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VIOL AND VSTOL HANDLING CUALITIES SPECIFICATIONS AN OVERVIEWOF THE CURRENTSTATUS Kevin W. Goldstein Aerospace Engineer Naval Air Development Center Warminster, PA The highlights of a canparative analysis Multi-Purpose System (LAtJPS) SHdOB, the Army Utility Tactical Transport Aircreft System between the current helicopter and VSTOL (UTTAS) UH-6OA, and the Advenced Attack hendlinp qualities specifications and four representative state of the art rotary wing Helicopter (AAH) all use advanced flight control systems for stability and control aircraft are presented.
Longitudin21, eugmentation. The need to adequately address lateral, and directional control power 2nd the flying qualities of these state of the dynamic stability cheracteristics were art vehicle/control systems has necessitated analyzed for hovering conditions. Forward the use of "type specific2tions1' or "prime flight static and dynamic stability were item developnnent specifications" uniquely anelyzed for the longitudinel and devised for e2ch new aircraft/control system.
lateral-directional axes. Results of the Pany papers have been written describing the analyses in terms of the numerous shortcanings of PIL-H-8501A in- applicability/utility of the VIL-H-85OlA realistically regulating handling aualities criteria are presented for each of the ebove of present and future helicopters2'6, areas. The review of the YIL-H-E5OlA indicating a very real need for 2n updeted criteria 2painst those in MIL-F-83300 and version of YIL-H-85OlA. A summary of the AGARD577 indic2ted many areas in which major problem ereas described by the ebove ML-H-8501A does not give 2dequate design papers is presented as a b2ckground and guidance.
overview of the current status.
To facilitate the development of revlised Notation criteria it is necessary first to canpile a deta bese of past and present helicopter Pitch Rate Damping (second-')
Mq
stability and control charlcteristics.
'Ihis Pitch Control Sensitivity (r2d/seaond2/inch) paper presents the beginning of such a M6B canpilation.
Six degree of freedom math models of the SP-60B and the CH53D single Yaw Rate Damping (second-') Nr rotor helicopters were an2lyzed ageinst the fundanental stability and control espects Yaw Control Sensitivity (red/second'/inch) addressed by PIL-H-8501A. Vertical control Worms1 Acceleration (feet/second') response and 2utorotation criteri2 were not included et this time.
Angle of Attack (radians) Flight test deta for the XH-59A Advancing Blede Concept (ABC), the Later21 Control Deflection (inch) XV-15 tilt-rotor, and the CH-46A tandem rotor were also included 2nd discussed.
Undamped Natural Period (r-ad/second) % 5 In the development of the present day Damping Ratio ,VSTCL handling qualities specifications, Roll Angle Attained within @l PIL-F-83300'2nd AGARD 577' extensive rotary One Second (degrees) CT@L Conventional Take-off and Landing wing pilot rating data were enalyzed to substantiete the finalized hover/low speed VSTOL Vertic2l/Short Take-off and Landing criteria. Although AGARD 577 is not intended to be a helicopter specification and ML-F-83300 has not been used by the Navy or Introduction Army for a helicopter development program, these specific&ions do supply alternative With the development of a new generation methods of addressing VTOL handling qualities Of rotary wing eircraft for military characteristics.
operations, The alternative criteria it has becane annarent that the from !JIL-F-E3300 2nd AGARD577 were directly present helicopter handling-qualities canpared with the criteria frun ML-H-8501A specification, ML-H-85OlA', cannot accuretely assess the characteristics of to highlight helicopter specification !deficiences and vehicle encmalies.
these aircraft. The fact that PIL-H-8501A was last updated 20 years ago only tends to amplify this point.
The Navy Light Airborne stabilization system. ‘Ihere is little YIL-H-8501A Deficiencies quantitative guidance available defining sufficient levels of control or stability.
As described ebove, the mejor military With the canplex augmentation systems being helicopter development programs since 1965 employed on the SH-60B and the CH-53E there have used type specifications designed is a need to set minimun quantitative levels exclusively for the flying qualities of degreded flying qualities for partial AFCS characteristics of a particular vehicle failures and single or dual engine failures.
mission 2nd rotor configuration. Although The three levels of flying qualities (see the type specifications were at first Table 2) used in the VSTOL and CTOL basically FIL-H-8501A with slight revisions, specifications could be incorporated in recent development of the SH-6OF and the AAH YIL-H-8501A to specify quantitative levels of was besed on type specificetions very degraded flying qualities for control different fran NL-H-8501A. ‘Ibis is due to response, static stability, and dynamic the need to address the increased mission stability in eny flight mode.
requirements of these helicopters. lhe launch and recovery of the SH-60B from a seaborne pl2tform .in up to Sea State 5 conditions is an example of these Table 1. Ex2mple of ML-H-85OlA criteria for stabilization system failures requirements. Recent work with the HXY type specificetion highlighted new problem areps, Helicopters employing eutometic including the need to address characteristics 3.5.9(d) that may be unique to a tilt-rotor stgbilization 2nd control or configuration. Through the past decade many stability augmentation equipment papers have been written describing specific or both shall possess a sufficient degree of stability and control areas in which PTL-H-85OlA is deficient.
Three of these areas are discussed in the with all the equipment disengaged to allow continuation of norm21 following paragrephs.
level flight and the meneuvering PIL-H-8501A presently addresses necessary to permit a safe 12nding helicopter flying qualities in terms of the under visual flight, condit.ions.
longitudinal, lateral, directional, and verticel 2xes. Thera is no systematic delineation between hover/low speed Teble 2. Flyjr2 qualities levels ch2racteristics and forward flight cheracteristics. In hover 2 helicopter pilot tends to use longjtudinal, lateral and Pilot FC! FO directional controls independently. For Rating Level Cescription example, in a station keeping task, transletion along the longitudinal 2nd 1.0-3.5 1 Flying oualities cleerly adequete leter21 exes is implemented by the respective for the mission Flight Phase cyclic input, while heading angle is controlled by pedel inputs. Forward flight 3.5-6.5 2 Flying Qualities adequete to cherecteristics of a helicopter tend to sccanplish the mission Flight resemble those of an airplene, thus the pilot Ph2sa but some increase in pilot needs to use lateral 2nd direction21 controls worklo2d or degr.zdation in mission in a coupled manner. Also meny single rotor effectiveness or both, exists.
he1 icopters show a coupled pitch-roll dynamic oscillation in hover, whereas in forward 6.5-9.0 3 Flying qualjties such th2t the flight 2 dutch-roll type response is often airplene c2n be controlled safely, A breakdown of the he1 icopter found.
but pilot workload is excessive or specification into hover/loh~ speed criteria mission effectiveness is inadequate, 2nd forward flight criteria (similar to or both.
VIL-F-83300) would be 2 me2ns to address the different axis couplings between hover and forward flight .
A third area that could benefit from 2 restructuring of tJILiH-8501A is in defining A sug;pest.ion bv Kev’ is that a criteria that are mission oriented. Tbe restructuring of FnIL-H-85OlA in line with relicopter specification currently uses a NL-F-83300 and VIL-F-8785C would allow for a weight paremeter for hover control power more thorough treatment of degredcd flying considerations that is the result of scaling qualities. YJL-H-8501A presently has laws and not meant to represent the qualitative criteria for feilures of power verietions in control response which may be boosted controls, automatic stabilization required for vehicle mission differences.
systems and engine failures. Table 1 Foth the VSTC!L and CTOL specificetions define presents one section of the criterion four classes of vehicles according to over211 eddressing failure of an autcm2tic mission requirements, although in ML-F-83300 the vehicle gross weight for all three the cless distinctions are only used for specifications are shown in Fig. 1. The control force limits and roll control lower bounderies of all three specifications effectiveness in forward flight.
Table 3 are substantiated by the level 2 rating given shows a general breakdown of mission as used to the XV-15 with augmentation off. There in tJIL-F-83300.
Shipboard recovery and ere two other major points to be raised from nap-of-the-earth (NCE) flight mission Fig. 1. First the CH-53D AFCS on response categories could be incorporated into these -has been described 2s quite adequate for the type of cl2ss divisions.
assault mission, yet the vehicle does not This then satisfy the VSTOL boundary.
substentiates the need for some type of weight dependency as used by ML-H-8501A. It Table 3. FIL-F-83300 clessification of aircreft is questioneble though whether or not pilots will eccept a lower response for extremely CLASFm DESCRIPTION lerge vehicles. For example, 2 vehicle in the heavy lift helicopter (HLH) gross weight I Sm211, light aircraft such as category (gw=130000 lb) would only need to - light utility attain a b2nk angle of 2.1 degrees within one - light observation second for a one inch leterel stick displacement to satisfy the tEIL-H-8501A II pedium weight, low-to-medium requirement.
maneuverability aircraft such as - utility The second point fran Fig. 1 is the - search and rescue large difference in roll response between the - enti-submarine similer weight SH-60B and CH-46A (ten degrees - 2ssault transport per inch versus four degrees per inch). lhe CH-46A has been described 2s having very III ,satisfactory response ch2racteristics for its Lerge, heavy, low-to-medium m2neuverebility aircraft such as assault and verticel replenishment missions.
- heavy transport The SH-6OB has been qualitatively described - heavy bomber as having just adequate response chzacteristics for a turbulent, high se2 IV High maneuverability aircraft state condition, indicative of the LACPS such as mission. Yet the SH-60B shows a response - fighter well ebove the visual flight rules WFR) or - atteck instrument flight rules (IFR) ML-H-850lA bounderies. The difference bethreen these two vehicles then raises the point of h2vin.g ettitude response criteria dependent on the The Navy h2s begun a program essessing vehicle mission 2nd weight. In particular the b2sic flying qualities criteria in the small landing pletforms and dynemic E"JL-H-85CJlA against the VSTOL specificetions atmospheric conditions Navy helicopters will (YIL-F-83300 and AGARD 577) 2nd be expected to 12unch and recover fran ere en representative present and future rotary wing exwple of a mission that may not be eircraft. The significent results fran the edequately designed for by the still wind, assessment of hover control power criteria out-of-ground effect control power criteria and dynemic response criteria are presented presently in ML-H-8501A.
in the following sections.
Hover Control Power Helicopter control power requirements are usually determined by the hover mission control requirements.
As described above, ML-H-P50lA uses a weight paremeter to specify attitude response within one second or 1QSS.
In an extensive review of YIL-H-P50lA, Walton 2nd Ashkenas2 suggest that the InIL-H-P5OlA weight dependency is too simplified to give adequate guidance for verious vehicle missions.
In canparison to ML-H-850lA the two VSTCL specifications define a constant limit of ettitude response.
Fig. 1. Hover roll response canparisons The boundaries for roll 2ttitude per inch of lateral control displecement 2s a function of To insure that the helicopter response Overall it was found th2t the is not initially too sensitive PIL-H-8501A YIL-H-8501A attitude response and enpuler also has minimum engular rate danping rate d2mping criteria gave minimal design criteria for the longitudinal, lateral, and guidence in canparison to the vehicles direction21 2xes. Using these d.zmping analyzed. Further enalysis and data are bounderies with the ebove attitude response needed to determine the effect of vehicle criteria, rate danping versus sensitivity mission and veried rotor configurations.
bounderies can be developed. Fig. 2 shows the ABC and tilt-rotor canpared to the VIL-H-8501A requirements for the yaw axis.
‘Ihe interesting point here is that neither Dynamic Stability aircraft satisfied the requirement yet. the ABC has been described in 2 recent Navy Following a disturb2nce (control or flight test progr2m ’ 2s having “crisp, 2tmospheric) to a helicopter in hover the predictable” yaw control 2nd that the “high rate danping criteria discussed above should yaw rates (in excess of 45 degrees per ensure 2n initiel satisfactory response.
second) that resulted fran one inch pedal After this initial response the aircraft may step inputs were well-d2mped 2nd easily still have an unacccpteble dynamic response.
errested , all owing 1erge, rapid heading In a precision hover task it is mandetory Changes.” The m-15 in canparison was that the pilot be 2ble to correct eesily for described as sluggish and not adequate. The unwanted oscilletory responses. Uncommanded point here is not that the ABC is good 2nd pitch or roll responses ten cause tracking or the XV-15 bad, but the differences in the two station keeping errors, plus any short period rotor configurations. The ABC develops yaw dynamic responses must be well-d2mmped so 2s control t,hrough differential collective of not to impede precise control of the the two rotor systems while the tilt-rotor helicopter.
develops yaw control via differential cyclic inputs. The results presented in Fig. 2 show Satisfactory boundaries for dynamic an epparent anomaly between tJIL-H-850lA and stability characteristics are defined by eech the different rotor configuretions of the ABC of the specifications reviewed through the and tilt-rotor. Fig. 3 shows the pitch use of second-order response parameters. The response charecteristics of the SH-60B, general trend is similar for 211 the CH-53D and the XV-15. Similer to the specificetions such that short period directional axis tJIL-H-85OlA 2dequately oscillations require a d,mped response while predicts the single rotor vehicle ratings for longer periods, neutral stability to (the SH-6OE and the CH-53D) but again the slight instebility is acceptable. Fig. 4 tilt-rotor shows a discrepancy. shows a plot of nondimensional damping ratio versus d2mped netural period with a canparison of the three specifications for pitch or roll hover dynamic responses. Note that only VIL-H-AOIA has a separete boundary for VFR conditions.
.6 .5 Ol 0 .25 .50 rdhc’ I6 p (TF-1 Fig. 2. yaw rate vs. sensitivity canparisons am Fig. 4. Hover longitudinal dynamic stability requirements Pig. 3. Pitch rete vs. sensitivity canparisons It should be noted that it is assuned within Each aircraft has also been given level 1 ML-F-83300 that “IFR capability is inherent ratings, in particular the SH-60B is in all military aircraft operational described as having excellent phugoid missions.” For the limited data aveilable damping. It should be noted that both VSTOL very few conclusions can be drawn about the specifications have additional requirements adequacy of the specifications boundaries. for short period oscillations such that the Of the three aircraft shown only the SH-609 damping ratio must be at least 0.3. AGARD shows a “conventional” phugoid mode. Within 577 defines a short period response such that reference 3 the point is presented that for the dwped period is less than 3 to 6 modern helicopters the MAIL-F-E3300 boundary seconds. MIL-F-83300 specifies short period shown in Fig. 4 is generally undemanding. requirements according to Fig. 6. Note that This is questionable considering the SH-6OB the frequency boundary is a function of the response that Navy pilots described 2s vehicle n/a ratio. The CH-53D was the only adequate for the LAMPS mission. Both the vehicle analyzed that showed 2 short period CH-53D and the XH-59A have also been type response, and it canpared favorably with qualitatively described 2s having level 1 the Fig. 6 boundaries (e.g. G > 0.3). For the characteristics. In particular the CH-53D vehicles canpared against YIL-H-850lA, the specification gives lenient but adequate has essentially dead-beat dynamic responses in hover. From the data analyzed it appears guidance for normal flight conditions.
that ML-H-85OlA gives adequate guidance for hover dynamic responses.
Just as in hovering conditions, it is necessary that a helicopter have satisfactory dynamic response characteristics in forward flight . For ex anple , in contour flying or mine sweeping missions, a slowly divergent phugoid response with a gradual altitude loss would be objectionable. YIL-H-8501A specifies VFR and IFR dynamic response criteria for the longitudinal axis (the same as the above hover requirements), while only stipulating IFR criteria for the lateral-directional axes.
Looking first at the longitudinal criteria, Fig. 5 shows a canparison between the VSTOL and helicopter specification Fig. 6. VSTOL specificet,ion short period boundaries. lhe he1 icopter specification is reouirement’s by far the most lenient in specifying stability requirements,. in particular for The lateral-directional dynamic long period responses (>20 seconds) under VFR conditions. stability requirements as specified by thQ In contrast., the VSTOL specifications do not 2110~ divergent long VSTPL and helicopter specifications are shown period dynamic responses. With augmentation on Fig. 7. The same general trend is followed by each criterion. Note that on, the three vehicles shown on Fig. 5 easily YIL-H-8501A has no requirement for VFR satisfied all the specifications.
lateral-directional dynamic stability.
-Fig. 5. Forward flight longitudinal dynamic stability requirements guidance to address the differences in The cluster of open symbols shows a camnon handling qualities charecteristics drmped dutch roll response for the single between hovering and forward flight rotor helicopters (SHdOB, CH-53D, SH-3A) conditions.
analyzed. This type of yaw-roll coupled dynamic response has been given ML-H-8501A has very limited guid2nce unsatisfactory ratings for single rotor for degraded flying qualities, he1 icopters. Thus there should at least be a especially towards defining minimun base1 ine criteria limiting all owabl e characteristics for AFCS failures.
divergent responses for VFR conditions. For 2ugment2tion on the responses are all ‘Ihe hover control power criteria well-damped over 2 wide range of frequencies.
(2ttitude response and rete dwping An interesting canparison between v2ried criteria) inabequat.ely address v2ried rotor configurations is shown on Fig. 7 as mission characteristics or rotor the ABC has a dutch roll response that falls configuration differences.
right on the ML-F-83300 level 1 bound2ry.
Pilots described the ADC as having very Dynamic response criteria are in general satisf2ctory later21-directional forward 2dequate but very lenient, in particular flight characteristics that were very similar for VFR mission reouirements where no to a fixed wing aircraft. A Sikorsky report guidance is given for (reference 10) on the ABC compared this leteral-directional responses.
response to lr”IL-F-8785, the fixed wing flying qualities snecification. The ABC aaain Analyses in the 2reas of height control appears as an anomaly in canparison-to the response, aerodynamic and gyroscopic helicopter sprcificetion boundary. For the cross-coupling characteristics, and vehicles analyzed PIL-H-8501A gives adequate autorotation criteria are underway.
guidance for IFR 12teral-direction21 dynamic responses but has no guidence for VFR conditions.
r -.5 20 25 5 0 3 10 15 Damped satur.1 period (5ecoml.)
Pig. 7. Forward eight lateral-direction21 dynemic stability requirements References Conclusions 1. Anonymous, “He1 icopter Flying 2nd Ground Although the need to update UL-H-850lA Handling Qualities; Generel Requirements hes been known for many yeers, very little for,” PIL-H-85O?A, 7 Sep 7961.
systematic work has been directed towards developing modern criteria. A step towards 2. Walton, R. P. and AshkenPs, I. L., this goal is the future Army-Navy progrzn “Analytical Review of. k?litary Helicopter designed to develop an updated rotary-wing handling qualities specification. This paper Flying Qualities, ” Systems Technology, Inc., Technical Report No 143-1, Aug 1967.
bes presented the major deficiences in YIL-H-85Q1A es cited by many previous papers 3. Green, D. L. and Richards, R. F. Jr., as well 2s the signific2nt results of a “Review of KL-F-83300 ‘Flying Qualities of preliminary Navy assessment of YIL-H-P5OlA.
Piloted VSTOL Aircraft’ to Assess the In particular: Applicability to Helicopters,” Pacer Systems, Inc., Technical Report No PWR-054-72, Yar ML-H-8501A does not give edequate 1972.
p. Anonymous, 'VSTOL Handling Qualities 4. Key, D. L., "A Criticue of Handling Criteria, Part I - Criteria and Discussion Qualities Specifications for US Military Dee 1970; Part II - DocldTlentation," NATO Helicopters," AIAA Paper 80-1592, Aug 19PO.
AGARD Report 577, Jun 1973.
5. Dooley, L. W., "Handling Qualities 9. MacDonald, LCDR T. L., USN, and Kolwey, Considerations for NOE Flight," American "Advanced Helicopter Rotor Systems Second S., Helicopter Society Journal, 22, (41, Ott NAVY Evaluation of the XH-59A Advancing Plede 1977.
Concept (ABC) Demonstrator Aircraft," NATC Report RW-39R-80, 24 Dee 19PO.
6. Pitt,D. M. and Heacock, F. E., "Advanced Scout Helicopter Flying Qualities 10. Ruddell, A. J., et al, "Advancing Flade Requirements, How Realistic Are They?" AHS Concept (ABC) Technology Demonstrator," Report 79-Z, May 1979.
.USAAVRADCCY-TR-Pl-D-5, Apr 1981.
"Flying Qualities of Piloted 7. Anonymous, VSTOL Aircraft," MIL-F-83300, Dee 1970.