DC-8 Super Seventies Conversion - effect on performance

[Mickey Kaye]

As a kid (and adult) I used to see quite a few DC-8s but unfortunately I never got to fly one and suspect that I never will.

Could anyone who has flown both the non CFM powered and CFM powered versions explain what sort of effect the upgrade had on aircraft performance and operating costs?

[SpringHeeledJack]

I flew on a good number of diesel DC-8's and they seemed to be somewhat underpowered, especially the -63 versions which took ages to get off the ground and climb sluggishly. Otherwise a nice aircraft all in all. I stand to be corrected, but apart from a VIP version, I'm not sure if any of the uprated -73's were passenger versions, only UPS led cargo ships. No doubt the economics improved markedly when they had 4 CFM56's compared with the JT3D's as did the climb and cruise and uplift capabilities. Are there many freighters still flying ? All the African one's seem to have been retired, but maybe in the USA there are examples still going.


SHJ

[Cymmon]

Many passenger -70's, the improvements in all parameters was excellent. That's why airlines paid for the changes.

Quieter, less runway, better fuel economy, cheaper to upgrade than buy new a/c, built like the proverbial ......

[Shaggy Sheep Driver]

Didn't the 'stretch 8' need more runway for t/o because it could only rotate to a shallow angle due the length of fuselage behind the main gear?

[DaveReidUK]

Didn't the 'stretch 8' need more runway for t/o because it could only rotate to a shallow angle due the length of fuselage behind the main gear?

That may well be true, though of course it would apply equally to the -60 Series (P&W), not just to the -70 Series (CFM).

[4Screwaircrew]

I rode the jumpseat with UPS a number of times, the 2 stage rotation was very noticeable, watching them depart from Cologne with a full load and fuel for Philadelphia was interesting; they used an incredible amount of runway prior to leaving the ground.

[thing]

they used an incredible amount of runway prior to leaving the ground.

Rated take off?

[TowerDog]

The old engines produced 18,000 lbs of thrust, the CFMs 22,000. Net gain of 16,000 lbs, almost a fifth engine.
Fuel flow went from 18,000 lbs per hr to 12,000, same tanks.
More power and more range on less fuel, clever conversion for sure..
Yes, 2-stage rotation: Rotate at 3 degrees per second up to 9 degrees, lift off, then continue rotation to target pitch.
The -73 was my first jet, quite a handful for a young guy coming from DC-3s but great planes, flew 'em on a cargo contract for Air India some 26 years ago.:cool:

[barit1]

Douglas Tulsa did the prototype conversion, and Delta received their first ship from Douglas (same ship maybe?).

And Delta decided they would buy parts from Tulsa to convert the rest of their fleet themselves in Atlanta; they had no plan to do any third party work. But other airlines started lining up - Delta offered faster/cheaper work; eventually Delta converted more ships than Douglas!

[thegypsy]

4Screwaircrew

Ever seen an A340-300 take off at 270 tons? The run goes on forever even at full chat.

[Capot]

The most exciting take-off I ever experienced in a jump seat was a DC8 flying direct from Exeter (2000m) to Toronto; it was the inaugural flight for a charter series. It only happened once; all subsequent flights went via a fuel stop.

As the roll just went on and on and on and on, I was whimpering with fear.

I was told afterwards that the main wheels left the ground 150m short of the end. The aircrew had completed the loadsheet, no copy could be found. The aircraft was operated by a fairly short-lived company based in Scotland, whose name I forget.

I've been in the jump seat of a BAC 1-11 taking off from Bail al Falaj with one engine deliberately failed at VR plus a second or two (CAA test flight), and of a Concorde departing from Exeter (twice).

But nothing came close to the terror of that DC8 take-off.

[A30yoyo]

Empty the DC-8-63 could have almost STOL performance like many aircraft :-)
https://www.youtube.com/watch?v=6bvK6enoQDg
One of the strange things about the transformational CFM56 is how long it took to find a market ...even Boeing thought its use in the 737-300 was just a stop-gap until UDFs took over apparently

[barit1]

The big marketing hurdle was the fact CFMI was a joint venture, two companies in two countries, two languages, two legal systems, separated by a pond. Few thought the deal could reach Vr, let alone survive. The venture was within weeks of collapse when the first order came through.

Yet it turned out to be incredibly successful (http://www.cfmaeroengines.com/engines).

[A30yoyo]

I believe the US Govt was fining GE at one point in a dispute over technology rights....but eventually it got settled
1999 | 1357 | Flight Archive (http://www.flightglobal.com/pdfarchive/view/1999/1999%20-%201357.html)

[tdracer]

I found the -60 series DC-8 a little scary.
As teenager, back in the early 1970's, I was flying back from London to Bangor on a DC-8-60 ONA charter. A high school concert band tour - 250 passengers, crew, plus luggage, band instruments, a months worth of souvenirs, and gas to go across the pond.
I had a window seat for takeoff from London - we trundled down the runway - and trundled, and trundled, and trundled. A bunch of mainly teens, we were chanting "get it up, get it up". Finally the nose came up and we gave a cheer "come on". The main gear finally left the ground, and an instant later the runway ended :eek: :eek:. The part I found really amazing was the instant silence through the cabin - somehow even those without window seats knew how close it had been .:uhoh:
We landed in Bangor, Maine to refuel and go through customs. On takeoff from Bangor, they banged the tail :ugh:

[SpringHeeledJack]

Every time I flew on a 60's series the take-off followed the same pattern as described above and no matter how many times it happened my palms started to sweat and fear surfaced..Perhaps the cockpit crew were the only ones without this feeling ;) The two stage rotation was no doubt very trying, especially when the crew was fatigued and the odd tail scrape not uncommon.

Within the last decade a cargo DC-8-60, perhaps with an optimistic load sheet, took off at night in the UK for the dark continent. It made it skywards due to the curvature of the earth, but the next day tyre tracks on the grass extending from the runway were observed…..:ooh:


SHJ

[JW411]

If I have already told this story on prune before then I apologise. In the 1980s I was flying DC-10s based at JFK. Our company had a lot of DC-8s of just about every variety (-54, -61, -62, -63 and -73). I was in the bar one night with one of my friends who was on the DC-8 and asked him which one was his favourite. "Without a doubt it would be the -62" said he. I asked him what he thought of the -63. "Hell" he said "it's like flying a dog with worms." Very descriptive!

[ATNotts]

Within the last decade a cargo DC-8-60, perhaps with an optimistic load sheet, took off at night in the UK for the dark continent. It made it skywards due to the curvature of the earth, but the next day tyre tracks on the grass extending from the runway were observed…..

That would be from EMA carrying, if my memory serves me correctly, a cargo of freshly printed bank notes?

[tornadoken]

A30 #14: aero-engine IPR. Tks for the Flight item on F101 technology transfer (to an Ally!) UK twice went through the same exercise..but with prospective targets (as in, military) for engine IPR: 1946, centrifugals/USSR and 1975 (reheated turbofan/PRC). The IPR owner may receive near-term benefit - cash, perhaps - but the recipient may (expects to) capture long-term benefit.

The Flight article was wrong to dismiss objectors as "ossified" civil servants. These are not easy issues. Everyday, right now, China comes along offering deals of near-term benefit: the London taxi, MG Cars. But will long-term jobs flow down the Yangtze? The logic of Protection says: exactly that; the theory of Free Trade says: overall market expansion to mutual benefit...which is the outcome of transfer F101 core into CFM56 (in late-1980s its largest Customer was USAF - KC-135 upgrades).

[A30yoyo]

tornadoken...I do sometimes speculate on what might have happened if Rolls has built a CFM56 class engine in the early Seventies instead of the RB-211...an engine that size could have extended the lives of the BAC-111 and VC-10 programs, kept the DC-8 in production.....might have made a better Mercure :-)...instead Rolls bankrupted themselves and the big 3 American companies went head-on at each other until only Boeing was left doing civil airliners.

I read a curious thing about the KC-135...the CFM-56 version though radically improved didn't have a higher MTOW but it had a higher empty weight (heavier engines) so, if there was unlimited runway length, the original KC-135A could carry more transfer fuel to a nearby refuelling point (though it might need an extra mile of runway to get off) EDIT...think I got it somewhat wrong....may have been the KC-135E version and it only applied to a hypothetical refuelling transfer closeby the base

[barit1]

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)

[A30yoyo]

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

[WHBM]

tornadoken...I do sometimes speculate on what might have happened if Rolls has built a CFM56 class engine in the early Seventies
They did, a bit later. They went in equally with P&W to do the IAE V2500, which although not as successful as the CFM56, nevertheless sold plenty of units on a good range of types.

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.

[A30yoyo]

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

http://i809.photobucket.com/albums/zz20/A30yoyo/N8184Awinter70-71_zpsddd78d2e.jpg (http://s809.photobucket.com/user/A30yoyo/media/N8184Awinter70-71_zpsddd78d2e.jpg.html)

[Rick777]

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.

[barit1]

A30yoyo

Thanks for the table of weights. Now you've got me busy on my end, seeing just what "bare engine" includes. :confused::}

[RedhillPhil]

You want long scary take-offs?


Russian cargo plane needs more runway - YouTube (http://www.youtube.com/watch?v=d7q3j69-SHM&feature=player_detailpage#t=3)

[A30yoyo]

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 (http://en.wikipedia.org/wiki/Boeing_KC-135_Stratotanker)

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

[tonytales]

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.

[sardinesnack]

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.:p

[tonytales]

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.