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XLA2008
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Engine cooling on short hops

Tue Nov 07, 2017 10:38 am

From what I’m aware, airlines like Hawaiian Airlines, utilize the 717 and Aloha (when flying) 737-200 were and are used for those islands hops due to the capability of performing short turnarounds and allowing the engines time to cool, aircraft on those hops don’t reach altitudes high enough to cool the engines themselves, making these aircraft desirable to retain and maintain despite the fact they are aging. And as time goes on will become more expensive to maintain. I get that Hawaiian will have the 717 for many years to come and I have no doubt they will get more or newer frames if needed in time... so I don’t want to really go off topic debating Hawaiians next replacement, I’m just using them as an example for the question at hand.

My question is, given this being a definitive requirement for airlines that perform operations like this, why have engine manufacturers like GE, PW, RR etc not applied the ability for engine cooling like this on short hops into their mainstream aircraft, allowing the aircraft to be versatile for all types of operations? Or even regional jet manufactures like Bombarbier or Embraer integrate this ability into their aircraft? The 717 and both the Classic 737-100/200 both operated on normal and regular commercial operations as well as having the ability to operate the niche flights on short and quick Island hops... why has his not continued to be intergrated? Surely for companies like Embraer, Bombardier with the CS series, it would open a new market for aircraft sales and make the aircraft extremely versatile for various operations!

Is it just that it isnt possible to do this on more modern engines due to how they are made? Is it due to being to expensive to integrate this into engine manufacturing? Is it too expensive to do this for such a niche operation, because outside of Hawaiian Airlines and maybe a few other operators doing short and quick Island hops with jet aircraft I get that cost vs market sales could play a major factor, im just unsure as to why this hasn’t been done. Every manufacturer out their know that Hawaiian are going to need a 717 replacement at some point and other airlines with similar ops (Hawaiian is just the one that is most promenant to me)

Any information into this would be appreciated because I am very intrigued!

Thanks Guys!
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mmo
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Re: Engine cooling on short hops

Tue Nov 07, 2017 12:50 pm

Simply because the engines do get cooled. The engines are not operated at MCT power, in fact, a long way from it. So, cooling isn't a problem. There is more of an issue with the use of reverse and then shutting down without an adequate cooling period. If my memory serves me correctly, the JT-8 had to have 2 minutes at idle after using reverse.
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XLA2008
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Re: Engine cooling on short hops

Tue Nov 07, 2017 9:50 pm

mmo wrote:
Simply because the engines do get cooled. The engines are not operated at MCT power, in fact, a long way from it. So, cooling isn't a problem. There is more of an issue with the use of reverse and then shutting down without an adequate cooling period. If my memory serves me correctly, the JT-8 had to have 2 minutes at idle after using reverse.



So why are engines now not capable of the same task? Or manufactured to be able to do the same thing?
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fr8mech
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Re: Engine cooling on short hops

Tue Nov 07, 2017 9:58 pm

XLA2008 wrote:
cool the engines


XLA2008 wrote:
applied the ability for engine cooling


What, exactly, are you talking about? What are you cooling? Turbine engines cool themselves using secondary airflow through the engine. They do this from idle to take-off power. Modern engines are better at it, because they need to be. But, older engines do just fine without "cooling" between flights.

As mmo mentioned, the only cooling requirement I'm aware of was/is time at idle after landing to thermally stabilize the engine. I think it was 5 minutes on a JT9, less for smaller engines. I'm sure there's a requirement on newer engines. I'll see if I can find it later.

We have a procedural requirement the exhaust temp (EGT) be below 100c before introducing fuel, but that is easily accomplished by motoring engine with the starter until that occurs. I don't recall if that's an AFM//AMM requirement or company.
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XLA2008
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Re: Engine cooling on short hops

Tue Nov 07, 2017 10:46 pm

fr8mech wrote:
XLA2008 wrote:
cool the engines


XLA2008 wrote:
applied the ability for engine cooling


What, exactly, are you talking about? What are you cooling? Turbine engines cool themselves using secondary airflow through the engine. They do this from idle to take-off power. Modern engines are better at it, because they need to be. But, older engines do just fine without "cooling" between flights.

As mmo mentioned, the only cooling requirement I'm aware of was/is time at idle after landing to thermally stabilize the engine. I think it was 5 minutes on a JT9, less for smaller engines. I'm sure there's a requirement on newer engines. I'll see if I can find it later.

We have a procedural requirement the exhaust temp (EGT) be below 100c before introducing fuel, but that is easily accomplished by motoring engine with the starter until that occurs. I don't recall if that's an AFM//AMM requirement or company.


Ok well explain to me why the 717 is capable of doing Island hops and short quick flights that HA operates and the 737 current generation along with the A319/320 is incapable of handling such routes along with most regional jets? Because from almost every forum post I’ve ever read on here it’s due to engine cooling...

Infact in articles online and on this forum I have read it is due to heat issues... so what I am asking makes perfect sense!!

Here is a an example for you ... “Short flights with high humidity takes longer for the engines to cool, unless heat issues are fixed with new engine cores, they need much more time after each flight to cool the engines for the next” something that isn’t an issue for the 717...

So please explain why what I am asking makes no sense to you?

viewtopic.php?f=3&t=1368257&hilit=Hawaiian+airlines+Hawaiian+Airlines+717+replacement

Topic explaining why the 717 works for Hawaiian and its operations and other aircraft don’t, due to engine cooling time, my question is based on that fact of why haven’t engines on newer aircraft been designed to manage these issues and be versatile enough to tolerate the operations of airlines like Hawaiian.
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Flow2706
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Re: Engine cooling on short hops

Tue Nov 07, 2017 11:21 pm

No issues with engine cooling - there is no such limitation on A320s that I am aware of (the only thing is leaving the engine run for 3 minutes before shutdown - most of the time, taxi times are at least around 3 minutes so its not really an issue). A320s are used for very short flights with some airlines...the only issue you might get with cooling is brake cooling if you combine short runways with short flights and short turn around times...but even then, the brake fans are usually effective enough to avoid delays due to brake cooling. I guess there are other reasons that make a 717 preferable on these routes over an A320.
 
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XLA2008
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Re: Engine cooling on short hops

Tue Nov 07, 2017 11:43 pm

Flow2706 wrote:
No issues with engine cooling - there is no such limitation on A320s that I am aware of (the only thing is leaving the engine run for 3 minutes before shutdown - most of the time, taxi times are at least around 3 minutes so its not really an issue). A320s are used for very short flights with some airlines...the only issue you might get with cooling is brake cooling if you combine short runways with short flights and short turn around times...but even then, the brake fans are usually effective enough to avoid delays due to brake cooling. I guess there are other reasons that make a 717 preferable on these routes over an A320.


Ok... haha so what is the issue? Because everything I read is due to engine cooling and engine cores needing to cool, otherwise why would HA still operate the 717 when a newer more efficient A319 (or similar) with the same capacity, more flexibility with range and better Comfort not be sought considering they have the A321 already, also keeps costs down with crew training... so if everything I am reading about the fact that engine cooling is the issue then and all of that is wrong then what is the problem? If you click the link I posted in my previous comment, it’s a link to a forum article from here, scroll a few posts down and it’s an entire topic on engine cooling for the ops that HA has... so are they all wrong?

I am not saying I disbelieve what any of you have posted, but everything I’ve read online, all the forum posts on here etc all contradict your responses, so if what I’ve read and what has been said on the forum here is wrong, then what is the issue? This is something I’m keen to learn.

Basically from my research it’s said, the high amount of cycles, extremely short flight times, lower altitude flying as not enough time to reach high altitude, short turnarounds roughly 15mins each time, the hot environment, do not allow current engines to operate these routes, yes they are capable of operating these flights, but not on the amount of cycles with such short turnarounds, it doesn’t allow the engines enough time to cool properly. Which is why airlines like HA have gone from DC-9 to 717 or 737-100/200... even an article elsewhere I was reading mentioned that Aloha took delivery of the 737-300 however it couldn’t manage the operations and flight cycles they did and eventually had to remove it from inter-Island flights... so clearly there is some issue outside of those on the 737-100/200 DC-9 & 717...
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fr8mech
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Re: Engine cooling on short hops

Wed Nov 08, 2017 1:41 am

XLA2008 wrote:
Ok well explain to me why the 717 is capable of doing Island hops and short quick flights that HA operates and the 737 current generation along with the A319/320 is incapable of handling such routes along with most regional jets?


I've no idea.

XLA2008 wrote:
so if everything I am reading about the fact that engine cooling


Fact, or opinion?

Look, I've been in aircraft maintenance for over 30 years, and have operated and maintained JT3, JT8, JT9, CFM56-2, CF6, RB211 (524 & 535), PW2000 & PW4000 and have never heard of a cooling issue on short hops. Maybe it is, maybe it isn't. Maybe ask a powerplant engineer about it? But, a pilot, mmo, says he's never seen an issue and me, a 30+ year technician, hasn't heard about the issue of "engine core cooling" limiting flight operations. I'm not sure what Flow2706 does, but his number is spot on.

As I mentioned earlier, engines are cooled using secondary airflow through the engine to cool various components and provide a barrier between the hot gases of combustion and the surrounding engine structure, including the rotating mass. That cooling begins with engine start and stops when the engine stops. Now, let's understand that cooling is a relative term. The cooling air, depending on internal engine location, can be 400c or 500c.

Engines are allowed to "cool down" at idle (for instance, 2 mins for the RB211-535) in order to stabilize them thermally. In fact, this directly from its maintenance manual:

CAUTION: DO NOT SHUTDOWN THE ENGINE UNTIL THE ENGINE HOT SECTION BECOMES STABLE AT AN EQUAL TEMPERATURE. OPERATE THE ENGINE AT MINIMUM IDLE TO COOL THE ENGINE HOT SECTION. THE TURBINE COULD BECOME SEIZED.
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XLA2008
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Re: Engine cooling on short hops

Wed Nov 08, 2017 2:06 am

fr8mech wrote:
XLA2008 wrote:
Ok well explain to me why the 717 is capable of doing Island hops and short quick flights that HA operates and the 737 current generation along with the A319/320 is incapable of handling such routes along with most regional jets?


I've no idea.

XLA2008 wrote:
so if everything I am reading about the fact that engine cooling


Fact, or opinion?

Look, I've been in aircraft maintenance for over 30 years, and have operated and maintained JT3, JT8, JT9, CFM56-2, CF6, RB211 (524 & 535), PW2000 & PW4000 and have never heard of a cooling issue on short hops. Maybe it is, maybe it isn't. Maybe ask a powerplant engineer about it? But, a pilot, mmo, says he's never seen an issue and me, a 30+ year technician, hasn't heard about the issue of "engine core cooling" limiting flight operations. I'm not sure what Flow2706 does, but his number is spot on.

As I mentioned earlier, engines are cooled using secondary airflow through the engine to cool various components and provide a barrier between the hot gases of combustion and the surrounding engine structure, including the rotating mass. That cooling begins with engine start and stops when the engine stops. Now, let's understand that cooling is a relative term. The cooling air, depending on internal engine location, can be 400c or 500c.

Engines are allowed to "cool down" at idle (for instance, 2 mins for the RB211-535) in order to stabilize them thermally. In fact, this directly from its maintenance manual:

CAUTION: DO NOT SHUTDOWN THE ENGINE UNTIL THE ENGINE HOT SECTION BECOMES STABLE AT AN EQUAL TEMPERATURE. OPERATE THE ENGINE AT MINIMUM IDLE TO COOL THE ENGINE HOT SECTION. THE TURBINE COULD BECOME SEIZED.



Well I have found for a fact that the engines are the major factor in what are the issues and being able to handle those types of operations that HA has... so being someone with so much experience 30+ years and working on all these various engine types... you tell me why?

That’s why I posted a question for an answer, whether it be related to the original question or not... it’s still a question I’m seeking an answer too.. so if it isn’t a cooling issue then what is the issue preventing current engines from being able to handle the strain that the 717’s have? You have 30+ years and have worked on the JT’s and current PW so please explain...

I mean even Aloha Airlines removed aircraft that weren’t JT powered from inter-Island flights... so there has to be a reason
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fr8mech
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Re: Engine cooling on short hops

Wed Nov 08, 2017 2:23 am

XLA2008 wrote:
you tell me why


As I've stated, I have no clue. Maybe it is related to reliability, maybe it isn't. Maybe it's related to operating costs, including maintenance. I have no idea why Aloha made that business decision.

I was questioning this issue of core engine cooling. It may be "a thing", one that would force an airline to abandon one frame for another on a given route, but it's not one that I've come across, nor a couple of the others that have posted here.
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GalaxyFlyer
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Re: Engine cooling on short hops

Wed Nov 08, 2017 5:10 am

Are you talking about rotor bow? That’s not cooling strictly; it’s because of the heat rising into the top of the cowl and causing differential heat on the core and the rotor to “bow”. It is solved by dry motoring the engine during start to equalize temps and unbow the rotor shaft.

GF
 
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XLA2008
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Re: Engine cooling on short hops

Wed Nov 08, 2017 6:17 am

GalaxyFlyer wrote:
Are you talking about rotor bow? That’s not cooling strictly; it’s because of the heat rising into the top of the cowl and causing differential heat on the core and the rotor to “bow”. It is solved by dry motoring the engine during start to equalize temps and unbow the rotor shaft.

GF


Honestly... in terms of the industry, aircraft and operations I would like to say without being full of myself, that my knowledge is pretty established, when it comes to the operation of an actual engine, I know the basics of how it operates, but the in depth detail I have little to no knowledge at all... which is why I was reaching out for help, guys here that have posted obviously have more knowledge on the operations than I do, and I respect all the replies, but it’s still left me baffled as to an understanding as to why exactly Aircraft that with the likes of DC-9, 737-100/200 had JT8D engines, while the 717 has the RR BR715 turbofan... and through several topics online I’ve been intrigued as to what HA will do eventually for replacement of the 717, and online reading mixed with forum posts here as I’ve mentioned, it all comes back to “something” to do with engines currently available are not capable of the missions HA deploys the 717 on with regards to inter-Island hopping, combination of very very quick turnarounds, multiple daily rotations, extremely short flights, hot environment, low altitude flying because of such short hops meaning engines outside of the 737-1/200, DC-9 and 717 just do not work, evidence backing this up was that Aloha introduced 737’s like the 300/400/700 they attempted to use them on inter island flights, within similar rotation and turnaround times and flight times and the engines just didn’t work for those ops, it was consistent delays, needless to say those aircraft were withdrawn from inter-Island and used on continental flights, further reading into these scenarios the general consensus always seems to come back to the engines having time to cool appropriately in order to operate these routes, however asking on here, people that do have much more in depth experience than I do in terms of engines have all said contrary to this and that cooling isn’t an issue, so it has left me baffled as to what the underlying issue is then if it has nothing to do with cooling. If it is cooling related I have no idea what type, whether it be certain components, the entire engine... I do not know? Which is why I have reached out for help! I understand that HA needs an aircraft similar in size to the 717 for these flights, which rules out smaller regional jets anyway just due to capacity, however the A319 or A320 would be a perfect fit for Hawaiian given the introduction of the A321, it would bring fleet commonality, lower maintenance costs operating the same aircraft, lower training costs, however the A319/A320 keep coming back as being incapable of operating these routes....

So now, I guess the question is, if it isn’t engine cooling that’s the issue then what is the issue preventing newer variants operating these inter-Island flights, or if it is an engine cooling issue, then why haven’t engine manufacturers over come this problem to enable more versatility with its engines and thus making them more preferable for both regular flight operations and niche market operations such as Hawaiian Airlines... I guess what ever the issue is the question still remains as to why something hasn’t been done to make the aircraft more versatile for those markets... although I am aware HA had a very unique operation and quite possibly no other airline in the world utilizes their fleet quiet the way Hawaiian do...

So if someone with excellent knowledge on the reason behind this, or excellent knowledge as to why the DC-9, 717, 737-1/200 are perfect candidates, so much so that they were worth the financial costs to keep them in operation for years after many were obsolete.

I do thank you for all of your responses, but I guess we are all still sat here without a real answer, and as said before all my reasearch keeps coming back to the same point of engine cooling, which everyone else seems to disagree with, and I can’t argue it because I have little knowledge about the actual full function of the engines and why those are best!

I am not looking for a what is Hawaiians replacement for the 717, more so the fact of why newer more efficient aircraft aren’t capable of Hawaiians route network, and then as to why either airline manufacturers or engine manufacturers have not overcome the issue with their products to make it more versatile for all markets even the niche ones like HA, which I guess could be a cost thing, for example the cost to implement those systems outweighs the money earned for such a small amount of orders from a niche market, which still wouldn’t make so much sense providing the aircraft was capable of operating regular commercial ops, meaning they would make their money back either way...


So please somebody explain to me the actual reason why these aircraft aren’t working for these markets... if the A319 or A320 was capable then why aren’t they being used or with Aloha why did the 737-300/400/700 fail to perform and eventually get stopped on Short Island hops.

Thanks guys!
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pikachu
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Re: Engine cooling on short hops

Wed Nov 08, 2017 8:09 am

Your fascination with this non-subject is bizarre. What concept of "cooling" are you specifically concerned with? The engines running too hot in flight or are not cooling enough on the ground before the next flight?
As clearly stated already there is usually a few minutes required after landing before shutting an engine down. That's it. No cooling issues.
I have never experienced a jet engine that has a time limit or EGT limit on the ground that must be adhered to before the next start. I've done 12 minute flights and 12 hour flights. Engines get treated the same.
As for Aloha and the NGs doing the flights to the mainland... I don't recall what leasing company owned the airplanes but when they found out Aloha's plan was to use them interisland and run the cycles through the roof the leasing company was less than impressed. Thus the NGs flew to the mainland.
 
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Re: Engine cooling on short hops

Wed Nov 08, 2017 8:39 am

XLA2008 wrote:
GalaxyFlyer wrote:
Are you talking about rotor bow? That’s not cooling strictly; it’s because of the heat rising into the top of the cowl and causing differential heat on the core and the rotor to “bow”. It is solved by dry motoring the engine during start to equalize temps and unbow the rotor shaft.

GF


Honestly... in terms of the industry, aircraft and operations I would like to say without being full of myself, that my knowledge is pretty established,

Thanks guys!


Have you ever worked on a plane? If not then you have zero knowledge. Demanding answers here and then refuting what is being said is plain arrogance.

The only issue with modern engines is rotor bow. As most people have mentioned, the time it takes to taxi to the gate is sufficient for engine cooling. The old JT9's were a problem and the answer was to motor the engines for 5 minutes after shut down. The only limiting thing would be brake temps, especially on B737's. I remember reading about JAL's 747's that were used for short hops, the landing gears were never retracted so that they could cool the brakes down.
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77west
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Re: Engine cooling on short hops

Wed Nov 08, 2017 9:47 am

I think the OP is confusing "cooling" with short cycle fatigue. The 737NG and A320 series dont like short 20 minute flights in a high humidity salty environment. Sure, the planes can do it, just that maintenance goes through the roof compared to the 717 and the old JT8 737-200. Combination of tighter tolerances in modern engines coupled with the average 737 and A320 stage length increasing well beyond interisland flying since their original designs. They are simply not optimised for this unique environment.
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BravoOne
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Re: Engine cooling on short hops

Wed Nov 08, 2017 11:27 am

Engine cooling can be an issue and the MD11 (PW) had a Engine Cool light. It was a small blue light within the engine display that would come on after landing and reverse. It would usually appear after two or more minutes after coming out of reverse. The idea was to inhibit excessive coking that could occur due to a rapid shutdown after landing. I don't know if this was a customer option or a mandatory SB?..

The 717 uses a derivative of the same RR engine that is found on the Gulfstream V There are significant procedures on the GV that deal with rotor bow after shutdown. Don't know if those are part of the 717 SOPs as well?
 
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Re: Engine cooling on short hops

Wed Nov 08, 2017 1:04 pm

I have flown both the CFM and V2500 powered 320 family. There is NO restriction about cooling other than ensure the engine idles for 2 minutes after reverse before engine shutdown. I have operated in warmer more humid conditions that the Hawaiian Islands and have never had a problem. I don't know what type of publication you are reading this information, but it is absolutely incorrect. You might want to contact them to find out where they are coming up with this information!

As everyone has told you, it is a non-issue and no one can figure what you are trying to prove/disprove. It would be a good idea if you could provide a link for these references.
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BravoOne
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Re: Engine cooling on short hops

Wed Nov 08, 2017 1:46 pm

mmo wrote:
I have flown both the CFM and V2500 powered 320 family. There is NO restriction about cooling other than ensure the engine idles for 2 minutes after reverse before engine shutdown. I have operated in warmer more humid conditions that the Hawaiian Islands and have never had a problem. I don't know what type of publication you are reading this information, but it is absolutely incorrect. You might want to contact them to find out where they are coming up with this information!

As everyone has told you, it is a non-issue and no one can figure what you are trying to prove/disprove. It would be a good idea if you could provide a link for these references.



MMO, who are your directing your comment to?
 
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XLA2008
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Re: Engine cooling on short hops

Wed Nov 08, 2017 2:05 pm

Balerit wrote:
XLA2008 wrote:
GalaxyFlyer wrote:
Are you talking about rotor bow? That’s not cooling strictly; it’s because of the heat rising into the top of the cowl and causing differential heat on the core and the rotor to “bow”. It is solved by dry motoring the engine during start to equalize temps and unbow the rotor shaft.

GF


Honestly... in terms of the industry, aircraft and operations I would like to say without being full of myself, that my knowledge is pretty established,

Thanks guys!


Have you ever worked on a plane? If not then you have zero knowledge. Demanding answers here and then refuting what is being said is plain arrogance.

The only issue with modern engines is rotor bow. As most people have mentioned, the time it takes to taxi to the gate is sufficient for engine cooling. The old JT9's were a problem and the answer was to motor the engines for 5 minutes after shut down. The only limiting thing would be brake temps, especially on B737's. I remember reading about JAL's 747's that were used for short hops, the landing gears were never retracted so that they could cool the brakes down.


Yes I’ve worked on a plane and still do, been in the industry for a long long time, when it comes to ops, aircraft and the industry my knowledge is pretty widespread however, it isn’t really arrogance asking for an answer, isn’t that what this forum is for? It’s a knowledge base (engine design & performance) I am unfamiliar with, and as I mentioned I have little experience in that area, working on a plane does not mean you know every single little operation of the aircraft down to its engine! To speculate that isn’t arrogance it’s pure ignorance which you clearly are, I can guarentee that pilots flying for 30+ years have little to no knowledge on Cabin equipment and procedures from behind the flight deck door, or an engineer would have absolutely no knowledge on cabin procedures for flight attendants, working on a plane in any capacity does NOT mean you know everything about everything so your comment is just plain ignorance, and you have made yourself look arrogant in your own response! I also mentioned that if it isn’t a cooling problem then, what is the issue that faces companies like Hawaiian that doesn’t allow them to operate aircraft outside of the 717 on these inter-Island flights... if you do a search yourself in the forum you will find numerous topics from plenty of members outside of this post...

viewtopic.php?t=1337129

Another link to another topic, explaining that engines don’t like the quick turns that HA operates, and also many posters mention engine cooling times, I simply am reciting what I have been reading and researching, if all of these people are wrong as mentioned also in my comments then what is the underlying issue preventing them from operating a more modern aircraft on these routes. Many people questions issues as to whether the GTF can handle the quick cycles.

Your response was unnecessary and rather arrogant yourself, if your here to name throw or cause problems then perhaps you shouldn’t post at all. And move on to somebody else’s topic. Take a read of the link I posted above, and then post a reply to me... because if what they are saying is wrong then explain to me why it’s wrong, that’s what I am seeking an answer for...

Aside from that I appreciate the replies! Thanks guys.
Last edited by XLA2008 on Wed Nov 08, 2017 2:25 pm, edited 2 times in total.
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Eng23
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Re: Engine cooling on short hops

Wed Nov 08, 2017 2:22 pm

I think the argument regarding the hi number of cycles and higher maintenance costs rather than any cooling issue is a more valid one maybe for the newer engines, it is interesting to think about it from an aircraft leasing point of view aswell, would be interesting to hear from people in that field to see if that would discourage them from leasing the aircraft to the operator or whether they would just increase the cost, obviously this doesn't seem to effect the 717 as badly
 
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XLA2008
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Re: Engine cooling on short hops

Wed Nov 08, 2017 2:36 pm

http://m.aviationweek.com/commercial-av ... ting-issue

An article relating to the issue with PW1100G, from which I am aware they are fixing the issue, but it also goes into more detail regarding engine cooling to some extent, to which previous topics have mentioned being the issue with certain aircraft replacing the 717. I am asking a valid question, and have found various forum posts and outside sources stating concerns around if GTF’s can handle the ops they run etc... which is what my entire post has been the question of.

“First, the engines must be able to handle the high-stress - short-turnaround schedule the interisland flying requires. The current engines that do well on longer flights won't do well interisland because there isn't enough time to cool down between flights. That is what killed Aloha's attempt to use the 737-300 with CFM engines. After a high power takeoff there isn't enough time to cool off in cruise before descent and landing. Then after a short turn it's back up into the air with a hot engine. AQ burned through a bunch of CFMs before going back to the -200.”

Also a quote I read moments ago. So if this is a non issue as mentioned then why is it being raised multiple times as an issue?

I get that other factors around a replacement for the 717 such as additional weight on aircraft etc make a direct replacement outside of a regional jet hard, however a one for one replacement isn’t really the topic I’m looking for, I was more interested in why engines couldn’t handle it, if you guys say that they can... well I guess they can! Simple as that, I was merely pointing out that more people have posted that engines are an issue, than people have posted in here saying they aren’t... so what should I think? I’m not saying someone is right or someone is wrong, because I am unfamiliar with this subject which is why I turned to the community for help. If they aren’t an issue then why do multiple people and multiple online articles and multiple forum posts say they are? That’s all... no need for some posters to start name calling or being ignorant, I’m not here to argue just to try and understand why someone is saying A and others are saying B. If engines are fully capable of handling these ops then... well I guess they are, but everyone else who says they aren’t seem to have an idea why they aren’t and I’m looking to clarify where they would get this idea, it’s not like it’s just one person saying it. That’s all.

Thanks guys
| A.J-B |

“For once you have tasted flight you will walk the earth with your eyes turned skywards, for there you have been and there you will long to return.“
 
GalaxyFlyer
Posts: 259
Joined: Fri Jan 01, 2016 4:44 am

Re: Engine cooling on short hops

Wed Nov 08, 2017 3:23 pm

It’s NOT cooling, it’s ROTOR BOW. The rotor is bowed due to uneven heating in the cowl which is solved by dry motoring to even the temps. It’s an issue for all flights because now occurs after shutdown—12 hours or 20 minutes. But the start procedure does increase start times and may cause a taxi delay post-start. Please accept that fact before going on.

The BR715 has a rotor bow issue— between 20 minutes and 5 hours AFTER shutdown, it requires a rotor bow start, basically 30 seconds of dry motoring to equalize temps and take out the “bow”. The same engine on the Global does the start automatically by the FADEC. On the Gulfstream, it is a manual start by the crew dry motoring the engine BEFORE adding fuel and ignition. Can’t say on the 717.

Again, it is not cooling, but post-shutdown rotor bow. BTW, the Concorde engines had the same issue, as do all jet engines to some degree. It depends on the engine, the mounting system used and time. The 777X will have a “jacking motor” to rotate the engine at the gate while on ground power to equalize temps.

GF
 
Alias1024
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Re: Engine cooling on short hops

Wed Nov 08, 2017 3:53 pm

BravoOne wrote:
Engine cooling can be an issue and the MD11 (PW) had a Engine Cool light. It was a small blue light within the engine display that would come on after landing and reverse. It would usually appear after two or more minutes after coming out of reverse. The idea was to inhibit excessive coking that could occur due to a rapid shutdown after landing. I don't know if this was a customer option or a mandatory SB?..

The 717 uses a derivative of the same RR engine that is found on the Gulfstream V There are significant procedures on the GV that deal with rotor bow after shutdown. Don't know if those are part of the 717 SOPs as well?


The 717 will display an Engine Cool message when the engines have cooled sufficiently for shutdown.

GalaxyFlyer wrote:
It’s NOT cooling, it’s ROTOR BOW. The rotor is bowed due to uneven heating in the cowl which is solved by dry motoring to even the temps. Please accept that fact before going on. The BR715 has a rotor bow issue— between 20 minutes and 5 hours AFTER shutdown, it requires a rotor bow start, basically 30 seconds of dry motoring to equalize temps and take out the “bow”. The same engine on the Global does the start automatically by the FADEC. On the Gulfstream, it is a manual start by the crew dry motoring the engine BEFORE adding fuel and ignition. Can’t say on the 717.


During normal starts the EEC will dry motor automatically on the 717. During manual starts with an inoperative FADEC the engine should be dry motored for 30 seconds at 19% N2 or greater, or longer if necessary to get TGT below 150 degrees C.

But rotor bow on the BR715 doesn't really explain the question of the OP. The question, based on many threads in this site's history, is what makes the BR715 more suitable than a CFM-56 or V2500 to the inter-island flying Hawaiian operates. That's been the conventional wisdom for years on this site. Rotor bow could be a problem for that type of operation, but doesn't cause issues for the BR715 for Hawaiian, and could be solved in other engines presumably by dry motoring. So is the conventional wisdom wrong about the BR715, or is there something else about it that makes it perform better that other modern turbofans in a short hop, quick turn environment?
It is a mistake to think you can solve any major problems with just potatoes.
 
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XLA2008
Topic Author
Posts: 327
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Re: Engine cooling on short hops

Wed Nov 08, 2017 4:00 pm

GalaxyFlyer wrote:
It’s NOT cooling, it’s ROTOR BOW. The rotor is bowed due to uneven heating in the cowl which is solved by dry motoring to even the temps. It’s an issue for all flights because now occurs after shutdown—12 hours or 20 minutes. But the start procedure does increase start times and may cause a taxi delay post-start. Please accept that fact before going on.

The BR715 has a rotor bow issue— between 20 minutes and 5 hours AFTER shutdown, it requires a rotor bow start, basically 30 seconds of dry motoring to equalize temps and take out the “bow”. The same engine on the Global does the start automatically by the FADEC. On the Gulfstream, it is a manual start by the crew dry motoring the engine BEFORE adding fuel and ignition. Can’t say on the 717.

Again, it is not cooling, but post-shutdown rotor bow. BTW, the Concorde engines had the same issue, as do all jet engines to some degree. It depends on the engine, the mounting system used and time. The 777X will have a “jacking motor” to rotate the engine at the gate while on ground power to equalize temps.

GF


Thank you for the clarification... that makes sense to me! And a decent answer to my question
| A.J-B |

“For once you have tasted flight you will walk the earth with your eyes turned skywards, for there you have been and there you will long to return.“
 
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XLA2008
Topic Author
Posts: 327
Joined: Mon May 30, 2016 8:53 pm

Re: Engine cooling on short hops

Wed Nov 08, 2017 4:14 pm

Alias1024 wrote:
BravoOne wrote:
Engine cooling can be an issue and the MD11 (PW) had a Engine Cool light. It was a small blue light within the engine display that would come on after landing and reverse. It would usually appear after two or more minutes after coming out of reverse. The idea was to inhibit excessive coking that could occur due to a rapid shutdown after landing. I don't know if this was a customer option or a mandatory SB?..

The 717 uses a derivative of the same RR engine that is found on the Gulfstream V There are significant procedures on the GV that deal with rotor bow after shutdown. Don't know if those are part of the 717 SOPs as well?


The 717 will display an Engine Cool message when the engines have cooled sufficiently for shutdown.

GalaxyFlyer wrote:
It’s NOT cooling, it’s ROTOR BOW. The rotor is bowed due to uneven heating in the cowl which is solved by dry motoring to even the temps. Please accept that fact before going on. The BR715 has a rotor bow issue— between 20 minutes and 5 hours AFTER shutdown, it requires a rotor bow start, basically 30 seconds of dry motoring to equalize temps and take out the “bow”. The same engine on the Global does the start automatically by the FADEC. On the Gulfstream, it is a manual start by the crew dry motoring the engine BEFORE adding fuel and ignition. Can’t say on the 717.


But rotor bow on the BR715 doesn't really explain the question of the OP. The question, based on many threads in this site's history, is what makes the BR715 more suitable than a CFM-56 or V2500 to the inter-island flying Hawaiian operates. That's been the conventional wisdom for years on this site. Rotor bow could be a problem for that type of operation, but doesn't cause issues for the BR715 for Hawaiian, and could be solved in other engines presumably by dry motoring. So is the conventional wisdom wrong about the BR715, or is there something else about it that makes it perform better that other modern turbofans in a short hop, quick turn environment?


Yes... same question as you.

I have an understanding of rotor bow and how that operates and affects the aircraft now.
| A.J-B |

“For once you have tasted flight you will walk the earth with your eyes turned skywards, for there you have been and there you will long to return.“
 
Flow2706
Posts: 73
Joined: Sat Jan 28, 2017 7:20 pm

Re: Engine cooling on short hops

Wed Nov 08, 2017 4:15 pm

The CFM56 (on the A320) doesn't do any dry cranking before the start so I guess rotor bow is not much of an issue with this engine. In practice it usually takes around 30 to 32 seconds from start valve opening till start valve closure (which occurs at around 50% N1) - in my company we have to run the timer to make sure this time does not go above the limit (2 minutes), which is a bit pointless as it is monitored (at least during a "normal" automatic engine start) by the FADEC anyway...the IAE on A320 does a dry crank during automatic start (around 30 seconds) so the time from start valve opening to closure is usually around one minute, sometimes in excess of one minute. I haven't flown the NEO, but it heard its more of an issue there compared with the CEO.
 
mmo
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Re: Engine cooling on short hops

Wed Nov 08, 2017 5:58 pm

MMO, who are your directing your comment to?[/quote]

Sorry it was to XLA2008
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trex8
Posts: 4892
Joined: Sat Nov 02, 2002 9:04 am

Re: Engine cooling on short hops

Thu Nov 09, 2017 2:43 pm

Im not a technical guy but being here for years and seeing these discussions, isnt the issue simply higher maintenance costs from higher cycles, fewer hours?? Theres no technical reason you cant "abuse" a CFM etc powered plane on inter island hops, you just pay through your nose for the mx!
 
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ThrottleHold
Posts: 561
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Re: Engine cooling on short hops

Thu Nov 09, 2017 4:20 pm

GE90 recommends 3 mins at idle before shutdown. (recommends, not mandates).
The famous GE90 growl on start up is a direct result of Rotor Bow.

RR Trent 900 series recommends 2 mins at idle before shut down.
On start up, FADEC will motor the engine until EGT below 100C, then introduce fuel.

Like the others, I've never heard on this supposed cooling problem.
 
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Balerit
Posts: 310
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Re: Engine cooling on short hops

Thu Nov 09, 2017 8:48 pm

That cooling down period is critical. We once had a B747 engine change where we had six hours before departure and rushed to get the job done and still do a ground run. Unfortunately they rushed to finish and didn't do a sufficient cooling down after the high power ground run. The plane was ready to depart on time but when they tried to start the new motor, the turbine case had cooled down quicker than the turbine rotor, resulting in the N2 being jammed solid. It took about four hours for it to finally cool and come free.
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fr8mech
Posts: 6878
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Re: Engine cooling on short hops

Fri Nov 10, 2017 2:04 am

[*]
trex8 wrote:
Im not a technical guy but being here for years and seeing these discussions, isnt the issue simply higher maintenance costs from higher cycles, fewer hours?? Theres no technical reason you cant "abuse" a CFM etc powered plane on inter island hops, you just pay through your nose for the mx!


That's my feeling. Take-offs are hard on engines. The more take-offs, the more wear and maintenance. My guess is, that older, low-bypass engines, with looser tolerances are better able to deal with more cycles. Just a guess.
When seconds count...the police are minutes away.
 
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Faro
Posts: 1610
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Re: Engine cooling on short hops

Fri Nov 10, 2017 8:08 pm

The most demanding regime in terms of engine core cooling (high pressure turbine) is neither post-shutdown nor even takeoff. It is top of climb. From this thread and reply No 7 by Lightsaber:

viewtopic.php?t=1366965

"Top of climb has the worst cooling for the high turbine. It determines high turbine wear and thus overhaul intervals. This is the initial climb from ground, not the step climbs. This is due to lower airframe Mach number at a high demand. Once the plane is at cruise there is more cooling. It has to do with the pressure differences at the inlet guide vanes and high turbine.

Lightsaber"


Faro
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StereoTechque
Posts: 139
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Re: Engine cooling on short hops

Sat Nov 11, 2017 1:20 pm

ThrottleHold wrote:
The famous GE90 growl on start up is a direct result of Rotor Bow..

Ive come across this GE90 growl quote many times across this forum. Any reference to this phenomenon?
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77west
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Re: Engine cooling on short hops

Mon Nov 13, 2017 2:17 am

StereoTechque wrote:
ThrottleHold wrote:
The famous GE90 growl on start up is a direct result of Rotor Bow..

Ive come across this GE90 growl quote many times across this forum. Any reference to this phenomenon?


I read that it is due to the way the air flows at a specific RPM during start that causes a resonance in the combustors. Nothing to do with rotor bow.
77West - AW109S - BE90 - JS31 - B1900 - Q300 - ATR72 - DC9-30 - MD80 - B733 - A320 - B738 - A300-B4 - B773 - B77W
 
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Balerit
Posts: 310
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Re: Engine cooling on short hops

Tue Nov 14, 2017 10:33 am

This will help with the cooling problem in the air but the rotor bow will still be a problem on the ground. Also some good info on what the cooling problem is.

https://www.google.ch/patents/US6931859
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DashTrash
Posts: 1271
Joined: Mon Aug 21, 2006 8:44 am

Re: Engine cooling on short hops

Tue Nov 14, 2017 5:58 pm

The engines I've flown have a max ITT before introducing fuel. I think on the AE3007 it was 200. If you're starting engines with temp above that you motor the engine until the temp is below 200 before introducing fuel. Oil temps are not a problem.

Brake temps between short turns are a bigger issue.

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