5000hp; 6000lbs -Lycoming

Let'sgoflying!

Let'sgoflying!

Touchdown! Greaser!
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Dave Taylor
XR7755 (7750 cu in)
Largest piston a/c engine ever. Never made production; one (of only 2) restored - resides @ the Smithsonian. (Never powered an aircraft.)

9 banks of 4 cylinders; bore & stroke not enormous...comparing to our big bore 6's.

"Separate cams for takeoff and...cruise" - pilot selectable!

Original design so powerful it would have beat the air to death, so the -3 model had prop gearing (with 2 selectable speeds)

Help with that bsfc conversion, is that 700gph @T-O?
if so, that's 3500$/hr; $1.00 per second, today?

w7gal3.jpg
 
Can't imagine the size of the starter. Engine reliability must be very poor. If on a 4 cylinder engine you need to replace a cylinder every 2000 hrs on this one would be 2000/9 = 222hrs per engine. For a twin would be every 111 hours. Like on the DC-6 you need to carry the six pack cylinder kit on the plane together with the mechanic. This definitely is not a profitable engine for commercial use.

José
 
Piloto said:
Can't imagine the size of the starter. Engine reliability must be very poor. If on a 4 cylinder engine you need to replace a cylinder every 2000 hrs on this one would be 2000/9 = 222hrs per engine. For a twin would be every 111 hours. Like on the DC-6 you need to carry the six pack cylinder kit on the plane together with the mechanic. This definitely is not a profitable engine for commercial use.

José
Click to expand...

Huh? If a four-banger needs a cylinder every 2000 hours, that means the cylinders are good for 2000 hours, whether there are four of them or 36 of them. More cylinders don't mean more trouble. More cylinders mean a bigger airplane which means more payload per crew and more profit per flight.

This engine didn't reach production because the jet engines arrived and made it obsolete before anyone wanted it, not because it was a pain to maintain. Early on it did have reliability issues, but those are the usual bugs that need working out of any new design. The project was terminated before they perfected it.

Dan
 
The R7755 arrived just as the jet came on line, that is the reason you did not see this engine in service.

Anyone see a major design difference between it and most radials?

notice the prop shaft? what's different about it?

notice the cylinder heads and their arrangement? what is different about them?

This engine was revolutionary in its re-design of an old concept .... Why/how?
 
Tom-D said:
The R7755 arrived just as the jet came on line, that is the reason you did not see this engine in service.

Anyone see a major design difference between it and most radials?

notice the prop shaft? what's different about it?

notice the cylinder heads and their arrangement? what is different about them?

This engine was revolutionary in its re-design of an old concept .... Why/how?
Click to expand...

The OP's picture shows the contra-rotating shafts. The original iteration of the engine drove a single propeller;

avco.xr7755.3e2c.600.jpg


It's basically an opposed engine with many cylinder banks. Not a true radial. A development of the X-engine:

http://en.wikipedia.org/wiki/Packard_X-2775

Dan
 
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Tom-D said:
The R7755 arrived just as the jet came on line, that is the reason you did not see this engine in service.

Anyone see a major design difference between it and most radials?

notice the prop shaft? what's different about it?

notice the cylinder heads and their arrangement? what is different about them?

This engine was revolutionary in its re-design of an old concept .... Why/how?
Click to expand...

I see 2 splines on the crankshaft. Did it have a gearbox for contra-rotating props?

Also, the rocker covers look a liitle odd. Multiple intake and exhaust valves per cylinder or perhaps a hemispeherical cumbustion chamber?
 
Tom-D said:
The R7755 arrived just as the jet came on line, that is the reason you did not see this engine in service.

Anyone see a major design difference between it and most radials?

notice the prop shaft? what's different about it?

notice the cylinder heads and their arrangement? what is different about them?

This engine was revolutionary in its re-design of an old concept .... Why/how?
Click to expand...

It's 9 water cooled inline 4 cylinder engines, driving 2 contra-rotating props. I would give a nut to get one, it's the coolest engine been made. If the RAF would have just withheld Whittle's funding another 6 months, there would probably be a few more around.
 
Dan Thomas said:
Huh? If a four-banger needs a cylinder every 2000 hours, that means the cylinders are good for 2000 hours, whether there are four of them or 36 of them. More cylinders don't mean more trouble. More cylinders mean a bigger airplane which means more payload per crew and more profit per flight.

This engine didn't reach production because the jet engines arrived and made it obsolete before anyone wanted it, not because it was a pain to maintain. Early on it did have reliability issues, but those are the usual bugs that need working out of any new design. The project was terminated before they perfected it.

Dan
Click to expand...

You are right Dan this is a water cooled engine. So unlike radial engines you just change engine blocks when a cylinder goes bad. Because the block would be too heavy for one mechanic now you need two. And instead of the six pack cylinder kit you now carry two engine blocks, two mechanics and plenty of engine coolant. And if your starter fails can this be hand proped??

José
 
And if your starter fails can this be hand proped??
Click to expand...

Hey that reminds me a question I have been meaning to ask...
those huge ship's engines, how do they start them??
Like this one, worlds largest:

qqes7p.jpg
 
Me too... compressed air injected into the cylinders

Altho I do see a ring gear on the flywheel too.:dunno::dunno:
 
I am looking for a huge gas cylinder...maybe that shiny thing at the top? Where's Henning, he's probably got this in his log book!
 
Let'sgoflying! said:
I am looking for a huge gas cylinder...maybe that shiny thing at the top? Where's Henning, he's probably got this in his log book!
Click to expand...

Ha.. Henning has probably worn out a few of those monsters..:yesnod::yikes:;)

Ps.. I think the big shiny thing on top is the exhaust manifold.
 
Piloto said:
You are right Dan this is a water cooled engine. So unlike radial engines you just change engine blocks when a cylinder goes bad. Because the block would be too heavy for one mechanic now you need two. And instead of the six pack cylinder kit you now carry two engine blocks, two mechanics and plenty of engine coolant. And if your starter fails can this be hand proped??

José
Click to expand...

It was water cooled, and had twin overhead cams (not a cam ring for each bank of cylinders) each cylinder barrel could be changed but you were required to pull the head assembly for the whole bank. it was able in the dash 3 model to turn contra rotating props.

A big change from the P&W 2800/4360
 
I took a tour of the aircraft carrier Midway a few months back. It is one huge ship. I wanted to see the engine room, so I did. I was expecting something like the above picture, some huge monstrous contraption, but no. They showed us this little bitty room, with a steam turbine engine in the floor. What a let down. It was hard for me to comprehend how such a huge ship could be powered by something that looked like it would easily fit in your garage.

-John
 
On a locomotive, since the diesel only turns a generator, as I suspect these ship engines do, the generator is used as a motor to start the engine. They don't need to spin up fast to start. They idle at about 200 rpm and at full speed make just under 1000 rpm. But they do make the torque!
 
Keith Lane said:
On a locomotive, since the diesel only turns a generator, as I suspect these ship engines do, the generator is used as a motor to start the engine. They don't need to spin up fast to start. They idle at about 200 rpm and at full speed make just under 1000 rpm. But they do make the torque!
Click to expand...

I believe that huge ship engine is a two-stroke that is directly connected to the propeller. They run the engine backwards for reverse. The starter would likely be another, much smaller diesel engine. Old earthmoving equipment was started that way: with a "pup" engine.

Dan
 
Piloto said:
You are right Dan this is a water cooled engine. So unlike radial engines you just change engine blocks when a cylinder goes bad. Because the block would be too heavy for one mechanic now you need two. And instead of the six pack cylinder kit you now carry two engine blocks, two mechanics and plenty of engine coolant. And if your starter fails can this be hand proped??

José
Click to expand...

As an aircraft mechanic I can tell you that cylinders seldom go "bad." A water-cooled engine will have even less trouble that way. That big Lycoming wouldn't give any more trouble than the Lycomings in countless light aircraft and probably less.

Hand-propping that engine would be impossible, but it's also impossible to hand-prop big radials or jet engines of any sort.

Dan
 
Keith Lane said:
On a locomotive, since the diesel only turns a generator, as I suspect these ship engines do, the generator is used as a motor to start the engine. They don't need to spin up fast to start. They idle at about 200 rpm and at full speed make just under 1000 rpm. But they do make the torque!
Click to expand...
The only diesel electric boats I know of are the Washington State ferries and the last was taken out of service 5 years ago.

most large engines like shown actually will run in both directions and are run direct drive. So they actually shut them down and start them up in reverse.
 
Tom-D said:
The only diesel electric boats I know of are the Washington State ferries and the last was taken out of service 5 years ago.

most large engines like shown actually will run in both directions and are run direct drive. So they actually shut them down and start them up in reverse.
Click to expand...
A lot (most?) of the cruise ships are diesel-electric. The diesel runs a generator that powers everything else, encluding the propulsion.
 
Cap'n Jack said:
A lot (most?) of the cruise ships are diesel-electric. The diesel runs a generator that powers everything else, encluding the propulsion.
Click to expand...

I've never been on a cruise ship, but it was a good design for the short trip ferries, the boat never had to turn around.
 
Dan Thomas said:
As an aircraft mechanic I can tell you that cylinders seldom go "bad." A water-cooled engine will have even less trouble that way. That big Lycoming wouldn't give any more trouble than the Lycomings in countless light aircraft and probably less.

Hand-propping that engine would be impossible, but it's also impossible to hand-prop big radials or jet engines of any sort.

Dan
Click to expand...

I would rather not have water pump failures, radiator leaks and cracked hoses. Not to mention the added weight of water cooled engines. That's the beauty of air cooled engines. On this 36 cylinder engine you bet you are going to have more maintenance headaches than an air cooled 4 cyl engine. 72 plugs, 18 magnetos, 72 valves just to start.

José
 
Piloto said:
I would rather not have water pump failures, radiator leaks and cracked hoses. Not to mention the added weight of water cooled engines. That's the beauty of air cooled engines. On this 36 cylinder engine you bet you are going to have more maintenance headaches than an air cooled 4 cyl engine. 72 plugs, 18 magnetos, 72 valves just to start.

José
Click to expand...
I respectfully disagree...

The biggest enemy is heat and an aircooled motor that runs cylinder head temps of 400 f and then back to ambient repeatedly will suffer metal fatigue faster then a watercooled motor will suffer a coolant leak.. I have three cars /trucks and water cooled plane in my possesion now... Not once in the combined 1 million miles on the vehicles and 400+ hours on the plane have I had a liquid coolant issue. I am betting the vehicle you drive is pretty much bulletproof too..:yesnod::yesnod::yesnod:.

That reason to not use liquid cooled motors in a plane is just an Old Wives Tale..........
IMHO.
 
N801BH said:
I respectfully disagree...

The biggest enemy is heat and an aircooled motor that runs cylinder head temps of 400 f and then back to ambient repeatedly will suffer metal fatigue faster then a watercooled motor will suffer a coolant leak.. I have three cars /trucks and water cooled plane in my possesion now... Not once in the combined 1 million miles on the vehicles and 400+ hours on the plane have I had a liquid coolant issue. I am betting the vehicle you drive is pretty much bulletproof too..:yesnod::yesnod::yesnod:.

That reason to not use liquid cooled motors in a plane is just an Old Wives Tale..........
IMHO.
Click to expand...
This guy knows engines :yesnod:
 
Let'sgoflying! said:
Hey that reminds me a question I have been meaning to ask...
those huge ship's engines, how do they start them??
Like this one, worlds largest:

qqes7p.jpg
Click to expand...


You jack the motor to a timing point (typically just ATDC comp stroke #1 Cyl, but it can be whichever) with an electric motor and then inject high volume air into the cylinder. There are also shot gun shell starters on medium and large Diesels. I used to run a tug with an Enterprise that used them. It was a direct reversing engine, so to go from forward to reverse, you had to stop the engine, swap the cams and restart with the shell starter. Obviously you need an engineer just to shift gears. Docking barges with that boat really helps fine tune your energy management to a honed edge lol.
 
N801BH said:
I respectfully disagree...

The biggest enemy is heat and an aircooled motor that runs cylinder head temps of 400 f and then back to ambient repeatedly will suffer metal fatigue faster then a watercooled motor will suffer a coolant leak.. I have three cars /trucks and water cooled plane in my possesion now... Not once in the combined 1 million miles on the vehicles and 400+ hours on the plane have I had a liquid coolant issue. I am betting the vehicle you drive is pretty much bulletproof too..:yesnod::yesnod::yesnod:.

That reason to not use liquid cooled motors in a plane is just an Old Wives Tale..........
IMHO.
Click to expand...


The only reason there is a choice is weight, otherwise all of them would be liquid cooled. It's not a reliability issue.
 
N801BH said:
Me too... compressed air injected into the cylinders

Altho I do see a ring gear on the flywheel too.:dunno::dunno:
Click to expand...


Drives a generator to supply ships power which will also serve as the jacking motor. If the engine is warm and there is a diesel starting circuit (typical), a slick Chief can sometimes get the engine to pop up on a jacking motor in a bind if you're maneuvering and lose air, but I wouldn't count on it.
 
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John Baker said:
I took a tour of the aircraft carrier Midway a few months back. It is one huge ship. I wanted to see the engine room, so I did. I was expecting something like the above picture, some huge monstrous contraption, but no. They showed us this little bitty room, with a steam turbine engine in the floor. What a let down. It was hard for me to comprehend how such a huge ship could be powered by something that looked like it would easily fit in your garage.

-John
Click to expand...


You only saw the tail of the engine, did you go up to the boilers? There is where the size is.:eek:
 
Piloto said:
I would rather not have water pump failures, radiator leaks and cracked hoses. Not to mention the added weight of water cooled engines. That's the beauty of air cooled engines. On this 36 cylinder engine you bet you are going to have more maintenance headaches than an air cooled 4 cyl engine. 72 plugs, 18 magnetos, 72 valves just to start.

José
Click to expand...

Well yeah, but what kind of comparison is that. That's like saying "It's gonna take a lot more to maintain a sky scraper than a single level house. Of course it is, but they don't do the same thing.

The 7755 would have been much more reliable and lower operating costs in applications like the B-36 which it was meant for. They were looking for a more reliable alternative alternative to the 4360 and the experience with the Allison, Merlyn, Griffon and other water cooled aircraft engines They learned that it can work quite well and allows you to generate more power for greater altitude since you aren't limited to the cylinders surface area to dissipate the heat to the atmosphere, and you can gain a significant improvement in the drag profile again, because you are not restricted to dissipating the engine heat directly from cylinders to atmosphere.

With light planes the weight penalty for water cooling is a pretty hefty chunk of useful load, heavy lift airplanes, not so much so.
 
Tom-D said:
The only diesel electric boats I know of are the Washington State ferries and the last was taken out of service 5 years ago.

most large engines like shown actually will run in both directions and are run direct drive. So they actually shut them down and start them up in reverse.
Click to expand...


There's more than a few new Diesel Electric drive systems out/coming out.
Most notably is the Azipod/Azipull systems which have a fully azimuthing drive pod on a turntable built into the bottom of the ship. Most of these are set up with an electric motor sealed into the drive pod below the surface with a CP prop directly on the shaft.

The disadvantage to D/E drive is initial cost and weight as well as a loss in efficiency over a shaft drive type system since you have the generator and motor which weigh considerably more than the gearboxes and shafts and have a greater energy loss in the transference of the energy from the flywheel to the prop.

However, these are outweighed in displacement mode (non planing) vessels though as the weight is of minor consequence and if dealt with by increasing the displacement to compensate by adding it to the length rather than beam. The great advantage though is in flexibility in power supply as well as being able to eliminate a separate "House Power" electrical generation system. Many D/E vessels will have 6+ main engines and can use, swap, and combine the out puts of any one of the engines to any electrical system on the ship including the propulsion. This reduces parts and spares stores onboard to be greatly reduced and provides the greatest assurance that mechanical difficulties will not cause interruptions in service or safety hazards.
 
Henning said:
There's more than a few new Diesel Electric drive systems out/coming out.
Most notably is the Azipod/Azipull systems which have a fully azimuthing drive pod on a turntable built into the bottom of the ship. Most of these are set up with an electric motor sealed into the drive pod below the surface with a CP prop directly on the shaft.

The disadvantage to D/E drive is initial cost and weight as well as a loss in efficiency over a shaft drive type system since you have the generator and motor which weigh considerably more than the gearboxes and shafts and have a greater energy loss in the transference of the energy from the flywheel to the prop.

However, these are outweighed in displacement mode (non planing) vessels though as the weight is of minor consequence and if dealt with by increasing the displacement to compensate by adding it to the length rather than beam. The great advantage though is in flexibility in power supply as well as being able to eliminate a separate "House Power" electrical generation system. Many D/E vessels will have 6+ main engines and can use, swap, and combine the out puts of any one of the engines to any electrical system on the ship including the propulsion. This reduces parts and spares stores onboard to be greatly reduced and provides the greatest assurance that mechanical difficulties will not cause interruptions in service or safety hazards.
Click to expand...


Another big advantage to the azipods is the ability to dock the ship without harbor tugs... With azipods and bow thrusters I watched them dock a BIG Carnival cruise ship I was on and it was pretty amazing to see it done.. The only people that hated it were the mexican tug boat operators who make / made damn good money for that chore..
 
N801BH said:
Another big advantage to the azipods is the ability to dock the ship without harbor tugs... With azipods and bow thrusters I watched them dock a BIG Carnival cruise ship I was on and it was pretty amazing to see it done.. The only people that hated it were the mexican tug boat operators who make / made damn good money for that chore..
Click to expand...


You don't need pods to dock em without tugs.;) Does make it a heck of a lot easier though ONCE you realize that each of those handles in your hand is a tiller handle and not a steering wheel lol.
 
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Piloto said:
I would rather not have water pump failures, radiator leaks and cracked hoses. Not to mention the added weight of water cooled engines. That's the beauty of air cooled engines. On this 36 cylinder engine you bet you are going to have more maintenance headaches than an air cooled 4 cyl engine. 72 plugs, 18 magnetos, 72 valves just to start.

José
Click to expand...

Ok, then. How would you propose to power a large airplane? With an O-320 of 160 HP????

Be realistic, man. Large airplanes required large engines beofre the age of turbines, and to make those large engines as four-bangers just wasn't practical or safe. And why would you claim that this engine requires 18 magnetos? Even the big R-4360 3000-hp engine of 28 cylinders only had four mags.

Big airplanes, like I said, get the big jobs done and make the big profits. That's why big engines are necessary and why the maintenance is affordable. If you think a big engine like the 7755 would be expensive to feed, maintain and overhaul, try a turbine....


Dan
 
Dan Thomas said:
Ok, then. How would you propose to power a large airplane? With an O-320 of 160 HP????

Be realistic, man. Large airplanes required large engines beofre the age of turbines, and to make those large engines as four-bangers just wasn't practical or safe. And why would you claim that this engine requires 18 magnetos? Even the big R-4360 3000-hp engine of 28 cylinders only had four mags.

Big airplanes, like I said, get the big jobs done and make the big profits. That's why big engines are necessary and why the maintenance is affordable. If you think a big engine like the 7755 would be expensive to feed, maintain and overhaul, try a turbine....


Dan
Click to expand...

That's exactly why turbine engines are powering big airplanes today and not these piston monster. It's all about profitability and reliability

José
 
Piloto said:
That's exactly why turbine engines are powering big airplanes today and not these piston monster. It's all about profitability and reliability

José
Click to expand...

But that wasn't the comparison, yours was to a 4 cyl air cooled Lycoming and the supposition that the reliability would be exponentially less for the larger engine which I don't accept. The real issue was it's design as revolutionary to the 4360 Pratt. It addressed the issues that the B-36 had in a pre turbine industry and it was truly a revolutionary engine and the real shame was they had just got it right. If I ever hit a big jackpot I'd build 1500hp scaled down one and then scale up a Hughes H-1 to go behind it.:D
 
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