The reason they did that was that they could use 70 percent Islander structure 'Off the shelf' and 98 percent common operational spares
The fuse extention in the Trislader is an Islander centre section with an extra window each side replacing the small forward Islander fuse section
So in effect The Trislander fuse is a nose section then a modified Islander centre section followed by a standard Islander centre section followed by a optional Isalnder rear section followed by a new tail cone.
The larger span wing and larger tyres are Islander options.
The rear engine is standard Islander with only the empenage, rear nacelle and tail cone new with a bit of local strengthening here and there.
It only took a couple of months to design and knock up the first Trislander which was named appartently after someone cracked a joke at Farnborough about the so called, at the time, Three Engingined Islander....."Wot, ya mean a Trislander
![Laughing :lol:](./images/smilies/lol.gif)
"......or so the story went at the time
I always though the DC 10 a very clever design...surely......no one could build such an ugly aeroplane by accident, it must have involved very carefull planning. Then it was, of course, followed by the improved (that is, even more ugly) MD-11.
![Hiding :hide:](./images/smilies/hiding.gif)