Sikorsky S-76: Ask Nick Lappos

[Sarbe]

s76 Cabin Noise

Does anyone have any idea how loud it is (in decibels) in the cabin of the 76 with standard paneling ?.

I was recently asked this question and can not find any answers.

Cheers

[GLSNightPilot]

I don't routinely carry a decibel meter with me when I'm flying, but I would estimate the noise as <90dB.

[verticalflight]

This may help you:

S76
Heater off - 105.1 dB(A)
Heater on - 106.1 dB(A)

If you need more information e-mail me.

[email protected]

[GLSNightPilot]

Heater off - 105.1 dB(A)
Heater on - 106.1 dB(A)

Is this with the vents open or closed? Side popout vents open or closed? ISTM that the noise is a lot higher with the side vents open, especially if the open side is forward, & the airspeed also makes a difference.

I don't think you can make one number cover all the possibilities.

[Old cynic]

Sarbe

Suggest you call the guys at either Keystone in the US or what was Air Hanson (now Signature, Blackbushe) in the UK. They will have done loads of cabin noise measurement.

[C+]

stand-by AH

Question. On the latest/greatest version of the 76C+ why would Sikorsky wire the Standby Art. Horizon (the fancy kind with flt. director bars and stuff) to the number 1 Nav assuming that if everything were going to crap you would probably lose your number 1 Nav?
Should it not be on the number 2 side? Given a dual gen. fail and most everything is switched off or some other fail resulting in the same situation wouldn't it be better to be driven off the bus that will still be giving you some power?

Anybody?

[widgeon]

Hmmm i thought the stdby normally had a battery pack . Is this defined as co -pilot horizon or stand by horizon ?

[C+]

stand-by ah

Please read carefully... THIS PARTICULAR KIND OF AH HAS COMMAND BARS as in flight director command bars that must get a NAV SIGNAL from somewhere. So yes there is an emergency battery self just for this AH. Do you think this battery also powers the Nav radio required to supply the signal to the command bars?? I DON'T THINK SO.

Anyone else with an idea?

[USRotor]

Maybe seems stupid, but do you have allready tryed:

- the manufacteur

or

- the maintenance manual

[C+]

stand-by AH

I did not expect the manual would help too much and our mechanics had no answer for me. This is our 5th and newest C+ and the first with this type of AH.
Next time I see the Rep. I will query him but I do not run into him that often. Just thought I might get a quick answer through these boards.
I never posted here before and rarely looked but most of my colleagues use this place for info so I thought, what the hey, give it a shot.

[Heliport]

"I never posted here before and rarely looked but most of my colleagues use this place for info so I thought, what the hey, give it a shot."

Welcome to Rotorheads.
Helicopter people from all over the world post questions here.
I don't know the answers to your questions, but there's a good chance others will.

Heliport

[USRotor]

ok, let's se

- maintenance manual/mechanics

imagine that you have a small problem with the system (we are on a scenario), ask what they will do?? 2 optinios, or fix it (and they need manuals and drawing of the system (thats what you need ) or send it to someone that will fix it, right (and that will be the people that maybe will know...)

(mechanics/maintenance "allways know" at least is what they said )

- the manufacteur

a little more dificult... normally the guys that sells the heli, or answer the phone, don't know it... but it is allways a way, a mail or a phone call to the tecnhical/publications department can help...


sincerely, i prefer the first one

PS: Maybe the last option:with the drawing of the various bus, and using the breakers, try to simulate the condition ...



"children! don't try it at home!!!"

[NigD]

C+

I dont work on helis (so maybe I should just shut up now) but on corporate aircraft the No.1 nav is hooked to the emergency busbar (battery), as is the no.1 comm/stby inst setc.

I believe that the FD V-bars would not be a requirement to work under emergency conditions (double genny failure) anyway and just the attitude (No.1 AHRS/VG), airspeed (No.1 ADC), altitude (No.1 ADC), heading information (No.1 compass) and other essential services required for the 1 hour duration to get you down safely.

Possibly Nick L. can enlighten the reasoning.

Regards

NigD

[almost canadian]

I agree witht the simulation theory,
next time you have 5 minutes to spare on the ground, leave the machine running and start simulating failures, pulling breakers.
If there's FD bars on the AH, there's also warning flags, so just pull breakers untill they pop up.
Try different scenarios as well, 1 gen versus the other, emerg bus on or off etc., I'm sure this way you will figure it out + it will give you a better understanding how your machine is wired.
By the way do you need any extra pilots out there?

[Shawn Coyle]

There is always a danger of using circuit breakers to simulate failures, as pulling the CB on say, an attitude gyro will automatically disconnect the gyro from the display or autopilot, because the 'power to gyro valid' signal says there is no power. This is a lot different from a gyro which is getting power but sending stupid information to the autopilot or display - how do you know it is going to ignore invalid information?
So, be careful pulling circuit breakers - the real failure can be something different!

[Nick Lappos]

The answer is simple:

The main thing to understand is that the ADI-335 meets two different requirements in one instrument. Standby ADI for power failures and standby CDI for display failures in single pilot operations.

The nav function is a way of meeting the backup CDI (nav control/display) requirement for Single pilot IFR. The idea of the CDI is to cover display failures. If the displays on the pilot's side fail or the bus fails the backup CDI will pick up the other (#1) NAV. If the pilot's symbol generator fails he will be able to use the reversionary mode to copy the copilot's displays on his own normal display but will not be able to control the nav through the display controller ....therefore the backup CDI. If you aren't single pilot IFR you don't need either nav on the standby. Baseline prior to a/c 528 doesn't have it.

[NigD2]

Nick

Whats the reasoning behind not having any nav set hooked up to the emergency bus??

Not as essential to do a precision approach in a heli???

NigD

[Avnx EO]

I can't resist chiming in when Nick starts talking avionics. But this has actaully been a hot issue on a number of airframes, driven by a lot of tradition (this is the way we've always done this.) The back up CDI has been a vestige for some time. In most modern electronic (EFIS) cockpits it is no longer required - as can be shown by ARP-4761 hazard analysis. (Loss of all "radio" nav and com in IFR typically being "hazardous" while loss of all radio Nav with com remaining being "major") Most modern EFIS designs could support "Hazardous" level for loss of radio nav without a backup CDI. For example, on the S-76 you can recover from a failed symbol generator by selecting reversion (as Nick mentioned), or from a failed display tube by selecting composite. And that's all still all at the pilot's station. The combined probability of both failures is easily better than 10e-6 and likely approaching 10e-7.

It was a different story with an electromechanical HSI with a failure rate of less than 1000 hours. With no ability to recover information on another display at the pilots station, the back-up CDI was essential. However, even with electronic displays and all their reversion and redundnancy, old traditions die hard with our regulatory agencies. For Example, the EFIS-equiped B-430 was initially required to carry two backup CDIs - one for each pilot (so much for single pilot being the driver in that case.) That has since been reduced to one after significant effort.

So why do we still provide a back-up CDI on the standby for electronic cockpits? In some cases - just because it's there. That was pretty much the case for the BA-609 architecture. We didn't need to by hazard or worload analysis, but since the GH-3000 had the capability, and our pilots agreed it didn't add too much clutter, why not. After all, as an engineer, you never walk away from the oportunity to provide extra cabapility when it's free.

Why the connection to NAV-1? I've heard the arguments that this allows the pilot to cross-check NAV1 while he flys NAV2 (with pilot on the right) - but unless you are flying CAT II approaches, this is a rationalization and not really an issue. The real reason is that most aircraft power distributions are designed to protect NAV1 & COM1 because these were traditionally considered the pilot's radios - something from the starch-wing boys. In the 412 for example COM1 is on the emergency bus, NAV1 is on essential, and COM2/NAV2 are on non-essential. And in the 412, you don't lose the essentials unless you select EMERG LOAD (Which you'd only do to get extended 90-minute battery only ops.)

I and several others have attempted schemes to protect the pilot's NAV/COM for helicopters, but with no success. The problem is that we tend to sell VFR versions with only one NAV & COM installed. And it's just too wierd to install the number 2 system first. It confuses the hell out of pilots, and it makes the guys who do Circuit Breaker panels go nuts. So until the day when we call it Pilot/Copilot or Left/Right rather than 1/2, NAV1 will remain the limp-home, last ditch, protected pilot's nav radio.

Sorry, that was probably a bigger brain dump than you were expecting.

[widgeon]

Thanks for the info Erik , One more question on SPIFR aircraft which bus would the autopilot system be powered from ?.

[Avnx EO]

That's also an issue that generates a lot of controversy. It is really a matter of both the inherent aircraft stability and the perceived workload of flying the unaugmented aircraft in IMC. That establishes the hazard level of losing the autopilot function, which then dictates which power bus it gets put on.

Autopilots, themselves, are typically "non-essential" functions for IFR (typical for fixed wings), but for many helicopters, the autopilot system also provides the stability augmentation and attitude hold capability necessary to make the aircraft tame enough for IFR flight. (keeping the dirty side down).

In single pilot IFR, the pilot has to be able to take his attention away from the controls long enough to get an approach plate out or do similar tasks, without looking up to find that the world has inverted on him. Judging the un-augmented aircraft's tendancy to get to an unrecoverable or vertigo-inducing attitude is a very subjective thing, and there is very little guidance material on the subject. (How organized was the pilot before the failure, how far is the aircraft allowed to go with the hands off the controls for how long, etc.) It's really been a judgement call by the test pilot community and certification authorities. For DPIFR (Dual Pilot IFR), if the autopilot fails, its assumed that one pilot can be totally devoted to actively flying the aircraft, and so there are less issues involved.

In most of the twins I'm familiar with, the hazard level of would fall somewhere in the "Major" to "Hazardous" level. And that is why they typically have dual autopilot systems. I've been told the EC-135 has dual system with a third, limited back-up (I'm not sure what that says about the hazard level, since it's beyond what would typically be required for "hazardous", and less than what would qualify for "catastrophic." - or maybe I don't know enough about that system. )

As far as power goes, I can tell you that on the 412EP (same system as the S-76) that that the pilot's FCC is on the emergency bus. The co-pilot's is on the essential. But that's to preserve SAS and ATT hold capability. The flight director functions and coupled nav are all expendable.

Hope that answers you question.