Ferry flight - single engine debate
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Joined: Mar 2008
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From: South Africa
Ferry flight - single engine debate
An interesting topic came up in a discussion on ferry flights, and I would appreciate some input from all the experience out there.
Question - Why not fly on one engine at normal flight power, and the other at idle ? We are obviously talking twin engine helicopter here, ferry flight with no pax and the reason for stretching the flight is to avoid a costly dogleg to refuel en route. Cruise also at a height that would allow enough time to bring up the other engine from idle, should one have to enter autorotation from a cruise on the engine at flight power.
I expect the saving in range might not be all that much, but could be just sufficient to make the difference.
It would be interesting to see what figures drivers out there might come up with, hopefully from personal experience.
Keep the revs up fellows, the moon is yellow tonight.
Question - Why not fly on one engine at normal flight power, and the other at idle ? We are obviously talking twin engine helicopter here, ferry flight with no pax and the reason for stretching the flight is to avoid a costly dogleg to refuel en route. Cruise also at a height that would allow enough time to bring up the other engine from idle, should one have to enter autorotation from a cruise on the engine at flight power.
I expect the saving in range might not be all that much, but could be just sufficient to make the difference.
It would be interesting to see what figures drivers out there might come up with, hopefully from personal experience.
Keep the revs up fellows, the moon is yellow tonight.
Avoid imitations
Joined: Nov 2000
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From: Wandering the FIR and cyberspace often at highly unsociable times
One at idle? This would most likely result in an overall increase in fuel consumption, not a saving. At idle a turbine engine consumes a considerable amount of fuel for no useful output to the transmission - it would disengage.
Think OEI transmission limits, this isn't an emergency so normal limits would apply, resulting in a reduced cruise speed.
For example, normal cruise Tqs = 80/80% = 160% total.
When OEI, 100%/0% = 100% total.
If flying into a headwind, the range might be considerably reduced.
If one engine were completely shut down, the extra "idle" fuel wouldn't be consumed but the OEI limits still apply. Again, the headwind would need to be considered. Endurance would be increased, but possibly not range.
Think OEI transmission limits, this isn't an emergency so normal limits would apply, resulting in a reduced cruise speed.
For example, normal cruise Tqs = 80/80% = 160% total.
When OEI, 100%/0% = 100% total.
If flying into a headwind, the range might be considerably reduced.
If one engine were completely shut down, the extra "idle" fuel wouldn't be consumed but the OEI limits still apply. Again, the headwind would need to be considered. Endurance would be increased, but possibly not range.
Joined: May 2007
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From: Worldwide
avoid a costly dogleg to refuel en route
If a/c ferried for maintenance or relocation of base etc., the cost must have been part of the decision making process for base location.
In the end, if your particular type twin delivers similar TAS with single engine, why not remove the other engine? This will increase your payload (tools, lubes etc.) for the ferry and will make bean counters even happier! (I'm hoping it is them wanting you to save costly dogleg, I personally don't mind the break after 2-3 hrs in the saddle).
Final question. Do you drive your five speed motor vehicle in third, on the red line, to maintain 80mph, just because it is able to?
........wow, which side of the bed did I get up from this morning
......ps: Management, 6P's
Joined: Jul 2001
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From: the cockpit
Actually, the thought process is sound in one respect: the turbine engine of helicopters is far more efficient at high power settings such as that required by an OEI situation, that is, the helicopter will have increased range (headwinds aside) OEI.
Because of the enormous (and sometimes ill-informed) customer desire for "full CAT A", modern twins are being fitted with two huge engines that are each capable fo OEI flight across the weight range of the helicopter. To achieve this, the engines run at a low power setting when AEO, and thus are running very innefficiently. The lack of range in the AW139 is testament to this issue.
An engine left at idle will, however, burn more fuel than that saved by the more efficient power setting of the one left taking the load. So dont do it to increase range in a ferry flight. If you are in an emergency situation and running short of fuel with no where to land, you will increase your range by shutting down one of the donks - though make sure the wind profile supports this as stronger headwinds will reverse the equation.
Why would I only do this in an emergency? despite all the engineering specs, etc, there have been too many stories of transmissions damaged by extended flight on one engine to make it worth considering unless life was at issue.
Because of the enormous (and sometimes ill-informed) customer desire for "full CAT A", modern twins are being fitted with two huge engines that are each capable fo OEI flight across the weight range of the helicopter. To achieve this, the engines run at a low power setting when AEO, and thus are running very innefficiently. The lack of range in the AW139 is testament to this issue.
An engine left at idle will, however, burn more fuel than that saved by the more efficient power setting of the one left taking the load. So dont do it to increase range in a ferry flight. If you are in an emergency situation and running short of fuel with no where to land, you will increase your range by shutting down one of the donks - though make sure the wind profile supports this as stronger headwinds will reverse the equation.
Why would I only do this in an emergency? despite all the engineering specs, etc, there have been too many stories of transmissions damaged by extended flight on one engine to make it worth considering unless life was at issue.
Joined: Jul 2008
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From: Midwoud, the Netherlands
Another thing to consider might be that you will get a split in your fueltanks. With the S76b you can have an acceptable fuelsplit of 250 lbs. If the split becomes more we have to consider crossfeeding or shifting pax to get the w&b within limits. Crossfeeding in flight is in our sop an emergency procedure only. Single engine this split will be reached within 40 minutes.
The other thing you could do is swithching between the engines. 30 minutes idling engine #1 followed by 60 minutes idling engine #2. I think that you will be asking for problems as a mistake can always be made.
The other thing you could do is swithching between the engines. 30 minutes idling engine #1 followed by 60 minutes idling engine #2. I think that you will be asking for problems as a mistake can always be made.
Joined: Feb 2002
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From: N20,W99
The Bell 206LT had a procedure where you could SHUT DOWN an engine in cruise and then get it spinning again before landing.
I don't know what the reasoning behind it was. Time keeping had to be nightmare.
I don't know what the reasoning behind it was. Time keeping had to be nightmare.
Joined: Mar 2008
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From: A land not far from here.
I wouldnt agree with idling an engine to reduce the fuel consumption, because as stated above the turbines use more fuel when at idle!!!
Turbines prefer power and more fuel, as the more heat created from combustion of fuel ensures no surging and the like, i dont really keep the theorectical terms in me head, i just know how they operate! Either way, a turbine is more economic at full torque than idle.. believe it or not!!!
I will try and get the location of this info for you via a link as to ensure its not crap! (For all i know i could of been fed sh1te info!!) Hold on....!
Turbines prefer power and more fuel, as the more heat created from combustion of fuel ensures no surging and the like, i dont really keep the theorectical terms in me head, i just know how they operate! Either way, a turbine is more economic at full torque than idle.. believe it or not!!!
I will try and get the location of this info for you via a link as to ensure its not crap! (For all i know i could of been fed sh1te info!!) Hold on....!
Joined: Aug 2001
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From: Cornwall
single engine ops
Before diving into the performance section of the RFM check out the rest of it first. If it does not offer you the opportunity to cruise on one engine then at least check it out with the regulators before going down that road. In the UK, and probably in the rest of EASA-land you would have to demonstrate in your Ops Manual that the risks involved are in no way increased - which is a bit tricky!!!
I know of only one twin helicopter certified for single engine flight and that is the independently developed 'Gemini' version of the Longranger which, if my memory serves me right was eventually taken over by Bell. I assume this unique approval was due to the fact that it was originally certified as a 'single' and the second engine was an addition.
G
I know of only one twin helicopter certified for single engine flight and that is the independently developed 'Gemini' version of the Longranger which, if my memory serves me right was eventually taken over by Bell. I assume this unique approval was due to the fact that it was originally certified as a 'single' and the second engine was an addition.
G
