Blackbird From United States, joined Oct 1999, 3436 posts, RR: 5 Posted (1 year 6 months 4 weeks 1 day 17 hours ago) and read 1793 times:
The Boeing 707 and DC-8's both have plenty of their share of proponents, and for a number of different reasons.
I ask, which aspects of the 707 do you like over the DC-8, and also what aspects of the DC-8 do you like over the 707? It could be something minor, or major. I'd love to hear what people who actually worked on 707's and/or DC-8's have to say.
For example...
-The 707 is slightly faster than the DC-8
-The DC-8 doesn't experience mach tuck to the same degree that the 707 does
Talk about whatever variants you want... feel free to go into great length.
Blackbird From United States, joined Oct 1999, 3436 posts, RR: 5 Reply 2, posted (1 year 6 months 4 weeks 1 day 17 hours ago) and read 1767 times:
I remember reading somewhere that that was a myth and that the 707 could have been stretched further (as long as the ventral fin was removed), but Boeing felt that going for a new design (Which ultimately became the 747-100) would be a better idea. At least that's what I remember.
The DC-8, though was more rugged structurally, and seem to have a greater longevity.
SEPilot From United States, joined Dec 2006, 3030 posts, RR: 9 Reply 4, posted (1 year 6 months 4 weeks 1 day 6 hours ago) and read 1679 times:
Quoting Blackbird (Reply 2): The DC-8, though was more rugged structurally, and seem to have a greater longevity.
The main reason for the DC-8's longevity is due to the stretched versions and the fact that an engine conversion was available for it. I brought this issue up on another thread and suspected that more 707's were still flying than unstretched DC-8's, and someone posted figures that confirmed it. As to stretching the 707, it does seem that they built the 747 in place of stretching it; the impetus was Pan Am desiring a jumbo, and a stretched 707 just wouldn't do it.
Where do these figures come from? I'm sure many 707's have gone well beyond 40,000 hours, and I haven't seen any reports of any with fatigue issues. There also have been no crashes attributed to fatigue failure that I know of, and I have looked. I would be interested if anyone has any info on high-time records for 707's and/or DC-8's.
The issue of the 707 being faster is due primarily to the fact that Boeing had much more experience with jets from the B-47 and B-52 programs than did Douglas, and had their own high-speed wind tunnel, which Douglas did not. The high-speed high-altitude aerodynamics on the 707 were better as a result.
The problem with making things foolproof is that fools are so doggone ingenious...
CaptOveur From , joined Dec 1969, posts, RR: Reply 5, posted (1 year 6 months 4 weeks 1 day 6 hours ago) and read 1667 times:
Quoting SEPilot (Reply 4): The main reason for the DC-8's longevity is due to the stretched versions and the fact that an engine conversion was available for it.
I am almost certain Boeing offered the same engine mod for the 707 that was done to quite a few of the KC-135 fleet with CFM-56s. Nobody wanted it though.
Trichos From United States, joined Sep 2003, 22 posts, RR: 0 Reply 6, posted (1 year 6 months 4 weeks 1 day 5 hours ago) and read 1655 times:
I read somewhere that the DC8 had better landing characteristics than the 707. It was attributed to wing sweep. DC8 at 30 and 707 at 35, so the 707 was a little harder to control at slow speed. I have no way to confirm this.
The greater sweep may have contributed to greater speed in the 707 at cruise.
411A From United States, joined Nov 2001, 1538 posts, RR: 5 Reply 8, posted (1 year 6 months 4 weeks 1 day 4 hours ago) and read 1628 times:
I'm afraid you have had little experience (if at all) in the air transport world, SEPilot.
The design service life of the respective aircraft I mentioned is well known, and comes directly from the respective manufacturer.
No fatigue issues with the B707 you say?
Well, if we ignore the fuselage crown skin cracking experienced early on, and the temporary fix developed (straps) and the necessity of reskinning the entire area, not to mention the wing spar doublers required and entire upper wing skins needing replacement on some models, I 'suppose' we could say that the B707 airframe is ah...trouble free.
Original design service life is just that.
It is a design, not a limit as to what can be achieved with life extensions to the airframe.
Now, lets address the stretch issue, beyond the possibility from the last design, the -320B/C.
The geometry of the airplane, the effect of the leading edge devices, the angle of movement possible with the horizontal stabilizer, the elevator effectiveness at slower speeds, indeed, the whole size of horizontal tail surfaces...all precluded the stretch possibilities.
A required entire redesign of the B707 airplane precluded ANY stretch of the airframe. The B747 had absolutely nothing to due with any of this.
SEPilot From United States, joined Dec 2006, 3030 posts, RR: 9 Reply 9, posted (1 year 6 months 4 weeks 1 day 3 hours ago) and read 1602 times:
Quoting 411A (Reply 8): I'm afraid you have had little experience (if at all) in the air transport world, SEPilot.
Quite right, I haven't. I have long been interested in the subject, however, and have read whatever I could find about it. I was unaware of these issues with the 707; thanks for educating me on them. I was aware that the 707 was much less amenable to being stretched than was the DC-8; but the fact that Pan Am wanted the 747 made the whole question moot. Whether or not Boeing ever considered it I don't know; considering all that was on their plate in the 60's, I doubt it. I do know that Juan Trippe really pressured Bill Allen for the 747; nobody else in Boeing management was very enthusiastic about doing it at the time, as they were doing the SST, the 737, and the 727-200 at the same time.
The problem with making things foolproof is that fools are so doggone ingenious...
Blackbird From United States, joined Oct 1999, 3436 posts, RR: 5 Reply 10, posted (1 year 6 months 4 weeks 17 hours ago) and read 1485 times:
411A,
You're sure if the 707 wasn't fitted with slats on the wing's leading edge, and some vortex generators on the tail (or a slot that would close once the flaps went up or something) it wouldn't be able to takeoff with a fuselage stretch?
Viscount724 From Switzerland, joined Oct 2006, 7102 posts, RR: 1 Reply 11, posted (1 year 6 months 4 weeks 16 hours ago) and read 1466 times:
Quoting Blackbird (Reply 10): You're sure if the 707 wasn't fitted with slats on the wing's leading edge, and some vortex generators on the tail (or a slot that would close once the flaps went up or something) it wouldn't be able to takeoff with a fuselage stretch?
Without major redesign, any significant stretch of the 707 (comparable to the 37 foot stretch of the DC-8-61/63) would probably almost have resulted in very little rear fuselage/tail clearance. Look at photos of the 707 and DC-8. The DC-8, especially the unstretched models, have a pronounced nose-down attitude when on the ground. The 707 is much more level and almost seems to be sitting slightly tail-down compared to the DC-8. It was thus much easier to stretch the DC-8 without major redesign of the landing gear etc.
I'm not even sure Boeing would have wanted to stretch the 707 if it had been possible. Many reports say McDonnell-Douglas could have sold more stretched DC-8s but they ended production prematurely to avoid cannibalizing early DC-10 sales. Some Boeing customers may similarly have delayed ordering the 747 if a 707 with significantly greater passenger capacity had been available at the time.
ImperialEagle From United States, joined Jan 2006, 633 posts, RR: 9 Reply 12, posted (1 year 6 months 4 weeks 16 hours ago) and read 1465 times:
The draw-back of having so much aviation "stuff" is not being able to find something when you want it. (Or procrastination has kept me from properly filing things away!)
Somewhere I have some "pie-in-the-sky" literature from Boeing showing a "proposed" stretched 707 Intercontinental. It was not stretched by much though, and it used a (proposed?) higher powered version of the JT-3D. I'll dig around and see if I can find it and I'll scan it for 'ya. I just remember thinking it looked kind of stupid.
As previously discussed the lighter structure of the 707 did not lend it to longetivity, however one of the trade-offs was percieved as higher profitability. And lower operating costs---at least for the first ten years or so. Also the wing-sweep did give the 707 a slight edge in cruise speed, and speed was what it was all about. Oh, and Doug had to clean-up the drag around those nacelles---which they did beautifully on the -62 and -63's.
(However,let us not forget that it was the DC-8 (a 40 and a 50 series) that went supersonic (twice)!)
Douglas's heavier structure can be directly traced to the "Comet scare", and Doug's lack of jet experience. They had to hurry up and try to build something superior to Boeing, and given what they had work with they did a great job.
As discussed, the wing sweep was a bit less than Boeing's and that gave the 8 better stability at slow speeds---although there were some early problems with instability during climb with a full load. Nonetheless, just the lack of vortex-generators on the wing of the 8 says something about the level of engineering expertise that went into the design.
Whether by coincidence or not, Doug was smart to give the 8 a tall gear and thereby allowing for a stretch. Also by the mid-sixties, just when Doug (oops, by then "McDac") was desperate for a cash-transfusion and trying to keep the DC-8 assembly line open, Boeing fired longtime engineering and sales "guru" Wellwood Beall, (who certainly was aware of the 707's limitations), and Mcdac "snatched him up". It didn't take long before McDac was knocking on the door with proposals on a stretched 8.
O.K. well, I'll dig around and see what I can find. In the meantime I really enjoy picking my mind for information on these topics.
"If everything seems under control, you're just not going fast enough!"
747400sp From United States, joined Aug 2003, 1700 posts, RR: 2 Reply 13, posted (1 year 6 months 4 weeks 14 hours ago) and read 1452 times:
Quoting CaptOveur (Reply 5): I am almost certain Boeing offered the same engine mod for the 707 that was done to quite a few of the KC-135 fleet with CFM-56s. Nobody wanted it though.
You are right! Around 1977-79 Boeing was testing a 707 with CFM-56-2 ( the same CFM-56 that is use on KC-135R and DC-8 super 70 ) called the 707-700. I read somewhere that the reason 707-700 project did not work, was because Boeing did not want to hurt 757 and 767 sells. The RAF, French Air Force E-3 Sentry and USN E-6B Mercury are basically 707 700.
Uscgc130 From , joined Dec 1969, posts, RR: Reply 14, posted (1 year 6 months 4 weeks 12 hours ago) and read 1437 times:
Quoting 411A (Reply 8): Well, if we ignore the fuselage crown skin cracking experienced early on, and the temporary fix developed (straps) and the necessity of reskinning the entire area
[...]
Did this affect only the 707, or the 727 and 737 as well?
The reason I ask is that twenty-odd years ago, I began noticing that 727s sported a doubler plate shaped like an inverted funnel just above the junction of the left and right windshield panels. (I'd never noticed that on 707s, but by then the 707 was no longer common at any airports I frequented.) Is that what you're referring to by "fuselage crown skin?"
Uscgc130 From , joined Dec 1969, posts, RR: Reply 15, posted (1 year 6 months 4 weeks 12 hours ago) and read 1432 times:
As a passenger, I never had any preference for one over the other. Then again, my exposure to DC-8s was limited; I flew on a Delta Series 50 (SFO-DAL) in 1967, and didn't set foot on another DC-8 until 1979. That was the year I took a United DC-8-62 from SJC to HNL on what had to have been of the last (pre-757) narrowbody flights between the Mainland and Hawaii. I was astounded at how quiet the airplane was. I didn't even know that the engines had been started until we began taxiing away from the gate.
I've always wondered whether the reason the DC-8 sits tail-high on the ground was because it had been designed with an eye toward stretching, or for some other (aerodynamic?) reason. It's ironic, considering that the DC-6 and DC-7 sit tail-low.
ImperialEagle From United States, joined Jan 2006, 633 posts, RR: 9 Reply 16, posted (1 year 6 months 4 weeks 7 hours ago) and read 1395 times:
Quoting Uscgc130 (Reply 15): I didn't even know that the engines had been started until we began taxiing away from the gate.
Yeah, with the -50's and -61's there was no mistaking that start sequence! (That wonderful mating-call!)
Quoting Uscgc130 (Reply 15): considering that the DC-6 and DC-7 sit tail-low
Well, you weren't too worried about over-rotation on those old windmills anyway. (Although if you did, they had pretty stout tail-skids.) You tended to fly off with not much change in angle unless struggling to clear some obstacles in the windscreen, and with a full load on a hot day you usually got a pretty good look at those obstacles.
"If everything seems under control, you're just not going fast enough!"
Buzz From United States, joined Nov 1999, 691 posts, RR: 20 Reply 17, posted (1 year 6 months 4 weeks 4 hours ago) and read 1366 times:
Hi USCGC130, Buzz here. Those doublers around the cockpit window frames were installed "as needed" when cracking was found, it's a standard repair. And there's a standard repair for cracked door corners called a "Texas patch", by it's shape.
Crown Skins would be the entire sheet of skin on the top of the fusel-sausage. Back in the '80's UAL was doing 737-200 belly skin changes, replacing the laminated skin (better crack resistance but the glue would wick moisture and corrode the skin) for a 1 piece skin. The crown skins on the 727 and 737 seem to have stood up well.
In contrast, the DC-8-71's in the next dock over were rather over-built. I figured it was a reaction to the DH Comet structural problems. Of course Douglas was building carrier airplanes when the DC-8 was designed (A3D "Whale") so Douglas wasn't entirely ignorant of large jet powered airplanes.
DC-6 and DC-7 sit tail low... aren't those a stretched DC-4? (grin) OK, so under the skin the systems and structure are quite different.
I'm fond of the DC-8 series... they have some limitations but I kind of like 'em. I've never worked on / flown with the KC-135 / 707 series. So my observations are biased.
Baroque From Australia, joined Apr 2006, 7879 posts, RR: 29 Reply 18, posted (1 year 6 months 4 weeks 4 hours ago) and read 1361 times:
My first encounter as a pax was a VC10 followed by a 707 and the VC10 won! Then 707 vs Convair 880 and 990, Convairs won. I am not sure if they were more comfortable or anything like that, but a heck of a lot more interesting.
Then five years later, 707 vs stretched DC8 and oh were the stretched 8s nice, largely due to incredibly long pitch for the seats.
After all those, I had a short trip in a Comet 4C, which was also fascinating.
So good as it may have been, the 707 came last in that list of first generation jets!
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