Majesco Posted July 11, 2012 Posted July 11, 2012 Sorry, i didn't track this DCS sub-forum for a long time, just have a question on Ka-50 rotor blade: I don't understand why Ka-50' lower rotor blade are always incline to the upper right corner and getting closer (able to collide) to the upper rotor blade when increasing airspeed by lifting the collective stick can anyone explain me this ? :smartass:
GGTharos Posted July 11, 2012 Posted July 11, 2012 The rotor on this side is advancing forward, so when you are also moving forward, it has more speed than the other side of the rotor, and more lift. Opposite sides for the top rotor, and you have the situation you describe. [sIGPIC][/sIGPIC] Reminder: SAM = Speed Bump :D I used to play flight sims like you, but then I took a slammer to the knee - Yoda
ShuRugal Posted July 11, 2012 Posted July 11, 2012 yes, the phenomenon is called "asymmetry of lift" and it occurs exactly as the poster above describes. As the helicopter increases forward speed, the coning angle of the disk will shift from level towards the side with the retreating blade. since the rotors on the shark counter-rotate, the cones will shift in opposite directions: directly into each other. The solution is not to use much collective at high airspeed. I've more than once cut my rotors off just by trying to use the collective to climb while maintaining 250+ IAS. On the other hand, i have leveled out of dives in excess of 400 IAS with no problem, at 1 degree of collective pitch.
Daniel M Posted July 11, 2012 Posted July 11, 2012 The rotor on this side is advancing forward, so when you are also moving forward, it has more speed than the other side of the rotor, and more lift. Opposite sides for the top rotor, and you have the situation you describe. This, plus there's a pretty good description and graphs in the manual (trying to be helpful, not trolling :D)
mvsgas Posted July 11, 2012 Posted July 11, 2012 As Daniel M posted, a lot of this is covered in the manual. If you are looking for supplementary information on helicopters, the FAA library have some good info http://www.faa.gov/library/manuals/aircraft/media/faa-h-8083-21A.pdf To whom it may concern, I am an idiot, unfortunately for the world, I have a internet connection and a fondness for beer....apologies for that. Thank you for you patience. Many people don't want the truth, they want constant reassurance that whatever misconception/fallacies they believe in are true..
Majesco Posted July 11, 2012 Author Posted July 11, 2012 thank you all for the help, i'll read the flight manual again :book:
effte Posted July 11, 2012 Posted July 11, 2012 (edited) Asymmetry of lift due to airspeed (advancing/retreating blade) causes both rotors to tilt back. This is known as rotor blowback or flapback. The right/left tilt is due to the angle of attack increasing on the blades in the forward sector of the disc, due to airspeed and coning. Remember, all changes will happen around 90 degrees later in the rotation, due to gyroscopic precession. More lift on advancing blade -> Forward edge of disc tilts up. More lift on forward blade -> retreating side of disc tilts up. Edited July 11, 2012 by effte Edit: Added terms for the google minded. ----- Introduction to UTM/MGRS - Trying to get your head around what trim is, how it works and how to use it? - DCS helos vs the real world.
Yurgon Posted July 11, 2012 Posted July 11, 2012 (edited) A very good explanation can also be found on SimHQ: DCS: Black Shark and Coaxial Rotor Aerodynamics Edit: Or take it with a grain or two of salt, according to the next posts. Edited July 11, 2012 by Yurgon
effte Posted July 11, 2012 Posted July 11, 2012 Yurgon, that article unfortunately very pedagogically presents the incorrect explanation, so I'd hesitate to call it good. ----- Introduction to UTM/MGRS - Trying to get your head around what trim is, how it works and how to use it? - DCS helos vs the real world.
Bushmanni Posted July 11, 2012 Posted July 11, 2012 In transverse flow effect that Effte is referring the rear sector of the disk has reduced angle of attack due to coning and transverse flow and this causes the advancing side of the disk to tilt down. In Ka-50 we see advancing side tilt up. DCS Finland: Suomalainen DCS yhteisö -- Finnish DCS community -------------------------------------------------- SF Squadron
effte Posted July 11, 2012 Posted July 11, 2012 Really? Let's see, lower rotor rotating CCW viewed from above, right (advancing) side should tilt down. Upper rotor the opposite, of course. Is this not the case? ----- Introduction to UTM/MGRS - Trying to get your head around what trim is, how it works and how to use it? - DCS helos vs the real world.
ShuRugal Posted July 11, 2012 Posted July 11, 2012 Is this not the case? it is not. In DCS (and in videos of the real thing) the right side of the lower disk elevates at high forward speed.
effte Posted July 11, 2012 Posted July 11, 2012 Interesting. Do you have a link to a video where this can be seen? ----- Introduction to UTM/MGRS - Trying to get your head around what trim is, how it works and how to use it? - DCS helos vs the real world.
GGTharos Posted July 11, 2012 Posted July 11, 2012 (edited) Look here, time 4:09: THe problem is that all the pure high aspect high-speed aproach clips are either too short, too far, or taken from an angle where you can't see the coning effect, or taken at too low a speed. You have to catch the right moment. Also, rotor intersection in RL: Edited July 11, 2012 by GGTharos [sIGPIC][/sIGPIC] Reminder: SAM = Speed Bump :D I used to play flight sims like you, but then I took a slammer to the knee - Yoda
effte Posted July 11, 2012 Posted July 11, 2012 GGTharos, yeah, seen that one. Looks like it at a glance, but considering perspective, coning etc it doesn't really add anything conclusive. Besides, the airspeed in that shot isn't high. You really need a good, steady front or rear aspect shot of a helo in flight at a reasonably good clip, with the camera in the rotor plane. Kamov don't seem to publish their chase plane footage online, unfortunately. I've been considering whether this is something you could compensate for, at least partially, in a coax rotor system so it'd be interesting to see such footage. Second clip is a bad one. Pilot didn't make it, I assume? :( ----- Introduction to UTM/MGRS - Trying to get your head around what trim is, how it works and how to use it? - DCS helos vs the real world.
GGTharos Posted July 11, 2012 Posted July 11, 2012 Nope, not enough time to eject :( [sIGPIC][/sIGPIC] Reminder: SAM = Speed Bump :D I used to play flight sims like you, but then I took a slammer to the knee - Yoda
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