Adding Undercarriage to the Twinstar


Undercarriage was added to the Twinstar so that ground take-off's and taxing could be added to the flight rosta.

 

 

 

 

 

 

 

 

There were already some great instructions on the internet by Bill Glover who had made some undercarriage for his MK1 Twinstar. These instruction can be found at :

http://www.plawner.net/4/twinstar/bill_glover/twinstar_bill.html

This undercarriage design was heavily based on Bill's, it was the same trike formation, however it had 2 struts to support the rear wheels instead of 1, to remove the twisting moment that would otherwise occur on the support points at the fuselage. Some nose wheel steering was also incorporated into the design which was connected to the rudder servo. The wheels were designed to be removable so that the plane could be returned to its original state if required.

The wheels chosen were 2.25" diameter foam wheels, with plastic hubs.

Rear Wheels

2 aluminium tubes were pushed through the side of the fuselage and glued in place to support the rear wheels. This aluminium tube had an inside diameter of 3/32".

4 pieces of 3/32" piano wire were bent and brazed to make the A-frame for each back wheel.

Piano wire is high carbon steel which can be difficult to work with. It can be cut with a hacksaw and files but the most effective tool was a 'Dremel' style power tool, used with the grinding and cutting discs.

Bending was done in the vice with a hammer.

The wheels were secured to the axle using 2 brass bushes. The bushings were like 'top-hats' in cross-section and 2 of these were super-glued to each axle with enough free play left so that the wheel could spin freely on the brass.

Later some epoxy resin was added to make sure the bushes stayed in place.

Front Wheel

The front wheel was also mounted on 3/32" piano wire bent as shown. A lightweight aluminium bush was turned and glued into the underside of the fuselage. A brass fixing nut was also used inside the fuselage to help secure the bush.

A servo arm was screwed to the top of the piano wire shaft to be connected to the rudder servo.

The wheel was held in place with 2 more brass bushes.

 

 

 

 

 

 

 

 

The total weight of the undercarriage was 60g.

The only critical points when building the undercarriage were that the back wheels should be just behind the plane's centre of gravity. This needed to be kept in mind when building the A-frames or installing the Aluminium tubes.

Ideally when the plane is rocked back so that the tail touches the ground it should just about drop forward on to the front wheel. If the plane stays tipped back then there is a danger that the tail may drag on landing. If the plane tips forward too fast, then this indicates that the tail may have problems lifting the front wheel to initiate the take-off.

This picture shows the plane with the undercarriage fitted.

 

 

 

 

 

 

 

 

 

Unfortunately the plane was crashed before the wheels could be tested !

 

 HOME

 

EMAIL

 

RC Flying