nr limits s76c

[Twin Head]

Does anyone know why the 109% nr limit was introduced on the s76c model, and what are the implications of exceeding 109+ in such manouvres like a quick stop when required

[gulliBell]

I didn't know it had changed. The numbers I remember for C and C+ are both 107% power on, and 122% power off. Why I remember 122% in particular is that on one occasion I saw 120%, which of course was reported to maintenance, and the good book said no further action was required. 122% would have required a factory powertrain overhaul.

I'd be interested to read a more definitive response from esteemed members here.

[soggyboxers]

TH,

I think you're getting a bit confused. There's a transient maximum of 109%N2 power on and 115% power off.

Nr limits are:

Power Off -
Maximum 115% Nr
Minimum 91% Nr

Transient Maximum 121% Nr
Transient Minimum 74% Nr
Transient Minimum 68% Nr (at touchdown when executing an autorotative landing)

Power On
Maximum 108% Nr (except transient maximum 109% Nr for 20 seconds)

Minimum 106% Nr for twin engine operations
Minimum 100% Nr for single engine operations

Transient 91% Nr
Transient 68% Nr at touchdown while executing a single engine landing

One engine operation up to Vbroc 100 - 108% Nr
One engine operation above Vbroc 106 - 108% Nr

Even if you were referring to Nr, you'd be unlikely to exceed the 109% transient limit of 20 seconds in a quickstop

Hope that helps.

[Twin Head]

Thanks for your replies, soggy boxers - no confusion exists.

NR limits are now limited to 108%.
Max for 20 seconds 109%

I am wondering what are the implications of exceeding 109+ (say 110) are.

Nick Lappos - do you know about this for the c model

[Gomer Pylot]

The person(s) to ask about this is your maintenance shop. The maintenance manuals spell out rather specifically what has to be done for any exceedances.

[Twin Head]

gomer

there has not been any maintenance ammendments for the new nr limits. Are currently waiting on sikorsky for further information.

[NickLappos]

Twin, first I have heard of it, I will check.

[R. Cal]

The Turbomeca engine installation manual has a N2 limit of 108.5%. I believe that's what sets the limit for the power on Nr.

At least that's how it is on the C+ & ++.

[NickLappos]

No change to rotor limits on any model. The engines have always been limited (power on) to values below the rotor. Rotor is 115% steady, 121 transient on all 76 models. Engines are all in the 109 to 112 neighborhood, with transients above. Never saw a healthy engine overspeed by following the rotor up in an auto.

[Twin Head]

Nick

Flight Manual Ammendment last month from sikorsky limits power on to 108% . 109% max 20 seconds for s76c.

TH:8

[NickLappos]

Yes, Power On, which has always been well below Power Off, due to engine shaft limits. Of course, the N2 and Nr are married Power On, so it is the N2 that establishes the power on limit.

On each model, the typical N2 limit has been between 108 and 109 steady, and up to 112 for brief transients. This is an engine limit. The rotor has been at 115% since the beginning.