- a/c floor is exceedingly thin. Virtually all helis larger than a Bell 47 have their fuel stored under the cabin (any higher and conventional refuel vehicles/ FARP installations would not be able to fill the tank(s)). I suggest a floor at least 25cms thick under the cabin.
- with the currently-modelled a/c, when static on ground (on its relatively-tall reverse-tricycle undercarriage) the main rotor thrust-line tilts aft of the vertical. All helis compromise between optimisation for work in the hover (vertical thrust line) or at higher speeds (thrust line tilted forward of vertical). No heli that I can think of is configured so that, once the rotors are turning, the a/c starts to move backward - as is the case with your Mi-48. Such a configuration would at best restrict available-forward-cyclic and at worst be uncontrollable even before take-off. I would suggest a low nose-wheel design to overcome this issue, possibly involving moving the Mi28-style 30mm turret up and forward to replace the under-nose sensor.
- My tandem-rotor experience is restricted to 9 years/ 2700 hours on CH47 and I have absolutely no experience whatsoever on co-axial types. However, I understand that to control a co-ax in yaw during autorotation, significant inputs from vertical control surfaces (rudders) are required. Such rudders either need to be large surface area if close to the rotor thrust line (eg Ka25, 27, 32 et al), or (if small) need to be further away from the thrust line (eg Ka50) to achieve the necessary moment. The current Mi-48 V-tail appears not to offer very much in the way of yaw controllability in autorotation, but would definitely provide a large nose-down force in descent which would require considerable aft-cyclic to overcome. I suggest a conventional vertical surface/twin-tail combination to replace the current V-tail/small horizontal stab/small fin set-up currently fitted.
There are other observations which detract from the overall believability of the design, in particular the excessive height of the airframe (in targetting terms, it's a flying barn door; in aerodynamic terms it has excessive keel area forward of the head...) but the above points are those I suggest could be addressed to make the aircraft 'work'.