ben88
Posts: 1037
Joined: Fri Dec 31, 1999 4:49 pm

Is The DC-8 Overpowered?

Sun May 28, 2000 2:57 am

I've seen a few DC-8 photos recently and i'm kinda surprised that it has four rather hefty engines. The fuselage of the plane doesn't look very large. Here are a couple of examples that show the apparent size of the DC-8's engines:


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Photo © James Fullworth




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Photo © Brian Stevenson



These look like replacement engines, because other pictures i've seen have 737-200 type engines. (the long narrow type) e.g:


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Click here for full size photo!

Photo © Pierre Langlois

 
Guest

RE: Is The DC-8 Overpowered?

Sun May 28, 2000 3:35 am

Don't you remember in the early 80s where there was a program that re-engined the noisy smoky P&W JT3D powered long 60 series DC-8s with CFM56s which became 70 series? Many airlines like Delta & United had their DC-8 60 series re-engined to the CFM56 for better fuel ecomony and stricter noise standards. UPS and EMERY later purchased these aircraft from those airlines and are flying them today.
 
Guest

RE: Is The DC-8 Overpowered?

Sun May 28, 2000 5:36 am

The photographs of the DC-8 70 series show the CFM-56-2 engines. These are single stage turbofans that produce 22,000--24,000lbs of thrust. The CFMs went into service in 1982 in a joint venture between GE and SNECMA. They are particularly useful for hot airfields and are also used to power the KC-135.

The older JT3Ds were first produced in the 1950s and stayed in production through 1985. The KLM Super 60 that you showed, has those engines and is one of about 8600 aircraft that did. When the DC-8 60 series shifted to the CFM, the series changed to 70

Now for your question. The super 70 series carried passengers (with United and Delta being the last scheduled users) in the USA until the early 1990s. This was a time when better performance and quieter standards of operation became the norm. Since the CFM offers about a 19% increase in power, some might argue that it is overpowered. But keep in mind that it makes a very reliable airframe quite attractive for serving a wide variety of airfields (economically) for cargo use. Airborne, Emery, BAX, and UPS utilize the CFM on their 8s. There are still a number of KC-135s in use with the Air Guard.

I would call it power improvement, not overpower
 
acvitale
Posts: 1911
Joined: Sat Aug 18, 2001 8:25 am

RE: Is The DC-8 Overpowered?

Mon May 29, 2000 1:05 am

The original DC-8 was actually underpowered. I believe the only commercial jet that cannot lose an engine on takeoff and survive. Hence with the 19% additional power offered by the CFM's I would call them adequate at best...

To ferry a DC-8 with an engine out and empty is even perilious... Look at the crash in MCI a few years back and in DTW a few years before that. Even empty on a ferry flight the DC-8 is underpowered..
 
FLY DC JETS
Posts: 191
Joined: Sat Feb 26, 2000 1:13 pm

RE: Is The DC-8 Overpowered?--JT3D

Mon May 29, 2000 12:00 pm

Just to let the forum know, more than 28,000JT3C, JT3D (J57, TF33) engines were produced. I think the underpowered statement is a bit misguided, however, I will not disagree until I find something that proves otherwise.
 
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asqx
Posts: 591
Joined: Tue Jun 15, 1999 4:56 pm

RE: Acvitale

Mon May 29, 2000 3:55 pm

Both of the accidents you mention in stating the DC-8 was (is) underpowered were caused more so by deficiencies in piloting and inadequate procedures of the airlines, not the direct fault of the aircraft's engine power.

The crash at DTW was determined to be the fault of an improper trim setting and the failure of the pilot in command to detect and correct the situation. As a result the aircraft stalled after takeoff and the crew was unable to recover.

The crash at MCI is more a result of pilot fatigue and poor training than the aircraft not having enough power. The ferry crew did not recieve what the FAA determined to be an adequate rest period after completing their incoming flight. The flight crew also did not have adequate knowledge or training in the proper method of 3 engine takeoffs.
 
albatross
Posts: 53
Joined: Wed May 17, 2000 5:24 pm

RE: Is The DC-8 Overpowered?

Thu Jun 01, 2000 4:43 am

There is no such thing as too much power in flying.
Even then, depending on the circumstance you may not have enough but otherwise there is no such thing as an overpowered airplane.
 
goingboeing
Posts: 4727
Joined: Sat Dec 04, 1999 1:58 am

RE: Acvitale

Thu Jun 01, 2000 5:19 am

The MCI accident was not because of lack of power. VMCG speed was incorrectly calculated and full power was brought up on the asymetrical engine too soon (before full rudder control was available). The aircraft began to veer off the runway and the pilot attempted to rotate below the computed rotation speed.

Just nit-picking here, though.
 
Guest

RE: Is The DC-8 Overpowered?

Thu Jun 01, 2000 6:15 am

Actually, That was a Pratt and Whitney JT4A They were used in 1 or 2 DC-8 planes and the rest were JT3. Those were used for 1 year and then they came out with JT3D.
 
exPratt
Posts: 306
Joined: Wed Mar 08, 2000 6:15 am

RE: Is The DC-8 Overpowered?

Thu Jun 01, 2000 7:01 am

The original DC8s were delivered with the JT4s. With the development of the JT3D engines, the DC8-50, -61, and -63s had JT3D engines installed.

As for the DC8 being underpowered, there are probably no flightcrews that will say the airplane they are flying has too much power. The statement that a DC8 cannot survive an engine out on take off is incorrect. For any multiengine airplane, be it a commercial jet or a ga twin, to be certificated, it must be capable having a positive rate of climb after losing an engine on take off. It may not be an eardrum shattering climb rate, but the DC8 will climb with one engine out. To enhance engine performance on takeoff, most operators would turn off the air conditioning packs that tap off air from the engines to eliminate the thrust loss.

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