Sikorsky S-76 [Archive Copy]
Join Date: Apr 2003
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FH,
Take care with how you read the limitations. You are trying to mix cargo limits with a fuel tank structural limit, which is different. The tank is individually certified to its full capacity as mounted structurally on the forward wall of the baggage compartment, as well as on the floor, and its capability is not limited to the weight bearing limits of the baggage compartment, at all.
The tank has 106 US gallons usable fuel (from memory) and about 110 gallons total volume, and the tank weighs about 100 lbs, so it will weigh as much as 840 lbs total, fully fueled.
As I recall, the tank is covered in a suppliment to the RFM, perhaps a call to the local Sikorsky rep (or the factory) would unearth a copy.
Take care with how you read the limitations. You are trying to mix cargo limits with a fuel tank structural limit, which is different. The tank is individually certified to its full capacity as mounted structurally on the forward wall of the baggage compartment, as well as on the floor, and its capability is not limited to the weight bearing limits of the baggage compartment, at all.
The tank has 106 US gallons usable fuel (from memory) and about 110 gallons total volume, and the tank weighs about 100 lbs, so it will weigh as much as 840 lbs total, fully fueled.
As I recall, the tank is covered in a suppliment to the RFM, perhaps a call to the local Sikorsky rep (or the factory) would unearth a copy.
Join Date: Oct 1999
Location: UK
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There are two sizes of Aux tank. We use the smaller which holds 340 lbs. I would suggest you look VERY closly at your C of G when using the Aux tank. we are limited on AUW and a very aft C of G with the tank in and fuelled. I would guess with the larger tank you won't have any space for baggage anyway!
There is a RFM supplemant for it. I'll see if I can email you a copy of the one we have.
There is a RFM supplemant for it. I'll see if I can email you a copy of the one we have.
I've used the larger tank for a ferry, and if you have all the usual paraphenalia (= crap!) in the cabin, the c of g works out fine.
Join Date: Nov 2003
Location: Canada
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Thanks Nick, that what I thought, but it is hard without reference to prove your point.
Magbreak, yep I agree,, you have to be carefull with the aux tank versus C of G.
Thanks again gents.
FH
Magbreak, yep I agree,, you have to be carefull with the aux tank versus C of G.
Thanks again gents.
FH
Join Date: Apr 2003
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I flew the flight tests on the big tank, I found CG to be no problem if you had a cabin load and burned the tank first (which you must anyway).
Bill Kramer and I used the aux tank to set a pair of city to city records a while back, including a Chicago to New York World Record that still stands, average speed 201 MPH for 611 NM!
(Caution - done by professionals - do not try this at home! ;-))
Bill Kramer and I used the aux tank to set a pair of city to city records a while back, including a Chicago to New York World Record that still stands, average speed 201 MPH for 611 NM!
(Caution - done by professionals - do not try this at home! ;-))
Strangely: The supplement in the RFM of the 76 I fly is from a Canadian Design Approval Organisation ( DAO ) with Canadian DOT approval stamp and states under Loading Limits that "Auxiliary Fuel tank weight and fuel weight combined shall not exceed 600 lbs"
The fuel loading table however goes all the way to 721 lbs.
I wonder if the 600 lbs max total is only a limit in a Canadian registered a/c or it is also a limit elsewhere? I guess it depends who did the Design approval application and where the approval was granted.
Is the Aux tank a Sikorsky Factory option or an after market part?
Does anyone have a copy of a supp. allowing loading to the 720 lbs max?
I would like to get a copy.
The fuel loading table however goes all the way to 721 lbs.
I wonder if the 600 lbs max total is only a limit in a Canadian registered a/c or it is also a limit elsewhere? I guess it depends who did the Design approval application and where the approval was granted.
Is the Aux tank a Sikorsky Factory option or an after market part?
Does anyone have a copy of a supp. allowing loading to the 720 lbs max?
I would like to get a copy.
Join Date: Apr 2006
Location: Australia
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A question of gradient
Can anyone tell me the maximum slope (gradient) that an S76 can comfortably taxi up and down under its own power? I’m going to be asked this question in the next day or two and it’d be nice to have a definitive answer.
Due to a comedy of errors years ago we find our hangar 430mm above the height of the new apron currently under construction nearby and so will need to extend the joining taxiway to a suitable length to accommodate the maximum gradient.
Mike
Due to a comedy of errors years ago we find our hangar 430mm above the height of the new apron currently under construction nearby and so will need to extend the joining taxiway to a suitable length to accommodate the maximum gradient.
Mike
Join Date: Dec 2005
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Random thoughts
1. Runways are allowed 2% slope. 430 mm height delta graded at 2% would equal a sloping ramp to the hangar door with a lateral base of 21.5 meters. This should be a an acceptable and affordable paving job.
2. I'd look at the statis slope limitations, nose-up and nose-down. Take whichever is less. Convert the angle to percent slope and you'd be surprised at the steepness. Example (working without trig tables here...approximation only): a 10 degree slope over a lateral distance of 10 meters would be a rise of approximately 1.75 m, i.e., an approximate 17.5% grade.
3. Why not find an acceptable compromise within the range of 1 to 2 above, and simply tow the helicopter in an out?
2. I'd look at the statis slope limitations, nose-up and nose-down. Take whichever is less. Convert the angle to percent slope and you'd be surprised at the steepness. Example (working without trig tables here...approximation only): a 10 degree slope over a lateral distance of 10 meters would be a rise of approximately 1.75 m, i.e., an approximate 17.5% grade.
3. Why not find an acceptable compromise within the range of 1 to 2 above, and simply tow the helicopter in an out?
Join Date: Apr 2006
Location: Australia
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Thanks for your reply Arismount.
Your option 1 sounds best to me. Option 2, too steep and option 3 is no good as the idea is to be able to ground taxi with pax to the runway and get away from our current situation where we air taxi (at 90 degrees Matthew) over to the main pax terminal and then depart from there.
Your option 1 sounds best to me. Option 2, too steep and option 3 is no good as the idea is to be able to ground taxi with pax to the runway and get away from our current situation where we air taxi (at 90 degrees Matthew) over to the main pax terminal and then depart from there.
Join Date: Feb 2005
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MJH1
"tow the helicopter in an out?"
Surely it would be towd one way only.
Put yourself way ahead of the opposition with a running start!
Tourists love those sorts of gimmicks.
Surely it would be towd one way only.
Put yourself way ahead of the opposition with a running start!
Tourists love those sorts of gimmicks.
Join Date: Apr 2003
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For Nick Lappos,
1. Why was the S-70 aft quadrant not used on the S-76. This would of allowed full control with a single tail rotor cable failure?
2. Also how did the test run go for the S-76 landing sequence with a double tail rotor servo actuator pressure failure. Is it similar to the S-70?
1. Why was the S-70 aft quadrant not used on the S-76. This would of allowed full control with a single tail rotor cable failure?
2. Also how did the test run go for the S-76 landing sequence with a double tail rotor servo actuator pressure failure. Is it similar to the S-70?
1) The 76 aft quadrant is actually very similar to the BH, and allows almost the entire envelope to be flown with a single cable failure, because the tensioning device pops out and tightens the remaining cable. A dual cable failure turns the quadrant into a centering spring. It is not as elaborate as the Hawk, but then again, the odds of major control damage (combat damage that would take out a cable) is considerably less.
2) Without any pressure to the TR, some control is possible, as long as the isolation valve to the primaries is actuated, so that #1 mains stay pressurized. Hover is not possible, but quite a bit of range about the neutral TR pitch point is possible. I do not specifically recall the airspeed range (which really depends on weight/power required of course) but I believe it is about 40 Kt to 120 Kt.
On the subject of the 76 tail rotor, why does it look so un-aerodynamic??
It has lumps and bumps and odd bits that look like they don't help generate lift at all, and then about halfway out it turns into an aerofoil.
Is it because there is little appreciable lift/drag until about half the span, so you can use the first half for strength and the outer bit for effect?
It has lumps and bumps and odd bits that look like they don't help generate lift at all, and then about halfway out it turns into an aerofoil.
Is it because there is little appreciable lift/drag until about half the span, so you can use the first half for strength and the outer bit for effect?
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Ascend,
The tail rotor on the 76 is very similar to that on the Black Hawk, that bolted joint at the mid span is the biggest difference. The BH as a bonded joint where the blade cuff meets the spar - recall that the spar twists to allow feathering, and the twisting force is applied through the cuff and through that joint. The CF from the cuff is also resolved at that joint, so it is a busy place.
It happened that the 76 TR was being designed as the BH TR was being tested, and some difficulties were being identified with the bond at that time. Because there was some doubt about how easily it would be solved, the S-76 designer (a fantastic guy named Al Albert, who also lead the design teams for the Black Hawk, the XH-59 ABC and the S-67 Blackhawk) said "Just bolt it and forget about it." The lumps are the smoothed over blot and nut heads.
Regarding its aerodynamic cleanliness, K. D. Wood, an Aero Professor who wrote a great design book said "If it looks like a wing, it will fly almost as good as the best wing." The S-76 can go 50 knots sideward at max gross, so those buried bolt-heads don't harm things that much. Sure does look like a sack full of doorknobs, though.
The tail rotor on the 76 is very similar to that on the Black Hawk, that bolted joint at the mid span is the biggest difference. The BH as a bonded joint where the blade cuff meets the spar - recall that the spar twists to allow feathering, and the twisting force is applied through the cuff and through that joint. The CF from the cuff is also resolved at that joint, so it is a busy place.
It happened that the 76 TR was being designed as the BH TR was being tested, and some difficulties were being identified with the bond at that time. Because there was some doubt about how easily it would be solved, the S-76 designer (a fantastic guy named Al Albert, who also lead the design teams for the Black Hawk, the XH-59 ABC and the S-67 Blackhawk) said "Just bolt it and forget about it." The lumps are the smoothed over blot and nut heads.
Regarding its aerodynamic cleanliness, K. D. Wood, an Aero Professor who wrote a great design book said "If it looks like a wing, it will fly almost as good as the best wing." The S-76 can go 50 knots sideward at max gross, so those buried bolt-heads don't harm things that much. Sure does look like a sack full of doorknobs, though.
