Mr Spaceman
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Jet Engines Mounted On An Angle?

Thu Dec 20, 2001 7:42 am

Hi guys.

In the photos below of the TU-154, you can clearly see that the 2 side-mounted engines are angled so that their tailpipes are pointed inward toward the fuselage. Why is this done? Is it for aerodynamic reasons that involve the direction of engine thrust, such as directional stability? Could it be for mechanical reasons?


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Photo © Charles Falk



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Photo © Colin K. Work


In these photos of B-727s, the side mounted engines appear to be on an angle as well. However, these 727 photos don't show this feature as clear.

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Photo © AirNikon



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Photo © AirNikon



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Photo © Hiromichi Miyagaki


Also, do any airliners that have only wing mounted engines such as the 747, 777, A320, A340 etc, have their engines mounted on an angle? Or even an L-1011 or DC-10...are their wing mounted engines on an angle?

I find this very interesting.

Chris  Smile


"Just a minute while I re-invent myself"
 
VC-10
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RE: Jet Engines Mounted On An Angle?

Thu Dec 20, 2001 8:18 am

The Inbd engines of the 747 are canted in 3 degs to pick up the "bow wave"
 
mandargb
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RE: Jet Engines Mounted On An Angle?

Thu Dec 20, 2001 8:51 am

Actually it has always appeared to me that on MD-80 series; engines are not horizontal

Is it true that the engine axis (front center to rear center of the engone) is not parallel to ground (of course when plane is stationary) for MD 80 series?

Thanks in advance
 
A330-243
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RE: 747

Thu Dec 20, 2001 9:16 am

Have a look at the angle of 747 engines in this photo. Just as VC-10 states above.


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Photo © Anton Pettersson

 
Mr Spaceman
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RE: Jet Engines Mounted On An Angle?

Thu Dec 20, 2001 9:18 am

Hi guys. Thanks for your replies.

>VC-10, like always, you are a great source of info. OK, the inboard engines of a 747 are canted 3 degrees in order to catch the "Bow Wave". I suspect you mean the "front" of the engines are angled inward because a bow wave sounds like a wave of airflow which would be flowing rearward off the nose. Could I be correct? And if so...are the inboard engines set up differently than the outboard ones, because of this bow wave?

Here's a cool pix showing a 747's profile from below. You can almost see the 3 degress...I think.

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Photo © Chris Sheldon



>Mandargb, I believe you are "right on the money" regarding your observations of the horizontal angle of the engines on MD-80's It looks to me like the front of the engines are angled upward a few degrees.

Here's some photos that clearly show the different angle between the fuselage and the engines.

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Photo © Jason Taperell



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Photo © Jim Gartman


Chris  Smile
"Just a minute while I re-invent myself"
 
Mr Spaceman
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RE: Jet Engines Mounted On An Angle?

Thu Dec 20, 2001 9:25 am

Hi guys. Well, Thanks to A330-243's photo that he posted, I can see that the inboard engines on a 747 are not canted 3 degrees inboard, but rather 3 degrees "downward".

This Bow Wave must be pretty important!

Chris  Smile
"Just a minute while I re-invent myself"
 
Goldenshield
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RE: Jet Engines Mounted On An Angle?

Thu Dec 20, 2001 2:37 pm

I have read this somewhere else, but the reason why the the engines on the 727, and Dc-9 series are angled upwards is so that the intake does not get the spoiled air off the wings, when at a relatively high AoA.
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cv640
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RE: Jet Engines Mounted On An Angle?

Thu Dec 20, 2001 2:50 pm

The CRJs are canted inward very slightly also, was told this is to help with single engine control, limits the yaw.
 
Mr Spaceman
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RE: Jet Engines Mounted On An Angle?

Fri Dec 21, 2001 1:48 am

Hi CV640.

I had a feeling the engines were canted inward for aerodynamic reasons such as directional stability (around the vertical axis).

In the photos below of some CRJs, you can see that the engines are indeed canted inward just a little. It also appears that they are angled horizontally so that the intake is a bit higher than the exhaust.

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Photo © Konstantin von Wedelstaedt



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Photo © Jonathan Derden



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Photo © James Richard Covington, Jr


Chris  Smile
"Just a minute while I re-invent myself"
 
VC-10
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RE: Jet Engines Mounted On An Angle?

Fri Dec 21, 2001 6:23 am

Looking at my course notes both the inbd & otbd 747 nacelles are canted in 2 degs to pick up the bow wave.

On the VC10 in an effort to reduce the unexpectedy high drag encountered during flight testing, the Super VC10 engine nacelles were attached to the fuslage at a 3 deg nose up angle and the stub wing span increased to get the inbd engine intakes out of the 11 inch thick boundary layer in that area.
 
Mr Spaceman
Topic Author
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RE: Jet Engines Mounted On An Angle?

Fri Dec 21, 2001 7:05 am

Hi VC-10

Thanks for your info. Once again you've mentioned the "bow wave". What exactly is the bow wave? Also, why is it so important for the engine intakes to catch this wave?

Chris  Smile
"Just a minute while I re-invent myself"
 
VC-10
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RE: Jet Engines Mounted On An Angle?

Fri Dec 21, 2001 9:21 am

You know the wave generated in the water by the bow of a boat, well the a/c nose also generates a similar wave. By angleing the a/c engines just right you can collect it for extra ram effect.
 
TimT
Posts: 168
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RE: Jet Engines Mounted On An Angle?

Fri Dec 21, 2001 10:42 am

Here's another tidbit-- the DC-10 likes to fly between 3 and 5 degrees nose up. Not sure about the others, but I suspect the same thing. If that's the case, the engineering department canted the engines so they are "square" to the airflow. I know that on a ground runup, it's a really bad idea to pull high power without being pointed into the wind. Makes exciting things happen. (including getting yelled at)
 
Guest

RE: Jet Engines Mounted On An Angle?

Fri Dec 21, 2001 11:00 am

One more tidbit you you guy that are interested in Learjets. On all but the earliest tip-tanked models the tip tanks are canted downward 3 degrees (as I remember) to keep them square with the world during crusing flight at altitude. One of the explinations that I remember from one of my type rating ground schools regarding the outward canting of the engines (as seen from the front) was to minimize the rudder forces required in the case of engine loss. Whether or not that's a valid reason, I honestly don't know but it sounds good and does make some sense. It's common to mount the engines on larger sengle-engine aircraft with a significant cant. Next time you get a chance go look at a late model Bonanza. It will really surprise you. You'd think the airplane would fly sideways through the air.  Big grin
 
Guest

RE: Jet Engines Mounted On An Angle?

Fri Dec 21, 2001 11:49 am

On the L1011, the #2 engine (on top of fuselage) is tilted 12 degrees down. This is because if there is a loss of pitch control the engine can better be used to in effect "pitch" the aircraft.

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