Question on angle of attack in MD-80.

[brucek]

Is there any specific reason for the apparent (as seen from the ground) high angle of attack in the MD-8x at take-off (as compared to a B737)?

Thanks,

Bruce.

 

[DoinTime]

Possibly an opticle illusion created by the amount of fuselage that sits forward of the CG on the MD-8X as compared to the 737.

 

[generaltso]

The answer is yes.

 

[enigma]

Here's my take on the subject. Simply, the wings are different. The Douglas wing changes it's chord more (more taper) and is higher aspect ratio. The Douglas is equiped with "stronger" (more effective) leading edge devices. But the most important factor in the overall equation is that the Douglas wing is working harder than the 737 wing at the speeds after take off. The full length, no-gap, slats afforded by having the engines on the tail, allow an otherwise small wing to make enough lift to safely operate at approach and departure speeds, while also allowing the wing to cruise at over M.80 when clean. At least in theory, truthfully, the 80 doesn't have enough wing. At the weights I fly them, the 80 has a hard time getting over FL330. A lower span loading would have given better altitude and climb performance. They will go M.80 or M.81, but it takes a lot of gas.

I wish that Douglas has stuck with the DC9-50 fuselage, when they built the -80's. That is essentially what a MD87 is, and the 87 performs much better than the long fuselage 80's.

Back to the take off angle of attack, in short, the 80 wing design requires a larger angle of attack to make the required lift necessary to fly at take off/departure speeds; but the high lift devices allow the 80 wing to do so with a perfectly adequate margin between normal climb angle of attack and a stall. In other words, the 80 has the same safety margin as does the 737, it just looks like it's closer to the edge.

hope this makes sense : -)
8N

 

[EagleRJ]

A similar question...

Has anyone noticed that the 777 has an enormous amount of dihedral compared to other twins with underwing engines? I wonder why?

 

[brucek]

Thanks for the replies....

Interesting information on the wing design.

 

[A Squared]

Re: A similar question...

Has anyone noticed that the 777 has an enormous amount of dihedral compared to other twins with underwing engines? I wonder why?

Maybe because it has HUGE engines? I dunno, just a guess but those engines are big. I heard that the 777 engines are about the same diameter as a 737 fuselage .... bs or true? anyone know?

 

[Khirsah]

At its largest point the diameter of a GE90-115B engine is 135 inches. According to Boeing the cabin width on the 737 is 139 inches. Pretty close.

 

[flyn96]

yup, add all the accesories and the cowling and the 777 is the same size a 737