T54A
Topic Author
Posts: 109
Joined: Mon Oct 19, 2015 11:47 am

P-8 Poseidon raked wingtip

Fri Jul 06, 2018 12:39 pm

Why did the P-8 Poseidon get raked wingtips and not winglets or the split scimitar like other B737’s?
T6, Allouette 3, Oryx, King Air, B1900, B727, B744, A319, A342/3/6 A332/3
 
ZaphodHarkonnen
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Re: P-8 Poseidon raked wingtip

Fri Jul 06, 2018 2:12 pm

My understanding is for the long range flights that the P-8 is designed for the raked wingtips are of more benefit than the more traditional wingtips.

Plus given they won't be using gates like normal 737s they've got more room to play with.
 
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Florianopolis
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Re: P-8 Poseidon raked wingtip

Fri Jul 06, 2018 5:01 pm

Anti-icing on your typical 737NG ends at the penultimate slat section. That's okay for an airliner, which doesn't spend much time in icing conditions. Airliners live at cruise altitudes, and are only going through icing for a minute or two on their way up and down.

But a maritime patrol airplane will spend much more time in low-mid altitude icing conditions, and the factory commercial 737 anti-icing wasn't gonna do the job. So they put their heads together and decided that replacing the winglet with a raked thing would either reduce the amount of ice collected, or that it was easier to install anti-ice ducting out to the tip if it wasn't a winglet. To be honest, they probably could have just deleted the wingtip device entirely and 99% of the missions would have been fine.

The big vertical wingtip may also block some ESM stuff, but I don't think that's a big deal. The radar lives in the nose and might have been able to see the winglet, but for a sea-search radar, that only matters if the ship or periscope is above the airplane.

I don't understand why they deleted the eyebrow windows, though. Eyebrow windows are useful for low-altitude, high-bank-angle turns. The only 737s in the world doing that are . . . P-8s !
 
VSMUT
Posts: 1901
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Re: P-8 Poseidon raked wingtip

Fri Jul 06, 2018 6:36 pm

ZaphodHarkonnen wrote:
My understanding is for the long range flights that the P-8 is designed for the raked wingtips are of more benefit than the more traditional wingtips.

Plus given they won't be using gates like normal 737s they've got more room to play with.


The blended winglets are superior, even for longer flights (hence why you find them on 767s, A321neoLRs and 757s these days).

It is as Florianopolis writes, the low-altitude requirement. I believe the crosswind performance was part of it too.
 
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Florianopolis
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Re: P-8 Poseidon raked wingtip

Fri Jul 06, 2018 11:06 pm

Florianopolis wrote:
Anti-icing on your typical 737NG ends at the penultimate slat section. That's okay for an airliner, which doesn't spend much time in icing conditions. Airliners live at cruise altitudes, and are only going through icing for a minute or two on their way up and down.

But a maritime patrol airplane will spend much more time in low-mid altitude icing conditions, and the factory commercial 737 anti-icing wasn't gonna do the job. So they put their heads together and decided that replacing the winglet with a raked thing would either reduce the amount of ice collected, or that it was easier to install anti-ice ducting out to the tip if it wasn't a winglet.


Upon further review, the raked wingtips, and the vertical and horizontal stabilizers, have a fancy Electro-Mechanical Expulsion Deicing System (EMEDS), which you can read more about here:

http://www.coxandco.com/products/low_po ... stems.html
 
Max Q
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Re: P-8 Poseidon raked wingtip

Sat Jul 07, 2018 12:03 am

Florianopolis wrote:
Anti-icing on your typical 737NG ends at the penultimate slat section. That's okay for an airliner, which doesn't spend much time in icing conditions. Airliners live at cruise altitudes, and are only going through icing for a minute or two on their way up and down.

But a maritime patrol airplane will spend much more time in low-mid altitude icing conditions, and the factory commercial 737 anti-icing wasn't gonna do the job. So they put their heads together and decided that replacing the winglet with a raked thing would either reduce the amount of ice collected, or that it was easier to install anti-ice ducting out to the tip if it wasn't a winglet. To be honest, they probably could have just deleted the wingtip device entirely and 99% of the missions would have been fine.

The big vertical wingtip may also block some ESM stuff, but I don't think that's a big deal. The radar lives in the nose and might have been able to see the winglet, but for a sea-search radar, that only matters if the ship or periscope is above the airplane.

I don't understand why they deleted the eyebrow windows, though. Eyebrow windows are useful for low-altitude, high-bank-angle turns. The only 737s in the world doing that are . . . P-8s !



Agree on the eyebrow windows, especially in this application, in the cruise they’re
an annoyance but while maneuvering in the traffic pattern on the B727 they were very useful and they would have been for this aircraft banking at low altitude
The best contribution to safety is a competent Pilot.
 
Woodreau
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Re: P-8 Poseidon raked wingtip

Sat Jul 07, 2018 12:56 am

Gotta have those eyebrow windows to line up on the smoke marker the P-8 dropped to drop the torpedo from the bomb bay.
Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
 
Max Q
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Re: P-8 Poseidon raked wingtip

Sat Jul 07, 2018 4:13 am

Woodreau wrote:
Gotta have those eyebrow windows to line up on the smoke marker the P-8 dropped to drop the torpedo from the bomb bay.



That’s it !
The best contribution to safety is a competent Pilot.
 
ZaphodHarkonnen
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Re: P-8 Poseidon raked wingtip

Sat Jul 07, 2018 9:22 am

VSMUT wrote:
ZaphodHarkonnen wrote:
My understanding is for the long range flights that the P-8 is designed for the raked wingtips are of more benefit than the more traditional wingtips.

Plus given they won't be using gates like normal 737s they've got more room to play with.


The blended winglets are superior, even for longer flights (hence why you find them on 767s, A321neoLRs and 757s these days).

It is as Florianopolis writes, the low-altitude requirement. I believe the crosswind performance was part of it too.


Cheers.

As for no eyebrow windows. I thought that they had been removed from the design entirely? As in the airframe had even been modfied around that point to delete the extra structure.
 
T54A
Topic Author
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Re: P-8 Poseidon raked wingtip

Sat Jul 07, 2018 8:54 pm

Low level/low speed drag deduction does seem like a probable contender. Icing theory sounds possible, but could easily be mitigated with improved anti ice system
T6, Allouette 3, Oryx, King Air, B1900, B727, B744, A319, A342/3/6 A332/3
 
KCharlie
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Re: P-8 Poseidon raked wingtip

Sun Jul 08, 2018 10:31 pm

VSMUT wrote:
ZaphodHarkonnen wrote:
My understanding is for the long range flights that the P-8 is designed for the raked wingtips are of more benefit than the more traditional wingtips.

Plus given they won't be using gates like normal 737s they've got more room to play with.


The blended winglets are superior, even for longer flights (hence why you find them on 767s, A321neoLRs and 757s these days).


That's generally not true. For a given length, straight wingtips are better: http://www.smartcockpit.com/docs/Wingtip_Devices.pdf
 
VSMUT
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Re: P-8 Poseidon raked wingtip

Mon Jul 09, 2018 7:15 am

KCharlie wrote:
VSMUT wrote:
ZaphodHarkonnen wrote:
My understanding is for the long range flights that the P-8 is designed for the raked wingtips are of more benefit than the more traditional wingtips.

Plus given they won't be using gates like normal 737s they've got more room to play with.


The blended winglets are superior, even for longer flights (hence why you find them on 767s, A321neoLRs and 757s these days).


That's generally not true. For a given length, straight wingtips are better: http://www.smartcockpit.com/docs/Wingtip_Devices.pdf


Well it does state that raked wingtips are better on new designs, and that it isn't necessarily the case for retrofits. This is perfectly in line with reality, where new-builds like the 777, 787 and A350 received "straight" wingtips, while 767-300, 737 and A320 families and 757 are all retrofits.
 
jagraham
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Re: P-8 Poseidon raked wingtip

Wed Jul 11, 2018 5:50 am

VSMUT wrote:
KCharlie wrote:
VSMUT wrote:

The blended winglets are superior, even for longer flights (hence why you find them on 767s, A321neoLRs and 757s these days).


That's generally not true. For a given length, straight wingtips are better: http://www.smartcockpit.com/docs/Wingtip_Devices.pdf


Well it does state that raked wingtips are better on new designs, and that it isn't necessarily the case for retrofits. This is perfectly in line with reality, where new-builds like the 777, 787 and A350 received "straight" wingtips, while 767-300, 737 and A320 families and 757 are all retrofits.


The 767-400 also has raked wingtips. Comes with the plane, of course.
 
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Erebus
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Re: P-8 Poseidon raked wingtip

Thu Jul 12, 2018 10:57 pm

VSMUT wrote:
Well it does state that raked wingtips are better on new designs, and that it isn't necessarily the case for retrofits.


I can't argue if it is better or worse with regards to aerodynamics for retrofits, but I think a big part of the reason why no raked wingtips found their way into B737s and A320s is to keep them within the Code C of the ICAO aerodrome reference code. As it is, with the blended winglets, they are already pushing it at just under the maximum of 36m. A quick glance at wiki, if it is correct, shows that the P8 has a wingspan of 37.64m.
 
Chaostheory
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Re: P-8 Poseidon raked wingtip

Fri Jul 13, 2018 6:45 am

VSMUT wrote:
KCharlie wrote:
VSMUT wrote:

The blended winglets are superior, even for longer flights (hence why you find them on 767s, A321neoLRs and 757s these days).


That's generally not true. For a given length, straight wingtips are better: http://www.smartcockpit.com/docs/Wingtip_Devices.pdf


Well it does state that raked wingtips are better on new designs, and that it isn't necessarily the case for retrofits. This is perfectly in line with reality, where new-builds like the 777, 787 and A350 received "straight" wingtips, while 767-300, 737 and A320 families and 757 are all retrofits.


Raked wingtips work better on legacy platforms too.

As jagraham points out, the 764 has them. The raked tips lower fuel burn by nearly 7% on longhaul flights. I'm told they don't require as much weight or reinforcement going into the wing either.

Worth mentioning at this point that the apb blended winglet on Boeing types has started to suffer from fatigue issues with cracks developing. A number of ADs have been posted recently.
 
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DocLightning
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Re: P-8 Poseidon raked wingtip

Fri Jul 13, 2018 9:10 pm

VSMUT wrote:
The blended winglets are superior, even for longer flights (hence why you find them on 767s, A321neoLRs and 757s these days).


Not necessarily. A highly-swept coplanar wingtip extension has some advantages and disadvantages. For advantages, it gives the same extra drag reduction as a nonplanar winglet with less overall structure and wetted area. In addition, because the center of lift on the wingtip extension is aft of the center of lift of the wing, a gust striking the wingtip will cause a slight downward deflection of the leading edge, which grants gust unloading. For disadvantages, there is the increased span and also the fact that the increase in lift occurs further outboard than with a winglet (where the increase in lift occurs over the outer section of the main wing), so the planar wingtip extension will cause more of a bending moment on the inner spar, requiring more reinforcement there.

Airbus wings are stiffer than Boeing wings, so the aeroelastic gust unloading granted by a coplanar, swept wingtip extension would be significantly damped. Airbus still went with an extension, but then blended it upwards into a nonplanar winglet. This decreases the overall span.

If blended winglets were superior, Boeing would not be installing folding swept wingtip extensions on the 777X.
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