MR/TR compared with Coaxial Aircraft Design
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Originally Posted by Nick Lappos
I published several papers that show the actual HP consumed by the TR, that data is real.
Other ABC papers i have found:
Rotor Technology for New Generation Helicopters - David S. Jenney
Multi Service Applications for Advancing Blade Concept Aircraft - L. G. Knapp
Status Report on the ABC UtUm Technology Demonstrator Program - Vincent P. Bailey
I'm planning to order any recommended papers with the S76 Honeywell SPZ7600 paper. Any S76s near me would be Aberdeen way.
Mart
Last edited by Graviman; 21st Nov 2006 at 21:30. Reason: Typos
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The forgoing discussion in this thread implies that widening the chord allows for a decrease in the speed of the rotors.
In addition, Wieslaw Z. Stepniewski was recommending twin single-speed slow turning rotors for faster, quieter rotorcraft.
Therefore, these calculations were done to get a better understanding about the subject. They suggest that a single-speed slow turning rotor will be slightly more efficient in hover than it will in cruise.
The original Coaxial ABC helicopter had a two-speed rotors. The tip speed was 650 fps for hover and 450 fps for cruise. The slower speed in cruise was necessary so that the advancing blade tip would not approach the speed of sound.
It will be very interesting to see if the new X2 Coaxial ABC implements multi-speed rotors or single-speed rotors.
Dave
Opps!
This post (and most of the following posts) should have been placed on the [Why are Helicopters with the Flettner-System so slow?] thread.
In addition, Wieslaw Z. Stepniewski was recommending twin single-speed slow turning rotors for faster, quieter rotorcraft.
Therefore, these calculations were done to get a better understanding about the subject. They suggest that a single-speed slow turning rotor will be slightly more efficient in hover than it will in cruise.
The original Coaxial ABC helicopter had a two-speed rotors. The tip speed was 650 fps for hover and 450 fps for cruise. The slower speed in cruise was necessary so that the advancing blade tip would not approach the speed of sound.
It will be very interesting to see if the new X2 Coaxial ABC implements multi-speed rotors or single-speed rotors.
Dave
Opps!
This post (and most of the following posts) should have been placed on the [Why are Helicopters with the Flettner-System so slow?] thread.
Last edited by Dave_Jackson; 7th Dec 2006 at 04:25. Reason: Opps! ~ added
Hidden in plain sight!
L = Cl * ((ρ * A * Vfwd ^ 2) / 2)
It will be very interesting to see if the new X2 Coaxial ABC implements multi-speed rotors or single-speed rotors.Dave
"The main rotor will be slowed during high speed flight to keep the rotor tips below supersonic speeds."
-- IFMU
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IFMU,
Thanks. The incomplete algorithm has been removed.
Strange. 
It makes sense for a compound helicopter, such as the Piasecki, to have a higher RRPM in hover than in cruise since the rotor will off-load some of its lift to the wings during cruise. However, the Advancing Blade Concept does not have wings.
On the X2, The propeller will provide the forward thrust. The rotor is responsible for lift and this lift will not vary much between hover and level forward flight. Therefore, wide chords and slowed rotors should be ideal for all modes of flight.
The single speed should also reduce the weight and complexity of the transmission.
Dave
Thanks. The incomplete algorithm has been removed.
"The main rotor will be slowed during high speed flight to keep the rotor tips below supersonic speeds."
It makes sense for a compound helicopter, such as the Piasecki, to have a higher RRPM in hover than in cruise since the rotor will off-load some of its lift to the wings during cruise. However, the Advancing Blade Concept does not have wings.
On the X2, The propeller will provide the forward thrust. The rotor is responsible for lift and this lift will not vary much between hover and level forward flight. Therefore, wide chords and slowed rotors should be ideal for all modes of flight.
The single speed should also reduce the weight and complexity of the transmission.
Dave
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A bit technical, sorry folks.
Dave,
Prouty sums it up nicely for us sad engineering types in his "big red book of helicopters" (Or was it "Helicopter Performance Stability and Control" - i'll put down my crayons and check). He has an equation on page 26 that for ideal twist goes:
Figure_of_Merit =
1 / (1 + ( 1.5*Tip_Speed / (Cl/Cd)*SQRT(2*Disk_Loading/Air_Density) ))
This equation is a rewrite of the equation he actually derives:
Figure_of_Merit = 1 / (1 + ( 1.5*SQRT(3) / (SQRT(Solidarity_Ratio)*(Cl^1.5/Cd)) ))
The results are plotted for ideal twist on page 28 (fig 1.13), and show without doubt that the higher the solidity ratio the higher the figure of merit. I was hoping for Nick's comment on this, but he gave up on me as a lost cause and ran for the hills - i get that a lot.
My interpretation of the above info is that a helicopter runs at peak efficiency when the blades are operating just below stall, for maximum Cl/Cd. Using wide chord blades then allows a nice low tip speed, by chosing a low Nr for hover. Forward flight Nr is a compromise on fixed Nr conventional helis, due to the need to avoid retreating blade stall (particularly increasing loading during sharp manouvres
). Counterrotators do not have this constraint so can reduce Nr to keep advancing blade airspeed ~constant.
Mart
Prouty sums it up nicely for us sad engineering types in his "big red book of helicopters" (Or was it "Helicopter Performance Stability and Control" - i'll put down my crayons and check). He has an equation on page 26 that for ideal twist goes:
Figure_of_Merit =
1 / (1 + ( 1.5*Tip_Speed / (Cl/Cd)*SQRT(2*Disk_Loading/Air_Density) ))
This equation is a rewrite of the equation he actually derives:
Figure_of_Merit = 1 / (1 + ( 1.5*SQRT(3) / (SQRT(Solidarity_Ratio)*(Cl^1.5/Cd)) ))
The results are plotted for ideal twist on page 28 (fig 1.13), and show without doubt that the higher the solidity ratio the higher the figure of merit. I was hoping for Nick's comment on this, but he gave up on me as a lost cause and ran for the hills - i get that a lot.
My interpretation of the above info is that a helicopter runs at peak efficiency when the blades are operating just below stall, for maximum Cl/Cd. Using wide chord blades then allows a nice low tip speed, by chosing a low Nr for hover. Forward flight Nr is a compromise on fixed Nr conventional helis, due to the need to avoid retreating blade stall (particularly increasing loading during sharp manouvres
). Counterrotators do not have this constraint so can reduce Nr to keep advancing blade airspeed ~constant.Mart
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Doh!
The original Comanche/LHX design was derived from a tradeoff contest between a conventional single rotor and an ABC, an effort that I strongly pushed for (in the hopes that an ABC would win). The 10,000 lb class helos that emerged were the same in payload, but the ABC weighed about 500 lbs more empty weight, and cost about 10% more as a result (more complex transmission, controls and rotors. Obviously, since their numbers were all nearly doubled, and they are the expensive bits.
The ABC had a 1/2 g maneuver advantage, and a 10 knot speed advantage (no compounding was added), both great combat virtues, but not valued in the LHX mission scenarios, which were low speed battle.
The ABC had a 1/2 g maneuver advantage, and a 10 knot speed advantage (no compounding was added), both great combat virtues, but not valued in the LHX mission scenarios, which were low speed battle.
Any news on X2? I have never known a technically ambitious project to make the deadlines, but i'm just curious...
Mart
