Previous Thread
Next Thread
Print Thread
Rate This Thread
Hop To
#3214663 - 02/22/11 11:18 AM Not really a sim question, but ...  
Joined: Dec 2009
Posts: 748
AndyB Offline
Member
AndyB  Offline
Member

Joined: Dec 2009
Posts: 748
Ayrshire, Scotland
Hi Guys,
This is more of a real life helicopter question, but I've noticed a lot of you have a great deal of knowledge in the real world so, here goes.

This has been doing my head in for some time. I know about the basics of swatch plate, blade hinges etc and how the collective / cyclic work.

The think I can't work out is:

If you are at maximum collective ( all blades at max angle of attack ) and you move the cyclic, how can the angle of attack on the blades as they come round increase if they're already at maximum ?

Yeah! I know, probably don't have enough happening in my life to be sitting thinking about things like that.....

Cheers,

Andy


Andy's simpit: http://www.simpit.me.uk
Inline advert (2nd and 3rd post)

#3214737 - 02/22/11 01:11 PM Re: Not really a sim question, but ... [Re: AndyB]  
Joined: Nov 2006
Posts: 3,453
Flyboy Offline
Senior Member
Flyboy  Offline
Senior Member

Joined: Nov 2006
Posts: 3,453
England, UK
Well in my experience (basically what I've seen in sims) when you are at maximum collective the rotor blades are coned slightly upwards. I don't know anything about angle of attack. So when the blades are coned upwards at max collective, when you move the cyclic you are tilting the rotor disc in its entirety forwards, backwards, left or right. If anything, the rotors lose some of their coning when cyclic input is done.

I don't quite get your question as I've never seen the term 'angle of attack' used for rotor terminology (not that I can remember anyhow). Why would the AoA have to increase when you move the cyclic? You only move the rotor disc tilt direction with cyclic, and as I said, the rotors would flatten out from their upwards cone at max collective when a cyclic input is made. Unless this is what you mean? I'm guessing by having what you can a max AoA that that is when you have the best chance of pulling the heli through the air? In which case, maximum collective (rotor disc coning) and cyclic input (rotor disc angle and flattening) would indeed be the best angle of attack.

This is just what I've gathered, mainly from Longbow 2, but even the rotor dynamics in that have been questioned. If anyone else can back me up or knows the correct answer, please do tell!

#3214756 - 02/22/11 01:37 PM Re: Not really a sim question, but ... [Re: Flyboy]  
Joined: Jun 2006
Posts: 2,288
arneh Offline
Member
arneh  Offline
Member

Joined: Jun 2006
Posts: 2,288
Oslo, Norway
Originally Posted By: Flyboy
I don't quite get your question as I've never seen the term 'angle of attack' used for rotor terminology (not that I can remember anyhow). Why would the AoA have to increase when you move the cyclic? You only move the rotor disc tilt direction with cyclic



I think you may not understand how the rotor tilts. It's not, as one may easily assume, because the entire rotor hub tilts. The tilting is a just a by-effect of the blades being hinged, and them producing differing amounts of lift. So when the rear blade is producing more lift than the front blade, it will move more up than the front blade, and the rotor disk will appear to tilt forward. But it's just aerodynamics causing this, not something which actually tilts the rotor hub. And hence, the rotor will not tilt if it's not spinning. If the rotor is not spinning, the only effect of moving the cyclic is that you can see the blades change pitch angle (though this may not be correctly modelled in every sim).

Originally Posted By: AndyB
If you are at maximum collective ( all blades at max angle of attack ) and you move the cyclic, how can the angle of attack on the blades as they come round increase if they're already at maximum


You seem to assume that max collective will produce an angle which is the abolute maximum the blades can have (before stalling I assume?). But having max collective right on the edge of stalling would be quite dangerous, since it then wouldn't take much to put them over the edge (like a little gust of wind from the wrong direction, or some turbulence), something you don't want to be happening all the time. So max collective will produce something which is well below the stalling angle for the blades, and even full cyclic adding some more pitch on the blades shouldn't but them above the stalling angle during normal conditions.

Also note that the amount of pitch the cyclig needs to make to the pitch is quite small compared to the collective. It takes a lot of force to carry the weight of the entire helicopter (what the collective controls), but in comparison it doesn't take much force to make the helicopter roll, just a small difference in lift from side to side or front to back is enough.

#3222075 - 03/02/11 10:45 AM Re: Not really a sim question, but ... [Re: AndyB]  
Joined: Dec 2009
Posts: 748
AndyB Offline
Member
AndyB  Offline
Member

Joined: Dec 2009
Posts: 748
Ayrshire, Scotland
Thanks Arneh,

I hadn't thought about the danger of the blade stalling. Your explanation makes perfect sense to me.

Sorry if I confused you Flyboy, but thanks for replying anyway. I'm an ex-aircraft engineer but never worked on rotary wings so used the terminology I was used to i.e. when pulling up on the collective it rotates all the blades and therefore changes their angle of attach to the air. Larger angle means more lift.

As I understand it, when you change the cyclic input each blade has it's angle of attack changed as it comes around to the same spot therefore producing more/less lift at that point. Because of the hinges on the blades that causes the whole rotor cone to tilt.

Thanks again guys,

Andy


Andy's simpit: http://www.simpit.me.uk
#3222549 - 03/02/11 07:49 PM Re: Not really a sim question, but ... [Re: AndyB]  
Joined: Apr 2008
Posts: 300
JayPee Offline
Member
JayPee  Offline
Member

Joined: Apr 2008
Posts: 300
The Netherlands
Originally Posted By: AndyB
Hi Guys,
This is more of a real life helicopter question, but I've noticed a lot of you have a great deal of knowledge in the real world so, here goes.

This has been doing my head in for some time. I know about the basics of swatch plate, blade hinges etc and how the collective / cyclic work.

The think I can't work out is:

If you are at maximum collective ( all blades at max angle of attack ) and you move the cyclic, how can the angle of attack on the blades as they come round increase if they're already at maximum ?

Yeah! I know, probably don't have enough happening in my life to be sitting thinking about things like that.....

Cheers,

Andy

FM 3-04.203 Fundamentals of Flight
http://www.chinook-helicopter.com/Publications/Fundamentals_of_Flight/fm3_04x203.pdf

Great document, contains a lot about how helicopters fly and function! And while you're at it you may also want to download:

FM 3-04.240 Instrument Flight for Army Aviators
http://www.chinook-helicopter.com/Publications/Instrument_Flight_for_Army_Aviators/fm3_04x240.pdf

Last edited by JayPee; 03/02/11 07:52 PM.

Moderated by  RacerGT 

Quick Search
Recent Articles
Support SimHQ

If you shop on Amazon use this Amazon link to support SimHQ
.
Social


Recent Topics
Carnival Cruise Ship Fire....... Again
by F4UDash4. 03/26/24 05:58 PM
Baltimore Bridge Collapse
by F4UDash4. 03/26/24 05:51 PM
The Oldest WWII Veterans
by F4UDash4. 03/24/24 09:21 PM
They got fired after this.
by Wigean. 03/20/24 08:19 PM
Grown ups joke time
by NoFlyBoy. 03/18/24 10:34 PM
Anyone Heard from Nimits?
by F4UDash4. 03/18/24 10:01 PM
RIP Gemini/Apollo astronaut Tom Stafford
by semmern. 03/18/24 02:14 PM
10 years after 3/8/2014
by NoFlyBoy. 03/17/24 10:25 AM
Copyright 1997-2016, SimHQ Inc. All Rights Reserved.

Powered by UBB.threads™ PHP Forum Software 7.6.0