Avro RJ 85

[dudubrdx]

Hello,

Is it the APU starting that we hear a few minutes after take-off, around the acceleration altitude? I've always wondered what the noise was, it does sound like the crew is starting the 4th engine or something. Thanks for your enlightment

[Tu.114]

While I have not flown this type, I do remember a highly distinctive wailing sound the flaps emit when travelling through a certain setting from my flights as pax. As You have heard this during acceleration, this might be the cause. In fact, one of the many nicknames the 146 bore was "Hound of Hatfield" due to this noise...

EDIT:
Starting from 0:39 in this video, You can hear the sound I was referring to.

[Mach E Avelli]

It is indeed airflow as a result of the flaps running through a certain position. The airline I worked for had the cabin crew include a short spiel about this in their pre takeoff passenger brief.
The BAC 1-11 made a similar racket, though the engines were so noisy on takeoff that the flap howl was only audible on approach at idle thrust.

[fleigle]

The Phantom (F-4) had wonderful noises when on final for landing, due to the various engine intake door(s) scheduling I think.
I lived for a while on the approach to a US ANG (Air National Guard) base and couldn't resist rushing outside whenever a flight pair made their approaches.
Great stuff !!

[alidad]

Fleigle,

An F4 pilot eating cabbage would emit more thrust than 4 hairdryers on an RJ85:p

[renard]

It is the flaps moving from flap18 to flap0. It makes the same noise going from flap0 to flap18.

It won't be APU starting. You wouldn't start the APU after take off. Normally you took off with it off. It is was running on take off you would switch it off after flap0. On approach you would switch the APU on at about 5000'.

[ImbracableCrunk]

An FAA inspector allegedly tried to write up one of our Avro crews for starting an engine during the climb out.

[dudubrdx]

Haha I don't get it then: Has the Avro got too much power or not enough :E

And thanks for your replies. Indeed I was not convinced myself that this noise was due to an APU (or even engine!) starting

[Uplinker]

Yep, it is flap howl. Caused by the airflow resonating when the flap gap is a certain size, and changing in pitch as the gap size changes when the flaps are running in or out. A similar process to organ pipes, where air is blown across a gap to produce a note.

When I flew the 146, I was told that the Queen's Flight, (which used 146 or variants) had a modification to reduce the noise, but I can't imagine what that would be, or even if it was true.

[WHBM]

One of the most regular questions about the 146/Avro type. The flap howl is is an aerodynamic harmonic between the inner flap edge and the fuselage side at certain settings, it makes the ascending tone as the flaps come in on departure, and the opposite descending tone as they are deployed on approach. It was apparently a surprise on first flight, the wind tunnel tests hadn't identified it. BAe did indeed develop a modification to overcome it but it weighed 100 kg, two pax, and I always thought nobody took it until reading above that the RAF VIP ones put it on.

I've heard cabin crew say the descending tone is the cue to them to give cabin secure. On departure from London City on 28 and turning right, the flaps normally come in overhead Stratford and the Olympic stadium at 3,000 feet. The howl from this is quite audible when standing out on the train station platform at Stratford as the aircraft passes overhead. I was wondering if the commentators were going to pick up on it in the Olympics !