WESTLAND WYVERN LANDING GEAR
By David Wigley
Unquestionably, one of the most dynamic and interesting aircraft of the 1950s was the Westland Wyvern S4. It was designed from the outset as a carrier-based strike fighter for the British Royal Navy. It was a huge aircraft with a takeoff weight of 24,500 pounds and was powered by a 4000 HP turbo-prop engine. The contra-rotating propellers kept the diameter down but the landing gear had to be long enough to provide clearance for the Wyvern’s under-slung torpedo.
Designing and fabricating the landing gear for my 1/5-scale Wyvern certainly was a challenge. I made everything the old-fashioned way with a lathe, milling machine and a pair of calipers. These days, with AutoCAD and CNC machines, a set of landing gear like these can be made relatively quickly and very accurately. I duplicated the full-sized gear leg (strut) by first drawing it to scale and then making a wooden mockup to confirm the geometry and fit in the wheel well. I then machined the metal parts from bar-stock aluminum. It took about two hours to make the wooden mockup and almost two months to fabricate the aluminum units! There are 22 individual pieces in each main gear leg, excluding the commercially available retract unit to which the gear attach.
Although the main landing gear looks somewhat small for the size of the aircraft, it is actually very robust. Each main leg consists of a front and rear strut connected by an upper and lower fork. The oleo shock absorber is in the rear strut, similar to the Hawker Sea Fury and Tempest, but with a much longer stroke. Both legs are operated pneumatically. They retract inward with sequenced inner doors that are closed when the gear is extended and retracted. I use an Ultra Precision sequencing air valve, which is reliable and provides realistic movement of all the components. The tail unit is a conventional design and retracts forward into the fuselage.
MAIN GEAR STRUT
Each main gear leg consists of four main pieces: The front strut with the wheel and axle, the rear strut containing the shock spring, and the upper and lower forks. Fortunately, with the exception of a small bevel at the top of the front strut, these parts are not “handed.” Meaning, you don’t have to make different parts for the left and right legs. The rear strut is machined from a piece of 1.5 inch square 6061 T6 bar-stock aluminum. I first marked out the pivot hole locations and then drilled and reamed them out. Next, the piece is turned on the lathe by clamping it off-center in a four-jaw chuck. A lot of material is removed to get the upper part of the strut down to the correct diameter. The leg is then transferred to the milling machine, where the arms that support the lower fork are machined. The final step is back to the lathe where the bore for the shock spring is drilled out.
The front strut is also made from 1.5 inch square bar stock. It is fabricated in a similar way, except the upper portion is turned to a taper. A lot of material needs to be removed from the lower area to accommodate the wheel. I used a band saw to cut away most of the material, and then milled and filed it to the final shape.
The upper and lower forks are both different, but are relatively easy to machine. These are fabricated from 2024 aluminum because of its superior strength. The final pieces are the shock-strut piston and linkage that connects it to the lower fork. The correct strength of compression spring is important. A good rule of thumb for a straight shock strut is to use a spring rated for the weight of the airplane in each strut. So for a 40-pound model, use a 40-pound spring in each retract strut. Because of the leverage in the cantilevered Wyvern gear, I calculated that a 200-pound, heavy-duty spring was needed. This has proved to be correct. The leg is assembled using steel-dowel pins that are held in place with small-set screws. The 6-inch block tread wheels are available from Glennis Aircraft. The axle is made from 1/4-inch music wire that is pressed into the fork. I don’t trust wheel collars to retain the wheel. Instead, I anneal the end of the axle and cut 1/4-28 threads about 1/2-inch long. After the wheel is installed, I screw on a castle nut and use a cotter pin to secure it. Not only is this a better method of securing the wheel, but it also looks more scale.
The pneumatic retract unit is not shown on the drawing. I had Ultra Precision make my units, but they are only now making retract valves. Sierra Giant Scale has a large variety of retract units that can be fitted with the Wyvern gear.
Although I designed and machined my tailwheel fork and retract unit for my prototype Wyvern, Sierra Giant Scale sells a forward-retracting tail unit and their Sea Fury/Tempest fork is very close to the scale Wyvern shape. I would recommend purchasing these. A Robart 3-inch wheel fits nicely to finish the tail-wheel unit.
The landing gear is now ready for action. Adding some scale details such as brake lines, the step, towing eye and hubcap make the gear look a lot more realistic. I also made simulated hydraulic cylinders from aluminum tubes. The rod attaches to the back of the rear strut and the cylinder disappears into the wheel well, where it is anchored to the main wing spar. It looks very convincing.
The Wyvern has many distinctive features that set it apart from other aircraft. The shock-absorbing landing gear is one of those interesting things that not only make it look good, but are also functional. You can grease on more than a few landings with this scale landing gear!
Sierra Giant Scale www.sierraprecisi
Robart Mfg. www.robart.com
Click here to download a PDF of the machine drawings.
Basic wooden mock up in place
Milling the Rear Fork
Disassembled view of parts
Main Landing Gear parts
Close-up of left gear in Wheel Well
Center Wing Underside. Gear is a Snug Fit
Dummy Hydraulic Cylinder added
Main landing gear installed with gear door attached
Gear With Step And Brake Line Detail
Right Gear front view
Left Leg Details Added
Flyby with gear extended