Douglas DC-8

[KJ_Lesnick]

I was thinking about the DC-8 design and while it was a great aircraft (by commercial standards sturdy, with immense longevity, it's wings didn't require vortex generators, and had no serious  mach-tuck problems), In some respects, it was such an ugly, clunky design that looked like an older design than the B-707, even though it flew slighly later and were otherwise contemporaries.  The design had these huge widely spaced windows which looked like they came off a propeller-plane design (and unless the airline positioned every seat 40-inches apart, some rows would not have windows), as did it's control-surface hinge-joints which were hugely clunky looking.  The fact that it's rudder leading-edge actually popped out, or was in one way or another aft of the tailfin's trailing-edge also looked very piston-era, as did it's huge double-bubble fuselage.

Lucky the airplane was a lot more advanced than it looked, but it did fall short in a number of areas...

- The design was initially intended to have stall-speeds only 10 knots higher than a DC-7, even going so far as to choose a 30-degree (at 1/4 chord) wing-sweep instead of a 35-degree sweep (which would have made achieving high-speed performance easier) to produce more favorable low-speed handing -- and probably more lateral-stability (Interestingly they were able to achieve good high-speed handling qualities even with the 30-degree sweep due to clever aerodynamic fine-tuning of the airfoil).  The stall speeds to my knowledge are significantly higher than the DC-7, and so is the airplane's landing speed. 

- The airfoil was tested at very low reynolds-numbers (which are a function of scale) and apparently due to some complicated factors and the fact that the wing was just above a certain threshold, they made an error regarding the leading-edge when scaling up the wing -- it was too blunt and produced too much drag, and more pronounced shockwaves than desired resulting in increased fuel-burn, and some variants requiring a 1.5 degree flap-detent in cruise to lower the AoA (figuratively flying the plane on the step).  Oddly the plane had no serious mach-tuck problems and could fly as high as Mach 0.95 safely (during dives).  Eventually this problem was rectified with the addition of a 4-percent chord-extention featuring a sharpened leading-edge, re-profiled surfaces behind the leading-edge, and revised slots on applicable designs (all models other than the DC-8-11 had slots)

- The airplane's speedbrakes were designed in the same style as those used on fighter-planes -- split-brakes mounted on the lower section of the fuselage behind the wings, and unfortunately were nearly useless.  Luckily the thrust reversers were more effective than predicted, but the vibration produced scared passengers and pilots were often reluctant to use them.


The idea I was thinking up was a DC-8 that looked more like it was part of the jet-age and less out of the piston-era, and also managed to sidestep all the serious land-mines the actual DC-8 program ran into.


1.) To allow the lower-speed handling qualities desired, all the DC-8's should have used the 142 foot span (instead of all but the -11), in addition to greater commonality, it would produce more lift which is useful for takeoffs.  All of them should have been fitted with slots, and larger ones too -- the DC-8-10/-20 would probably have worked well with slots as large as those used on the DC-8-61, with the DC-8-30 and DC-8-40 using ones as large as the -62.  The double-slotted trailing-edge flaps should have featured more rearwards travel to them (if you look at the L-1011, Il-62, and Convair 990, you'd know what I mean, although no more extreme than that) which would have also greatly increased lift.  That should have reduced the stall and landing speeds (and probably takeoff speeds too) significantly

2.) They should have been more careful regarding scaling up the wind-tunnel model of the wing to actual scale in regards to reynolds numbers.  That would have likely allowed them to realize they leading-edge was too blunt. 

3.) They should have simply designed the spoilers, which were only designed for ground use as flight-spoilers which were incrementally deployed.  They'd need to be scaled up to about the size you'd see on the DC-9 or A-330 (short chord is all you need with good deflection).  While at it, it would have probably been wise had they designed the flight-spoilers to perform roll-functions at all speed instead of gear-down only (and if possible using all 5 spoilers instead of just the outboard 3). 


4.) There was one other issue that the DC-8 was involved with which had to do with the pylon set-up which produced too much drag even by standards of the day with the top of the pylon going over the top of the wing...  they fixed it by the time the test program was finished.  It would have been better if at the very best that was fixed earlier. 


As for making the plane look less piston-ish, and more jet-like...

1.) Use windows as large as those on the DC-10... those didn't require a much larger structure than those use don the B-707 and would be overall lighter than the DC-8's set-up, and provided plenty good view.  These windows could be spaced 20-inches apart like the B-707 two windows for the price of one for airlines that keep the seats spaced 40" apart... and when IATA reduced the spacing to 34", no problem, plus some airlines were using less than 40" spacing anyway even before that -- some of Douglas's launch customers even.

2.) Use balance panels instead of having the leading-edge of the surface popping out.  The sealed balance bay uses aerodynamic forces to help move the control surfaces just as good as designs which featured a rudder who's surface popped out and it looks better.  With all that make sure the tail won't flutter or be to heavy or anything.

3.) Use some skin manufacturing styles that Convair uses and more creative use of stringers.  This would allow a sturdier skin which won't flex as much in flight and thus reduce turbulence, this would allow the double-bubble to be faired over. 

4.) Eliminate the aft-translating ejector and use a nacelle more like the B-707 design.  The lower takeoff speed from the flap mods should eliminate the need for them (the ejector added acceleration from 0 to 100 kts), the sound-suppressors as is are plenty good enough.  Modify reversers as necessary to be deployable to 385 kts IAS minimum and ideally 390 like the DC-8 as designed could do.

5.)  If possible try to get rid of small amounts of weight in key areas of the plane.  The DC-8 was a very heavy plane, the lightest variant was 18,000 lbs heavier than the early B-707-120 designs.  At least getting it down to 260,000 if not 257,000 (which was the B-707's weight when the more powerful JT3C variants came out that did not need water-injection).  That would also help with landing distance and takeoff, and acceleration.


Other ideas

1.) Assuming it was possible with metallurgical technology of the day to fabricate a "foot-stool" type cutback pylon, that would be a good idea -- it would completely eliminate the pylon overhang drag problem.  At least for the -30's and -40's, if not for all.

2.) Put a blade-style tailcone (B-777 and MD-11 style) on the back to reduce drag a little bit



What do you think?  And I know I have too much time on my hands


KJ Lesnick

[Captain Canada]

Yup...you've got too much time on your hands !



I'm not to up on all the technical speak going on here, but I do know the DC-8 was a damn sexy aeroplane...so anything you can do to keep her around a little longer would be fine by me ! What kit are you going to use to build her ?

[Captain Canada]

I saw this one in Toronto a few years back....

[Mossie]

Okay, it's a grainy B&W shot but it's still my favourite!  Smokin'!!!

[Jeffry Fontaine]

Maybe the DC-8 could have been converted to an ASW/Maritime Patrol aircraft. 

[B777LR]

Theres one type ive only ever seen once in my life. The retired firetrainer in Copenhagen International...

[KJ_Lesnick]

Jeffry Fontaine,

Maybe the DC-8 could have been converted to an ASW/Maritime Patrol aircraft.

Sounds really cool, although I'm not sure it would have the loiter time that the P-3 Orion has... (Although with a DC-8-62 model which is just *LOADED* with fuel -- who knows?)


KJ Lesncik

[Jschmus]

I spotted this re-engined model on the DHL ramp at CLT a couple of years ago.

[Daryl J.]

A quote from Clayton Johnston, aDHL pilot that I know:   "DC-8's fly way too far and carry too much gas!"  said with a big grin on his face.     He'd love to fly one but doesn't want to spend that much time in the air at one time this late in his career.   

Personally, I think Jack Daniels should have a pair of them for rapid delivery of Great Kentucky Product into the more urban areas.   If not Uncle Jack, certainly Johnny Walker.     Who said they needed to be military to whiff???   


Daryl J., who's tooth ring was a plastic DC-8 in 1967

[elmayerle]

Maybe the DC-8 could have been converted to an ASW/Maritime Patrol aircraft. 

You could fit the weapons bay in the lower lobe and use much of the rest for auciliary fuel tanks, palletized as used by several Boeing aircraft, to really extned range.  It'd certainly give you a roomier interior than the P-3 has, an ELINT version would make sense, too.

[Daryl J.]

Short-field, rough field capability from the get-go allowing the mass migration to the cities of America to slow significantly starting in about 1960.    Eastern Airlines, Western, and Braniff still exist, of course.   

[KJ_Lesnick]

Daryl J.

Short-field, rough field capability from the get-go allowing the mass migration to the cities of America to slow significantly starting in about 1960.    Eastern Airlines, Western, and Braniff still exist, of course.

Even the ideas I thought of of having a lower landing speed, increased flap area, and enlarged slots...  I don't know how short you'd be able to get the takeoff run down to. 

The airplane still would be quite underpowered... assuming each JT3C produces 12,000 lbs thrust at dry power, 12,500 when below 40-F, and 13,500 with water-injection, and the -11 at full weight, the lightest model weighs 265,000, and the -12 weighed in at 273,000 -- and these were the lightest models. 

Granted, my ideas did include lightening the plane up a bit, but that was more speculative than the other stuff. 


KJ Lesnick

[elmayerle]

Short-field, rough field capability from the get-go allowing the mass migration to the cities of America to slow significantly starting in about 1960.    Eastern Airlines, Western, and Braniff still exist, of course.   

with a low wing with underslung engines, I think I'd be too leery of trying for too much short/rough field capability; there's only so much you can do affordably.  Mind you, to deal with short & Rough fields, I'd probably suggest an updated and modernized C-102 Jetliner (as a first step, perhaps re-engining with Orendas followed by any other system upgrades available then).

[KJ_Lesnick]

Did Douglas have the metallurgical-capability to make a cut-back pylon for an airliner design (I mean, if they actually knew what they were doing, could they have slung the right parts and metals together and made a cutback that didn't weigh too much)?


KJ Lesnick
BTW:  If anybody doesn't know what I a cut-back pylon is, just ask, and I'll post a picture showing the difference.

[Archangel]

One of these flys in and out of Epply Airfield in Omaha Nebraska al the time.