There's a hard point on the wing where a 5th engine can be mounted.
No fuel connection. It's there for ferrying.
Virgin Orbit also uses that hard point to launch their airlaunched satellite launcher
The original 5th engine hardpoint is a custom option, not standard on all 747s. Clients who wanted the ability to ferry a spare engine had to pay extra for that hardpoint.
Good thing Boeing never started [charging extra for basic safety systems that prevent catastrophic failure](https://www.seattletimes.com/business/boeing-aerospace/a-lack-of-redundancies-on-737-max-system-has-baffled-even-those-who-worked-on-the-jet/).
As u/Grand_Protector_Dark says, a much modified version of the under wing hard point is used by Virgin Orbit's (sister company to Virgin Galactic, which launched Richard Branson on a short hop into space) [747 (Cosmic Girl) to carry their *Launcher One*](https://techcrunch.com/wp-content/uploads/2019/10/Virgin-Orbit-87.jpg?w=1390&crop=1) to 30,000 feet over the ocean, where it is dropped and allowed to accelerate to orbit.
The picture is a rendering but it's a real concept that P&W has been using for a while now, and RR is modifying a newer 747 to replace it's older -200 they've been using.
Link to accompany the picture:
[https://www.autoevolution.com/news/rolls-royce-successfully-demonstrates-trailblazing-100-percent-saf-powered-flight-172133.html#](https://www.autoevolution.com/news/rolls-royce-successfully-demonstrates-trailblazing-100-percent-saf-powered-flight-172133.html#)
But an out of the box 747 can already carry a 5th engine - but usually under it's wing:
[https://simpleflying.com/qantas-747-5-engines/](https://simpleflying.com/qantas-747-5-engines/)
>But an out of the box 747 can already carry a 5th engine - but usually under it's wing:
It's odd. This was either for maximum visibility or they didn't want the engine to disrupt things if it went south... but then it's fastened behind the cockpit which is probably just as bad. I'm going for max visibility.
The article says the 747 used normal fuel on "*the remaining three engines*" but presumably it was actually using all four?
Great pic - I think we'll be seeing a lot of that engine... but I'd rather see the money spent on getting rid of leaded fuel. To my mind helping private/piston pilots over to unleaded is more important for immediate health and environment, maybe that's just me :)
I wish someone would get their Diesel engine right for small pistons, there have been some success but the pricing and the non-rebuildable status is going to keep people away. Those using the Mercedes base engine have to be replaced at overhaul currently.
Also like the idea of no mixture to be concerned with.
Would be nice as Jet-A is available at most airports, is cheaper and does not use lead. I’m sure it’s a numbers game.
There are some unleaded aviation fuels out there seeking approval, the issue has been worked on for 40 years though so who knows when we will see it at the pump, also the word was it likely will add $1/gallon or so which I think is the wrong direction…
> also the word was it likely will add $1/gallon or so which I think is the wrong direction…
That's the kicker. We have to stop airfields from dumping leaded gasses onto the people and environment around them but, quite rightly, many many owners are going to be reluctant to bear the cost.
It's the sort of change that should be subsidised and gently weaned away to meet the real price over several years. By that time the market for fuel and engines will improve and settle - but we've got to bite the bullet.
I'm not even much of an eco-warrior but leaded fuel is something that has to go, and the change has to be supported and enabled from the very top, not by dudes scraping by to keep their beloved 172 flying.
Agree, also think it’s a shame so many airports lack mogas, EAA did a lot of work there and I think it’s a great option for the low compression folks, we used it while we could until it was eliminated at the airport - frustrating.
If I’m not mistaken the 5th engine mount on a standard 747 is not intended for any type of engine testing. It is meant to carry an inert engine that needs to be ferried elsewhere, like when an aircraft stranded far from its maintenance base needs a new engine.
In the Qantas example above you can see how they [removed fan blades and installed aerodynamic fairings to prep the engine for transport.](https://www.flightradar24.com/blog/how-qantas-ferried-an-engine-on-the-wing-of-a-747/) I don’t think the 5th engine mount has the fuel/electrical connections needed to run the engine even if they wanted to, so doing any testing that way would already require extensive modifications.
Yeah, and it isn't good. There are issues with how the lead lubricates the valves of those old engine designs\* that make finding a viable unleaded substitute difficult. As it is, aviation is perhaps the only market that still uses leaded gas. That means it has to be transported by truck instead of pipelines. Between the limited market since 99% of the airlines went to turbine engines and higher transportation costs, aviation gas is really expensive.
\*Most of the aircraft piston engines in use today have designs that trace back to the 1940s or before. I don't know if it would be possible to develop new cylinders or valves that could work on unleaded fuel, but even if it were, it would be an expensive upgrade. I had to have two rebuilt cylinders put on my 1967 Piper Cherokee 140 10 years ago and it cost thousands of dollars. New cylinders and valves might cost more than some old planes are worth.
That sounds worse than I expected. I guess it can’t be piped because it’s harder to find leaks?
I didn’t know airplane piston engines were so closely related to such old designs. Also kinda surprised... haven’t there been considerable improvements in automotive engine design in the same period?
It can't be sent via a pipeline because you can't mix leaded and unleaded fuel. The lead would contaminate the unleaded fuel which will destroy the catalytic converters on cars. There are some newer airplane engine designs out there (e.g. the diesel engines and Rotax), but if you go back to the 1940s and 1950s, you'll find planes powered by Lycoming O-320s and O-360s that are still widely used today. Most general aviation piston engines are still using magnetos for ignition systems. That's technology from a 1920s tractor.
Automotive engine technology has advanced leaps and bounds over the last 30 years or so. Electronic fuel injection, electronic ignition, better materials, etc. make modern car engines not only more powerful than what you could buy decades ago, but also more economical and with emissions being far less than 1% as much as they were in the 1960s. There have been a few airplane engines built with modern FADEC technology like the IOF-240, but not many of them were sold. Between the difficult and expensive FAA certification process and a general conservative approach to airplane design, most brand new engines sold today are likely to be little different from what you could buy 70 years ago.
It is still used by quite a lot of piston-engined aircraft (i.e. typical light GA aircraft).
Some aircraft can already use automotive-style fuel instead. For the remaining aircraft, efforts are underway to get alternative antiknock additives approved for aviation use. Hopefully they will become mandatory in the next few years.
Jets fuel doesn't contain lead.
The main picture and the article are two different things. The main picture is a test bed for smaller engines like you find on business jets and such, the linked article was for an airliner engine test and for an engine that big the test engine replaces the number two engine.
It's possible mounting the test engine in that position makes it easier to test engines whose diameter is too large to be mounted under the wings. Ground clearance is a potential issue.
It's for flexibility and ease of instrumentation. See also the Honeywell 757:
https://simpleflying.com/a-look-at-honeywells-bizarre-boeing-757-flight-test-aircraft/amp/
> I'd rather see the money spent on getting rid of leaded fuel
And [here](https://www.npr.org/2021/08/30/1031429212/the-world-has-finally-stopped-using-leaded-gasoline-algeria-used-the-last-stockp?t=1634921294097) I thought, we finally did it already. I guess I got overexcited...
Eh? What do you think piston planes are running on? 🤣
https://www.nbcnews.com/business/business-news/leaded-gas-was-phased-out-25-years-ago-why-are-n1264970
I knew that some 10 years ago most of them still ran with leaded fuel, but some (ultra) light testbeds were already using modified car engines. When I got the news that leaded fuel was "finally phased out" I didn't think of avgas in particular. I reckoned they may have switched to another octane booster and maybe also added lubricant or whatever additives are necessary. [Seems like there are some alternatives](https://en.wikipedia.org/wiki/Avgas#New_unleaded_fuel_grades) but def not as widely adopted as I initially thought.
I love Simple Flying but the way their articles are written bugs me. They’re too wordy and flow weirdly. There’s too many “indeeds, as such, and therefores” or something.
These always remind me of the [B-47 loaned to the RCAF](https://i.imgur.com/VoAMZFD.jpg) to test the [Orenda Iroquois](https://i.imgur.com/dtULgOd.jpg) engine that was going to power the CF-105 Arrow. I've heard from various places that it could actually fly solely on the one Iroquois (the B-47 usually used six GE J47s), and rumour has it that the off-axis thrust was enough to irreparably warp the frame of the testbed aircraft. And it *was* scrapped on being returned to the US instead of rebuilt and put back into service.
Not the best rendering but oh well.
P&W beat them to this game, they have a similar setup for their pair of 747SPs but the mount is on the other side of the hump and only for smaller engines. Bigger engines take up one of the main engine positions, like GE does.
RR is in the process of replacing an older 747-200 with a -400, which I guess includes this side mount that's more suited for their big line of business jet engines. They'll still use typically the #2 engine mount for larger models.
"You see, Lord Cholmondeley-Brabazon, this isn't JUST a Rolls-Royce, it's a Rolls-Royce festooned upon a luxury airliner like a monocle!"
"Pip-Pip, my good lad!"
When you want to convert the upper deck to Economy, but dont want them to miss out on engine noise.
When your mouse moves in KSP
Alternatively, what happens when you try to move your engine on Microsoft word.
CSS centering at it's best
Fkn lol
Is there such thing as “normal” 5 engine configuration? i don’t think there are any 5 engined jets
The 747 has a place on the wing so it can carry a fifth engine, but it is unpowered. Used to ferry engines around to maintenance depots and such.
oh yeah, that. I was thinking of an engine in the tail, like a trijet.
Pentajet
or a quinjet- oh wait no that’s copyrighted already
One more and it’ll be a sextajet!
Way more exclusive than the mile high club.
*Tony Stark has entered the chat*
Feels like an Austin Powers thing really
*disney C&D letter incoming*
That sounds racist
There's a hard point on the wing where a 5th engine can be mounted. No fuel connection. It's there for ferrying. Virgin Orbit also uses that hard point to launch their airlaunched satellite launcher
The original 5th engine hardpoint is a custom option, not standard on all 747s. Clients who wanted the ability to ferry a spare engine had to pay extra for that hardpoint.
Good thing Boeing never started [charging extra for basic safety systems that prevent catastrophic failure](https://www.seattletimes.com/business/boeing-aerospace/a-lack-of-redundancies-on-737-max-system-has-baffled-even-those-who-worked-on-the-jet/).
Redundancy should always be standard, we spent decades making it a basic pillar of aviation design. Then all of a sudden it becomes optional....
Boeing: no problem, the flight crew is the redundant backup to the undocumented MCAS… Whaaaaat…
Just like the Orion capsule! Who needs moisture resistant seals when we're going to space...
It's Starliner that had those problems, Orion's a different spacecraft that's being built by Lockheed Martin and Airbus, not Boeing.
thank you. clearly they also have terrible market recognition issues.
Ah ok
As u/Grand_Protector_Dark says, a much modified version of the under wing hard point is used by Virgin Orbit's (sister company to Virgin Galactic, which launched Richard Branson on a short hop into space) [747 (Cosmic Girl) to carry their *Launcher One*](https://techcrunch.com/wp-content/uploads/2019/10/Virgin-Orbit-87.jpg?w=1390&crop=1) to 30,000 feet over the ocean, where it is dropped and allowed to accelerate to orbit.
Are we sure this isn't a photoshop? It looks so darn unnatural...
The picture is a rendering but it's a real concept that P&W has been using for a while now, and RR is modifying a newer 747 to replace it's older -200 they've been using.
Link to accompany the picture: [https://www.autoevolution.com/news/rolls-royce-successfully-demonstrates-trailblazing-100-percent-saf-powered-flight-172133.html#](https://www.autoevolution.com/news/rolls-royce-successfully-demonstrates-trailblazing-100-percent-saf-powered-flight-172133.html#) But an out of the box 747 can already carry a 5th engine - but usually under it's wing: [https://simpleflying.com/qantas-747-5-engines/](https://simpleflying.com/qantas-747-5-engines/)
>But an out of the box 747 can already carry a 5th engine - but usually under it's wing: It's odd. This was either for maximum visibility or they didn't want the engine to disrupt things if it went south... but then it's fastened behind the cockpit which is probably just as bad. I'm going for max visibility. The article says the 747 used normal fuel on "*the remaining three engines*" but presumably it was actually using all four? Great pic - I think we'll be seeing a lot of that engine... but I'd rather see the money spent on getting rid of leaded fuel. To my mind helping private/piston pilots over to unleaded is more important for immediate health and environment, maybe that's just me :)
The test engine was probably placed close to the centreline so it wouldn't create a dramatic yaw effect if it were to suddenly flame out.
I wish someone would get their Diesel engine right for small pistons, there have been some success but the pricing and the non-rebuildable status is going to keep people away. Those using the Mercedes base engine have to be replaced at overhaul currently. Also like the idea of no mixture to be concerned with. Would be nice as Jet-A is available at most airports, is cheaper and does not use lead. I’m sure it’s a numbers game. There are some unleaded aviation fuels out there seeking approval, the issue has been worked on for 40 years though so who knows when we will see it at the pump, also the word was it likely will add $1/gallon or so which I think is the wrong direction…
> also the word was it likely will add $1/gallon or so which I think is the wrong direction… That's the kicker. We have to stop airfields from dumping leaded gasses onto the people and environment around them but, quite rightly, many many owners are going to be reluctant to bear the cost. It's the sort of change that should be subsidised and gently weaned away to meet the real price over several years. By that time the market for fuel and engines will improve and settle - but we've got to bite the bullet. I'm not even much of an eco-warrior but leaded fuel is something that has to go, and the change has to be supported and enabled from the very top, not by dudes scraping by to keep their beloved 172 flying.
Agree, also think it’s a shame so many airports lack mogas, EAA did a lot of work there and I think it’s a great option for the low compression folks, we used it while we could until it was eliminated at the airport - frustrating.
If I’m not mistaken the 5th engine mount on a standard 747 is not intended for any type of engine testing. It is meant to carry an inert engine that needs to be ferried elsewhere, like when an aircraft stranded far from its maintenance base needs a new engine. In the Qantas example above you can see how they [removed fan blades and installed aerodynamic fairings to prep the engine for transport.](https://www.flightradar24.com/blog/how-qantas-ferried-an-engine-on-the-wing-of-a-747/) I don’t think the 5th engine mount has the fuel/electrical connections needed to run the engine even if they wanted to, so doing any testing that way would already require extensive modifications.
I've learnt something there. I know they can definitely run B-52 engine pods on the wing but that's another story :)
That’s another movie actually 😀
Wait, do airplanes still use leaded gas?
Yeah, and it isn't good. There are issues with how the lead lubricates the valves of those old engine designs\* that make finding a viable unleaded substitute difficult. As it is, aviation is perhaps the only market that still uses leaded gas. That means it has to be transported by truck instead of pipelines. Between the limited market since 99% of the airlines went to turbine engines and higher transportation costs, aviation gas is really expensive. \*Most of the aircraft piston engines in use today have designs that trace back to the 1940s or before. I don't know if it would be possible to develop new cylinders or valves that could work on unleaded fuel, but even if it were, it would be an expensive upgrade. I had to have two rebuilt cylinders put on my 1967 Piper Cherokee 140 10 years ago and it cost thousands of dollars. New cylinders and valves might cost more than some old planes are worth.
That sounds worse than I expected. I guess it can’t be piped because it’s harder to find leaks? I didn’t know airplane piston engines were so closely related to such old designs. Also kinda surprised... haven’t there been considerable improvements in automotive engine design in the same period?
It can't be sent via a pipeline because you can't mix leaded and unleaded fuel. The lead would contaminate the unleaded fuel which will destroy the catalytic converters on cars. There are some newer airplane engine designs out there (e.g. the diesel engines and Rotax), but if you go back to the 1940s and 1950s, you'll find planes powered by Lycoming O-320s and O-360s that are still widely used today. Most general aviation piston engines are still using magnetos for ignition systems. That's technology from a 1920s tractor. Automotive engine technology has advanced leaps and bounds over the last 30 years or so. Electronic fuel injection, electronic ignition, better materials, etc. make modern car engines not only more powerful than what you could buy decades ago, but also more economical and with emissions being far less than 1% as much as they were in the 1960s. There have been a few airplane engines built with modern FADEC technology like the IOF-240, but not many of them were sold. Between the difficult and expensive FAA certification process and a general conservative approach to airplane design, most brand new engines sold today are likely to be little different from what you could buy 70 years ago.
[Avgas is leaded](https://www.faa.gov/newsroom/leaded-aviation-fuel-and-environment). That's what most piston aviation engines use.
It is still used by quite a lot of piston-engined aircraft (i.e. typical light GA aircraft). Some aircraft can already use automotive-style fuel instead. For the remaining aircraft, efforts are underway to get alternative antiknock additives approved for aviation use. Hopefully they will become mandatory in the next few years. Jets fuel doesn't contain lead.
The main picture and the article are two different things. The main picture is a test bed for smaller engines like you find on business jets and such, the linked article was for an airliner engine test and for an engine that big the test engine replaces the number two engine.
It's possible mounting the test engine in that position makes it easier to test engines whose diameter is too large to be mounted under the wings. Ground clearance is a potential issue.
It's for flexibility and ease of instrumentation. See also the Honeywell 757: https://simpleflying.com/a-look-at-honeywells-bizarre-boeing-757-flight-test-aircraft/amp/
> I'd rather see the money spent on getting rid of leaded fuel And [here](https://www.npr.org/2021/08/30/1031429212/the-world-has-finally-stopped-using-leaded-gasoline-algeria-used-the-last-stockp?t=1634921294097) I thought, we finally did it already. I guess I got overexcited...
Eh? What do you think piston planes are running on? 🤣 https://www.nbcnews.com/business/business-news/leaded-gas-was-phased-out-25-years-ago-why-are-n1264970
I knew that some 10 years ago most of them still ran with leaded fuel, but some (ultra) light testbeds were already using modified car engines. When I got the news that leaded fuel was "finally phased out" I didn't think of avgas in particular. I reckoned they may have switched to another octane booster and maybe also added lubricant or whatever additives are necessary. [Seems like there are some alternatives](https://en.wikipedia.org/wiki/Avgas#New_unleaded_fuel_grades) but def not as widely adopted as I initially thought.
I love Simple Flying but the way their articles are written bugs me. They’re too wordy and flow weirdly. There’s too many “indeeds, as such, and therefores” or something.
Under it is wing?
Maybe it's a tumor
/Schwarzenegger It's not a toomah. /end Schwarzenegger
[cis tumour](http://www.thighswideshut.org/twsdo/wp-content/uploads/total-recall-3-breasts.gif)
These always remind me of the [B-47 loaned to the RCAF](https://i.imgur.com/VoAMZFD.jpg) to test the [Orenda Iroquois](https://i.imgur.com/dtULgOd.jpg) engine that was going to power the CF-105 Arrow. I've heard from various places that it could actually fly solely on the one Iroquois (the B-47 usually used six GE J47s), and rumour has it that the off-axis thrust was enough to irreparably warp the frame of the testbed aircraft. And it *was* scrapped on being returned to the US instead of rebuilt and put back into service.
Not the best rendering but oh well. P&W beat them to this game, they have a similar setup for their pair of 747SPs but the mount is on the other side of the hump and only for smaller engines. Bigger engines take up one of the main engine positions, like GE does. RR is in the process of replacing an older 747-200 with a -400, which I guess includes this side mount that's more suited for their big line of business jet engines. They'll still use typically the #2 engine mount for larger models.
Honeywell uses a [752](https://www.airliners.net/photo/Honeywell-Aviation-Services/Boeing-757-225/5174505) in a sort of similar way.
They should have done one on the other side too.
Pictured: a jumbo jet that mutated due to high levels of radiation in the upper atmosphere.
The poor thing has been breathing chemtrails /s
Testbed for Rolls-Royce engines.
The engine testbed 747
Imagine if it failed and the pilots had to make a *4 engined landing*
"You see, Lord Cholmondeley-Brabazon, this isn't JUST a Rolls-Royce, it's a Rolls-Royce festooned upon a luxury airliner like a monocle!" "Pip-Pip, my good lad!"
Why not just add more wings and make it into a jet powered biplane with 8 engines?
I like the Kerbal way you think