Rear engined airliners

[Dr Jekyll]

As I understand a big disadvantage of this layout is the difficulty in recovering from a stall because the tailplane is masked by the wing at high angles of attack. Another, particularly on the VC10, was that the centre of gravity was so far back that the tail had to be huge to make up for the lack of leverage.

There was obviously a good reason why rear engined airliners and bizjets were never built with a canard instead of a tailplane, but what would be the downsides of this layout?

[Allan Lupton]

I'm sure the aerodynamics of the deep stall have been covered ad nauseam elsewhere so I will not repeat it all here.

Canards were considered, but the obvious disadvantage is that your main lifting surface can be compromised by living in the foreplane's wake.
As you can see in this diagram, de Havilland considered a rear-engined canard when scheming a trans-Atlantic mail plane in 1945, but access to the work of (inter alia) Lippisch changed all that.

http://upload.wikimedia.org/wikipedia/commons/thumb/c/c8/Design_Studies_for_the_DH_106_Comet.jpg/370px-Design_Studies_for_the_DH_106_Comet.jpg

[DaveReidUK]

A Comet with a swept tail would have looked rather smart !

[Allan Lupton]

Quote
A Comet with a swept tail would have looked rather smart !

Only if it also had both the wings swept 45 deg. as per the port one in the diagram!
Mmo around 0.90???

[Alan Baker]

Deep stall was not the big disadvantage with rear engined, T tailed airliners. Once understood it was easily managed. The big disadvantage of this layout is excess structural weight. The fin has to be stronger to take elevator loads, the rear fuselage has to be stronger to take thrust loads and the wing has to be stronger to resist bending (wing mounted engines provide wing bending relief). In all these cases for stronger, read heavier. After all this the need for fuel lines to run through the fuselage was a minor inconvenience. The bigger the aircraft, the bigger the problem, which is why nobody (except BAC) seriously considered a widebody rear engined design. The fact is that Boeing got it completely right in 1952 with the design for the 367-80 and all modern airliners are built in it's image.

[DucatiST4]

It's also easier to make a longer version of an aircraft with engines on the wing simply by inserting a fuselage "plug". With the engines on the tail there is only so far you can extend it before you get major issues.

[DaveReidUK]

With the engines on the tail there is only so far you can extend it before you get major issues.

Worked for the DC-9 ...

[ICT_SLB]

And for the CRJ - the 1000 has twice the pax load of the 100.

[Capetonian]

The BAC 1-11 was also lengthened by adding a fuselage section.

[DaveReidUK]

And the Caravelle too, come to that.

[joy ride]

Super VC10 was longer too.

[A30yoyo]

#5.....The fact is that Boeing got it completely right in 1952 with the design for the 367-80 and all modern airliners are built in it's image.


Well nearly right...most modern airliners have the DC-2/DC-3 pattern of just 2 powerful engines, wing mounted, fairly close to the fuselage so how important is the bending relief especially now that wings are looking skinny and 'bendy' (787)?

[evansb]

http://i141.photobucket.com/albums/r68/convair640/Fokker20F2681192155_std_zps3e32726c.jpg

[ICT_SLB]

Two advantages for rear-mounted engines:
Shorter - and therefore lighter - gear especially with high bypass ratio engines.
Easier ground operations - less chance of equipment & personnel being ingested.

[gruntie]

the rear fuselage has to be stronger to take thrust loads

Add that the rear fuselage also has to be stronger to take weight and inertia; additionally the wing centre-section. I read somewhere in the VC10 vs 707 debate that the 10 suffered a 5-tonne penalty because of this.

ExwU6FScZ94

[Allan Lupton]

I think this thread has run its course when it reached the "I read somewhere" level.
There are sound reasons for most configurations and compromises have to be made. A relevant example might be that the rear-engined aeroplane has a clean wing with uninterrupted high lift devices which is, to an extent, offset by the short tail arm requiring a higher tailplane load.

[Capetonian]

I think this thread has run its course when it reached the "I read somewhere" level. It is perhaps a little unfair to denigrate the views of others purely on that basis. We are not all a/c engineers or designers, but most of us have enough knowledge of, or interest in, the question to hold a discussion.

[Stanwell]

evansb,
Do you have any info relating to that Fokker concept? (Post #13)


It looks like an amalgam of:
Fuselage of a Boeing 307,
Wings by North American,
Tail feathers by Douglas
and powered by RR Nenes on steroids.
The apparent C/G vs C/L also looks interesting.

[ruddman]

That is an amazing looking aircraft, evansb.

The beauty of that design is that if there is any engine problems in flight, the pilots can reach down with a spanner and fix it themselves or remove the offending bird etc.


Still, nobody has answered the important question. How fast would it have gone? :ok:

[con-pilot]

Still, nobody has answered the important question. How fast would it have gone?

Not all that fast I'd say looking at the wing and tail design, but what I'm more curious about is, how would one load the passengers seeing that the door is not only above the wing, but the left engine as well. :p

[DaveReidUK]

Still, nobody has answered the important question. How fast would it have gone?

Cruise would have been around 430kts, pretty much the same as the 146 and a bit slower than the F-28.

[evansb]

Here is a link regarding the Fokker F.26 Phantom: Fokker F26 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Fokker_F26)

http://up-ship.com/blog/wp-content/uploads/2010/10/fokker-f26-phantom.jpg

[ruddman]

The F.26 Phantom. Even the name exudes sleekness, comfort and superiority over everything else. Amazing.

Even more amazing is Fokkers futuristic plan at that stage to put a desktop computer behind the pilot so passengers could check their emails in flight. Very impressive.

[India Four Two]

ruddman,


I thought the same thing, but I don't see any satcom antennae, so maybe it's just a local network?


Dutch designers obviously don't travel with much luggage and looking at the layout, I don't think I would want to be in rows 1 or 2 if a turbine disk lets go!

[DaveReidUK]

Here is a link regarding the Fokker. F.26 Phantom: Fokker F26 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Fokker_F26)

Good old Wikipedia:

"Powerplant: 2 × Rolls-Royce RB.41 Nene (https://en.wikipedia.org/wiki/Rolls-Royce_RB.41_Nene) centrifugal compressor turbojet, 46 kN (10,000 lbf) thrust each" :ugh:

[joy ride]

I had not heard of the F26, fascinating looking machine, at first I assumed it was a Boeing. Presumably it was conceived as a tail dragger.
The front view does look a little, er, like it has breasts!

[Stanwell]

evansb,


Thanks for the extra illustration and link. I hadn't heard of it before.


Now, if that engine configuration resembles breasts, then rear-engine craft must be sporting gonads!

[FlightlessParrot]

Good old Wikipedia:

"Powerplant: 2 × Rolls-Royce RB.41 Nene centrifugal compressor turbojet, 46 kN (10,000 lbf) thrust each"

And also, in the Design section, it quoted the thrust as 2.3 kN. The problem with the Powerplant section is that there is a terse data entry format, and someone misunderstood and put total thrust, instead of thrust per engine (total power is, I believe, the nautical convention). So, I corrected it. Yes, good old Wikipedia, but one can do something about its errors.

[evansb]

Yes indeed! Correcting errors is honorable. A moral imperative.

Confucius say, "To make a mistake is an error. Failure to correct a mistake is another error".

[evansb]

Canada's mid-century airliner swan song: http://www.argc-art.com/shop/image/data/%20Avro%20Canada%20C-102%20Jetliner.jpg

[Stanwell]

Ah yes, the Avro Canada C102 Jetliner of '48/'49.
I believe it exceeded 500mph and had a good deal more potential than the DH Comet.


Another sacrifice on the altar of political expediency?




p.s. What a beautiful painting!

[evansb]

No buyers. Regardless of several speed/category records, even Howard Hughes, (who actually flew the AVRO Jetliner), didn't buy it.

The design was too Canadian, meaning "Not American".

As evidenced on the photo link, AVRO Canada considered wing mounted turbojets: (Note the Viscount-sized port holes)

http://vipmedia.globalnews.ca/2013/03/global-news-pictures-001-e1364258365758.jpg