S92 Rotor Tip Speed

[andTompkins]

Anyone know the tip speed of the S92 main rotor? Uncle Nick?

Thanks!

[GoodGrief]

I don't fly those big bombers:{
But I'd love to (lacking JAA-IR).
Here's my guess:
Rotor diameter = 17,17 meters
RRPM = 258
Diameter x PI = circumference = 53,941 meters.
at RRPM = 1 Rev per minute that's 3,236 km/h (53,941x60/1000)
x 258 (RRPM ) gives 835 km/h.

[rotordk]

257.8 rpm to be excact (105%).

[GoodGrief]

297,9 to be precise
www.easa.eu.int/doc/Certification/Design_Appro/Rotorcraft/TC_R_001_Sikorsky_S92A.pdf

[GoodGrief]

darn, finger trouble...

[rotordk]

RFM states 258, Flightsafety 257.8...........Nick !?

[GoodGrief]

Let's not count beans here ( I knew that would happen).
258/257,8-> we are talking about 0,07% here.

[rotordk]

If it was your pension it would matter.......

[212man]

Well, when I went to school I'd have said it was 0.08% (0.0775%) but then that just goes to show what a futile quible it is: we don't even see the actual Nr in the cockpit! Nr=105% end of story (well except when reinstating DEO from OEI training, when it runs up to 108%, for some bizarre reason (that seems to have escaped those E people) :confused:)

Rather than worry about Nr at FLY, why not ask "why does the pilot have to manipulate the throtles to set Nr outside the avoid range, at IDLE, in a FADEC equiped aircraft" ? Seems very 1980's S-76A to me :ugh:

[Blackhawk9]

As 212 man said ,if the 92 had 4 t/r driveshafts (like the Blackhawk) instead of 2 bloody long driveshafts which gets a harmonic wobble at the wrong rpm and hit the fire extinguisher mount (as has happened to a couple of operators) you wouldn't care what rpm the machine was doing as the FADEC controls it beautifuly.

[Aser]

Rather than worry about Nr at FLY, why not ask "why does the pilot have to manipulate the throtles to set Nr outside the avoid range, at IDLE, in a FADEC equiped aircraft" ? Seems very 1980's S-76A to me

Really strange to touch the throtles at all, do you have the off,start,idle,fly typical switch, in the 92?
In that case, don't you need to put the FADEC in manual mode to have any effect the change in throtles position?

Regards.
Aser

[212man]

ASER, to paraphrase (slightly) George Orwell: "all FADEC systems are equal, but some are more equal than others!"

The throttles behave more or less like standard Speed Select Levers (SSL) in normal operation. You press START, and then set the throtle to IDLE and the engine auto starts and sets IDLE Ng (about 67%), however this is not enough to keep the Nr out of the lower Nr/Np avoid band (36-49%) so you manually set 'about' 70% Ng with the throttle to set Nr/Np to 50-55% to stay out of the upper avoid band of 56-67% Nr/Np (necessary for carrying out the MGB BYPASS test). Then you advance the Throttle(s) to FLY, Np governing takes over and you have 105% set. Scheduling limits Tq to 30% max if you are heavy handed with advancing.

Once in FLY, if you retard the throttles, the Nr will decrease, just like a normal SSL. So, on the face of it you have greater control than with a simple switch arrangement. However, there is no direct mechanical linkage, so in the event of a dual FADEC channel failure, the engine shuts down, and in the event of a fixed power failure, you have no control of the engine.
I suppose there could be a back up system, but that just so Provencal ;)

[DeltaFree]

Apart from the minor Nr debate the advancing tip will also have the aircraft speed added. Not being a 92 jock I cannot give any help here, but any offers on cruise/ Vne?

[Aser]

However, there is no direct mechanical linkage, so in the event of a dual FADEC channel failure, the engine shuts down, and in the event of a fixed power failure, you have no control of the engine.
The slogan could be: "Sikorsky, a different way of thinking" :E
Interesting read, like when I learned in this forum about the fuel system without fuel pumps to prevent leaks if the line breaks, only engine driven pump.
I'd like to hear the reason behind the no mechanical linkage, to be able to control one engine in "manual" mode.
Anyway I remember once in the 139, during the test we found the backup cable jammed. :ouch:
Regards.
Aser

[widgeon]

of course to be rally pedantic one should first calculate the rotor diameter at 105% , how much does the centripital force cause the MRB to "stretch" ?

[JohnDixson]

A bit afield of a tip speed discussion, but there were, as you might imagine, some "spirited " meetings about digital engine control configuration early in the S-92 design phase. There were the S-76B configuration advocates, wherein you had a dual digital control with a water-faucet type mechanical backup. Had one VP who adhered to the fly-by-wire philosophy which proclaims that fly-by-wire is acceptable as long as the wires go thru the center of the push-pull tubes!

But the research exposed that there were zero instances of the S-76B ever reverting to manual-only ( what I called water-faucet a moment ago ) control. Further, the reliability numbers of the digital side of the T-700 control system were superior to the mechanical side. We also looked into the dual digital control situation in the B-777 and concluded that the mechanical backup was both unnecessary but would also complicate the design so that the final reliability would in fact be lower.

All that said, there were some interesting get-togethers! My recollection is, that during the entire S-92 development and certification program, we had four channel reversions.

Technology has certainly advanced. For the longer-in-tooth, remember the SH-3d in the late 1960's with GE's first electronic analog supervisory control called PMS ( Power Management System, not what you all were thinking )? That system gathered a track record of failure modes that soon led to a bright red PMS-OFF switch on the cyclic.

[dangermouse]

not heard of any problems on the EH101 either

DM

[Gomer Pylot]

Cruise speed is 140-ish, depending on how much of a hurry the captain is in. Almost identical to an S76. I haven't flown one, but I've outrun a couple in an S76, barely.

[rfernando]

hey, does any one know the RPM of the tail rotor for S-92A?

[Jack Carson]

The S-92 rotor speed has been increased from 100% (258 rpm) to 105% (271 rpm) over the period of the H-92’s development to accommodate for increases in both empty and maximum gross weights. At the same time the main rotor diameter was increased from 53.66 feet to 56.33 feet. These combined increases in rotor diameter and speed have resulted in a corresponding increase in main and tail rotor tips speeds.

The S-92 has a design tip speed is in excess of what is recommended as a maximum in R. Prouty’s text Helicopter Performance Stability and Control due to potential noise problems. At –3 degrees Celsius and 165 knots the S-92 main rotor advancing tip speed will be at exactly 1.0 mach. This would require that the S-92 be operated at a reduced speed during winter operations in noise sensitive areas.

[Tcabot113]

The tip speed is fast enough to cause hearing problems. So too fast. That advancing blade pressure pulse easily defeats traditional head sets. Read nor ways report.

TC

[JohnDixson]

761 ft/sec @ 105% Nr. Tail is about 722.

The original Nr was 245.8, which was then increased during development by 5% to 258 ( present 105% ). Jack's note re reaching a free stream mach no of 1.0 at 165 @ -3C is therefore off a bit. Need to get to 191KCAS or so to get the tip free stream mach no up to 1.0.

BTW, UH-60 has been there and has data.