Due to the instability, I tried to make controller for Longitudinal and Lateral direction. There is no proper design for Observer; it is just for possibility check for control surfaces.
We could figure out that aircraft is very-unstable for lateral direction as we discussed; however proper controller could mitigate the problem.
This is a kind of reverse engineering contents for MQ-25 which I have interest for its beginning. Still there is no exact data for this aircraft, so I should imagine or estimate some part of design. It does lead to in-exact prediction, but I hope it can provide some provision.
Progress are shown in below
1. Shape Design and Sizing for Initial Estimation
2. Aerodynamic Characteristics
3. Stability and Control Characteristics
4. Performance (Flight Trajectory) Analysis
1. Shape Design and Sizing for Initial Estimation
Roughly designed MQ-25 style model is shown; Planform of main-wing and v-tail is from 3-view while airfoil is approximated as 0.1c thickness with CL 0.2. Canted angle is 70deg from vertical plane.
Based on geometric design, rough sizing is done. Empty weight, baseline fuel, and cruise condition are configured to fit known data. Breguet Range equation shows that it is similar to the mission profile; delivering 17,000lb for 500nm distance.
Result is 502nm with 3,750lb fuel; it means that the modeled MQ-25 is very efficient for aerial refueling compared to F/A-18E/F. Heavier F/A-18E/F carrying much more fuel than MQ-25 for the same mission.
2. Aerodynamic Characteristics
Baseline model carrying pair of pod depicting A/A42R-1 pod contributed to drag. CG is assumed to 7.1m from the Nose (Total length of aircraft is 17m). Control surfaces are v-tail, inboard and outboard of main wing.
At Cruise condition (M0.6), OpenVSP provides 6DOF aerodynamic coefficients. L/D is from 12 to 17 at AoA 0~2deg.
M0.2 w/ 30deg flap is powered approach condition; flap is deflection of in and outboard conforl surfaces which are shown in several pictures. it decreaes max L/D due to excessive drag but good at AoA 0 deg.
3. Stability and Control Characteristics
OpenVSP provides full 6DOF coefficients and inserted these to longitudinal & lateral matrix to get SnC characteristics. Inertia of model is harder than predicting pure-aero; inertia value is assumed as 1/8 of small transport aircraft.
It results that 1.5min period of Phugoid w/ 4min of 1/e attenuation. Important thing happened at lateral motion. As shown in coefficient result, it did not have directional stability which requires active damper for real application.
4. Performance (Flight Trajectory) Analysis
Engine is modeled by parametric ideal engine; fortunately Rolls Royce AE 3007 engine has well known data. Thrust and Fuel-Flow table is generated for flight condition while thrust is degraded for 5% to account inlet/exhaust shape.
Trajectory of 1st mission shows modeled aircraft deliver up to 17,000lb fuel for 500nm distance using 3,750lb own fuel. M0.6 at 25,000ft cruise condition is assumed while 17,000lb fule is gone at 500nm. CL conditino change shows that aircraft flew designed condition and CD is about 0.02.
Max-ferry mission is calculated; if external fuel can be used for MQ-25 entirely, it can fly almost 7000nm for 22hr. There is a doubt about its performance.
There are several cases; detailed discussion will be shown.
Result for several mission expected for MQ-25; specification is fitted to reference mission.
MQ-25 can reach 6930nm if it can use whole fuel for own flight; 19,730lb is used.
Light-patrol mission carrying two 500lb shows 509nm with standard internal fuel.
If MQ-25 goes 35kft to save fuel, it can extend its range for 70nm.
1. Demo-Test II for Flight-SIM w/ single-aisle Airliner
Configuration of the code and its simple demo is shown in the previous articles; further test is performed to validate the SIM. I use Sim-Brief to refer the weight and fuel usage of the A320.
Flight-SIM and its Database of the generic single-aisle Airliner is checked for three cases, short, medium, and long range case.
Fligh-SIM over-predicts range of the aircraft for about 10% while aircraft DB does not consider trim-drag and engine DB is based on pure-estimation. Although DB is not perfect, overall result is reasonable.
1. Demo-Test for Flight-SIM w/ single-aisle Airliner
Configuration of the code is shown in the Previous work status. After the works for debugging and DB generation, I could show you the flight trajectory or range performance of the aircraft with specified DB. This test is not based on the realistic data but generic or typical data of the single-aisle airliner. Please enjoy it.
1) Input : Trajectory set up
Flight-SIM has several options for the trajectory prediction as described in the previous WIP articles; On/Off of SID/STAR, Optimization or Manual Climb/Descend can be selected from the input excel file. Example is shown in Fig. 1 with this demonstration case. Cfg and Cfg_eng numbers mean that the Flight-SIM could simulate trajectory simulation with variable geometry or multi-mode engine if the DB were available.
Fig. 1 Trajectory input table for the Flight-SIM
2) Input : Airliner / Engine DB
Aerodynamic characteristics and weight specification are provided in the Airliner DB while Engine has own separated DB. Weight specification is shown in Fig. 2 which is similar to typical single-aisle airliner; aerodynamic characteristics varied by Mach number, Reynolds number, and AoA are recorded in table with breakpoints. Flight-SIM uses 4th order polynomial fitting to calculate the aerodynamic force with proper input.
Fig. 2 Aircraft DB
DB structure of the engine is similar to that of aircraft however, more breakpoints should be provided for the throttle change. 0% for flame out, 70% for idle, 85% for middle, 100% for climb or military thrust, and 110% for TOGA or Afterburner. In Flight-SIM, non-throttle specified step like Cruise, SID/STAR automatically find the proper thrust for its trim while Climb, Descend, TO/LD will use specified breakpoints like 70%, 100%, or 110%.
More detailed structure of the simulation or input DB is available at previous articles.
Fig. 3 Engine DB
3) Output : Demo RUN
Execution of the Python code for the Flight-SIM is done for two cases of demonstration;
(1) Uniform Cruise Altitude with 6t of fuel
(2) Two Cruise Altitude with 12t of fuel
Idle execution screen is shown in Fig. 4. Whole trajectory data is recorded by specified excel file; each step provides finish status report. Optimized cruise Mach number and altitude is shown in Fig. 4; Figure shows progress of the running code.
Fig. 4 Idle Screen for run of Flight-SIM
Result of (1) is shown in Fig. 5; Raw result summarized flying status of each time step.
Fig. 5 Raw result of Case (1); part of them are only shown
Result of (1) is shown at Fig. 6; flying distance, altitude, speed, and AoA change during the flight are calculated. Corresponding change of engine, atmosphere, and fuel are also shown.
Fig. 6 Few graph of Single-Airliner Trajectory
Result of (2) is shown at Fig. 7; flying distance, altitude, speed, and AoA change during the flight are calculated. Corresponding change of engine, atmosphere, and fuel are also shown.
Fig. 7 Few graph of Single-Airliner Trajectory with more fuel and step climb
4) Conclusion
Flight-SIM is completed and tested for typical single-aisle airliner DB. Although flying range is too exaggerated, the code itself provides proper reasonable flying trajectory based on the DB. Tool will be developed for not only aircraft also aerospace plane or space-craft. My next aircraft design will be evaluated based on this simulation.
