Concorde Engine 4

[frgthy]

Why does engine number four have a "de-rate" selection for takeoff, is it aerodynamic problems, engine surge or noise?

[Bellerophon]

It's called an N1 limiter, and only operates during the very early part of the take off run.

On take off, at full power, but with low forward speed, the smooth airflow into the #4 engine intake can sometimes be slightly distorted by air from the wing leading edge.

This has the potential to cause minor LP compressor blade vibration, so #4 engine is electronically limited to 88% N1 until 60 kts, when the intake airflow has smoothed out. The limiter then disengages and the engine goes to full power.

Concorde take offs are always full power :) :)

[frgthy]

Thanks but your reply raises another question, why just engine number four? Engine one would have exactly the same aerodaynamic location and would receive the same turbulence at low speed,so why is'nt number one engine limited as well?

[Bellerophon]

Think again about one of the assumptions you have made in your post.

Then see if you can work out why #1 engine doesn't suffer the same effect. :)

[Desk Driver]

Eh???????

[380]

Bell,

Give us one more hint!

[Yogi-Bear]

Direction of rotation?

[Desk Driver]

Of course! All engines turn the same way which means number 1 would not be affected

[frgthy]

bell

sorry if I'm being a bit thick but, the only assumption I can see is that I've assumed its just on engine #4? your going to have to spell this one out...please.

[Tinstaafl]

The airflow pattern on the L & R side of the fuselage are mirror images of eachother eg a vortex on one side will rotate clockwise, where as on the other side it will be anticlockwise.

Engines 1 to 4's moving parts are the same ie rotate the same way eg clockwise or whatever. They are not mirror images of each other when 1, 2 & 3, 4 are compared.

As a result the interactions between airflow & engine are different between each engine.

[This message has been edited by Tinstaafl (edited 23 May 2001).]

[WOK]

Spot on!

Prior to fitting the limiter in the development programme the MTBF for no.4 was apparently eye-wateringly low!

[Bellerophon]

Tinstaafl

Well Done! Couldn’t have put it better myself!

frgthy

I wasn't trying to be awkward, but when you said ...Engine one would have exactly the same aerodaynamic location and would receive the same turbulence at low speed... I hoped I might nudge you into reconsidering that assumption.

Sorry if I confused you!

[frgthy]

All

Thanks for your replies, all is now clear.