The lightweight military transport aircraft (typically 15-19 seater) normally use fixed-type ground ladder or aircraft mounted one/two-step ladder for boarding and deplaning of their military personnel. Sometimes, these aircraft are used for transporting military VIP guests also. Currently, the use of fixed-type ground ladder at each military base for these short range/light weight transport aircraft is not an economical and faster solution. The one/two-step on-board ladder has Cesser footstep area, more inter-step distance and ground clearance, which may sometimes lead to falling or injuring of passenger/ crews.
In this scenario, a requirement arises to design a ladder, which is lightweight, foldable type with bigger step area, occupies less stowage space inside the aircraft cabin.
4.2. Object of the Invention:
. The object of the invention is to design a compact on-board ladder, which can be folded and stowed inside the aircraft. Optimum inter-step height and large step' area to be adopted to assist the safer and faster boarding and deplaning of military personnel. The lighter footstep design and bush controlled hinge joints are used to aid flexibility to fold and unfold it inside the cabin for anticipated operation. Additionally, the ladder should have provision of height adjusting mechanism to cater the height variation between ground and cabin resulting *from compression and extension of main landing gear struts. At any instance, the ladder footsteps - need to be in horizontal position (within 5°) at any payload values.
4.3. Summary of Invention:
A foldable ladder is invented which consists of four steps with sufficient pedal area and inter-step distance for human comfort. The ladder is supported on aircraft hinge brackets at one end and on the ground at other end. The hinge bracket to ground distance varies up to 108 mm due to compression and extension of the oleo pneumatic landing gear struts depending upon the payload on the aircraft. To keep the ladder footstep parallel to the ground at any aircraft payload, various locking positions are envisaged for locking of ladder in extended configuration.
4.4. Description of Invention:
Ladder assembly broadly consists of Footstep Panels 1, Horizontal Beams 2,

Oblique beams 3 and 4, Channel Support 5, Bush 6, Lock Plate 7, Wheel Bush 8, Bearing 9, Nylon Wheel 10 and Bolt Pins 11 and 12.
Fig. 1 shows the Honeycomb made Footstep Panels 1 positioned on the side edges of Horizontal Beams 2 and secured with four countersunk screws. The top metallic plate of item 1 is bored with countersunk depression to flush the attaching fasteners on its top surface. Honeycomb core is crushed on the side edges and sealed with relevant core filler at the locations where fasteners are used for tightening of item 2 and Oblique Beam 3.
Fig. 2 represents the attachment and stiffening provisions made for ladder frame structure. Channel Support 5 is stiffening each item 1 at two places to avoid its bending against passenger loads. Item 2 and item 3 are press fitted with Bush 6 at each joining location. The thickness of the item 6 is 0.5 mm more than the beam thickness to allow 1.0 mm clearance between beams 2 and 3. It avoids direct metal to metal contact during folding and extension of the ladder. Honeycomb core is crushed on the side edges and sealed with relevant core filler at the locations where fasteners are used for tightening of item 2 and item 3.
The ground, to ladder hinge axis height changes with the variation in payldad. At no payload condition, all footsteps remain horizontal with the inter-step distance of 8 inch. When the payload starts increasing due to boarding of passengers inside the cabin, the ground to ladder hinge axis height starts decreasing. At maximum .payload, the ground to ladder hinge axis height reduced by 108 mm. In this situation, maximum angle of footsteps with respect to horizontal plane remains within 5°. Lock Plate 7 is used to lock the ladder during loading and unloading of passengers as shown in Fig. 1. It is connected with item 2 through a pinned joint. The other end of item 7 contains four holes to accommodate the variation of ground to ladder hinge axis height at different aircraft payloads. During loading and unloading of passengers, suitable holes of items 2 and 7 are matched. It is ensured in the design that at any payloads, the item 1 should remain tilted clockwise within 5° with respect to flight direction.
During boarding of passengers, the locking holes of item 2 and 7 are matched to maintain the item 1 in horizontal position. As the payload increases, aircraft cabin floor to ground height decreases and the ladder wheels move away from the aircraft. As a result, footsteps start tilting clockwise up to the maximum limit of 5° at maximum payload. During unloading of passengers, the locking, holes of item 2 and 7 are matched to keep the item 1 initially at approximately 5°. When the

payload reduces, the ladder wheels move towards aircraft and the footsteps starts tilting to reach horizontal position. The horizontal-position is achieved when all passengers deplane the aircraft. Therefore, to maintain the footsteps within 0 to 5° at any payload between zero to maximum, provision for different matching combinations of locking holes needs to be adapted.
Fig. 3 depicts the top and bottom attachment configuration of the ladder. The bottom most item 3 on both LH and RH side are fitted with Wheel Bush 8, which has the stepped shank diameter for mounting of Bearing 9. The Nylon Wheel 10 is attached to bearing through interference fit and moves both forward and backward to cater the variation in ladder height due to change in payload. Item 10 also offers easier transportation of ladder on ground from one place to another in extended and locked position. To attach the ladder on aircraft, bottom edge of the cabin door has two existing brackets, previously used for integration of one-step fixed type (welded) ladder. The same brackets are used here to integrate the newly designed four-step ladder on the aircraft. Bolt Pins 11 and 12 are keeping the ladder attached to the bracket. One Bolt Pin has through hole on its shank for provisioning of cotter pin to constrain the motion in lateral direction (along and opposite flight direction) while allowing the rotational motion..
Fig. 4 shows the overall swept volume (730mm x 445mm x 160mm) of the ladder in folded configuration.
The material and primary dimensions of the detail parts are depicted below:

Item No. Description Qtv. Material Size
1 Footstep Panel 4 Metal Honeycomb L= 364 mm, W= 250 mm
2 " Horizontal Beam 8 Al Alloy Plate L= 265 mm
3 Oblique Beam 1 6 Al Alloy Plate L= 474 mm
4 Oblique Beam 2 ' 2 Al Alloy Plate L= 402 mm
5 Channel Support 8 Al Alloy Sheet L= 370 mm
6 Bush .42 . Cu Alloy Rod D= 20 mm
7 Lock Plate 2 Al Alloy Plate L= 144 mm
8 Wheel Bush 2 Cu Alloy Rod D= 44 mm
9 Bearing 2 Purchased Part
10 Nylon Wheel 2 Nylon Rod D= 100 mm
11 Bolt Pin 1 1 Steel D= 40 mm
12 Bolt Pin 2 1 Steel D= 40 mm

We Claim

The "4-Step Foldable Passenger Ladder" comprising of Footstep Panels,
Horizontal Support Beams, Oblique beams, Channel Support, Bushes, Lock Plate
and Nylon Ring fitted Bearing.
The technique as claimed in claim 1 wherein Footstep Pianels are made of metal
Honeycomb supported by Sheet Metal C-channels from bottom side for light weight
rigid construction.
The technique as claimed in claim' 1 wherein Horizontal'Beams and Oblique Beams
are fitted with Bushes at each rotational joint for constrained and aligned motion
during opening and folding of ladder.
The technique as claimed in claim 1 wherein Lock Plate is used for locking and
controlling the height between datum ground to hinge bracket at different aircraft
payloads.