1. Extremely Maneuverable UCAV
Team Zebra
Andrew Fischer, Team Leader
Matthew Everingham, Structures and Costing
Connor McCarthy, Aerodynamics and Propulsion
Jim Lang, Project Advisor
Blaine Rawdon, Boeing Company Sponsor

2. Outline of Presentation
UAV Opportunities
Project Requirements
Mission Profiles
Configuration
Performance
Aerodynamics
Propulsions
Stability and Control
Low Observables
Structure
Future Work
Schedule and Timeline
Conclusions
Special Thanks

3. UAV Opportunities
This chart shows that the purpose of a UAV is to exceed human limits. Current UAVs, such as the Predator and Global Hawk, lean more to the endurance phase of the graph. The ExMan UCAV is designed to exceed human limits in maneuverability, agility, and acceleration.

4. Project Requirements
Create design concept for an extremely maneuverable UCAV that can perform two distinct missions
Performance up to 9g’s comparable to F-16 & F-15 aircraft for subsonic to transonic flight
Extended maneuvering capabilities up 20g’s due to increased structural limits and the use of dynamic lift
Estimate “Value of Maneuverability”

5. Mission Profiles Missions comparable to F-16 and JSF missions
Defensive counter air mission is an F-16 mission. While the JSF can fly the Hi-Lo-Lo-Hi mission.
Missions comparable to F-16 and JSF missions

6. Defensive Counter Air Mission
Phase 1 – Take off and acceleration allowance
Phase 2 – Climb from sea level to optimum cruise altitude
Phase 3 – Cruise out at optimum speed and altitude for 700 nm
Phase 4 – Combat allowance
Fuel to perform at 25,000 ft with maximum thrust and fuel flow
One sustained 360º (PS) at M=0.8
Four maneuver-point (instantaneous) 90º turns, recovering to M=0.8 and 25,000 ft altitude after each
Phase 5 – Climb from 25,000 ft to optimum altitude
Phase 6 – Cruise back at optimum speed and altitude
Phase 7 – Descend to sea level
Phase 8 – Reserves: fuel for 30 minutes at sea level at speed for maximum endurance

7. Hi-Lo-Lo-Hi Interdiction Mission
Phase 1 – Take off and acceleration allowance
Phase 2 – Climb from sea level to optimum cruise altitude
Phase 3 – Cruise out at 500 nm at optimum speed and altitude
Phase 4 – Descend to 200 ft
Phase 5 – Dash out 100 nm at M=0.8 at 200 ft
Phase 6 – Weapons Delivery:
Small Diameter Bombs are delivered in aggressive turning maneuvers. Retain air-to-air missiles throughout the mission
Phase 7 – Dash back 100 nm at M=0.8 at 200 ft
Phase 8 – Cruise back 500 nm at optimum speed and altitude
Phase 9 – Descend to sea level
Phase 10 – Reserves: fuel for 30 minutes at sea level at speed for maximum endurance

8. Target Laydown
Here we have a sample target laydown with 11 pre-planned primary targets and 4 pop-up targets. The flight path is assumed to take into account both terrain and threats. Each of the targets is represented by a 500' radius release circle which is determined by the glide slope of a small diameter bomb and the vehicle altitude of 200'. The small diameter bombs are assumed to be GPS guided. The flight path is constructed such that it leads directly towards each target and upon intersection with the release circle, the vehicle begins turning towards the next target. When the heading has reached the direct path towards the next target the flight path becomes straight again. Each turn in the primary flight path shown is 2000'.
The red circles represent pop-up threats, which appear during the mission. The maneuverability of the ExMan allows it to rapidly reverse turn direction. This ability allows it to acquire all of the pop-up threats in one pass, in line with the pre-determined flight path.
The measure of merit for this mission is targets/minute. This drove the design to high speed and thus requires the aircraft to pull lots of g's.

9. Maneuverability and Speed Issues
Higher speed requires greater load factor capabilities
Symmetrical design allows pitching oriented maneuver to replace roll maneuver
Negative Ps during high g turns complicates the maneuvering
The maneuverability of the ExMan allows higher speeds though the same flight path, which means that it must be able to handle higher load factors than conventional aircraft.
The ExMan is designed to be symmetrical so that it can fly at positive and negative angles of attack. The benefit of this feature is that it enables very fast change in turn direction during high g turns.
Also of note: When the flight through the sample target laydown with taking into account the Ps capabilities of ExMan, the flight time through the course is only ten seconds longer than when velocity is assumed to be constant. The projected course time changes from about 130s to about 140s. Since the high g turns will be happening at 200' altitude, during negative Ps maneuvers, we were driven towards keeping the altitude constant while the velocity of the aircraft decreases. When keeping a constant turn radius, this results in decreasing the induced load factor during the turn. However, the aircraft is moving so fast that most turns take only a couple of seconds, minimizing the effect of negative Ps during high g turns.

10. Here we see the kinematic relationship between required load factor and the speed through the target laydown shown. We can see where the F-16 lies at about 9gs allowing a speed around 400 knots, and where the ExMan lies at 20gs with a speed close to 600 knots. The need to move through the course quickly drives the need for a high design load factor in order to make the same radius turns at higher velocities.

11. Here we see how the number of targets attacked per minute relates to the load factor required. This again reinforces the need to increase the design load factor in order to improve the targets hit per minute. With the F-16 at 9gs and the ExMan at 20, the ExMan can hit about 2 more targets per minute, translating to about 120 more targets per hour for the given target laydown. This kinematic relationship pushed the design towards high design load factor in order to maximize the kills per minute measure of merit.

12. Here is a chart of roll angle vs load factor for a sustained turn, another completely kinematic relationship. The ExMan, pulling 20gs would be at a roll angle of 87 degrees, very close to 90 degrees. This means that for ExMan, when changing turn direction, it is much quicker to roll past 90 degrees to the same angle on the other side instead of rolling back to level and then rolling to 87 degrees in the other direction. This drove the design of ExMan to a symmetrical airfoil section. The maneuver could be visualized similarly to a skier shifting weight from one foot to the other while racing through a slalom course. The possibility of hitting threats designated in real time as the UCAV flies its course at very high speeds is realizable through this type of maneuvering. The military spec on roll rate is 180 degrees in 2.85 seconds for air to air fighter aircraft. The ExMan's special maneuver allows it to change turn direction by pitching 40 degrees in 1 second or less.

13. Performance: PS
For subsonic values, the ExMan UCAV performs similar to an F-15 and F-16. For 1-g the ExMan UCAV has comparable Ps values to that of the F-15 /F-16. At M=0.8 and Alt = 52,000 ft for the F-15 the Ps = 0 ft/s. For the ExMan UCAV it Ps = 40 ft/s. For the 5-g Ps graph the stall mach moves to about M = 0.4 at 0 ft. For the F-15 the stall Mach is M = 0.4 at 0 ft. At M = 0.8 at 16,000 ft Ps = 0 ft/s. For the ExMan UCAV, Ps = 300 ft/s. The ExMan UCAV has more specific excess power because it has less SW/SR, which makes the CD,0 (zero lift drag) less, thus the Ps less.

14. Performance: PS
Due to the SW/SR being less on the ExMan UCAV, the Ps values are higher than the F-15/F-16. At 20-g’s, even at 0 ft there is not any positive specific excess power, but where we are doing our maneuvering at M = 0.8 at 200 ft Ps = -600 ft/s. At this Ps the change in velocity with respect to time (dV/dt) is -24 ft/s. If we make a maneuver that takes 3 seconds while maintaining constant turn radius and turn rate, the velocity is still 1.4*Vstall. The F-15/F-16 cannot pull 20-g’s.

15. Performance: Turn Rate vs. Mach
This shows the Ps for the ExMan UCAV and the F-15, assuming no dynamic lift. The ExMan UCAV has a higher g limit so the max turn rate, 45 deg/sec, occurs at M = If the g-limit were the same as the F-15, 9 g’s, the max turn rates would be comparable within 15 %. The max turn rate for the F-15 is 24 deg/sec at M = 0.5

16. ExMan Exclusive: Dynamic Lift
This shows that with dynamic lift the stall velocity moves to the left, as shown. The dynamic stall limit is calculated the same way as the non-dynamic stall limit except that Cl,max,dynamic = Cl,max + (9.0 Cl,alpha MAC)/(2*v). This shows the exclusive region where the ExMan UCAV can perform that the F-15/F-16 cannot due to structural limits and dynamic lift. With dynamic lift the max turn rate goes from 45 deg/sed to 68 deg/sec. This a gain of 50 % better turn rate. At the max turn rate, the F-15/F-16 would take over 5 seconds to make a 180 deg turn. A human cannot sustain 9 g’s for that long, so the pilot would have to slow down or increase the turning radius, thus taking a lot longer than 5 seconds to make the turn. The ExMan UCAV would take less than 3 seconds, in a much smaller radius and there are no human limits to factor in.

17. Take-off and Landing Parameters
Take-off distance = 1230 ft
Landing distance = 3678 ft
Vstall,TO = 155 ft/s
The take-off and landing distances were calculated using formulas from Nicolai.

18. 3-View of Planform

19. This is a very qualitative diagram comparing the span loading concept to the conventional wing-body loading. The main idea is to reduce the bending moments that the primary structure has to withstand, allowing the dependence of the empty weight on load factor to be reduced.

20. Internal Components

21. Aerodynamic Characteristics
Leading edge wing sweep - 50°
Aspect Ratio – 4
Taper Ratio, λ
Root Chord – 20 ft
MAC – 14 ft
t/c - .09
NACA 0009 Airfoil
Uncambered
Clmax – 1.32
The airfoil, NACA 0009, was used because it is uncambered and has a relatively high sectional lift. There is also a lot of data, and the section needs to be optimized for further study. This allows for the aircraft to behave aerodynamically the same inverted as it would in regular flight. The high leading edge sweep raises the critical mach number to about 0.95, which means the K and Cd don’t start increasing until after .95.

22. Drag due to Lift Factor, K
K is constant until M=0.95, then as it passes the critical mach it is based on the inverse the lift curve slope. Since the combat segment is performed at M=0.8, the aircraft doesn’t have a drastic jump in K to worry about.

23. Zero Lift Drag Coefficient, CD0
The drag coefficient is based on the subsonic estimate that varies with t/c and a correlation factor, R. However, it can be seen until the velocity hits the critical mach number, the coefficient doesn’t change enough to notice. After the critical mach the coefficient makes a drastic jump due to the transonic flow. The critical mach is high enough that the aircraft doesn’t get a huge drag penalty when it performs its combat segment.
Drag Polar – CD= CL2

24. (L/D)max
After the aircraft reaches the critical mach, the L/D drops drastically. However, this is not a problem because the aircraft’s combat segment is performed at a mach lower than the critical mach.

25. Stability and Control Aerodynamic Center – .25 of MAC
Static Margin
Longitudinal, lateral and directional neutral stability
Large control surfaces for high pitch acceleration (°/s2)
Leading edge controls for high lift
Chord length – 3 ft
Acting over >90 % of wing area
Trailing edge controls for maneuvering
Chord length – 3.8 ft
Acting over 80% of wing area
Plain flaps
The aerodynamic center on the longitudinal axis occurs around the CG and the neutral point of the aircraft at 15 ft. The static margin based of the neutral point and the MAC gives a small positive values, which indicated stability. The lateral and directional stability which are neutrally stable, are beyond the scope of this project. The leading and trailing edges were size from the MAC and the coefficient of lift verses angle of attack data. Refined sizing was made after the pitch acceleration based of the IYY moment of inertia was found to be low. The flaps function as control surfaces, and even as an option could function as a thrust vectoring system as well.

26. High Lift Devices
Leading and trailing egde control surfaces that are bi-directional. This graph represents both regular and inverted flight. The stall happens at both 25 and -25 degrees for the 0 degree flaps.

27. High Lift Devices, cont.
High lift flaps increase camber of the wing. The change in Clmax for the leading edge is much more significant than the trailing egde. Therefor leading edge flaps can be the high lift device rather than the trailing edge. The trailing edge will be the controls. The graph represents both regular and inverted flight.

28. Dynamic Lift ΔCLmax,dynamic is proportional to ά/V
The use of dynamic lift on a unmodified NACA 0009 wing gives a small increase in CLmax. As the pitch rate increases, the CLmax,dynamic increases. For the benefits to be noticed the rate change of alpha should be up around 90 deg/sec or above. Implementing such high rates of change would only be dependent on the sizing of the control surfaces and pitch acceleration. Combining dynamic lift with high lift devices could produce a very high lift wing at points where the aircraft is loosing energy in a turn a lower speeds. At M=0.4 ΔCLmax,dynamic will be twice as large than at M=0.8. Also twice the pitch rate will give twice the change as well.

29. Longitudinal Stability
The downward slope on this plot indicates that the aircraft is stable. However, the slope is so small that the aircraft could be considered neutrally stable. To trim the aircraft in the longitudinal direction after CG travel, the flaps would only have to be adjusted slightly to make the aircraft stable.

30. Propulsion System
Two Pratt & Whitney F-100-PW-100 engines scaled down a factor of lbs each
Combined SLS thrust of lbs
Dimensioning:
Engine length – in
Compressor face diam.– in
Max diam. – 35.5 in
Airflow to each engine – lbm/sec
Bleed airflow for each engine – 0.4 lb/sec
Possible options for operating over 9g’s
Dual-cycle engine (turbofan and ramjet)
Build a 20g engine
The engine selection was made on the assumption of a rubber engine. However, this is so a comparison to the F-15 and F-16 can be made. The scaled down engines were scaled of the performance assumption of a thrust to weight ratio of approximately 1.2, which is similar to the F-15 and F-16 as well. In looking at a realistic option for an engine setup, the GE-404 could be looked at as well. Another thing to consider in the propulsion system is the high g’s that the aircraft can pull. Over the normal operating limit placed on engines at 9 g’s, there are a couple options. One is to use a ramjet on the afterburner and kill the engine to give thrust up to 20 g’s. Another is to machine a 20 g engine, which could cost much more to develop.

31. Maximum Thrust
At 0 to 5000 ft, where combat is performed for the Hi-Lo-Lo-Hi mission, the max thrust is suitable. For the interdiction mission a lower maximum thrust is provided. The engine won’t operate at less than mach 0.2 above 10000ft.

32. Military Thrust
Scaled down from the maximum thrust

33. TSFC
As the altitude increases, the overall TSFC decrease due to its dependence on air density.

34. Inlet and Nozzle Details
Axisymmetric pitot inlet – subsonic consideration
Dimensioning:
Inlet diameter – in
Diffuser length – in
S-shape diffuser to reduce radar detection
Pressure recovery in diffuser – %
Short convergent nozzle
Good overall
Potential for thrust vectoring
Slight drag penalty
Long fairing between nozzle exits
Reduce acoustic interference
The type of inlet chosen was a pitot inlet, which functions best at subsonic speeds. The inlet diameter was based off of the throat mach number needing to be M=0.67 for the speed at the compressor face to be M=0.4. Instead, of a circular inlet being used, an axisymmetric inlet face was chosen to fit on the leading edge of the wind. The diffuser length was based on the compressor diameter. The S-shape diffuser provides some protection against a radar signature being read off of the compressor face. The pressure recovery in the diffuser is relatively high, so there isn’t a marked reduction in thrust. The nozzle chosen was a short convergent nozzle, which is simple. However, the nozzle does have the highest drag penalty of the all the types of nozzle. Another choice could be a simple ejector, but large airflows are needed. The fairing between the two nozzle outlets will probable be a couple feet to reduce signature and modal virbrations.

35. Low Observables: Options
4 spike configuration
Head on into radar w/ minimal detection
S-inlet duct w/ radar absorbing material
Increase in LO
decrease in thrust
Edge Treatments
Wempty increase
The delta planform lends itself to a 4 spike radar configuration, where 2 of the spikes are perpendicular to the leading edge, which means that the aircraft could fly into a radar head on with minimal detection. The S-inlet in combination with a radar absorbing material can help scatter radar energy in the diffuser. It also can reduce heat signature. Edge treatments to the leading and trailing edges help reduce radar and IR signature as well.

36. Center of Gravity
This shows the center of gravity of each internal component and its location on the planform of the aircraft.

37. Travel of Center of Gravity
Future studies will show that this can be made smaller because fuel can be pumped to forward fuel tanks to keep the center of gravity forward.

38. Structure 20g structure Lower factor of safety Span Loading
maneuverability outside of human limits
higher lethality
higher survivability
Lower factor of safety
Lowered from 1.5 to 1.25
exploitation of opportunities exclusive to UAVs
Span Loading
decrease in bending moments on main wing structure
reduces dependence of structure weight on load factor
The benefits of a 20g structure include improved survivability, higher lethality, as a result of the increased maneuverability. The aircraft is intended for positive and negative load factors of 20g. This allows the ExMan to move faster through the same maneuvers than a conventional aircraft such as the F-16, as shown previously.
It will also be shown that the ExMan can have better capabilities than the F-16, while keeping the weight of the ExMan lower than the F-16.

39. Structure Empty Weight Dependence on Load Factor
The reduction of load factor dependence between span loading and non-span loading was determined using MATLAB model of a basic wing box.
The exponent of load factor was found to be reduced by 0.2, from 0.59.
Normally, a refined empty weight estimate made based on historical data for A/C components.
In this case, the load factor dependence determined from the MATLAB program was used with the historical data to produce an empty weight estimate of ExMan.
An empty weight estimate of the F-16 configuration was also created, using the same historical relations, but with the body-wing dependence on load factor.
In order to determine the dependence of empty weight on the design load factor, a MATLAB script was written to qualitatively determine the difference in dependence on load factor between a span loaded design and a non-span loaded design.
This load factor dependence was then used in the refined empty weight calculations, which are based on historical data.
The weight of an F-16 scaled up to handle different load factors was then compared to the ExMan as scaled to handle different load factors.

40. Structure Empty Weight Dependence on Load Factor (continued)
The relation of empty weight to load factor based on the actual empty weight of the F-16 was created to determine the empty weight of an F-16 which has been scaled up to handle up to 20gs.
A similar relation for the empty weight of ExMan was determined assuming the same quantity of non-load factor dependent weight.
Targets hit per minute was related to empty weight for each aircraft through the design load factor and minimum required turn radius for sample target laydown.
The relation shows that the ExMan UCAV will weigh less than the F-16 for any given load factor.
The ExMan UCAV at a design load factor of 20 is lighter than the F-16 at a design load factor of 9.
In order to determine the dependence of empty weight on the design load factor, a MATLAB script was written to qualitatively determine the difference in dependence on load factor between a span loaded design and a non-span loaded design.
This load factor dependence was then used in the refined empty weight calculations, which are based on historical data.
The weight of an F-16 scaled up to handle different load factors was then compared to the ExMan as scaled to handle different load factors.

41. This chart shows the change in empty weight required as the load factor is increased. The slope of the curve is predominantly determined by the dependence on load factor. For this chart, the two aircraft are assumed to have the same amount of weight which is not dependent on load factor, and are assumed to have the same weight at a design load factor of For the same Load Factor Capability, the ExMan is lighter than the estimated F-16 weight.

42. Possible Trade Studies
PW-F-100 vs. GE-404 engine
Double vs. single engine design
Leading edge inlets vs. top-bottom bifurcated inlets
Inlet flaps for flow straightening
Control effectors (ie. Thrust vectoring)
Mission Radius
Fuel layouts
Check into a single engine design for cost and weight distribution. Look at a GE-404 engine, which is comparable to the scaled size, weight and thrust of the F-100. Measure effect and penalties of the top-bottom wing mounted inlets. Flaps directing the air more efficiently into the inlet would be another thing to consider. Mission radius and endurance could be looked at varying with cost and fuel. This could also show the UCAV entering the High performance and high endurance arena. The fuel layout can be varied to get better CG travel, but cost would have to examined. Control effectors such as surfaces directing nozzle output can be looked for performance and cost.

43. Here the targets attacked per minute is plotted against load factor
Here the targets attacked per minute is plotted against load factor. The targets attacked per minute is based on the target laydown shown earlier. We see that the targets attacked per minute increases much faster for ExMan than for the same change in the F-16 based estimation. Also, this chart shows that for the same empty weight, the ExMan is able to

44. Conclusions
Performance up to 9g’s comparable to F-16 & F-15 aircraft for subsonic to transonic flight
Extended maneuvering capabilities up to 20g’s due to increased structural limits and the use of dynamic lift
Symmetric design able to perform positive and negative maneuvers with equal performance
Span loading concept results in a lightweight aircraft

46. Schedule and Timeline