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Is The DC-8 Overpowered?  
User currently offlineBen88 From United States of America, joined Dec 1999, 1093 posts, RR: 2
Posted (14 years 7 months 6 hours ago) and read 1752 times:

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:


Click for large version
Click here for full size photo!

Photo © James Fullworth




Click for large version
Click here for full size photo!

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:


Click for large version
Click here for full size photo!

Photo © Pierre Langlois



9 replies: All unread, jump to last
 
User currently offlineTEDSKI From , joined Dec 1969, posts, RR:
Reply 1, posted (14 years 7 months 6 hours ago) and read 1654 times:

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.

User currently offlineDC-9CAPT From , joined Dec 1969, posts, RR:
Reply 2, posted (14 years 7 months 4 hours ago) and read 1618 times:

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


User currently offlineAcvitale From United States of America, joined Aug 2001, 922 posts, RR: 10
Reply 3, posted (14 years 6 months 4 weeks 1 day 8 hours ago) and read 1575 times:

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..


User currently offlineFLY DC JETS From United States of America, joined Feb 2000, 199 posts, RR: 0
Reply 4, posted (14 years 6 months 4 weeks 21 hours ago) and read 1548 times:

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.

User currently offlineAsqx From United States of America, joined Jun 1999, 619 posts, RR: 0
Reply 5, posted (14 years 6 months 4 weeks 17 hours ago) and read 1531 times:

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.


User currently offlineAlbatross From United Arab Emirates, joined May 2000, 55 posts, RR: 0
Reply 6, posted (14 years 6 months 3 weeks 5 days 5 hours ago) and read 1513 times:

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.


User currently offlineGoingboeing From United States of America, joined Dec 1999, 4875 posts, RR: 16
Reply 7, posted (14 years 6 months 3 weeks 5 days 4 hours ago) and read 1501 times:

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.


User currently offlineSouthwestJG737 From , joined Dec 1969, posts, RR:
Reply 8, posted (14 years 6 months 3 weeks 5 days 3 hours ago) and read 1483 times:

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.

User currently offlineExPratt From United States of America, joined Mar 2000, 311 posts, RR: 0
Reply 9, posted (14 years 6 months 3 weeks 5 days 2 hours ago) and read 1472 times:

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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