Complete Specification of
HARD LANDING DETECTOR FOR AIRCRAFT

S.No. Content Sheet No
1 Title of the invention
2 Field of invention
3 Use of invention
4 Prior art
5 Draw backs of prior art
6 Comparison between prior art and present invention
7 Aim of the invention
8 Summary of the present invention
9 Brief description of drawings
10 Statement of invention
11 Detailed description of invention
12 Drawings & worked examples

1. Title of the invention
HARD LANDING DETECTOR FOR AIRCRAFT

2. Field of invention
It is a mechanical engineering design used in aircraft landing gear system

3. Use of invention
This invented Hard Landing detector could be used in both Civil & Military Aircrafts.

4. Prior art
Inertia based hard landing detectors working on the principle of accelerometer were in use in the industry in the beginning. These are mounted on the Landing gear or structure close to landing gear which is expected to trigger an indicator based on the accelerations experienced by it. However, getting feed back from pilot & flying crew is being practiced predominantly in the industry to decide whether hard landing has occurred or not.

5. Draw backs of prior art
Inertia based detectors trigger based on the accelerations experienced by them in a particular orientation. As the functioning of these detectors depends mainly on accelerations, these units could also trigger based on the aircraft maneuvers in flight. Hence it is difficult to isolate that indications of these units are associated with the landing event or not.

In the other method, the pilot determines whether a hard landing has occurred based on pilot's experience and perception of the landing events which could be subjective and erroneous at times.

This may lead to unnecessary grounding of aircraft for detailed checks on the landing gear and other structural components at considerable cost & time, or conversely damaged aircraft can continue in service compromising the safety. Thus, lack of quantitative data on hard landing event may lead to erroneous assessment.

6. Comparison between prior art and present invention
Inertia based detectors trigger based on the accelerations experienced by them in a particular orientation. As the functioning of these detectors depends mainly on accelerations, these units could also trigger based on the aircraft maneuvers in flight. Hence it is difficult to isolate that indications of these units are associated with the landing event or not.

Present invention gives the indication only when the shock absorber pressure reaches a preset value. As the shock absorber pressure depends on Load experienced by the landing gear, the indication of this devise can be clearly associated with the landing event of the aircraft.

7. Aim of the invention
The landing loads are due to the a complex combination of landing conditions including vertical sink rates, aircraft mass, attitude etc. However, the damage to the landing gear mainly depends on the actual load experienced by the landing gear by the ground impact while landing.
The main objective of this invention is to devise a method to accurately detect that Hard Landing based on the load experienced by the landing gear which is the prime factor for structural damage. Landing gear shock absorber pressure is one of the important indicative parameter of the actual landing gear load. Hence this invention aims at designing a detector which can be integrated in the shock absorber to capture such event by when shock absorber pressure exceeds a predetermined value by providing a visual indication.

8. Summary of the present invention
If the load experienced by any component of the landing gear exceeds the allowable stresses during landing, then landing gear along with aircraft is deemed to have experienced hard landing.
Subsequent to hard landing, the aircraft is subjected to "Hard landing checks" which involves detailed inspection of landing gear & structural attachments which may lead to potential replacement of landing gear and attachments.

This invention involves a devise integrated on to the shock absorber which provides a visual indication by popping out a colored button. The devise is tamper proof such that, Indicator once triggered can only be reset by manually opening the threaded cap which is secured in place by wire locking after tightening.

9. Brief description of drawings
Fig-1 shows the cross sectional view of the Hard Landing detector.

Fig-2 Exploded view of Hard landing detector.
Fig -2 shows the hard lading detector integrated on to the landing gear shock absorber.

10. Statement of invention
A devise integrated on to Landing gear shock absorber to give a tamper proof visual indication when the shock absorber pressure exceeds a predetermined value. Once triggered, the unit can only be reset manually.

11. Detailed description of invention
Refer fig-1. Housing (1) is cup shaped part with threaded protrusion at the bottom which is compatible with oil filling port of Shock absorber. Housing (1) has external threads on the other side which receives the mating part retainer (8) as shown. The piston (2) with a dynamic seal (10) slides inside the hole in the housing (1). Other side of the piston (2) moves against a preloaded spring (6) which is compressed based on the hydraulic force exerted on it by shock absorber pressure. The collet (3) supported by the piston (2) slides inside the retainer (8). Collet (3) has two collet arms with a cam profile as shown in the fig 2. The cam surface provided on the collet makes it to deflect radially as it slides up through the retainer (8). If the collet (3) is lifted up by the piston(2) beyond the preset stroke, the col let(3) travels beyond its cam profile & hence it comes back to its original shape. Once the collet retains it shape it gets retained in the position inside the retainer(8). The collet(3) has two arms of unequal length. When collet moves up & retained in the position inside the retainer (8), one of its arms protrude out of the CAP (9) which is threaded on to retainer (8).

Resetting the indicator involves deflecting both arms of the collet (3) radially and pushing inside the retainer (8) such that collets sits on the piston (2). Unless both the arms of the collet are pressed radially, it is not possible to push the collet back in to its original position. As only one arm of the collet (3) protrudes out it cannot be reset unless CAP (9) is manually opened. Thus the indication is tamperproof.

When the shock absorber pressure is less than the preset value, the piston(2) & collet (3) will be moving inside the housing and the movement of collet (3) will not be sufficient enough to regain its original shape. However, to ensure that the collet (3) always buts on to piston (2), a push back spring(7) is provided inside a sleeve (5) as shown.

Claims

1. Method of sensing shock absorber pressure by activating a piston of the unit which is directly mounted on the oil port of the shock absorber.

2. Method of retaining the plunger in position once it travels beyond preset stroke by a special cam.

3. Method of resetting the indicator by manually opening the CAP.