Aircar
Well-Known Member
As threatened -here is a place to evaluate and discuss the just announced Terrafugia TFX (no relation to the TFX Tactical Fighter Experimental that led to the F 111)- Various comments have been made on the roadable thread and revolutionary design but this stands to be a very 'influential' program in more ways than one and certainly makes some great claims.
A hardnosed design evaluation seems to be in order for starters so that is invited (maybe Carl Dietrich will respond.... )
One poster made the comment "where are the wings" which highlights the obviously very minimal wing area which is something common to many (military by neccessity) previous VTOLS --with rotors or some other powered lift supplying the 'anti gravity' force from stationary until some speed to hand over to a fixed wing the wing can be made much smaller than one required to lift the aircraft at an FAR mandated 'maximum-minimum' speed (ie one not to be exceeded before the aircraft stalls, if it does stall ) Terrafugia deliberately designed the Transition to have a VERY high take off (and landing) speed despite the LSA stall speed in free flight --claiming that this was safer and imposed by the weight distribution on the wheels suited to road travel plus thrust moment and rear fuselage pressure field and propwash effects --the first flight videos showed this very clearly.
Their new design recognizes the limitations of needing long smooth runways and goes to the opposite extreme for zero speed lift off and dispenses with all that wing,tail and tailcone area by relying on rotary lift and VTOL (horizontal take off might be possible also but not specified --the tilt rotor Osprey cannot do so except with a lot of rotor tilt that creates downwash on the wing which is self defeating to an large extent. Incidentally the most recent iterations of the Osprey and derivatives feature fixed tip engines and only tilt the rotors .
Just from the basic geometry something looks wrong with the TFx -- the wing carries the rotors at it's tips well ahead of the wing which is itself swept forward . In hover the centre of mass and the centre of thrust must be in line (above or below each other) much like a helicopter having the centre of gravity underneath the mast ) -in this case though the rotors end up far ahead of the centre of gravity which must be somewhere near or slightly aft of the 25% MAC point (which is of course well within the wing itself) --the downwash from the high speed props felt by that part of the wing it hits will add extra 'weight' aft of the static centre of gravity further driving the nose up --it is not clear what could prevent a runaway nose up pitch .
(this is all before you get off the ground or anywhere near to transition which is where the fun always starts with VTOLs ... Moller has never transitioned his aircraft in 40 years plus -actually he 'celebrated' 50 years of VTOL R&D recently on his website )
Anyway that should get the ball rolling and maybe next we can look at the effects of that "1 Megawatt ( 1000 Kilowatts)" of power and the downwash on the aircraft itself and, not least, the neighbours....
A hardnosed design evaluation seems to be in order for starters so that is invited (maybe Carl Dietrich will respond.... )
One poster made the comment "where are the wings" which highlights the obviously very minimal wing area which is something common to many (military by neccessity) previous VTOLS --with rotors or some other powered lift supplying the 'anti gravity' force from stationary until some speed to hand over to a fixed wing the wing can be made much smaller than one required to lift the aircraft at an FAR mandated 'maximum-minimum' speed (ie one not to be exceeded before the aircraft stalls, if it does stall ) Terrafugia deliberately designed the Transition to have a VERY high take off (and landing) speed despite the LSA stall speed in free flight --claiming that this was safer and imposed by the weight distribution on the wheels suited to road travel plus thrust moment and rear fuselage pressure field and propwash effects --the first flight videos showed this very clearly.
Their new design recognizes the limitations of needing long smooth runways and goes to the opposite extreme for zero speed lift off and dispenses with all that wing,tail and tailcone area by relying on rotary lift and VTOL (horizontal take off might be possible also but not specified --the tilt rotor Osprey cannot do so except with a lot of rotor tilt that creates downwash on the wing which is self defeating to an large extent. Incidentally the most recent iterations of the Osprey and derivatives feature fixed tip engines and only tilt the rotors .
Just from the basic geometry something looks wrong with the TFx -- the wing carries the rotors at it's tips well ahead of the wing which is itself swept forward . In hover the centre of mass and the centre of thrust must be in line (above or below each other) much like a helicopter having the centre of gravity underneath the mast ) -in this case though the rotors end up far ahead of the centre of gravity which must be somewhere near or slightly aft of the 25% MAC point (which is of course well within the wing itself) --the downwash from the high speed props felt by that part of the wing it hits will add extra 'weight' aft of the static centre of gravity further driving the nose up --it is not clear what could prevent a runaway nose up pitch .
(this is all before you get off the ground or anywhere near to transition which is where the fun always starts with VTOLs ... Moller has never transitioned his aircraft in 40 years plus -actually he 'celebrated' 50 years of VTOL R&D recently on his website )
Anyway that should get the ball rolling and maybe next we can look at the effects of that "1 Megawatt ( 1000 Kilowatts)" of power and the downwash on the aircraft itself and, not least, the neighbours....
