Sikorsky S-76: Ask Nick Lappos
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gullibell:
I've flown the A, A+, and A++.
I found that the A+ didn't perform any better than the A. At 30 C the A+ N1d out at about the same Q as the A Temped out. Now the A++ was a real performer it Torqued out at 30 C.
Midniteblues: The Initial course is probably around $20K US. The last time I was on the recurrent A [2001] it was $6,995 USD.
I've flown the A, A+, and A++.
I found that the A+ didn't perform any better than the A. At 30 C the A+ N1d out at about the same Q as the A Temped out. Now the A++ was a real performer it Torqued out at 30 C.
Midniteblues: The Initial course is probably around $20K US. The last time I was on the recurrent A [2001] it was $6,995 USD.
"Come on down to the GOM. There are plenty of As still flying around..."
As much as I would like to come down, but not to fly an old A-model. If there are any C+'s or C++'s then this 4000hr S76A/C/C+ pilot might be tempted!
As much as I would like to come down, but not to fly an old A-model. If there are any C+'s or C++'s then this 4000hr S76A/C/C+ pilot might be tempted!
Join Date: Apr 2007
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76A++ question, for Nick Lappos
In a 76A++, Phase 2, if you had a faulty N1 tach gauge, would fall below 60% and then back to say 98%, would this cause the AC generator to come off and on line? Does the AC generator get its information to come off line from the N1 tach gauge? Thanks
Nick,
I think the question relates to the fact that the AC gen drops offline when the engine out warning activates. As the engine out warning comes from the N1 signal, if that signal is then faulty and fluctuating, presumably the AC gen will drop offline (and come back on again) as the fluctuation occurs. Presumably along with the engine out warning and tone.
Comprenda a amigo?
I think the question relates to the fact that the AC gen drops offline when the engine out warning activates. As the engine out warning comes from the N1 signal, if that signal is then faulty and fluctuating, presumably the AC gen will drop offline (and come back on again) as the fluctuation occurs. Presumably along with the engine out warning and tone.
Comprenda a amigo?
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Thanks
Yes, I probably did not word that question well. We had a tach gen. that was croaking, it went up to 97, down to 50, with engine out tone. The AC gen. was kicking off and on line. Old phase 2 bird, so we would get an AFCS chatter in the controls as the AC gen came off line before the invertor picked up the load. (for maybe one second) Reset master caution all good, then N1 tach would drop below 50, engine out audio, control chatter again. Our techs just finished up some research, looks like signal for the AC gen to come off line does come from the N1 tach gauge. Thanks the responses, this is a great forum.
Well, my memory doesn't extend to the GCU theory, but does clearly recall the AC generator running off the MGB and not the reduction gearbox. It is vertically orientated and can 'drop' onto the secondary bearing when the primary fails (with 5 hours continued use allowed).
On the S76 Arriel installation on A++, C, C+ (do not know about the C++) the AC gen kicks out when one engine warning triggers to gain OEI performance. This function is inhibited if A-I with snow protection is ON, or with CSN76-223 and hoist power is ON.
On the early A++ this feature was overseen and a TR to the RFM was issued to reduce Cat A weight with 150 lbs if I remember right, until corrected.
CB
On the early A++ this feature was overseen and a TR to the RFM was issued to reduce Cat A weight with 150 lbs if I remember right, until corrected.
CB
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I don't recall ever hearing about a C+ with TWO AC generators. Only the one gearbox mounted AC Gen along with the dual static inverters. Each engine has one DC Starter/Generator on the N1 section. Further, I believe there are many C+'s flying around without any AC Gen because of no heated windshields installed. The (DC powered) inverters carry all AC loads.
Of course since the AC gen sucks power directly from the gearbox, it's a detriment to OEI flight performance. But remember, *IF YOU'RE N1 LIMITED* you'll actually get more power to the rotor while on the limter with the DC generator loaded to it's limit. Counter-intuitive, perhaps, but true.
Again, lacking the military training required to pilot such a complicated and difficult machine, my comments are simply pedestrian.
Of course since the AC gen sucks power directly from the gearbox, it's a detriment to OEI flight performance. But remember, *IF YOU'RE N1 LIMITED* you'll actually get more power to the rotor while on the limter with the DC generator loaded to it's limit. Counter-intuitive, perhaps, but true.
Again, lacking the military training required to pilot such a complicated and difficult machine, my comments are simply pedestrian.
There is still hope
Again, lacking the military training required to pilot such a complicated and difficult machine, my comments are simply pedestrian.
http://www.myhometownnews.net/index.php?id=24496
-- IFMU
Last edited by IFMU; 24th Apr 2007 at 17:54. Reason: forgot something
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*IF YOU'RE N1 LIMITED* you'll actually get more power to the rotor while on the limter with the DC generator loaded to it's limit
I'm with Brian, I don't understand either. What does loading a DC generator to it's limit mean? How do you get a DC gen to its load limit in a C+? when OEI the high current sucking aircon load is dropped from the #2 DC gen (from memory) so there's plenty of excess load generating capacity. And in any event, surely the more current the DC gen is producing the more Tq it's sucking out of its engine?
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S76 Reduced Nr on taxiway
Question for Nick:
Greetings Nick and thanks for the wealth of info you have posted!
I would like to know if there are any components on the 76 that would be adversely affected by operating on a taxiway at approx. 80% Nr. At the airports we service we are routinely required to taxi long distances. The reduction in Nr has reduced our brake wear by 50%, long term fuel saving benefits as well as, I believe, less potential for F.O.D.
Your thoughts would be most appreciated.
Thanks.
Greetings Nick and thanks for the wealth of info you have posted!
I would like to know if there are any components on the 76 that would be adversely affected by operating on a taxiway at approx. 80% Nr. At the airports we service we are routinely required to taxi long distances. The reduction in Nr has reduced our brake wear by 50%, long term fuel saving benefits as well as, I believe, less potential for F.O.D.
Your thoughts would be most appreciated.
Thanks.
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dbcooper2,
(Nice user-name!)
I can't possibly advocate taxiing at Nr below the green arc, frankly. Operation at low Nr is not tested, and could lead to heartaches in places we just don't know. Sorry I can't be encouraging!
For brake wear, the best technique is to be SURE the disk is level (the stick is back) during taxi. If you leave the disk tilted down so the blade tips are at or below the horizon as seen from the pilot's eye position, the aircraft scoots along too much, and the brakes will wear. This is because the 5 degrees of forward main shaft tilt mean that neutral cyclic is actually lots of forward disk tilt.) If you practive holding the disk above the horizon by about 1/2 meter (the same at the nose as it is at the sides) the aircraft won't accelerate at all.
You can practive this cyclic position by going to the runway, making the cyclic truly neutral, and then just lifting the collective a bit. Then tilt the disk aft a touch and note a rearward taxi. Then tilt it a touch forward and note the forward taxi. As the aircraft rolls forward, lower the collective and let the aircraft achieve a slow forward roll, then stop the forward with just pulling the cyclic back to neutral with a little up collective (don't use much aerodynamic braking, it is a bad habit in all helos to use a big aft stick, especially causing complaints from the mechanics when you take a divit out of the tail driveshaft cover!)
Also taxi turns with moderate speed require no brakes if you use moderate cyclic in the direction of the turn to keep the aircraft level as you turn. This means that you don't have to brake and slow down before you turn. Unlike some bigger helos with slab sides and narrow gear, the 76 has no great propensity to roll over (a rare case did occur once, but it was a soft ground, muddy terrain roll-over nightmare that is not the general case.)
(Nice user-name!)
I can't possibly advocate taxiing at Nr below the green arc, frankly. Operation at low Nr is not tested, and could lead to heartaches in places we just don't know. Sorry I can't be encouraging!
For brake wear, the best technique is to be SURE the disk is level (the stick is back) during taxi. If you leave the disk tilted down so the blade tips are at or below the horizon as seen from the pilot's eye position, the aircraft scoots along too much, and the brakes will wear. This is because the 5 degrees of forward main shaft tilt mean that neutral cyclic is actually lots of forward disk tilt.) If you practive holding the disk above the horizon by about 1/2 meter (the same at the nose as it is at the sides) the aircraft won't accelerate at all.
You can practive this cyclic position by going to the runway, making the cyclic truly neutral, and then just lifting the collective a bit. Then tilt the disk aft a touch and note a rearward taxi. Then tilt it a touch forward and note the forward taxi. As the aircraft rolls forward, lower the collective and let the aircraft achieve a slow forward roll, then stop the forward with just pulling the cyclic back to neutral with a little up collective (don't use much aerodynamic braking, it is a bad habit in all helos to use a big aft stick, especially causing complaints from the mechanics when you take a divit out of the tail driveshaft cover!)
Also taxi turns with moderate speed require no brakes if you use moderate cyclic in the direction of the turn to keep the aircraft level as you turn. This means that you don't have to brake and slow down before you turn. Unlike some bigger helos with slab sides and narrow gear, the 76 has no great propensity to roll over (a rare case did occur once, but it was a soft ground, muddy terrain roll-over nightmare that is not the general case.)
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Hi Nick
Even the Coaxial Kamovs are taxied in the manner you described.In the turn though due to poor directional control on ground,the manual advices to touch up on Collective and turn with the Cyclic into the turn.
Brakes are hardly used
Even the Coaxial Kamovs are taxied in the manner you described.In the turn though due to poor directional control on ground,the manual advices to touch up on Collective and turn with the Cyclic into the turn.
Brakes are hardly used
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Nick:
Excellent response on the Nr and how to use the cyclic to control the aircraft speed and reduce the break wear.
We had to get our pilots to do the same in Manila with the S76A++ when doing long taxi's and this technique greatly reduced the wheel brake wear.
Excellent response on the Nr and how to use the cyclic to control the aircraft speed and reduce the break wear.
We had to get our pilots to do the same in Manila with the S76A++ when doing long taxi's and this technique greatly reduced the wheel brake wear.
Another one for Nick and others Re. S76
Is there any history of a blade letting go or failing in flight on a S76?
No reason for asking except just looking up at our blades manufactured many years ago and wondered about one of these 4 things which keep us aloft maybe departing the a/c.
I don't mean any struck by lightning. Know about that one already, just actual blade failures.
No reason for asking except just looking up at our blades manufactured many years ago and wondered about one of these 4 things which keep us aloft maybe departing the a/c.
I don't mean any struck by lightning. Know about that one already, just actual blade failures.