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Maximum DC-8 Mid-Air Thrust Reverser Speed  
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Posted (6 years 11 months 1 day 2 hours ago) and read 4470 times:

The DC-8 from what I was told can extend the reversers at a maximum airspeed of 390 kts. Was the fact that the reversers were mounted in an aft-translating ejector that made them able to activate at such high speeds? I mean could a thrust reverser design of a 707-type be activated safely at such a high speed without the risk of sustaining damage?

Also, while at it...

1.) The 390 kt speed listed, does that mean just at sea-level reading on the gauge (The DC-8's speed gauges are not particularly reliable at high altitude with IAS readings that seem to creep up and up and up, particularly when close to VMO)

2.) What's the maximum mach number you can use the reversers at in mid-air safely?

3.) Can the B-707's reversers use full reversing power, or like the CV-880 desgn can only use 50 percent power for reversing?


Andrea Kent

10 replies: All unread, jump to last
 
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 1, posted (6 years 11 months 4 hours ago) and read 4416 times:

Nobody?

Andrea Kent
"Private Cowboy, Private Joker: As soon as you finish your bunks I want you two turds to clean the head -- I want that head so sanitary and squared-away that the Virgin-Mary, herself, would be *PROUD* to go in there and take a dump!" -- Gunnery Sergeant Hartman
Full-Metal Jacket (1987)


User currently offlineSfomb67 From United States of America, joined Dec 2005, 417 posts, RR: 0
Reply 2, posted (6 years 11 months 2 hours ago) and read 4398 times:

Quoting Blackbird (Thread starter):
Was the fact that the reversers were mounted in an aft-translating ejector that made them able to activate at such high speeds? I

When the DC8's were re-enginned into the 70 series, they also replaced the t/r's with cascade vane type reversers, although i don't know the speed at which they cold be used.



Not as easy as originally perceived
User currently offlineViscount724 From Switzerland, joined Oct 2006, 24824 posts, RR: 22
Reply 3, posted (6 years 10 months 4 weeks 1 day 23 hours ago) and read 4380 times:

Quoting Sfomb67 (Reply 2):
When the DC8's were re-enginned into the 70 series, they also replaced the t/r's with cascade vane type reversers, although i don't know the speed at which they cold be used.

If not mistaken the DC-8-50 and -61 series also had cascade type thrust reversers, while the -62 and -63 had target-type (clamshell) reversers.


User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2543 posts, RR: 24
Reply 4, posted (6 years 10 months 4 weeks 1 day 18 hours ago) and read 4354 times:

Quoting Blackbird (Thread starter):
1.) The 390 kt speed listed, does that mean just at sea-level reading on the gauge (The DC-8's speed gauges are not particularly reliable at high altitude with IAS readings that seem to creep up and up and up, particularly when close to VMO)

2.) What's the maximum mach number you can use the reversers at in mid-air safely?

3.) Can the B-707's reversers use full reversing power, or like the CV-880 desgn can only use 50 percent power for reversing?

1.) If the limit is 390 then that must be IAS. The crew have no indication of "sea level airspeed".

2.) If no Mach limit is given then only an airspeed limit applies.

3.) Most engines have reduced maximum power settings in reverse, automatically applied by the FCU. 50% limit would be lower than the norm. The Convair engines had an aft fan IIRC, which might have been a limiting factor.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 5, posted (6 years 10 months 4 weeks 1 day 14 hours ago) and read 4337 times:

The DC-8 to my knowledge could achieve MCP on the inboards, and somewhere from zero to 32 pct MCP on the outboards... to my knowledge way above 50 percent while in the air to my knowledge... but why would you use reduced power in reverse?

BTW: Convair 880 was a turbojet...


Andrea Kent


User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2543 posts, RR: 24
Reply 6, posted (6 years 10 months 4 weeks 1 day 14 hours ago) and read 4335 times:

Quoting Blackbird (Reply 5):
Convair 880 was a turbojet...

Sorry, I confused it with the Convair 990 while trying to think what might differentiate it.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 7, posted (6 years 10 months 4 weeks 1 day 10 hours ago) and read 4309 times:

For the DC-8 (10 to 70 series are all the same), maximum speed for extending thrust brakes is 390 kts. or Mach .88, which happens to be the aircraft's Vmo/Mmo.


Don't blame me, I don't work here...
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 8, posted (6 years 10 months 4 weeks 1 day 6 hours ago) and read 4297 times:

I thoght it's VMO was like 340 kts indicated.

Andrea Kent


User currently offline737tdi From United States of America, joined Sep 2007, 785 posts, RR: 1
Reply 9, posted (6 years 10 months 4 weeks 1 day 3 hours ago) and read 4277 times:
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Blackbird: As my first real post, I'll answer a portion of your question. The DC-8 could deploy it's inboard reversers at any speed. It has no speed/altitude input, it is strictly mechanical off of the nose gear torque links. Using the same mechanism underneath the throttle pedestal the outboard thrust reversers were locked out. Believe it or not I have been on test flights where a misrig of the cables off the torque links allowed all four engines to go into reverse(it was a test flight check), talking about scary, it felt like we had come to a complete stop in the air. Hope this explains some. Karl

User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 10, posted (6 years 10 months 4 weeks 10 hours ago) and read 4234 times:

Were the reversers as effective, more effective, less effective than the B-707's speedbrakes?

Andrea Kent


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