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Starting Bell 407 With Rotor Brake Engaged


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#1 GMCK13

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Posted 09 September 2018 - 20:17

What kind of damage could happen if you started a Bell 407 with the rotor brake engaged? What if the start was aborted at 25% NG? Thanks.



#2 SBuzzkill

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Posted 10 September 2018 - 10:36

IIRC that was around the time you should abort the start if the blades don't turn, yes?  Talk to your maintenance personnel.  Better to let them know and ensure the aircraft is still safe than try to hide a mistake and make a problem worse.  


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#3 Nearly Retired

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Posted 10 September 2018 - 13:25

When I worked in the GOM, one of the unwritten, unapproved and untalked-about techniques was the rotor-brake-on start in a 206.  It was used on really windy/gusty days when you were on a sketchy platform that made a lot of turbulence on the heliport, but you made the mistake of parking with a blade sticking out over the windward edge of the deck and just had to, had to, had to get going.

 

You'd pump that brake up and get it on real good.  Then you initiate the start and get it lit off.  Around 30% or so, you reach up and snap the brake off.  You wanted to get the brake off *before* the engine started overpowering the brake.  Doing this would get that rotor spinning up in no time!  (It was easier in a 206B of course, but not impossible in an L-1/L-3 if you had one with a predictable start.  Not that I would know.)

 

No one taught the technique.  No one acknowledged it or even admitted to knowing about it - or using it.  In fact, it may not exist at all.  

 

Seems to me that they use a similar technique in the Sikorsky S-76 equipped with the C-30 engines.  The brake holds the N2 wheels from turning while the compressor and gas producer wheels start normally.  Doesn't seem to damage those engines.  And as long as the TOT doesn't go over the limits, why would it?  Ever seen the suddenness with which the S-76 rotor begins spinning upon brake release?


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#4 Eric Hunt

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Posted 10 September 2018 - 13:46

Any damage would be uneven heating of the turbine wheels, with the hot gases only hitting a couple of parts of the wheels instead of being spread all over it. I have seen one person start a 206 and get to full throttle before he realised the blade was still tied down.

 

Yes, in the S-76 B it was accepted practice to start one engine with the brake on when the VIP passengers arrived in their car and boarded. Once they were inside, release the brake, spin up the rotor to 85%, and start the other engine.



#5 apacheguy

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Posted 10 September 2018 - 16:17

Any damage would be uneven heating of the turbine wheels, with the hot gases only hitting a couple of parts of the wheels instead of being spread all over it. I have seen one person start a 206 and get to full throttle before he realised the blade was still tied down.

 

Yes, in the S-76 B it was accepted practice to start one engine with the brake on when the VIP passengers arrived in their car and boarded. Once they were inside, release the brake, spin up the rotor to 85%, and start the other engine.

 

Rotor brake starts are accepted practice in the AH-64, though pretty rare for various reasons.  Supposed to be a valid technique for shipboard or dusty area starts.  Never heard that it was a maintenance problem as it is in ATM and therefore a normal/accepted startup procedure. 


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#6 iChris

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Posted 11 September 2018 - 22:54

What kind of damage could happen if you started a Bell 407 with the rotor brake engaged?

 

What if the start was aborted at 25% NG? Thanks?

 

Worst case, a little ware on the friction linings (pads) If the brake disc was slipping against the friction of an engaged break prior to shutdown; otherwise, it’s not much of an event, no maintenance action is required.

 

Engine starts with rotor brake engaged to hold the drivetrain and rotors stationary, while the engine runs at idle, is more common with large twin-engine helicopters were there is an increased demand for more powerful hydraulic and electrical systems. Has been popular with Sikorsky models like the CH-53E, H-60, CH-54A, S-58T etc. 

 

As an example, the S-64E’s fully articulated main rotor head is around 7 feet in diameter and weighs approximately 1,900 pounds. This is in addition to its 6 main rotor blades totaling 2,100 pounds (350lbs./blade). Therefore, you can’t engage and control a rotor system with that amount of turning mass without hydraulic assist. The centrifugal force combined with that amount of mass creates a significant vibratory load.

 

With the S-64E (CH-54A) you get the ball rolling by starting the 72 HP turbine auxiliary power plant (APP, APU, or aka the "P"), that brings the Utility, Hoist, and Make-up hydraulics on line along with electrical; thereby, allowing you to start the 4,500 SHP Pratt & Whitney engines via the hoist pump that supplies the engine hydraulic starter motors.

 

In order to safely engage the rotors and accomplish the main rotor servo and flight control checks, you first need to power-up one of two stages of the main rotor tandem servos. In the S-64E the #1 engine drives the 2nd stage servo pump; therefore, the rotor brake is set to hold and delay rotor engagement until the #1 engine is started and the 2nd stage hydraulic pressure is up at its normal (2,000psi) allowing the preflight servo and flight control checks to be completed. Thereafter, the rotor brake is released and the drivetrain and rotors start turning and the 1st stage hydraulic system (3,000psi) and remaining systems come online.

 

You have to be specific to the helicopter type because systems vary. With the S-64F (CH-54B), there’s no need to set the rotor brake, the APP drives the 1st stage hydraulic pump from the accessory section of the main rotor transmission without the engine running or the rotors turning. In any case, you need hydraulic assist prior to rotor engagement.

 

We also covered a bit on starts with the rotor brake engaged back in 2015 at the following link:

 

Free Wheeling unit question that I can't figure out


Edited by iChris, 12 September 2018 - 00:39.

Regards,

Chris

#7 Fred0311

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Posted 12 September 2018 - 10:28

Nearly Retired, you'll be happy to know that your secret handshake is still "not" in use in the gulf.
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#8 Nearly Retired

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Posted 13 September 2018 - 11:23

LOL Fred, I don't know what you're not talking about ;-)

#9 Spike

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Posted 13 September 2018 - 12:36

What kind of damage could happen if you started a Bell 407 with the rotor brake engaged? What if the start was aborted at 25% NG? Thanks.

 

While your question doesn’t provide any context regarding the circumstance surrounding your question, I’ll ask the following; did you utilize the checklist or, miss that specific item during your start-up? Regardless, anytime a situation such as this occurs, inform your maintenance personnel and get their input. While the responses here have provided some good information, don’t think your employer will have the same opinion. Fess up, no matter how minor the error and learn from your mistake…..


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#10 WolftalonID

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Posted 18 September 2018 - 08:43

Reducing blade flap on windy days when a blade is hanging over the edge of a platform....it works..just dont let it wind up too much. 10-15% is what seems to be the unspoken we dont talk about it technique.
Just saying from a friend who I know whos second cousins fathers cats breeders neighbor knew about back in nam.
Sometimes we think we know it all....only later to discover we only knew all we had learned. Never stop learning.

#11 helonorth

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Posted 23 September 2018 - 18:31

Reducing blade flap on windy days when a blade is hanging over the edge of a platform....it works..just dont let it wind up too much. 10-15% is what seems to be the unspoken we dont talk about it technique.
Just saying from a friend who I know whos second cousins fathers cats breeders neighbor knew about back in nam.

Ugh. I hope you don't work where you say you work.

#12 iChris

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Posted 26 September 2018 - 13:34

Supposed to be a valid technique for shipboard or dusty area starts.  Never heard that it was a maintenance problem as it is in ATM and therefore a normal/accepted startup procedure. 

 

Reducing blade flap on windy days when a blade is hanging over the edge of a platform....it works..

 

Seems to be the unspoken we dont talk about it technique.

 

Correct, it's valid and not so unspoken. It's documented in Navy/USMC helicopter flight manual and operation manuals with respect to shipboard operations. Civilian flight manuals often lack such sufficient operational detail.

 

Army H-60 helicopters (with the exception of the MH-60K) do not have rotor brakes, while Air Force HH-60G helicopters are not universally equipped with them. With these aircraft, rotor blades begin turning upon engine startup. Extended rotor coast down times can be expected on shutdown. Coast down times can vary with relative wind speed and direction, and can exceed 8 minutes in winds as light as 20 knots.

 

Non-rotor brake-equipped H-60 helicopters are more susceptible to flapping than their Navy counterparts. During rotor start and coast down, changing wind conditions, gusts, flight deck turbulence and rotor downwash from other helicopters can create excessive blade flapping and cause aircraft damage. Extreme caution should be exercised when starting or shutting down these helicopters on board ship. 

 

Relative crosswinds that create strong updrafts at the ship’s deck edge are especially conducive to excessive blade flapping, and should be avoided. 

 

Startup/shutdown of these aircraft should be treated similar to a USN/USMC helicopter with a rotor brake failure. The ship should provide optimum winds for the start or wind milling stop of the rotor system.   REF: NAVAIR 00-80T-122


Edited by iChris, 26 September 2018 - 14:09.

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Regards,

Chris

#13 superstallion6113

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Posted 26 September 2018 - 13:58

 

 

Correct, it's valid and not so unspoken. It's documented in Navy/USMC helicopter flight manual and operation manuals with respect to shipboard operations. Civilian flight manuals often lack such sufficient operational detail.

 

Army H-60 helicopters (with the exception of the MH-60K) do not have rotor brakes, while Air Force HH-60G helicopters are not universally equipped with them. With these aircraft, rotor blades begin turning upon engine startup. Extended rotor coast down times can be expected on shutdown. Coast down times can vary with relative wind speed and direction, and can exceed 8 minutes in winds as light as 20 knots.

 

Non-rotor brake-equipped H-60 helicopters are more susceptible to flapping than their Navy counterparts. During rotor start and coast down, changing wind conditions, gusts, flight deck turbulence and rotor downwash from other helicopters can create excessive blade flapping and cause aircraft damage. Extreme caution should be exercised when starting or shutting down these helicopters on board ship. 

 

Relative crosswinds that create strong updrafts at the ship’s deck edge are especially conducive to excessive blade flapping, and should be avoided. 

 

Startup/shutdown of these aircraft should be treated similar to a USN/USMC helicopter with a rotor brake failure. The ship should provide optimum winds for the start or wind milling stop of the rotor system.   REF: NAVAIR 00-80T-122

 

Just to update old info, Army Hawks actually started being built with rotor brakes with the introduction of the H-60M into the fleet. I haven't turned wrenches on a Mike model that didn't have one. The old A and L Hawks did not have rotor brakes on them. 


Edited by superstallion6113, 26 September 2018 - 13:59.


#14 Wally

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Posted 26 September 2018 - 16:24

Nobody has mentioned a torque issue in this thread.  My recollection is that that was the also a factor in popping the brake.  One needed to release the rotor brake before the engine could deliver enough power in accelerating the rotor to damage the drivetrain.?

 

Positioning the helicopter favorably relative to wind and turbulence is a better bet than the rotor brake trick.  Which I deny ever hearing of much less attempting in the Gulf.- and you can't prove otherwise....

Or a broom start,


Edited by Wally, 26 September 2018 - 16:27.

Just a pilot (retired, so I have a LOT of time)...


#15 Eric Hunt

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Posted 26 September 2018 - 18:43

I have seen a person (from an opposition company) start a B206 and run it up to full throttle without noticing the blade was tied down. Realised, shut down, untied the blade, started up again and departed.



#16 Wally

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Posted 26 September 2018 - 18:53

I have seen a person (from an opposition company) start a B206 and run it up to full throttle without noticing the blade was tied down. Realised, shut down, untied the blade, started up again and departed.

Yeah, it's all good until the N2 starts driving....  Wish the issue away.


Just a pilot (retired, so I have a LOT of time)...


#17 helonorth

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Posted 26 September 2018 - 21:51

 

 

Correct, it's valid and not so unspoken. It's documented in Navy/USMC helicopter flight manual and operation manuals with respect to shipboard operations. Civilian flight manuals often lack such sufficient operational detail.

 

 

 

 

One question: have you ever worked offshore oil and gas? I did it for ten years and never heard of this nonsense. I'm also pretty sure something that hasn't been tested or approved in the flight manual is a little different than it "lacks sufficient operational detail." So what about this is "valid"? You are advocating a procedure that has no testing, precedent or FAA approval for that particular aircraft. To be honest, it's disappointing coming from you. Don't be a test pilot. If it's not in the FM for that aircraft...DON'T DO IT. 


Edited by helonorth, 26 September 2018 - 22:12.


#18 iChris

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Posted 29 September 2018 - 12:36

One question: have you ever worked offshore oil and gas? I did it for ten years and never heard of this nonsense. I'm also pretty sure something that hasn't been tested or approved in the flight manual is a little different than it "lacks sufficient operational detail."

 

So what about this is "valid"? You are advocating a procedure that has no testing, precedent or FAA approval for that particular aircraft. To be honest, it's disappointing coming from you. Don't be a test pilot. If it's not in the FM for that aircraft...DON'T DO IT.

 

Most of my time flying over water was off naval vessels and tuna boats, no offshore oil rigs.

 

Your level of knowledge, or lack thereof, the technique doesn’t set any precedence. This technique does exist and is valid for many helicopters; however, that does not necessarily mean it’s valid for your aircraft.

 

If you’ve never heard of engine starts with the rotor brake set to prevent blade sailing, check-out Shawn Coyle’s book Cyclic & Collective, Chapter 19, Peculiarities of the Helicopter. Hopefully, you’ll have the next ten years doing caught-up on the stuff you never heard of.  

 

This is something that has been tested and approved on numbers of helicopters, some of which have already been listed in this post. All valid information in valid FAA and U.S. Military approved flight manuals. It all speaks to the validity and background of the technique itself. I never stated it was applicable to all helicopters or any one Bell helicopter. 

 

On the Civilian flight manual often lacks detail. That’s nothing new. 

The military FM is completely different, and in most cases much more comprehensive than the civilian version. Typically, it has more detailed descriptions of the airframe, systems and so on, and much more performance information. 

 

“One of the reasons for the greater performance information is that military fleets will have a great number of identically–equipped helicopters, and so it is relatively easy to make sure the data is there for each machine.

 

Another reason is that the FAA is only concerned with safety, and the military is concerned with safety, performance and military effectiveness.

 

Warnings, cautions and notes are typically more pronounced, and emergency procedures are separated into critical (often called bold-faced, which must be committed to memory) and non-critical emergencies…” Shawn Coyle “Cyclic & Collective

 

Also, your quote, “Don't be a test pilot. If it's not in the FM for that aircraft...DON'T DO IT.”

 

The premise is not entirely correct, as only the "Limitations" section of your flight manual is FAA-approved and mandatory. Per Chief Counsel Interpretation 04/22/2011. Any operation need only be within the limitation set forth in section 1 (LIMITATIONS).

 

Until some years ago, you were actually within the limitations; however, currently Bell has a line in the limitation section (206L4, 407, 212, 412) that reads as follows: “Engine starts with rotor brake engaged are prohibited.” Bell knew about the technique and they knew it was being used.

 

407 NORMAL PROCEDURES: Instructions and procedures contained herein are written for purpose of standardization and are not applicable to all situations.

 

407 LIMITATIONS: Compliance with Limitations section is required by appropriate operating rules. Anytime an operating limitation is exceeded, an appropriate entry shall be made in helicopter logbook. Entry shall state which limit was exceeded, duration of time, extreme value attained, and any additional information essential in determining maintenance action required.

 

Lastly, back to the original question, post #1

 

“What kind of damage could happen if you started a Bell 407 with the rotor brake engaged? What if the start was aborted at 25% NG? Thanks.”

 

Worst case, a little ware on the friction linings (pads) If the brake disc was slipping against the friction of an engaged break prior to shut-down; otherwise, it’s not much of an event, no maintenance action is required. However, it will require per the 407 LIMITATIONS above an appropriate entry in helicopter log since paragraph 1-18, limitations, prohibits rotor brake starts. 

 

The engine produces torque against the stalled drivetrain, but that’s what the drivetrain is designed to handle. As long as shut-down occurred prior to 30% Ng and the MGT temps are within the start limits you’re OK. At most, you may want to take a look at the rotor brake itself and make sure there was no overheating due to slippage.

 

This is not new stuff, happens occasionally. Bell Product Support 450-437-2862 requires no maintenance if only the above is the case. Blades tied-down events are more frequent and more often lead to maintenance.

 

Rolls-Royce Field Support 315-405-5469 has no problem with the N2 wheel held stalled on the 250-C20, 250-C30, or 250-C47, as long as temps are within the normal limits.


Edited by iChris, 29 September 2018 - 14:31.

Regards,

Chris

#19 helonorth

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Posted 29 September 2018 - 15:51

 

 

 

 This technique does exist and is valid for many helicopters; however, that does not necessarily mean it’s valid for your aircraft.

 

 

 

 

 

 

 

Not in the 407 it doesn't. We are talking about the 407.

 

Anyway, fortunately, I do not work offshore anymore. But even if I did, it wouldn't really matter what other stupid crap I could learn myself on in the next ten years: if it's not approved in the FM and not a procedure in your GOM, don't do it. That is my point.

 

This is a very good technique to use in a 407 if you want to lose your job, though. PHI would fire you in a heartbeat for doing this. Gee, I wonder why the 407 FM tells you specifically NOT to do this? 






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