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By: - 15th February 2008 at 18:28 Permalink - Edited 1st January 1970 at 01:00
Is PMN1 the same person as PMN?
By: - 15th February 2008 at 18:48 Permalink - Edited 1st January 1970 at 01:00
Is PMN1 the same person as PMN?
No, I think this one is an imposter.
Although actually, its quite possible that PMN is the imposter...?
The other disadvantages to the tail mounted design that I can think of off the top of my head is that the fuel system onboard has to be more complex than a wing mounted design. Most of the fuel is carried in the wings, so the fuel has to travel further to get to the engines.
Also, (although this has pretty much been mitigated in todays aircraft - and very trivial), its likely to be louder right at the back of the aircraft on a tail mounted design.
Also, on a tail mounted design, the engines are further from the ground so its possible that the likelihood of engines being hit or damaged by FOD is lower.
By: - 15th February 2008 at 19:32 Permalink - Edited 1st January 1970 at 01:00
Is PMN1 the same person as PMN?
He's the mini version :)
By: - 15th February 2008 at 20:07 Permalink - Edited 1st January 1970 at 01:00
Is PMN1 the same person as PMN?
Nope, this I am a completely different person with the initials PMN, i had to have the username PMN1 as PMN was taken on the EZ (now Yuku) boards I am also on - important note, if anyone ever hears of this board going to Yuku, be afraid, be very afraid.....:mad:
Anyway another option, how about on the wings but without pylons as with the DH119 and DH120 proposals and with Concorde?
By: - 15th February 2008 at 20:11 Permalink - Edited 1st January 1970 at 01:00
Anyway another option, how about on the wings but without pylons as with the DH119 and DH120 proposals and with Concorde?The windflow from the fuselage/wings into the engines will be too turbulent. That's why there is (almost) always a small distance between the engine inlet and the plane. Even on fighters you will find this.
By: - 16th February 2008 at 01:32 Permalink - Edited 1st January 1970 at 01:00
Most of the fuel is carried in the wings, so the fuel has to travel further to get to the engines.
And the fuel lines run through the fuselage aft of the wings, which some claimed was a safety hazard in a crash.
By: - 16th February 2008 at 21:48 Permalink - Edited 1st January 1970 at 01:00
All airliners have fuel lines that run aft of the wings in order to feed their APU's.
By: - 4th March 2008 at 16:30 Permalink - Edited 1st January 1970 at 01:00
When the designers of the DC-10 and the Tristar were looking at engine placement, did they consider putting all three engines at the tail?
In the same way, did the 727 and Trident designers look at 2 wing and 1 tail mounted engine?
By: - 4th March 2008 at 17:05 Permalink - Edited 1st January 1970 at 01:00
The ‘deep stall’ phenomenon emerged in accidents during early fight testing of the Boeing 727, HS Trident and BAC1-11, with tragically fatal consequences for the test crews involved.
The 727 did not have a deep stall crash in testing.
I believe it was a Trident crash that brought that issue to the forefront.
Some early 727s were lost in landing accidents...basically pilots weren't flying them by the book and landing with too much/not enough speed.
By: - 4th March 2008 at 19:39 Permalink - Edited 1st January 1970 at 01:00
Where to put the jets?
Rear mounted jets may do more damage to the aircraft, and/or slice & dice
persons, in some cases...:eek:
1) News report of accident:
http://www.cnn.com/US/9608/15/engine.failures/index.html
2) Jet powered P-51!
http://www.combatreform2.com/p51wingtipjets.jpg
:D
By: - 4th March 2008 at 22:34 Permalink - Edited 1st January 1970 at 01:00
The 727 did not have a deep stall crash in testing.
I believe it was a Trident crash that brought that issue to the forefront.
Correct two Trident 1C's were lost in deep stalls ie G-ARPY on a test flight in 1966 and G-ARPI on 18th June 1972 (commercial flight) due to pilot error ,and a BAC 1-11 was lost (during testing) BUT a Northwest Orient Airlines 727 (N247US c/n 202960) was lost on the 1st December 1974 due to a deep stall,this problem is prevelent in rear engined and high T tailed aircraft.So sadly the 727 was prone to it as well as other types with this layout.:(
By: - 5th March 2008 at 09:59 Permalink - Edited 1st January 1970 at 01:00
Are the engines any less effecient at the rear of the fuselage ? It must be difficult for them to get clean undisturbed air at least some of the time ?
By: - 5th March 2008 at 12:21 Permalink - Edited 1st January 1970 at 01:00
He's the mini version :)
Mini version? What are you trying to say, Spalds?! :D
Paul
By: - 5th March 2008 at 13:10 Permalink - Edited 1st January 1970 at 01:00
Deep Stall,in a nutshell:
Aircraft are supported in the air by an aerodynamic force called lift, which is generated by the wings of the aircraft as air is forced past the wings by the forward movement of the aircraft. The wings of the aircraft generate lift when they are pointed slightly upward with respect to the direction of the air flowing towards them. If the pilot tilts the aircraft upward, the wings form a larger angle with the airflow, and lift increases. This angle is called the angle of attack, or AOA, and is often symbolized with the Greek letter alpha. All else being equal, the heavier the aircraft and/or the slower the aircraft is flown the greater must be the angle of attack to generate the lift force necessary to maintain altitude.
Although raising the nose of the aircraft increases angle of attack and thus increases lift, this cannot be done without limit. Up to a certain angle of attack, called the critical angle of attack, pointing the wings upward continues to produce more lift. However, beyond the critical angle of attack, the airflow behind the wing separates from the wing and becomes turbulent, the aerodynamic effects that produce the lifting force largely disappear, and the wing stalls—that is, it suddenly and dramatically ceases to provide enough lift to support the aircraft. At the same time, the turbulence greatly increases drag, which slows the aircraft down as it moves through the air; this also reduces lift. As a result of these changes, the aircraft begins to fall towards the ground.
In many aircraft recovering from a stall is simple. Since the stall is caused by an excessive angle of attack, simply pointing the nose of the aircraft downward will arrest the stall by reducing the angle between the wings and the flow of air (this is for a fixed wing aircraft rather a helicopter). Some aircraft have a natural tendency to pitch downward (sometimes dramatically) when the wings stall; others must be directed downward by the pilot. As soon as the angle of attack drops below the critical angle, the aerodynamic stall of the wings will cease: the wings will start to produce lift and far less drag. However, the aircraft may still be flying too slowly to generate enough lift to prevent the aircraft from continuing to descend: complete stall recovery includes regaining this necessary speed.
In some circumstances stalls can result in more complicated problems, such as a 'spin' or a 'deep stall' (see below).
Typically a stall is caused by the pilot attempting to fly the aircraft too slowly, or to pull up too quickly from a dive, or to turn too steeply. Each of these causes the nose to be lifted until the wing's critical angle of attack is exceeded. Increasing engine power counteracts the increased drag caused by the stall and also increases air speed, and this helps in recovery from a stall. The critical action in recovering from a stall is, however, reduction in the angle of attack, i.e., lowering the nose.
Altitude (height above the ground) is lost by the aircraft during the stall itself but considerably more height can be lost during the recovery. If the aircraft is already at a high altitude this is not a problem. If the aircraft is very close to the ground, however, a stall may cause the aircraft to lose so much altitude that it hits the ground before recovery from the stall is possible. For this reason, pilots are especially careful to avoid stalls during take-off and landing procedures, when the aircraft is very close to the ground.
Stalls in aircraft usually do not occur without warning. In addition to specialized sensors which alert the pilot when the aircraft is about to stall, experienced pilots can sense an incipient stall by noting changes in the behavior of the aircraft. Since the conditions that produce stalls are very well understood, pilots can easily avoid stalls, and many pilots never experience stalls outside of their pilot training. Standard pilot training includes training in the proper ways to avoid, recognize, and recover from stalls.
A few types of aircraft with a T-shaped tail or rear-mounted engines can enter a deep stall or superstall. This is a type of stall that produces turbulence behind the wings that can interfere with the operation of engines or the tail of the aircraft. Recovery from a deep stall can be impossible, resulting in a crash. Some aircraft with such characteristics are fitted with special control devices to prevent the aircraft from ever approaching a position that can cause a deep stall. An example of such a device is a stick pusher, which forces the nose of the aircraft down whenever it approaches a stall, regardless of any actions taken by the pilot.
By: - 5th March 2008 at 13:18 Permalink - Edited 1st January 1970 at 01:00
Diagram of the stall,note bottom pic showing the disturbed air over the tail and engines.
Hope this helps explain the situation a tad better.:D
By: - 6th March 2008 at 19:49 Permalink - Edited 1st January 1970 at 01:00
So, Deep Stall is a stall+engine starvation.
The Nimrod AEW had a similar thing, the bulbous nose was starving the engines on certain manouvres. Vortex generators were stuck all over the bulb to ensure it held onto the breeze.
By: - 7th March 2008 at 16:38 Permalink - Edited 1st January 1970 at 01:00
All airliners have fuel lines that run aft of the wings in order to feed their APU's.A lot of airliners also carry fuel in the fin i.e. 747, VC-10, Tri-Star and Concorde though the latter is of no account here or the VC-10 for that matter. Pod mouted engines are fine the way they are on the 737 but on pylons then the pylons create drag. Basically you pay your money and take your choice. they all have advantages and disadvantages.
Posts: 338
By: PMN1 - 15th February 2008 at 18:19
From BAC Three-Eleven: The British Airbus that should have been by Graziano Freschi
BAC’s engineers listed several ‘significant’ advantages of the rear-mounted layout, including superior cross-wind landing capability; better directional control with asymmetrical thrust; negligible trim changes with power adjustment; power-plants being less prone to bird and debris ingestion during take-off and landing; greater safety in wheels-up landing; the aircraft’s lower height allowing a high degree of compatibility with existing hangers and current new generation ground equipment; quieter cabin.
However, aerospace engineers know that the rear-mounted engine configuration also gave rise to some disadvantages, which BAC took care not to highlight in its marketing literature. The principal disadvantages include:
Lack of wing bending relief, this being one of the main benefits for an aircraft when the engines are mounted under the wing. The lack of bending relief usually requires the wing to be strengthened structurally, resulting in a higher weight penalty.
The presence of the engines at the rear of the fuselage also requires the tail structure of the aircraft (the area aft of the rear pressure bulkhead, and which includes the tailcone, fin rudder, tailplane and elevators) to be strengthened, and this again incurs an extra weight penalty.
Rear-engined aircraft present centre of gravity issues, which are addressed with the greater length of the fuselage (and any significant fuselage stretches) ahead of the wing.
T-tailed aircraft have a tendency to enter a ‘deep stall’ under certain conditions (when the wing reaches very high angles of attack and the resulting turbulent air nullifies the efficiency of the tailplane and elevators). The ‘deep stall’ phenomenon emerged in accidents during early fight testing of the Boeing 727, HS Trident and BAC1-11, with tragically fatal consequences for the test crews involved.
On large aircraft like the Three-eleven, the rear-engine configuration makes engine inspection and maintenance more difficult than in underwing configuration, as the engines are higher up from ground level.
Does anyone have other advantages/disadvantages of the two positions?