Hi Pete - how's life in Yorkshire, sorry Lancs
I can sense the armchair experts out there desparate to chip in with their years of knowledge and experience - keen to overload you with science, mirrors and smoke.
K.I.S.S.: If rotor blades were reduced in length to stop them bumping into confined areas, they would have to spin much faster to maintain their lift capability.
This then imposes serious strain on the bearings/hinges/materials due to centripetal / centrifugal forces. In addition, the tip of the advancing blade starts working its way towards compressibility etc etc.
Increasing the chord length increases the lift vector which increases the loading on the disc.
Smaller blades also make more noise than larger ones and Mr ICAO doesn't like noise for downtown commuter helicopters so he puts a noise limit on them. [Ever noticed a 109 coming? You can hear it in the next county!]
You still fly the Robbo: Measure the blade length, look at its nominal Nr and work out how fast your tip is going (2 x Pi x r). See how close it is to the speed of sound when it's going at full chatter @ say 100kts still air.
Fun and games.
From here on it gets murky:
Chord twist.
modern materials.
wing fences
winglets
berp
anhydral
yawn yawn..................
