1. Model Problems of Compound Flight
Configuration I
Configuration II
1) Mx – 1018 project
B-29/F-84
2) Tom-Tom Project
B-36F/F-84
C-27
C-5
Compound Aircraft Transport

2. Vortex Lattice Calculations
Tools and Facilities
Wind Tunnel Tests
Finite Element Structures
Flight Controls
Propulsion Studies
Water Tunnel
Vortex Lattice Calculations
Compound Aircraft Transport

3. Calculated C-5 / C-27 Drag Coefficients
Induced drag reduction as tips approach each other
Compound Aircraft Transport

4. Compound Aircraft Transport

5. Effect of Hitchhiker Size on Range
0.2
0.4
0.6
0.8 1
1.2
Scale of Hitchhiker
System Range
Ratio
Compound Aircraft Transport

6. Mothership/Hitchhiker Attached by Hinge
Carbon Fiber/foam fixed wing
Balsa wood hinged wing (NACA airfoil)
has option to add varying masses to the tip of the hinged wing
Wind Tunnel Experiment
Compound Aircraft Transport

7. Normal mode analysis of C-5/C-27 C-5 Solo 1st Bending Mode 1.4 Hz
In plane bending
( New mode)
Mode # 1. Torsion , 0.25 Hz
Mode # 2. Bending , 0.50 Hz
Mode # 3. In plane bending , 0.53 Hz
Mode # 4. Bending , 1.20 Hz
Mode # 5. In plane ending , 2.11 Hz
Compound Aircraft Transport

8. Total Fuel Flow for C-5 + 2 HH
THH/THHsolo=1.275
THH/THHsolo=1.0
THH/THHsolo=0.0
Compound Aircraft Transport
Compound Aircraft Transport

9. Maximum stress shifted closer to the tip
FE Static Analysis
C-5/C-27 Combined
lb/ft2
Maximum stress
Maximum stress shifted closer to the tip
Compound Aircraft Transport

10. All Aircraft get Lift Benefit and Drag Reduction
Conclusions
All Aircraft get Lift Benefit and Drag Reduction
- Attached Flight: system drag is less than mother ship alone
- Formation flight: hitchhiker benefits in lift and drag
- Optimal position: hitchhiker behind, inboard and above mother ship wing
Compound Aircraft Transport

11. Attached hitchhikers ride stably and with minimal control
Conclusions
Attached hitchhikers ride stably and with minimal control
Hinged connection should be stable with no need for active control
- Hitchhikers may turn engines off or operate at low throttle
Compound Aircraft Transport

12. Significant fuel savings
Conclusions
0.2
0.4
0.6
0.8 1
1.2
Scale of Hitchhiker
System Range Ratio
Significant fuel savings
THH/THHsolo=1.275
THH/THHsolo=1.0
THH/THHsolo=0.0
Minimum fuel consumption
Hitchhikers ride for free and may even chip in gas.
Mother ship may save fuel.
Local minimum fuel consumption can be achieved with:
transport providing all thrust or
by splitting thrust between transport and hitchhiker
Compound Aircraft Transport
Compound Aircraft Transport

13. Compound Aircraft Transport
Conclusions
Structural modifications are needed to improve the static and dynamic response of the compound
Maximum stress shifted towards the tip of the wing
- Presence of new normal modes of the compound system
Problems can be solved by structural reinforcement and/or controls
Compound Aircraft Transport

14. Attached or in Formation ?
Conclusions
Attached or in Formation ?
Attached:
a little greater drag benefit
with hitchhiker engines off, significant increase in range
stable and safe flight with no controls
Formation:
flight control nightmare
requires running VSTOL engines that are inefficient for high speeds
Compound Aircraft Transport

15. Compound Aircraft Transport
Phase II
Multidisciplinary Design and Optimization (MDO)
Evaluation of MDO platforms (e.g. Model Center: Phoenix Integration, insight: Ingenious Software)
Parametric detailed (realistic) structural analysis models for MDO
Identification and coordination of systems and subsystems variables for MDO
Response surface models for representation of disciplines within the MDO
Compound Aircraft Transport

16. Aerodynamic/Aeroelastic Considerations
Phase II
Aerodynamic/Aeroelastic Considerations
Wind tunnel tests with hinged attached models
Measure forces and moments
Measure unsteady pressures on wing models
Monitor the wakes with high frequency-response 7-hole probes
Study the flow field with particle-image velocimetry
Model the dynamics of hinged aircraft motion
Couple aerodynamics with structural codes to predict aeroelastic behavior
Employ the codes thus develop in design
Compound Aircraft Transport

17. Compound Aircraft Transport
Phase II
Structural analysis and design
Detailed high fidelity analysis of compound aircraft
configurations
Steady and unsteady aeroelastic analysis
Identification of cost effective structural modification for existing aircraft
Development of design tools for new aircraft designed specifically for compound flight
Compound Aircraft Transport

18. Compound Aircraft Transport
Phase II
Propulsion
Expand current engine fuel consumption analysis to account for various sized transport and hitchhikers.
Develop engine models to allow examination of engine configurations to allow high bleed flow rates.
Integrated computational/experimental study of the aerodynamics of a CAT
Design code for required camber /twist and simulation using devices
Compound Aircraft Transport