I dont have the conklin figures for DMC but have been told that they are actually close to a 206L. Main reason is there are very few life limited parts .Transmission overhauls and Hydraulic repairs can be expensive especially if you are in a corrosive environment . In the US there are many choices for engine overhaul and quite a few approved PMA parts for them the help keep down the engine overhaul costs. There have been 56 105 LS delivered in total. The German wermacht were selling a load of 105's with military certification for bargain prices some time ago.

Thanks guys for all the info,I appreciate the input,

Safe Flying,

Kiwi Skiv

BK-117, BO- 105 Rotor blades
 

What do the weight things on the BK and BO blades do. They look like a small weight on each side of the blade which is free to rotate, but Im stuffed if I can figure out what its for.
Help needed. THanx

Centrifugal or, is it centripetal
 

These weights are thrown outward by centrifugal force. As the blades rotational velocity builds up the centrifugal force builds up increasing the apparent mass of the pendulum weights. The helicopter blades as they rotate will form a traveling wave from the tip to the root. An example of this would be if you tied a rope to a fixed point and then raised and lowered the free end very rapidly. The rope would have a traveling waveform running from the free end to the fixed end. As this traveling wave on the rotorblade moves inward the increased mass of the pendulum weights must be displaced in order for the waveform to be reacted by the rotorhead. The energy of the traveling wave is cancelled out in the attempt to displace the pendulum weights. In plain English they are vibration dampers.

Some Bell blades accomplish this by having a weight imbedded at the nodal point on the blade while other helicopters have dual pendulum weights that react to different frequencies.

:ok:

Lu,

Congratulations, that's the best description I've read!

Spaced,

They are also there to severely bruise your fingers when you let the weight fall on your hand during a pre flight ;)

Slightly off topic, how many operators are currently suffering due to the KSB on blade cuff inspections? 3 weeks downtime and $A50k to establish that the blades are serviceable is a real PITA :(

Lu, thanx for the amazingly simple and concise explination. Is this due to the nature of the rigid rotor system? Or do all rotor blades have a dampner of some sort?
John, Thanx for the heads up. Hopefully oneday Ill get to fly one and be able to put the advice to good use.:D

Vibration dampers
 

To: Spaced

Not all helicopters incorporate vibration dampers and those that do utilize as many designs as there are helicopters that employ them.

The bell 412s use pendulum dampers while some two blade Bell rotors incorporate a tuned weight inside the blade at the nodal point. Remembering the example of the moving rope and the traveling wave this included weight keeps the vibration from passing to the root of the blade by absorbing the energy of the wave.

The Bristol Sycamore has three weights suspended on flexible shafts, which are attached to the transmission. These weights vibrate on the flexible shafts in tune with the vibration generated by the blades. The vibrating weights absorb the energy of the vibration keeping it from passing into the fuselage.

The MIL Mi-17 uses a Bifiler system similar to that used on Sikorsky helicopters. I am not too clear on how the weights move in relation to the attaching arms in that they move to absorb loads generated by lead and lag or if they move up and down to absorb the traveling wave or, if they do both.

Many Eurocopter helicopters have a weight mounted on a coil spring which is mounted under the coollie hat on the rotorhead. The incoming vibrations excite the weight and in doing so the vibrations are cancelled out.

Bell helicopter devised an electronic system on the Huey that sensed the incoming vibration and the device generated a signal (vibration) that canceled out the incoming vibration. The unit was installed in the nose compartment.

Boeing has a mechanical system that mounts under the pilots’ seats on the CH-47 and this device absorbs vibrations. If it ever goes unserviceable the vibrations would be so great that the helicopter could not be flown. The poor guys in the back don’t have this convenience.

The most unique way of absorbing vibration induced by rotor movement is the NodaMatic system designed by Bell. This system allowed the transmission to move up and down in relation to the fuselage. The suspension system had a tunable weight that would be displaced by the linkage on the suspension. The displacement of the weight absorbed the incoming vibration that caused the transmission to move up and down keeping any vibration from passing through the fuselage. The system worked great but it caused a lot of problems.

The Hiller UH-12 had flexible arms attached to the flight controls below the rotor. Attached to the flexible arms were metal weights. Any vibration that would feed-back from the flight controls would cause the weight to deflect thus absorbing the feed-back forces.

:ok:

You want to see some complex vibration dampers? Look at a Sikorsky S76 rotor head. Stay away from whatever drugs that design engineer was on!

Regarding the BK 117, the best comment I heard about the dampers was from a woman who looked at the two pendulous ball-shaped items hanging from each blade root, and said, with a grin:
"I suppose this is a BOY helicopter?":uhoh:

Mr Selfish

The EC120B appears to have 'Chinese weights' in its tail rotor. When used in a main rotor, they are perpendicular to 'in-plane', and are used to counter the centrifugal flattening moment of the blade. (Tennis Racket Effect).

These weights have been call "Chinese balls". Does this make the EC 120 a BOY helicopter, also. :D


Cannot respond to 'Meaning of Life', since it is off-topic. ;)

Advancements in aerodynamics
 

It is my personal opinion that the incorporation of these various devices that counter rotor induced vibrations were incorporated after the development of cambered airfoils on rotor blades. This added a degree of instability that resulted in vibrations that either were not there on NACA 0012 blades or they were not as prominent.

Fire away engineers.

:ooh:

Lu,

Can you please expand on your comment that the Nodamatic system devised by Bell "worked well but caused problems".

Are you referring to any particular Bell model that incorporated this system or just generally?

Thanks in advance

NodaMatic
 

To: Aladdinsane

My only experience with the NodaMatic suspension was on the Bell 214. Other Bell models had this system installed but I can’t say that the problems if any were the same.

As indicated in my post the transmission moves up and down in relation to the fuselage and by definition the engine. Connecting the engine to the transmission is a short shaft with couplings at either end. These couplings were filled with a viscous grease and the movement of the transmission relative to the engine caused the couplings to extend and retract turning them into grease pumps. The grease that was extruded from the couplings would be injected into the airflow going into the engine.

This grease would plate out on the engine inlet bell and it would attract sand and small debris. The engine was very sensitive to airflow distortion and would result in compressor stalls. The compressor stalls would generate a shock load into the drive line and rotor system resulting in frequent major inspections and resultant change out of dynamics and drive line components. More serious compressor stalls would result in airframe damage.

The problem was solved locally by frequent detergent washes of the engine, which ran up the maintenance rate, which was already over 70 MMH/FH

:sad:

Thanks Lu, only played with the smaller "nodal beam" Bells without problem so was wondering about your comment.

Question for BO105 pilots
 

Hi everyone...

I am flying a HEMS BO105 since June on a 35-40ºC/no winds/high altitude enviroment.

SOPs on my company said I have to shut off the engines before get the injured in the helicopter.

Sometimes I need to start the engines on less than 15 minutes and the TOTs are over 270ºC.
FM say "engine start is not permitted if TOT is higher than 150ºC."

On this situation, fellow pilots use starter gen for cooling the engines.

Is the use of the starter gen the right way?
What is your procedure?


Thanks in advance. (...and sorry for my english)

You are permitted to vent the engines useing the starter/gen before commencing the start.

Most of the time this is not required as the TOT limit of 150 is for the moment you chuck the fuel in, not when you press the starter.

So it is normally below this after the engine has run up to 12-15 % anyway!

Best method is to Vent run the engine (Dry motor) it to 15% N1. Wait for the N1 to drop back to 0% N1 then start it.. In my experience, if the Temp is below 200 deg on fuel input, she will not hot start..
However, do NOT attempt to modulate the start (using fuel flow lever) at all. This messes with the fuel bellows and will constantly give you hot starts. The fuel flow must be moved into the idle gate for start.
PM me if more info is needed.
C4

Hi Talvin, no problem with your english, as Bosher has stated as long as your TOT is around 150 at light off there should be no problem. I do not agree with C4 and the start/stop /start method. If you have a weak battery you are then trying to do two starts when one is enough. If you have a problem at over 12%N1, 150 c and the temp is looking like a hot start it is time to talk to the other side (engineer's) and have them readjust the start (mixture.)It can be done, I mean taiking to an engineer, just take's time and free beer.

what you could try is shut down one engine and vent it while the other one is still running, thereby using its generator instead of the battery. Then shut the other one down as normal.

This should give you a cold and a hot engine for the start. Start the cold engine first, then vent the hot engine if required using the generator from the running engine.

It is probably not a practice recommended by the manufacturer, but it should work on twins.

brgds, S76Heavy

It is probably not a practice recommended by the manufacturer
 

Dead right there, RR/Allison are quite specific in mandating against "venting" their engines after shut down, citing thermal shock damage as a likely consequence. Conversely, the LT101 is required to be motored for 10 seconds after shut down, to move the oil around and prevent coking in the oil galleries :rolleyes:

Also, the practice of cross starting is allowed by some manufacturers, and not by others. It can put a strain on the starter/gen quill shaft, leading to failure, when the extra load is applied during cross start. Watch the ammeter load go off the clock, and consider the effect it might be having!

C4's reply is as good as you'll get.

Thank you very much for your responses.

I've sent a mail to Rolls Royce asking about this topic.

As soon as I receive an anwser, I'll post it here.


Talvin.

:ok: