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

I believe that was the original configuration, but improved since then

Phil

The head is two pieces, bolted on top of each other. Bell hired Rube Goldberg to design the entire aircraft, and a wonderful job he did.

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!

http://i199.photobucket.com/albums/a...t/DSC03220.jpg

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

Oscar Bravo,

Thanks for the pic. That's just like what I saw.

Wil

The Hughes 500c has two overlapping strap packs.

When you set up the pitch links one pair are longer than the other to compensate.

So nothing new really.

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.

You obviously haven't flown many of the later EP's. Typically they can be tracked in 3 flights or so. 4P's are a lot less too. EP's are a significate improvement over the early 412's in many ways.

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).

412 M/R head
 

I've heard that Bell is considering going to a composite head on the 412 due to a worldwide shortage of titanium. Not holding my breath!

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.

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.

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

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!

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.

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?

"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.

Simul8, thanks for the correction. A quick look at a picture online looked the same as the 412, but the closeup revealed what you said.

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.