code: private void calculateTurns(){
  
  		for (int i = 0 ; i< groups.length; i++){
  			for (int turn = 3; turn <= 5; turn++) {
  
  				if (i+turn >= groups.length) continue;
  
  				//Check for H bond from NH(i+n) to CO(i)
  				if (isBonded(i, i+turn)) {
  					logger.debug("Turn at ({},{}) turn {}",i,(i+turn),turn);
  					getSecStrucState(i).setTurn('>', turn);
  					getSecStrucState(i+turn).setTurn('<', turn);
  					//Bracketed residues get the helix number
  					for (int j=i+1; j<i+turn; j++){
  						Integer t = turn;
  						char helix = t.toString().charAt(0);
  						getSecStrucState(j).setTurn(helix, turn);
  					}
  				}
  			}
  		}
  	}
docs: Detect helical turn patterns.