan, and a turbine bypass turbojet
M
M
for supersonic aircraft. This type of air- was carried out. The aircraft assumed was a craft requires a low frontal area whereas lift clipped delta wing with canard configuration.
w
systems tend to increase the frontal area., A VTOL deck launched intercept, DLI, mission Some of the concepts that have been studied with Mach 1.6 dash and cruise segments was thus far l , 2 are shown in figure 1. The used as the design mission. Several alternate missions requiring extended subsonic capabili- VATOL concept requires the aircraft to takeoff ties were analyzed. Comparisons were made and land in a vertical attitude and may be between the turbofan (TF) and the turbine objectionable from the pilot's viewpoint. The lift plus lift-cruise (L+LC) system carries bypass turbojet (TBE) engines in airplane dedicated lift engines. This would tend to types using a Remote Augmented Lift System, improve engine performance at cruise. Since RALS and a Lift plus Lift Cruise system they would not be oversized for takeoff, they (L+LC). The figure of merit was takeoff gross need not be throttled back drastically at weight for the VTOL DLI mission.
cruise with resulting penalties in specific The results of the study show that the fuel consumption. However, unless the lift turbine bypass turbojet and the conventional engines can be used for other flight condi- tions they represent a weight penalty. Also, turbofan are competitive engines for both type the two engine types may result in higher life of aircraft in terms of takeoff gross weight and range. However, the turbine bypass turbo- cycle costs.
jet would be a simpler engine and may result The remote augmentor lift system (RALS) in in more attractive life cycle cos"s and figure 1 is powered by a turbofan engine. The reduced maintenance. The RA I .$ and L+LC air- engine duct flow is directed to the remote plane types with either TBE or TF engines have burners during vertical takeoff and landing.
approximately the same aircraft takeoff gross This system is less compact than the L+LC weight.
system because of the RALS ducting. Also, it N,ould have a hot footprint during VTOL opera- NOMENCLATURE tion, The tandem fan system is similar to remote Afterburner AB lift fan systems. Separate air intakes are bypass ratio BPR provided for the front fan and for the main deck launched intercept DLI engine when in VTOL operation. An attractive fan pressure ratio FPR feature of this system is that the front fan feet ft is used during both VTOL and cruise flight.
gravitational gas constant pound lb lift plus lift-cruise The turbojet would be a compact engine for L+LC Mach number a VTOL aircraft. However, an undesirable M problem in using the turbojet is that part of maximum max minimum the hot exhaust gas must be ducted to the min nautical mile forward lift point. A mean: of avoiding this n.mi.
overall pressure ratio problem is provided by the turbine bypass OPR engine (TBE). This concept was first reported optimum opt degrees Rankine by Boeing in their supersonic cruise airplane R second studies contracted by NASA-Langley. In this sec specific fuel consumption conceptual turbojet some of the compressor SFC discharge air is bypassed around the burner sea level SL turbine bypass engine and turbine and reinjected into the nozzle.
TBE For aircraft requiring wide variations in temperature temp engine power, the turbine bypass provides a turbofan TF better cycle match and improved performance.
takeoff gross weight TOGW Studies have been made of the turbine bypass corrected airflow rate W'(4/a turbojet(TBE) for a commercial supersonic transport.
ripts Subsc mass Since the compressor discharge air of the m force TBE provides an attractive air supply for the f
RALS during VTOL, in-house studies of this inlet and nozzle drags. The inlet drags
concept have been carried out at NASA-Lewis. include cowl pressure drag, bypass drag, and
In these studies, the TBE and a convzntional spillage drag. Nozzle performance includes
mixed flow turbofan were analized it both the the boattail drag.
RALS and L+LC airplane systems. Engine per-
formance and missions studies were performed The installed propulsion system weight for th.cse engine concepts. The ;p otential of includes the engine, inlet, and nozzle. The the engines was assessed in terms of the per- propulsion system weight was calculated using formance of an advanced supersonic VTOL an engine weight computer code.5 fighter. This paper provides the results of these studies.
III. DISCUSSION II. METHOD OF ANALYSIS The Turbine Bypass Engine The airplane used for the study is shown For most aircraft turbine engines the in figure 2. The baseline aircraft has two turbine is choked for nearly all operating main engines. For the RALS, main engine air conditions. Therefore, for a fixed turbine, is ducted forward to a remote augmentor for
the turbine corrected airflow will be constant
vertical thrust in addition to the vectored for nearly all operating conditions. In a thrust of the two main engines. For the L+LC conventional turbojet, the compressor
will
system, one scaled XL99 lift engine is located operate at pressure ratios and airflows to forward for the front thrust. The location of match the constant value of turbine corrected the front thrustor was adjusted for center of airflow. This places limitations on the gravity. Reaction controls powered by main throttle excursions the turbojet can achieve.
engine air are located at the wing tips. At high throttle (high turbine inlet tempera- These provide pitch, yaw and roll control by ture) the compressor operating point moves modulating thrust vectors. As shown in figure toward the surge region. At low throttle the 2 the airplane is a clipped delta wing with compressor operates at low pressure ratios canard configuration. The weight and dimen- which deteriorate engine performance. One sions of the airplane vary with propulsion means of reducing these restrictions is a system type and mission constraints. variable area turbine. This permits the tur- bine corrected airflow to vary, permitting The five missions included in the study wider excursions in throttle without affecting are shown in figure 3 and 4. As indicated in the compressor noerating point. The objective the figures, the deck launched intercept and of the turbine bypass concept is very similar combat air patrol missions are for VTOL. The to that of the variable area turbine. How- other three missions are for short takeoff or ever, instead of varying the turbine area, the landing (STOL). The airplane was designed for turbine airflow is varied. Figure 5 shows a the deck launched intercept (DLI) mission schematic of this concept for a single-spool (figure 3). The design was held fixed for the turbojet. The compressor is matched to an remaining missions and the takeoff weight undersized turbine and provision is made for adjusted for the fuel and weapons required for bypassing some compressor discharge air around each mission. A fuel reserve of 5 percent was the burner and turbine and into the nozzle.
assumed in the study. As shown in the figure, the turbine inlet temperature for zero bypass is 2100 0 R.
As The airplane/mission calculations were the turbine inlet temperature is increased, performed with the NASA Lewis Airplane Mission the bypass airflow is increased. The actual Analysis Code (AMAC) which computes the vol- turbine airflow is reduced to maintain a con- umes, dimensions, weight, and aerodynamics of stant turbine corrected airflow. In this the airplane and "flies"- it over the pres- example, the compressor operates at a single cribed mission. The airplane and engine were point for turbine inlet temperature variations sized to meet the design constraints listed in from 2100 O R to 3260 0 R. In addition to the figure 3. The first three constraints are engine performance benefits provided by the satisfied by engine sizing. The specific TBE, this concept js an attractive alternative excess oower (PS) goal and the one minute for the remote augmentor lift system for VTOL acceleration from Mach 0.8 to Mach 1.6 at aircraft.
35000 feet are usually the most critical con- straints and engines sized for these two met the other constraints including VTO. The last Propulsion Systems constraint (6.2 g's at Mach 0.6, 10:10 -feet) was satisfied by adjusting the wing loading. As mentioned before, the TBE and a conven- tional, mixed flow turbofan were studied for The uninstalled engine performance was both the RALS and L+LC airplane types. The first calculated without inlet and nozzle engine cycle characteristics for these engines drags using the Navy-NASA Engine Program are provided in Table 1. Schematics of the The engine component aerodynamic propulsion system arrangements for the RALS (NNEP). 4 characteristics, efficiencies, and cooling systems are shown in figure 6. For the RALS/ requirements used in the program are compat- turbofan system the bypass air is supplied to ible with a mid-1990's technology level. The the remote burner where the air is heated to 3260 O R installed engine performance is the unin- during VTOL operation. For this adjusted for the stalled performance system the RALS supplied 30 to 50 percent of the total lift. For other flight condi- larger than the TBE aircraft.
tions the engines operate as mixed flow turbo- fans, For the RALS/TBE system the compressor Figure 9 shows a comparison of aircraft bypass air is directed to the remote burner TOGW for RALS and L+LC systems with TBE and for VTOL and to the engine nozzle at other turbofan engines. All of these enginesexcept flight conditions. During vertical takeoff the XL99 engine are equipped with after- ` ' f t the engines are operated at maximum power and burners. The high thrust/weight ratio oP' the the amount of bypass air going to the remote XL99 lift engine (about 14 installed) provides burner is a maximum. This amounts to about 20 a lightweight lift system competitive with the percent of the engine airflow in this exam- RALS. As seen in the figure the RALS and the ple. The RALS provides about 17 percent of L+LC propulsion system result in about the the total lift in the RALS/TBE system, For same TOGW. It should be emphasized that the other flight conditions where high power is turbofan requi r es afterburners for both RALS required such as acceleration and combat the and the L+LC aircraft to perform the DLI and bypass air is injected into the engine noz- CA • missions ;,rile the TBE does not. This is* zle, As indicated in figure 6, the duct sizes due to the climb to supersonic speed segment for the RALS/TBE would be about 1/3 the size of this mission.
of those for the RALS/turbofan system.
Figure 10 compares the propulsion systems For the L+LC propulsion systems, the TBE for the alternate missions. Since the large or turbofan engines are the main engines and TOGW of the airplanes with dry turbofans the performance and weight characteristics of (figure 8) indicate dry turbofans are not suitable for this type of airplane, only the XI.99 are used for the lift engine. The lift engine is sized to provide 30 percent of afterburning turbofans are considered in this the total lift for VTOL operation. comparison.
Figure 7 shows a comparison of the turbine In comparing the dry TBE with the after- bypass engine (TBE) and turbofan engine (TF) burning TBE for both RALS and L+LC aircraft, performance at Mach 1.6 and 0.8. Some typical it is seen that the dry TBE is better than the operating points for a DLI mission are also afterburning TBE for Combat Air Patrol VTOL shown in the figure. The indicated climb (CAP) and Strike. Engines sized for the supersonic Deck Launched Intercept mission thrust is the climb throttle setting at Mach 1.6. About 65' of the usable fuel is consumed give adequate power without afterburning for during the three flight segments at Mach 1.6. the subsonic CAP and Strike missions, The For climb and combat the TBE has about 13% afterburning engines are smaller and lighter lower fuel consumption than the turbofan. For and operate at better SFC's during dry opera- dash and the Mach 0.8 cruise the fuel consump- tion (not throttled back as far) than the dry tion of the two engines is about the same. TBE's. However, the use of afterburning The better supersonic SFC's of the TBE lead to during climb and combat results in excessive lower overall fuel consumption compared to the fuel consumption and less range. For Subsonic turbofan. As shown in Table 1, the dry Surveillance about 50% of the mission fuel is thrust/engine weight (FN/W) ratios of the TBE used during loiter and for the Ferry mission is better than that of the TF and the after- about 85% of the mission fuel is used for burning FN/ 14 ratios are nearly the same. subsonic cruise. Both the dry and after- It will be shown later that the heavier engine burning TBE's operate dry for these missions weight of the TBE compared to the turbofan and the loiter time and range about the same.
(for the same airflow) offsets this advantage to some extent. Ln comparing the turbofan with the TBE, it is seen that the turbofan does somewhat better that the TBE on all of the alternate mis- Mission Results sions. Since these mission are all subsonic, the SFC's of the turbofan are better than those of the TBE (figure 7) resulting in bet- Figure 8 shows a comparison of the TBE and turbofan engines in L+LC aircraft in terms of ter range and loiter capabilities.
takeoff gross weight (TOGW). Both dry and afterburning engines are shown. As indicated In comparing the RALS and L+LC aircraft in the figure, the aircraft are sized for the for the alternate missions both systems pro- VTOL DLI mission and the comparisons in this vide about the same alternate mission capabil- figure are for this mission. The climb thrust ities.
of the dry turbofan is marginal for this mis- sion resulting in large engines and excessive fuel consumption, The aircraft with dry tur- CONCLUDING REMARKS bofans is about 85% heavier tnan the dry TBE aircraft. Afterburning does not improve the The turbine bypass engine and a medium TBE aircraft significantly (about 8A reduced bypass ratio mixed flow afterburning turbofan TOGW), but results in large improvements to are competitive engines for a VTOL aircraft in the turbofan aircraft. This shows that the terms of takeoff gross weight. Afterburning turbofan requires afterburners, but the TBE provides a small benefit for the TBE, but is may not need afterburners resulting in a much required in the turbofan to make it competi- simpler propulsion system. However, when both tive with the TBE. For the RALS system the engines are compared with afterburners the TBE would result in smaller duct sizes and TON of the turbofan aircraft is only slightly lead to less complexity. Since the TBE does ik II
ORIGINOL 'I
QUALITY
not need an afterburner for either the RALS or OF pooR the L+LC aircraft and being a simpler engine than the turbofan it may be a more attractive M engine in terms of life cycle costs. Compari- sons of the RALS and L+LC systems show that both provide about the same takeoff thrust/ weight ratios and result in about the same + aircraft takeoff gross weight.
x REFERENCES 1. W. R. Boruff and A. J. Roch, "Impact of Mission Requirements on V/STOL Propulsion Concept Selection," Journal of Aircraft, Vol, 18, No. 1, pp. 43-50, January 1981.
2. R. W. Luidens, G. E. Turney and J. Allen, "Comparison of Two Parallel/Series Flow Turbofan Propulsion Concepts for Super- sonic V/STOL," AIAA Paper 81-2637, December 1981.
3. L. C. Franciscus, "Turbine Bypass Engine - A New Supersonic Cruise Propulsion Con- cept," National Aeronautics and Space Administration TM-82608 (1981).
L. H. FishGach and M. J. Caddy, "NNEP - 4.
The Navy-NASA Engine Program," National Aeronautics and Space Administration TM X-71857 (1975).
E. Onat and G. W. Klees, "A Method to 5.
Estimate Weight and Dimensions of Large and Small Gas Turbine Engines Final Report," National Aeronautics and Space Administration CR-159481 (1979).
ENGINE CHARACTERISTICS TABLE I - TF TBE ENGINE CYCLE DESCRIPTION 175 175 lbm/sec W s/:&/ 6, --' 3 FPR 15 15 OPR 1.0 --- BPR MAX CET, °R MAX AB, °R MAX RALS TEMP,, °R ENGINE WEIGHT Engine + Nozzle + RALS, lbm 6.2/7.5 5.3/8.0 THRUST TO WEIGHT - DRY/AB PAGZ
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