why aren't there three engine airliners?
 

727s, L-1011s and DC-10/MD-11s are out of service as airliners. Are there flaws inherent to the three engine concept or did the executions just not have staying power?

Sixto
87 300D

KLM still operates the MD-11, so the tri-jets aren't entirely gone from the passenger jet scene. 727s and DC-10s can still be found doing cargo duty, but L-1011s are just about all relegated to the private and military scene now.

Since the 60s and 70s when those aircraft were designed and introduced, jet engines have become more fuel efficient and more powerful. Thus, the need for 3 engines dropped when the same flights could be accomplished with 2 engines with less fuel burn to boot. There was also one less engine to maintain and you know how airlines like to save money.

Just take a look at what 2 engined jets those tri-jets have been typically replaced with.

727= 737-800/900, 757-200, A320/321
L-1011= 767-400, 777-200, A330
DC-10/MD-11= 767-400, 777-200, A330

The only real problem with the third engine was that it tended to be in the tail. On the off chance that it blew up, there was a good chance of it taking out the hydraulics for the flight controls. Not good.

$$$ mostly, in production, maintenance & operation

they would like to go to one, but it wont fly with "0" engines in an emergency

FAA rules used to require > 2 engines for over water flights, incase one failed.
With newer more powerful engines, 2 engine planes are now certified for over water flights.
Even older 737s with newer engines are now used over water too.

Damn if an engine fails it fails. I don't give a ***** if it's over water or land.

Its also pretty noisy back there, from what I remember.

The L-1011 and DC-10 used three engines to achieve a longer ETOPS (Engines Turn Or Passengers Swim) and thus able to cover long distance routes over water without stops with the then-current engine technology.

The B727 was a compromise a/c designed to fill the multiple needs of airlines for short runway capability, high altitude runway capability and ETOPS.

Newer engines have been certified for longer ETOPS so an extra engine is redundant nowadays. Engines are significantly more powerful now as well.

I also believe they do not have the hush kits, or they are less effective for tail mounted engines.
Despite the enormous size of todays engines, the core engine itself hasn't gotten that much bigger (% wise). The increase in size creates bypass air, which is used to increase the engines effiency and decrease it noise.

:confused:

ETOPS -
It's a time and distance thing. Not a water thing.
It's not all about the engines either.
And then there's crew certification...

Odd as this may sound - I have flown Boeing 757s that were ETOPS certified and some that were not. Both with the same RB211 engines.

As for the Q - Post #2 from H-Town pretty much answered the OP question.

You are right - In fact, they've gotten smaller.

Right, time/distance...to a suitable landing site. I maintain that the driving force is over water ops because it just so happens that there are more suitable landing sites on land than in the middle of the Pacific.

FWIW, see attached great circle mapper with 60 and 120 min ETOPS on rte to SYD from LGA via SFO...light blue is 60min...all of the continental US is within 60min B757 ETOPS. Not so for mid-ocean.

That answers why I've seen similar a/c at terminals, some with ETOPS on the nose gear door, some without.

Isn't it also true that tri-jets were tail heavy which caused some interesting handling characteristics? (I remember seeing some photos from a few inexperienced pilots who managed to scrape the tails on landing)

Nope - CG is CG no matter how it's made.

That wasnt because the aircraft was tail heavy.

Not true -
Over the pacific, all the landing sites are suitable. Not so when over land. :D


Hope ya know I'm just josh'n ya here.

Isn't the polar moment relevant as well?

A 10kg ball and a 10kg dumbell both have their CG at the geometric center but they respond differently to certain forces.

Sixto
87 300D

Sure it will, at least to the scene of the crash:devil:

I forgot about the noise issue. I don't recall flying in a tri-jet, but I have flown in C-9's, which have the engines mounted on the fuselage. If you sat near the engines, you got a loud ride.

Every tail skid and/or tail contact incident that I am familiar with (lots, btw) regarding transport category aircraft are related to pilot error, and most are the result of over rotation on takeoff. No relation to where the CG happened to be, nor what factors produced said CG location.

I do know that it doesn’t take much weight movement (location) to drastically change the CG of large aircraft with major results. For instance – If you take all the fuel out of a DC-8 you’d better tie a cement block to the nose or put the tail post (long pole) in place on the rear skid. Otherwise, 3 grown men can walk from the front of the aircraft to the rear and put it on its tail. :eek:

Very weird feeling. :o

Tell Robert Piche and (his first officer) Dirk De Jager of Air Transat and Airbus (A330) that and see what they have to say. ;)

DC10/L1011 were fuel hogs. The MD-11 never met what MD promised in terms of performance and was definately orphaned when Boeing bought MD.

The MD-11 has a spotty history and has had a few nasty crashes of late (Fed Ex in Newark, Narita and recently a MD-11 Freight dog in China) and many owners did not do the upkeep the airframe required (The Varig DC-10/MD-11's that were converted to Freight Dogs were in such poor shape that 1 was written off and turned in to beer cans-my buddy at JAX did the work on 8 of them and said the amount of "wildlife" that was found in the cabins required a major tent and gas job and they were still killing the vermin as they stripped the interior).

Boeing has a definate aversion to anything they didn't design-they killed the MD-90/B717which turned out to be a much desired airframe for certain airlines. Their solution was the 737-900 which does not do it for certain fleets (Airtran for one).

Think about it this way, Northwest/Delta has a number of DC9's that are close to 40 years old that are at work daily. One thing Douglas knew how to do was over engineer their designs for longevity. 40 years! There are Airbus A320's that have been scrapped at 26000 cycles and dumped in the desert and the crews fly home on a 40 year old DC9!

And lets not forget there are DC3/C47's that were built for WW2 that are still flying somewhere in the world...

Only if yer name is Sully.

Thanks to you, I missed a bagpipe performance to read this:

http://www.moptc.pt/tempfiles/20060608181643moptc.pdf

Actually it was worth it and quite an interesting read. I'm surprised it took the crew that long to figure out they had a bad fuel leak, even with the lack of training on the subject. I guess I'm just used to driving stuff that springs leaks a lot.

I remember flying from Cincy to St Louis in an L1011, in the rear, near the center. That center engine was loud! (RR, I think) We left 5.5 hours late and I think the pilot tried to make up all the time. Plane was at an awful angle. Must have had it floored. (Floored?) Poor attendents had a terrible time pushing carts uphill. Poor woman by me was flying with a less than one year old child. She was not having a good time. We of course missed our connection to OKC. I was so mad at TWA, I drove home for the return 4 weeks later.

this happened to flight 232 back in the late 80's.lost all hyd's and had to steer with engine power with the 2 remaining engines.all they could do was make left turns so ended up slowly spiraling down to the sioux city iowa airport.the tail engine fell off and landed about 10 miles from here in a cornfield.

There was a real concern about the DC-9-80 suffering from the exact same condition. With the engines in the tail, the wings are set quite far aft on the fuselage. In theory, a full set of passengers in the rear of the aircraft (upon disembarking) could lift it off it's nosewheel............but, in practice, it hasn't happened.

It's an interesting aircraft from a weight and CG perspective.

His reference was to this specific flight, although it wasn't stated. It happened on a single DC-10 due to a defect in a titanium fan disc. The tail engine did not "fall off".

The reference to all tri-jets suffering from the same malady is completely without merit.

Yes..........floored............:rolleyes:

For your reference, the faster the aircraft flies, the flatter it's angle. If the aircraft was heavily noseup for some reason, the speed would be significantly reduced from the typical operating parameters at that altitude.

The aircraft flies noseup on climbout to achieve the highest rate of climb with the maximum lift...........sacrificing speed to do so.

It flies almost level at cruising altitude.

It flies level or slightly nose down on decent...........depending on speed. If it's fast........it will be nose down...........sometimes significantly so.

On approach, you'll always notice the nose lift upward due to the fact that the aircraft has given up most of its speed and needs the increased angle to keep itself in the air.

Yep, looking at them from the ground on short final they appear to do a funny bobbing nose up/down thing...probably no different that any other aircraft but noticeable on the DC-9, MD-80 because of the amount of fuse in front of the wings compared to what's behind them.

It must be an optical illusion because inside they ride about the same.

I hate the back row seats in them. Noisy and I cannot help but think of uncontained engine failures.

Definitely avoid the last row and the row just forward of that. You and the fan are far too close and personal..............:eek:

When the ***** hits the fan, the fan turns to *****.:D

Well, it might..........but you turn into a pile of pulp............

This seems like an inconsistancy to me. First you say the aircraft flies nose up and bleeds off speed. Then you say on landing the aircraft goes nose up because it needs more speed??

Maybe because airodynamics are different on landing? Pitch is used to control speed and throttle is used to control altitude.

Anyway, Form what I've read the AOA (Angle Of Attack) dictates airspeed.

Danny

If the aircraft flies nose up..........it's generating more lift for the available speed. This is necessary on climb out and also necessary on landing. Both flight regimes suffer from insufficient airspeed to keep a level attitude.

Aerodynamics is the same...........whether on takeoff or landing. If you increase the pitch, you increase the lift for a given airspeed.

And all this time, I thought I was pointing the nose up or down because that was the direction I wanted to go. Silly me. :D

Yep........pull that nose up to about 25 degrees..........see if it goes in chosen direction............:D

It might, if you floor it...

...........it'll "floor" itself.........

I did have that flight in mind.

Completely? While it's rare, all jet engines are occasionally subject to catastrophic failure, and sending a load of shrapnel through a tail is probably a bit more of an immediate problem than sending an equivalent amount through a wing.

The last time I tried that in the 750, I made 460 in just under 20 min.:eek:
AOA and LRI “in the green” for about 75% of the climb.
(Of course, the remaining ~5k took another 15+ min., but you aren’t flooring it at that alt. Not to mention, I cut my range in half, but...:o)

The J3 on the other hand...:rolleyes:

Too many variables in play for either situation.

I’d call them both immediate problems. ;)
Both are certainly “Whiskey Fox” conditions. :D

Wasn’t the L1011 set up with a fan brake system that stopped the #2 fan in some unbelievable time (like < .5 sec.) if it separated?
I have little L1011 time with a few (right seat) ferry flights to Evergreen. The only thing I remember liking about the aircraft was the one button engine start system. That’s it.

Since the wing carries the fuel and ailerons, you might wish to reconsider that conclusion.

If a wing mounted engine comes apart, yes there's a high probability of it taking out nearby fuel tanks. As the incident WVO brought up shows, you can be out of fuel and still make a controlled landing. The shrapnel is less likely to hit the ailerons, since they are on the back of the wing, while the engines tend to be front mounted. I'm not saying an exploding wing mounted engine is anything less than a large problem, but I still think the odds are better than with a tail mounted engine grenading.

If I'm sitting in the row of seats that are parallel to the fan, my estate may have a bone to pick with you.

Consider the issue of flammability when a foreign object penetrates the fuel tank at high speed. You may recall a specific supersonic aircraft that is no longer flying.............

The only issue with the tail mounted engine is the severing of all hydraulic systems to the tail............with the loss of control of the ailerons. It's only happened once on a DC-10 and that specific issue is now corrected via FAA mandate and the use of hydraulic stop valves to prevent such a scenario.

I did not know that. Thank you.

There's really only one aircraft type I would have serious misgivings about flying on: the V-22 Osprey. However, if ordered to do so, I would reluctantly take a ride on one.

Try it sometime
http://img51.imageshack.us/img51/921...workdeluxe.jpg

If you really want some pucker factor, try bringing the B-737 in for a landing in 1/4 mile visibility without the use of the autopilot. :eek:

I think WVO mentioned this model once. Something about having upgraded landing gear and mug guards as well as other rough field equipment?


Also, speaking of rough field tri-jets....

http://img710.imageshack.us/img710/8...polevtu154.jpg

But do not ever (as in EVER EVER EVER) compare that to doing the same thing in the real aircraft.

Doing so in the real aircraft (for a somewhat experienced/rated pilot) is FAR EASIER than trying to pull it off sitting at a computer. Depending on the certification of the aircraft that is (and crew for that matter).

Which is why some air carriers will not allow it at all.
An example of which an American MD-80 set in Little Rock Arkansas not too long ago.
(Check those CVR tapes for how many times visibility numbers are mentioned.)