• Hi Guest! Forum rules have been updated. All users please read here.

Podded engines

uk 75

CLEARANCE: Top Secret
Senior Member
Joined
Sep 27, 2006
Messages
2,565
Reaction score
1,178
Found this piece about podded engines on airliners
British airliners seem to have favoured embedded (Comet and VC7) and tail mounted (111, Trident and VC10). Was this because we did not have the technology to mount podded engines on swept wings like Boeing, Convair and Douglas? (Boeing also seem to be able to routinely offer wider fuselages)
 

starviking

CLEARANCE: Top Secret
Senior Member
Joined
Sep 29, 2006
Messages
1,054
Reaction score
141
If I recall correctly, embedded engines made for a more aerodynamic airframe, tail mounted engines lowered the engine noise in the cabin.

Wing pod engines eased maintenance, and counteracted the upward bend of the wings in flight - thus gaining lift.
 

SSgtC

CLEARANCE: Secret
Joined
Jul 13, 2020
Messages
320
Reaction score
332
I doubt the UK lacked the technology to build podded engines. And they weren't alone with embedded and rear mounted engines. The DC-9 family all used rear mounted engines as did the 727. Which also had an embedded engine. As did the L-1011.

As for fuselage width, Boeing bet the company on the 747 and designed it to meet a request from Pan Am (IIRC, double the passengers of the 707 over the same range). Not many companies would be willing to do that. Or have such a demanding requirement to meet.
 

riggerrob

I really should change my personal text
Joined
Mar 11, 2012
Messages
1,038
Reaction score
519
You are close dear starviking,
If you spread the weight of engines along the wings, you can reduce point-loading and can install fewer, lighter reinforcements where each engine attaches. Note how modern airliners carry most of their fuel in wing tanks, again to help spread the load across the entire wingspan.
A disadvantage - of podded engines - is that they slow roll rate. Not a big deal on transports and airliners, but a major limitation on fighters.

The other issue is aerodynamic flutter.
Boeing learned while developing B-47 and B-52 that hanging engines in front of wings helps reduce flutter ... again allowing lighter wings to carry the same load. Think of engines as counter-weights hung forward of the wings' hinge line (... er ... structural centre).
 

Schneiderman

CLEARANCE: Top Secret
Senior Member
Joined
Oct 19, 2012
Messages
1,420
Reaction score
440
...... Was this because we did not have the technology to mount podded engines on swept wings like Boeing, Convair and Douglas? (Boeing also seem to be able to routinely offer wider fuselages)
There was a series of articles on this subject in Flight in the mid-40s in which all the pros and cons were discussed. I find it odd that just about all British designers chose to go down the embedded engine route, very little dissent of note. Whether this was customer favour or just following the trend is not clear to me.
 

taildragger

You can count on me - I won a contest
Joined
Nov 2, 2008
Messages
302
Reaction score
172
The other obvious advantage of a podded engine is that they're much less dangerous when they catch fire or come apart. Boeing apparently initially favored buried engines when laying out the B-47 but was directed to attach them outside by the USAF or USAAF, for safety reasons. One apparent reason for the enthusiasm for buried engines was that drag estimates were derived from experience with piston engine nacelles and it wasn't understood how much drag was generated by cooling air pulled through and ejected from the nacelle.
I don't know of that many aircraft losses that can be attributed to the British compulsion to bury jets, especially given the unreliability of early jets. A Nimrod lost over Afghanistan with all hands comes to mind.
 

Hood

CLEARANCE: Top Secret
Senior Member
Joined
Sep 6, 2006
Messages
1,845
Reaction score
1,116
Vickers did look at some podded variants of the VC.7 in September 1955 as an attempt to keep the project alive, both with twin-engine and single-engine nacelles but the whole project died soon after.
I think the decision for buried engines probably was influenced by RAE wind tunnel tests in the late 40s/early 50s in regards to low drag and a desire to avoid any possible sources of wing flutter.
I can't think of many British airliner designs that had podded engines in the 1950s, the exception being Armstrong Whitworth; the AW.174 of June 1956 with paired podded Conways and smaller AW.175 with twin podded BE47C engines, also of 1956.
 

riggerrob

I really should change my personal text
Joined
Mar 11, 2012
Messages
1,038
Reaction score
519
Dear taildragger,

On 2 September 2006, an RAF Nimrod crashed in Afghanistan. It was providing electronic over-watch to Coalition troops. The official explanation was that it developed a fuel leak after air-to-air refueling. Most likely the leak started at an over-flow valve. Leaked fuel drained into the lower, starboard fuselage, then into the starboard wing root where it saturated some insulation near hot air ducts. Eventually it got so hot that it burst into flames. The pilot immediately dived from 23,000 to 3,000' and turned towards Kandahar Airfield. A Harrier followed him down and watched a wing explode, soon followed by a second explosion. Fourteen crew members died when it crashed 25 miles west-northwest of Kandahar Airfield.

That was the official story, but I long suspected that the fire started in some experimental avionics (e.g. L3 electro-optical turret) only recently installed, specifically to track Taliban fighters on the ground.

OTOH Dozens ... er ... more than airlines are willing to admit ... podded engines have exploded or completely fallen off of airliners and the planes still landed safely on runways.
 
Last edited:

Foo Fighter

I came, I saw, I drank some tea (and had a bun).
Joined
Jul 19, 2016
Messages
1,543
Reaction score
518
It seems to me that podded engines have much easier access for maintenance. Having seen recently, the ground crew of XH558 crawling around inside trying to work on hard to access parts, it's not something I would look forward to.
 

uk 75

CLEARANCE: Top Secret
Senior Member
Joined
Sep 27, 2006
Messages
2,565
Reaction score
1,178
Concorde had its engines in pairs in single housings whereas the Boeing SST designs had single podded engines. Arguably the podded ones were safer.
 

Zoo Tycoon

CLEARANCE: Secret
Joined
May 27, 2008
Messages
372
Reaction score
382
Dear taildragger,

On 2 September 2006, an RAF Nimrod crashed in Afghanistan. It was providing electronic over-watch to Coalition troops. The official explanation was that it developed a fuel leak after air-to-air refueling. Most likely the leak started at an over-flow valve. Leaked fuel drained into the lower, starboard fuselage, then into the starboard wing root where it saturated some insulation near hot air ducts. Eventually it got so hot that it burst into flames. The pilot immediately dived from 23,000 to 3,000' and turned towards Kandahar Airfield. A Harrier followed him down and watched a wing explode, soon followed by a second explosion. Fourteen crew members died when it crashed 25 miles west-northwest of Kandahar Airfield.

That was the official story, but I long suspected that the fire started in some experimental avionics (e.g. L3 electro-optical turret) only recently installed, specifically to track Taliban fighters on the ground.
I doubt if engine configuration made much difference in this crash.

So let’s look to Hadden Cave investigation report ( https://www.gov.uk/government/publications/the-nimrod-review ) for the full explanation, if you would allow me to summarise;-

Nimrod’s engine starting system was based on bleed air taken from one of the HP compressors. Being HP air it was hot. The pipe (duct) was externally insulated with a porous lagging. A valve opened to allow air into the pipe as required at engine start. When used the pipe got hot, but when the valve was closed it cooled, normally achieving ambient in approx 20 mins.

The air to air refuelling system has a surge tank to absorb flow fluctuation as a result of fluid inertia within the tanks. To avoid the fuel lines/tank being over pressured, a relief valve was set to open and fuel was vented into draining sump in the aircraft’s belly. This was a relatively rare but happened from time to time.

The problem occurred because the bleed air pipe was in the vicinity of the fuel vent valve. Normally the pipe was cold so presented no hazard. What happened was the bleed air valve stuck slightly, not enough to be noticed but enough to prevent the tube from cooling down so it was hot throughout the entire flight. This provided the ignition point when fuel vented from the surge tank during an air to air refuelling. I understand the valve was recovered from the accident site and demonstrated to be leaking when indicating closed.

The unexpected/undetected hot tube is known as a dormant failure/hazard and should be identified as part of a zonal safety review. When the original Safety assessment was done in a hurry due the Falklands war, this condition was missed. Over the years several dormantly failed starter bleed valves were found and replaced. In one such incident there was signs that combustion was briefly present but self extinguished. In the late nineties/early naughties, the MOD commission a specific Nimrod airworthiness review to cover all such issues and re-baseline the safety case. This incident occurred in 2006 and justly illustrated the safety review had failed to address this well known/documented hazard, hence was systemically regarded as flawed.

As for poded engines this accident has no relevance.

The one thing I do remember that is appropriate came from having two engines in close proximity was isolating one engine from its neighbour was very difficult. This was true both for fire and dynamic resonance in the event of an out of balance damage.

Nimrod/Concorde/Vulcan all had SoP’s that if one engine was damaged it’s neighbour underwent a precautionary replacement. Not sure about’s others such as Victor, VC10 etc but I don’t know how they could have avoided it.

Concorde had a very expensive Niobium fire shield between the engines to arrest a torching flame. We didn’t need that on Nimrod because the bypass duct would act to suppress such a failure.

BTW it’s nonsense to suggest the U.K. didn’t have the technical expertise to design a podded engine as one was flown in Nov 43. It’s really not that difficult once the need has been identified to do it.

3434D99A-00A0-4314-A03D-383C65EE0D45.jpeg
 
Last edited:

Similar threads

Top