BooDog wrote:To piggyback on this question: Why is the center engine on a DC10/MD11 not level? Why does it have that slight downward tilt?
MDGLongBeach wrote:Hello there,
I’m a huge trijet fan and I still have a lot to learn. My question with the trijets is about the middle engine. If you look at an L1011, or DC-10, the middle engine is smaller than the other wing-mounted engines. My question is, are all the engines the same type, or is the middle engine different than the others, and if they are all the same, how did the manufactures compact the engines to fit in the cowling, and how does compacting them affect performance? (Another thing I’d like to know is what number engine, the middle one is considered.)
kearnet wrote:The same reason wing mounted engines are ever so slightly, toed-in toward the fuselage; as the air goes around the plane, it doesn’t parallel the plane, it splits (think of the v shaped wake waves a boat makes going through the water). On some 3 holders (DC-10/MD-11) it was found that that air “arched down” when it got to the tail, so they set the #2 at the best angle to accept the air flow at cruises to the chance of reduce stalls/flameouts. Lockheed and Boeing design didn’t have such affect on air so the kept there fairly in line (straight) with the fuselage.
GalaxyFlyer wrote:The L-1011 has an S-duct (from the looks of it, so does the 727), that is why you cannot see the engine. DC-10 and MD-11 have basically a straightthrough-duct hence why you can see the engine if the aircraft is positioned at a correct angle.The engines are all the same on the DC-10; probably a visual illusion due to the long cowl thru the fin. Although, it could be a rearrangement of the accessory case on #2. The L-1011 engine cannot be seen from outside, it’s buried in the tail.
GalaxyFlyer wrote:The L-1011 engine cannot be seen from outside, it’s buried in the tail.
GalaxyFlyer wrote:The #2 (center) engine has a higher, by .03 EPR, than #1 and #3 due to the outboard engines are bleed for the A/C packs and the center engine isn’t bleed.
The engines are all the same on the DC-10; probably a visual illusion due to the long cowl thru the fin. Although, it could be a rearrangement of the accessory case on #2. The L-1011 engine cannot be seen from outside, it’s buried in the tail.
smithbs wrote:A tri-jet is also interesting from a structures point of view. There is a lot of load-bearing structure you need in that area, but you need to put in a big air duct through the center of everything along with an engine that's going to be pushing and pulling pretty hard.
Great thread here on DC-10's center engine structure: viewtopic.php?t=776385
"S" Duct design appears to be the most successful
GalaxyFlyer wrote:In the normal bleed configuration, #2 isn’t bleed, it can be in an abnormal condition.
Max Q wrote:GalaxyFlyer wrote:In the normal bleed configuration, #2 isn’t bleed, it can be in an abnormal condition.
That’s right, it’s coming back now,
#2 could be used for bleed air but it only provided eighth stage unlike 1 and 3 that had 8th augmented by 13th stage
As a result you often needed considerably
more than idle thrust in a descent when using #2 bleed to keep the cabin coming down
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