This is particularly true when loading and unloading the plane on three or four aft-mounted engine designs.
There are numerous instances where sloppy work had led to the front raising in air and tail hitting the ground while stationary on tarmac.

One of the "bibles" of aeronautical engineering, Torenbeek, dedicates a couple of pages on that very subject. It even shows drawings from two competing groups at Boeing for what became the 737. You can see a 737 with tail mounted engines in there (looks odd).

What Torenbeek says is that there is no clear cut answer. In some cases, the fuselage mounted engine configuration is best, in others, the wing mounted engine configuration wins. So this question is evaluated on a case by case basis.

It seems that the wing mounted configuration is always lighter (because the weight of the engine doesn't need to be carried by the fuselage), except for smaller aircraft where the taller landing gear starts offsetting the weight gain.

Generally speaking, the ground clearance with the engine needed to prevent gravel being sucked in is a distance that is not proportional to the size of the aircraft. You would need a couple of feet for a small business jet, and four or five feet would be ok for an aircraft five time its weight. So you need taller landing gear, proportionally, with smaller jets.

That's one of those factors that makes fuselage mounted engines preferable for all business jets, and most small regional jets.

As far as the main drawback of T-tails, what some of you are referring to is called "deep stall" where the horizontal tail is getting "stuck" in the aerodynamic wake of the main wing when it is stalled.

The BAC1-11 crash in London awhile back claimed the life of my uncle. I was surprised to realize that as I was studying the subject awhile ago during my engineering degree.

Deep stall is a situation from which one cannot recover. The pilot can move his stick or yoke all he wants, the aircraft won't get out of it. Most airliners are protecting themselves from it by installing stick-pushers that prevent the aircraft from stalling in the first place. Smaller business jet (such as Learjets) are installing ventral fins under the tail.

Off my soapboax, I don't want to be too boring with this stuff

(I design small jets for a living)

The Caravelle indeed had more or less triangular windows. Albeit with rounded up corners. The plane had been designed soon after the Comet, the first version of which would crash mysteriously, with the fuselage breaking in two after a very predictable number of cycles. Eventually, after it was pulled form service and after water tank testing, it was found that fatigue due to stress concentration in the corners of its very square windows had been the culprit.

However the Caravelle did not really have a T-shaped tail. Rather, the horizontal stabilizer was more or less half-height. I would say (from memory) somewhat below half. Also, the vertical stabilizer did not have the shape that we are now familiar with, but instead, was rather round, more like in the previous generation of piston engined planes.

Might be that its cruise speed would have been lower than newer jets?

As to noise, I don't recall that it made noises particularly different than other planes of that time. Strangest noise that I can remember were on BAE146. I also remember some 320 in which a hydraulic pump sounded real funny.

But coming back to the Caravelle, it had funny airbrakes. Board with holes, which would come up on top of the wings. And at low speeds it would seem to crawl. I still remember an approach in Marseille, probably coming in from either Constantine or Annaba (in Algeria anyway), fly quite low over roofs at low speed; felt like it was barely hanging there.

Some were still flying in Brazil in the seventies, operated by an airline that was eventually bought by RG, called Cruzeiro do Sul (Southern cross). One of which crashed somewhere in northern Brazil; a colleague of mine had been booked on that flight but cancelled at the last minute. I believe their last one was destroyed on landing in Manaus, with no casualties. Months or perhaps years later, the burnt carcass was still lying there.

Stranger, you're right about the Caravelle's horizontal stabilizer less then halfway up on the tail. I thought it looked kind of unusual when I first flew on the plane out of MAD, kind of like the designers couldn't decide where to put it on the empanage.

Machdiamond thanks for the info, and it's definately not boring. Your info about the deep stall characteristic of the T-tails finally answered my wondering about why most the of the RJ's seem to land in a flat touchdown rather then the nose-up final of the larger, lower tailed aircraft. Keeping the tail surface above the height of the wing vortices for the T-tails would result in more of a level three-point landing. Might even explain why some of my MS FlightSim98 and Pro-Pilot simulator flights begin to "porpoise" when I try steep takeoffs with high-tailed aircraft.

bj-21.

Actually, this is completely unrelated. The deep stall is an event that occurs after the aircraft stalls, something you will never see in normal operations.

The reason why the CRJ and the Dash-8 have more of a noze down attitude compared to a Boeing or an Airbus has to do with the type of airfoil (wing cross section shape), the wing incidence (angle at which the wing is attached to the fuselage), the flap system and different "downwash" (the angle of the airflow behind the wing) that affects T-tail and low tails in a different way. So there are many factors playing there, but deep stall is not one of them.

(writing this from YYZ T1 MLL)

That was very informative..thanks!

Great thread. Moving to TravelBuzz for wider reach

Sean
Moderator - AC/Aeroplan

Coming in late to the thread...

That is known as a 'cruciform' tail, for obvious reasons.

Wing mounted engines tend to produce a stronger pitch-up moment upon power addition than engines more closely aligned (vertically) to the center of gravity. How important this is, I don't know. It can't be that big an issue, there are at least a few designs out there like this.

The TU-154 still has this problem... and last year's crash in Ukraine was due to this exact problem.

I imagine there is a way to recover from this.... do a rapid weight shift inside hte plane.... pile on all pax onto the front of the cabin one on top of another. Sure someone'll get hurt, but it's better than dying . This will cause the plane to nosedive, diverting the flow, and allowing the pilot to regain control.

You know what, this sounds like a wacky idea but it is likely to work on some airplanes (if you have the time).

The airplanes I've worked on during wind tunnel testing didn't exhibit deep stall at most forward center of gravity.

The biggest tail-engined jets are the quads Vickers VC-10 and Il-62. Both fully T-tailed, both about 45 m wingspan and 150 t MTOW (roughly the size of classical 707 and DC-8) - and both with low-bypass turbofans. They are appreciably bigger than the largest all-tail trijets (Boeing 727 and Tu-154).

Once upon a time, there was a VC-10 trijet. With the normal pair of low-bypass engines on one side of tail - and a single high-bypass turbofan opposite. No passengers, I think.

Would it be technically feasible to build a VC-10 twin, with high-bypass turbofan on the other side as well?

Also, I understand that BAC 3-11 was supposed to be a widebody twin - with tail engines. Does anyone know the specifications?

Just to add some points.

Fuselage mounted engines at the tail are an advantage in the event of an engine failure, as the resulting assymetric thrust from the remaining engine is not as far from the centreline of the aircraft as is the case with wing-mounted engines. Therefore the aircraft is more controllable. It took a while for a combination of yet more powerful engines and more effectively designed aerodynamic controls (in particular the rudder) to handle this situation. This is why all the early twin jets (Caravelle, Tupolev 104, One-Eleven, DC9) had fuselage-mounted engines. The Tu104 had them buried in the wing root, the others at the tail. Boeing was first off with a twin-jet with wing-mounted engines more than 10 years after these others started to appear.

The Caravelle took a lot of design ideas from the Comet, which started the jet age off. Not only did it take ideas of how NOT to do it in terms of sharp corners and metal fatigue, but the nose section was from the Comet (de Havilland built them under licence) as were the engines, Rolls Royce Avons.

There are a range of inefficiencies with both approaches that just need to be optimised. Tail-mounted engines need a substantial support structure (in the VC-10 it was a huge stainless steel fabrication which weighed several tons) which is not required if you don't have engines in this position.

The superstall situation destroyed the prototype BAC One-Eleven during testing, when the issue first became apparent with high-tail aircraft. BAC's chief test pilot realised what had happened to them and that it was unrecoverable. He kept up a running commentary onto the black box voice recorder and his thoughts for how to prevent it in future during the uncontrolled dive until the aircraft hit the ground.

Chorned Snorkack :

Your reference to the BAC Three-Eleven and the VC-10 with the big fan jet engine is (maybe inadvertently) referring to the same programme. The VC-10 was modified to test the early Rolls Royce RB.211 engine, which was similar in power and weight to the pair of Rolls Royce Conway engines normally fixed each side of a VC-10. It flew from an airfield at Hucknall near Derby (where the RR engines are made). The engine went on to the Lockheed Tristar but the Three-Eleven which was also based around the engine was cancelled - some might say postponed, as the concept and indeed several of the team members popped up again at an upstart aircraft manufacturer also thinking of this type of aircraft in the 1970s, called, er, Airbus. The Three-Eleven was so-called because it held 300 seats. The original A300, same reason. Laker Airways ordered both (they were the only airline to order the Three-Eleven). The designs of the Three-Eleven wing went into that first Airbus, and every Airbus type since, including the A380 has had wings designed and built in Britain. It's just been announced that the old BAC factory in Filton, Bristol, now part of Airbus, will do wing work on the A350. The Three-Eleven still lives on !

There's a good discussion about why engines are tail-mounted or not here