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AW169

Old 11th Feb 2016, 11:38
  #41 (permalink)  
 
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Thanks for the pictures John,

Now I Understand why AW (sorry Finmeccanica Helicopters) has delivered just 8 AW109 last year, customers were waiting for this very nice machine !
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Old 11th Feb 2016, 11:42
  #42 (permalink)  
 
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Why this concern about OEI and the unusable fuel on the failed side?

If you are OEI, the good engine gets what it needs. You actually have better fuel endurance since only one engine is running. Once you get down to the flange, you still have sufficient fuel from the good side for your 20-minute reserve.

If you are OEI and you are already below the flange, you would logically be within landing distance from somewhere to go. If you are not, what were you doing there in the first place?

Boost pumps in the 139 are only there to provide the initial pressure for engine start. They are not actually necessary in flight. If you lose an engine, you have the very same condition as above. The only difference is in the case of a pump failure on the good engine side. Crossfeeding will give access to that "20-min" fuel on the opposite side. So, in the end, the two aircraft have the same fuel capability.
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Old 11th Feb 2016, 12:16
  #43 (permalink)  
 
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I agree that the boost pumps are only there for initial starting, once running the engines are quite capable of drawing fuel from the tank.

But.... Have you ever lost prime in a 76? What a pain in the backside when you lose prime on the engines.

And John is correct, there is no Xfeed in the 169, so if OEI that 200 liters is not available to you. 200 liters on the good side when OEI is 35 minutes flying at max power.
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Old 11th Feb 2016, 12:42
  #44 (permalink)  
 
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Crossfeeding will give access to that "20-min" fuel on the opposite side.
Let's see....OEI cruise fuel burn 300 Kgs/hr, fuel below the flange 228 kgs.....math is sure not my strong suit but I'm pretty sure that is not 20 mins.

So having a flame out and forced landing with about 45 mins fuel left onboard seems ok to you?
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Old 11th Feb 2016, 12:50
  #45 (permalink)  
 
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Very good video that TalkSpike posted, someone went thru a lot of trouble to make that.

Pay very close attention to what he says at time 4:06...."don't forget to do that"
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Old 11th Feb 2016, 16:01
  #46 (permalink)  
 
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Outwest et al

There is no crossfeed so the calculations are even simpler. No OEI performance data in the Section 9 of the RFM yet so we will have to wait and see how the fuel consumption works out but as you say, nobody is going to be excited at the prospects of losing access to that much fuel.

G.
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Old 11th Feb 2016, 16:29
  #47 (permalink)  
 
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[Let's see....OEI cruise fuel burn 300 Kgs/hr, fuel below the flange 228 kgs.....math is sure not my strong suit but I'm pretty sure that is not 20 mins.].

Sorry, early morning brain fade on the number. The quotation marks were to indicate approximate 139 OEI value but should have been more like "~45 min".
I have confirmed there is no crossed valve of any kind in the 169. It is not necessary and I suspect it could not be certified without boost pumps (can't compare to older designs with different engines and fuel configurations subject to different - some now outdated - certification standards). No offense intended to other types.
Each engine draws fuel from it's on-side tank. Since the tanks are inter-connected like the 139, engine fuel is essentially combined until the flange is reached (collector cell capacity app. 160kgs). This is to assure at least one engine has fuel in case of a tank leak. It's one of the ways to meet twin-engine certification requirement for independent fuel supply. If OEI, the only unusable fuel is on the failed engine side, but only once the flange level is reached.
Not having boost pumps saves cost/weight/etc. The only drawback is that the collector cell fuel unavailable in case of OEI.
Regardless, most of us always want more fuel but if that unavailable fuel is a concern when OEI, I repeat my question: Why, by that time in the flight, would you still be out of range of a place to land. Baring some significant other problem, I just can't figure that out. What am I missing?
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Old 11th Feb 2016, 16:54
  #48 (permalink)  
 
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HLCPTR. How about this: you don't get in with your IFR approach at the destination, as the weather has deteriorated. Now you need to fly a missed approach, route to your alternate, and fly another IFR approach. If you have lost access to a significant portion of your fuel in the event of OEI, (= range + endurance) this makes for interesting fuel planning for commercial IFR operators.
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Old 11th Feb 2016, 18:38
  #49 (permalink)  
 
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As I said:
Baring some significant other problem.

More fuel is always better than less if you have the power to haul it around and you can use it. But ultimately, this configuration is certified per the relevant regulations, so it's not as if it's deficient.

Just not optimal to some.

We are as one!
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Old 11th Feb 2016, 20:53
  #50 (permalink)  
 
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HLCPTR

That argument doesn't stand up if your national regulator insists on the carriage of 200 litres of additional fuel as that amount may become unusable following a single failure.

G.
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Old 11th Feb 2016, 21:09
  #51 (permalink)  
 
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Then I would suspect that your national regulator might not certify the aircraft if it insists on that amount following an engine failure.
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Old 11th Feb 2016, 21:22
  #52 (permalink)  
 
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You're a weird mob. Fancy arguing that it is perfectly reasonable to face a possible (remote, but nonetheless possible) scenario where you have a functioning machine flying on one engine but unable to access ~45 minutes of fuel.

Maybe it suits some to take a contrary view, for the sake of it
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Old 11th Feb 2016, 22:51
  #53 (permalink)  
 
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So it would appear in a twin, it's more likely a fuel tank will fail than an engine. Astonishing!
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Old 12th Feb 2016, 01:40
  #54 (permalink)  
 
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Chop jock HLCPTR

That said there is no denying that aviation authorities have always insisted on engine accountability within their possible failure scenarios. There's none that I've come across that will allow the predication of fuel requirements post-OEI on the basis of the OEI fuel consumption.

Anyway it's always been the case that fuel planning arrangements are an operational facet of regulation - not a certification aspect. There is no doubt that the 169 fuel system complies otherwise it would not be certified but what is then required to meet the required operating standards is another matter.

My bet is that it would need a very strong case to find a way around the current rules and the jury is out on that pending publication of the necessary data in the Part 9 of the RFM. I still think we will see a mod at some stage and my guess is that it would be a low level connector pipe between the two tanks with a valve in the line and a switch in the cockpit. Light weight and simple.

The 169 is shaping up well and has the makings of another big success for the Helicopter Division of Finmeccanica. There are just a few wrinkles to smooth out along the way. One wrinkle to fix will be the company name as that's a bit of a mouthful as it stands, maybe 'HDF' will do it.


G.
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Old 12th Feb 2016, 07:13
  #55 (permalink)  
 
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Any empty weight [no crew, no fuel] for a given configuration?
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Old 12th Feb 2016, 14:19
  #56 (permalink)  
 
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Geoffers, the solution to this perceived problem is actually a lot simpler than that. Put in a XFEED valve.
That is all that is different about this fuel system.
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Old 12th Feb 2016, 14:44
  #57 (permalink)  
 
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Nooby

See my earlier post. Methinks this is one reason why a cross-feed alone will not work.

The laws of physics dictate that if the engine sucks through the crossfeed then in theory both tanks will supply the one live engine. I suspect that those same laws of physics will generate a pressure drop across the crossfeed lines leading to a preferential supply from the most direct tank - the one supplying the live engine.

As the fuel level drops the imbalance will grow until the live engine's supply runs out. This will turn into a big headache because once the engine sucks air it will wrap its hand in. Methinks that hauling that inaccessible fuel (200 litres?) around will become tiresome for it can never be part of your reserves.

G.
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Old 12th Feb 2016, 15:51
  #58 (permalink)  
 
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Geoffers, surely that is only valid if the crossfeed is permanently open? A simple switch to open and close it would ensure each engine feeds from its own tank unless you choose otherwise (in the event of emergency or simply fuel balancing). Although without booster pumps, balancing might be trickier.
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Old 12th Feb 2016, 19:28
  #59 (permalink)  
 
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Crab

Imagine a 'H' shape with the tanks at the bottom of each leg and the fuel valve on the top of each leg. After each fuel valve will be the engine driven pumps sucking the fuel.

The crossed line is the horizontal part of the 'H" with the valve in the middle. That bit would be the same as the 139 but whereas we have booster pumps the 169 doesn't.

With the crossfeed valve closed each engine sucks from it's own tank - no problem. If you lose an engine then the fuel will be consumed by the remaining engine until the tank splits into two at the the 200L/200L mark. The live engine suction pump cannot then access the other tank so 200L is unavailable. Open the crossfeed and the engine driven pump should (I don't know for sure) have enough puff to suck from both tanks. My intuition tells me that there will be an uneven rate of pick-up that favours the live engine's tank due to a small pressure drop across the crossfeed line and valve. You would have to close the crossfeed as the live engine's tank approach the minimum in order to avoid sucking air.

There would be an unknown and possibly variable amount that remains inaccessible. That's why I favour the low level connector between the two tanks as there would be much less unusable fuel at the end of the day. A valve controlled by a guarded and (tell-tale) wire-locked switch in the cockpit would do the job. We had such an arrangement in the S61N and some S76B's.

The 169 tank(s) are similar in layout to the 139/189 in true 'family' style.

G.
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Old 12th Feb 2016, 21:04
  #60 (permalink)  
 
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Geoffers - sorry to cause confusion but I was assuming the crossfeed would be in a pipe that is fed from the bottom legs of the H, not the middle.

The alternative is a transfer pump but again that would need to suck from the bottom of each tank - putting the interconnect so high up seems a very odd design choice.
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