1.0 Scope

This document describes the functional requirement the scheme of fluid porting during Aircraft Landing Gear operation from two independent Hydraulic Systems using Hydraulic Release Valves.

2.0 Description

The aircraft hydraulic systems are either duplex in nature or triplex in order to meet the reliability requirements. The multiple systems are independent in nature and are designed to operate with a requirement of "fail operational - fail operational" and "fail operational - fail safe" principle. The Landing Gears are generally operated by Hydraulic system. The hydraulic system architecture for the Landing Gear operation in aircrafts is duplicated with system A used for normal operation and system B for emergency operation or viz. In the case of normal operation the fluid is drawn from the system A reservoir and returned back to the same reservoir. During the emergency extension of the Landing Gears the fluid from the system B reservoir is utilized. The fluid from the up-line of the Landing Gear circuit is either vented to the atmosphere or the same needs to be ported back to system B reservoir.

Venting of the fluid to atmosphere is the safest option provided that much of additional volume of fluid is available in the reservoir. In certain cases, when the Landing Gear Jack volumes and the Door Jack volumes are very high, venting the fluid is no longer a good option. In such cases porting of the fluid back to the system B reservoir is to be followed. This invention is on the "fluid porting from two independent Systems for Landing Gear operation using Hydraulic Release Valves.

3.0 Technical Specification

PART A

3.1 FUNCTIONAL SPECIFICATION

3.1.1) Specification As per MIL / SAE AS Standards

3.1.2) Type Fluid Porting from two independent Systems for Landing Gear operation using Hydraulic Release Valves.

PARTB

3.2 LEADING PARTICULARS

• Operating Pressure 280 Bar or suitable for any other operating Pressure

• System A Normal operation of Landing Gears

• System B Emergency Extension of the Landing Gears

• Operating fluid MIL or Any other Standard Aircraft Hydraulic Fluid

• Architecture Suitable for Aircrafts with duplex Hydraulic Systems.

2.0 FIELD OF INVENSION AND THE NEED FOR INVENSION:

2.1 BASIC AIRCRAFT

The hydraulic system architecture for the Landing Gear operation of one of the basic aircraft variants is duplicated with system A used for normal operation and system B for emergency operation. In the case of normal operation the fluid is drawn from the system 1 reservoir and returned back to the same reservoir. During the emergency extension of the Landing Gears the fluid from the system B reservoir is utilized. The fluid from the up-line of the Landing Gear circuit is vented to the atmosphere.

2.2 NEW VARIANT

The same concept could not be adopted in a new variant. The subsequent paragraphs gives the details of the challenges that were faced and the design solutions adopted to overcome the challenges.

3.0 DIFFERENCES BETWEEN BASIC AIRCRAFT VARIANT AND NEW VARIANT :

The following table gives the differences in terms of the volume of fluid required for operation of Landing Gears between LCA Airforce and Naval aircrafts. As it is evident from the above table that the volumes required for operating the New Variant's Landing Gears was more the existing architecture of operating the New variant's Landing Gears was not possible with the existing reservoirs. The new reservoir volume required for New variant was estimated 2 Its more than the existing reservoir. This new reservoir requirement necessitated the development of a new LRU, QT etc. More over the new reservoir size could not be accommodated in the new variant due to the fact that the Reservoirs are located in the Landing Gear bay and the New variant's Landing Gear which is bigger in size had to be accommodated in the same bay. The New variant's Landing Gear size is huge as compared to the Basic aircraft Landing Gear due to the fact that it has to operate under different conditions of higher sink rates. The New variant's Landing Gear Bay Structural designs had to be bulky with additional reinforcements to cater for the higher Landing Gear loads. As the structural designs did not permit provision of cutouts nor dishing, a bigger reservoir could not be located in the aircraft and hence this led to a no-go situation. There was also a weight penalty of around 5 to 6 kgs for the two reservoirs.

In order to overcome the above problem and to use the same size reservoir for the New variant, an architecture was evolved to return back the fluid to the reservoir instead of venting the fluid to atmosphere. This could be achieved by using two Hydraulic Release Valves in the return lines. The circuit is so configured that during the normal operation of the Landing Gear, fluid is drawn from the System A reservoir and returned back to the same reservoir. During Emergency operation of the Landing Gears the fluid is drawn from the System B reservoir and returned back to the same reservoir. This has avoided the use of a bigger, heavier reservoir which could not be accommodated in the Landing Gear bay. Also the new architecture has resulted in a weight saving of around 5 to 6 kgs. As the same reservoir was used, this resulted in additional saving in terms of cost, efforts and time for design and development of a new LRU. The associated Qualification and Certification cost, time and efforts was also saved.

4.0 OBJECTIVE OF THIS INVENSION

The main objective of this invention was to continue to use the existing qualified reservoirs to enable the "fluid porting from two independent Systems for Landing Gear operation using Hydraulic Release Valves.

5.0 DESCRIPTION OF THE SYSTEM (Ref Figure 1)

During normal operation of the Landing Gears System A operates Landing Gear electro-selectors and Door electro-selectors (open-neutral). The return fluid from the electro-selectors is routed through the two System A and System B Hydraulic Release Valves. Due to presence of pressure in System A and absence of pressure in System B, System A release valve is closed and the System B release valve is open. Due to this the return fluid from the electro-selectors is ported back to System A reservoir through the System B release valve. Also the additional Release Valves in the Landing Gear up-line and Door Close lines are blocked due to the presence of System A pressure. During emergency extension of the Landing Gears pressure from System B is fed directly through a manual selector valve to the shuttle valves mounted on the Landing Gear and Door jacks. The Landing Gear electro-selectors and Door electro-selectors are de-energized upon selection of emergency lowering by the pilot and would be in neutral position. The return fluid from the electro-selectors is routed through the two System A and System B Hydraulic Release Valves. Due to presence of pressure in System B and absence of pressure in System A, System B release valve is closed and the System A release valve is open.

Due to this the return fluid from the electro-selectors is ported back to System B reservoir through the System A release valve. Also the additional Release Valves in the Landing Gear up-line and Door Close lines are open due to the absence of System A pressure, this would create additional passage for porting back the up-line fluid to System B reservoir in case of failure of the electro-selectors in struck closed position.

CLAIM:

We claim that

1. The fluid porting from two independent Systems for Landing Gear operation using Hydraulic Release Valves will enable usage of optimum size of the reservoir there by resulting in saving of weight.

2. The fluid porting from two independent Systems for Landing Gear operation using Hydraulic Release Valves has been configured and designed at ARDC, HAL for use on aircrafts with dual hydraulic systems. This circuit is safe and can work satisfactorily even in case of jammed Door and Landing Gear electro-selectors.

3. By using the scheme of fluid porting from two independent systems for Landing Gear operation using Hydraulic Release Valves, a smaller size reservoir can be used because additional volume of fluid that is drained overboard during emergency operation need not be carried.

4. Using the scheme of fluid porting from two independent systems for Landing Gear operation using Hydraulic Release Valves results in saving of weight and space for the aircraft as a smaller reservoir is used.