NAVAIR Internship (Summer 2017)

Introduction

In summer 2017, I joined the Naval Air Systems Command (NAVAIR) in Patuxent River, MD as an intern through the Pathways program. I worked in the Vehicle Performance Branch headed by William Schork; my supervisor for the program was Mackenzie Rhinehart.

Projects

T-6 Trainer Aircraft Landing Analysis

Background

About a year before my internship began, the branch had received word from the base’s test aircraft center that some T-6 Trainer aircraft were requiring longer landing distances in practice than what was recommended by simulations and Naval Air Training and Operating Procedures Standardization (NATOPS) manual for the aircraft.

A member of the branch had begun trying to find the reason for this discrepancy, first by trying to match the NATOPS gliding distances by modifying the drag polars. Through this they found that the NATOPS charts were based off higher drag values than those that were actually observed in T-6 Trainer flight. To try and fix this, they ran some field performance models, but the results of these were unavailable by the time my internship began because that member had left NAVAIR.

Analysis

I followed the same trail that the member had, and begun running field performance simulations as well. I constructed two models:

1. A model with constant landing gear delta for each flaps configuration; and
2. A model with varying landing gear deltas for each flaps configuration

Varying landing gear deltas was intended to check for effects of landing gear drag on landing distance. These two models were also updated to include propulsion data from a January 2017 report by the manufacturer of the aircraft.

I then used a field performance tool designed by our branch to simulate landing and braking of the aircraft for various environmental conditions (temperature, etc.) and aircraft configurations (weight, power setting, altitude of descent, etc.) to try to figure out which combination of these parameters may have produced the charts displayed in the NATOPS manual.

As part of this simulation, I wrote scripts in Matlab for the following purposes:

• Calculating NATOPS landing distance from digitized charts based on given input conditions;
• Creating time history plots of landing distance, acceleration, thrust, etc. from field performance software output files;
  • In order to visually compare the data for each combination of simulation parameters
• Extracting and manipulating field performance braking time history data from field performance software’s output files, calculating parameters of interest for analysis (average friction coefficient, NATOPS landing distance, total stopping distance, deceleration rate, etc.), and printing the parameters to Excel workbook.

Through my analysis, I discovered that the deceleration values given in the manufacturer’s report were averaged over stopping distance rather than a discrete time series. This resulted in the field performance tool unable to implement such a deceleration function. I worked backward to determine the values of friction coefficient that resulted in NATOPS landing distances and deceleration rates in the report, and found that manipulating the friction coefficient failed to match both landing distance and deceleration rate. To fix this issue, I implemented a differential friction coefficient table for the simulation tool in which the braking friction coefficient is increased from a low value at a constant rate until a certain lower airspeed is reached, after which it is held constant.

Unfortunately, my time at NAVAIR was up before I could finish my analysis, but I noted that future analysis of the topic might vary this friction coefficient differential table to try to match more closely with the NATOPS charts and also examine the effect of touchdown speed on landing distances.

Other

T-6 Trainer Aircraft Data Export / Analysis

As a side project, I digitized several flight performance charts and tables, particularly airspeed conversion plots, and converted the data contained in them into an N-x-N table format for quick lookup in Excel.

Fighter Aircraft Launch Simulation Data

For a potential future project to develop a more efficient fighter pilot instrument display during catapult launch (in which an aircraft is “catapulted” off an aircraft carrier), I calculated several aircraft energy state parameters of interest for potential launch trajectory analysis.

Takeaways

• Gained deep understanding of flight takeoff and landing
• Learned to read and interpret complex flight parameter charts like drag polars
• Constructed lookup tables in Excel