Bachelor Thesis Department Automotive and Aeronautical Engineering Balanced Field Length Calculation for a Learjet 35A/36A with Under-Wing Stores on a Wet Runway Florian Ehrig 31. August 2012 2 Hochschule für Angewandte Wissenschaften Hamburg Fakultät Technik und Informatik Department Fahrzeugtechnik + Flugzeugbau Berliner Tor 9 20099 Hamburg In Cooperation with: GFD Gesellschaft für Flugzieldarstellung mbH An EADS Subsidiary Flugplatz Hohn 24806 Hohn Author: Florian Ehrig Date of Examination: 31.08.2012 1st Examiner: Prof. Dr.-Ing. Dieter Scholz, MSME 2nd Examiner: Prof. Dr.-Ing. Hartmut Zingel Industrial Supervising Tutor: Dipl.-Ing. Enrico Busse 3 Abstract The Learjet 35A/36A is a twin-engine business jet. In a special configuration, it can be fitted with under-wing stores, a configuration for which no takeoff performance data on wet run- ways is currently available. This report outlines the creation of a numerical takeoff perfor- mance simulation for this specific aircraft on wet runways. The results shall be used to set up takeoff performance charts that can be used in daily flight operations. To obtain Balanced Field Lengths and Decision Speeds according to EASA CS-25 certifica- tion specifications, the aircraft acceleration, takeoff and braking performance was determined. A comprehensive aircraft parameter estimation has been performed, permitting to consider the forces acting on the aircraft in various takeoff phases accurately in their dependency of time and speed. A focus of the parameter investigation was put on the precipitation drag acting on the aircraft due to the wet runway conditions. A specific geometry-based investigation of the factors de- termining the amount of spray drag acting on the Learjet 35A/36A airframe with under-wing stores was performed. This permitted a conclusion on the additional drag due to water im- pingement on the aircraft in the special takeoff configuration. The results of the simulation were set in relation with the existing aircraft performance data and a simplified calculation method. It was found that the simulation produces results of high accuracy and the results show consistent behavior with a variation in input parameters. 4 DEPARTMENT FAHRZEUGTECHNIK UND FLUGZEUGBAU Balanced Field Length Calculation for a Learjet 35A/36A with Under-Wing Stores on a Wet Runway Task for a Bachelor Thesis according to University Regulations Background Eleven aircraft of type Learjet 35A and Learjet 36A are operated by the company GFD Ge- sellschaft für Flugzieldarstellung mbH based on the Military Airfield Hohn in the north of Germany. The GFD-owned aircraft can be operated as Special Mission Aircraft with stores mounted under each wing carrying external loads of up to 900 lbs (408 kg) on each side. Of interest is the calculation of the Takeoff Field Length (TOFL) of the GFD Learjets when op- erated with under-wing stores on a wet runway. The TOFL is the greater of the Balanced Field Length (BFL) and 115% of the All-Engines-Operative Takeoff Distance. The BFL is determined by the condition that the distance to continue a takeoff following a failure of an engine at a critical engine failure speed is equal to the distance required to abort it. It repre- sents the worst case scenario, since a failure at a lower speed requires less distance to abort, 1 whilst a failure at a higher speed requires less distance to continue the takeoff. V1 during takeoff is the maximum speed at which the pilot is able to take the first action to stop the air- plane (apply brakes) within the accelerate-stop distance and at the same time the minimum speed at which the takeoff can be continued to achieve the required height above the takeoff surface within the takeoff distance. The title of the project names specifically the BFL as it is usually the distance that determines the TOFL for aircraft with two engines. 1 Critical Engine Failure Recognition Speed or Takeoff Decision Speed 5 Task Set up a calculation / simulation based on the integration of the differential equation describ- ing the aircraft motion under BFL conditions to output the BFL and V1. The calculation should be done for a set of specified input data. The simulation should be compared to per- formance data from the Airplane Flight Manual (AFM). Detailed tasks are: Literature review and description of operational hazards during takeoff on wet and contaminated runways. Collection of all required geometrical and performance data of the Learjet 35A/36A. Detailed review of certification rules related to takeoff performance calculations. Derivation of equations required for the calculation / simulation of the BFL. Literature review and extraction of key equations for the calculation of drag on a roll- ing aircraft caused by a wet or contaminated runway (in contrast to a dry runway). Investigation of further details for the performance calculation of the Learjet 35A/36A: Aircraft drag polar, drag due to spoilers, lift decrease due to spoilers, thrust decay with speed and air density, idle thrust, brake coefficients, braking capabilities, ... Set up, description, calibration and verification of the calculation / simulation. Calculation of BFL and V1 for a set of specified input data. Comparison of calculation results with simpler approaches (BFL from Raymer 1989; other TOFL estimation methods). The report should be written in English based on German standards on report writing. 6 Declaration I affirm that this report has been written entirely on my own, having used only the indicated references and tools. Where citations have been taken from other work than the present report, the source has been fully acknowledged and referenced. Date Signature 7 Acknowledgements I would like to express my sincere appreciation to all supervisors that have been accompany- ing me during the course of the project. Without the invaluable advice that only their experi- ence and expertise could have provided, this work would not have been possible. I am indebted to Prof. Dr.-Ing. Dieter Scholz, MSME, Dipl.-Ing. Enrico Busse and Dipl.-Ing. Svend Engemann for having given me the opportunity to elaborate my bachelor thesis on this exciting topic, and for their assistance and support provided in solving the challenges it in- volved. My special gratitude goes to Mr. Enrico Busse, who took a lot of time to provide excellent advice, suggestions and help towards the creation of a sound report. His experience as certifi- cation engineer and Learjet pilot that he shared with me on numerous occasions has contribut- ed greatly to my formation in becoming an aeronautical engineer. 8 Table of Contents List of Figures ......................................................................................................................... 12 List of Tables ............................................................................................................................ 16 List of Symbols ........................................................................................................................ 18 Greek Symbols ......................................................................................................................... 20 Indices for Flight Phases .......................................................................................................... 21 Indices for Aircraft Components .............................................................................................. 21 Other Indices ............................................................................................................................ 21 List of Abbreviations ................................................................................................................ 23 1 Introduction ......................................................................................................... 24 1.1 Motivation ........................................................................................................... 24 1.2 Definitions ........................................................................................................... 25 1.3 Project Objectives ................................................................................................ 27 1.4 Main Literature .................................................................................................... 28 1.5 Structure of the Report ......................................................................................... 29 2 Operational Hazards .......................................................................................... 31 2.1 Hazards from Wind, Rain, Snow and Ice ............................................................ 31 2.2 Definitions for Wet and Contaminated Runways ................................................ 32 2.3 Wet Runway Effects on Aircraft Performance .................................................... 33 2.3.1 Aquaplaning ......................................................................................................... 33 2.3.2 Acceleration .......................................................................................................... 35 2.3.3 Deceleration ......................................................................................................... 37 2.3.4 Directional Stability ............................................................................................. 38 2.4 Responsibilities, Precautions and Airmanship ..................................................... 39 3 Certification Regulations ..................................................................................