You want this.

http://www.airliners.net/photo/American-Airlines/Boeing-707-123/0541868/L/

specter177 wrote on Dec 17^th, 2009 at 10:56pm:

C wrote on Dec 18^th, 2009 at 4:14am:


Vicker planes always remind me of this:

http://i50.photobucket.com/albums/f313/JasonFromOz/012_Ajax_cu.jpg
http://i50.photobucket.com/albums/f313/JasonFromOz/017_Ajax.jpg

They haven't solved the asymmetric problem though.

I can tell you exactly why the blended wing concepts have not been pursued, not enough windows.  You would have most of the passengers sitting in the middle of that large aircraft, with only a few of the expected window seats.  Airlines wouldn't buy it.

I believe that's one of the reasons many light twin engined aircraft actually have worse safety records compared to single engined light aircraft. If one engine fails at low speed, the plane will probably crash as the rudder doesn't have enough authority to counteract the torque generated by asymmetric thrust. The solution was to build a physically asymmetrical aircraft, like the Scaled Composites Boomerang. This allows the engines to be spaced much closer together, with the CoG in between them, so an engine failure has only a small impact on flying qualities.



Airliners don't have this problem, however. Only a bigger rudder is required. I wonder if FBW in some aircraft automatically adjusts for an engine out...?



Also, on the flip side... if an engine disintegrates on the VC-10, for example, then it has the possibility of taking out the other engines. If it is anything like the MD-80 (and DC-9), a disintegrating engine is more likely to puncture the pressure vessel (causing rapid decompression, or worse), or injure a passenger (or kill - which has happened before) edit: Of course, the engines could be mounted behind the cabin, but that is likely to waste space and either reduce passenger count, or make the plane longer than it would otherwise need to be, adding weight. Also, wing mounted engines typically counter the bending forces generated by the wings, so more weight is needed with a tail-mounted design.... Lastly, tail mounted designs also need a way to transfer the "force" (for lack of a better word) from the engines to one of the main sources of drag... the wing, this adds even more weight. (and the problems with a tail-mounted design continue...)

The aft (tail) mounted engine on the DC-10 and MD-11 cannot operate on suction (from the engine mounted boost pump) alone, but requires the tank mounted Jettison/Override pumps to be operating. The wing mounted engines on said aircraft can operate from suction alone.

Are all tail-mounted aircraft like this, or only the DC-10 / MD-11?

Thanks.

specter177 wrote on Dec 17^th, 2009 at 10:56pm:
Problem with that design, is every time it banks, one side where passengers will be sitting will become weightless, while the other side of the plane will be subjected to G force. So only in level flight does every one across the plane have even gravity like a normal plane. They are still working on a way around that last I herd.



C wrote on Dec 18^th, 2009 at 11:08am:
This fact has yet to stop any 4 engine plane, let alone a twin engine plane. On September 11th when all flight got ground a watched a C-5B land with #1 & #2 motors flamed out, only had the right side, and it made a perfect landing like all were still working, they just landed long since only the reverser's on the one side worked. As long as they have a rudder you should be fine...unless you fly the B-2A, in witch case there are so many other flight surfaces that the Flight Control Computer(FCC) will just take care of every thing any way, just like any other modern plane with FCC's


If they figure out a way to make inertia dampeners, and a way to properly pressurize odd shapes, that will be when we get to see really cool designs be implemented.

That's the difference between the "cool" planes of yesteryear and the "boring" planes today. The new planes engines are very reliable. The chance of one flaming out on takeoff are very low.

Quote:

Only one. It is perfectly fine for an airliner to go down due to two engines failing on takeoff - like the geese in the A320 over Hudson.

I think a 747 crashed in Holland for losing 2 engines on the same side.
Quote:

Some have +-tails.
Quote:

CRJ? ERJ?

Either way, all other factors aside, with the engines on the fuselage, you get less of an asymmetric issue.

There is a reason for that.  If you took the engines on the 777 and tried to mount them on the tail, you'd have a heck of a CG problem.

DaveSims wrote on Dec 20^th, 2009 at 12:55am:


Not really, you'd just need to move the wings and put a new tail on...


...Simples!

C wrote on Dec 20^th, 2009 at 3:43am:


The problem with that is you move the center of gravity closer to the tail, which reduces the distance from the CoG to the elevator.  That makes the elevator more effective, making the aircraft very sensitive.  Sure computers can handle the problem, but why go through the trouble when you can just make a wing mounted engine.

Its not the elevator, its the yaw stability of the shorter fuselage that messes up the flight character of those very short machines.

747SPs also have a higher tail.

And most fighter planes operate on stall edge on takeoff, thats why they fly around with absurd elevator angles. those almost-flat stabilizers arent that helpful either

chornedsnorkack wrote on Dec 27^th, 2009 at 3:37pm:

I think that was mainly political.

OVERLORD_CHRIS wrote on Dec 27^th, 2009 at 10:40pm:


That was probably part of the 777's ETOPS certification.  Many years ago, aircraft were required to have four engines for long overwater flights (think 747).  About 20-30 years ago, the FAA changed the rule, as aircraft such as the 757/767 came out and were more than capable of flying on one engine for extended periods of time.