aerodynamics of ka 50

[Yo-Yo]

The coaxial rotor is an analog of a biplane wing. If the biplane wingbox (2xLx(b/2)) is compared to the equivalent area and span wing Lxb dimension the inductive drag will be less. The reason is the same - more air to react with.

[-Skipper-]

The coaxial rotor is an analog of a biplane wing. If the biplane wingbox (2xLx(b/2)) is compared to the equivalent area and span wing Lxb dimension the inductive drag will be less. The reason is the same - more air to react with.

 

That is one point and the other one is probably, that the airframe must be shaped differently for tandem-configuration, removing the useless tail by additional storage-room.

I can also imagine, that the balancing of a tandem-configuration is much better. Compared to an airplane, it's like having 2 wings not staggered like a biplane, but on the front and aft of the airframe. So I guess it not only improves overall lift, but also the possibilities of how and what is transported.

[RvETito]

I wouldn't say the tandem design has any balance advantages over the coaxial. But it's true that the rotors arrangement determines the overal structure and size of the helicopter- while the tandem requires a very long fuselage (that provides a lot of room for internal cargo) the coaxial design allows to make a very compact helicopter because of the lack of torque balancing tailboom. Crucial factor for naval operation, that's why you won't see anything but Kamov helicopters on russian ships ;) Another fact- nothing hovers better than coaxial helicopter.

[Duke49th]

I have a question about the stall(Blade-stall?) with the KA-50.

 

Is the chance of a stall(Blade-stall?) more or less then in a regular Helo?

 

Stall or Blade-stall is the reason for the most crashes in EECH for me, when I'm going into a hover position(Apache) :)

Edited September 13, 2008 by Duke49th

[RvETito]

I suppose you mean vortex ring state. Yes, it's there. Blade stall is defined for retreating blade in forward flight, not in hover.

[Draco]

or are you referring to the rotor stall that occurs during low-RPM conditions from pulling to much collective? Or from the opposing flow condition that occur during powered descent? having never played EECH I'm not sure what dynamics are modeled. from what I've read that last one is LETHAL if not caught and corrected for quickly.

[Duke49th]

I suppose you mean vortex ring state. Yes, it's there. Blade stall is defined for retreating blade in forward flight, not in hover.

 

Copy. But what would you say? Is the KA-50 more stable then any other Helo?

[Peyoteros]

Check this mama...

 

http://ru.youtube.com/watch?v=Maqy-I9zceM

 

:bounce:

[Draco]

Copy. But what would you say? Is the KA-50 more stable then any other Helo?

 

if you are referring to retreating blade stall which is different from rotor stall then yes coax systems are more stable in that the loss of lift is symmetrical across the two rotor disks.

[Duke49th]

I mean that kind of "stall", where you are i.e. hovering and you try to lower your alt. Then you sometimes, if you sink too fast, the Helo starts to shake and you fall down like a stone if you not imediateley push cyclic to any direction and give some collective to come out of this "stall".

 

In EECH I hate this effect.:D

 

 

Hope you understand what I try to explain:)

[AlphaOneSix]

I mean that kind of "stall", where you are i.e. hovering and you try to lower your alt. Then you sometimes, if you sink too fast, the Helo starts to shake and you fall down like a stone if you not imediateley push cyclic to any direction and give some collective to come out of this "stall".

 

In EECH I hate this effect.:D

 

 

Hope you understand what I try to explain:)

 

Yep, all helicopters have this problem, even coaxial rotor helicopters like the Ka-50.

[Draco]

that's vortex ring state also called settling with power as Tito mentioned and it'll definatly kill you if you let it get away from you. you're descending into your own down wash causing the rotor system to loose lift. adding collective actually makes it worse. the recommended recovery procedures are moving the cyclic forward and to one side and wait until you've left the disturbance. if you get into a really deep VRS dropping collective into an auto rotation may be necessary to break up the vortex.

 

I got to experience a deep one a few months ago. my instructor and I pulled into a hover at 8000'. I lowered the collective until the onset of VRS then raised collective to max allowable manifold pressure and just dropped like a rock for about 4000'. to recover I just lowered collective to enter an auto, built forward airspeed and added power and all was well again. VRS scares the crap out of me as I used to have a tendency to bleed air speed before altitude on approaches ending up slow and high over my landing spot and being very nervous ridding just outside that zone to not overshoot. but I have since corrected this bad habit. starting to feel the vibrations start during a pinnacle approach over a bunch of trees will definitely cause some pucker.