9v-svc
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Can An Aircraft Use 2 Different Types Of Engines?

Sun Apr 17, 2005 4:57 pm

For example :

A Boeing 777-200ER using GE engines . The first engine = GE90-94B and the second engine = GE90-115B . Is this possible ? Are there any airlines that are doing this arrangement?


Thanks

Charles
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RightWayUp
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Sun Apr 17, 2005 5:15 pm

I cannot comment re the 777, but on the 737 we used to sometimes have what is called an engine intermix. The more powerful engine is derated to the same level as the other engine, and we had to do full power takeoffs everytime. As long as the FMC was aware of the intermix we were allowed to use autothrottle.
 
IanatSTN
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Sun Apr 17, 2005 5:22 pm

9V-SVC

I was doing a database project a while back, and choose BA aircraft as my subject. I remember whilst doing my research seeing a BAE146 with 3x Lycoming LF507-1F engines, and 1 of another type, but unfortunately I can't remember the name.

So, the short answer to your question must be yes, it is possible to mix engine types.

Cheers,
Ian.
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LAXintl
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Sun Apr 17, 2005 6:01 pm

Have seen B747-100/200/300 operators quite frequently intermix engine types amongst the different Pratt sub variants.
The key always was that the performance was always based on the lowest thrust version. So in other words, if one had a mix of JT9D-7A, 7J, 7Q's etc they would consider all operating to the -7A limits.
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air2gxs
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Sun Apr 17, 2005 7:52 pm

Quoting Laxintl (Reply 3):
The key always was that the performance was always based on the lowest thrust version. So in other words, if one had a mix of JT9D-7A, 7J, 7Q's etc they would consider all operating to the -7A limits.

Not to be picky, but this intermix wouldn't work. The 7A & 7Q engines use different EGT's and acceleration curves. The only intermix I've ever seen on a Jumbo is a 7A/7AH intermix, which affects thrust ratings just a bit, but does not require any instrumentation change on the flight deck, except for an intermix placard.
 
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Jetlagged
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Sun Apr 17, 2005 8:59 pm

You can intermix a -7Q on a -7A, -7F, -7J aircraft so long you apply the correct thrust ratings. At the same EPR the -7Q will develop different thrust to the -7A/-7F/-7J, so derate charts which provide -7A/-7F/-7J thrust for a -7Q engine would be used, rather than the -7A/-7F/-7J EPR limits. The limit would be selected manually on the EPR gauge, not from the TAT/EPRL computer.

Regarding acceleration the difference is not noticeable unless you slam the throttles. It's likely that auto-throttle use would be avoided on takeoff and climb (not a big disadvantage on a 747 Classic). It could be used in cruise because it drives all four throttles together, through clutches. The odd engine throttle can be offset manually and this offset would be maintained.

EGT limits are lower on the -7Q, so ideally a different EGT gauge should be installed, but the crew should know and apply the limits without referring to the red line on the gauge. The difference in limits on the -7Q is mainly because the EGT is measured in a cooler part of the airflow, so although the limit is lower, EGT indications are also correspondingly lower too.

Intermixing is quite common (and safe) especially on fleets with a variety of engines installed. Better to fit an odd engine and get the aircraft back to a maintenance base, than wait for the correct engine to be flown out.

I worked on a 747 flight simulator years ago where one customer specification was for training with three -7F engines and one -7Q engine. Unusual, but it shows that it might be done in service.
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USAFMXOfficer
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Sun Apr 17, 2005 9:17 pm

Gotta love the intermix on the B-36...

Six P&W R-4360 Wasp Majors at 3,800 hp each....plus four GE J-47 Turbojets at 5,010 lbs thrust.

They used to say "Six turning and four burning...." when everything was fired up on the ground.

http://www.zianet.com/tmorris/6BWB-36formationbig.jpg
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air2gxs
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Sun Apr 17, 2005 9:21 pm

Jetlagged,

Agreed, but my concern is the EGT indication. If I remember correctly, it is substantially lower on the -7Q and may cause an issue during abnormal operations when the flight crew is operating from training and instinct (you know, emergencies). Also, isn't the -7J rated at a higher temerature due to design? We have indicators installed on our aircraft that will illuminate yellow and red lights when you have an impending excedence or excedence, respectively. Operating the -7J at its upper limits would cause the lights to illuminate without cause.

Just a couple of concerns I have intermixing the -7A and -7J and -7Q.
 
LAXintl
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Sun Apr 17, 2005 10:37 pm

The 747 Classic intermix is certainly something to keep the F/E busy, however is done routinely.
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OPNLguy
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Mon Apr 18, 2005 3:03 am

Quoting USAFMXOfficer (Reply 6):
Gotta love the intermix on the B-36...

The B-36 was the first thing that popped into my mind (Strategic Air Command was on just recently), but you beat me to it...  Wink
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B747FE
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Mon Apr 18, 2005 3:07 am

Quoting 9V-SVC (Thread starter):
Can An Aircraft Use 2 Different Types Of Engines?

As others have said, yes. The Engine Intermix involves the installation of different models of the same general engine type. In a mixed configuration, the airplane is operated and performance calculations made, per instructions in the airplane flight manual, to the lowest rated engine installed.
The intermix includes the installation of identification placards in the engine instrument panel and the revision of the AMM/AFM.


Now, regarding engine intermix in the 747 Classic:

* Rolls Royce RB211-524B2/C2/D4 engines can be intermixed.

* Pratt & Whitney JT9D-3A, -7, -7A, -7H, -7AH, -7F, -7J and -7Q can be intermixed.

* I don't know if intermix is allowed P&W JT9D-7R4 and -70 engines.

* I have no data about intermix with GE CF6-45/50/80.

There are several modifications to perform depending on the engine model, configuration and the applicability of certain Service Bulletins to the Airframe/Engine.

.Fire protection system compatibility (Kidde or Graviner)
.Turbine thrust reverser
.Water injection system
.Cowlings replacement
.Ignition requirements
.Engine bleeds configuration
.Engine indications (EGT, F/F, Breather Press, TCCS, Oil Qty indication......)

In the case of an intermix with -7Q engines, EGT indicators and Fuel Flow electronic module circuit card should be replaced.

Quoting Laxintl (Reply 8):
The 747 Classic intermix is certainly something to keep the F/E busy, however is done routinely.

Indeed, and not only the F/E. The amount of paper work involved is quite important.

Quoting Jetlagged (Reply 5):
It's likely that auto-throttle use would be avoided on takeoff and climb (not a big disadvantage on a 747 Classic).

Correct. Although it could be used, with intermix configuration we don't use FFRATS, manual engine trim is preferred.


Regards,
B747FE.
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ShyFlyer
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Mon Apr 18, 2005 4:19 am

It's done frequently in test programs:

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SlamClick
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Mon Apr 18, 2005 6:14 am


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Photo © Fred Hartman


How about these two types? Big radial, little jet. Both ran on avgas. Photographer is just a bit mistaken about the use of the jets - engines have no effect on "lift" and very little help shortening the takeoff roll. (Puny thrust rating.) They were really to help out in the event of the loss of one of the recips like a re-usable JATO.

* * *


Not sure of the real intent of the thread question. Having a JT-8D-7 on one side and a JT-8D-9 on the other is indeed an "intermix" but it is still the same "type" engine, just a different series.

I've not seen anything here yet about a production, normal category airplane having a non-symmetrical engine mix of different actual types, such as a RB-211 on one side and a CFM-56 on the other.
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troubleshooter
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Mon Apr 18, 2005 8:39 am

I have read somewhere that the Boeing 787 will be able to have either the GE or RR engines installed on the same mounts using the same engine-to-aircraft interfaces. But I doubt that we will see a 787 with a GE engine on one wing and one RR engine on the other.
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Accidentally
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Mon Apr 18, 2005 8:55 am

The 727 /RE has those big honkin JT8D-217 (think MD80) on the outboards and I think a -17 in the middle.

Heres some data - you can see the differences
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Jetlagged
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Mon Apr 18, 2005 9:07 am

Quoting Air2gxs (Reply 7):
Agreed, but my concern is the EGT indication. If I remember correctly, it is substantially lower on the -7Q and may cause an issue during abnormal operations when the flight crew is operating from training and instinct (you know, emergencies). Also, isn't the -7J rated at a higher temperature due to design? We have indicators installed on our aircraft that will illuminate yellow and red lights when you have an impending excedence or excedence, respectively. Operating the -7J at its upper limits would cause the lights to illuminate without cause.

All true, but you can get around all this by installing the correct EGT indicator for the engine. The -7J and -7F are the same engine aerodynamically, but the -7J has higher EGT limits due to design changes in the hot section. The -7Q has lower temperatures because they are measured further downstream.

Sounds like you have strip indicators (round dials only have amber lights) so installing a different EGT gauge for one engine is not possible. However if you intermixed -7F and -7J, you would operate at -7F EPR limits, so the -7J would not illuminate the lights (at the same EPR a -7J would give you the same EGT as a -7F).
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greasespot
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Mon Apr 18, 2005 9:40 am

You can also intermix a JT8D-7/ 7B or a 9A on a B727 or a -9 or a -17 on a B737. Best part is you do ot even have to tell the crew they are flying with intermix engines....

GS
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lowrider
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Mon Apr 18, 2005 9:59 am

You can intermix the GE CF34-3A1 and 3B1 provide the performance is planned off of the 3A1 engine.
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HAWK21M
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Mon Apr 18, 2005 1:11 pm

Quoting Greasespot (Reply 16):
You can also intermix a JT8D-7/ 7B or a 9A on a B727 or a -9 or a -17 on a B737. Best part is you do ot even have to tell the crew they are flying with intermix engines....

Since Intermix requirements require Instrument changes too.And the Performance is limited to the Lower thrust Engine.
If not wrong,The Cockpit placarding indicating intermix is done too.
regds
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9v-svc
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Tue Apr 19, 2005 9:20 pm

Thank you very much guys for your inputs, my question has been answered, I have a few more in my mind now but currently in a rush to go to work. Will post the question in here once I am free to do so.

Cheers

Charles
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CaptOveur
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Wed Apr 20, 2005 6:14 am

Quoting Accidentally (Reply 14):
The 727 /RE has those big honkin JT8D-217 (think MD80) on the outboards and I think a -17 in the middle.

I think they call this the Valsan conversion or something. I think FedEx is the only operator of 727s that were delivered like this.
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mandala499
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RE: Can An Aircraft Use 2 Different Types Of Engines?

Thu Apr 21, 2005 6:00 am

intermixing is "normal"... you put the PLACARD stating the engine types above the gauges.

I've been told that on the 732 the simple rule of thumb is to follow the EPR settings on the lower thrust engine when mixing -7 with -9, or -15 with -17... -9 and -15. Though I wouldn't wanna be in a lightly loaded 732 on a go around when it's a -7 mixed with a -17  Smile

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