Happy-flier
Topic Author
Posts: 287
Joined: Sat Dec 25, 1999 4:41 pm

DC-8 Taking Off With Cascades Open?

Tue Mar 23, 2004 2:52 am

I just found this picture of a -50 series DC-8 taking off with the cascades open on engine #3. Is this a potentially dangerous situation? Can the bypass-reverse system engage in such a situation? I wonder if the crew would be able to correct this in flight, or whether they were even aware that it happened.

Link to picture.

[Edited 2004-03-22 19:08:20]
May the wind be always at your back . . . except during takeoff & landing.
 
broke
Posts: 1299
Joined: Wed Apr 24, 2002 8:04 pm

RE: DC-8 Taking Off With Cascades Open?

Tue Mar 23, 2004 3:24 am

While the shutters covering the cascades are slightly ajar, they are not open enough for the reverser to be deployed. In reverse, the shutters are perpendicular to the nacelle. Also, the shutters are covering the by-pass portion of the reverser, the hot stream is also reversed and that section is definitely not deployed.
 
TechRep
Posts: 1877
Joined: Sun Jan 13, 2002 6:53 am

RE: DC-8 Taking Off With Cascades Open?

Tue Mar 23, 2004 3:27 am


I have a lot of experience with those old cascade doors so allow me to answer. Based on what I see in this photo the top "louver" is missing and the louvers are slightly open.

The #3 engine is not in reverse because the cascade assembly is stowed. Remember this is a pneumatic thrust vectoring system and louver chatter or partially open partitions is not uncommon. There seems to be a pneumatic leak in the system allowing the louver doors not to stow properly.

The reason for this is a bad shuttle valve spring mechanism or people are injecting penetrating oil into the system or both. This penetrating oil makes the system function great for about 1 week, then it begins to gum up and the system will not function correctly. A common fix in a line maintenance environment and makes problems go away for a quick dispatch but this is not an approved maintenance practice.

I haven't seen one of these operate with one of the "Venetian blinds" missing expect by Kalitta and they’re a Mutha-F**er to change. In fact Cascade assemblies are so hard to change while at ABX we had stations dedicated to doing this task, with extra training and tooling. The system is entirely inefficient; they weigh a ton, break down about every other trip and constantly will not go into interlock and have lots and lots of pneumatic leaks.

TechRep

 
Happy-flier
Topic Author
Posts: 287
Joined: Sat Dec 25, 1999 4:41 pm

RE: DC-8 Taking Off With Cascades Open?

Tue Mar 23, 2004 4:32 am

Thanks very much guys. That just about says it all!
May the wind be always at your back . . . except during takeoff & landing.
 
Happy-flier
Topic Author
Posts: 287
Joined: Sat Dec 25, 1999 4:41 pm

RE: DC-8 Taking Off With Cascades Open?

Tue Mar 23, 2004 5:58 am

As I was reading through Techrep's reply, I got to wondering why Douglas ever went with the admittedly cumbersome nacelle design for the -50 and -61 series. Just comparing the cascade/"venetian-blind" assembly to the straight nacelle and single bucket-type reversers found on the -62 and -63 series aircraft, there's no comparison as to which is the better of the two systems - from a maintenance standpoint and, I would argue, that of performance as well.

All things told, the old turbojet nacelles with the aft-moving "sound suppressors" was even worse!!
May the wind be always at your back . . . except during takeoff & landing.
 
broke
Posts: 1299
Joined: Wed Apr 24, 2002 8:04 pm

RE: DC-8 Taking Off With Cascades Open?

Fri Mar 26, 2004 2:38 am

The entire nacelle for the DC-8-50 series and the DC-8-61's were developed by Pratt & Whitney and they were (and are in some places) maintenance and reliability headaches.

The entire nacelle for the DC-8-62's and -63's are Douglas designs and are much more superior in operation, ease of maintenance, and aesthetics than the early configurations.

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