. NASA Technical Memorandum 100048
Application of Empirical and Linear Methods to VSTOL Powered-Lift Aerodynamics
Richard Margason and Richard Kuhn
February 1988
National Aeronautics and Space Administration ~~
NASA Technical Memorandum 100048
Application of Empirical and Linear Methods to VSTOL Powered-Lift Aerodynamics
Richard Margason, Ames Research Center, Moffett Field, California Richard Kuhn, V/STOL Consultant, Valencia, California
February 1988
National Aeronautics and Space Administration Ames Research Center Moffett Field, California 94035 APPLICATION OF EMPIRICAL AND LINEAR METHODS TO VSTOL POWERED-LIFT AERODYNAMICS
Richard Margason and Richard Kuhn
Ames Research Center
ABSTRACT borne flight. Proper design of VSTOL aircraft requires an accounting of these complex phenom- ena. Unfortunately, the flows involved are not This paper critically reviews available amenable to purely theoretical predictions at prediction methods and provides an assessment of this time. Improved prediction methods are their strengths and weaknesses. The methods are needed to guide experimental programs and to applied to selected problems which represent the reduce the testing requirements in the future, major aero/propulsion interactions for short as well as to provide an understanding of the takeoff and vertical landing (STOVL) aircraft of flow physics. One motivation of this paper is current interest. The first two problems deal to identify areas where modern computational with aerodynamic performance effects during fluid dynamics (CFD) methods can provide hover: a) out-of-ground effect, and improvements to the current computational capa- b) in-ground effect. The first problem can be bilities. The ultimate goal would be to develop evaluated for some multijet cases; however, the the ability to completely analyze the aerody- second problem is very difficult to evaluate for namics throughout the entire flight envelope of multijets. The ground-environment effects due an arbitrary VSTOL aircraft. to wall jets and fountain flows directly affect Traditionally, prediction techniques appli- hover performance. In a related problem c) hot- cable to VSTOL aircraft (1-8)* consist of gas ingestion affects the engine operation. potential-flow methods with empirically derived Both of these problems as well as jet noise corrections and/or adjustments to account for affect the ability of people to work near the viscous effects which significantly affect aircraft and the ability of the aircraft to aerodynamidpropulsion interactions. Some of operate near the ground. Additional problems these methods are simple to use but provide are d) the power-augmented lift due to jet-flap results with only limited applicability. Other effects (both in- and out-of-ground effects) and procedures build on potential-flow-panel e) the direct jet-lift effects during short methods. The input data tend to be complex and takeoff and landing (STOL) operations. The difficult to prepare, and often the results have final problem is f) the aerodynamic/propulsion limited usefulness. interactions in transition between hover and In recent years there has been rapid pro- wing-borne flight. Areas where modern computa- gress in the development of CFD. This progress tional fluid dynamics (CFD) methods can provide is due in part to improvements in digital com- improvements to the current computational cap- puters (9) which provide rapid computation abilities are identified. speeds (up to hundreds of millions of floating- point operations per second), and larger memo- FOR OVER THIRTY YEARS, vertical or short takeoff ries (up to hundreds of millions of words). and landing (VSTOL) aircraft have been developed This growth was clearly described in Jameson's primarily from experimental investigations survey (10) of the evolution of computational because there are many unique aerodynamic/ propulsion-induced effects which occur with these vehicles. These problems are especially *Numbers in parentheses designate significant at low speeds from hover to wing- references at end of paper.
1 methods for conventional aerodynamics. Numeri- VSTOL. One of the first stage I11 analyses was cal approximation methods were examined for a by Baker (12). This calculation of the flow hierarchy of models in ascending order of com- field caused by a jet in a crossflow used a plexity, ranging from the linearized potential- finite-element, pressure-interaction, parabolic flow equations to the Reynolds-averaged Navier- approximation to the Reynolds-averaged full Stokes equations. In a study (11) of the influ- Navier-Stokes equations. The other papers ence of CFD on experimental aerospace facili- (13-16) in the present session will present ties, four main stages (I-IV) of approximation current examples of several Stage II and Stage to the full Navier-Stokes equations were identi- 111 approximations applied to either STOL- or fied. For completeness in relation to short STOVL-aircraft-related flow fields. takeoff and vertical landing (STOVL) aero/ This paper critically reviews available propulsion interactions, 'the present authors stage 0 and stage I prediction methods, and have added a Stage 0 to represent the empiri- attempts to provide an assessment of their cally based methods, and Stage Ib to represent strengths and weaknesses. Existing methods will linearized inviscid methods which include an be discussed based on six selected problems approximate model for jets: which represent the major aero/propulsion inter- actions for STOVL aircraft of current inter- Stage Approximation est. This paper presents examples using avail- able methods. The first two problems deal with 0 Empirical methods aerodynamic performance effects during hover: a) out-of-ground effect and b) in-ground I Linearized inviscid effect. Both problems are reasonably well la Linearized inviscid plus boundary understood for the case of a single jet. The layer (BL) first problem can be evaluated for some multijet Ib Linearized inviscid plus modeled jets cases; however, the second problem is very difficult to evaluate for multijets. The next I1 Nonlinear inviscid three problems are related to operations near IIa Nonlinear inviscid plus interacting BL the ground: c) the ground-environment effects due to wall jets and due to surface breakdown, I11 Reynolds-averaged Navier-Stokes d) hot-gas ingestion effects on the engine operation, and e) short takeoff and landing IV Full Navier-Stokes (large-eddy (STOL) ground effects. These problems affect simulations with small-scale both the ability of people to work near the turbulence modeling) aircraft and the ability of the aircraft to operate near the ground. The final problem Stage 0 has been the mainstay method for extra- f) is the aerodynamic/propulsion interactions in polating experimental data beyond the original transition between hover and wing-borne flight. wind tunnel test conditions up to the present time for VSTOL aero/propulsion interactions. NOMENCLATURE Stage I is currently used for engineering anayl- sis of conventional airplanes. The Navy V/STOL A jet area Aerodynamics, Stability and Control Manual (4,5) BL butt line utilizes Stages 0, I, and Ib methods, and repre- CD drag coefficient sents the current state of the art in V/STOL CL lift coefficient computational methods. For conventional air- CM pitching-moment coefficient planes without propulsion-induced effects, CT thrust coefficient limited to moderate use is also being made of CU jet momentum coefficient stage I1 solutions; Stage I11 is expected to be cL section lift coefficient widely used in the next 10 years. The principal C pressure coefficient I items pacing introduction of Stage I11 into the P C' section jet momentum coefficient aerodynamic design process are: a) development DM plate or jet diameter of improved turbulence models; b) geometry grid d jet diameter generation difficulties and limitations; EVD elementary vortex distribution c) development of more efficient and reliable FS fuselage station numerical algorithms; and d) development of more H,h height powerful scientific computers. upflou jet thickness At this time some initial efforts have been turbulent intensity made to use stage I1 and I11 approximations for
2 up from ground plane to undersurface Kh factor for effect of forward speed on UP suckdown V ground vortex L lift W wake e stagnation line X x direction LID lift improvement device m free stream M Mach number NPR nozzle pressure ratio Superscript P,P pressure I 9 dynamic pressure section R radius, radial distance *n Reynolds number MULTI-JET OUT-OF-GROUND EFFECT HOVER S wing area INTERACTIONS S' distance between jet impingement points on a ground plane STOL short takeoff and landing During hover, there is a base loss due to STOVL short takeoff and vertical landing interactions between the lifting jets and the T thrust, temperature lower surface of the aircraft which results in a V velocity - distribution of induced suction pressures which /q/qj loss. 'e 'e effective velocity ratio, produce a lift Additional performance VSTOL vertical or short takeoff and landing losses include inlet-flow distortion, hot-gas WL water line ingestion, hot-day conditions, control bleed, x,y,z Cartesian coordinates internal nozzle flow, thrust vectoring, and a angle-of-attack static ground effect. There are many items 6 sideslip angle related to the details of the aircraft design AL aero/propulsion lift-interference which determine the magnitude of the losses. increment Even though the sum of these losses may be only AM aero/propulsion lift-interference a few percent of rated thrust, an accurate increment knowledge of each is required to make a realis- AT inlet temperature rise, Ti - To tic estimate of the aircraft's performance. An 6 deflection angle error of as little as 3% in thrust would reduce 6' section deflection angle the gross weight, which in turn would reduce the 0 velocity potential fuel capacity, and hence the design range, by as 0' computational polar angle measured in much as 10%. the ground plane about a jet impinge- The classic form of an axisymmetric free ment point referenced to the line jet with a uniform nozzle exit dynamic pressure joining two jet impingement points profile and low turbulence is sketched in P,O polar coordinates Fig, 1. In the jet there are two regions of flow: a) the short potential-core region (up to Subscripts six nozzle diameters long) which has a conical shape and a uniform velocity profile, and b) the e effective or exit fully turbulent region. In an early program edi3 edge intended to evaluate base losses during hover, a ej jet exit NASA investigation (17) evaluated the effect of F fountain the character of the jet on induced lift loss. f flap or fountain The results showed that a relation exists h height or hover between the lift loss and the rate of decay of i inlet or point of maximum rate of change nozzle dynamic pressure. of decay parameter Both of these parameters are functions of in inlet face the amount of air entrained into the jet and the J Jet proximity of the entrainment to the plate. A L LID correlation between the slope of the lift-loss inax maximum curve and a parameter indicative of the dynamic- n nozzle pressure decay was developed. As indicated in N normal Fig. 2, this parameter is the maximum slope of 0 ambient dynamic-pressure decay divided by the distance PI ,P2 wall jet downstream where that slope occurs. The data of t total (17) were used to obtain the correlation pre- und under surface sented in Fig. 2.
3 -0.64 1.581 !!kT = -0.0002528$[5)AP >]e (2)
where Prt is the total perimeter of all of the where jets in the configuration. It is noted that Eq. 2 implicitly accounts for the higher decay s=planform area rate of multiple-jet configurations in terms of equivalent jet diameter, but does not account for higher decay rates caused by jet-exit condi- A=total jet-exit area tions involving high entrainment rates. If de = diameter of an equivalent single nozzle higher than normal turbulence levels and decay Eq. having an area equal to the total of the rates are involved, 1 should be used. areas of the multiple nozzles MULTI-JET IN-GROUND EFFECT HOVER INTERACTIONS
= maximum rate of decay of dynamic pressure During hover close to the ground, the lifting jets impinge on the ground and form wall jets flowing radially outward from their (x/deIi = downstream distance at which the impingement points. These outward-flowing wall dynamic pressure decay rate is maximum jets entrain air beneath the configuration and lower the pressure on the bottom surface, caus- ing a jet-induced down load or suckdown. When It should be pointed out, however, that the the wall jets from adjacent jets meet, an upwash dynamic-decay parameter is quite sensitive to or fountain flow is created between them. If the details of how the data are faired. Since there are only two jets, this upwash takes the the magnitude of the lift loss is usually a few form of a fan-shaped fountain as shown in percent of thrust, a potential estimation error Fig. 3. If there are more than two jets, a fan- of 10% amounts to only a few tenths of a percent shaped fountain is formed betueen each adjacent of the thrust and is not very serious. The pair of jets, and a "fountain core" is formed solid data symbols in Fig. 2 were obtained from near the centroid of the area enclosed by the a large-scale test which used a J-85 turbojet jets where the fountain fans from each pair of engine to provide a hot jet (approximately jets meet. When these fountain flows impinge on their 1000° F, and pressure ratios up to 1.73). The the lower surface of the configuration, resultant lift-loss data agree with the momentum imparts an upward force, or lift, that correlation derived from small-scale data. tends to offset the suckdown created by the Subsequent investigations by Lockheed- entrainment action of the wall jets. Georgia (181, under contract to NASA on configu- The flows involved are highly turbulent and rations derived from the XV-4B airplane, show are not amenable to potential-flow analysis. for that this type of correlation can be suitable Consequently, the only methods available the configuration €or additional configurations. However, it was estimating their effects on determined that the effect of jet-pressure ratio (7,191 are empirically based. Both methods use needed to be included in Eq. 1 by multiplyin essentially the same data base for multiple-jet the right side of the equation by (pn/p)-0.6f, configurations as does Wyatt's method (20) for (21), and by changing the constant from -0.009 estimating the suckdown and Yen's method to -0.016. or a similar approach, for estimating the foun- (20) A more direct, easier-to-use method for tain effects. Wyatt developed an empirical estimating these hover lift losses was developed method for estimating the suckdown for single- by McDonnell Aircraft (see Equation in Fig. 33 jet configurations that has become widely from (2)). Correlation of data from various accepted. References (7) and (19) use slight single- and multiple-jet configurations resulted modifications of Wyatt's method to estimate the in the following expression suckdown for multiple-jet configurations; refer- ence (19) calculates the suckdown of the indi- vidual jets and sums them, and (7) uses Wyatt to calculate the suckdown due to an equivalent
4 single jet haging the total area and thrust of there is a net lift gain or loss depends on all the jets of the configuration. which predominates. Yen's method (21) for estimating the lift Unfortunately, at the time the methods of due to the impingement of the fountain basically (7,191 were developed there were no other pres- calculates the flow in the sector of the wall sure data of the type shown in Fig. 7 that COUlO jet from each jet that impinges on the lower help as a guide in developing the method for surface of the configuration. The momentum of estimating multiple-jet effects. More recently this flow, when it reaches the lower surface of similar data (also for a twin-jet configuration) the configuration, is estimated by applying have been published in (24), which show the empirically derived factors to account for the effects of height (Fig. 7) and jet deflection on velocity decay in the flow along the ground these pressure distributions. Additional data (wall jet) and in the fountain. Unfortunately, of this type are needed to provide a better the sum of the suckdown based on Wyatt's method, foundation for estimating the multijet suckdown. and the fountain lift based on Yen's approach, The methods of (7,19) also include factors do not equal the net induced lift for most to account for the effects of lower-surface multijet configurations. In fact, in some (fuselage) contour, and lift improvement devices cases, as shown in Fig. 4, the twin-jet configu- (LIDs) to increase the fountain lift. These ration has more net lift loss than the single- factors are based on a very limited data base, jet Configuration. Figure 4 is from (221, which and the applicability of the methods to non- presents data on a twin-jet configuration, and planar configurations is therefore limited. on a single-jet configuration using one of the Nevertheless, the methods work well on configu- jets and a planform of half the area of the rations that fall within the data base. Fig- twin-jet configuration (thus maintaining the ure 8 shows good agreement between estimates by same planform-to-jet area ratio). The results the method of (7), and data for a Harrier model indicate that, in addition to the fountain (25), with and without LIDs. effect, an additional suckdown can be generated On the other hand, Fig. 9 shows a compari- on multijet configurations. son with more recently acquired data (26) for a In (7) the increment of additional suckdown configuration with a different jet-spacing-to- experienced by multiple jet configurations was fuselage-width ratio. The method badly over- extracted from the data base by subtracting the estimates the fountain contribution. There are equivalent single-jet suckdown (based on Wyatt) other shortcomings in the available methods. and the fountain increment (based on Yen) from Reference (26) presents a modification of the data. Expressions for estimating this Wyatt's method for single jets to account for multiple jet suckdown were developed from an the effects of jet-pressure ratio that appeared empirical correlation of this multiple jet to exist in much of the single-jet data base. suckdown with the geometric characteristics of However, more recent results from a full-scale the configuration. As shown in Fig. 5, the investigation (27) of the suckdown induced on an multijet suckdown term can be larger than the 8-foot-diameter plate by the exhaust of a 5-97 fountain increment. The probable cause of this engine impinging on a ground plane, shows no additional suckdown is shown in Fig. 6 (from effect of pressure ratio (Fig. 10). These (23)). Vortex-like flows are formed between the results also show significantly more suckdown at fountain and each of the adjacent jets. The low heights than was predicted by any of the pressure distributions show that, as expected, available methods (Fig. 11). On the other hand, the impingement of thefountain flow produces work by Lummus and Smith (22) has shown a small high lifting pressures on the center region of effect of both pressure ratio and jet turbulence the plate between the jets, but the vortex-like (Fig. 12) on a twin-jet configuration. flows between the fountain and the jets induce Before significant improvement can be made equally strong suction pressures. The estimated in the methods to estimate the suckdown for suckdown for a single-jet configuration with the multiple-jet configurations, it will be neces- same planform-to-jet-area ratio would correspond sary to understand and resolve these difficul- to a suction-pressure coefficient, averaged ties in predicting the suckdown for the simple across the area of the plate, about equal to the single-jet case. The turbulence measured in outer contour line shown in Fig. 7 (22) was the turbulence in the jet itself. (Cp = -0.004). Thus, both the lifting pressures However, it is the wall jet that is entraining and the additional suckdown pressures are much air from between itself and the model, and it is greater than the pressures induced on a single- probably the turbulence in the wall jet that is Jet configuration, and the question of whether important. A significant factor in the turbu- lence Of the jet leaving the model, and probably
5 in the turbulence of the wall jet, is the ring that can produce a favorable induced lift can vortices generated and traveling downstream in also transport hot gases to the vicinity of an the shear layer of the jet (Fig. 13-photo- unfavorably placed inlet. The hot gas causes graphed by Drubka and Nagib and taken from either elevated inlet temperatures or inlet (28)). It is the growth of these vortices that temperature distortion across the engine fan entrains the surrounding air and causes the jet face. Either of these factors will reduce the to decay by transferring energy from the jet to engine thrust. Alternate engine inlets may be the entrained air, and the transition to turbu- needed to avoid the hot gas. The Fountain flows lence and subsequent jet decay. have been the subject of numerous investigations Reference (29) has noted that when the jet ((30-36) for example). The entrainment, veloc- impinges on the ground, these ring vortices ity decay, and spreading rates of the wall jet expand outward with the wall jet. They probably and fountain flows have been studied, and empir- play a major role in the entrainment of the air ical methods for estimating these factors have between the model and the ground. A better been determined. Kotansky (2) summarized much understanding is needed of the suckdown effects of this work and presented the methods developed due to jet-induced flows. These flows include for estimating the location of the stagnation the ring vortices, the turbulence of the flow in line on the ground between the jets (Fig. 151, the jet before it leaves the nozzle, and the the deflection angle of the upwash fountain if wall-jet development and turbulence. A proper the jets are of unequal thrust, and the momentum modeling of the major features of the flow, of the flow in the fountain. including the turbulence in both the free jet .;reen and Zanine (37) have used the same and the wall jet, will be required to develop an data base to develop a method for estimating the adequate method for predicting suckdown of inlet-temperature rise due to fountain flows. single-jet configurations. Their method uses the empirically determined Obtaining a better understanding of the velocity and temperature-decay rates developed flow and an adequate method for predicting the in the same data base to trace the temperature suckdown of single-jet configurations is a decay from the impingement point, through the necessary first step to developing improved wall jet and fountain, along the lower surface methods For predicting the ground effects on of the configuration to the vicinity of the multiple jet configurations. Once these are in inlet as depicted in Fig. 16. The method pre- hand, the work of Kotansky (21, Saripalli (301, dicts the stagnation lines on the ground and on Jenkins and Hill (311, Kind and Suthanthiran the under surface of the configuration as shown (32), Gilbert (33), Foley and Finley (341, Rizk in Fig. 17. The method adequately predicts the and Menon (35), and Childs and Nixon (36) on rise in inlet temperature as the aircraft fountain flows can be reexamined. approaches the ground (Fig. 181, and for some The ring vortices created in the shear configurations predicts a reversal of tempera- layer of the free jet (Fig. 13) that expand ture rise at the lowest heights that appears to outward in the wall jet emanating from the be confirmed by the data. impingement point may also be responsible for The method of (37) does not include the the extreme unsteadiness of the fountain flow. effects of LIDS because the data base on these When these vortices meet at the base of the devices is too limited. It also applies only to fountain (as depicted in Fig. 14), their veloc- hover in no-wind conditions. If there is a wind ity components will not cancel unless they are (or in STOL operation) the forward-flowing wall exactly in phase. The relationship of these jet will be turned back toward the aircraft in vortices to the fountain strength and unstead- the form of the ground vortex, and this provides iness should be examined. However, the primary another path for hot gases to find their way to need in connection with improving our ability to the vicinity of the inlet. predict the ground effects on multijet configu- The inlet temperature rise is often greater rations is to obtain a better understanding of at forward speed than at hover. The inlet the multijet suckdown and the vortex-like flows temperature rises with forward speed (Fig. 19) between the fountain and the jets that appar- because, as the velocity increases, the leading ently generate it (Fig. 6). edge of the ground-vortex flow field is moved closer to the configuration, and the flow path HOT GAS INGESTION and time for mixing to reduce the temperature of the gas is shortened. Eventually, a maximum temperature is reached. Finally, as the veloc- When a jet VTOL configuration hovers in ity is increased further, a point is reached ground effect, the same fountain flows (Fig. 3) where the hot gas cloud is blown below or behind
6 the inlet, and no inlet temperature rise is In the pressure coefficient plot in Fig. 20, the experienced. computed pressure difference has been combined Rudimentary correlations of the maximum with the pressure distributions over an ellipse inlet temperature rise experienced are presented to obtain the total pressure distribution for an in (38,39). For configurations arranged to elliptical airfoil with a jet flap. This formu- minimize ingestion, the height of the inlet lation is valid up to a point near the trailing above the ground was found to be the primary edge as shown in Fig. 20. parameter. It was found that the maximum tem- Based on Spence's vortex-sheet approxilna- perature rise tended to be inversely propor- tion for the two-dimensional jet wake, a number tional to the square of the inlet height-to- of three-dimensional methods for jet flaps were diameter ratio. These results are based on a then developed. The earliest three-dimensional very small data base and should be used with jet-flap methods, which included those of caution. Most of the data did not go to high Maskell and Spence (44), Hartunian (45), and Das enough velocities to establish a correlation of (461, assumed a large aspect ratio and an ellip- the velocity needed to avoid ingestion, but a tical spanload distribution. More general method of estimating this speed based on the three-dimensional jet-flap methods have been effect of forward velocity on the depth and developed from methods developed for conven- forward projection of the ground vortex flow tional wings (Fig. 21)-that is, they assumed field is presented in (39). Improvements in the potential flow and used numerical integration of ability to estimate inlet temperature rise will influence coefficient matrices to obtain a depend on developing better methods to predict solution. The methods extended conventional both the fountain flow field and the ground- theory by including Spence's relationship for vortex flow field. the high-momentum jet wake. This implies the assumptions of thin jet sheet and modest wake- JET FLAP IN- AND OUT-OF-GROUND EFFECT deflection angles. Some of these methods include lifting-line methods by Lissaman (47) and by Lopez and Shen (48) and lifting-surface Propulsive lift began in the early days of methods by Coldhammer, Lopez, and Shen (49). In aviation when the propeller slipstream flowing addition, Hackett and Lyman (50) developed an over the wing was used to attain increased equivalent mechanical-flap method. lift. Configuration concepts developed include Reference (41) presents many comparisons propeller slipstream, internally blown jet flap, between these theories and experimental data. upper surface blown flaps, and externally blown One example is presented in Fig. 22 for a model flaps. Along with the concept development and with a jet-blown flap over the inboard two- accompanying experimental work (40,41), a number thirds of the span, a 45" flap deflection, and of theoretical and computational methods have jet-momentum coefficient values ranging from 0.5 been developed to predict the aerodynamic char- to 4.0. The lift, drag, and pitching-moment acteristics of these configurations. coefficient results were obtained experimentally The first theoretical method for a wing using this model, and the corresponding calcu- with powered lift was developed by Spence lated values were obtained using the elementary (42,431. This method gave the lift and pressure vortex distribution (EVD) lifting-surface theory distribution on a two-dimensional wing with a (49). The data show generally very good agree- jet flap. Spence used a vortex sheet whose ment between theory and experiment, especially vorticity depended on the section momentum for the lift and pitching-moment coefficients. coefficient and curvature of the sheet to repre- It should be noted that the profile drag has not sent the thin jet wake behind the wing. He been included in the EVD calculations; adding it obtained the general results shown in Fig. 20. would bring the calculated drag into closer The lift results in Spence's method are in the agreement with the experimental values. form of two equations-one for lift-curve slope An example of an application of the jet- and the other for lift due to jet deflection. flap theory to a configuration for which the Both equations contain terms that depend on the assumption of a thin jet exhausting near the section-momentum coefficient. The lift-curve trailing edge of the wing was violated is pre- slope, for example, is (2H) modified by two sented in Fig. 23. The experimental data, pre- additional terms that account for section- sented in (511, are for an external-blown flap momentum coefficient effects. The pressure configuration having four engines whose exhausts difference between the upper and lower surface impinge on a double-slotted flap. Calculations is a function of jet-deflection angle, section- were made for this configuration using experi- momentum coefficient, and chordwise location. mentally measured distributions of the exhaust
7 deflection angle and momentum coefficient at the for hover ground effects to account for the flap trailing edge (shown on the right in effects of forward speed, and modifies the Fig. 23). Such calculations might not be prac- method of section 2.2.1 of (4) (also in (54)) tical in the general situation, of course, since for the jet-induced effects in transition out- this information would not ordinarily be avail- of-ground effects to account for the effects of able. However, this example shows that jet-flap ground proximity. To these is added an empiri- methods can give useful results even though the cal method, developed in (261, for estimating powered-lift system and resulting flow pattern the ground-vortex effects, and a fourth term to were more complicated than a simple jet flap. account for forward-speed effects on the foun- The data show that the maximum and minimm tain contribution. The terms involved are shown deflection angles occurred on approximately the schematically in Fig. 24. centerlines of the inboard and outboard engines, A key factor in the ground effects experi- respectively, whereas the peak momentum coeffi- enced in STOL operation is the location and cient occurred between the centerlines. strength of the ground vortex (Fig. 25). This The results on the left in Fig. 23 show ground vortex is formed where the forward flow- that the two jet-flap theories-Lissaman (47) ing wall jet is opposed by the free-stream flow and EVD (49)--give fairly good approximations of and turned back on itself. This ground vortex lift coefficient for momentum-coefficient values induces suction pressures on the ground (and on of 0 and 2, but not at a momentum coefficient of the lower surface of the aircraft) as shown at 4. The EVD program underpredicted the lift, and the top of Fig. 26. An empirical correlation of the Lissaman program overpredicted it. At least the location of the ground vortex was developed part of this discrepancy could be attributed to in (26) (see also, Fig. 26). and used in the the fact that the flap, rather than having a method for estimating the lift loss induced by thin jet sheet emanating from its trailing edge, the ground vortex, and for estimating the effect was operating within a relatively thick jet. As of forward speed on the hover suckdown term. a result, noticeable jet interference effects As discussed above, and shown in Fig. 24, I come into play which are not accounted for by the method of (26) for estimating the lift and I the jet-flap theory. Further improvements are moment in-ground effect is made up of four needed to deal with complete configurations terms. The ground-vortex term (L/T), and the including all of their complexities. Ultimate hover suckdown term (L/Tlh induce a negative solutions for propulsive-lift configurations may lift; the jet-wake term (LIT), also usually require solution the use of Navier-Stokes induces a lift loss out-of-ground effect, but equations. the proximity of the ground reduces this loss; and the fountain term (L/TIf produces a favor- JET STOVL CONFIGURATIONS IN STOL OPERATION able or positive lift. There is a limited data base with which to evaluate the method, and most of it is contained The prediction of the aerodynamic forces or referenced in (26). Figures 27 (using exper- and moments experienced by jet- and fan-powered imental data from (26)) and 28 (using experimen- STOVL aircraft operating in ground proximity at tal data from (53)) indicate how well the method forward speed (STOL operation) requires modeling reproduces some of the data on which it is a complex set of jet-induced flows in order to based. The estimates of the effects of ground cover the entire height and speed range. These proximity in STOL operation will be most reli- induced flows include the flow fields causing able if hover and out-of-ground-effect, jet- the induced lift losses in hover (in- and out- induced increments are available on the configu- of-ground effect), the jet/free-stream interac- ration as a starting point. Additional discus- tion at forward speed, and the ground vortex sion of pertinent methods may be found in (52). created by the interaction of the free stream with the wall jet flowing forward from the jet JET INDUCED EFFECTS IN TRANSITION impingement point. Any method for predicting the aerodynamics of STOVL aircraft in STOL operation must reduce to a method which accounts The transition flight regime ranges between only for the jet-induced effects at forward hover and wing-borne flight, and uses the combi- speeds. nation of jet lift and aerodynamic lift to An empirical method for predicting the support the aircraft weight. The lifting jets effects of ground proximity in STOL operation induce significant changes in the flow field in was developed in (261, and is also available in the vicinity of the aerodynamic lifting sur- (6). Reference (26) modifies the method of (7) faces. The interactions between the lift jets
8 and the free-stream flow field are due to jet from simple flat plates (Figs. 29 and 30) to blockage, entrainment, separation in the jet more realistic aircraft configurations wake, and lift-induced vortices. These interac- (Fig. 31). These comparisons provided a basis tions generate a complex flow field which is for refining the estimates to account for con- extremely difficult to analyze. figuration variables such as jet-nozzle locatir Existing prediction methods (2-8) usually relative to the wing and fuselage, planform- consist of either empirical procedures or to-jet exit area, jet deflection angle, aid potential-flow methods with empirical correc- fuselage lower surface contour. These compari- tions to account for many features of the lift- sons also identified limitations of the met>od jet/free-stream interactions listed in the (Fig. 32). Configurations with a jet located previous paragraph. The empirical procedures near the wing or other lifting-surface trailing tend to be easier to use and are often used in edge have additional jet-flap-like induced lift the preliminary design stage to identify the which is inadequately accounted for by this configurations which are the most appropriate method. These effects were discussed earlier in for further design effort. The latter group of the section entitled "Jet Flap In- and Out-of- methods tend to require input data which are Ground Effect," and may be accounted for by any very time-consuming to prepare, and can require of the several extensions of Spence's jet-flap large amounts of computer time. As a result, theory (40-47). they may be used for more detailed configuration Several potential-flow, vortex-lattice or evaluation; however, at their present state of panel-method-based schemes have beer developed development they are not consistently reliable which account for jet-induced interactions. A nor are they adequately validated, and they comparison of five production-surface panel cannot be counted on to provide more accurate methods (57) demonstrated that good agreement results than the empirical methods. for conventional aircraft aerodynamics can be The most commonly used empirical method for achieved between panel-method results and estimating the jet-induced effects on VSTOL experimental data. One of the earliest compre- configurations in the transition flight regime hensive methods which used a vortex-lattice is the one developed by Kuhn (in section 2.2.2 aircraft model (58) and a source-doublet jet of (41, and also in (54)). A less general model was developed by Wooler (1,59). This version of this method which is suitable for a method provided good comparisons between calcu- simplified preliminary design was presented as a lated and experimental results for a limited computer program with a listing and sample input number of VSTOL aircraft configurations. and output data (5). In either version of this Examples of other methods have shown useful method, its application is limited to configura- results (60-64). tions which are consistent with the data base The complexity of predicting propulsive- used to develop the method. The approach used induced effects on VSTOL aircraft prompted in this preliminary design method is outlined in Wooler to use a modular approach (Fig. 33). The the following paragraph. jet model is incompressible and neglects viscous First, the pressure coefficient data effects other than the entrainment caused by obtained by Fearn (55,561 in an experimental potential flow sinks or doublets. The entrain- investigation were used to develop the empirical ment of free-stream flow into the jet and the formulation. These data were obtained for pressure force on the jet boundary govern the effective velocity ratios (Vel ranging from 0.10 equations of motion of the jet. The entrainment to 0.45 in an experiment which had a 4-inch- parameters are obtained from experimental diameter jet exhausting normally to the free data. The variation of the jet cross section is stream, and from a large flat plate. The data established, based on experimental observations, were presented in pressure coefficients which by a circular jet transforming into an represent the jet-induced increment. Equations ellipse. The induced-velocity flow field due to were fit to represent the measured pressure the jet interference is obtained from two distributions as a function of the effective singularities: a) a uniform sink distribution velocity ratio, as well as the longitudinal and on axes normal to the free stream at discrete lateral distances from the jet exit. Next, locations along the jet centerline represent the these relations were integrated over the plan- entrained flow, and b) a doublet distribution form of the configuration of interest relative along the jet centerline represents the blockage to the nozzle locations to estimate the jet- and jet-induced circulation effects. Additional induced aerodynamics in transition flight. The procedures are developed to represent results were then compared with available exper- nonaxisymmetric jets, jet pairs, and a jet in a imental data for configurations which ranged nonuniform free stream.
9 Another module evaluates the jet-induced cross-flow to provide the jet-blocking effect; forces and moments using a version of the and c) the jet formation along the ground which vortex-lattice method from (58) to represent interacts with other jets leading to the lifting planforms. The method also gives good "fountain" effect. agreement with experimental data for wing-body These jet data were combined with an exist- combinations by including the planform of the ing wing-body panel method (Fig. 37). The usual body in addition to the wing. Power-induced tero-normal-velocity boundary was used for the aerodynamic characteristics are evaluated by aircraft; the normal inflow velocity, simulating using a propulsion-induced camber distribution mass entrainment, was used for the jet and on the planform to satisfy the flow-tangency ground plane. In ground effect, the fountain condition at the three-quarter chord of the momentum and incidence are calculated sepa- horseshoe vortices of the lattice representa- rately, with empirical data used to calculate tion. This wing-body program was used to additional fountain forces and moments. One improve the method of (l), which represented correlation with test data from the VAK-191 VTOL only the wing. aircraft is presented in Fig. 38 for lift and Experimental data (65,66) from the model pitching moment coefficients. These data are shown in Fig. 34 were used to evaluate these for a lift engine thrust deflection of 77.5" and methods. These data were obtained in conjunc- a lift/cruise thrust deflection of 60° at an tion with the research program (1). Using the effective velocity ratio of approximately method of (11, Mineck (67) obtained good agree- 0.14. At an angle-of-attack of Oo, the computed ment with experimental data from the configura- power-off results agree well with the experimen- tion with the nozzles in the aft position tal data, and the computed power-on lift- (Fig. 35). For this case the jet-induced coefficient results agree well with experimental increase in wing lift (i.e., jet-flap effect) data. As in the computed results from Wooler's dominates. In contrast, poor agreement was original method by Mineck (67), the poor agree- obtained with the nozzles in the forwdrd ment for power-on pitching moment indicates a position (Fig. 35). The improved Wooler method need to include a separated-flow representation of (59) was also used to evaluate these cases in the wake portion of the jet. (Fig. 36). The wing-alone calculation based on A further indication of the need for a the original method provided poor agreement for method which accounts for the lifting-jet-wake- the forward jet position. To represent the induced separation is shown in Fig. 39 from a presence of the large nacelles and the body, a V/STOL aircraft transition flight analysis vortex-lattice method (58) was used to include (69). This analysis used the PANAIR panel them in the planform for the improved Wooler method to represent the aircraft with Neumann method. The improved correlation is shown in boundary condition and a parabolized Navier- Fig. 36. These results indicate that this Stokes solution for the lifting jet with an improved method (59) by Wooler is suitable for entrainment boundary condition. The jet shape propulsion-induced aerodynamic forces and and entrainment were determined using the Adler- moments at the conceptual and preliminary design Baron jet-in-a-crossflow method (70) and recent stage. The output from the jet-induced flow- unpublished experimental data acquired by field module can be used with a panel method for Adler. The method was applied to a simple high- more detailed analysis. wing aircraft configuration with a single lift- In an early application of panel methods to ing jet. Unfortunately, the calculated results model V/STOL aero/propulsion interactions, (Fig. 39) using this analysis do not account for Rubbert (68) used the Boeing TEA-230 panel the separated wake due to the lifting jet As a method to represent a jet in a crossflow. The result, the propulsion-induced lift loss s specification of the Neumann jet-boundary condi- underestimated by about 202 of the thrust tions proved to be difficult because the detailed distribution of jet entrainment around CONCLUDING REMARKS the curved, three dimensional lifting jet was unknown. A later attempt by Siclari (64) at Crumman was more successful. This method used For over 30 years, VSTOL aircraft have been empirical and theoretical data that describe the developed primarily from experimental investiga- development of free jets to specify the needed tions because there are many unique aerodynamic/ jet-boundary conditions. A set of mixing data propulsion-induced effects which occur with was developed which simulated a) the viscous these vehicles. The existing data base has been entrainment of ambient air for both free jets used to develop some empirical and modified- and wall jets; b) the free-jet shape in linear, potential-flow methods for predicting
10 the induced aerodynamic effects. The adequacy REFERENCES of available methods is graphically portrayed in Fig. 40. For propulsion induced effects incurred out-of-ground effect, available methods 1. Wooler, P. T.; Burghart, C. H.; and are adequate in hover and moderately adequate Gallagher, J. T.: V/STOL Aircraft Aerodynamic for transition flight. For propulsion-induced Prediction Methods: Vol I - Theoretical effects incurred in-ground effect the Developments of Prediction Methods; irol.11 - interactions are more complicated and available Application of Prediction Methods; Vol. Ill - methods are inadequate. Manual for Computer Programs; and Vol. IV - Improved prediction methods are needed to Literature Survey. AFFDL TR-72-26, January guide experimental programs and to reduce the 1972. testing requirements in the future, as well as 2. Kotansky, D. R.: Jet Flowfields. to provide an understanding of the flow ACARD R-710, 7.1-7.48, 1984. physics. The Navy V/STOL Aerodynamics, Stabil- 3. Kuhn, R. E.: An Engineering Method for ity and Control Manual (4,s) utilizes empirical Estimating the Lateral/Directional methods, linear-inviscid methods, and linear- Characteristics of V/STOL Configurations in inviscid plus boundary-layer methods, and repre- Transition. Rpt. No. NADC-81031-60, February sents the current state of the art in V/STOL 1981. computational methods. These methods are very 4. Henderson, C.; Clark, J.; and useful for preliminary design of configurations Walters, M.: V/STOL Aerodynamics, Stability and which are consistent with the underlying Control Manual. Rpt. No. NADC 80017-60, January empirical data base. These methods are usually 1980. not suitable for detailed aircraft design. 5. Walters, Marvin M.; and Palmer, Multiple jet aircraft out-of-ground effect Robert E.: Method for Predicting the hover interactions represent a lift loss of a Jet-Induced Aerodynamics of V/STOL few percent of the total thrust, and these Configurations in Transition. Rpt. interactions may be estimated adequately by No. NADC-80025-60, January 1981. empirical procedures to within a percent of the 6. Stewart, V. R.; and Kuhn, R. E.: A total thrust. In ground effect, the lift-jet/ Method for Predicting the Aerodynamic Stability ground interaction creates complex near-field and Control Parameters of STOL Aircraft fountain flows which are difficult to analyze Configurations. AFWAL TR-87-3019, June 1987. for induced forces and moments and for hot-gas 7. Kuhn, R. E.: An Engineering Method for ingestion. Jet-flap theories provide useful Estimating the Induced Lift on V/STOL Aircraft preliminary design estimates, but they do not Hovering in and out of Ground Effect. Naval Air account for all of the major jet interference Development Center, Warminster PA, effects. For lifting jet-induced effects in NADC-80246-60, January 198 1 . transition flight, the empirical methods of Kuhn 8. Platzer, Max F. ; and Margason, (54) are limited to configurations which are Richard J.: Prediction Methods for Jet V/STOL consistent with the data base used to develop Propulsion Aerodynamics. J. Aircraft, Vo1.15, the methods. No. 2, 69-77, February, 1978. While existing empirical methods are 9. Peterson, V. L.: Impact of Computers inadequate for detailed aircraft design, results on Aerodynamics Research and Development. from current applications of Reynolds-averaged Proceedings of the IEEE, Vol. 72, No. 1, 68-79, Navier-Stokes solutions ( 12-16,35,36) offer a January 1984. promising approach. Initial parabolic Navier- 10. Jameson, A.: The Evolution of Stokes applications (12,691 to STOVL aircraft Computational Methods in Aerodynamics. configurations do not adequately handle jet- Transactions of the ASME, Vol. 50, 1052-1070, wake-induced flow-separation effects. While December 1983. initial elliptic Navier-Stokes solutions are 11. The Influence of Computational Fluid demonstrating greatly improved results, there is Dynamics on Experimental Aerospace Facilities, a a need for improved turbulence models for the fifteen year projection prepared by the propulsion-dominated flows. Based on current Comittee on Computational Aerodynamics CFD activity, the Reynolds-averaged Navier- Simulation Technology Developments, National Stokes solutions should achieve major improve- Research Council, National Academy Press, ments in the next several years and lead to Washington, DC, 1983. analysis methods which can estimate aero/ propulsion interactions in a manner suitable for detailed aircraft design applications.
11 12. Baker, A. J.; and Orzechowski, J. A.: 24. Dudley, M. R.; Eshleman, J. E.; and Prediction of Turbulent Near-Field Evolution of Schell, C. J.: Full-scale Ground Effects of a Jet in Crossflow Using a PNS Solver. Twin Impinging Jets Beneath a Subsonic Tactical Rpt . No. NADC-86076-60, January 1986. V/STOL Aircraft. AIAA Paper 86-2704, October 13. Takanashi, Susumu; and Sawada, 1986. Keisuke: Numerical Simulation of Compressible 25. Johnson, D. B.; Lacey, T. R.; and Voda, Flow Field about Complete ASKA Aircraft J. J.: Powered Wind Tunnel Testing of the Configuration. SAE paper 872346, International AV-8B; A Straightforward Approach Pays Off. ?owered-Lift Conference, December 1987. AI AA Paper 79-0333, January 1979. 14. Roth, Karlin R.: Numerical Simulation 26. Stewart, V. R.; and Kuhn, R. E.: A of a Subsonic Jet in a Crossflow. SAE Paper Method for Estimating the Propulsion Induced 372343, International Powered-Lift Conference, Aerodynamic Characteristics of STOL Aircraft in December 1987. Ground Effect. NADC-80226-60, August 1983. 15. VanDalsem, W. R.; Panaras, A. G.; Rao, 27. Christiansen, R. S.: A Large Scale K. V.; and Steger, J. L.: Numerical Investigation of VSTOL Ground Effects. AIAA Investigation of Single and Multiple Jets in Paper 84-0336, January 1984. Ground Effect. SAE Paper 872344, International 28. VanDyke, M.: An Album of Fluid Powered-Lift Conference, December 1987. Motion. The Parabolic Press, Stanford, CA, 16. Childs, Robert E.; and Nixon, David: 1982. Study of Turbulence and Fluid/Acoustic 29. Cimbala, J. M.; Stinebring, D. R.; Interaction in Impinging Jets. SAE Paper Treaster, A. L.; and Billet, M. L.: Experimen- 872345, International Powered-Lift Conference, tal Investigation of a Jet Impinging on a Ground December 1987. Plane in the Presence of a Cross Flow. 17. Gentry, Carl L.; and Margason, NADC-87019-60, March 1987. Richard J.: Jet-Induced Lift Losses on VTOL 30. Saripalli, K. R.: Laser Doppler Configurations Hovering In and Out Of Ground Velocimeter Measurements in a 3-D Impinging Effect. NASA TN D-3166, February 1966. Twin-Jet Fountain Flow. NASA CP-2462, 147-160, 18. Shumpert, P. K.; and Tibbetts, J. C.: August 1985. Model Tests of Jet-Induced Lift Effects on a 31. Jenkins, R. C.; and Hill, W. G. Jr.: VTOL Aircraft in Hover. NASA CR-1297, March Investigation of VTOL Upwash Flows Formed by Two 1969. Impinging Jets. Crumman Research Dept., Rpt. 19. Foley, W. H.; and Sansone, J. A.: No. RE-548, November 1977. V/STOL Propulsion-Induced Aerodynamic Hover 32. Kind, R. J.; and Suthanthiran: The Calculations Method. Naval Air Development Interaction of Two Opposing Plane Turbulent Wall Center, Warminster PA, NADC-78242-60, February Jets. AIAA Paper 72-211, January 1972. 1980. 33. Gilbert, E. L.: An Investigation of 20. Wyatt, L. A.: Static Tests of Ground Turbulence Mechanisms in V/STOL Upwash Flow Effect on Planforms Fitted with a Centrally- Fields. Grumman Aerospace, Rpt. No. RE-688, Located Round Lifting Jet. Ministry of Aviation 1984. CP 749, June 1962. 34. Foley, W. H.; and Finley, D. B.: 21. Yen, K. T.: On the Vertical Momentum Fountain Jet Turbulence. AIAA Paper 81-1293, of the Fountain Produced by Multi-Jet Vertical June 1981. Impingement on a Flat Ground Plane. Naval Air 35. Rizk, M. H.; and Menon, S.: Numerical Development Center, Warminster PA, Investigation of V/STOL Jet Induced Interac- NADC-79273-60, November 1979. tions. NASA CP-2462, 161-194, August 1985. 22. Lummus, J. R. and Smith. E. W.: 36. Childs, R. E.; and Nixon, D.: Unsteady Flowfield Characteristics and the Effect of Three-Dimensional Simulations of VTOL Upwash Jet-Exhaust Simulation for V/STOL Vehicles Near Fountain Turbulence. NASA CP-2462, 195-206, the Ground. Proceedings of the NADC V/STOL August 1985. Aircraft Aerodynamic Symposium, Naval 37. Green, K. A.; and Zanine, J. J.: Postgraduate School, Monterey, CA, 293-313, May Estimation of Hot Gas Reingestion for a VTOL 1979. Aircraft at the Conceptual Design Stage. SAE 23. Hall, G. R.; and Rogers, K. H.: Paper SP-591, V/STOL: an Update and Overview, Recirculation Effects Produced by a Pair of 51-66, October 1984. Heated Jets Impinging on a Ground Plane. 38. Kuhn, R. E.: Design Concepts for NASA CR 1307, May 1969. Minimizing Hot-Gas Ingestion in V/STOL Aircraft. AIAA Paper 81-1624, August 1981.
12 39. Kuhn, R. E.: Hot Gas Ingestion and the 53. Margason, R. J.; Vogler, R. D.; and Speed Needed to Avoid Ingestion for Transport Winston, M. M.: Wind Tunnel Investigation at Type STO/VL and STOL Configurations", AIAA Low Speed of a Model of the Kestrel (XV-6A) Paper 84-2530, October 1984. Vectored Thrust V/STOL Airplane. NASA 40. Loury, John C.; Riebe, John M.: and TN D-6826, July 1972. Campbell, John P.: The Jet-Augmented Flap. 54. Kuhn, A. E.: An Empirical Method for Preprint No. 715, S.M.F. Fund Paper, Inst. Estimating the Jet-Induced Effects on V/ST?'. Aeronaut. Sci., January 1957. Configurations in Transition. Rpt. 41. Margason, Richard J.; Yip, Long P.; and NO. R-AMPAC-113, Aerospace Mass Properties Gainer, Thomas G.: Recent Developments in Analysis, Inc., November 1979. Propulsive-Lift Aerodynamic Theory. Aerodynamic 55. Fearn, R. L.; and Weston, R. P.: Anayses Requiring Advanced Computers, Part I, Induced Pressure Distribution of a Jet In a NASA SP-347, 543-565, 1975. Crossflow. NASA TN D-7916, July 1975. 42. Spence, D. A.: The Lift Coefficient of 56. Fearn, R. L.; Kalota, C.; and Dietz, 3 Thin, Jet-Flapped Wing. Proc. Roy. SOC. W. E., Jr.: A Jet/Aerodynamic Surface (London), Ser. A, Vol. 238, No. 1212, 46-68, Interference Model. Proceedings NADC V/STOL December 4,1956. Aircraft Aerodynamics, May 1979. 43. Spence, D. A.: Some Simple Results for 57. Margason, R. J.; Kjelgaard, S. 0.; Two-Dimensional Jet-Flap Aerofoils. Aeronaut. Sellers, W. L., 111; Morris, C. E. K., Jr.; Quart., Vol. IX, Pt. IV, 395-406, November 1958. Walkey, K. B.; and Shields, E. W.: Subsonic 44. Maskell, E. C.; and Spence, D. A.: A Panel Methods - A Comparison of Several Theory of the Jet Flap in Three Dimensions. Production Codes. AIAA Paper 85-0280, January Proc. Roy. SOC. (London), Ser. A, Vol. 251, 1985. No. 1266, 406-425, June 9, 1959. 58. Margason, R. J.; and Lamar, J. E.: 45. Hartunian, Richard A.: The Finite Vortex-Lattice FORTRAN Program for Estimating Aspect Ratio Jet Flap. Rep. No. A1-1190-A-3 Subsonic Aerodynamic Characteristics of Complex (Contract No. DA 44-177-TC-439). Cornel1 Planforms. NASA TN D-6142, February 1971. Aeronaut. Lab., Inc., October 1959. 59. Wooler, P. T.: "Propulsion - Induced 46. Das, A.: Theoretical and Experimental Effects on a Supersonic V/STOL Fighter/Attack Testing on Jet Flap Wings. Part I: Testing of a Aircraft. Proceedings NADC V/STOL Aircraft Rectangular Wing at Various Aspect Ratios. Aerodynamics, May 1979. NASA TT F-13715, 1971. 60. Beatty, T. D.: A Prediction Methodol- 47. Lissaman, Peter B. S.: Analysis of ogy for Propulsive Induced Forces and Moments in High-Aspect-Ratio Jet-Flap Wings of Arbitrary Transition and STOL Flight. Proceedings NADC Geometry. NASA CR-2179, 1973. V/STOL Aircraft Aerodynamics, May 1979. 48. Lopez, M. L.; and Shen, C. C.: Recent 61. Knott, P. C.: A Review of Some Funda- Developments in Jet Flap Theory and Its mentals of Lifting Jet Interference with Partic- Application to STOL Aerodynamic Analysis. AIAA ular Reference to U.S. Navy Type A and B Con- Paper 71-578, June 1971. cepts. Proceedings NADC V/STOL Aircraft 49. Goldhammer, M. I.; Lopez, M. L.; and Aerodynamics, May 1979. Shen, C. C.: Methods for Predicting the 62. Perkins, S. C.; and Mendenhall, Aerodynamic and Stability and Control M. R.: Surface Pressure Distribution on a Flat Characteristics of STOL Aircraft. Plate or Body of Revolution from which a Jet is Volume I - Basic Theoretical Methods. Issuing. Proceedings NADC V/STOL Aircraft AFFDL-TR-73-146, Vol. I, U. S. Air Force, Aerodynamics, May 1979. December 1973. 63. McMahon, H.: Flap Surface Pressures 50. Hackett, J. E.; and Lyman, V.: The Behind a Jet Issuing from a Wing in Crossflow. Jet Flap in Three Dimensions: Theory and Proceedings NADC V/STOL Aircraft Aerodynamics, Experiment. AIAA Paper 73-653, July 1973. May 1979. 51. Johnson, William G., Jr.; and Kardas, 64. Siclari, M.; Migdal, D.; and Palcza, Gerald E.: A Wind-Tunnel Investigation of the J. L.: Development of Theoretical Models for Wake Near the Trailing Edge of a Deflected Jet Induced Effects on V/STOL Aircraft. Pro- Externally Blown Flap. NASA TN X-3079, 1974. ceedings NADC V/STOL Aircraft Aerodynamics, May 52. Ransom, E. C. P.; and Smy, J. R.: 1979. Introduction and Review of Some Jet Interference 65. Mineck, R. E.; and Schwendemann, Phenomena Relevant to V/STOL Aircraft. AGARD M. F.: Aerodynamic Characteristics of a R-710, 2.1-2.23, 1984. Vectored-Thrust V/STOL Fighter in the Transition-Speed Range. NASA TN D-7191. 1973.
13 ~~
66. Nineck, R. E.; and Margason, R. J.: 70. Foley, W. H.; and Sansone, J. I.: Pressure Distribution on a Vectored-Thrust V/STOL Propulsion-Induced Aerodynamic Hover V/STOL Fighter in the Transition-Speed Range. Calculation Method. NADC-78242-60, February NASA TM X-2867, 1974. 1980. 67. Mineck, R. E.: Comparison of 71. Bore, C. L.: Ground Based Testing Theoretical and Experimental Interference Without Wind Tunnels. AGARD-R710, 10.1-10.6, Effects on a Jet VTOL Airplane Model. 1984. Proceedings NAVAIR Prediction Methods for Jet 72. Siclari, M. J.; Barche, J.; and Migdal, V/STOL Propulsion Aerodynamics, July 1975. D.: V/STOL Aircraft Prediction Technique 68. Rubbert, P. E.: Calculation of Jet Development for Jet-Induced Effects. NAPTC Interference Effects on V/STOL Aircraft by a Report No. PDR-623-18, April 1975. Nonplanar Potential Flow Method. Proceedings 73. Kuhn, R. E.; DelFrate, J. H.; and Analysis of a Jet in a Subsonic Crosswind, NASA Eshleman, J. E.: Ground Vortex Flow Field SP-218, 181-204, September 1969. Investigation. NASA CP (ground vortex 69. Howell, G. A.: Automated Surface and workshop), April 1987. Plume Simulation Procedure for Use with Aerodynamic Panel Codes. NASA CR 177420, May 1986.
TURBULENT MIXING BOUNDARY
2 4 6 8 10 12 xlD
Fig. 1. Schematic of the decay and spread of the jet efflux with distance downstream from the nozzle exit.
14 a JNx Fig. 3. Fountain flow developed between a pair t of lifting jets.
0 SINGLE JET MODEL A MULTISLOT "
-AL,T -.2 - m -.w4 - -AI. T
-.006 I I I 1 I I 0 .1 .2 .3 .4 .5 .6 -.4 -
-.6 I I I I 0 2 4 6 8 hld
Fig. 2. Correlation of induced loads with jet Fig. 4. Some multiple-jet configurations can decay parameter (pt /p = 2.0). tP experience more suckdown than an equivalent single-jet configuration (22).
15 Or
0 EXP.DATA
ESTIMATES REF. 7 --- EQUIVALENT SINGLE JET -MULTIPLE JETS
I I 1 I 1 I I 0 2 4 8 8 101214= hid,
Fig. 5. Fountain lift and the additional multiple-jet suckdown generated on a simple twin- jet configuration (7).
GROUND PLANE
Fig. 6. Flow field and induced pressure distribution for a twin-jet configuration (23).
16 WING HORIZONTAL VERTICAL TAIL TAIL FLAP EXTENDED 5" POSITION SPAN, m (ft) 11.18 (38.67) 3.56 (11.67) - AREA, m2 wt21 16.44 (177) 3.07 (33) 3.53 (38) ASPECT RATIO 7.6 4.1 0.95 LEADING EDGE SWEEP, 2.5/-7.5 25 40 TAPER RATIO 0.466 0.489 0.53 DIHEDRAL DEG 01131-7 0 - AIRFOIL - NACA 64A012 NACA 64A012
a) -0.04
h/D= 1.33
. , ,.I.
Fig. 7. Three-view configuration and geometry (a) and pressure contours (b) of a twin-jet configuration (24).
17 hid 0 1.57 0 2.55 0 3.55 (x ? STD. DEV.) A 4.93 0.031 t 0.006 0
.. 0 IT .. -.2 L;I U + 0.174 2 0.014 5 - a -.4 FOUNTAIN LIFT ESTIMATES (REF. 7) I I -.2 I 1 1 1 I 1 1 1 J -.6 0 2 4 6 8 101214 00 1.o 1.4 1.8 2.2 2.6 3.0 NPR hid,
Fig. 8. Lift induced on a Harrier-type config- Fig. 10. Effect of nozzle pressure ratio on uration hovering in ground effect (25). single-jet suckdown (27).
0 EXPERIMENTAL DATA, (REF. 26) Dfd = 7.93 TURBOFAN .2 - FOUNTAIN LIFT - .J ----- TURBO JET I MULTIJET ESTIMATE, (REF. 2) --- WYATT = -.4 tu
-.2 I 1 I 1 1 l -.6 0 4 8 12 16 20 oo 1 3 5 7 9 hldp HEIGHT ABOVE GROUND, Hid
Fig. 9. Lift induced on a simple twin-jet high- Fig. 11. Suckdown induced by full-scale jet wing configuration hovering in ground effect engines (27) compared with Wyatt correction (20) (6). based on small-scale data.
18 NPR BASELINENOZZLE 0 - 1.5 s1 0 --- 2.0 S2A -*-
OS hID = 10.0 4
-.6 - NPR = 2.0 .. -.7 --- ..NPR = 1.5 h/D a 2.5 0 - -NPR 2.4- -.a -I I I I 1 1
Fig. 12. Turbulence screen and nozzle pressure Fig. 13. Shadowgraph of jet (R, = 10,000) ratio effects on net induced lift for a twin-jet showing initial laminar jet, the formation of configuration (27). ring vortices in the shear layer, and the transition to turbulence (28).
Fig. 14. Shear layer vortices may be the cause of fountain unsteadiness.
19 STAGNATION
JET 1 JET 2 IMPINGEMENT IMPINGEMENT POINT POINT
Fig. 15. A method for estimating the location and strength of the upwash fountain generated between impinging jets is presented in (2).
INLET FACE
Fig. 16. A method for estimating the inlet Fig. 17. Stagnation lines on the ground and on temperature rise due to fountain flows by the aircraft lower surface calculated by the tracing the flow from impingement to the inlet method of (37). is presented in (37).
20 NOZZLE SPLAY FRONT - 5" UNDERSURFACE REAR - 12" GROUND PLANE
EXPERIMENTAL DATA FOR CLEAN AIRCRAFT
I TTJF = 130°F c" .06 TTJR = 400°F I NPRF = 2.26 NPRR = 1.9 Mi -0.66
0 12345 678 h/d,j 0 FORWARD SPEED, V, knots
Fig. 18. Inlet temperature rise for a Harrier- Fig. 19. Typical variation of inlet temperature type aircraft estimated by the method of (37). rise with forward speed.
-a c* = 2n(1+0.161c;" + 0.219 c;' 16- * 14 -
XI0 n -3r hp=2 [.- xc:l-xJ 6i -2
cp -1
0
1 0 -1234s 0 .2 .4 .6 .8 1.0
Fig. 20. Variation of lift and pressure coefficients according to Spence's two-dimensional jet-flap theory (43).
21 b I I I I I I I I I I I I I va. I I -1 I I I I- I I I I I I I I I I I I F-2 1
Fig. 21. Schematic of three-dimensional jet-flap wing lifting line and lifting surface methods.
-2 cm hhhhhhb..
#61 = 45”
CL cP 0 0.5 0 1.0 A 1.5 b 2.0 n 4.0 1 2l -EVD THEORY 0 -5 10 15 -2 -1 0 1 2 a. dsg CD
Fig. 22. Comparisons of EVD jet-flap theory with experimental data for two-thirds span jet- blown flap model.
22 C, EXPERIMENT THEORY 0 0 - EVD 2.0 0 --- LISSAMAN 4.0 0
0- 0- 4j; CL 3
o .2 .4 .6 .a 1.0 9 I II 21i1
Fig. 23. Comparison of jet-flap theory with experimental data for an externally blown flap configuration.
-, ir -
GROUND VORTEX
Fig. 24. Schematic of the effect of height on Fig. 25. Formation of the ground vortex. the induced lift increments in ground effect (26).
23 va 00 0 0.1 0 0.22 A 0.33 ESTIMATES -- REF. 2. Ve = 0 REF. 26
FREE AIR ,- Y u-
FREE AIR
0
-.2
AL -.4 -T
I 1 ~~ -.a I I I I I 0 4 8 12 16 0 4 8 12 16 20 hld -h d
Fig. 26. Forward projection of the wall jet and Fig. 27. Comparison of estimated ground effects gound vortex flow field (26). with experimental data for a high-wing single- jet configuration from (26).
24 6 Q
0660 86 L&J+ A60 0 EST. (REF. 261 - Ve * 0.3
0 -
-AL -.2 - %i$@&~ 32
-.4 1
Fig. 28. Comparison of estimated ground effects with experimental data for a Harrier-type configuration of (53).
MANUAL PREDICTION, REF. 4 0 EXPERIMENTAL DATA, REF. 5
dj = 1.75 de = 3.5
U
.8 -.8 I I 1 I .1 .2 .3 0 .1 .2 .3 we Ve
Fig. 29. Comparison of predicted and Fig. 30. Comparison of predicted and experimental data of clipped delta-wing experimental data of clipped delta-wing configuration for a single-jet configuration, configuration, Sj/S = 0.024. a) Single-jet Sj/S = 0.024. configuration. b) Four-jet configuration.
25 -. 0
Fig. 31. Comparison of predicted and experimental data of a single-Jet high-wing configuration.
26 .2 r 0
0
AL AL - -.4 - - -.2 - T
-A -
a) 1 I I -.a ? I 1 I -.6. b)
Fig. 32. Comparison of predicted and experimental data of a twin-jet, high-wing configuration. a) Nozzles in the forward position. b) Nozzles in the aft position.
+
((8'
DOUBLETS SINKS + DOWNWASH CONTROL PTS
Fig. 33. Wooler method for computing the jet-induced effects on the wing using superposition of lifting-line wing and sink/doublet jet representations.
27 n
FORWARD NOZZLE AFT NOZZLE POSITION POSITION I I
Fig. 34. Wind tunnel model of a subsonic VSTOL fighter concept ( 1 65 and 66).
EXP. THEORY a 0-0 0 -e-- 10
I - I .6 I // -h 0 .4 0 0 5 .2 a - a
-.2
-.4 0 .1 .2 .3 .4 .5 .0 0 .I .2 .3 .4 .5 .6 "e "e
Fig. 35. Comparison between Wooler's original method and experimental data obtained on the model in Fig. 34.
28 A TEST, FWD POS, 90" DEFL, Q = p = 0 0 CALCULATION, WING ALONE 0 CALCULATION, VORTEX LATTICE a 1.4
WALL JET 11,111,, \ 8 .6 / - 0 .1 .2 .3 .4 .5 .6 v,
Fig. 36. Comparison among Wooler's original Fig. 37. Three-dimensional singularity-panel method ( 1 ) , Wooler 's improved method (59), and approach to VSTOL aircraft prediction methods experimental data (1, 65, and 66) obtained on (64). the model in Fig. 34 with the nozzles in the forward position.
LIFT JET ', 'x-\\LIFT JET
\ LIFT/ '\ CRUISE *A JETS THEORY EXP. Ve 00-3 20.14 .6 - 0 .4 - 0
.2 - 0 C 0 0 co U 0 0 O m 3 L -h I -404 8 12 -.2 0 .2 a CM
Fig. 38. Correlation between three-dimensional singularity-panel method and experimental data (64).
29 0- a=roo THEORY 0 I0 0 -.2 - I' & T - -A /
-.6 I I 1
Fig. 39. Analysis of a VSTOL aircraft in transition flight using a PANAIR panel method and a parabolized jet wake model (69). HOVER TRANSITION
4 3 OUT OF GROUND FORCES AND 4 EFFECT MOMENTS 5 6 59 60 62 72
4 6 IN GROUND FORCES AND 6 26 EFFECT MOMENTS 7 20 21 70
37 HOT GAS 38 INGESTION 71
26 GROUND 29 ENVIRONMENT 73
Fig. 40. Adequacy of available prediction methods; shaded area indicates percent of need covered; numbers indicate key references. MOrI &3nwh-s aNl Report Documentation Page %.rrcu/\sA4wr.ymIoi 1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No. NASA TM-100048 5. Report Date February 1988 Application of Empirical and Linear Methods 6. Performing Organization Code to VSTOL Powered-Lift Aerodynamics
7. AuthorM 8. Performing Organization Report No. A-88038 Richard Margason and Richard Kuhn 10. Work Unit No.
9. Performing Organization Name and Address 505-61-7 1 11. Contract or Grant No. Ames Research Center Moffett Field, CA 94035 13. Type of Report and Period Covered 12. Sponsoring Agency Name and Address Technical Memorandum National Aeronautics and Space Administration 14. Sponsoring Agency Code Washington, DC 20546-0001
15.upplementary Notes
Point of Contact: Richard Margason, Ames Research Center, MS 247-2 Moffett Field, CA 94035 (415) 694-5033 or FTS 464-5033
17. Key Words (Suggested by Authorls)) 18. Distribution Statement VSTOL Unclassified-Unlimited Powered-lift Computational methods Subject Category - 02
19. Security Classif. (of this report) 20. Security Classif. (of this pagel 21. No. of pages 22. Price Unclassified Unclassified 31 A03