Item 1117
OTHER:
Aerodynamics - Rotor Theory - Momentum Method
This is just the single rotor calculations which are developed further in the twin rotor pages. It is probably temporarily here
Power:
P = Tvind ≡ Tvhov
= T√(T/2ρAS)= (2T3/2)/(√2ρAS) = 2ρASvind3 [Source ~ PHA p.41]AS
is the area of a single disk.vho
v is the induced velocity in hover.
FORM: Momentum Method ~ Code
Hover:
Public Sub Hover()
'Calculation of info for hovering.
On Error GoTo hover_Err
''DL = Forms![Helicopter].Form![DL] 'Disk loading
Me!DL = GW / AT 'I am going with the Total
'and the Effective disk area for the Blade element.
Me!vv1hov = Sqr((1 / (2 * rho))) * Sqr(Me!DL) 'Induced velocity at rotor disk. [Ref: RWP1, p. 4 & RWA, book I, p. 52, (2.13)]
Me!P = hp_by_momentum_method(GW) 'Power [hp]
Me!PLh = GW / Me!P 'Thrust or Weight per horsepower in hover.
'## DOES THE FOLLOWING LINE SERVE ANY PURPOSE??
mm = rho * AT * Me!vv1hov 'Mass flux through the disk. Used in blade_element_moment_of_inertia()
hover_Exit:
Exit Sub
hover_Err:
MsgBox Err.Description
Resume hover_Exit
End Sub
_______________________
Public Function hp_by_momentum_method(GW As Single) As Single
' Required horsepower; by momentum method. [Ref: RWP1, p. 7 & RWA, book I, p. ??, (2.??)]
Dim T As Single ' Thrust [lb]
Dim DV As Single ' Drag - Vertical
Dim hpi As Single ' Induced horsepower
Dim hpact As Single ' Actual horsepower
On Error GoTo hp_by_momentum_method_Err
DV = 0.3 * PA * Me!DL ' Drag-Vertical is 30% of
projected area (plan view of fuselage under downwash) times disk loading.T = (1 + (DV / GW)) * GW
hpi = (T * Sqr(Me!DL / (2 * rho))) / 550
hpact = hpi / FM ' Actual hp is induced hp divided by figure of merit.
hp_by_momentum_method = hpact
hp_by_momentum_method_Exit:
Exit Function
hp_by_momentum_method_Err:
MsgBox Err.Description
Resume hp_by_momentum_method_Exit
End Function
Vertical:
States:
Climb, Descent and Vortex ring.
Forward:
Notes:
Froudes' Momentum Theory: (Actuator Disk Theory)
From a PPRuNe Posting:
As an aside;
Momentum Theory is a reasonable method of performing an initial assessment of rotor performance. This is because all single rotors are basically the same except for the nuances such as; twist, taper, etc., plus blade count.
However, IMHO, Momentum Theory totally breaks down when it come to the consideration of multiple, aerodynamically interactive main rotors.
This is why I express my disappointment that Igor led rotorcraft away from the aerodynamically superior twin rotors. It should be noted that virtually all of the research and development followed along behind the single rotor.
Rotorcraft have always been inefficient. However, when electric drives start permeating the fields of transportation the rotorcraft industry must look back to the past for it to move forward.
Dave
The PPRuNe posting on the thread [2007: Centennial of the Helicopter] appears to support the above.
Introduction Page | SynchroLite Home Page | UniCopter Home Page | Nemesis Home Page
Last Revised: December 28, 2007