Bell 412
Thread Starter
Join Date: Sep 2005
Location: US
Posts: 194
Likes: 0
Received 0 Likes
on
0 Posts
Bell 412
Just got a closer look at an airmed 412n the other day. Am I wrong or are the four blades just a combination of two 2-bladed systems set at 90* to each other? They llok as if they were two separate teetering hinges on two different planes.
Other four bladed rotor heads I've seen had all four blades in the same plane.
Monk
Other four bladed rotor heads I've seen had all four blades in the same plane.
Monk
Join Date: Dec 2003
Location: Ripon, CA
Posts: 59
Likes: 0
Received 0 Likes
on
0 Posts
For those who have never seen one up close
Can be a real bear to track and balance one of these things, the blade tips look kind of funny from inside the cockpit too...as one would imagine, two different tip paths.
I haven't weighed one myself but it seems someone told me just one of those "dingle-balls" weighs 17 pounds!
I haven't weighed one myself but it seems someone told me just one of those "dingle-balls" weighs 17 pounds!
Join Date: Mar 2003
Location: the hills of halton
Age: 71
Posts: 809
Likes: 0
Received 0 Likes
on
0 Posts
quite surprising how slender the mast is . Is it a lifed item on this aircraft ?
neat site shows many rotor heads.
http://www.b-domke.de/AviationImages/Rotorhead.html
neat site shows many rotor heads.
http://www.b-domke.de/AviationImages/Rotorhead.html
Last edited by widgeon; 16th Sep 2007 at 15:55.
Join Date: Oct 2003
Location: Over here
Posts: 1,030
Likes: 0
Received 0 Likes
on
0 Posts
No, it's not new. It's just impractical. The blades are in different planes, and I've spent weeks trying to get one smooth enough to be acceptable. You can't really track them, you just get them to an acceptable ride. The first ones came out without the weights on the head, and most couldn't be tracked at all, so Bell put a couple of hundred pounds of weight up there to make it work, and that was payload lost immediately. The 412 is just a UH1 with 2 engines and a slapped-together 4-blade system, nothing new about it. Bell is so far behind the rest of the industry it may never recover.
Join Date: Feb 2001
Location: GOM
Age: 66
Posts: 69
Likes: 0
Received 0 Likes
on
0 Posts
Gomer Pylot said:
You can't really track them, you just get them to an acceptable ride.
You can't really track them, you just get them to an acceptable ride.
The early 412's flying in the GOM are all getting long on the tooth, have had a lot of blade repairs done over the years which affects how they work. Many of the repairs were done in-house and the trailing edge of the blades got thinned out which greatly affects how the blades fly. At lot of rotor working troubles have been locally made. Like mis-matching blades across the fleet.
The pendelum absorbers had nothing to do with rotor working they were put on to reduce the 4P in plane vibration. Yes they do affect the payload...
Actually the 412 and its little cousin the 430 have stacked rotors and both can be worked quite well.
Having a stacked yoke is not all bad:
A lot easier for shipping; two long boxes in lieu of a huge rectangular box. Make's a big difference when you're grounded wayyyyy out there. Also the issue of tip path being different for each yoke has no negative effect on ride quality. The Bell 430 also has stacked yokes and has one of the smoothest rides of any helicopter. A lot of the issues with working Bell 412 rotors are related to either bad rubber (seperated/too old) or bad blades (too many repairs/paint touch-ups)
As for the weigths added to the M/R head, SPA (simple pendulum absorbers) weights, they are there for the 4/rev. They were not there originally but were added aerly on to help control 4/rev. Same type of device can be found on other four bladed system (BO-105/BK-117).
A lot easier for shipping; two long boxes in lieu of a huge rectangular box. Make's a big difference when you're grounded wayyyyy out there. Also the issue of tip path being different for each yoke has no negative effect on ride quality. The Bell 430 also has stacked yokes and has one of the smoothest rides of any helicopter. A lot of the issues with working Bell 412 rotors are related to either bad rubber (seperated/too old) or bad blades (too many repairs/paint touch-ups)
As for the weigths added to the M/R head, SPA (simple pendulum absorbers) weights, they are there for the 4/rev. They were not there originally but were added aerly on to help control 4/rev. Same type of device can be found on other four bladed system (BO-105/BK-117).
Join Date: Feb 2005
Location: KPHL
Posts: 340
Likes: 0
Received 0 Likes
on
0 Posts
Monk, it is two pairs of rotors flying in two different planes, but they aren't on teetering hinges, they are semi rigid. If you look at other helicopters, you may see a similiar configuration on the tail rotor.
As far as track and balance, yes, normally complete in three flights, and normally very smooth.
As far as track and balance, yes, normally complete in three flights, and normally very smooth.
Haven't had a 412 i couldn't get in limits some have taken 2-3 days and upward of a dozen flights , but got them eventualy!! even mismatched -104 blades, have used 8500 and Rads-at, like the rads better with problem blades, and yes the 412 is a bitch to balance compared to other helo's, get rid of any blade thats not a -109 and take your time with the balancing and start at basic with everything!, sometimes you may have to swap blades beside each other (not opposite)but a smooth 412 at 120 kn is possible.
Thread Starter
Join Date: Sep 2005
Location: US
Posts: 194
Likes: 0
Received 0 Likes
on
0 Posts
Mathew,
Thanks for that info. I did noticed that it wasn't a teetering hub, 'cause I was very interested so I looked at it very close. The pilot let me hop up on it to get real close.
Blackhawk,
Can anyone (me) w/o an A&P just go out and buy a Chadwick, get familiar with the hows and the whys and get busy on these? In short, do blade balancers need to be certified?
Perhaps someone familiar with FAA regs can charm in. I'm in the US, private pilot helo with time in R22 and TH55 only. Oh yeah time in Cessnas too, buy never did finished the fixed wing add-on.
Monk
Thanks for that info. I did noticed that it wasn't a teetering hub, 'cause I was very interested so I looked at it very close. The pilot let me hop up on it to get real close.
Blackhawk,
Can anyone (me) w/o an A&P just go out and buy a Chadwick, get familiar with the hows and the whys and get busy on these? In short, do blade balancers need to be certified?
Perhaps someone familiar with FAA regs can charm in. I'm in the US, private pilot helo with time in R22 and TH55 only. Oh yeah time in Cessnas too, buy never did finished the fixed wing add-on.
Monk
Join Date: Jan 2006
Location: Western MA
Posts: 455
Likes: 0
Received 0 Likes
on
0 Posts
Not to sound too harsh but if the best Bell can come up with after all these years is to simply plop one 2-bladed head atop another they, and their customers are in trouble. Are those metal to teflon PCR bearings also? One great step backward!
Join Date: Aug 2004
Location: northeast usa
Posts: 86
Likes: 0
Received 0 Likes
on
0 Posts
Rotor Track and balance
The balancing gear should be either recognized or approved by the aircraft OEM. Tracking and balancing are maintenance actions so you need an A&P, AME, JAR66. It takes quite a while to master using this gear and some never do, but it is not something that can't be learned.
Join Date: Feb 2005
Location: KPHL
Posts: 340
Likes: 0
Received 0 Likes
on
0 Posts
Dan said,
"Not to sound too harsh but if the best Bell can come up with after all these years is to simply plop one 2-bladed head atop another they, and their customers are in trouble."
What do you believe is the problem with designing a rotor system like this.
You'll find other manufacturers have used this idea on tail rotors of such aircraft as the Apache, the Mi-28, the Mi-35, and the EH101. Bell is also using this arrangement on the main rotors of the 427, and the 407 (OH58D). The UH1Y and AH1Z use a similiar design on the main rotor and the tail rotor.
The claimed benefits are in reduced weight, reduced manufacturing complexity, increased blade flapping angles and reduced logistical problems associated with transport of rotor hub components.
What is it that you know that these manufacturers don't know, Dan?
"Not to sound too harsh but if the best Bell can come up with after all these years is to simply plop one 2-bladed head atop another they, and their customers are in trouble."
What do you believe is the problem with designing a rotor system like this.
You'll find other manufacturers have used this idea on tail rotors of such aircraft as the Apache, the Mi-28, the Mi-35, and the EH101. Bell is also using this arrangement on the main rotors of the 427, and the 407 (OH58D). The UH1Y and AH1Z use a similiar design on the main rotor and the tail rotor.
The claimed benefits are in reduced weight, reduced manufacturing complexity, increased blade flapping angles and reduced logistical problems associated with transport of rotor hub components.
What is it that you know that these manufacturers don't know, Dan?
Join Date: May 2007
Location: Texas, USA
Age: 53
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
"Bell is also using this arrangement on the main rotors of the 427, and the 407 (OH58D)."
Not exactly...the 427 and 407 use the "soft in plane" rotor system. The only similarities between the soft in plane and the stacked are the elastomerics.
Not exactly...the 427 and 407 use the "soft in plane" rotor system. The only similarities between the soft in plane and the stacked are the elastomerics.
412 rotor is "soft-in-plane" too, you are correct about the rest.
While the 430 rotor is stacked, everything else is different about it, the lenght of the yokes, the way they attach to the blades etc.
412 rotor was adopted in the late 70s and it was a great impprovement over anything there was then.
While the 430 rotor is stacked, everything else is different about it, the lenght of the yokes, the way they attach to the blades etc.
412 rotor was adopted in the late 70s and it was a great impprovement over anything there was then.