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Question: High T/O Flap Settings In "the Old Days"  
User currently offlineHappy-flier From Canada, joined Dec 1999, 299 posts, RR: 0
Posted (9 years 7 months 2 days 4 hours ago) and read 4187 times:

This is something that I've wondered about for ages and it hasn't given me any peace yet! Just from many pictures that I've seen here on airliners.net and in films, it seems to me that in the early days of the classic "four-holers", flap settings for takeoff were much higher than they have been in my own memory (1980's to the present). Why was this? Here are just a few pictures illustrating what seems like a 35-40 degree flap extension for takeoff - something that just looks excessive by today's standards:

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Photo © Bob Garrard



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Photo © Frédéric Renaud



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Photo © Bob Garrard


My theory is this (and I would really appreciate any corrections to it): They used high flap settings for takeoff then, so as to achieve rotation not only at a slower speed, but at a lower angle than might otherwise be necessary - despite the attendant drag caused. This may have been an instinctive "carry over" practice from the days of the four-engined piston airliners, where rotation was slight on takeoff. In any case, in the majority of current pictures of 707s and DC-8s in takeoff configuration, you don't see what looks like 35-40 deg. flap settings for takeoff anymore!

Am I anywhere near the truth?

Thanks.


May the wind be always at your back . . . except during takeoff & landing.
13 replies: All unread, jump to last
 
User currently offlineSATL382G From , joined Dec 1969, posts, RR:
Reply 1, posted (9 years 7 months 2 days 1 hour ago) and read 4056 times:

I think they changed the take off flap settings for noise abatement.

Less flap = less drag = less thrust = less noise... I think. I may be over simplifying....


User currently offlineAloges From Germany, joined Jan 2006, 8615 posts, RR: 44
Reply 2, posted (9 years 7 months 2 days ago) and read 4024 times:

"Less flap = less drag = less thrust = less noise... I think."

Sounds reasonable. In addition to that, remember that flaps create vortices, so you should consider this, too:

less flap = less vortex = less noise



Walk together, talk together all ye peoples of the earth. Then, and only then, shall ye have peace.
User currently offlineOkie From United States of America, joined Jul 2003, 2847 posts, RR: 3
Reply 3, posted (9 years 7 months 1 day 23 hours ago) and read 3950 times:

The early designs of jet aircraft wings were for flight speeds in line with no/low bypass engines in the area of .90+ mach numbers and did not provide good lift capabilities at low take-off and landing speeds.

With the advent of high bypass engines, the need for more efficiency, the cruise speeds came down and the design of the wings were such that around .80 mach number became the design criteria, thus the wings are more in line with efficiencies at slower speeds involved with take-offs and landings.

Also if you look at the traffic situation around airports today an airplane spends considerable time in departure and landing assignments at <18,000ft/<250knots even on a long haul flight.

Look at your RJ's most without any leading edge devices, fly relatively slow generally less than .70 mach on short hops, (not much time above 18,000/250) Thus a simpler, wing to design and be economically feasible as well.

Okie



User currently offlineQantasA332 From Australia, joined Dec 2003, 1500 posts, RR: 26
Reply 4, posted (9 years 7 months 1 day 23 hours ago) and read 3937 times:

The '50s and '60s were a time of huge advancement in terms of aircraft speed and, with the developement of things such as the supercritical airfoil, commercial airliners were getting quite optimized for high subsonic flight regimes (as Okie suggested above). As a consequence, of course, wings became less capable at lower speeds, thus relying more on flaps for low-speed flight.

Cheers,
QantasA332


User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 5, posted (9 years 7 months 1 day 20 hours ago) and read 3834 times:

The earlier B707 models ( with straight pipe, ie: non fan engines) had flap settings of 10, 20, 30, 40, 50 degrees.
Takeoffs were always performed with the lowest flap setting possible, consistant with runway length, takeoff weight and airfield altitude/temperature.

Most takeoffs used 20 degrees.
Shorter runways needed 30.
High altitude altitude airfields (JNB for example) used 10 degrees at heavy weights due to second segment climb restrictions. Higth speed (225mph) tires were absolutely required for this.

When the fan engines appeared, full span leading edge devices were fitted, and the flap settings were changed to 14 (or 17 on a few early models), 25, 40, 50 degrees.

With these aircraft, takeoffs were always performed at one setting only...14.
With takeoffs, the flap settings (early straightpipe aircraft) were generally not considered for noise abatement.

Landings were done at 50 degrees EXCEPT at PanAmerican where 40 degrees was used in strong crosswinds with wet runways....Vref increased 2 knots in this case.


User currently offlineNewyork355 From France, joined Jul 2004, 148 posts, RR: 0
Reply 6, posted (9 years 7 months 1 day 20 hours ago) and read 3819 times:

I heard that the Boeing 747 was originally fitted with its huge triple-slotted flaps so that it could take off an land on the same size runways as a 727 or a 737. Just something I heard somewhere, and it probably doesn't fully answer your question happy-flier, but just a thought.

Sam



"No Way BA/AA"
User currently offlineHappy-flier From Canada, joined Dec 1999, 299 posts, RR: 0
Reply 7, posted (9 years 7 months 1 day 19 hours ago) and read 3806 times:

Many thanks for the detailed replies. I really appreciate those first-hand accounts of operating procedures from back then.

It never occured to me that the airfoil design of the wing (optimized for high-speed cruise) would have been a contributing factor to the greater reliance on flaps for low-speed flight.

I can bet that takeoffs in a straight-pipe 707 without full-span slats (as seen on the -320B/C series) must have involved a higher speed at rotation, and probably felt quite a bit different than it does in the JT3D-powered -320B/C.



May the wind be always at your back . . . except during takeoff & landing.
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 8, posted (9 years 7 months 1 day 18 hours ago) and read 3795 times:

Slightly higher speeds...yes, with the JT4A powered aircraft.
Even more interesting were the very long takeoff runs...nearly 11,000+ feet at max weight (317,000 pounds) on a warm(er) day.

Up close and personal with the far end of the runway was common.
No de-rated thrust either...full bore.
If an engine failed (at these heavier weights) just after V1, the resulting climb was at V2, 300 feet/minute, IF you were lucky.
Very little margin for error.

PS: Not 'slats' (on the 707)...leading edge devices. There IS a difference.

[Edited 2004-09-18 04:01:07]

User currently offlineHappy-flier From Canada, joined Dec 1999, 299 posts, RR: 0
Reply 9, posted (9 years 6 months 3 weeks 6 days 5 hours ago) and read 3568 times:

In browsing the latest additions to the 707 database, I came across this photo, which shows really well what I was talking about earlier:

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Photo © Bob Garrard


Now that LOOKS like an awful lot of flap for departure! It looks like it's set at something like 40 degrees, and would create lots of drag. Maybe it was a short runway scenario?



May the wind be always at your back . . . except during takeoff & landing.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 10, posted (9 years 6 months 3 weeks 5 days 23 hours ago) and read 3520 times:

I heard that the Boeing 747 was originally fitted with its huge triple-slotted flaps so that it could take off an land on the same size runways as a 727 or a 737. Just something I heard somewhere, and it probably doesn't fully answer your question happy-flier, but just a thought.


Not quite the same runways at the 727 and 737. The issue was mainly to keep approach speeds in the same range as other airliners without compromising the high speed of the 747 by, say, decreasing the wing sweep.

The only 747 variant not to have the triple-slotted flaps is the SP.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 11, posted (9 years 6 months 3 weeks 5 days 5 hours ago) and read 3457 times:

It may LOOK like 40 degrees, Happy-flyer, but could not be for two reasons.

1. The only certified TAKEOFF flap settings for the older 707's are 10/20/30 degrees.

2. If ANY other setting is used, the configuration warning horn will sound (beep...beep...beep) when the thrust levers are moved beyond (approximately) the 1.3 EPR position.
This alerts the crew that either...

1. the flaps are not set properly (ie: an approved takeoff position)
2. the speed brakes (spoilers) are not stowed
3. the stab trim is not in the takeoff range.

In addition, for those airlines that did NOT need the 10 degree flap position, according to the performance charts generated for the specific airfields that they used, the 10 degree position was blocked off for use during takeoff.


User currently offlineHappy-flier From Canada, joined Dec 1999, 299 posts, RR: 0
Reply 12, posted (9 years 6 months 3 weeks 5 days 1 hour ago) and read 3436 times:

Thanks 411A. Coming from you, I consider it "mystery solved"!  Smile

It must be an optical illusion in that case.



May the wind be always at your back . . . except during takeoff & landing.
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 13, posted (9 years 6 months 3 weeks 4 days 22 hours ago) and read 3419 times:

There are dangers in having multiple flap positions for takeoff, Happy-flier, if the computed flap position, as required by the takeoff weight/runway length, does not agree with the ACTUAL flap position selected.
PanAmerican had a very nasty accident in the early 1970's at KSFO, wherein a B747 crew had computed a flap 20 takeoff configuration, with the required flap 20 speeds on departure from runway 01R, but selected flaps 10 instead.
This error was not caught, and the aircraft rotated very late, and impacted the approach lights at the far end, injuring several passengers when bits if the light towers penetrated the lower fuselage.

To be absolutely SURE this did not happen again, PanAmerican incorporated a 'configuration check' as the LAST item in the before takeoff checklist, that was completed BEFORE takeoff thrust was selected.

This configuration check consisted of four items,

1. Flaps (set according to the computations previously computed for the runway in use,
2. Spoilers down,
3.Stab trim CORRECTLY set,
4. Compass heading (both HSI's and the standny compass) agreed with the runway heading.

This configuration check was used for all aircraft types in their fleet, and in addition, was adopted by several other airlines for their use.



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