C4 - The Plane Crash

[Sifly]

FuzzyLogic said:

coanda said:

You could say they are so close that there is no assymetric condition!

I can assure you that rear mounted jets are still noticeably asymmetric when you have full thrust on one side, you are climbing at V2 and don't yet have the autopilot in!

I flew the EMB145 for a while, and flying asymmetric had little more affect than a severe reduction in thrust. The 767 on the other hand can be a real handfull, especially at full chat!!

[dr_gn]

coanda said:

dr_gn said:

coanda said:

Early jet airliners had tail mounted engines to keep the wings clean for max aero efficiency (before we had CFD and someone did a bending moment / shear diagram of the wing with pod mounted engines and saw the structural benefits of such a solution).

But the Boeing 707 (and for that matter the Boeing B-47 which pioneered podded engines) predated the Boeing 727 and all other rear mounted engined passenger jets as far as I know. The first jet airliner (DH Comet) didn't have rear mounted engines either.

The comet solution is awful on a structural level though. You've got to pass your spars around the engines. Where you get your highest bending moment, and therefore requirement for strongest part of the spar someone wants you to design in big holes for engines!

I get the impression that, back in those days (comet time period) the chief engineer got what he wanted, and the staff just got on with it. Fortunately things have changed these days and we have to prove ideas via an evaluative trade study process before moving towards a design. Engineering judgement still exists, but in a much less patriarchal manner (in the UK anyway).

I had the B-47 in my mind whilst writing the previous post, and did think of including it. For me it is a strong forerunner of the modern airliner wing, with its high aspect ratio, sweep back and podded engines. The B-47 was initially designed (the project that ended up in the b-47 started in '43 I think) with a straight wing until someone from Boeing got to go and look at German research on swept wings and sent message back that the aircraft should have swept wings. There were few tools (only wind tunnel and I'm not sure how good that would have been) back then that could accurately (even just ball park) analyse whether the podded position was good or not, and it seems that the engines on the B-47 were arbitrarily moved around the wing before the design was finalised. I don't know what the internal structure of the B47 engine pylon/wing mount is like so I don't know if they managed to realise the full potential of both wing bend and twist relief.

I should have rephrased the start of the bit you quoted. Reading around, and seeing that there was a specific need for three engines, good high altitude take-off/landing performance and small airport access, the tail-mounted engine solution looks pretty good, for that set of requirements. It's all down to the compromises!

Edit:-

I don't mean to say that the guys didn't understand what was going on back then - that isn't true, because you can see they've realised that the engines will be best out on clean air, and the best air is out in front of the wing. I just mean that the configuration wasn't fully optimised because of the available tools. And again, that isn't a criticism, its just the way it was - all these designs are a step on the evolutionary path of airliner design.

Edited by coanda on Friday 12th October 23:59

I always think that podded engines look really draggy and heavy, just from the additional pylon hardware needed to mount them and from a form/parasitic drag point of view (lots of surface area and lots of tight corners and bottlenecks for airflow. Obviously the benefits outweigh the drawbacks, but to me engines built into the wing at least *look* far nicer.

[FuzzyLogic]

Sifly said:

I flew the EMB145 for a while, and flying asymmetric had little more affect than a severe reduction in thrust. The 767 on the other hand can be a real handfull, especially at full chat!!

Fair enough. The EMB500 that I fly is a bit more of a handful than that. Possibly down to its smaller size.

[coanda]

FuzzyLogic said:

I can assure you that rear mounted jets are still noticeably asymmetric when you have full thrust on one side, you are climbing at V2 and don't yet have the autopilot in!

In the B727?

[jamiebae]

Surely the 727 wasn't picked because of its similarity to modern planes (plenty of 737, 757, A300 etc in bone yards would have been more suitable) but because it's the only jetliner you can parachute out of 100% safely?

It was an interesting programme, but with a fairly predictable outcome I think.

[Eric Mc]

The BAC 1-11 and DC-9 family also have rear airstairs. However, the 727 is the only airliner I know of where someone DID parachute from one as part of a ransom deal. He was never seen again.

[Cupramax]

Eric Mc said:

The BAC 1-11 and DC-9 family also have rear airstairs.

MD-80's as well I seem to remember... edit oops, just realised thats DC-9 derived.

[mcxuk1]

Eric Mc said:

The BAC 1-11 and DC-9 family also have rear airstairs. However, the 727 is the only airliner I know of where someone DID parachute from one as part of a ransom deal. He was never seen again.

Was that the hijack case?

[onyx39]

mcxuk1 said:

Eric Mc said:

The BAC 1-11 and DC-9 family also have rear airstairs. However, the 727 is the only airliner I know of where someone DID parachute from one as part of a ransom deal. He was never seen again.

Was that the hijack case?

http://en.wikipedia.org/wiki/D._B._Cooper

[Tony2or4]

The 'style' of the crash depicted in the programme made me think of the Eastern Airlines Tristar which crashed into the Everglades on 29/12/72: the flight crew had become preoccupied with sorting out a faulty light bulb on the control panel, failing to notice that the plane was gradually but steadily losing altitude. The result was that the aircraft was in effect flown into the ground by the autopilot, impacting at a fairly shallow angle of descent, pretty much (as I thought) like Big Flo. So it puzzles me that, whereas 'our' 727's fuselage remained essentially intact - apart from the nose snapping off - the Eastern Tristar suffered utter destruction.

[bennyboydurham]

Eric Mc said:

The BAC 1-11 and DC-9 family also have rear airstairs. However, the 727 is the only airliner I know of where someone DID parachute from one as part of a ransom deal. He was never seen again.

Surprised they didn't mention that, or the subsequent 'Cooper Vane' to keep the stairs from bring opened in flight. Would have been an interesting aside to pad out a program that clearly needed padding!

[tank slapper]

bennyboydurham said:

Would have been an interesting aside to pad out a program that clearly needed padding!

It didn't need padding, it just needed them to include more than the most superficial details. Anyone who can't fill 90 minutes with information about a project like that isn't trying very hard. It was probably decided that the intended audience mostly have room temperature IQs and couldn't cope with that though.

[Roop]

Tony2or4 said:

The 'style' of the crash depicted in the programme made me think of the Eastern Airlines Tristar which crashed into the Everglades on 29/12/72: the flight crew had become preoccupied with sorting out a faulty light bulb on the control panel, failing to notice that the plane was gradually but steadily losing altitude. The result was that the aircraft was in effect flown into the ground by the autopilot, impacting at a fairly shallow angle of descent, pretty much (as I thought) like Big Flo. So it puzzles me that, whereas 'our' 727's fuselage remained essentially intact - apart from the nose snapping off - the Eastern Tristar suffered utter destruction.

Don't know about the Tristar but the 727 was in landing configuration when they crashed it, doing about 130kts. If the Tristar was at cruise, it was probably four times that.

[Eric Mc]

Yes - the Tristar was not in landing configuration and didn't impact at a high rate of descent. It was a classic example of "Controlled Flight into Terrain" (CFIT).

[Justin Cyder]

Eastern 401 was travelling at about 230mph when it hit.

[Eric Mc]

What speed did the 727 smack into the desert? And what were the comparable rates of descent?

The Tristar is a much bigger aircraft than the 727 with a very different engine configuration - so it would break up in a different way to the more compact 727. In fact, if the 727 hadn't had it's wheels down, it probably wouldn't have broken up at all.

[Justin Cyder]

Eric Mc said:

In fact, if the 727 hadn't had it's wheels down, it probably wouldn't have broken up at all.

Perhaps Eric you could give me Saturday's lottery numbers as you seem to be enormously skilled at the unknowable predictions game. On second thoughts, perhaps you should keep them, the windfall would soothe your didactic soul.

[telecat]

The Speed was about 140mph and rate of descent was 1,500 feet per minute. Engines were set to idle speed on impact. The Normal Landing speed of the 727 is around that area with descent rate on landing of 15 to 20 feet per minute. Normal Descent speed before landing "flare" would be 750 Feet per minute.

Edited by telecat on Tuesday 16th October 14:33

[Super Slo Mo]

Roop said:

50m radio control radio range. Fifty metres...? Which tard designed that installation and who subsequently signed it off...? Just finished watching this and I am amazed at the apparent discrepancy between part of the team seeming to be extremely professional and part seeming like rank amateurs.

I haven't yet seen the programme, but 50 metres? Really? I could have supplied them with a radio system that'll do an easy 1,000 metres (we routinely get 5-600 m in built up environments), and, with a little tweaking, has been successfully used at around 15 miles distance between the transmitter and receiver (over open water).

[HoHoHo]

The distance between a model and transmitter before control is lost is often further than the eye can see.

However with all the metal and other rubbish in the line of sight from both the 727 and chase plane 50m might be all you get at best