GrandTheftAero From United States of America, joined Nov 2003, 254 posts, RR: 6 Reply 1, posted (6 years 2 months 3 weeks 1 day 3 hours ago) and read 6894 times:
Ah... very observant... before people start wildly speculating let me post this well-written article about (drum role) Nacelle Strakes!!!
from Dick Shevell's AIAA paper Aerodynamic Bugs: Can CFD Spray Them Away:
"DC-10 wind tunnel tests showed a significant loss in maximum lift
coefficient in the flap deflected configurations, with landing slat
extension, compared to predictions. This resulted in a stall speed
increase of about 5 knots in the approach configuration. The initial
wing stall occured behind the nacelles and forward of the inboard
ailerons. The problem was traced by flow visualization techniques to the
effects of the nacelle wake at high angles of attack and the absence of
the slat in the vicinity of the nacelle pylons. The solution was
developed in the NASA Ames Research Center 12 ft. pressurized tunnel and
turned out to be a pair of strakes mounted forward on each side of the
nacelles in planes about 45 degrees above the horizontal. The final
strake shape was optimized in flight tests. The strakes are simply
large vortex generators. The vortices mix the nacelle boundary layer air
with the free stream and reduce the momentum loss in the wake. The
vortices then pass just over the upper surface of the wing, continuing
this mixing process. The counterrotating vortices also create a downwash
over the wing region unprotected by the slat, further reducing the
premature stall. The effect of the strakes is to reduce the required
takeoff and landing field lengths by about 6%, a very large effect."
Nonfirm From United States of America, joined Sep 2005, 434 posts, RR: 0 Reply 2, posted (6 years 2 months 3 weeks 1 day 3 hours ago) and read 6865 times:
We were told by our instructor from Boeing that if the engine was to fall off in flight that the strake would allow the engine to fall away from the a/c that is why the strake needs to be there and we are not allowed to dispatch with out it.
GrandTheftAero From United States of America, joined Nov 2003, 254 posts, RR: 6 Reply 3, posted (6 years 2 months 3 weeks 1 day 3 hours ago) and read 6844 times:
Damnit!!! Even after posting the article...
Quoting Nonfirm (Reply 2): We were told by our instructor from Boeing that if the engine was to fall off in flight that the strake would allow the engine to fall away from the a/c that is why the strake needs to be there and we are not allowed to dispatch with out it.
This forum is going to drive me ape$hit.
McDonnell-Douglas jets have strakes on both sides of the nacelle thereby cancelling out any lateral forces they may produce on the nacelle. The engine would fall straight down if it departed the aircraft.
Boeing jets only have one strake. If anything, the rolling moment produced by the single strake would cause the nacelle to rotate as it was falling and cause more damage to the pylon and wing structure.
Jush From Germany, joined Apr 2005, 1636 posts, RR: 4 Reply 4, posted (6 years 2 months 3 weeks 1 day 2 hours ago) and read 6826 times:
Quoting Nonfirm (Reply 2): We were told by our instructor from Boeing that if the engine was to fall off in flight that the strake would allow the engine to fall away from the a/c that is why the strake needs to be there and we are not allowed to dispatch with out it.
Wow that is some serious bullshit. I can't believe anyone took it seriously.
Quoting GrandTheftAero (Reply 1): "DC-10 wind tunnel tests showed a significant loss in maximum lift
coefficient in the flap deflected configurations, with landing slat
extension, compared to predictions. This resulted in a stall speed
increase of about 5 knots in the approach configuration. The initial
wing stall occured behind the nacelles and forward of the inboard
ailerons. The problem was traced by flow visualization techniques to the
effects of the nacelle wake at high angles of attack and the absence of
the slat in the vicinity of the nacelle pylons. The solution was
developed in the NASA Ames Research Center 12 ft. pressurized tunnel and
turned out to be a pair of strakes mounted forward on each side of the
nacelles in planes about 45 degrees above the horizontal. The final
strake shape was optimized in flight tests. The strakes are simply
large vortex generators. The vortices mix the nacelle boundary layer air
with the free stream and reduce the momentum loss in the wake. The
vortices then pass just over the upper surface of the wing, continuing
this mixing process. The counterrotating vortices also create a downwash
over the wing region unprotected by the slat, further reducing the
premature stall. The effect of the strakes is to reduce the required
takeoff and landing field lengths by about 6%, a very large effect."
--Shane
Thank you for your explanation it does sound reasonable and if this 6% is a correct figure it is a very large effect indeed.
Regds
jush
There is one problem with airbus. Though their products are engineering marvels they lack passion, completely.
Monorail From United States of America, joined Sep 2004, 623 posts, RR: 5 Reply 5, posted (6 years 2 months 3 weeks 1 day 1 hour ago) and read 6788 times:
Quoting GrandTheftAero (Reply 1): from Dick Shevell's AIAA paper Aerodynamic Bugs: Can CFD Spray Them Away
That was a very good read. Thanks for shedding some light on this, I never would have suspected that to be its purpose.
Starlionblue From Greenland, joined Feb 2004, 15105 posts, RR: 69 Reply 6, posted (6 years 2 months 3 weeks 1 day 1 hour ago) and read 6773 times:
Quoting Nonfirm (Reply 2): We were told by our instructor from Boeing that if the engine was to fall off in flight that the strake would allow the engine to fall away from the a/c that is why the strake needs to be there and we are not allowed to dispatch with out it.
As some have said, that sounds rather implausible. Current thinking, and especially after the 747 crash in Amsterdam, is that engines should not be built to depart the aircraft unless they hit a tree or something. There are fewer risks involved in keeping the engine with the aircraft than in letting it depart.
Tact Is For People Who Aren't Witty Enough To Be Sarcastic
DC10GUY From United States of America, joined Feb 2000, 2685 posts, RR: 8 Reply 8, posted (6 years 2 months 3 weeks 1 day ago) and read 6735 times:
Ever notice that the dc8-71 doesn't have the strakes but the -73 does ? When the -71 first came out it had the strakes too. On the -73, the wing has "slots" above the engine pylons. The stakes smooth the air flowing around the nacelle and over the wing L/E and lowers the stall speed by a few knots. Everyone thinks they are there for "in case the engine falls off" that is not the case.
Next time try the old "dirty Sanchez" She'll love it !!!
Starlionblue From Greenland, joined Feb 2004, 15105 posts, RR: 69 Reply 9, posted (6 years 2 months 3 weeks 23 hours ago) and read 6712 times:
Quoting Bobster2 (Reply 7): Quoting Starlionblue (Reply 6):
engines should not be built to depart the aircraft unless they hit a tree or something
The engines should fall off before the wings break. The priority is always to save the wings.
Of course the priority is to save the wings, but in the last few decades thinking has changed on losing the engines.
Up to the about the 80s, the thinking was that nacelle mounted jet engines should separate from the wing in case of, say, an engine fire. But various accidents, mainly the 747 crash in Amsterdam, showed the flaws in the theory. The engines fell off the 747 but it still crashed catastrophically. Losing the engines can make matters worse by introducing instability at a critical time. The problems created by losing the engines are bigger than those created by retaining it.
Bobster2 From , joined Dec 1969, posts, RR: Reply 10, posted (6 years 2 months 3 weeks 22 hours ago) and read 6700 times:
Quoting Starlionblue (Reply 9): Engines nowadays shear off only if they encounter something hard, like a tree
Both engines separated from AA587 before it hit the ground. I was not able to find an explanation for the separation on the NTSB site. It's probably there but I am frustrated by my inability to find it. I remember reading somewhere the engines separated when the plane turned sideways and the wind forces on the engines caused the pylons to separate, and if they had not separated, the wings would have broken off.
Nonfirm From United States of America, joined Sep 2005, 434 posts, RR: 0 Reply 11, posted (6 years 2 months 3 weeks 22 hours ago) and read 6682 times:
The instructor told us that the vortex control device is to smooth the airflow to the leading edge but the vcd would help to allow the end to dislodge away from the fuselage also on the 737-400 the Eng control cables switch to a smaller diameter at the pylon in case the Eng does come off it will not be held to the a/c by the cables.I have read the mm's and what they say about the vcd's but i thought it was odd that he would tell the whole class about this but someone he works with must have told him the same thing.
Starlionblue From Greenland, joined Feb 2004, 15105 posts, RR: 69 Reply 12, posted (6 years 2 months 3 weeks 22 hours ago) and read 6674 times:
Quoting Nonfirm (Reply 11): The instructor told us that the vortex control device is to smooth the airflow to the leading edge but the vcd would help to allow the end to dislodge away from the fuselage also on the 737-400 the Eng control cables switch to a smaller diameter at the pylon in case the Eng does come off it will not be held to the a/c by the cables.I have read the mm's and what they say about the vcd's but i thought it was odd that he would tell the whole class about this but someone he works with must have told him the same thing.
The 734 is an older design so maybe engine falling off was still in the cards. However the main purpose of the strake is to fiddle with airflow.
Tact Is For People Who Aren't Witty Enough To Be Sarcastic
DC10GUY From United States of America, joined Feb 2000, 2685 posts, RR: 8 Reply 13, posted (6 years 2 months 3 weeks 22 hours ago) and read 6674 times:
Engines & pylons are designed to stay on the aircraft, not to shear off. The over all redundancy of the pylon structure is for load support. If a DC10 landed with the gear up the engines would simply mangle up under the wing. They would not take off and fly somewhere. The fins or strakes are for lowering stall speeds that's all.
Next time try the old "dirty Sanchez" She'll love it !!!
AeroWeanie From United States of America, joined Dec 2004, 1588 posts, RR: 54 Reply 14, posted (6 years 2 months 3 weeks 22 hours ago) and read 6676 times:
Quoting Nonfirm (Reply 2): We were told by our instructor from Boeing that if the engine was to fall off in flight that the strake would allow the engine to fall away from the a/c that is why the strake needs to be there and we are not allowed to dispatch with out it.
What BS! If someone had told me this, I would still be on the floor convulsing in laughter.
The late, great Dick Shevell tells it correctly in that quote...
Lehpron From United States of America, joined Jul 2001, 7028 posts, RR: 25 Reply 15, posted (6 years 2 months 3 weeks 20 hours ago) and read 6651 times:
They are vortex generators. During a high angle of attack manuover, like take-off roll or landing, the engine is 'above' the wing. The air that doesn't get sucked into the engine must go around it before over/around the wing. Sometimes the flow separates from the engine, screwing with the lift on the wing aft of the engines.
If the air is spun up with a generator, this tube or vortex of low pressure air ends up sticking to the wing just aft of the engine. Any air that would normally get separated going around the engine is caught in the spinning and the lift is maintained.
See this picture of a MD-11 taking off in, the vortex is thestream that goes over the wing. While it doesn't touch the wing, it forces the air around it to stick to the wing.
David L From United Kingdom, joined May 1999, 8994 posts, RR: 44 Reply 16, posted (6 years 2 months 3 weeks 5 hours ago) and read 6514 times:
Quoting Nonfirm (Reply 2): We were told by our instructor from Boeing that if the engine was to fall off in flight that the strake would allow the engine to fall away from the a/c
For one nasty moment there I thought this was going to finish with "... and fly itself back to base".
Elvisisalive From United States of America, joined Aug 2005, 24 posts, RR: 0 Reply 17, posted (6 years 2 months 3 weeks 3 hours ago) and read 6481 times:
The NSL6051- nose cowl goes on the DC10-30 and the A300-200 acft.
The -531 goes on the DC10 and has strakes while the -533 on the A300
does not have strakes , their is a plate that goes over mount on the nose cowl.
Not an engineer but would'nt the A300 benefit from the strakes ?
474218 From United States of America, joined Oct 2005, 6340 posts, RR: 11 Reply 18, posted (6 years 2 months 2 weeks 6 days 21 hours ago) and read 6403 times:
Quoting Elvisisalive (Reply 17): Not an engineer but would'nt the A300 benefit from the strakes ?
No; if you look at the A300 leading edge slats they extend through the pylon area. Therefore, the nacelle wake, referred to in Reply 1 by Grand Theft Auto, does not exist.
777WT From United States of America, joined Jan 2005, 870 posts, RR: 1 Reply 19, posted (6 years 2 months 2 weeks 6 days 20 hours ago) and read 6400 times:
Sfomb67 From United States of America, joined Dec 2005, 416 posts, RR: 0 Reply 20, posted (6 years 2 months 2 weeks 6 days 20 hours ago) and read 6392 times:
Quoting Nonfirm (Reply 11): also on the 737-400 the Eng control cables switch to a smaller diameter at the pylon in case the Eng does come off it will not be held to the a/c by the cables.
Proves I'm not an engineer; I'd never have thought of this. I can see the engine now, dangling under the fuselage by the throttle cables. Wonder if they make a smaller wiring harness for fly-by-wire?
Lehpron From United States of America, joined Jul 2001, 7028 posts, RR: 25 Reply 21, posted (6 years 2 months 2 weeks 6 days 20 hours ago) and read 6386 times:
Quoting 777WT (Reply 19): Some images showing them working:
Those are better than what I picked (in haste), they are perfect!
The meaning of life is curiosity; we were put on this planet to explore opportunities.
Eilennaei From , joined Dec 1969, posts, RR: Reply 22, posted (6 years 2 months 2 weeks 6 days 17 hours ago) and read 6362 times:
Quoting Starlionblue (Reply 9): But various accidents, mainly the 747 crash in Amsterdam, showed the flaws in the theory. The engines fell off the 747 but it still crashed catastrophically. Losing the engines can make matters worse by introducing instability at a critical time. The problems created by losing the engines are bigger than those created by retaining it.
Did you find anything written about this? So different 747 generations would then have different pylons with less sensitive overloading protection as the versions progress? The Amsterdam 747 was a -200.
Nonfirm From United States of America, joined Sep 2005, 434 posts, RR: 0 Reply 23, posted (6 years 2 months 2 weeks 6 days 15 hours ago) and read 6348 times:
Quoting Sfomb67 (Reply 20): Proves I'm not an engineer; I'd never have thought of this. I can see the engine now, dangling under the fuselage by the throttle cables. Wonder if they make a smaller wiring harness for fly-by-wire?
The mm reads.the cables consist of a 3/32 cable and end fitting.Cables in the wing leading edge consist of a short length of 1/16 cable that acts like a fuse in case of strut breakaway.
Wow, these pics are truly magnificient. Thank you for posting them here.
Regds
jush
There is one problem with airbus. Though their products are engineering marvels they lack passion, completely.
25 Wing: Seeing is believing,thanks for the great pictures
26 Starlionblue: I'm sure it's in an old thread somewhere Here's a start: Require the Boeing-proposed B-747 engine pylon structural modification program to include in
27 Eilennaei: Thank you for the info! I quote directly: "Boeing performed a finite element analysis of the forward portion of the pylon structure. This analysis sho
28 Yikes!: In the separation of the wing-mounted engine of the AA DC10 at ORD in the 1970's, the engine departed the aircraft over the top of the wing. It detach
29 Starlionblue: It was indeed recoverable. However the posted engine out speed led to a stall since the LE devices on the damaged wing had retracted (unknown to the
30 Andz: little ones on the 346.. hard to imagine that such an innocuous looking blade of metal is so important.
31 Starlionblue: Indeed. I am reminded of that kid's game: holding your hand out of the car window to make it fly. Methings a hand would deflect quite a bit of air at
32 A/c train: NONFIRM, That statement was embarassing to engineers, you must be on a wind up!!!
33 474218: Remember that these added things (stakes, stall fences, vortex generators, etc) are there to correct faults. If the engineering is correct from the s
34 Starlionblue: Not necessarily. If you hang an engine under the wing you're pretty much guaranteed it will interfere with airflow. I think in such a case you can ex
35 474218: Then you design the nacelle so that it does not interfere with the airflow. There are many different aircraft flying today that don't have these adde
36 OldAeroGuy: However, at 350 kt., the nacelle chine/VG/VCD (take your pick) is aligned with the flow. Starlionblue has the right perspective. The most important p
37 474218: OldAeroGuy and Starlionblue, You guys are undoubtedly right, I live in the past. I worked for Lockheed for over thirty years and Kelly Johnson's engin
38 OldAeroGuy: While you and I, like most airplane design engineers of our generation, have the greatest admiration for Kelly Johnson, what he is suggesting in your
39 MD11Engineer: BS! The engine control cables from the throttle and engine start lever of a B737 classic end in a drum control box in the leading edge of the wing ju
40 Litz: This also happened w/ the 747 (although engine pylons without stress cracks in them may not have broken in that case) and happened with the DHL 757 m
41 LongHauler: Good one .... that one made me spit out my coffee!!!
42 BuyantUkhaa: Great pictures! I remember an earlier thread about this showing an FR 737 in a humid take-off, that was probably the best pic demonstrating the effec
43 FLY2HMO: So what about this freak: From pictures I've seen, it has no strakes on the nacelle (not needed for the wing obviously), but is the horizontal stabili
44 OldAeroGuy: The VFW614 needed more help than a nacelle chine/VG/VCD could ever give it. First of all, they obviously installed the wings upside down.......
46 GrandTheftAero: The Honda design is pure hotness... common thinking is that putting the engine over the wings is not a good idea but check out the following abstract
47 GrandTheftAero: My comment about the Honda design is now irrelevant because the moderators have deleted the postings about the HondaJet however the quoted abstract ma
48 Sideflare75: What about the strakes on a MD-80 or a 717 engine cowl. What's the reason there?
49 Starlionblue: They make it look cool Seriously, they align airflow to ensure there is less drag when the airflow separates from the aircraft at the tail. Or someth
50 AeroWeanie: No, they are there to cure a deep-stall problem that the MD80 was found to have during wind-tunnel tests.
51 OldAeroGuy: Agree. Similar strakes were on the proposed 727-300 for the same reason.
56 AeroWeanie: The nose strake was also developed during a wind tunnel test to prevent the nose from "slicing" (yawing uncontrollably) at high angles of attack.
57 DocLightning: That is not necessarily true. Perfecting the exact and precise shape of the nacelle so that it doesn't interfere with airflow at high AOA may involve
59 HAWK21M: If thats what he meant.Then its Time to get a new Instructor...... The Strake is only for Aerodynamic reasons to improve airflow in that zone. regds
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