Fins on Engine Cowling
Joined: Jan 2008
Posts: 761
Likes: 9
From: Herts, UK
A boundary layer going turbulent can cause a lot of low frequency noise and/or vibration, and even if not really audible, it can still make the pax uncomfortable, and possibly even sick.
Turbulent boundary layers are much more resistant to separation than laminar ones.. some obviously know this, quite a few don't. That's why we stir up the flow in the boundary layer (with say voretx generators), to get an early transition to turb b.l and re-energise it.
It's interesting some of the differences in minimum speeds quoted for flow modifiers around the nacelle/wing junctions - they're quite significant.
To whoever it was suggested that Boeing 'invented' the nacelle strake or vortex generator - sounds like another re-writing of history to me
Last edited by HarryMann; 9th November 2009 at 21:35.
Joined: Nov 2004
Posts: 259
Likes: 57
From: Asia
Back in the late 70's when I briefly worked for a DC10 operator I came across a file of newsletters produced by Douglas (I think they were titled "Know Your DC10" or something similar). One of them discussed the reason for nosecowl strakes which was as described in depth in several earlier posts (disturbed airflow off the nosecowl in the landing configuration interacting with the gap in the LE slats for the pylon was going to result in missing their target landing distance due to too high a reference speed). According to the article they started out with a strake on the inboard side that extended from the nosecowl right across the fan cowl and then shortened it bit by bit until they established the minimum size of strake that allowed them to acheive their target landing distances. Another stake was installed on the outboard side to make the nosecowl fully interchangeanle L & R.
Joined: Jun 2001
Posts: 4,777
Likes: 9
From: Blighty
FNP's picture in post 28 has 4 CFM56s, but isn't a 340 as i) judging by the engines, the wing is too small ii) the wing has vortex generators which the airbus FBW designs don't and iii) that wing has Kruger style LE devices which airbuses don't. It's either a 707 airframe which would make it an E3 or a C135 derivative or a DC8 conversion. The CFMs weren't certified on civil 707s and as the engines have the CFM logo which wouldn't be put on a military aircraft, I reckon it's a DC8.
Joined: Aug 2007
Posts: 69
Likes: 0
From: Between East and West Poles.
Not a DC-8 as none had leading edge flaps/slats. By the vortex generators on the wing it has to be a 707. Not up to speed re Airbus but think that they would have an extendable leading edge like a B767.
Joined: Jun 2001
Posts: 4,777
Likes: 9
From: Blighty
They do. In fact, I think it's this aircraft. The one and only prototype 707-700.
A website on the 707s history mentions that it wasn't continued because it would compete with the 757. However, someone I know who was partly responsible for the introduction of the KC135R (with CFM56s) into the USAF mentioned that the aircraft had handling issues which Boeing realised would make civil certification difficult.
A website on the 707s history mentions that it wasn't continued because it would compete with the 757. However, someone I know who was partly responsible for the introduction of the KC135R (with CFM56s) into the USAF mentioned that the aircraft had handling issues which Boeing realised would make civil certification difficult.
Last edited by Dan Winterland; 11th November 2009 at 12:32.
