BAe 146/Avro RJ question

nwa757 · Post by **nwa757** » 10 Apr 2004, 22:58

Does anyone know why BAe chose to put air brakes, instead of engines with reverse thrust capability, on the BAe 146/Avro RJ? Any info would be very appriciated.

Jester · Post by **Jester** » 10 Apr 2004, 23:20

Don't know if this is yhe exa&ct reason but the Airbrake gives the AVRO RJ/BAe 146 the capability to perform very steep approaches and the Carbon brakes are so effevtive that thrust reverse is not nessecery ...

that is what I guess ... will inform whit someone who knows ...

Post by **luchtzak** » 10 Apr 2004, 23:50

Indeed Jester,

the original design of the RJ/BAe was military, they designed it so it could be used for short runways. That's why they have the airbrake and lots of carbon-fibre brakes to stop very fast on short runways.

greetz,

Bart
:rock:

nwa757 · Post by **nwa757** » 11 Apr 2004, 03:12

Thanks guys. I never knew that the BAe 146/Avro RJ was designed for the military. Did any countries order it for military use?

Fiero · Post by **Fiero** » 11 Apr 2004, 03:59

Normally the very first design was supposed to be used for that purpose but than it would have been an Avro with props because the original design was made in '52 and than it was put in the fridge for a while to restart it and make the avro RJ . Even tough you can find parts from a Lancaster in it.
And I think with the current design of the avro engines it would be virtually inpossible to put thrust reversers on it.
And as Bart said. They brake very good. So its just not needed.
Greetz

Post by **sn26567** » 11 Apr 2004, 10:15

Aren't carbon fibre brakes very expensive to maintain? I guess that they must be replaced quite often, and at a steep cost... Whereas reverse thrust need little maintenance.

P.S. Topic transferred from 'Latest news' to 'General aviation'

Comet · Post by **Comet** » 11 Apr 2004, 12:03

nwa757 wrote:Thanks guys. I never knew that the BAe 146/Avro RJ was designed for the military. Did any countries order it for military use?

Trevor - the aircraft is used by the Royal Air force as a VIP/Royal transport aircraft. The Queen's Flight is operated by a BAe 146 and the body of Princess Diana was returned to the UK in one.

Avro · Post by **Avro** » 11 Apr 2004, 12:09

original design of the RJ/BAe was military

Isn't that also the reason why it has the wings over the fuselage !!!! Hereby it would have been able to land on runways which aren't paved without damaging the engines too much

Chris
8)

Post by **luchtzak** » 11 Apr 2004, 12:51

Indeed Chris, I think they are designed to land on gras-runways. (not sure though)

tapclassic · Post by **tapclassic** » 17 Dec 2005, 20:35

Normally the very first design was supposed to be used for that purpose but than it would have been an Avro with props because the original design was made in '52 and than it was

Wow

Is there a photo our blueprint of that?

realplaneshaveprops · Post by **realplaneshaveprops** » 18 Dec 2005, 00:51

Aren't carbon fibre brakes very expensive to maintain? I guess that they must be replaced quite often, and at a steep cost... Whereas reverse thrust need little maintenance.

Well, what do call quite often? I think they are on the aircraft (new rotors and stators) for about 5 to 6 months, then they go to the wheel & brake shop to be checked. The same rotors and stators are installed again + an extra spacer. And so they are ready for some months.

New brakes (without spacer) are removed from the aircraft when the wearpin is about 4mm. With overhauled brakes (with spacer), they can be used until the wearpin is flush.

The wear of the carbon brakes on the RJ is around 1mm/week

Thrust reverser add a lot of weight.

Koen

fokker_f27 · Post by **fokker_f27** » 18 Dec 2005, 10:40

So why 4 engines on such a small jet?

realplaneshaveprops · Post by **realplaneshaveprops** » 18 Dec 2005, 10:51

Well, the thing was designed for operations out of small airports, and even unpaved runways in the middle of nowhere. So in case of an engine failure on take-off, the aircraft would lose only 25% thrust. Aircrafts with 2 engines would lose 50% thrust.

Koen

Avro · Post by **Avro** » 18 Dec 2005, 11:42

realplaneshaveprops wrote:Well, the thing was designed for operations out of small airports, and even unpaved runways in the middle of nowhere. So in case of an engine failure on take-off, the aircraft would lose only 25% thrust. Aircrafts with 2 engines would lose 50% thrust.

Koen

Well I don't really agree here with you Koen.

When planes are designed they have to be able to fly a certain climb gradient after V2 with one engine out. This gradient is fixed by the authorities for the certification of the planes.

Now if you have a two engined plane and you lose one engine, you'll lose 50% of the thrust allright but the other 50% are able to cope with the climb gradient required. This means that each engine is "over powered" and able to handle the situation on its own. As terminology lets say that one engine can cope with 100% of the power required. A twin would have 200% of that power

Now if you have a 4 engined plane It'll have 4/3*100% of the requirements of thrust. If you lose an engine at V2, you indeed lose 25% of the plane's thurst (that is to say 33% of required 100%) but you cannot compare those 25% with the 50% of the twin engined plane. The 3 remaining engines will be able to handle the 100% required.

So in fact if you want to compare the figures with each other. If you lose one enigne on a twin you lose 100% from the 200% while on a 4 engined plane you lose 33% of 133% you initially have. But comparing those figures doesn't mean a lot either.

The important thing is that your plane whether it has 4, 3 or 2 engines will be able to climb following a minimum gradient set by the authorities with one engine out during take off.

Chris

fokker_f27 · Post by **fokker_f27** » 18 Dec 2005, 12:15

The maintnence costs will be much higher tough. Why didn't they make a civil version with 2 more powerfull engines?

Avro · Post by **Avro** » 18 Dec 2005, 12:22

That's a good question and honestly I don't know why they did this. You may always try to e-mail them and ask BAe.

They certainly found several advantages otherwise they wouldn't have done it.