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ENGINEerJW
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Installed Engine Attitude

Wed Nov 18, 2020 7:37 pm

Hi, I was wondering if anyone had any information on the following…

On the latest large wide body jets (777X, 787, A330neo, A350 etc) are the engines hung perpendicular to the ground or the wing?

If they are hung perpendicular to the wing, then there would be a right engine vs left engine difference in the attitude of the engine due to the dihedral of the wing.
Are there differences in approach between Boeing and Airbus? Comparing the Trent 1000 installed on the 787 and the Trent 7000 installed on the A330neo would be interesting as if there is a difference in approach between the airframers this would translate to a difference in the installed position of the engine, despite the Bill of Materials of these products being very similar.

Thanks for any help you can provide!
 
unimproved
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Re: Installed Engine Attitude

Wed Nov 18, 2020 8:31 pm

The engine is identical on both wings. During install they're rotated a few degrees by pulling them against the wing mount.
 
chimborazo
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Re: Installed Engine Attitude

Wed Nov 18, 2020 9:09 pm

unimproved wrote:
The engine is identical on both wings. During install they're rotated a few degrees by pulling them against the wing mount.


I would imagine the pylons account for the necessary geometry to “point” the engine in the right direction, rather than any rotation by pulling them when installed. There will be an allowable tolerance built into how much offset either side of “centred” but it would be a very small fraction of a degree.

Wing-mounted engines are generally slightly toed-in as-designed to account for the wake from the aeroplane nose. This can be seen when viewing a head-on photo of an airliner viewed directly from the front: you can see “a bit more” of the outboard side of the nacelle than would be possible If the engines were exactly parallel to the longitudinal axis.

Edit: I missed the bit about the ground so we are talking nose up/down. Same as above though: it will be a set angle on the pylon. I can’t see that there would be need for any adjustment.
 
N965UW
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Re: Installed Engine Attitude

Wed Nov 18, 2020 9:51 pm

chimborazo wrote:
Wing-mounted engines are generally slightly toed-in as-designed to account for the wake from the aeroplane nose. This can be seen when viewing a head-on photo of an airliner viewed directly from the front: you can see “a bit more” of the outboard side of the nacelle than would be possible If the engines were exactly parallel to the longitudinal axis.


Is this related to why contrails appear to "billow" out a bit before straightening? This photo from the DLR is a good example of what I'm talking about:

Image
You can always go around
 
kalvado
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Re: Installed Engine Attitude

Thu Nov 19, 2020 1:28 am

I always thought that it may make sense to install engines with thrust vector pointing a bit upward - to gain some upward force. At a small angle, lost of forward thrust vs gained vertical component may be better than the increase of drag required to create a comparable amount of lift.
As for engines parallel to the ground - I doubt that is a concern. A few aircraft families had floor angle changed between modifications - 737MAX being the latest one with longer nose gear compared to NG to accommodate those engines.

Lateral alignment.. There was a pretty strange story a few years ago when the shop messed with the job and unintentionally swapped engines (1 and 4, I believe?) after a major check. Comments were that engines ended up a bit misaligned as a result, and while safety was not really compromised (safety of jobs and licenses notwithstanding), but a few %% of efficiency were lost.
 
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Starlionblue
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Re: Installed Engine Attitude

Thu Nov 19, 2020 4:56 am

kalvado wrote:
I always thought that it may make sense to install engines with thrust vector pointing a bit upward - to gain some upward force. At a small angle, lost of forward thrust vs gained vertical component may be better than the increase of drag required to create a comparable amount of lift.
As for engines parallel to the ground - I doubt that is a concern. A few aircraft families had floor angle changed between modifications - 737MAX being the latest one with longer nose gear compared to NG to accommodate those engines.

Lateral alignment.. There was a pretty strange story a few years ago when the shop messed with the job and unintentionally swapped engines (1 and 4, I believe?) after a major check. Comments were that engines ended up a bit misaligned as a result, and while safety was not really compromised (safety of jobs and licenses notwithstanding), but a few %% of efficiency were lost.


I don't think a slight upward angle would make much difference. Much more important to be aligned with local airflow. As mentioned by N965UW, wing-mounted engines are typically toed in a bit. Tail mounted engines are toed out. You can see it on this MD-80.

Image



N965UW wrote:
chimborazo wrote:
Wing-mounted engines are generally slightly toed-in as-designed to account for the wake from the aeroplane nose. This can be seen when viewing a head-on photo of an airliner viewed directly from the front: you can see “a bit more” of the outboard side of the nacelle than would be possible If the engines were exactly parallel to the longitudinal axis.


Is this related to why contrails appear to "billow" out a bit before straightening? This photo from the DLR is a good example of what I'm talking about:

Image


Yes that might be the shape of the wake. Or simply expansion in the cool air.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
N965UW
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Re: Installed Engine Attitude

Thu Nov 19, 2020 5:45 am

Starlionblue wrote:
As mentioned by N965UW, wing-mounted engines are typically toed in a bit.


Credit for that belongs to chimborazo
You can always go around
 
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Starlionblue
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Re: Installed Engine Attitude

Thu Nov 19, 2020 5:48 am

N965UW wrote:
Starlionblue wrote:
As mentioned by N965UW, wing-mounted engines are typically toed in a bit.


Credit for that belongs to chimborazo


Oops!

Thanks for setting the record straight.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
kalvado
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Re: Installed Engine Attitude

Thu Nov 19, 2020 7:31 am

N965UW wrote:
chimborazo wrote:
Wing-mounted engines are generally slightly toed-in as-designed to account for the wake from the aeroplane nose. This can be seen when viewing a head-on photo of an airliner viewed directly from the front: you can see “a bit more” of the outboard side of the nacelle than would be possible If the engines were exactly parallel to the longitudinal axis.


Is this related to why contrails appear to "billow" out a bit before straightening? This photo from the DLR is a good example of what I'm talking about:

Image

Frankly speaking, 747 ad in this pic has a fairly interesting contrail configuration - and I am not sure it speaks about efficiency. look for air to air images. As far as I understand, outer lines in contrail belong to inner engines exhaust...
Most other planes seem to have more aligned configurations...
 
CRJockey
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Re: Installed Engine Attitude

Thu Nov 19, 2020 10:07 am

kalvado wrote:
Lateral alignment.. There was a pretty strange story a few years ago when the shop messed with the job and unintentionally swapped engines (1 and 4, I believe?) after a major check. Comments were that engines ended up a bit misaligned as a result, and while safety was not really compromised (safety of jobs and licenses notwithstanding), but a few %% of efficiency were lost.


That story seems unfounded in reality. All jet aircraft I have been working on or around had no restriction whatsoever with regards to installation position of an engine. The only restriction might be QEC-configuration which can be different (e.g. MD11 tail engine has a different QEC as in different engine accessory installations compared to the identical wing engine QEC). All other current aircraft I am aware of have identical installation whatever the engine position.
 
kalvado
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Re: Installed Engine Attitude

Thu Nov 19, 2020 12:13 pm

CRJockey wrote:
kalvado wrote:
Lateral alignment.. There was a pretty strange story a few years ago when the shop messed with the job and unintentionally swapped engines (1 and 4, I believe?) after a major check. Comments were that engines ended up a bit misaligned as a result, and while safety was not really compromised (safety of jobs and licenses notwithstanding), but a few %% of efficiency were lost.


That story seems unfounded in reality. All jet aircraft I have been working on or around had no restriction whatsoever with regards to installation position of an engine. The only restriction might be QEC-configuration which can be different (e.g. MD11 tail engine has a different QEC as in different engine accessory installations compared to the identical wing engine QEC). All other current aircraft I am aware of have identical installation whatever the engine position.

This is the only one I can find right now, I am pretty sure there was another one
viewtopic.php?t=370335
 
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SheikhDjibouti
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Re: Installed Engine Attitude

Thu Nov 19, 2020 1:43 pm

ENGINEerJW wrote:
On the latest large wide body jets (777X, 787, A330neo, A350 etc) are the engines hung perpendicular to the ground or the wing?

Taking the A330 example; most A330s point slightly nose down (in terms of fuselage alignment). Sometimes it screams, and sometimes it's just the camera angle. :lol:


But... the A330F has a revised nose undercarriage layout to provide a level deck during cargo loading.

ImageThx as usual to wikipedia/wikimedia

Hence your question might be... do they position the engines differently on the A330F to the other models?
I'm guessing the answer is no, because it is the engine/fuselage alignment in flight that is going to be most critical for efficiency.


FWIW here is an extreme example of engine re-alignment by means of custom made extendable nose gear. This adaptation was in order to provide "vectored" thrust when it was most needed - when taking off from the rather short deck of a Royal Navy aircraft carrier.
(Sorry about the people cluttering the scene, but it really is the best photo for showing the amazing angle attained by these RN F-4Ks)
Nothing to see here; move along please.
 
CRJockey
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Re: Installed Engine Attitude

Thu Nov 19, 2020 6:25 pm

kalvado wrote:
CRJockey wrote:
kalvado wrote:
Lateral alignment.. There was a pretty strange story a few years ago when the shop messed with the job and unintentionally swapped engines (1 and 4, I believe?) after a major check. Comments were that engines ended up a bit misaligned as a result, and while safety was not really compromised (safety of jobs and licenses notwithstanding), but a few %% of efficiency were lost.


That story seems unfounded in reality. All jet aircraft I have been working on or around had no restriction whatsoever with regards to installation position of an engine. The only restriction might be QEC-configuration which can be different (e.g. MD11 tail engine has a different QEC as in different engine accessory installations compared to the identical wing engine QEC). All other current aircraft I am aware of have identical installation whatever the engine position.

This is the only one I can find right now, I am pretty sure there was another one
viewtopic.php?t=370335


No offence intented, but not a plausible story, in my view. Maybe some thrust reverser installation has been incorrect for the installation side. I am no expert on this.

But neither on the CF6, PW4000, CF34, Trent 700 have I ever heard such thing apart from differing QECs (well, piping and cables).
 
kalvado
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Re: Installed Engine Attitude

Thu Nov 19, 2020 6:37 pm

CRJockey wrote:
kalvado wrote:
CRJockey wrote:

That story seems unfounded in reality. All jet aircraft I have been working on or around had no restriction whatsoever with regards to installation position of an engine. The only restriction might be QEC-configuration which can be different (e.g. MD11 tail engine has a different QEC as in different engine accessory installations compared to the identical wing engine QEC). All other current aircraft I am aware of have identical installation whatever the engine position.

This is the only one I can find right now, I am pretty sure there was another one
viewtopic.php?t=370335


No offence intented, but not a plausible story, in my view. Maybe some thrust reverser installation has been incorrect for the installation side. I am no expert on this.

But neither on the CF6, PW4000, CF34, Trent 700 have I ever heard such thing apart from differing QECs (well, piping and cables).

I cannot find it, I swear there was a lengthly thread here... But whatever... And since we're on a subject:
on a CRJ, what would it take to swap right and left engines? Do you have to flip engine up side down so that accessories which were on the bottom go on top, or there are two pylon attachment locations on the engine? Or something along the lines of Banjo fitting?
 
VMCA787
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Re: Installed Engine Attitude

Thu Nov 19, 2020 6:42 pm

SheikhDjibouti wrote:

FWIW here is an extreme example of engine re-alignment by means of custom made extendable nose gear. This adaptation was in order to provide "vectored" thrust when it was most needed - when taking off from the rather short deck of a Royal Navy aircraft carrier.


The extended nose gear for carrier ops was NOT for the "vectored" thrust as you state. The purpose of the extension was to increase the angle of attack on cat launches. So there was not the tendency to over-rotate by a massive input to the Stab. The F-4 had a tendency to nose up if you put too much of an input into the rotation.
Fly fast, live slow!
 
ENGINEerJW
Topic Author
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Re: Installed Engine Attitude

Thu Nov 19, 2020 6:48 pm

Hi All,

Thanks for your responses, some interesting observations and debate!

The engine attitude I was referring to in the original post was from the perspective of looking forward down the length of the plane. As can be seen on this image below there does appear to be a left engine vs right engine difference where the engines appear to be perpendicular to the wing, not the ground. From your experience and observations is this consistent across a number of aircraft?



(Hopefully, the image comes up... new to posting here!)

Thanks!
 
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Horstroad
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Re: Installed Engine Attitude

Thu Nov 19, 2020 8:08 pm

ENGINEerJW wrote:
Hi All,

Thanks for your responses, some interesting observations and debate!

The engine attitude I was referring to in the original post was from the perspective of looking forward down the length of the plane. As can be seen on this image below there does appear to be a left engine vs right engine difference where the engines appear to be perpendicular to the wing, not the ground. From your experience and observations is this consistent across a number of aircraft?



(Hopefully, the image comes up... new to posting here!)

Thanks!


On the aircraft I'm familiar with the engines are mounted perpendicular to the wing. That's why the oil levels on the left and right engines might be different, especially on the generators. The sight glass usually has two markings, one for the left wing and one for the right wing.

Image

On the 777 the engine is tilted about 7° relative to vertical.
 
unimproved
Posts: 260
Joined: Sun Jun 22, 2014 7:14 pm

Re: Installed Engine Attitude

Thu Nov 19, 2020 8:15 pm

ENGINEerJW wrote:
Hi All,

Thanks for your responses, some interesting observations and debate!

The engine attitude I was referring to in the original post was from the perspective of looking forward down the length of the plane. As can be seen on this image below there does appear to be a left engine vs right engine difference where the engines appear to be perpendicular to the wing, not the ground. From your experience and observations is this consistent across a number of aircraft?



(Hopefully, the image comes up... new to posting here!)

Thanks!

This is true for pretty much every aircraft type. The engines are identical, being titlted with hydraulic jacks or just plain hand operated chains during install.
 
Okie
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Re: Installed Engine Attitude

Thu Nov 19, 2020 8:38 pm

kalvado wrote:
I cannot find it, I swear there was a lengthly thread here... But whatever... And since we're on a subject:


The thread was about a 737 that had come out of heavy check and the cowling was switched between Left Engine #1 and the Right Engine #2.

That put the Strake for area ruling towards the wing tip instead of toward the fuselage where it was suppose to be.

I do not remember the thread topic was exactly but my thought at the time if the strake was just installed on the wrong side of the cowling as in there is a common cowling with positions to install the strake on either side or if they had to switch the cowls.

Okie
 
kalvado
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Re: Installed Engine Attitude

Thu Nov 19, 2020 8:43 pm

Okie wrote:
kalvado wrote:
I cannot find it, I swear there was a lengthly thread here... But whatever... And since we're on a subject:


The thread was about a 737 that had come out of heavy check and the cowling was switched between Left Engine #1 and the Right Engine #2.

That put the Strake for area ruling towards the wing tip instead of toward the fuselage where it was suppose to be.

I do not remember the thread topic was exactly but my thought at the time if the strake was just installed on the wrong side of the cowling as in there is a common cowling with positions to install the strake on either side or if they had to switch the cowls.

Okie

I saw that thread; and no, I am thinking about something different - but no trace though.
Biggest message, though - shit happens, and sometimes things are not that bad after all
 
kalvado
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Re: Installed Engine Attitude

Thu Nov 19, 2020 8:46 pm

Horstroad wrote:
On the 777 the engine is tilted about 7° relative to vertical.

is that tilted left to right, or total left-right and front-back tilt?
 
gloom
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Re: Installed Engine Attitude

Fri Nov 20, 2020 7:34 am

I seem to remember an article somewhere over the net (pdf or presentation) where they discussed attitude of engine to body. There seems to be general tendency to slightly turn the engine front up, by approx 3 degs, which would be more or less the attitude of body during cruise, and I guess that's the reason (to have engine "straight" when cruising). However, it's been quite different from plane to plane (which seems understandable, as they have different pitch on cruise as well), and the difference was from low 2s to 5 degrees, as far as I remember.

Also, some airplanes would probably use different values, for a purpose. For a short range hopper with STOL capability, for example. However, they're margin.

Cheers,
Adam
 
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Horstroad
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Re: Installed Engine Attitude

Fri Nov 20, 2020 12:24 pm

kalvado wrote:
Horstroad wrote:
On the 777 the engine is tilted about 7° relative to vertical.

is that tilted left to right, or total left-right and front-back tilt?

That's left to right. The engine is 0.35° nose up relative to the local wing chord line. But I don't know what angle this is relative to the fuselage. The toe angle is 1.75°.
 
kalvado
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Re: Installed Engine Attitude

Fri Nov 20, 2020 2:04 pm

Horstroad wrote:
kalvado wrote:
Horstroad wrote:
On the 777 the engine is tilted about 7° relative to vertical.

is that tilted left to right, or total left-right and front-back tilt?

That's left to right. The engine is 0.35° nose up relative to the local wing chord line. But I don't know what angle this is relative to the fuselage. The toe angle is 1.75°.

I guess its a pretty safe assumption that in cruise chord is pointing upward as well for AoA and lift reasons, for even more upward pointing engines
 
WIederling
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Re: Installed Engine Attitude

Fri Nov 20, 2020 2:23 pm

kalvado wrote:
I always thought that it may make sense to install engines with thrust vector pointing a bit upward - to gain some upward force.


Hmm.
the upward part of the thrust vector translates directly into an upward force / "lift".

the forward part of the thrust vector translates via the multiplyer ( ~~glide ratio resp. parasitic drag ) into upward force / "lift" .

Thus thrust upward is mostly wasted ?
Murphy is an optimist
 
kalvado
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Re: Installed Engine Attitude

Fri Nov 20, 2020 4:16 pm

WIederling wrote:
kalvado wrote:
I always thought that it may make sense to install engines with thrust vector pointing a bit upward - to gain some upward force.


Hmm.
the upward part of the thrust vector translates directly into an upward force / "lift".

the forward part of the thrust vector translates via the multiplyer ( ~~glide ratio resp. parasitic drag ) into upward force / "lift" .

Thus thrust upward is mostly wasted ?
If you apply force (thrust) at a angle x radians:
You get vertical thrust (I don't want to say "lift" not to confuse with aerodynamic force) is thrust*sin(x)~thrust*x;
You get forward thrust of thrust*cos(x)~thrust(1-x*x/2);
For a "lift to drag" ratio of x/(x*x/2) = 2/x
L/D ratio for airliners is in 15-20 ballpark, so you can benefit from vertical component of thrust up to x~0.1 rad = 5.7 deg.
Of course, this is physics 101 calculation which may change in a wonderful world of aerodynamics, but I suspect ballpark numbers are similar.
 
meecrob
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Re: Installed Engine Attitude

Fri Nov 20, 2020 5:36 pm

I thought the reason certain plane's engines are "pitched" relative to their deck angle was to better align the engines to thrust through the CofG and thus minimize adverse pitch when changing power settings, not to "vector" the thrust to increase lift.
 
kalvado
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Re: Installed Engine Attitude

Fri Nov 20, 2020 6:22 pm

meecrob wrote:
I thought the reason certain plane's engines are "pitched" relative to their deck angle was to better align the engines to thrust through the CofG and thus minimize adverse pitch when changing power settings, not to "vector" the thrust to increase lift.

Maybe for tail mounted turbine or nose mounted props, but wing mounted ones are pretty close to CoG anyway, so pitching will not do much.
Not sure where this image came from, but looks about right: http://www.aero.pub.ro/wordpress/wp-con ... 80x675.jpg
On the other hand, I heard that toe-in was needed to intersect thrust vectors in front of CoG and center of pressure as that improves stability. I find it hard to buy, though.
 
meecrob
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Re: Installed Engine Attitude

Fri Nov 20, 2020 7:40 pm

What I am saying is they do not angle engines to increase lift as that would reduce thrust due to cosign losses. It is far more efficient to increase your speed and take advantage of the fact that lift equals speed squared. Now, having said that, I'm sure there are plenty of examples of aircraft that have their engines angled that way due to a design compromise, but I doubt many designs had it as a feature from clean-sheet.
 
kalvado
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Re: Installed Engine Attitude

Fri Nov 20, 2020 9:31 pm

meecrob wrote:
What I am saying is they do not angle engines to increase lift as that would reduce thrust due to cosign losses. It is far more efficient to increase your speed and take advantage of the fact that lift equals speed squared. Now, having said that, I'm sure there are plenty of examples of aircraft that have their engines angled that way due to a design compromise, but I doubt many designs had it as a feature from clean-sheet.

And I am taking it one step further showing that this is not the case based on primitive math.
 
meecrob
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Re: Installed Engine Attitude

Fri Nov 20, 2020 11:00 pm

But you did not calculate the reduced angle of attack the wing is seeing due to your upward thrust vector.
 
gloom
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Re: Installed Engine Attitude

Sat Nov 21, 2020 7:02 am

Managed to find a paper I read earlier on:
http://www.icas.org/ICAS_ARCHIVE/ICAS2006/PAPERS/422

For those of you interested in examples, skip to attachments.
For those of you familiar with math, the documents body is yours and only.

Cheers,
Adam
 
Max Q
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Re: Installed Engine Attitude

Sat Nov 21, 2020 7:08 am

Cathay developed in cooperation with Boeing a modified mounting for their RR engines on their Classic 747 fleet

This mod angled the pods slightly ‘nose down’ to better align incoming air into the nacelle at the aircraft’s normal nose up cruising attitude


Apparently it was demonstrated to improve fuel efficiency
The best contribution to safety is a competent Pilot.


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