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Airtoi SPECIAL Nr 1, october 1999
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Flying Jet-powered models with THRUST VECTORING
to maximize future jet transport flight safety
ABSTRACT
At the end of the first 100 years of conventional, Aerodynamic Flight Control [AFC] based aviation, we now arrive at the gate of a much safer flight control methodologies and technologies. It is indeed the beginning of a new era in aviation; - an era marked by complete roll-yaw-pitch Thrust Vectoring Flight Control [TVFC] that is almost free from the dangerous characteristics of AFC.
TVFC becomes highly effective in the 'impossible-to-fly' post-stall domain and in the conventional domain. It is stall/spin-free and is to advance air transportation into a much safer era. Fighters, trainers, private, biz and airline transport jets will be vectored in the near future. By using rapid engine-nozzle jet deflections they would all maintain much safer flight control when AFC fails. And it can indeed prevent most air-flight catastrophes [Cf., e.g., US Patent 5,782,431 of July 21, 1998 on ‘Thrust Vectoring/Reversing Systems’] .
Since 1987 VTP has demonstrated, for the first time in aviation history, the ability of yaw-pitch-roll TVFC in the deep post-stall domain and the ability to civilize military TVFC to provide safe, stall/spin-free and AFC-free flight as well as the methodology to maximize range and fuel saving by actually flying tailless vectored prototypes. Our work is based in part on the use of flying jet-powered subscales under strict similarity rules to the full-scale aircraft. It shows that much of this new experience is to cause significant re-assessment of transport policy as well as of pilot and academic education.
Introduction
The first-ever TVFC jet-powered subscales were flight tested by the author in 1987 [5]. That included the first Tailless Vectored Vehicles [TVV] as defined and characterized by the author’s book [2]. It was conducted by flying TVFC jet-powered models with similarity rules to the full-scale fighter aircarft . New TVFC-induced post-stall maneuvers, up to 170 deg. angle of attack and turning at up to 50 deg. sideslip angles, have thus been substantiated for the first time.
These flight tests have demonstrated the highest payoffs of TVFC at the weakest domains of AFC, i.e., at low (or zero) speeds, conventionally-uncontrolled spins, very-short runways, and during rapid post-stall maneuvers. TVFC has thus been employed mainly when ailerons, elevators and rudders have been neutralized by a radio command during flight.
In 95 the author has also conducted the first flight tests with a sub-scaled TVFC Boeing 727 prototype to provide the first proof of maximized-safety, thrust-vectoring-based, alternative transport flight control for saving otherwise doomed jets [4]. The resulting technologies are estimated to potentially prevent more than 50% of jet crashes as caused by:
Thus the near-term availability of roll-yaw-pitch jet-deflecting engine nozzles for civil aviation opens the road to alternative methods for safer flight control. Yet, the situation in civilizing the more verified military thrust-vectoring technologies for maximizing air travel safety may be suffering today from a cultural skepticism somewhat greater than that encountered earlier in the military domain.
Use of Jet-Powered Models To Maximize Flight Safety
Most air catastrophes are caused by the limited capability of conventional Aerodynamic Flight Control [AFC] to prevent them or to actively save doomed passenger, business, and cargo jet transports during take-off, flight and landing under adverse conditions involving stall/spin, asymmetric icing, wind-shear/microbursts, partial loss of AFC and engines, total loss of all hydraulics, tire explosions and front-wheel collapse. Similar catastrophes are encountered by turbo-prop aircraft. Other catastrophes involve the loss of tail rotor or tail during helicopter flight [1-25].
Thrust Vectoring/Reversing Systems
Our research since 1980 relates to a family of retractable pitch, yaw/pitch and roll-yaw-pitch TVFC methods and systems, with and without thrust-reversing [TR] methods and systems. Its first purpose is maximization of air safety and energy saving in operating transport jets, turbo-props, helicopters and other, jet-generating vehicles. The resulting integrated TVFC/TR methods and systems are equally aimed to minimize installation complexity, weight and cost while allowing, under adverse conditions, the highest air-safety levels feasible in comparison with those extractable from conventional AFC means.
In their deployed TVFC mode of operation, our designs are intended for catastrophic failure prevention. In their retracted mode they do not interfere with engine/nacelle/airframe aerodynamics. The retracted modes are therefore intended for cruise flight and for conventional altitude changes with minimal fuel consumption.
An important purpose of the research is to provide alternative flight control when AFC fails, or
fails to function safely.
Another aim is to save a doomed aircraft whose AFC elements have failed, or whose all airframe
hydraulics/actuators are not functioning, or one or more of its engines is inoperative, or has
separated, or the vehicle is subjected to adverse flying conditions such as stall/spin, asymmetric
icing, and wind-shear/microbursts.
Another object is to provide the pilot with an improved capability to rapidly correct his
mistakes under adverse takeoff, flight and landing conditions.
In using one of our specific system configurations the loss of helicopter’s tail or tail rotor may
prevent a catastrophe by reducing the gas-turbine nozzle cross-sectional area and providing
anti-rotation moment by reverting to auto yaw TVFC mode of operation.
Similar, but more integrated and effective TVFC/TR/AFC modes of emergency operation, are intended
for preventing turbo-prop transport catastrophes.
In applying such TVFC/TR/AFC system configurations to jet transports, the heavy, complex and costly conventional TR doors/rods/hinges, retracting/sliding gear, actuators and TR-grid-nacelle-structures can safely be removed and cost-effectively replaced with a simpler and lighter-weight add-on TVFC/TR kit system.
The designs also allow TVFC/TR-induced short landing via reduced minimum control approach speed to be followed by conventional, post-touch-down TR.
All implementations and installations of related structures and flight-control means are also designed to take place without any change to the engine itself while providing low-cost, low-weight, retractable/integrated, TVFC/TR add-on kits for upgrading extant vehicles and for improved operation of new, cost-effective ones.
For catastrophic failure and crash prevention in other air, land and marine applications we thrust-vector surface sliding, out-of-conventional control, ground and sea vehicles to prevent collision and crash.
Useless Rocket-Type Nozzles
No modern jet engine can function with prior-art rocket-engine thrust-vectoring-nozzle mechanisms and methods [1-5]. Rocket-type nozzles fail during the typical prolonged operations which characterize jet engines, namely, thousands of hours, instead of minutes. Moreover, unlike the fixed, and highly divergent, internal duct shape of the rocket-nozzle, that of advanced supersonic jet-engine nozzles is made to geometrically vary internally with throttle change and flight conditions. Consequently, all rocket-TVFC-nozzle prior art is inherently irrelevant and useless with respect to aircraft TVFC [1-4].
Our TVFC methodology provides a number of independent methods for retracting and deploying thrust-vectoring/reversing means and families of various retractable pitch, yaw/pitch and roll-yaw-pitch TVFC structures, with and without TR methods and systems. While aimed mainly for air uses based on gas-turbines, our methods are also intended for land and marine applications, including those based on liquid jets, such as water-jet based vehicles.
Tailless Vectored Aircraft Proof-of-Concept, The Opposition to TVFC
TVFC F-15, F-16, F-18, F-22, JSF, X-36 and Su-37 represent a sample of highly active international development programs today. Any conventional air force fleet can now be upgraded to become ‘effectively vectored’. Yet there are no industrial and legal programs to civilize this technology to prevent most jet crashes and to bring about the saving of many lives. Amazing as it is, NASA, FAA, Boeing and AIRBUS as well as a great majority of well-educated aero-engineers and pilots oppose any use of TVFC in civil aviation. Some dismissed all TVFC ideas, claiming it is impossible to make thrust-vectoring-induced post-stall maneuvers, or spin recoveries under AFC-failure conditions; - that TVFC passenger aircraft are not even worthy of a feasibility study based on jet-engine-lab or sub-scale or Full-Scale flight tests.
Maximized Flight Safety Standards
Our estimations of expected public benefits from civil TVFC technology are based on U.S. NTSB’s detailed reports on causes of transport jets fatal accidents during the last 30 years. Using these reports we have examined under what realistic TVFC means and commands such crashes might have been prevented [4]. Our conclusions show that TVFC can prevent most air fatalities when the jets encounter:
The resulting flight safety levels are expected to be even higher for the following reason: All NTSB’s reported “Pilot Error” cases have not been counted by us. Yet, our many and various computer simulations demonstrate that with proper operative/deployed TVFC/TR means the pilot commands new options to correct his mistakes, for instance, during last-minute crash avoidance into a mountain in cases requiring post-stall maneuvers which had been filed by NTSB as “Pilot Error”. In addition the studies demonstrate the followings:
It thus remains for near-term international education, legislation and certification to help save many lives and prevent much damage by proper TVFC/TR.
Reassessing Academic Aero-Education
Jet engines are traditionally considered as providing only brute, unvectored, forward force. The required moments for maneuverability, controllability and air safety are traditionally reserved for aerodynamic-only flight control [AFC] surfaces which are a-priori limited by reactions to external-flow regimes, and, hence, limited by the so-called stall barrier and spin dangers.
This conservative educational-design approach should be re-assessed now. We can learn from what has happened in the educational reassessment in the military domain, where a fundamental change in such low-insight attitudes has already caused dramatic changes in maximizing agility, stealth and post-stall controllability and safety. Indeed, new attempts to revolutionize the mode of thinking of propulsion, aerodynamic, system design and flight-control engineers, currently dictate a radical change in basic aeronautical engineering and pilot education, theories and aircraft design practice.
Catastrophic Failure Prevention [CFP] by TVFC
We divide CFP by TVFC/TR into distinct classes:
Recovery by TVFC When Hydraulics/Actuators Fail
Our TVFC methodology for meeting Class 3 demands is based on actuating all TVFC flaps/vanes/nozzle-kits by extant hydraulic/air sources of the operating jet engines only. Namely, we avoid any safety reliance on airframe hydraulics, actuators and emergency-manual AFC-connections, except via redundant cross-linking options. Hence, when all airframe hydraulic systems fail, our designs provide easy-to-operate and safe roll-yaw-pitch TVFC that is entirely based on engine (independent) oil-pumps and/or compressor air.
Vectoring Categories vs Flight Safety Levels
Complete roll-yaw-pitch TVFC provides the highest air-safety level. And it should not be confused with other TVFC categories:
1 - AFC + Pitch-only-TV
This combination represents the lowest TVFC/AFC safety standard. As an example one may consider
the air safety levels provided by the F-22 pitch-only TVFC nozzles, which are currently equipped
only with rectangular [2D] TVFC-nozzles of the pitch-only jet-deflection type. In comparison, the
Russian versions are currently using rounded roll-yaw-pitch TVFC nozzles.
2 - AFC + Yaw-Pitch-TV
This combination represents the 2nd air safety level. Roll-TV for single-engine designs can
provide the next level of safety.
3 - Pure TVFC
This category was first demonstrated and flight tested by us in 1987, using various stealth,
unmanned, dynamic-similar configurations. It represents the highest safety level but it is not
practical for most uses without combining it with AFC [category 4].
4 - TVFC/TR/AFC
The TVFC/TR/AFC mix provides the highest air safety level feasible. It has been stressed and
demonstrated by us since 1987 [5].
Tailless Vectored Aircraft
Since 1987 we have also stressed and demonstrated, by flying jet-powered models, various tailless fighter aircraft and tailless transports. Each such design may represent the same safety level as that provided by category 4. This category-design was first flight tested by us in 1987 [5].
Other Factors Affecting Flight Safety Effectiveness
Flight safety also depends on the distance between engine nozzles [not necessarily between engines] and aircraft center of mass location, and on maximum feasible jet deflections and deflection rate values. Maximization of flight safety also requires automatic, or manual emergency transformation means from TVFC mode to AFC and vice versa, including emergency release/neutralization means to zero TVFC, or zero AFC moments. It also requires ‘CONTROL ALLOCATION’, a key concept that we study with new Minimum Time Standard Agility and Safety Comparison Maneuvers [SASCOM] and flight testing methodologies [7-25]
References