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Can An Aircraft Use 2 Different Types Of Engines?  
User currently offline9V-SVC From Singapore, joined Oct 2001, 1797 posts, RR: 10
Posted (9 years 6 months 1 week 5 days 20 hours ago) and read 9074 times:

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


Airliners is the wings of my life.
21 replies: All unread, jump to last
 
User currently offlineRightWayUp From United Kingdom, joined Oct 2001, 86 posts, RR: 0
Reply 1, posted (9 years 6 months 1 week 5 days 20 hours ago) and read 9036 times:

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.

User currently offlineIanatSTN From United Kingdom, joined Dec 2003, 577 posts, RR: 4
Reply 2, posted (9 years 6 months 1 week 5 days 19 hours ago) and read 9019 times:

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.



Ian@STN ::
User currently offlineLaxintl From United States of America, joined May 2000, 25786 posts, RR: 50
Reply 3, posted (9 years 6 months 1 week 5 days 19 hours ago) and read 8969 times:

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.



From the desert to the sea, to all of Southern California
User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 4, posted (9 years 6 months 1 week 5 days 17 hours ago) and read 8935 times:

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.


User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2565 posts, RR: 25
Reply 5, posted (9 years 6 months 1 week 5 days 16 hours ago) and read 8924 times:

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.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineUSAFMXOfficer From United States of America, joined Nov 2004, 174 posts, RR: 0
Reply 6, posted (9 years 6 months 1 week 5 days 16 hours ago) and read 8917 times:

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



44th Fighter Squadron Vampire Bats - 63 years of history
User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 7, posted (9 years 6 months 1 week 5 days 16 hours ago) and read 8917 times:

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.


User currently offlineLaxintl From United States of America, joined May 2000, 25786 posts, RR: 50
Reply 8, posted (9 years 6 months 1 week 5 days 14 hours ago) and read 8899 times:

The 747 Classic intermix is certainly something to keep the F/E busy, however is done routinely.


From the desert to the sea, to all of Southern California
User currently offlineOPNLguy From , joined Dec 1969, posts, RR:
Reply 9, posted (9 years 6 months 1 week 5 days 10 hours ago) and read 8841 times:

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


User currently offlineB747FE From Hong Kong, joined Jun 2004, 230 posts, RR: 4
Reply 10, posted (9 years 6 months 1 week 5 days 10 hours ago) and read 8840 times:

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.



"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
User currently offlineShyFlyer From , joined Dec 1969, posts, RR:
Reply 11, posted (9 years 6 months 1 week 5 days 9 hours ago) and read 8818 times:

It's done frequently in test programs:

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Photo © Ian Kirby



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User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 12, posted (9 years 6 months 1 week 5 days 7 hours ago) and read 8782 times:


View Large View Medium
Click here for bigger photo!

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.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineTroubleshooter From Germany, joined Feb 2005, 423 posts, RR: 5
Reply 13, posted (9 years 6 months 1 week 5 days 4 hours ago) and read 8738 times:

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.


This job sucks!!! I love this job!!!
User currently offlineAccidentally From United States of America, joined Dec 2000, 643 posts, RR: 0
Reply 14, posted (9 years 6 months 1 week 5 days 4 hours ago) and read 8728 times:
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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



Cory Crabtree - crab453 - Indianapolis - 2R2 - 1966 PA-32-260
User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2565 posts, RR: 25
Reply 15, posted (9 years 6 months 1 week 5 days 4 hours ago) and read 8719 times:

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).



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineGreasespot From Canada, joined Apr 2004, 3085 posts, RR: 20
Reply 16, posted (9 years 6 months 1 week 5 days 3 hours ago) and read 8706 times:

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



Sometimes all you can do is look them in the eye and ask " how much did your mom drink when she was pregnant with you?"
User currently offlineLowrider From United States of America, joined Jun 2004, 3220 posts, RR: 10
Reply 17, posted (9 years 6 months 1 week 5 days 3 hours ago) and read 8700 times:

You can intermix the GE CF34-3A1 and 3B1 provide the performance is planned off of the 3A1 engine.


Proud OOTSK member
User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 18, posted (9 years 6 months 1 week 5 days ago) and read 8669 times:

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
MEL



Think of the brighter side!
User currently offline9V-SVC From Singapore, joined Oct 2001, 1797 posts, RR: 10
Reply 19, posted (9 years 6 months 1 week 3 days 16 hours ago) and read 8549 times:

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



Airliners is the wings of my life.
User currently offlineCaptOveur From , joined Dec 1969, posts, RR:
Reply 20, posted (9 years 6 months 1 week 3 days 7 hours ago) and read 8472 times:

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.


User currently offlineMandala499 From Indonesia, joined Aug 2001, 6927 posts, RR: 76
Reply 21, posted (9 years 6 months 1 week 2 days 7 hours ago) and read 8380 times:

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

Mandala499



When losing situational awareness, pray Cumulus Granitus isn't nearby !
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