S76 MAUW limitation. ???

[helimutt]

I'm trying to find the answer to a question I was recently asked. The MAUW of an S76C++ is 11,700lbs. The RFM states max for take off and landing as 11,700. To me this would mean that at no time should the aircraft be over 11700. The RFM isn't totally clear and it can be interpreted differently. Is this 11700 a Sikorsky imposed limitation? Or can the aircraft be over that weight for taxi, to enable more fuel to be carried for taxiing before take-off.
Actual definitive Sikorsky answer would be appreciated.
Thanks

[Garfs]

Not an answer from Sikorsky but to me

11700 for take off means just that

So as far as I can see you can taxi with more as long as you are under 11,700 when you lift

I too would be interested in a definitive Sikorsky Answer tho.

[Ascend Charlie]

Nick Lappos is the one to ask.

But how much are you expecting to burn on taxy??

For an A380 that has to taxy a couple of miles to reach the runway threshold, it is a reasonable figure.

But a 76 is unlikely to taxy for more than a couple of minutes - your brakes will get rather hot and require 10 mins flight with the wheels down.

If your fuel/pax load is THAT critical, leave one person behind or refuel along the way.

[Fareastdriver]

Check on the undercarriage loading, it is nothing to do with the rotor loading. For example, if after take off at 11,600 lbs. you carry out a level 30 degree turn you are loading the rotor to 14,800 lbs. Brakes wont suffer as there is no residual thrust to overcome so braking action can be minimal.

If you are that desperate for fuel monitor the refuelling yourself and call 'Stop' slowly.

[Garfs]

But how much are you expecting to burn on taxy??

Well Ive seen people start to taxi with lets say 11730, and by the time they lift are at 11680 or so.

I only mentioned it because the OP asked if the 11,700 applied to actually taking off or taxiing as well

[John Eacott]

If there is a greater weight available it is normally listed as the Ramp Weight, followed by MTOW, allowing for a taxi fuel burn prior to lifting.

Unusual in a helicopter since taxiing isn't normally factored into the equation: ramp weight will be limited by the gear or mainspar strength.

[Aesir]

And the gear weight limit is tested to times 1.5G or whatever the certification standards are.

I doubt the wheels will break off during taxi for takeoff at a few lbs over limit :)

On Super Puma standard taxi fuel used is often 50kg.

[John Eacott]

I doubt the wheels will break off during taxi for takeoff at a few lbs over limit :)

Aesir,

Since there are quite a number of helicopters which have a significant MAUW increase for external loads compared to MAUW internal because of gear limits, I'd be a tad careful with that premise ;)

[helimutt]

But no-one has that definitive answer to the question. What if I asked the question "Can I taxi an S76 C++ at an AUW of 11750lbs to allow for taxiing and holding for other aircraft movements before take off?"

If the RFM is open to interpretation, I can't see from a legal position why not, but if you arent allowed to land at over 11700, then doesnt this mean its a limit? Why aren't things simply put in black and white? Litigation me thinks.


For an A380 that has to taxy a couple of miles to reach the runway threshold, it is a reasonable figure.

But a 76 is unlikely to taxy for more than a couple of minutes - your brakes will get rather hot and require 10 mins flight with the wheels down.

If your fuel/pax load is THAT critical, leave one person behind or refuel along the way.

We often start up on a busy ramp, have to taxy, and wait for fixed wing aircraft on approach often burning 50lbs + to go through this process. A S76 can be taxiied without having to constantly use the brakes if handled correctly. No need to be standing on the brakes constantly ;):ok: This isn't so much a Payload question but a limitation question. :E

[InspG]

You do not have to stand on an S76's brakes to get them hot because the pucks can be in constant contact with the discs.

Whilst it has one of the most beautiful undercarriage systems of any helicopter, just remember that it is, relatively, fragile especially when subjected to lateral forces.

[tottigol]

"This isn't so much a Payload question but a limitation question."
If OP asked you that question the answer is one and the same, yes it is about payload. You may want to check with Sikorsky and make sure you get a written answer with a solid reference behind it.

[SARBlade]

I too have to agree with tottigol, the OP asked a simple question to the mass of experts in the Rotorheads group and what he receives is 90% conjecture and opinions on how to conduct a mission he never even suggested existed. One can add their two cents but at least make an attempt to answer the question first.

I can't help because I don't know the answer but I would like to know. I flew the 101 and 92, both had max-taxi weights.

[Ian Corrigible]

SARBlade,

To help helimutt out, where did your source your S-92 taxi weight from? The only weights listed in the 76 and 92 RFMs are the standard take-off/landing weights, i.e. no taxiing weights listed (unlike for the AW101, EC155, etc.).

I/C

[tistisnot]

We asked Sikorsky for an answer and they ruled that 11,700 lbs is the maximum for taxy and take-off because of the landing gear and wheels structure; though declined to add any clarification to the RFM - Ramp Weight or whatever.

Sikorsky reply:


Weight limits are ruled by Part 1, Section 1 of the RFM,Sikorsky cannot allow taxi of the aircraft over 11,700 lbs without an RFMchange.

During initial flight test programs, the structural and much of the performance work were done at GW + 3% on takeoff, however, tocertify this capability the landing gear assemblies and the backup structure stresses will have to be tested and substantiated to the FAA that it's good for2 G taxi loads up to the increased GW.

[Fareastdriver]

There you are. As I said, say Stop slowly, lt saves worrying.

[Jack Carson]

Nick Lappos opined in a technical paper many years ago that limitations can be grouped into three categories, structural, performance, and financial. Structural limitations are physical limitations established with sufficient margin to insure the structural integrity of the vehicle throughout its flight envelope. Performance limitations are established based on installed engine power limitations and rotor system performance. In all cases, the published limitations are demonstrated by the manufacturer and verified by the certifying agencies. Lastly, financial limitations are just was they imply. The manufacturer has determined that even though the vehicle is capable of operations in excess of those already established it would not be cost effective to test and certify the vehicle to these increased limitations. This is the case when customer requirements do not dictate any requirement for and increase. The S-76A VNE chart is a good example. VNEs at higher cruise altitudes were established within the engine power limitations of the 250-C30 engines. When the B was certified those limitations were not lifted even though the B had a dramatic increase in installed power.

Some place in the bowels of my home office I have a copy of Nick report and will pass it on when located.

[SARBlade]

To help helimutt out, where did your source your S-92 taxi weight from? The only weights listed in the 76 and 92 RFMs are the standard take-off/landing weights, i.e. no taxiing weights listed (unlike for the AW101, EC155, etc.).


The max-taxi weight in the S92 was indeed the max-gross weight of 26,500. Its been awhile since I flew it and could remember monitoring the utility page Aircraft Gross Weight page to ensure that I wasn't over gross for the T/O. Sometimes we were "red" 265XX, prior to taxi. Sorry if I misled anyone with my previous post. The 101 did indeed have a max-taxi mass. I do not have an AFM to quote from.

[ericferret]

Not that long ago that a Bristow S76 had a brake fire (Amsterdam?) after a long taxi.

[212man]

Not that long ago that a Bristow S76 had a brake fire (Amsterdam?) after a long taxi.

Time flies - 12 years or so!

[industry insider]

The D will soon be certified to 11875lbs MTOW and there isn't any undercarriage modifications from the C++ as far as I know.