Mechanism and Improve Methods of Rudder Lock for Mechanically Controlled Aircraft

机械式操纵飞机自动上舵成因分析及气动改善方法

¹ College of Aeronautics, Northwestern Polytechnical University, Xi’an 710072, China
² AVIC The First Aircraft Institute, Xi’an 710089, China
³ China Aerodynamics Research and Development Center, Mianyang 621000, China

Received: 20 May 2017

Abstract

Rudder Lock is a threat to flight safety, which should be carefully considered in the airworthiness certification. Since general aircrafts which are equipped with mechanical control system and controlled by unprofessional pilots becomes more and more popular, researches on rudder lock are still necessary. In this paper, a mechanically controlled medium sized transport is studied as an example. By analyzing the steady straight sideslip flight test data and flow field numerical simulation results, the mechanism of rudder lock is analyzed. Two aerodynamic improving methods including double-triangle dorsal fin and reducing set-back hinge balance are proposed. The flow field numerical simulation results show that double triangle dorsal fin can improve the stall characteristic of vertical tail, but the strong vortex will move the center of pressure forward, which worsens the rudder lock. Reducing set-back hinge balance can improve rudder lock effectively, while the hinge moment and rudder force will be increased, therefore the gearing ratio and tab should be carefully designed.

摘要

自动上舵是威胁飞行安全、适航取证中必须关注的问题。随着机械式操纵、非专业驾驶通用飞机市场的逐渐广阔，自动上舵问题仍具有重要的研究意义。以某中型运输机为例，通过分析其协调侧滑试飞数据及数值模拟流场，对该飞机自动上舵的成因进行了分析。在此基础上，提出了双三角背鳍与降低轴式补偿 2 种气动改善措施，数值模拟结果表明，前者可有效改善垂尾失速特性，但过强的方向舵前缘涡会导致方向舵压心前移，恶化自动上舵现象；后者虽可有效改善自动上舵现象，但会带来铰链力矩与脚蹬力的增加，需对传动比与调整片进行精细化设计。