External load VNE
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External load VNE
while doing recurrent training the discussion of external load VNE came up. the 350 has a VNE of 80 knots. up until yesterday i had always been under the impression that this was to keep the empty longline out of the tail rotor. a very exprienced training pilot stated that it would be very difficult to get the LL in the t/r at even higher speeds. he stated that in bell products with the semi-rigid rotor system, there is a limit due to "mast bending" which is hard on the m/r transmission (as one would guess, given the name).
any thoughts on why the 350 for example, has an external load VNE?
any thoughts on why the 350 for example, has an external load VNE?
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Firstly, a longline with an empty hook can-has-and will end up in your tail rotor especially while decending at high speeds if you fail to consider the following. The factors to consider are longline length, type of longline (Steel, spectra, rope, or other) and the weight of the hook. Some lines with multiple hook control wires can have major aerodynamic drag so be carefull.
I assume that when you are conducting external load operations you have a door off, perhaps this is the reason for the VNE restriction.
Are you sure your training pilot said "mast bending" and not MAST BUMPING?
Cheers,
FA
I assume that when you are conducting external load operations you have a door off, perhaps this is the reason for the VNE restriction.
Are you sure your training pilot said "mast bending" and not MAST BUMPING?
Cheers,
FA
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1. You can get a long line in your T/R ..... in fact a friend of mine killed himself in New Guinea when he got a line up in his Hughes 500 T/R.
2. Both the Bell 212 and the 412 also have a sling Vne of 80 kts.
Reason ....don't know ...could be that they have only flown the A/C up to that speed to prove safety and controllability ... saves money not having to fly more ... so they make that the (somewhat artificial) speed limit!
Cheers
2. Both the Bell 212 and the 412 also have a sling Vne of 80 kts.
Reason ....don't know ...could be that they have only flown the A/C up to that speed to prove safety and controllability ... saves money not having to fly more ... so they make that the (somewhat artificial) speed limit!
Cheers
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Mast bending? Possibly - there is a couple between the rotor hub and the ship C of G.
The Bell 206 limit is thou shalt not pull more than 85% torque at speeds over 80 kts - one reason is because the mast is quite long, so there is a powerful moment arm which will increase upper mast bearing wear, and to prevent mast bending stresses.
Dunno why the AS 350 has it - I doubt whether a load would fly at more than about 60 kts anyway
phil
The Bell 206 limit is thou shalt not pull more than 85% torque at speeds over 80 kts - one reason is because the mast is quite long, so there is a powerful moment arm which will increase upper mast bearing wear, and to prevent mast bending stresses.
Dunno why the AS 350 has it - I doubt whether a load would fly at more than about 60 kts anyway
phil
fu 24 950,
You obviously don't know who Paco actually is. Not only is Paco a 'load lifting pilot', but he writes books on the subject. Or at least, 'chapters' in books.
A google search for 'Phil Croucher' should reveal all.
You obviously don't know who Paco actually is. Not only is Paco a 'load lifting pilot', but he writes books on the subject. Or at least, 'chapters' in books.
A google search for 'Phil Croucher' should reveal all.
Moderator
Though not an expert at this, I am aware of the "mast bending" issue. Mast bending is evaluated for drag inducing modifications to helicopters, I'm sure a long line qualifies.
All helicopters have masts. During a perfect hover, masts are loaded in tension and torque only, because the rotor is producing lift and torque only. Once the helicopter flies in a direction, the rotor is also producing thrust. The mast is then being "bent" to also produce thrust.
During original design approval, the mast strength is evaluated to assure that it will withstand all of the loads applied to it. This evaluation will be one of the considerations in determining the Vne. If the drag of the total helicopter is later increased by modification, the thrust must be increased to overcome the increased drag. This means that to fly at the original Vne, with more drag that originally considered, will result in more bending of the mast than originally considered by the manufacturer. In the absence of a complete re-evaluation of the strength of the mast (very costly engineering), modifiers will probably elect to accept a reduced Vne with the modification to assure that no additional bending loads are imposed on the mast.
There is a simplified flight test procedure to establish an appropriate Vne, which is conducted during the design approval program.
All of this is completely distinct from mast bumping.
So, if a pilot exceeds a reduced Vne with an external mod or load, they are exploring a previously unexplored realm in that helicopter.
I hope that helps,
Pilot DAR
All helicopters have masts. During a perfect hover, masts are loaded in tension and torque only, because the rotor is producing lift and torque only. Once the helicopter flies in a direction, the rotor is also producing thrust. The mast is then being "bent" to also produce thrust.
During original design approval, the mast strength is evaluated to assure that it will withstand all of the loads applied to it. This evaluation will be one of the considerations in determining the Vne. If the drag of the total helicopter is later increased by modification, the thrust must be increased to overcome the increased drag. This means that to fly at the original Vne, with more drag that originally considered, will result in more bending of the mast than originally considered by the manufacturer. In the absence of a complete re-evaluation of the strength of the mast (very costly engineering), modifiers will probably elect to accept a reduced Vne with the modification to assure that no additional bending loads are imposed on the mast.
There is a simplified flight test procedure to establish an appropriate Vne, which is conducted during the design approval program.
All of this is completely distinct from mast bumping.
So, if a pilot exceeds a reduced Vne with an external mod or load, they are exploring a previously unexplored realm in that helicopter.
I hope that helps,
Pilot DAR
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Of course, it depends on the load - I've not managed to get an Argo over 45 kts, even with a net to disturb the airflow. The perfect load of course will take a lot of speed, but my experience is that there is no such thing. About 60 is my comfort zone when the max VNE is 80. I like those margins!
Phil
Phil
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Yup, a bloody great amphibian with eight wheels, and can come with a frame on top that weighs an extra 140 lbs. With mud, probably another 50, and comes just inside the payload range of a 206L by 1 pound if you take the ski basket off and remove the survival kit. When you have to land with 140 lbs of fuel, it doesn't leave you much range!
Tip: Make sure you get the customers to tell you when they have left two spare batteries in the back!
Thanks, DAR for your explanation
Phil
Tip: Make sure you get the customers to tell you when they have left two spare batteries in the back!
Thanks, DAR for your explanation
Phil
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I once asked the experimental test pilot who carried out the certification on this aspect on the AS 350 this very question.
His answer was that he didn’t think that anyone would want to fly any faster than 80 knots with an external load and that consequently he didn’t carry out the testing necessary to certify it at a higher speed. He didn’t think that it was worth the financial investment necessary to expand the envelope.
His answer was that he didn’t think that anyone would want to fly any faster than 80 knots with an external load and that consequently he didn’t carry out the testing necessary to certify it at a higher speed. He didn’t think that it was worth the financial investment necessary to expand the envelope.
Avoid imitations
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The "Vne" limit is aircraft orientated, not load orientated.
The UK military use an Air Publication (1105? It's been a long time) issued by a specialist unit (JATE, used to be based at Brize Norton in my time) which flew USL trials and issued a clearances for specific loads, giving detailed rigging instructions and any limitations, warnings etc.
Some dense, heavy underslung loads we used to fly under the Puma would do 120 kts plus. Trick was to get the "mutual support" Wessex pilot to call "Buster!" on the Tac radio, meaning he couldn't keep up - without an underslung load!
The UK military use an Air Publication (1105? It's been a long time) issued by a specialist unit (JATE, used to be based at Brize Norton in my time) which flew USL trials and issued a clearances for specific loads, giving detailed rigging instructions and any limitations, warnings etc.
Some dense, heavy underslung loads we used to fly under the Puma would do 120 kts plus. Trick was to get the "mutual support" Wessex pilot to call "Buster!" on the Tac radio, meaning he couldn't keep up - without an underslung load!
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Just watching the logging boys yarding 10,000-20,000lbs of logs off a cut block 2000ft above a water drop.... They can go really fast.....
All kinds of loads will fly at a higher speed than 80kts, as will an empty long line. Just make sure the line is long enough, and with a heavy enough hook on it. Also be really careful slowing down with rear cyclic input in a decent, other than that, you should be just fine.
RH
All kinds of loads will fly at a higher speed than 80kts, as will an empty long line. Just make sure the line is long enough, and with a heavy enough hook on it. Also be really careful slowing down with rear cyclic input in a decent, other than that, you should be just fine.
RH
It may be due to this "mast bending" I remember for instance that the AS355 had speed limitations in relation with long line length, I think the slowest was around 30Kts with a 200 feet line.But it seems weird with articulated rotors...
In this case, don't you think the torque instead of speed is rather to be considered ?
On older helicopters I have flown (lama, alouette 3...) the limiting speed was based on load behaving.
I have witnessed AS 350 B3 currently flying their loads or empty lines/long lines at more than 80 Kts (.... myself included I should say) especially without load.
Beside the long line behaving, another thing we had to take care, was to avoid the cargo-swing frame touching the hull. Normally shouldn't happen on smooth normal ops.
In this case, don't you think the torque instead of speed is rather to be considered ?
On older helicopters I have flown (lama, alouette 3...) the limiting speed was based on load behaving.
I have witnessed AS 350 B3 currently flying their loads or empty lines/long lines at more than 80 Kts (.... myself included I should say) especially without load.
Beside the long line behaving, another thing we had to take care, was to avoid the cargo-swing frame touching the hull. Normally shouldn't happen on smooth normal ops.
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Note: .....
For the "new chums" of course ..... a "sling Vne" being what it is of course means you should not go above that speed during normal operation of the aircraft .... whether the load will fly at a higher speed or not!!!
And we alll obey the rules ......DON'T WE ?
For the "new chums" of course ..... a "sling Vne" being what it is of course means you should not go above that speed during normal operation of the aircraft .... whether the load will fly at a higher speed or not!!!
And we alll obey the rules ......DON'T WE ?
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Depending on the load,350 easily exceeds that 80 kt limit with external load. I haven't exceeded it of course, but that's what the big boys have told me..
Last edited by Finnrotor.com; 24th Mar 2007 at 00:57.
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A heavy, dense load may hang nearer the vertical whereas a lighter load or one that has properties that may cause it to generate lift may trail somewhat more.
Depending on the drag of the load a much greater nose down attitude may be required to overcome the drag (trail angle) of the load. This may exceed forward cyclic design criteria.
A heavy load, although hanging nearer the vertical may generate large pendular forces at low speeds.
It is correct that with a wider variety of loads to carry the military has an organisation (JATE) that conducts trials in this area. It is however an expensive business.
Generally anything in a net has a 'blanket' clearance but it doesn't absolve the crew from having to assess the handling properties of the load themselves as to whether it is feasible.
A blanket VNE must be a way of giving a clearance without requiring every load to be individually cleared at great expense to the manufacturer. How could they ever assess everything that may be lifted I guess
HEDP
Depending on the drag of the load a much greater nose down attitude may be required to overcome the drag (trail angle) of the load. This may exceed forward cyclic design criteria.
A heavy load, although hanging nearer the vertical may generate large pendular forces at low speeds.
It is correct that with a wider variety of loads to carry the military has an organisation (JATE) that conducts trials in this area. It is however an expensive business.
Generally anything in a net has a 'blanket' clearance but it doesn't absolve the crew from having to assess the handling properties of the load themselves as to whether it is feasible.
A blanket VNE must be a way of giving a clearance without requiring every load to be individually cleared at great expense to the manufacturer. How could they ever assess everything that may be lifted I guess
HEDP