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surrodox2001
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747-200/300 with GE engines...Why the lower fuel capacity?

Mon Apr 20, 2020 9:28 am

I assume we're going to get a lower range with this.

According to StartupBoeing's 747 classic PDF, Boeing gives a lower fuel capacity (few hundred gallons) for the GE engines in 747-200/300 compared to PW and RR engines.

Why we're getting a lower fuel capacity with GE? I don't think engine weight and MTOW is to blame as GEs have the same MTOW with other engines (833k)
and it's engine weight is right in the middle (PW-GE-RR) though.

Can someone enlighten me about this?
 
StereoTechque
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Mon Apr 20, 2020 11:28 am

Slightly off topic, the A320 with IAE engines have a slightly less Wing Tank capacity than the CFM counterparts due to the incorportaion of a Dry Bay inside the the Wing cell around the pylon area for additional safety. This can be a reason, however just a wild guess.
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mmo
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Mon Apr 20, 2020 3:11 pm

It could be just a situation where the temp of the fuel was different on the day the aircraft. And the VTO closed at a slightly earlier point. I can't think of any major structural differences so it should be pretty close on all aircraft.
If we weren't all crazy we'd all go insane!
 
surrodox2001
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Mon Apr 20, 2020 5:00 pm

mmo wrote:
And the VTO closed at a slightly earlier point.


What's a VTO?
 
mmo
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Mon Apr 20, 2020 6:00 pm

It is a switch that closes the fuel valve for a respective tank when it is full by volume. Depending on the density of the fuel the tanks could be full by volume and not be full by weight and visa versa. The difference in weight is within the realm of possibility given the total amount of fuel carried.
If we weren't all crazy we'd all go insane!
 
strfyr51
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Tue Apr 21, 2020 12:06 am

surrodox2001 wrote:
mmo wrote:
And the VTO closed at a slightly earlier point.


What's a VTO?

Volumetric top off. it shuts down wing fueling when it senses full. It can be set and calibrated by the airline as we had to check it coming out of a heavy check every year at United on our Maintenance fuel pits. it had to be pumped in at 20 PSI to locate the topoff point toward the end of fueling. it got to be if you had the APU Running, all you were doing was replenishing what the APU was burning. On our -422's we usually got to around 375K/Lbs fuel .
 
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77west
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Tue Apr 21, 2020 2:56 am

I think slightly different plumbing also affects this figure.
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andrej
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Tue Apr 21, 2020 10:13 am

I think that 77west is correct. Plumbing is different on respective engine variants.
Even various engines for B744 have different capacity for different engines (GE vs. PW/RR).

BTW, thanks for link to that pdf file. Very informative, especially the Mission Profile slide!
 
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747classic
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Tue Apr 21, 2020 1:16 pm

The mentioned Boeing PDF file contains a lot of errors, so far I was able to check on short notice :

- Page 23 : 747-200 engines is completely incorrect
- Page 24 : 747-300combi (Air india) powered by CF6-80C2B1 engines has also been produced.

IMHO an inaccurate copy/paste PR product, not checked afterwards by a technical expert.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
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jetmech
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Tue Apr 21, 2020 2:04 pm

surrodox2001 wrote:
Why we're getting a lower fuel capacity with GE?

StereoTechque wrote:
Slightly off topic, the A320 with IAE engines have a slightly less Wing Tank capacity than the CFM counterparts due to the incorportaion of a Dry Bay inside the the Wing cell around the pylon area for additional safety. This can be a reason, however just a wild guess.

I think this is the reason. The GE 742 / 743 (and 744) has dry bays above the #1 and #4 engine positions in #1 main and #4 main tanks. From what I've been told, this has to do with fire safety in the case of a turbine failure.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
surrodox2001
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Tue Apr 21, 2020 2:52 pm

747classic wrote:
The mentioned Boeing PDF file contains a lot of errors, so far I was able to check on short notice :

- Page 23 : 747-200 engines is completely incorrect
- Page 24 : 747-300combi (Air india) powered by CF6-80C2B1 engines has also been produced.

IMHO an inaccurate copy/paste PR product, not checked afterwards by a technical expert.


It looks like a badly scanned copy too. I think it's problems on Boeing part, but other specs are quite accurate. (Engine thrust, etc)
 
surrodox2001
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Tue Apr 21, 2020 2:54 pm

jetmech wrote:
surrodox2001 wrote:
Why we're getting a lower fuel capacity with GE?

StereoTechque wrote:
Slightly off topic, the A320 with IAE engines have a slightly less Wing Tank capacity than the CFM counterparts due to the incorportaion of a Dry Bay inside the the Wing cell around the pylon area for additional safety. This can be a reason, however just a wild guess.

I think this is the reason. The GE 742 / 743 (and 744) has dry bays above the #1 and #4 engine positions in #1 main and #4 main tanks. From what I've been told, this has to do with fire safety in the case of a turbine failure.

Regards, JetMech


But why we need dry bays on GE when others don't? Higher RPMs? (CF6s can rev quite high up over 100%, at least in DC-10s.) Newer design?
 
GalaxyFlyer
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Tue Apr 21, 2020 3:12 pm

The GE engine is longer than PW, so the turbine safety zone is further back in the wing. Just a guess but that’s a factor in other designs.
 
surrodox2001
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Tue Apr 21, 2020 3:35 pm

The GE engine is longer than PW, so the turbine safety zone is further back in the wing. Just a guess but that’s a factor in other designs.

What about RR? I think RR, PW's engine is also quite long too in terms of complete engine.
 
GalaxyFlyer
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Tue Apr 21, 2020 7:31 pm

RR with three spools was the shortest, hence the L1011 design.
 
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747classic
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Wed Apr 22, 2020 8:45 am

GalaxyFlyer wrote:
The GE engine is longer than PW, so the turbine safety zone is further back in the wing. Just a guess but that’s a factor in other designs.


It could be a turbine safety feature, but the 747 pylon has been redesigned for the CF6 engine, our two early built 747-200 aircraft (L/N 271 and 276) were original equipped with adapted JT9D pylons, but the inboard pylons were later replaced by the later redesigned special GE pylons, due excessive movements (under large loads) of the adapted pylons, causing several hydraulic system pylon panels (rear pylon panels) to disappear during flight. Also the outboard pylons were on later aircraft redesigned, but the adapted outboard JT9D pylons were retained on these two aircraft.

The GE CF6 engines are attached to the pylon by mounting points on the core. GE claims that this provides a lower engine weight and avoids the introduction of loads into the fan casing.
By way of contrast, both Rolls-Royce and P&W have chosen forward mounting points on the fan casing for the RB.211 and JT9D, and suggest that this allows the use of a lighter pod.

At that point in time the GE CF6 claimed to be 5% more fuel efficient than the JT9D-7, the later certified RR engine had a lower TSFC , but was far heavier, thus reducing the max payload.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
AC320tech
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Wed Apr 22, 2020 7:37 pm

747classic wrote:
At that point in time the GE CF6 claimed to be 5% more fuel efficient than the JT9D-7, the later certified RR engine had a lower TSFC , but was far heavier, thus reducing the max payload.


Did the lower fuel capacity on CF6 747s reduce the range much? Not to totally derail the thread, but were the later model JT9Ds better than the CF6 and RB211?
 
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747classic
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Re: 747-200/300 with GE engines...Why the lower fuel capacity?

Thu Apr 23, 2020 10:10 am

The question of the thread starter intrigued me, so I decided to search my 747 libary room for some info .

I found in my old 747 Aircaft Operation Manual the following :

PH-BUA -BUG (PW JT9D-7W powered), 7 fuel tanks

Wings full ------- 102.960 kgs : Reserve 1&4, both 1500 kgs, Main1 &4 both 13.260 kgs, Main 2&3 both 36.720 kgs (3.0 kg/USG)
Center wing tank 50.070 kgs
Max total fuel ---153.030 kgs.

PH-BUH - BUM (GE CF6-50E2 powered), 7 fuel tanks
Wings full ------- 102.300 kgs : Reserve 1&4, both 1500 kgs, Main1 &4 both 12.750 kgs, Main 2&3 both 36.900 kgs (3.0 kg/USG)
Center wing tank 51.000 kgs
Max total fuel ---153.300 kgs

PH-BUN & on (Volumetric Top Off adjusted), 7 fuel tanks
Wings full ------- 104.280 kgs : Reserve 1&4, both 1530 kgs, Main1 &4 both 12.960 kgs, Main 2&3 both 37.650 kgs (3.0 kg/USG)
Center wing tank 51.480 kgs
Max total fuel ---155.760 kgs

Both main tanks 1 &4 seem to have a slightly reduced volume *, with GE engines installed, however this compensated by larger quantities in Main 2 & 3 and the CW tank.
Total fuel quantity can be increased by optimal VTO adjustment.

Most probably (only one source, not confirmed by multiple sources) the max allowable M1 and M4 fuel qty has been reduced, because during flight testing with GE CF-6-50D engines at the 747 prototype during 1974, some wing flutter was observed due the heavier weight and different installation of the GE engines, compared to the JT9D.
Operating a twin over the ocean, you're always one engine failure from a total emergency.

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