Caetravlr From United States of America, joined Oct 2000, 874 posts, RR: 1 Posted (8 years 2 months 1 week 3 days 13 hours ago) and read 2103 times:
I know there was a thread about speculating which two suppliers will be chosen to provided engines for the 7E7, but I wanted to see what everyone thinks the ramifications of making them interchangeable as is mentioned in this article:
I can definitely see it being a major plus when it comes to reselling an aircraft, but that is the biggest benefit I can see at this point. No more worrying about commonality with your current fleet if you want to switch it out.
What I am really curious about, since they say that an engine can be changed out in 24 hours with an engine from either manufacturer, is will two different brands of engine be able to work side by side? Say a Pratt powered 7E7 runs into engine trouble while on the other side of the ocean from it's home base. Maybe a partner airline or other supplier has a Rolls engine available right then, and a Pratt from the home base would take upwards of a week to get there. Would this mean that if they wanted the airplane to be fixed right then and there, they would have to replace BOTH engines? Wouldn't be impossible to have two different brands of engine with the same thrust characteristics? I am no engineer, and I know that no one will know for sure what it means, I just wanted to get some conjecture.
Either way, I think it is a really great concept. I can't wait to see all of the developments that occur on the 7E7.
Regards,
CAETravlr
A woman drove me to drink and I didn't have the decency to thank her. - W.C. Fields
FoxBravo From United States of America, joined Nov 2003, 2703 posts, RR: 6 Reply 1, posted (8 years 2 months 1 week 3 days 12 hours ago) and read 2018 times:
Somehow I doubt that it will be possible to operate an engine from one manufacturer on one wing and one from another manufacturer on the other. It seems like there are too many performance variables for them to match perfectly enough. Then again, I am not an engineer, and this is all new territory, so who knows. Wouldn't that be a feat, though!
In any event, the interchangeable engine idea in itself is a fantastic concept, and should be a HUGE selling point for the 7E7. It potentially doubles (or triples, if three options are offered, though it sounds like only two at this point) the resale market, which should make airlines much more willing to commit to the type. Just one of the many exciting developments that we can look forward to with the 7E7...
Expratt From United States of America, joined Mar 2000, 311 posts, RR: 0 Reply 2, posted (8 years 2 months 1 week 3 days 12 hours ago) and read 2006 times:
Making engine models, from the same manufacturer, interchangeable has been possible for many years. With the basic JT8D series engine, higher thrust versions of the JT8D like the -15 or -17 could be installed in place of a lower thrust engine like a -7 or -9 if no other engines were available. The cockpit would have to be placarded to note the engine model difference so the crew could make the appropriate adjustments to EPR so all the engines would be operating at the same thrust level. On the 777, the three manufacturers various engine models are each constructed the same even though they have different thrust ratings. The thrust variations are controlled by a shorting cap that is connected to the FADEC that controls the thrust levels. So if UAL has a 4077 that needs to be changed out and the only engine on the spare line is a 4090, they can quickly change it to the 77,000 pound rating by repositioning the shorting cap.
Now making engines from different manufacturers interchangeable is another story. How GE engines are mounted is different from how Pratt engines are mounted and both are different from how Rolls engines are mounted. Are they now going to propose changing the pylon concurrent with the engine? (Remember AA 191?) In addition, the engine performance parameters the three manufacturers utilize are different. GE and Pratt have two rotors in comparison to most of Rolls' big engines using three spools. Weight would probably be the most critical factor since all airplanes have a limit on the unbalance. Typically, the unbalance is due to fuel because one of the engines may burn slightly more fuel than the other. But how would they account for the unbalance if it was due to one of the engines? And if they made up the difference by adding extra fuel to the opposite wing, could that fuel be counted on for use during the flight or would the extra fuel have to stay there until they changed the engine back and balanced out the load again. Since the various manufacturers engines have different TSFCs, would each wing have to be loaded per the scheduled fuel burn for that engine plus any fuel needed to maintain the fuel load balance throughout the flight plus the fuel load to balance out the weight difference of the engines.
Since airlines have extracted deals from the manufacturers to hang a particular engine on an airplane (only to be later screwed royally on the purchase of spare parts), it wouuld be interesting to see if similar deals could be made knowing that the next round of engines could come from other guy.
It is an interesting concept and I wonder if the engine manufacturers are ready to embrace it or is this just a dream of some marketing clown, I mean, vp, that doesn't know squat about those smelly things that hang on the wings of an airplane.
LMP737 From United States of America, joined May 2002, 4459 posts, RR: 27 Reply 3, posted (8 years 2 months 1 week 3 days 11 hours ago) and read 1937 times:
The biggest cost savings of having "interchangeable engines" is a common pylon. This lowers engineering and manufacturing costs. Once an airline chooses an engine it's highly doubtful they will switch over.
As for mounting another type engine to get an airliner back to "home base" this is somewhat unlikely. An airline will more than likely spend the money to have an engine shipped to a location rather than fly an airplane back with an engine they will have to remove anyway. Then there are certification issues. An airline is certified to fly with two engines of the same type. Not two of different make. Some might say "Boeing could have the 7E7 certified to fly with both." The problem with this is that it will cost $$$$$$. Money Boeing is unlikely to spend on something that will probably never happen.
DfwRevolution From United States of America, joined Jan 2010, 755 posts, RR: 54 Reply 4, posted (8 years 2 months 1 week 3 days 9 hours ago) and read 1920 times:
From a purely technical standpoint, such a ferry flight is possible. 7E7 engines will have identical aircraft fittings, pylons, ext. so the major airframe modification is software based. Boeing indicates that the avionics will need updating so the computers will know what engines it is opperating. If Boeing gave the avionics enough flexibility, then a 7E7 could hypothetically fly with mixed engines.
But invariably, the more flexibility a system is given, the more room for error is possible. Pocket calculatos don't lock-up like Windows ME because they follow a much simpler set of instructions. Simple = safe.
Gigneil From United States of America, joined Nov 2002, 15616 posts, RR: 90 Reply 5, posted (8 years 2 months 1 week 3 days 8 hours ago) and read 1901 times:
The biggest problem is avionics support in this theory.
You could hang two different kinds off the pylons, but the avionics would only know how to use one.
Okie From United States of America, joined Jul 2003, 2069 posts, RR: 4 Reply 6, posted (8 years 2 months 1 week 3 days 7 hours ago) and read 1891 times:
Control wise very doable, all computer/processors use generally pretty much use common types of inputs and outputs. It would just be which ones you would want to use and make pin assignments to the connectors, The engine manufacturers would just pick the ones they needed.
I think what we are missing here is that Boeing is trying to push engine manufacturers to figure out how to mount the engines to a common pylon thus forcing that part of the engineering costs onto the engine manufacturers.
The aircraft industry may eventually come to the point of "frame sizes/thrust ranges" that have certain assigned mounting and connection points. It was done with electrical motors 50 years ago. That would certainly increase the competition between the different engine manufacturers.
Now I do not think you will see very many planes with two different types of engines mounted on it however it certainly is going to impact how the engine manufacturers deal with the airlines on engine choices and how much they charge as they can be easily shifted from one brand to another on an airframe even after manufacture. Just some thoughts
Brons2 From United States of America, joined Sep 2001, 2927 posts, RR: 5 Reply 7, posted (8 years 2 months 1 week 2 days 11 hours ago) and read 1803 times:
I think what we are missing here is that Boeing is trying to push engine manufacturers to figure out how to mount the engines to a common pylon thus forcing that part of the engineering costs onto the engine manufacturers.
The thing that Boeing has quoted most often in their press blurbs is the resale value. It would be easier to move the planes around if the engines could be changed to suit the target airline.
Theoretically, with a universal mount point, it would make it possible for the engine manufacturer not chosen to still devlop an aftermaket engine for this aircraft! The big question of course is whether the FAA would issue a STC for it.
Firings, if well done, are good for employee morale.
SSTjumbo From , joined Dec 1969, posts, RR: Reply 8, posted (8 years 2 months 1 week 2 days 11 hours ago) and read 1793 times:
Theoretically, with a universal mount point, it would make it possible for the engine manufacturer not chosen to still devlop an aftermaket engine for this aircraft! The big question of course is whether the FAA would issue a STC for it.
In all likelyhood the FAA would issue an STC for an aftermarket engine if all the necessary performance requirements (not just engine performance, but overall a/c performance characteristics [then again you knew that ]) are met and someone's willing to shell up the dough for the tests. The FAA will give out STC's for almost anything, just don't expect them to come in Cracker Jack boxes.
Klaus From Germany, joined Jul 2001, 20144 posts, RR: 57 Reply 9, posted (8 years 2 months 1 week 2 days 9 hours ago) and read 1777 times:
Avionics in themselves would not necessarily be the big problem, if the system was preconfigured for individual setup for each engine.
The reason why I doubt that it could reasonably be done would be on the mechanical / aerodynamic side: As far as I know, different engines types have different dynamic behaviour. They accelerate, decelerate, produce thrust and react to external influences differently.
If you´d have different engine types on both sides, you´d have a yawing moment every time the thrust level was changed (possibly even first in one, then the opposite direction). I doubt that anybody would want to try certifying something like that.
Trying to compensate those differences away by software would be difficult and would almost certainly result in noticeable performance degradation overall.
DarkBlue From United States of America, joined Sep 2003, 233 posts, RR: 12 Reply 10, posted (8 years 2 months 1 week 1 day 19 hours ago) and read 1728 times:
Also, don't forget that GE engines are power managed to N1 while PW and RR engines use EPR. I guess you could design the cockpit so that the pilot uses one or the other and let the FMC figure out what signal to each the different engines, but things begin to get complicated real quick when you start to talk about derate, how the engines are trimmed to each other and other differences in operation. Doable, yes. Easy, no.
Also, I agree with Klaus, differences in actual engine dynamic presents a whole new set of issues. Yes it is possible, but certification would be too much of a headache.
OPNLguy From , joined Dec 1969, posts, RR: Reply 11, posted (8 years 2 months 1 week 1 day 16 hours ago) and read 1707 times:
Expratt,
>>>Are they now going to propose changing the pylon concurrent with the engine? (Remember AA 191?)
I enjoyed your detailed and very informative post, but I'm a little confused about your AA191 reference. I know that the pylon/engine on AA191 detached and flew up/over the the wing (and compromised hydraulics which led to the slats on that wing retracting under the airloads), but the pylon's separation was maintenace-related, and not (pylon) design-related, right?
Klaus From Germany, joined Jul 2001, 20144 posts, RR: 57 Reply 13, posted (8 years 2 months 2 days 22 hours ago) and read 1604 times:
BoingGoingGone: If they had the same mount and roughly the same thrust wouldn't FADEC resolve this issue.
Aligning dynamic behaviour would probably be difficult... And aligning reactions to external influences can be impossible, since it´s based directly on mechanical and aerodynamic effects which are not under FADEC control and can only be attempted to be counteracted.
When you´re thinking about the proposed P&W two-spool-plus-reduction-gear turbofan and the RR three-spool engines, for instance, I´d be suprised if they didn´t have significantly different characteristics.
In any case, you´d have to define the "lowest common denominator" which both engine types could conform to and then attempt to force the engines on a common path. This would mean that one or both engines would often run outside of their optimal operating regime.
FADEC can only attempt to force the engines to where they would not normally want to operate, but it can´t change the physical characteristics. And that can´t be good for both fuel burn and longevity...
Expratt From United States of America, joined Mar 2000, 311 posts, RR: 0 Reply 14, posted (8 years 2 months 22 hours ago) and read 1521 times:
OPNL,
You are correct on AA 191 that the separation of the engine/pylon was maintenance-related rather than design-related. Maintenance installed the engine and pylon together to the wing contrary to maintenance instructions. In so doing, the pylon was inadvertently jammed into the wing and damaged. The damaged pylon eventually broke that led to the engine pivoting around the forward mount to impact the upper surface of the left wing rupturing the hydraulic lines. With the hydraulic system compromised, the slats on the left wing, which are hydraulic actuated, retracted and the asymetrical lift caused the airplane to roll to the left and crash.
My reference to AA 191 was to highlight the inherent problems of installing engines and pylons as a unit. When installing the pylon to the wing, there will always be some torque factor unless the unit is perfectly aligned. When trying to install both the engine and pylon as one unit, the torque factor will be much, much greater unless the unit is perfectly aligned. Hence the possibility of doing similar damage that could lead to similar consequences.
Gigneil From United States of America, joined Nov 2002, 15616 posts, RR: 90 Reply 15, posted (8 years 2 months 11 hours ago) and read 1487 times:
Clearly, interchangeable engines would require either the plane to have the engine control parameters preloaded for all possible engines, or swappable avionics boxes that are quick to handle.
Mlsrar From United States of America, joined Mar 2000, 1417 posts, RR: 10 Reply 16, posted (8 years 1 month 4 weeks 1 day 15 hours ago) and read 1461 times:
In terms of a real-world implementation, the development of the software for the integration of multiple engine parameters would be the smallest hurdle.
As mentioned above, mating the engine/pylon assemblies from different manufacturers would clearly offer a far more difficult challenge.
I mean, for the right price I’ll fight a lion. - Mike Tyson
BoingGoingGone From , joined Dec 1969, posts, RR: Reply 17, posted (8 years 1 month 2 weeks 6 days 12 hours ago) and read 1264 times:
You mean universal like this????
For the first time in commercial jet history, both engine types will use the same standard interface with the airplane, allowing any 7E7 twinjet to be fitted with either engine at any point in time. Engine interchangeability makes the 7E7 a flexible asset that can easily be moved among carriers, an attractive feature for financiers, leasing companies and airlines. Other 7E7 innovations include the elimination of traditional bleed air systems in favor of an efficient, more-electric architecture.
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]) are met and someone's willing to shell up the dough for the tests. The FAA will give out STC's for almost anything, just don't expect them to come in Cracker Jack boxes.
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From , joined Dec 1969, posts, 
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