SAE AIR 4762-1994 Compilation of Freezing Brake Experience and Suggested Designs and Operating Procedures Required to Prevent Its Occurrence《防止发生冻结制动的经验和建议设计和作业程序的编制》.pdf
《SAE AIR 4762-1994 Compilation of Freezing Brake Experience and Suggested Designs and Operating Procedures Required to Prevent Its Occurrence《防止发生冻结制动的经验和建议设计和作业程序的编制》.pdf》由会员分享,可在线阅读,更多相关《SAE AIR 4762-1994 Compilation of Freezing Brake Experience and Suggested Designs and Operating Procedures Required to Prevent Its Occurrence《防止发生冻结制动的经验和建议设计和作业程序的编制》.pdf(5页珍藏版)》请在麦多课文档分享上搜索。
1、AEROSPACE INFORMATION REPORTAIR4762Issued 1994-02Reaffirmed 2010-01Compilation of Freezing Brake Experience and Suggested Designsand Operating Procedures Required to Prevent Its Occurrence1. SCOPE:This AIR describes conditions under which freezing brakes can occur and offers suggested design feature
2、s to minimize occurrence. It also suggests operating procedures which have been shown to prevent or lessen the severity of brake freezing.2. REFERENCES:There are no referenced publications specified herein.3. PROBLEM:Encountering frozen brakes is not an uncommon winter weather problem for some aircr
3、aft operators. During cold weather operation when snow, slush or wet runway departure conditions are present it is possible for brake freeze-up to be experience. Freezing can occur with minimal water present. It can result in tire skid damage on landing at subsequent destinations. The freezing occur
4、s because runway roll operations produce moisture contamination of the brake stack.Freezing can occur on the ramp, during taxi operation and prior to landing. The first two situations result in an inability to move the aircraft, while the latter results in a much more serious condition which can cau
5、se a locked wheel landing with attendant damage, tire blow outs and possible control problems.The normal or average shear strength of ice which forms between the rubbed surfaces of the brake is 30 psi. This strength will vary depending upon the thickness of the ice and the level of brake lining wear
6、 debris contamination of the surface. Very thin ice thickness results in even higher shear strengths. Wear debris can result in three times this normal strength level. The ice bond is strong enough to produce drag levels capable of skidding tires on dry runways.SAE Technical Standards Board Rules pr
7、ovide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the
8、user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2010 SAE International All rights reserved. No part of this publication may be reproduced, stored in a retrieval
9、system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA) Fax: 724-776-0790 Email: CustomerServic
10、esae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedbackon this Technical Report, please visit http:/www.sae.org/technical/standards/AIR4762Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without li
11、cense from IHS-,-,-SAE AIR4762- 2 -3.1 Contributing Factors:Factors which influence the potential for freezing brakes include weather, runway contamination (snow, slush and water), brake rubbed area, number of disk pair, brake stack location outside versus inside the wheel (wheel flange driven rotor
12、s versus wheel well driven), multiple wheel landing gear, aircraft design (specifically wheel well) and aircraft operating procedures.It is relatively independent of brake heat sink material since freezing occurs with both carbon and steel heat sink brakes. Although carbon brakes absorb moisture (ma
13、ximum of 4% by weight), their susceptibility to freezing is no greater than steel brakes.The problem is most prevalent on aircraft which have unheated or open wheel wells where the landing gear doors seal around the tire OD (wheel and tire exposed to the slip stream). It is exacerbated by low aircra
14、ft sink rates where wheel load is gradually applied during landing, making tire skids more likely.4. OPERATIONAL PROCEDURES FOR PREVENTING BRAKE FREEZE-UP:There are two basic types of corrective operational procedures. One depends on maximizing weight on wheels at touchdown to weaken the ice bond. T
15、he other relies on elevating brake stack temperatures during taxi operations to prevent ice formation.The greater mass and running clearance of the steel brake, as compared with the carbon brake, is an advantage when attempting to shear the disk ice bond by firm ground contact. The carbon brake is c
16、onsiderably more tolerant of heat than the steel brake, making prevention of ice bond formation the more practical approach for carbon brakes. The ideal temperature would evaporate all brake moisture accumulated at departure.It should be noted that brake heating by any method without monitoring the
17、brake temperature may increase the risk of blown wheel fuse plugs. Therefore, it is recommended that aircraft, which require heating of the brakes to prevent freeze up, be equipped with brake thermal monitoring systems (BTMS).4.1 Recommendations for Operating in Freezing Conditions:4.1.1 Parking: Wh
18、en icing or excessive moisture with freezing weather conditions exist, parked aircraft should have their brakes in “OFF condition“ (not pressurized) with wheels chocked.When washing the aircraft, be careful not to saturate the wheel or brake. Carbon brakes will achieve 98% of their water absorption
19、capacity within 15 min (over 50% within 3 min). Any water between the disks of both carbon and steel brakes can result in brake drag if it freezes.Application of hot air sources may be used on both steel and carbon brakes.Copyright SAE International Provided by IHS under license with SAENot for Resa
20、leNo reproduction or networking permitted without license from IHS-,-,-SAE AIR4762- 3 -4.1.1 (Continued):Suitable chemical anti-icing or defrosting agents (such as ethylene glycol) which do not have a detrimental effect on brake operation may be applied to STEEL BRAKES ONLY. Taxi stops made after ap
21、plication of chemical anti-icing agents will degrade their effectiveness in preventing freeze up. NEVER use chemicals on carbon brakes since this can have an adverse effect on vibration, oxidation and wear of the carbon.If the brakes are frozen, apply maximum brake pressure several times statically.
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