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Flap 80 on the Comet

Old 2nd Sep 2009, 09:13
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Flap 80 on the Comet

Just curious, what's the point of having flap 80 on the Comet and how often was it used? I understand that the Comet may have some brake performance issues but I can't think of any other reason for having such a high flap setting.
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Old 2nd Sep 2009, 10:17
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Flap deflection on the Spitfire is 85 so not unusual. Function of flaps basically is to,

1. Increase the maximum lift coefficient which permits a lower speed for the same weight. Result is take off and landing speeds are lower and less runway is required.

2. Reduce the lift/drag ratio which allows a steeper approach.

3. Side benefit is the pilot is afforded a better view of the runway due to increased nose down attitude.

4. Acceleration of jet engines from idle to full power is relatively slow, particularly the early generation as fitted to the Comet, so having lots of drag was beneficial in keeping the engines spooled up ready for a go around if need be. Doubt very much the flap setting had any thing to do with the ability of the brakes to do their job.
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Old 2nd Sep 2009, 16:38
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Thanks for the comment, I almost forgot about the spool up issue, as I didn't think the the Comet would require any steep approach capability. I think that a similar aircraft, the Tu-104, only have flap 35 max.

Thinking about it flap 80 would create so much drag, it would be almost as if the aircraft is flying with speedbrakes extended. How often was it used when compared to lower flap settings like 60 or 40? I recall from an earlier pprune thread regarding full flap (40) on the 727 is that it was rarely used mainly because of high fuel burn trying to keep the engines spooled up during the approach. Although the 727 has the same spool up issues with the Comet it has a T-tail and different wing/flap configuration.
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Old 2nd Sep 2009, 18:23
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This is what it looked like at Kai Tak in 1972. Sorry, the print quality was poor before the scan.
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Old 2nd Sep 2009, 18:47
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Now, them's what I call barn doors!
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Old 2nd Sep 2009, 19:51
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Same into CFU on the 4B
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Old 2nd Sep 2009, 20:55
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I think single Otter had a 90deg setting.

After an excellent landing you can use the airplane again!
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Old 3rd Sep 2009, 05:31
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Wasn't it only the inner, smaller split flap sections under the engines that went to a full 80 ? The outer main plain flaps went to something like 60-70


http://www.airliners.net/photo/Aeroplane-&-Armament/De-Havilland-DH-106/0129169/L/

I seem to remember reading somewhere that the final flap setting on the Comet 4's only moved these inner split flaps to this final 80 from a lesser angle, with the outers being already at their max travel?
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Old 4th Sep 2009, 04:43
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an old time Comet F/E

Gentlemen, you all seem to forget that the Comet had a rather gentle, swept back leading edge and a conventional, parallel trailing edge. She was very obliging in the circuit at 200-210 kts and in the landing configuration, she was checked on the stick-shaker. Though she landed fairly well, the distance between the wheels made heat dissipation through braking, critical. She needed those "Barn Doors". pjac
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Old 4th Sep 2009, 13:58
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>>the distance between the wheels made heat dissipation through braking, critical.

Hi pjac

Presumably you mean the fact that the wheels were necessarily 'thin' with only a narrow gap between wheels on the same bogie, which would tend to hinder cooling ?
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Old 4th Sep 2009, 15:11
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F L A P S ...

The Canberra too had 90 (or as near as dammit) flaps - and just two flap positions, UP or Down - made life simple, but if on one engine, you had to be sure you were going to land off that approach, before selecting Down, because those flaps were very effective, and just one engine wasn't going to get you very far upwards ....
Perhaps, as the Comet and Canberra were roughly contemporary, and the new jets were very slick indeed, it was though best to go for good flappery, and also save on the brakes and tyres ...







(edited for typos unseen on read-through ... sorry)
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Old 6th Sep 2009, 05:07
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pjac

The gap between the wheels (front and rear pairs) was small as compared to say, a 707 or DC8 and brake fans weren't enough sometimes, when operating on short sectors in a hot climate-such as SE Asia or the Middle East in summer.
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