DC-8 Super Seventies Conversion - effect on performance
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CFM56 heavier than the J57? I'd have to see the numbers.
But take that at face value; the mission fuel is considerably less, and with more thrust, the climb is considerably improved, reaching TOC sooner and higher.
This also translates to longer endurance and range, and/or more donor fuel to their "customers". (If USAF had put the bigger 707-320 wing on it, the advantage would have been even greater)
But take that at face value; the mission fuel is considerably less, and with more thrust, the climb is considerably improved, reaching TOC sooner and higher.
This also translates to longer endurance and range, and/or more donor fuel to their "customers". (If USAF had put the bigger 707-320 wing on it, the advantage would have been even greater)
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barit 1...apologies...I think I may have been thinking of a reference to the ANG KC-135E conversions where the JT3D fans replaced straight J-57s so were heavier but there does seem to have been a gross weight increase permitted so I'd better shut up until I find the reference :-)
EDIT bare engine weights seem to be
J-57 (JT-3C) as in KC-135A ~3495lb
JT-3D turbofan as in KC-135E ~4360lb
CFM56-2 as in KC-135R ~4671lb
EDIT bare engine weights seem to be
J-57 (JT-3C) as in KC-135A ~3495lb
JT-3D turbofan as in KC-135E ~4360lb
CFM56-2 as in KC-135R ~4671lb
Last edited by A30yoyo; 23rd Sep 2014 at 00:37. Reason: more facts
Regarding the DC8, I always got the impression that Douglas couldn't design a good wing. The leading edge slots were an early variation, they redid the wingtips and later the leading edge to reduce drag, then they found it worked better cruising with 1 degree of flap, and with the -62/63 they did a substantial wing redesign. Meanwhile a number of the early long-haul purchasers like Pan Am and Northwest didn't care for this lack of performance, and sold them off prematurely (very prematurely in the case of Northwest, cancelling the balance of their order and sending the five delivered so far back to Douglas), to place big orders with Boeing instead.
Last edited by WHBM; 22nd Sep 2014 at 20:49.
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Yes Northwest got rid of their DC-8-30s (1 in 1962, 3 in 1963 1 in 1964) as soon as JT-3D turbofan powered types were available and switched to Boeing 707-320Bs. Pan Am sold their DC-8-30s to Delta about 1968-1969,i.e. after some 7-8 years, one or two then reappeared in Europe freshly painted in Pan Am colours on some Delta/PanAm through-plane flights into 1971
I never flew the DC8, but I flew the KC 135 A and R. The CFMs were heavier so the gross weight was increased, but the fuel tanks still only held about 200,000 lbs. offload capability was much increased due to ability to get off the ground with more gas and much lower fuel burn. The KC135A had some truly scary takeoffs. We just rotated at 1000 feet to go regardless of speed. You usually had rotation speed a little before that though even when heavy. A KC 135R at max weight was a non-event just like most modern planes.
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barit 1 The reference to KC-135A having a somewhat greater theoretical fuel load than the KC-135E came from the Wikipedia page and is of no practical importance since the real-mission transfer fuel would be higher for the KC-135E
Boeing KC-135 Stratotanker - Wikipedia, the free encyclopedia
There is an interesting paper Air Force engineering paper on the ancient KC-135 ballast and tare weights which mentions a 'steel' and 'titanium' versions of the J-57 with a ~10% weight difference, (the latter going on the KC-135)
file:///C:/Documents%20and%20Settings/owner/My%20Documents/Downloads/ADA527036%20(1).pdf
Getting back to DC-8s, the early domestic DC-8-10 (EDITED) (J-57 powered) must have been a bit of a turkey and I think they were rebuilt with JT-3D fans?
EDIT...As tonytales corrects me next post it the DC-8-20 had JT-4 (J-75) engines (34 built, plus 15 conv. from -10). Of the 29 'domestic' DC-8-10 (J-57) the prototype N8008D was eventually re-engined with JT-3D fans and sold, of the 22 for United,by the mid-1960s 15 upgraded to -20 with JT-4 non-fan engines, 5 upgraded to -50 with JT-3D fans and 2 lost, all 6 built for Delta were upgraded to -50 with JT-3D fans (Source , the well-written Wiki page http://en.wikipedia.org/wiki/Douglas_DC-8 ).
(For 707 detail variations I like the Airliner Cafe page http://www.airlinercafe.com/page.php?id=72
Boeing KC-135 Stratotanker - Wikipedia, the free encyclopedia
There is an interesting paper Air Force engineering paper on the ancient KC-135 ballast and tare weights which mentions a 'steel' and 'titanium' versions of the J-57 with a ~10% weight difference, (the latter going on the KC-135)
file:///C:/Documents%20and%20Settings/owner/My%20Documents/Downloads/ADA527036%20(1).pdf
Getting back to DC-8s, the early domestic DC-8-10 (EDITED) (J-57 powered) must have been a bit of a turkey and I think they were rebuilt with JT-3D fans?
EDIT...As tonytales corrects me next post it the DC-8-20 had JT-4 (J-75) engines (34 built, plus 15 conv. from -10). Of the 29 'domestic' DC-8-10 (J-57) the prototype N8008D was eventually re-engined with JT-3D fans and sold, of the 22 for United,by the mid-1960s 15 upgraded to -20 with JT-4 non-fan engines, 5 upgraded to -50 with JT-3D fans and 2 lost, all 6 built for Delta were upgraded to -50 with JT-3D fans (Source , the well-written Wiki page http://en.wikipedia.org/wiki/Douglas_DC-8 ).
(For 707 detail variations I like the Airliner Cafe page http://www.airlinercafe.com/page.php?id=72
Last edited by A30yoyo; 25th Sep 2014 at 11:30. Reason: I wrongly ID'd the domestic DC-8
Actually, the DC8-20 series had JT-4 (J-75) engines not J-57 (JT-3C). Eastern delayed their initial DC-8 deliveries until the JT-4 powered -21 version became available.
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When I was a youngster I flew the Straight-Pipe and CFM powered DC-8's in the front seats at ATI, then rode side-saddle on them at UPS as a junior employee. One of the performance changes was VMCG for the CFM powered variants over the JT-powered aircraft due to the same standard tail surface being used through out. Power reductions where watched closer in the JT powered birds as an abrupt tug to idle could result in some impressive cabin pressure bumps or even a rapid-D event due to those aircraft still having turbo-compressors as pressurization devices. The double rotation maneuver was taught more as a check to see if your engineer had provided the correct V-speeds from the many charts measured with a micrometer, then hacked out with an axe, and the characteristic of the Douglasaurus having a very pitch sensitive manual trim-tab flying tail which could easily result in an over-rotation, or your destruction in severe turbulence. The saving grace of the DC-8 was its over-built Fuselage and DC-direct cable simple manual systems. The wing slats helped improve the tendency for the airplane to fly a nose-low approach. The wing was very advanced for its time and efficient, to include wing tip fuel tanks which decreased drag and moved the CG aft in flight. The DC-8 was a great airplane with an impressive service record. But it's true what they say, Boeing builds good airplanes, while Douglas builds better pilots.
Working for LASi, EAL, Orion Air and TIMCO I worked and saw a lot of DC-8 models. Even got called out one day to service the hydraulics one day on N808, the prototype DC-8 which by then was a -51. Hydraulic tank and plumbing in left wing root very odd compared to other DC-8.
Never worked the -10 or -30 but the -21 at EAL were similar. The JT-4 was a rugged engine, caused little trouble. Even the target reverser that slid back on rails gave little trouble, lot better than the 50/61 series.
I do remember the Alitalia -40 coming back from Project 61 upgrades to the hydraulic system including the flap lockouts and the mod to the hydraulic tank to increase capacity. Also the 4% leading edge mod which reduced the bluntness considerably. By the way, EAL never incorporated the 4% mod on their -21 models.
EAL sold its -21 and then had to reclaim some from Spain for non-payment. The airplanes sat for a while with no maintenance. The EAL crews ferrying them back through KJFK who I met said they were amazed at the engines starting and not a squawk on them on the flight. They said they wondered why EAL had sold them till they looked at the fuel Flows.
The -40 series I worked had the very good Conway engines. Little problem with them.
The 50 and -61 reversers gave us fits for years. There were three separate units on the engine, the hot section buckets in the back and the left and right fan panels. All controlled by a single pneumatic pilot valve. The three pieces were not linked otherwise and you could get partial deployment on one fan panel, full on the other and the hot section not doing anything. And the pilot valve would stick so you couldn't pull it into reverse. The fan panels were very heavy too if you had to open them for maintenance.
The -62 and -63 were another story. Slim nacelles, no fan reverse panels as it was ducted aft to the tailpipe. Due to the DC-8 not having speed brakes it used engine reverse for rapid or emergency descents. This meant it was critical to be able to get an engine out of reverse. The 62/63 had a powerful big spring that was compressed when engine was reversed. A gripper on the extension rod held it open. In an emergency you could release it and the spring drove it to forward thust. If you want to wake up a hangar full of mechanics, release a -62/63 reverser.
Airborne Express bought up a lot of -62/63 pylons and engines from aircraft being converted to -70 series with CFM.
They contracted to have their -61 stripped of the old pylons and engines and the 62/63 pylons and slim engine nacelles installed. They did not have the wing tip extensions fitted. Airborne also looked at having DC-8 converted to two engines, CF-6 models and actually had an old -50 at Wilmington Ohio fitted with a wooden mockup. Quite impressive looking. It would have taken a vertical fin expansion and, if I remember correctly, some counterweights out on the wing to compensate for the loss of the dampening effect of the outboard engines.
I remember the -73 at Orion Air which we operated for UPS. The only ill effect of the CFM conversion was that you couldn't slow the plane down. I saw this when I jump-seated when visiting stations. This necessitated more in-flight reversal than formerly and that proved a bit hard of the flaps which after all live aft of the engines.
All in all, my favorite airplanes, speaking as a mechanic, were the DC04, DC-8 and the DC-9.
Never worked the -10 or -30 but the -21 at EAL were similar. The JT-4 was a rugged engine, caused little trouble. Even the target reverser that slid back on rails gave little trouble, lot better than the 50/61 series.
I do remember the Alitalia -40 coming back from Project 61 upgrades to the hydraulic system including the flap lockouts and the mod to the hydraulic tank to increase capacity. Also the 4% leading edge mod which reduced the bluntness considerably. By the way, EAL never incorporated the 4% mod on their -21 models.
EAL sold its -21 and then had to reclaim some from Spain for non-payment. The airplanes sat for a while with no maintenance. The EAL crews ferrying them back through KJFK who I met said they were amazed at the engines starting and not a squawk on them on the flight. They said they wondered why EAL had sold them till they looked at the fuel Flows.
The -40 series I worked had the very good Conway engines. Little problem with them.
The 50 and -61 reversers gave us fits for years. There were three separate units on the engine, the hot section buckets in the back and the left and right fan panels. All controlled by a single pneumatic pilot valve. The three pieces were not linked otherwise and you could get partial deployment on one fan panel, full on the other and the hot section not doing anything. And the pilot valve would stick so you couldn't pull it into reverse. The fan panels were very heavy too if you had to open them for maintenance.
The -62 and -63 were another story. Slim nacelles, no fan reverse panels as it was ducted aft to the tailpipe. Due to the DC-8 not having speed brakes it used engine reverse for rapid or emergency descents. This meant it was critical to be able to get an engine out of reverse. The 62/63 had a powerful big spring that was compressed when engine was reversed. A gripper on the extension rod held it open. In an emergency you could release it and the spring drove it to forward thust. If you want to wake up a hangar full of mechanics, release a -62/63 reverser.
Airborne Express bought up a lot of -62/63 pylons and engines from aircraft being converted to -70 series with CFM.
They contracted to have their -61 stripped of the old pylons and engines and the 62/63 pylons and slim engine nacelles installed. They did not have the wing tip extensions fitted. Airborne also looked at having DC-8 converted to two engines, CF-6 models and actually had an old -50 at Wilmington Ohio fitted with a wooden mockup. Quite impressive looking. It would have taken a vertical fin expansion and, if I remember correctly, some counterweights out on the wing to compensate for the loss of the dampening effect of the outboard engines.
I remember the -73 at Orion Air which we operated for UPS. The only ill effect of the CFM conversion was that you couldn't slow the plane down. I saw this when I jump-seated when visiting stations. This necessitated more in-flight reversal than formerly and that proved a bit hard of the flaps which after all live aft of the engines.
All in all, my favorite airplanes, speaking as a mechanic, were the DC04, DC-8 and the DC-9.
