RJ Engine Mounts

[meritflyer]

Can anyone explain why the engines on the RJ are somewhat angled up?

[Alchemy]

I remember reading or hearing this at some point....

From what I recall it's to offset the fact that they are mounted on the upper part of the fuselage.

Engines with a center of thrust above the center of gravity create a downward force. Tilting them up slightly compensates for this.

[meritflyer]

Ahhhh...

[TXaviator]

wait, are they angled with the thrust going toward the tarmac or to the sky?

i guess ive never looked at them

[tgrayson]

Originally Posted by Alchemy

Engines with a center of thrust above the center of gravity create a downward force. Tilting them up slightly compensates for this.

Tilting them up should make it worse, if I'm picturing the geometry correctly. Tail-mounted engines, right?

The usual reason for canting an engine is to align the intakes with the actual airflow around the fuselage. Jet engines like smooth, straight-in airflow.

[Hacker15e]

Originally Posted by tgrayson

The usual reason for canting an engine is to align the intakes with the actual airflow around the fuselage. Jet engines like smooth, straight-in airflow.

Note the way the A-10 engines are mounted -- up at the 10 and 2 o'clock positions on the fuselage, and they're also angled with the intake higher than the exhaust.

It's not to vector the thrust, but to align the engine axis with the airflow over the top of the wing.

[meritflyer]

Picture the airplane in level flight (notice on the ground it sits a little nose-first). The engines are canted. Even on the ground they have a small positive angle to them.

[tgrayson]

Originally Posted by meritflyer

Picture the airplane in level flight (notice on the ground it sits a little nose-first). The engines are canted. Even on the ground they have a small positive angle to them.

Just wanted to make sure we were talking about the same airplane. ;-)

Remember that the nose down pitching moment produced by the the thrustline depends on the perpendicular arm between that thrustline and the CG.

If you draw the thrustline and find the perpendicular line to where the CG is, you'll see that the arm gets bigger the more the engine cants.

Overall, I'm not sure the nose down pitching moment is that big of a problem to merit an ill-positioned air intake.

[rausda27]

If you are talking about a CRJ-200, then it was probably an oversight by Candardier..

Along with small pax windows, ridiculously small lav and a slew of problems up front...

Most of which where fixed on the -700.

/sarcasm/

[H46Bubba]

Oh but the 700 and 900 have issues with the SFECU (Slat Flap Control Unit) and the Spolier PCU (Power Control Unit). Both are constantly TU! I'm not a big fan of Bomabardier. Their choice of component manufacturers and their spares support sucks beyond compare. I never had a problem getting spares from Embraer and if their wharehouse in FLL didn't have it, it needed to be manufactured in Brazil and would get it the next day, or was a Rolls Royce part.

[TXaviator]

also a similar angling on the DC-9