▁ 3 3 1 ▁is ▁a ▁development ▁of ▁the ▁Ul tras port ▁ 2 5 4 ▁and , ▁like ▁that ▁model , ▁is ▁named ▁for ▁its ▁empty ▁weight ▁in ▁pounds . ▁The ▁aircraft ▁was ▁designed ▁to ▁comp ly ▁with ▁the ▁US ▁Ex perimental ▁- ▁Am ateur - built ▁aircraft ▁rules . ▁It ▁features ▁a ▁single ▁main ▁rot or , ▁a ▁single - se at ▁en closed ▁co ck pit ▁with ▁doors , ▁sk id - type ▁landing ▁g ear ▁and ▁a ▁tw in ▁cyl inder , ▁air - co o led , ▁two - stroke , ▁dual - ign ition ▁ ▁H irth ▁ 2 7 0 6 ▁engine . ▁ ▁The ▁aircraft ▁fus el age ▁is ▁made ▁from ▁compos ites . ▁Its ▁ ▁diameter ▁two - bl aded ▁rot or ▁has ▁a ▁ch ord ▁of ▁ ▁and ▁emp lo ys ▁an ▁AT I ▁ 0 1 2 ▁( V R - 7 ▁mod ) ▁air fo il ▁at ▁the ▁bla de ▁root , ▁transition ing ▁to ▁an ▁AT I ▁ 0 0 8 ▁( V R - 7 ▁mod ) ▁air fo il ▁at ▁the ▁tip . ▁The ▁ring - mount ed ▁tail ▁rot or ▁has ▁a ▁ ▁diameter ▁and ▁a ▁ch ord ▁of ▁. ▁The ▁cy clic ▁control ▁is ▁mounted ▁from ▁the ▁co ck pit ▁ce iling , ▁but ▁otherwise ▁is ▁conventional . ▁The ▁horizontal ▁tail plane ▁mount s ▁end - f ins ▁for ▁direction al ▁stability . ▁ ▁The ▁aircraft ▁has ▁an ▁empty ▁weight ▁of ▁ ▁and ▁a ▁gross ▁weight