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They all look the same! (Read 7139 times)

Reply #15 - Dec 19^th, 2009 at 9:15am

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

What? That just looks like a longer 737 with four small engines instead of two big ones. Wink

Wink

What you want is this: http://www.nasa.gov/centers/langley/images/content/70059main_2003-81-01.jpg

That's different.

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:

Having the engines half way out along the wings make it fairly inefficient if one fails. Having them close to the centreline of the aeroplane, such as a DC-9, VC10, BAC 1-11 & 727, means it has a lot less of an effect should you lose an engine. In a 4 jet in the configuration of the A340, 747 and 707 type, lose two on one side, and compared to say the VC10/IL62, life could be very interesting, and lead to a very aching leg!

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.

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Reply #16 - Dec 19^th, 2009 at 10:48am

C Offline
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OVERLORD_CHRIS wrote on Dec 19^th, 2009 at 9:15am:

C wrote on Dec 18^th, 2009 at 11:08am:

Having the engines half way out along the wings make it fairly inefficient if one fails. Having them close to the centreline of the aeroplane, such as a DC-9, VC10, BAC 1-11 & 727, means it has a lot less of an effect should you lose an engine. In a 4 jet in the configuration of the A340, 747 and 707 type, lose two on one side, and compared to say the VC10/IL62, life could be very interesting, and lead to a very aching leg!

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.

That was landing, which is quite a different kettle of fish to take off. Having chatted to some USN 707-frame drivers last year in the desert, their biggest fear was losing two on take-off. Not guaranteed to ruin your day, but certainly going to make it more difficult.

As for the initial part of your reply, I guarantee that at some point, it has.

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Reply #17 - Dec 19^th, 2009 at 11:55am

specter177 Offline
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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.

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Reply #18 - Dec 19^th, 2009 at 12:30pm

NNNG Ex Member

Quote:

On 22 September 1995, a U.S. Air Force E-3 Sentry (Callsign Yukla 27, serial number 77-0354), crashed shortly after take off from Elmendorf AFB, AK. The plane lost power to both port side engines after these engines ingested several Canada Geese during takeoff. The aircraft went down in a heavily wooded area [21] about two miles northeast of the runway, killing all 24 crew members on board.[22][23]

http://en.wikipedia.org/wiki/E-3_Sentry

Never heard any such case of a modern passenger airliner going down due to the failure of both engines on one side. Airliners have to be able to handle an engine failure at V1 to get certified.

Also, tail mounted airliners always have T-tails, which can make the vulnerable to ice ingestion and deep stall. Lips Sealed

Lips Sealed

edit; apparently the Lear 24 with tail-mounted engines is very difficult to control in an engine-out situation.

etc.... point is, all this depends on the aircraft itself. Both configurations have their advantages and disadvantages. But honestly, having them mounted on the wings is a clear winner... as indicated by almost all aircraft designed in the last 30+ years having them.

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Reply #19 - Dec 19^th, 2009 at 3:56pm

chornedsnorkack Offline
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Quote:

Quote:

On 22 September 1995, a U.S. Air Force E-3 Sentry (Callsign Yukla 27, serial number 77-0354), crashed shortly after take off from Elmendorf AFB, AK. The plane lost power to both port side engines after these engines ingested several Canada Geese during takeoff. The aircraft went down in a heavily wooded area [21] about two miles northeast of the runway, killing all 24 crew members on board.[22][23]

http://en.wikipedia.org/wiki/E-3_Sentry

Never heard any such case of a modern passenger airliner going down due to the failure of both engines on one side. Airliners have to be able to handle an engine failure at V1 to get certified.

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:

Also, tail mounted airliners always have T-tails, which can make the vulnerable to ice ingestion and deep stall. Lips Sealed

Lips Sealed

Some have +-tails.
Quote:

etc.... point is, all this depends on the aircraft itself. Both configurations have their advantages and disadvantages. But honestly, having them mounted on the wings is a clear winner... as indicated by almost all aircraft designed in the last 30+ years having them.

CRJ? ERJ?

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Reply #20 - Dec 19^th, 2009 at 4:11pm

ApplePie Offline
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chornedsnorkack wrote on Dec 19^th, 2009 at 3:56pm:

Quote:

Quote:

On 22 September 1995, a U.S. Air Force E-3 Sentry (Callsign Yukla 27, serial number 77-0354), crashed shortly after take off from Elmendorf AFB, AK. The plane lost power to both port side engines after these engines ingested several Canada Geese during takeoff. The aircraft went down in a heavily wooded area [21] about two miles northeast of the runway, killing all 24 crew members on board.[22][23]

http://en.wikipedia.org/wiki/E-3_Sentry

Never heard any such case of a modern passenger airliner going down due to the failure of both engines on one side. Airliners have to be able to handle an engine failure at V1 to get certified.

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'm not sure if that's the best comparison. The E-3 NNNG was talking about lost thrust for half of its engines (2 out of 4), the A320 lost thrust for ALL of its engines (2 out of 2).

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Reply #21 - Dec 19^th, 2009 at 5:45pm

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

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Reply #22 - Dec 19^th, 2009 at 11:24pm

NNNG Ex Member

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 meant both engines on one side. Wink

Wink

Quote:

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

Engine pylons on modern aircraft are designed to shear when excessive loads are placed on them. With El Al Flight 1862, the fuse pins were fatigued, so the engines broke off improperly all by themselves, and damaged the wing in the process. Wing stalled & plane crashed. That could be a disadvantage of wing mounted engines.... although I would consider it a disadvantage of an inadequate engine pylon structure. Wink

Wink

Quote:

CRJ? ERJ?

Unless you count modernized (or copied) older aircraft, the ERJ, CRJ, & Tu-334 are the only airliners with tail-mounted engines that are still in production. All are regional aircraft, that are at or less than 100 seats. Maybe we'll see this configuration reappear with open-rotor engines in the future. However, for larger aircraft, I don't think there is any doubt that wing-mounted engines are better as shown with the 767, 777, 787, A330, A340, A350, A380, and the newer Bombardier and Mitsubishi regional jets. There has never been a widebody aircraft with tail-mounted engines, point is, there are reasons for this.

« Last Edit: Dec 20^th, 2009 at 2:39am by N/A »

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Reply #23 - Dec 20^th, 2009 at 12:55am

DaveSims Offline
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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.

Dave

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Reply #24 - Dec 20^th, 2009 at 3:22am

chornedsnorkack Offline
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Quote:

There has never been a widebody aircraft with tail-mounted engines, point is, there are reasons for this.

True. BAC 3-11 was not rolled out.

How does a BAC 3-11 simulator handle its CoG?

And how does the performance of a BAC 3-11 compete against Airbus 300?

Suppose that you were to build a suitably stretched BAC (the fuselage is wider than that of A300, something like DC-10 size, and close to 777). So BAC, say, 6-11, with a suitably bigger wing and a pair of Trent 8115 engines.

How will the CoG behave, and how will the performance compare against 777?

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Reply #25 - Dec 20^th, 2009 at 3:43am

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

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.

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

...Simples!

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Reply #26 - Dec 20^th, 2009 at 8:10am

expat Offline
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chornedsnorkack wrote on Dec 20^th, 2009 at 3:22am:

Quote:

There has never been a widebody aircraft with tail-mounted engines, point is, there are reasons for this.

And how does the performance of a BAC 3-11 compete against Airbus 300?

As pointed out, it was never built so the question is mute Huh

Huh

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Reply #27 - Dec 20^th, 2009 at 9:49am

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

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

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.

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

...Simples!

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.

Dave

www.flymcw.com

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Reply #28 - Dec 20^th, 2009 at 10:51am

NNNG Ex Member

Wouldn't that mean the elevator is less effective? Shorter distance means less torque... or torque = distance*force. For this reason, short variants of an aircraft usually have larger vertical stabs, while longer variants of the same aircraft have smaller vertical stabs.

e.g.

tail on the A318 is 12.56 metres (41 ft 2 in) high.
tail on A319/20/21 is 11.76 m (38 ft 7 in) high.

It can be seen on the F-35. The horizontal stabilizer is very close to the landing gear (i.e. turning point), so you can really see the horizontal stab digging in on rotation.

http://www.bidlink.net/images/F35.jpg

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Reply #29 - Dec 26^th, 2009 at 9:09am

Ivan Offline
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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

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