Happy-flier From Canada, joined Dec 1999, 299 posts, RR: 0 Posted (10 years 9 months 4 days 22 hours ago) and read 2533 times:
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.
Broke From United States of America, joined Apr 2002, 1322 posts, RR: 3
Reply 1, posted (10 years 9 months 4 days 21 hours ago) and read 2459 times:
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 From , joined Dec 1969, posts, RR:
Reply 2, posted (10 years 9 months 4 days 21 hours ago) and read 2460 times:
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.
Happy-flier From Canada, joined Dec 1999, 299 posts, RR: 0
Reply 4, posted (10 years 9 months 4 days 18 hours ago) and read 2309 times:
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.