Mr Spaceman
Topic Author
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

DC-8 Engines Question.

Tue Apr 09, 2002 3:00 am

Hi guys.

In the 3 photos below, you can clearly see that the DC-8's engines have a large vent on the side. At first I thought they might be access doors for maintenance, but in the third photo you can see them open during what looks like a landing rollout. This made me think of Thrust Reversers, however, the vent doors appear to be on backwards for that purpose...I think?

Can someone please explain what these openings are for? Also, are they on both sides of each engine?


Click for large version
Click here for full size photo!

Photo © Propfreak



Click for large version
Click here for full size photo!

Photo © Torsten Maiwald



Click for large version
Click here for full size photo!

Photo © Torsten Maiwald


Chris  Smile
"Just a minute while I re-invent myself"
 
TechRep
Posts: 1877
Joined: Sun Jan 13, 2002 6:53 am

Cascade Doors

Tue Apr 09, 2002 7:22 am

I can answer your question. Those doors are called "cascade doors" and are used for reverse thrust vectoring (Thrust Reversers). Now that’s what they are called but I call them something else, a piece of shit.

These are an absolute nightmare to maintain. If you expect any kind of reliability out of them you better spray them at every service check with graphite spray. The cascade doors are pneumatically actuated and pneumatically controlled no hydraulics at all and often hang open.

Mechanics in an attempt to outsmart the aircraft get into the bad habit of putting Marvel Mystery Oil or Mouse Milk into the T/R pneumatic system hoping it will penetrate and do some good, Which it does for about three flight legs. Then the system gets impregnated with oil, clogs up with micro particles and debris then the T/R quits working.

At Airborne Express they were so difficult to change and were changed on such a frequent basis they went with Cascade door stations. I am not lying, they had stations set aside to be the ones who changed these things on a regular basis, on top of their other duties of course. I guess they came up with some kind of life cycle and would change them at frequent intervals or when needed.

If I seen one of these come into my station you would just get a "O GREAT", a short ducter"!! The DC-8 had short duct (-3B) and long duct (-7B) powerplants. These short duct engines were a pain in the arse I hated them with a passion.

TechRep
 
JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: DC-8 Engines Question.

Tue Apr 09, 2002 2:59 pm

Just to add..... they didnt operate often. They were very slow to deploy when they did. The oil used to lubricate them form sticking was hardly a cure.

The cascade doors were used to reverse the fan thrust only.

They are on both sides of the engine.

JET



 
Mr Spaceman
Topic Author
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

RE: DC-8 Engines Question.

Wed Apr 10, 2002 2:16 am

Hi guys.

So they are thrust reversers, thanks for the info.

I'm confused about how the reversers on the DC-8 work. It doesn't seem like they could blast thrust forward because of how they move inward and appear to be hinged along the aft edge. I don't understand the mechanics involved. Can someone explain them?

In the photo below of the A340's engine, it's easy to tell how the reversers can divert thrust forward.

Click for large version
Click here for full size photo!

Photo © Jernej Verbovsek


Chris  Smile
"Just a minute while I re-invent myself"
 
JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: DC-8 Engines Question.

Wed Apr 10, 2002 9:51 am

The fan reverser on the JT3D-3B engine is covered by those slats. They open just like a venetian blind. hinged at the top. Behind these venetian blind fairings is the cascade reverser. The cascade moves outward through the open vane when the venetian blinds open.

The cascade directs the fan air foward.

This engine also incorporates a hot stream reverser also.

100% of the engines power is reverible. They were still worthless. Well almost....

JET
 
Mr Spaceman
Topic Author
Posts: 2723
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RE: DC-8 Engines Question.

Thu Apr 11, 2002 1:50 am

Hi JETPILOT.

OK, Thanks for that information. I knew there must have been more mechanical parts to the DC-8's reversers that you simply can't see from that photo.

Take Care,

Chris  Smile
"Just a minute while I re-invent myself"
 
JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: DC-8 Engines Question.

Thu Apr 11, 2002 7:57 pm

Here's a better pic of the venetian blinds in a closed position.


Click for large version
Click here for full size photo!

Photo © AirNikon



JET

 
Mr Spaceman
Topic Author
Posts: 2723
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RE: DC-8 Engines Question.

Fri Apr 12, 2002 12:33 am

Hi JETPILOT.

Yes sir, that's a much better photo. Thanks, it helps me understand how the T/R's work.

I must say, those DC-8 reversers sure look primative.

Chris  Smile
"Just a minute while I re-invent myself"
 
tt737fo
Posts: 468
Joined: Thu Jun 07, 2001 2:13 am

RE: DC-8 Engines Question.

Fri Apr 12, 2002 12:57 pm

Hey Jet,

Aren't those CFM-56 engines on that picture you posted?? I didn't know Fine had any of those.
 
JETPILOT
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RE: DC-8 Engines Question.

Sat Apr 13, 2002 4:38 am

This plane is parked in the desert somewhere. Fine own's it..... But it hasn't flown since the Delta got rid of it.

It's not my pic.... I dont know who took it.

No those are JT3D - 3B engines....

CFM's? You on crack?  Nuts

I see your on furlough but it can't have been that long since you've seen one of your engines.....  Smile/happy/getting dizzy

This is the First DC8 ever delivered for revenue service.

JET
 
tt737fo
Posts: 468
Joined: Thu Jun 07, 2001 2:13 am

RE: DC-8 Engines Question.

Sat Apr 13, 2002 1:54 pm

Just keeping you on your toes, Jet.

When I was over in Okinawa last month, I ran into a "Fine" gentleman flying the rotators who was pushing 60 in the Kadena O Club. This guy's name was Bob (forgot his last name)--gray hair, glasses. Real knowledgeable, good guy. Flew Commandos, 8s, and 11s for Rich before coming over to Fine.

Figured you might know who I was talking about.
 
JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: DC-8 Engines Question.

Sat Apr 13, 2002 7:37 pm

Bob Galloway?????

Ring a bell?

Thats the only Bob I know...... I'm not sure he if he flew the L1011 for Jeanie Rich or not.

But I havent worked over at Fine since 98.....

Whats the story on the furlough? Any recalls, or info on when they are expected?

JET
 
Happy-flier
Posts: 286
Joined: Sat Dec 25, 1999 4:41 pm

Cascade Reversers

Sat Apr 27, 2002 2:02 pm

I don't know why they ever bothered with such a cumbersome nacelle for the -3B engine on the DC-8. Couldn't they have made long-duct nacelles for the -3B when they were designing that particular model?
May the wind be always at your back . . . except during takeoff & landing.
 
Happy-flier
Posts: 286
Joined: Sat Dec 25, 1999 4:41 pm

Nacelles

Sun Apr 28, 2002 1:25 pm

Honestly, the more I think about it, the more I can't understand why they designed that particular nacelle for the -3B engine. I mean, just looking at the earliest models of the DC-8 -- the Series -10 to -40 -- the RR Conway fans were thoroughly ducted and the reverser was at the end (granted, part of the "sound suppressor" assembly). It just seems like a better system ... and easier to maintain. My 2¢ ...
May the wind be always at your back . . . except during takeoff & landing.
 
JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: DC-8 Engines Question.

Sun Apr 28, 2002 4:41 pm

Conway was a turbojet....

JET
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: DC-8 Engines Question.

Sun Apr 28, 2002 5:35 pm

The RR Conway was an early ducted turbo-fan. On the
540 series, VC10 naturally, the bypass ratio was 0.60:1
 
JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: DC-8 Engines Question.

Mon Apr 29, 2002 3:03 am

Right On !!!

Thanks

Jet
 
broke
Posts: 1299
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RE: DC-8 Engines Question.

Tue Apr 30, 2002 10:31 pm

The DC-8 was built with 4 different engines depending on the model.
The DC-8-10's had P&WA JT3C turbojets.
The DC-8-20's and DC-8-30's had P&WA JT4A tubojets.
The DC-8-40's had RR Conways, which is the earliest turbofan (low bypass).
The DC-8-50's, DC-8-60's had P&WA JT3D low by-pass turbofans.
Later 110 DC-8-60's were modified to -70 series with CFM-56's (Hi by-pass turbofan).
On the DC-8-50's and DC-8-61's (not -62's and -63's), the engine installation was developed by P&WA. Your photo is of that installation. The shutters open and reveal the cascades inside that deflect the fan air forward. This installation was complicated and not too reliable.
On the -62's and -63's, the installation was developed by Douglas and uses a pair of reverser doors (buckets) at the rear of the nacelle. It is more esthetic and more reliable than the P&WA installation.
 
Happy-flier
Posts: 286
Joined: Sat Dec 25, 1999 4:41 pm

Thanks For Solving The Puzzle!

Wed May 01, 2002 11:42 am

Thanks very much for the informative reply. I didn't know that the series -50 and -61 nacelles with the "cascades" were designed by P&W! That explains it to a certain extent. I have always had a lot of respect for the soundness of design found on the DC-8, and the nacelle used in the -62 and -63 versions seems to me to be in keeping with good design that tends both towards simplicity and reliability. And yes, it definitely does look better too!  Smile
May the wind be always at your back . . . except during takeoff & landing.
 
JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: DC-8 Engines Question.

Wed May 01, 2002 2:26 pm

It should be noted that the 50/61 series with the P&W nacelle had the JT3D-3B engine. The 62/63 series with the long duct nacelle had the JT3D-7 engine.

Along with a new engine, nacelle, and pylon the 62/63 series had a different wing.

JET

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