triumph Posted March 13, 2009 Posted March 13, 2009 i am sure everybody knows this, but here goes anyway. all surfaces on aircraft either generate lift or drag, when air passes over a surface that has a longer distance on one side than the other, the air on the longer side has to speed up, this causes a drop in barometric pressure generating lift, it also causes a certain amount of drag on the shorter side. this is true for rotor blades, tail rotors, rudders, stubby wings, and the body of the aircraft. twin rotor helicopters dont need a tail rotor, because contra rotating main rotors cancel out the precessional forces. but in zero wind, in a hover the rudder does not receive enough airflow to make a difference. then rotation is carried out using differential main rotor control, in common with all twin rotor helicopters not having a tail rotor, or like the chinook which has no rudder. the rudder is for forward flight, like a fixed wing aircraft it is used for making co-ordinated turns, this is what the little ball in the artificial horizon is for. the rudder is linked to the main rotors, but like all airofoils it needs an appreciable airflow to have any effect. helos are finely balanced, and inherently unstable in a hover with even a slight wind they will weathervane, because of the body of the aircraft, you counteract this with differential rotor control, sure the rudder moves as well doesnt do much unless the airflow is high, too much of this and you get pilot induced oscillation, which means a go around.the ap fixes as a snapshot in time its not able to continually adjust for constant changes thats the pilots job. asus p6t ws pro mobo.i7 975 extreme cpu..nvid rog strix 1070 gpu.1000+w enermax psu.12 gb domi ram.twin velociraptors.w7 64..ch stick,throttle,pedals,trakir..x52 pro stick,throttle.. thrustmaster warthog
Jack57 Posted March 13, 2009 Posted March 13, 2009 :unsure: "The only thing a chopper pilot should do downwind is take a leak" - CFI _______________________ CPL(H). AMD Athlon 64 X2 Dual Core 6000+ @3.3 GHz, 2GB Corsair DDR2 667, nVidia GeForce 9600 GT 1 GB, SB Audigy 2. Logitech Extreme 3D Pro modified: no centering springs, extended shaft. CH Pro Throttle; vertical chair mount. _______________________
Kuky Posted March 13, 2009 Posted March 13, 2009 I don't understand the meant point of this thread? No longer active in DCS...
shaggy Posted March 13, 2009 Posted March 13, 2009 I don't have a clue why you are telling us this triumph, but ii for one can indeed tell you I already knew this. So if you give me 5 mins I will give you all my recipe of how to make chocolate cake. I think everyone is eager to know that :D "Sorry for the sarcasm" 2 Intel Core i7-8700 3,20GHz - EVGA GeForce GTX 1080 Ti SC2 - 32Gb Ram - DCS on 500 GB SSD - Windows 10 - Thrusmaster Warthog - Thrustmaster TPR pedals - Track Ir 5 - Samsung Odyssey+ [sIGPIC][/sIGPIC] http://www.virtualredarrows.com
EtherealN Posted March 13, 2009 Posted March 13, 2009 (edited) all surfaces on aircraft generate lift and/or drag Fixed it. :) Edited March 13, 2009 by EtherealN [sIGPIC][/sIGPIC] Daniel "EtherealN" Agorander | Даниэль "эфирныйн" Агорандер Intel i7 2600K @ 4.4GHz, ASUS Sabertooth P67, 8GB Corsair Vengeance @ 1600MHz, ASUS GTX 560Ti DirectCU II 1GB, Samsung 830series 512GB SSD, Corsair AX850w, two BENQ screens and TM HOTAS Warthog DCS: A-10C Warthog FAQ | DCS: P-51D FAQ | Remember to read the Forum Rules | | | Life of a Game Tester
Boulund Posted March 13, 2009 Posted March 13, 2009 I'm also really sorry but I don't really understand the meaning of this post either. If you've read about people not knowing these things in other threads, why not post it there so the thread starter (or others in the thread for that matter) could learn from it there - where it connects to what is being said. Also I'm hurting from the horrible paragraphing, why not put some whitespace in the text to make it easier to follow or read - maybe this could even be improved a lot with a small paragraph at the top explaining why this thread was started? Just my humble opinions and constructive criticism =) Hope you don't take it the wrong way Core i5-760 @ 3.6Ghz, 4GB DDR3, Geforce GTX470, Samsung SATA HDD, Dell UH2311H 1920x1080, Saitek X52 Pro., FreeTrack homemade cap w/ LifeCam VX-1000, Windows 7 Professional x64 SP1. FreeTrack in DCS A10C (64bit): samttheeagle's headtracker.dll
AlphaOneSix Posted March 13, 2009 Posted March 13, 2009 because contra rotating main rotors cancel out the precessional forces. They cancel out each other's torque, not precession. rotation is carried out using differential main rotor control, in common with all twin rotor helicopters not having a tail rotor, or like the chinook which has no rudder. Only helicopters with a coaxial rotor system us differential torque for yaw control. Tandem rotor helicopters, like the Chinook, use cyclic inputs.
HansRoaming Posted March 13, 2009 Posted March 13, 2009 Only helicopters with a coaxial rotor system us differential torque for yaw control. Tandem rotor helicopters, like the Chinook, use cyclic inputs. Was curious about this, do you mean one speeds up and the other slows down or that one has a higher pitch angle than the other when commanding yaw?
AlphaOneSix Posted March 13, 2009 Posted March 13, 2009 Was curious about this, do you mean one speeds up and the other slows down or that one has a higher pitch angle than the other when commanding yaw? It's pitch angle. One rotor increases pitch while the other decreases pitch. The total lift generated remains the same, so the aircraft stays at the same altitude, but now one rotor is generating more torque than the other, resulting in a yaw in the opposite direction of the rotor with more torque.
Dark-Light Posted March 13, 2009 Posted March 13, 2009 So, how come we can hover and change our yaw attitude with the rudder? I've never thought about this before but it does seem to make some sense that you would need at least some airflow over the rudder to have it make a difference. Someone explain to me whats happening please!
EinsteinEP Posted March 13, 2009 Posted March 13, 2009 Dark Light, Try searching the forums: that topic has been discussed quite a bit here (e.g., look at the post just before yours). You can also google "coaxial helicopter yaw" for a few links, if you don't trust forum posts. Shoot to Kill. Play to Have Fun.
AlphaOneSix Posted March 13, 2009 Posted March 13, 2009 So, how come we can hover and change our yaw attitude with the rudder? I've never thought about this before but it does seem to make some sense that you would need at least some airflow over the rudder to have it make a difference. Someone explain to me whats happening please! Beside moving the rudders, moving the pedals also does this: One rotor increases pitch while the other decreases pitch. The total lift generated remains the same, so the aircraft stays at the same altitude, but now one rotor is generating more torque than the other, resulting in a yaw in the opposite direction of the rotor with more torque.
experimental_pilot Posted March 13, 2009 Posted March 13, 2009 I don't have a clue why you are telling us this triumph, but ii for one can indeed tell you I already knew this. So if you give me 5 mins I will give you all my recipe of how to make chocolate cake. I think everyone is eager to know that :D "Sorry for the sarcasm" :lol::megalol: :megalol:
CE_Mikemonster Posted March 13, 2009 Posted March 13, 2009 I knew someone would pick fault.. Too many cowboys. Not enough indians. GO APE SH*T
Obiwan Posted March 14, 2009 Posted March 14, 2009 (edited) [Removed post. Already covered.] Edited March 14, 2009 by Obiwan
Obiwan Posted March 14, 2009 Posted March 14, 2009 Only helicopters with a coaxial rotor system us differential torque for yaw control. Tandem rotor helicopters, like the Chinook, use cyclic inputs. In case anyone is curious about hover turns in a tandem rotor helicopter, this link is a pretty good one: http://www.helicopterpage.com/html/tandem.html 1
CE_Mikemonster Posted March 14, 2009 Posted March 14, 2009 Brilliant website! 'A runway is for people who do not know how to autorotate' Hehehe gonna see that on a few sigs.. Too many cowboys. Not enough indians. GO APE SH*T
HansRoaming Posted March 14, 2009 Posted March 14, 2009 It's pitch angle. One rotor increases pitch while the other decreases pitch. The total lift generated remains the same, so the aircraft stays at the same altitude, but now one rotor is generating more torque than the other, resulting in a yaw in the opposite direction of the rotor with more torque. Thanks for the heads up. Seems much more efficient than the traditional single rotor and tail rotor, wonder why more helicopters aren't COAX.
AlphaOneSix Posted March 14, 2009 Posted March 14, 2009 Well, if they were that much more efficient, everyone would be doing it. They are more efficient, but not *much* more efficient. Also, they are a little heavier and a little more complex.
ericinexile Posted March 15, 2009 Posted March 15, 2009 The part about lift...you know where two air molecules separate at the leading edge and race to the trailing edge but the top mol....yadayadayada...it's complete baloney! Lift is not generated because air must travel faster over the top of the airfoil--the increase in velocity is just a byproduct of the decrease in pressure. Lift is generated by the downwash resulting from the airmass returning to equilibrium after being constricted by the wing and the airmass above. The equal and opposite reaction to this downwash is LIFT. Any suction on the top of the airfoil amounts to just a fraction of one percent of the total lift generated. Smokin' Hole My DCS wish list: Su25, Su30, Mi24, AH1, F/A-18C, Afghanistan ...and frankly, the flight sim world should stop at 1995.
ericinexile Posted March 15, 2009 Posted March 15, 2009 Thanks for the heads up. Seems much more efficient than the traditional single rotor and tail rotor, wonder why more helicopters aren't COAX. Because... Other rotor systems don't generally run the risk of blade intersection and death during excessive blade flap. Because... Other rotor systems don't run the risk of reverse anti-torque control during autorotation (although apparently not an issue with the Ka50). Because... The constant climb state of the bottom rotor disk counteracts SOME of the efficiencies gained by not having a tailrotor. Smokin' Hole Smokin' Hole My DCS wish list: Su25, Su30, Mi24, AH1, F/A-18C, Afghanistan ...and frankly, the flight sim world should stop at 1995.
AlphaOneSix Posted March 15, 2009 Posted March 15, 2009 Because... Other rotor systems don't run the risk of reverse anti-torque control during autorotation (although apparently not an issue with the Ka50). Kamov have designed the flight controls in such a way that the "switch over" is handled automatically during an autorotation, although I do not know the specifics of how it works. I believe most of Kamov's current aircraft are built this way.
HansRoaming Posted March 15, 2009 Posted March 15, 2009 Because... Other rotor systems don't generally run the risk of blade intersection and death during excessive blade flap. Sikorsky seem to think 2' is enough on their X-2 as they have carbon blades which are quite rigid. Am guessing more COAX combat / civilian choppers will be coming down the road. I know I would certainly want to try out the COAX 412 if it ever makes the light of day.
ericinexile Posted March 15, 2009 Posted March 15, 2009 Sikorsky demonstrated a Coaxial design back in the eighties. It looked very cool and fast but for whatever reason didn't make it to production. Smokin' Hole My DCS wish list: Su25, Su30, Mi24, AH1, F/A-18C, Afghanistan ...and frankly, the flight sim world should stop at 1995.
AlphaOneSix Posted March 15, 2009 Posted March 15, 2009 Sikorsky is currently testing a coaxial, called the X2.
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