Blackbird From , joined Dec 1969, posts, RR: Posted (2 years 2 months 1 week 2 days 12 hours ago) and read 1574 times:
Why did the DC-10 use a 707-style inboard/outboard aileron set up instead of the split aileron style used on the DC-8? From what it would seem the DC-8 design seemed to be better as the outboard aileron position was regulated as a function of airspeed and not just by flap position, and with even the inboard most segment further outboard, it would give the design far more leverage.
BTW: Also, why did the DC-10 use a 35-degree sweepback, when many years earlier they were able to design the DC-8 with virtually the same cruise and maximum mach numbers with a 30-degree sweepback (which is more stable, and provides better low-speed handling)?
411A From United States, joined Nov 2001, 1594 posts, RR: 9 Reply 1, posted (2 years 2 months 1 week 1 day 14 hours ago) and read 1513 times:
Quoting Blackbird (Thread starter): BTW: Also, why did the DC-10 use a 35-degree sweepback, when many years earlier they were able to design the DC-8 with virtually the same cruise and maximum mach numbers with a 30-degree sweepback (which is more stable, and provides better low-speed handling)?
Don't know where you get your information, but the DESIGNED cruise speeds of the DC-8 versus DC-10 were totally different, just as the B707 and B747 were.
The earlier aircraft were designed with a NORMAL cruise speed of M.82, and a long range cruise speed of M.80.
Whereas, the later aircraft were designed to cruise NORMALLY much faster, M.84 to M.85, with a long range cruise speed of M.83 to M.84....depending on enroute weight, of course.
To assume otherwise is complete and utter nonsense.
737tdi From United States, joined Sep 2007, 66 posts, RR: 0 Reply 2, posted (2 years 2 months 1 week 1 day 11 hours ago) and read 1498 times:
The DC-8's aileron design is old. Same as the elevators. They depend on airspeed across the flight control. I think the elevator design is pretty cool. There are NO points of failure. No hydraulics, No electronics, just airspeed. If you aren't going fast enough you can't rotate. Pull back on the yoke and nothing happens??? STOP. As far as the ailerons, the inboards are hydraulic/aerodynamic. The outboard ailerons are srictitly aerodynamic with a mechanical input from the inboards though a torsion tube. A very reliable system. More questions? I can try.
Blackbird From , joined Dec 1969, posts, RR: Reply 3, posted (2 years 2 months 1 week 19 hours ago) and read 1463 times:
Look 411A,
I don't know what your story is, but some of the data you've stated about the 707 appears to be just flat out wrong
1.) You've told me that it's maximum speed is 0.84 mach. The FAA make and model database which you even said tells all said Mach 0.887 (for the B-707-320, it's 0.884 for the B-707-120, for the B-models it's 0.90, and for the B-720 its 0.906, and 0.90 for the B-720B) is the plane's maximum speed, and most data available indicates a cruise speed of 0.84 to 0.85. Although some of the B-707-400's had restrictions to 0.83 or so for some regulatory reason, but not a physical restriction -- you even said this. While the plane's long range cruise speed may indeed be lower at 0.80 to 0.83, it's standard cruise speed is not.
2.) The DC-8's maximum mach number is 0.88 with a similar cruise speed (0.84 to 0.85) which is approximately the same as the DC-10 -- Cruise 0.85, MMO = 0.880.
411A From United States, joined Nov 2001, 1594 posts, RR: 9 Reply 4, posted (2 years 2 months 1 week 17 hours ago) and read 1451 times:
Sorry, Blackbird, 'tis you who are slightly misinformed.
Now, as I've actually FLOWN the airplane, I should know.
Maximum limiting airspeeds/mach numbers have almost NOTHING to do with the desired cruise specifics of the design.
They are limiting...period, not necessarily desired, in day to day operation.
Lets look at the B707-320B (advanced cowl) airplane, as that is the one on which I have the most detailed data.
It comes with a '300 Fans Flight Conduct Chart'.
Two pages, laminated, so that it doesn't get worn out.
OK, so far so good.
NORMAL cruise speed, M.82
Long Range Cruise Speed, M.807, reducing slightly as the enroute weight decreases.
Low Level accelerated speed cruise (short dash), M.84, MAXIMUM.
Limits.
FL290 or below.
Careful account of fuel flow should be kept, as fuel flow at this speed is excessive, mach tuck is severely increased, stabilizer authority is reduced, and the onset of mach buffet is increased.
To be used ONLY when absolutely necessary.
Now, one might wonder, why FL290 as a maximum altitude?
The short answer is, max cruise engine thrust ratings would be exceeded, if it was attempted at higher altitudes.
737tdi From United States, joined Sep 2007, 66 posts, RR: 0 Reply 8, posted (2 years 2 months 1 week 8 hours ago) and read 1406 times:
The dump chutes (in ref. to fuel) on DC8's is just outboard of each main landing gear just behind the aft. wing spar. When not in use they are retracted. When needed to dump excess fuel (seriously frowned on now) it would extend, at the same time opening valves to each tank to gravity feed fuel out the chutes. It's operated by the flight engineer either using an electric motor or hand crank on the aft. edge of the engineers panel. Hope this explained it.
Blackbird From , joined Dec 1969, posts, RR: Reply 11, posted (2 years 2 months 5 days 12 hours ago) and read 1328 times:
I'm just wondering if the DC-8's aileron design worked better, why did the DC-10 revert to the less effective inboard/outboard aileron set-up?
Also, why did the DC-10 use a 35 degree wingsweep for a 0.85 to 0.88 Mach speed when a 30-degree sweep could do just as good and would provide more docile low-speed handling and less dutch roll problems?
411A From United States, joined Nov 2001, 1594 posts, RR: 9 Reply 12, posted (2 years 2 months 5 days 11 hours ago) and read 1322 times:
Quoting Blackbird (Reply 11): Also, why did the DC-10 use a 35 degree wingsweep for a 0.85 to 0.88 Mach speed when a 30-degree sweep could do just as good and would provide more docile low-speed handling and less dutch roll problems?
What makes you think that a 30 degree wing sweep would provide 'just as good' results with the higher desired cruise speed?
If you are studying high speed aerodynamics, I suspect you missed a few lectures.
Jetlagged From United Kingdom, joined Jan 2005, 2027 posts, RR: 13 Reply 15, posted (2 years 2 months 5 days 3 hours ago) and read 1285 times:
Quoting Blackbird (Reply 11): Also, why did the DC-10 use a 35 degree wingsweep for a 0.85 to 0.88 Mach speed when a 30-degree sweep could do just as good and would provide more docile low-speed handling and less dutch roll problems?
There are so many variables it is pointless speculating why this or that design decision was taken. Different wing sections for a start. Maybe the DC-10 had a higher thickness/chord ratio wing so needed more sweepback? Also the cruise Mach of the DC-10 is higher than the DC-8.
Quoting Blackbird (Thread starter): Why did the DC-10 use a 707-style inboard/outboard aileron set up instead of the split aileron style used on the DC-8? From what it would seem the DC-8 design seemed to be better as the outboard aileron position was regulated as a function of airspeed and not just by flap position, and with even the inboard most segment further outboard, it would give the design far more leverage.
The whole point of having high speed ailerons inboard is to reduce the moment they exert on the outer wing sections. Also the DC-10 is fully powered controls, which allows full deflection throughout the envelope. I suspect DC-8 manual controls would "blowdown" far easier.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
Starglider From Netherlands, joined Sep 2006, 599 posts, RR: 32 Reply 16, posted (2 years 2 months 5 days 3 hours ago) and read 1282 times:
Quoting Jetlagged (Reply 15): The whole point of having high speed ailerons inboard is to reduce the moment they exert on the outer wing sections. Also the DC-10 is fully powered controls, which allows full deflection throughout the envelope. I suspect DC-8 manual controls would "blowdown" far easier.
The DC-8 ailerons are powered and not manually controlled.
The lateral control system of the DC-8 consists of inboard and outboard ailerons that are connected by a torque tube that acts as a torsion spring. The inboard sections are power operated. The outboard sections only operate at the lower values of the dynamic pressure where they are needed. As the dynamic pressure increases, the aerodynamic resisting moment of the aileron becomes greater in relation to the torque that can be transmitted through the torsion bar; hence, the aileron deflection is reduced. The amount of deflection of the outboard aileron varies smoothly with variation in dynamic pressure and, therefore, provides the desired variation of aerodynamic control moment with speed and altitude.
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