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From: Belgium
Rowing rotors
bugdevheli
that idea has also occured to me when analysing the data.
My answer would be yes, but than what is rowing ?
I visualise this as follows: rotor drag can be decomposed in two components :
(1) the profile drag, which is the drag component of the aeroforces projected on the hubplane
(2) the induced drag, which is the lift component of the forces projected on the hubplane
If you look closely at the blade flow plot of the retreating blade (Figure A) (90° in my conventions) you see that the net flow (the green arrow) is quited tilted. The lift which is defined perpendicular to that flow is also tilted (to the left in the figure so the forward of the heli, since we are talking about a retreating blade) resulting in a significant induced drag. So for the retreating blade this force is indeed propulsing (=rowing) the heli (since it point forward)
On the other hand the forward blade has a far flatter pitch, the figure shows that the tip is almost autorotating and not producing a lot of lift nor induced drag
The overall drag is also displayed (Figure C) :
(1) the blue mesh is the profile drag,
(2) the green mesh the induced drag
(3) the multicolor plot the total drag : this shows the overal result of rowing
The fourth figure displays the resulting forces ('approx' used by the the dynamic simulation engine, 'precise' also fully calculates stall in the reversed flow area, differences are small)
The quantity DragHPx is the (rowing) forward force as projected to the hub-plane (in my definition the neutral plane of the rotor which is slighted tilted forward in the case of an R44) : for the given parameters it is between 163 and 194 newtons, which is more than half of the forward forced produced by the rotor lift which is 306N (because the rotor plane is tilted forward with respect to the hub-plane, as a result of flapping)
For who is not yet lost the total forward force of 952 N is greater than the som of 163 and 306 because of the 3 degree tilt of the hub-plane with respect to the heli, which gives an extra forward contribution by the main lift.
delta3
Figure A (retreating blade)
Figure B (forward blade)
Figure C (total drag)
Figure D (forces)
that idea has also occured to me when analysing the data.
My answer would be yes, but than what is rowing ?
I visualise this as follows: rotor drag can be decomposed in two components :
(1) the profile drag, which is the drag component of the aeroforces projected on the hubplane
(2) the induced drag, which is the lift component of the forces projected on the hubplane
If you look closely at the blade flow plot of the retreating blade (Figure A) (90° in my conventions) you see that the net flow (the green arrow) is quited tilted. The lift which is defined perpendicular to that flow is also tilted (to the left in the figure so the forward of the heli, since we are talking about a retreating blade) resulting in a significant induced drag. So for the retreating blade this force is indeed propulsing (=rowing) the heli (since it point forward)
On the other hand the forward blade has a far flatter pitch, the figure shows that the tip is almost autorotating and not producing a lot of lift nor induced drag
The overall drag is also displayed (Figure C) :
(1) the blue mesh is the profile drag,
(2) the green mesh the induced drag
(3) the multicolor plot the total drag : this shows the overal result of rowing
The fourth figure displays the resulting forces ('approx' used by the the dynamic simulation engine, 'precise' also fully calculates stall in the reversed flow area, differences are small)
The quantity DragHPx is the (rowing) forward force as projected to the hub-plane (in my definition the neutral plane of the rotor which is slighted tilted forward in the case of an R44) : for the given parameters it is between 163 and 194 newtons, which is more than half of the forward forced produced by the rotor lift which is 306N (because the rotor plane is tilted forward with respect to the hub-plane, as a result of flapping)
For who is not yet lost the total forward force of 952 N is greater than the som of 163 and 306 because of the 3 degree tilt of the hub-plane with respect to the heli, which gives an extra forward contribution by the main lift.
delta3
Figure A (retreating blade)
Figure B (forward blade)
Figure C (total drag)
Figure D (forces)
Last edited by delta3; 18th January 2005 at 17:57.
Thread Starter
Joined: Feb 2003
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From: ON A HILL
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Dave jackson. Thanks for the explanation. Makes sense now. Delta3 Thank you for exploring the rowing idea. I will tell my friend that he s not entirely mad. Regards Bug.
