Flap extension/retraction on 146/RJ

[Michael111]

Can anyone tell me if it is speed or hight that governs the extension or retraction of flaps before landing or after take off?

The reason I ask is that I live on Jerseys East coast and I often "hear" the Flap movement from the ground & it never seems to happen when the aircraft is in the same place.

Thanks

[fly4fud]

Hi Michael111,
it is neither speed nor height, but weight ;)
On the ARJ85/100 I have the pleasure flying, the procedure is as follows:
Departure: standard acceleration height, e.g. flaps retraction height is 800 feet. Some place have higher height, due to obstacles or noise abatement procedures. I suppose this is not the case where you live. So, to reach those 800' you will need a certain time and distance, and this will depend on the weight of the said aircraft.
Arrivals: you have to reduce the speed of the aircraft, either due to ATC instructions or, finally to just to land. We have so called speed booklets where we dial the actual mass of the aircraft (this we can get from our ever so clever GNS/FMS computers or by deducting the burned fuel from the take-off mass). For instance taking the speed booklet and an average landing mass for the RJ-100 of 38T, I will read that VER (V en route) speed, e.g. minimum clean speed of the aircraft is 186 knots. Add to this a safety margin of 20 knots = 206 knots. So, when approaching say 210 knots, I will verify to be below max flaps extension speed of 220 (215 for the RJ85) and order flaps extension to 18 degrees. With this flap setting my minimum speed will drop to 149 knots, thereby demonstrating how effective those flaps are :) So, here again, the distance from the airport at which we will extend the flaps varies according to the weight.

The noise you may hear on the ground is some aerodynamic effect of the air being forced pushed between the fuselage and the flaps and will happen only when selecting flaps 18 to 0 or 0 to 18.

Hope my explanations are not too foggy :)

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... cut my wings and I'll die ...

[Michael111]

Thanks for the info, I can now pass this on in response to my 4 year olds "what is that noise Daddy" questions.

[Xenia]

Hope your little boy will understand the explanation :) :) :)

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*************************Happy Landings! :)
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[spoilers yellow]

I fly the RJ100 into Jersey fairly frequently,our departure profile is such that we accelerate at 1000ft. above the airfield and make none of our turns below 1800ft. so as mentioned above it depends on variables such as a/c weight and ground speed(determined by the wind on the day) as to where exactly over the land we will be when flaps are retracted from 18 to 0.
It is also worth mentioning that we can do a number of different departures, all of which will vary our routing out over the island.
Hope this helps.