Something very strange

[prime_max]

Hi guys. I'm a new mi-8 flyer.I used to fly huey.

 

But when I fly the Hip,I found something very strange.

 

Dissymmetry of lift effcet of mi-8 is to roll left,as the huey does. but how could it be?

 

Logically,Mi-8's main rotor turns clockwise (top view) while Huey's turn Anti-Clock, so the retreating blade of Mi-8 is on the right.Dissymmetry of lift effcet should make the helicopter roll right.

 

Is this a bug of FM? :huh:

[AlphaOneSix]

EDIT:

Edited September 25, 2017 by AlphaOneSix

[Jester986]

Dissymmetry of lift is very much experienced in fully articulated rotors. They don't suffer from mast bumping like semi rigid do though. I haven't had the Mi-8 that fast but will check it out.

[Jester986]

Well, I've done some playing around tryingto get retreating blade stall and ended up with inconsistent results.

[msalama]

and ended up with inconsistent results.

 

Care to elaborate? I've definitely experienced retreating blade stalls in the Hip due to excessive airspeed, but have so far managed to recover before going all uncontrollable...

[Jester986]

I ended up getting only slight left and right rolls before violently pitching up and chopping the tail. I'm guessing the roll was unrelated to retreating blade stall as it seem random as to which side it would go. And the nose up wouldn't occur until 186-200 knots in a dive which I'm guessing is faster than it would really be able to handle. I have no experience on a helicopter of that size/type, but it didn't seem right. I wasn't really going to offer my opinion though because of lack of time on type as Belsimtek has an Mi-8 pilot on staff (at least a previous post about him getting fly a Huey said so). So I was just kinda hoping they'd notice and check it out. Although I've also heard they aren't to active on the English forums? Anyway I still like the module and don't want to be a downer but it could probably use some attention.

[msalama]

OK, thanks, good to know - never taken the bird that far so haven't experienced those symptoms myself. Yes, BST has a type-rated Mi-8 pilot on board, so let's hope he sees your post and offers his comments too...

[Rogue Trooper]

The Hip also has Auto pilots on board so ensure these are off during testing as they will compensate chopper attitude to ensure a correct flight line.

 

 

A five bladed chopper does not suffer obvious retreating blade stall like a 2 bladed chopper. No serious modern day military chopper has 2 blades.

The Huey (and all 2 bladed choppers) show the theory of blade stall to perfection. Once you increase the blade number, say with the Hip, the single retreating blade stalling at 90 degrees to the airframe is helped by the decreasing lift of the blade that follows it and (to a lower degree) the increasing lift of the blade that proceeds it.

[Jester986]

Thank you for pointing out the autopilot, I didn't think of that and will try it again. However you are incorrect about multi-bladed helicopters not suffering from retreating blade stall. Multiple blades do allow them to reach higher speeds than a two bladed system but it will still occur. I am a professional helicopter pilot and have spent countless hours studying helicopter aerodynamics. Helicopters with two set of counter rotating blades can go even faster because one side of each set of rotors is still producing lift but this is even limited by blade flapping, which is why you'll get intersecting rotors if you take the KA too fast. Sirkorsky's X2/ raider program uses this idea. Eurocopter on the other hand with their X3 does it by off loading the lift required to be made by the rotors on to small wings at high speeds.

Edited September 27, 2017 by Jester986
clarity

[Rogue Trooper]

The stall effect is not as obvious, this is more what I was trying to say but obviously not very well.

The 5 blades also ensures when retreating blade stall occurs at 90 degrees to the airframe there is no blade producing maximum lift on the opposite side.

Edited September 27, 2017 by Rogue Trooper

[msalama]

Meaning a 5-bladed chopper doesn't roll towards the stalling side so easily, right?

 

Anyway, would be interesting to know what AlexandrT thinks of this, since he's the man in here as it comes to the Mi-8. Alex, you around?

 

No serious modern day military chopper has 2 blades.

The AH-1 Cobra does and AFAIK it's still used operationally by the USMC at least.