Go Back  PPRuNe Forums > Aircrew Forums > Rotorheads
Reload this Page >

Hanging one side low

Rotorheads A haven for helicopter professionals to discuss the things that affect them

Hanging one side low

Old 5th Sep 2002, 17:31
  #41 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 9,662
Received 108 Likes on 51 Posts
Blimey Jeep and you an A1 an'all, fancy not knowing simple stuff like that!!!

No, I am taking the p*** mate, good luck with the bag, it doesn't sound much fun- especially for an old knacker like you!!!!

Flygunz, you are just too anal for remembering the page ref in the PoF book, I will just go and look in the copy PD gave me to see if you are right!
crab@SAAvn.co.uk is offline  
Old 11th Sep 2002, 23:44
  #42 (permalink)  
 
Join Date: Jun 2002
Location: east ESSEX
Posts: 4,271
Received 5 Likes on 4 Posts
one-hung low

The reason the fuselage hangs low is primarily determined by the position of the tail rotor in relation to the a/c`s CofG,Longitudinal,lateral and vertical. The moments derived by the t/r in producing "t/r drift" or "translating effect" have to be opposed by the moments produced by the rotor,and it doesn`t matter what type of rotor it is,rigid,semi-rigid,teetering,etc,those factors relate to sensitivity,response,and control power.If you are in a hover at fully fwd.c of g,and note the a/c attitude,then go to fully aft and hover, the a/c attitude will be more "left side down"(for CCW rotor rotn.)If you can now change the lateral CofG,you will now see an even greater variation in attitudes,and finally ,if you can find the vertical CofG and change it from it`s normal position,usually fairly high on modern helos,and use depleted uranium to lower it sufficiently(even as an u/s load-rigidly attached) and always using the same a/c weight,you can draw a matrix of attitude/weight(K)/CofG(lat/long/vert.).From the known a/c attitudes ,the position of the t/r relative to the a/c CofG can be ascertained and should show that an aft,high and left CofG will give the most adverse left roll!Of course ,if you are French and dress the other way,then you`ll roll right,and if you`re Oz then use a mirror-This ,of course could all be b*****ks,as this Chilean red is slipping down too easily,and I might have it all wrong!!!!
sycamore is offline  
Old 20th Mar 2020, 14:45
  #43 (permalink)  
 
Join Date: Mar 2020
Location: Rio de Janeiro
Posts: 2
Likes: 0
Received 0 Likes on 0 Posts
Why helicopter takes off one side first?

I´m helicopter pilot in Brazil and CFI.
When I´m teaching a new student, they keep asking me why a Robinson helicopter takes off the right side first.
I lot of friends here, explain that the reason is ´cause the main tank is at the right side, so the aircraft is havier in this side. But I really dont believe in it. The tank is so near to the main rotor shaft that I dont believe that the small amount of weight can change so drastically th CG.

When you have to taxi the helicopter and you are in a low fuel condition, the R66 for example, seems to have this condition maximised.

At second, I thought It could be as a result of tail rotor thrust, so to compensate this force, the main rotor shaft is tilted a little to the right. But this is just a guest. And I couldnt find anything in the maintenance manual that could validate my guest.

This morning I was in a Helicenter here and I was watching a Squirrel (Eurocopter AS-350) landing and it was easy to see the same thing happening.

Well, I still think that it has something to do with the engineering stuff, not just a matter of weight.
Can someone help me with this and explain why the helicopter takes off and land one side first?
Haga Martins is offline  
Old 20th Mar 2020, 18:40
  #44 (permalink)  
 
Join Date: Nov 2000
Location: White Waltham, Prestwick & Calgary
Age: 70
Posts: 4,018
Likes: 0
Received 2 Likes on 1 Post
Or rather one skid hanging low, depending on which way the rotors spin. Helicopters using anticlockwise rotation will have the tail rotor thrust slightly out of alignment with the main rotor, because they are set to be level with each other in the cruise. As a result, the TR thrust line is below the level of the MR hub and will produce a couple that makes the left skid lower in the hover - the reverse for clockwise rotating rotors.

Should an anticlockwise rotating helicopter end up hovering right skid low, you've left the refuelling hose in

Phil
paco is offline  
Old 20th Mar 2020, 18:48
  #45 (permalink)  
 
Join Date: Dec 2011
Location: US
Posts: 3
Likes: 0
Received 0 Likes on 0 Posts
From the Helicopter Flying Handbook (FAA-H-8083-21B) Chapter 9 states:
"Helicopters usually hover left side low due to the tail rotor thrust being counteracted by the main rotor tilt."

Left side low implies a anticlockwise rotation of the main rotor.

Helicopter ASI is offline  
Old 20th Mar 2020, 19:10
  #46 (permalink)  
 
Join Date: Jan 2000
Location: Bar to Bar
Posts: 784
Received 6 Likes on 1 Post
Originally Posted by paco View Post
Or rather one skid hanging low, depending on which way the rotors spin. Helicopters using anticlockwise rotation will have the tail rotor thrust slightly out of alignment with the main rotor, because they are set to be level with each other in the cruise. As a result, the TR thrust line is below the level of the MR hub and will produce a couple that makes the left skid lower in the hover - the reverse for clockwise rotating rotors.

Should an anticlockwise rotating helicopter end up hovering right skid low, you've left the refuelling hose in

Phil
Brilliant. Hours wasted trying to understand that just in case the feared Trapper asks me and you explain it it half a dozen lines. I hate you.
Sloppy Link is offline  
Old 20th Mar 2020, 20:45
  #47 (permalink)  
 
Join Date: Mar 2002
Location: West of zero
Posts: 240
Likes: 0
Received 0 Likes on 0 Posts
Brought to you by your friendly FAA

Page 2-15, Translating Tendency
Buitenzorg is offline  
Old 20th Mar 2020, 20:50
  #48 (permalink)  
 
Join Date: Jul 1999
Location: Warrington, UK
Posts: 3,737
Received 2 Likes on 2 Posts
Hmm...am I the only one who thinks an instructor should know that?

Maybe he should go here:
Principles of Flight books
MightyGem is offline  
Old 20th Mar 2020, 22:13
  #49 (permalink)  
 
Join Date: Dec 2006
Location: yes
Posts: 324
Likes: 0
Received 3 Likes on 3 Posts
Originally Posted by paco View Post
Or rather one skid hanging low, depending on which way the rotors spin. Helicopters using anticlockwise rotation will have the tail rotor thrust slightly out of alignment with the main rotor, because they are set to be level with each other in the cruise. As a result, the TR thrust line is below the level of the MR hub and will produce a couple that makes the left skid lower in the hover - the reverse for clockwise rotating rotors.

Should an anticlockwise rotating helicopter end up hovering right skid low, you've left the refuelling hose in

Phil
really?

Hanging one side low
JimEli is offline  
Old 21st Mar 2020, 00:22
  #50 (permalink)  
 
Join Date: Sep 2002
Location: Great South East, tired and retired
Posts: 4,046
Likes: 0
Received 15 Likes on 11 Posts
You have two opposing Moments.
The first is the T/R thrust, acting to the right and lower than the rotor head, and the other half of the moment is the horizontal component of the main rotor thrust, which has been set at an angle to oppose the drift effect. This first moment tries to roll the aircraft to the left.

Opposing that, once the aircraft rolls a little bit, is the CG, which is no longer in line with the vertical component of the rotor thrust. It acts straight down, and is off set to the right from the main rotor thrust, acting straight up. This moment tries to roll the aircraft right.

The two moments fight a little, the more the T/R moment tries to roll to the left, the more the CG moment is offset and opposes that roll.

(


Last edited by Ascend Charlie; 21st Mar 2020 at 00:44.
Ascend Charlie is offline  
Old 21st Mar 2020, 02:10
  #51 (permalink)  
 
Join Date: Mar 2006
Location: UK
Posts: 94
Likes: 0
Received 0 Likes on 0 Posts
I can't believe we're up to 50 posts on something as simple as tail rotor roll. As I recall, it took Uncle Dennis about 5 mins on day 2 at Ternhill, shortly before he rode his bike into the lake..
rotarywise is offline  
Old 21st Mar 2020, 03:40
  #52 (permalink)  
 
Join Date: May 2002
Location: Downeast
Age: 74
Posts: 17,785
Received 143 Likes on 57 Posts
Did anyone bring up Transmission mounting that differs from a true vertical to the Airframe?

Memory serves me the Alouette III had a 3.5 Degree tilt to it.
SASless is offline  
Old 21st Mar 2020, 03:46
  #53 (permalink)  
 
Join Date: May 2002
Location: Downeast
Age: 74
Posts: 17,785
Received 143 Likes on 57 Posts
Did anyone bring up Transmission mounting that differs from a true vertical to the Airframe?

Memory serves me the Alouette III had a 3.5 Degree tilt to it.
SASless is offline  
Old 21st Mar 2020, 06:08
  #54 (permalink)  
 
Join Date: Apr 2007
Location: Out there
Posts: 350
Received 8 Likes on 5 Posts
If you’re a flight instructor and you don’t know why this happens, perhaps you should be hanging up your instructor wings
Evil Twin is offline  
Old 21st Mar 2020, 06:22
  #55 (permalink)  
 
Join Date: Sep 2002
Location: Great South East, tired and retired
Posts: 4,046
Likes: 0
Received 15 Likes on 11 Posts
...but hang them left wing low...
Ascend Charlie is offline  
Old 21st Mar 2020, 07:13
  #56 (permalink)  
 
Join Date: Oct 2009
Location: the far south
Posts: 568
Likes: 0
Received 0 Likes on 0 Posts

and Kaman did something completely different with offset transmission ans servo flaps.



Last edited by typerated; 21st Mar 2020 at 07:49.
typerated is offline  
Old 21st Mar 2020, 09:12
  #57 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 2,911
Likes: 0
Received 3 Likes on 3 Posts
Originally Posted by rotarywise View Post
I can't believe we're up to 50 posts on something as simple as tail rotor roll.
The thread is only up to 50 posts because 2 threads have been merged together.
Bravo73 is online now  
Old 21st Mar 2020, 12:29
  #58 (permalink)  
 
Join Date: Apr 1998
Location: Mesopotamos
Posts: 4
Likes: 0
Received 0 Likes on 0 Posts
When I first flew the R22 20 years ago it hung left skid low. Then I flew it a couple of years ago and it hung right skid low. Now I only fly the AS350 and my conscience remains clear.
cattletruck is offline  
Old 21st Mar 2020, 12:48
  #59 (permalink)  
 
Join Date: Dec 2009
Location: Southwater
Age: 72
Posts: 0
Likes: 0
Received 0 Likes on 0 Posts
Hanging one side low sounds like my testicles
RedhillPhil is offline  
Old 21st Mar 2020, 17:26
  #60 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 9,662
Received 108 Likes on 51 Posts
The right roll in ACs diagram (opposing TR roll) is a result of the arm between the action of the TR thrust and the vertical position of the C of G. All forces act around the C of G whether it be vertical, horizontal or lateral. I believe that was the point Nick Lappos was making 18 years ago.
crab@SAAvn.co.uk is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell or Share My Personal Information

Copyright © 2023 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.