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breadbasketbomb
08-02-2012, 04:54 AM
During the Second World War, aircraft had large powerful engines that to our standards, are actually week, inefficient and bulky. And it will be like that for engines of now, in the future. Today, we can modify modern engines, or make engines of very high output for there size compared to WW2. Today, an engine used to power aircraft that is fast to some extent in WW2 can be used in some street legal cars, or at least possible.

http://www.nelsonracingengines.com/cars-and-projects.html

Let's go insane on this. 705 ci twin turbocharged V8 with 3000 horsepower. Multiply it by 4 because let's say we are using it to replace a twin wasp which is 4 times the displacement, and we get around 12000 horsepower. Now it's a wankel engine with he same displacement, and we get 24,000 horsepower. We have an aircraft that has a power to weight ratio of 1.4. Also the blades are swept.

If such an aircraft were to exist, and there are no mechanical issues. There are two I am considering actually, a conventional front mounted propeller blade, and a less conventional rear mounted version. How would those two fly?

And now I am going to take this to the extreme. Burt Rutan flies in with his flying Kevlar composite carpet and cast a spell upon the airplane and most of it's structure is now carbon fiber and magnesium lithium alloys of the lightest type.

what would happen then?
all I know is that it would be really loud and fast, hell maybe even supersonic.

Chevan
08-02-2012, 06:33 AM
And now I am going to take this to the extreme. Burt Rutan flies in with his flying Kevlar composite carpet and cast a spell upon the airplane and most of it's structure is now carbon fiber and magnesium lithium alloys of the lightest type.

Hi breadbasketbomb.Its very interesting topic.
Do you mean D_ick Rutan's Voayger (http://en.wikipedia.org/wiki/Rutan_Voyager)?How exactly are you going to make this else to extreme?Any flying projects planns available?

Nickdfresh
08-02-2012, 06:57 AM
My very limited knowledge tells me that "extreme" power often comes with a huge price in reliability, service life, ease-of-maintenance, and a whole hose of other issues--especially when we're talking about lives of pilots whom aren't easy to train and develop...,.

breadbasketbomb
08-02-2012, 10:22 PM
My very limited knowledge tells me that "extreme" power often comes with a huge price in reliability, service life, ease-of-maintenance, and a whole hose of other issues--especially when we're talking about lives of pilots whom aren't easy to train and develop...,.

Yes, but it's a wankel engine so it will blow up. SO in the entirety of the time that we can fly this thing, about 10 minutes in the air what could we do.

pdf27
08-03-2012, 01:22 PM
Lots of issues here:
1) Engine cooling. As engines get bigger, they get harder to cool. Higher power densities compound this process. I know for certain that Rolls-Royce bench tested engines of pretty similar power densities to this (the Rolls-Royce Crecy, a two-stroke producing equivalent to 5,000 bhp from 1536 cubic inches in single-cylinder tests). The majority of problems were to do with extreme overheating, even using sleeve valves (less problematic than poppet valves).
2) Absorbing the power. It is next to impossible to drive a propeller aircraft through the sound barrier - all sorts of nasty things happen at the blade tips, essentially turning most of your power to noise and heat and unless you have very short, stubby propeller blades probably ripping them off too. It should be noted that even with enormously powerful turboprop engines available today (11,000 BHP per engine on the A400M for instance) the fastest propeller aircraft around are still WW2 warbirds racing at Reno. More power in this case does NOT equal more speed.
3) Jet engines exist, and have since the early 1940s. They are massively more reliable than piston engines, much more pleasant to fly with (next to no vibration), and much more fuel efficient at high speed.
4) Reliability - big powerful piston engines running at high specific powers have very low reliability. Not the end of the world in a car race - you'll accept losing the odd race in return for winning a lot more. In an aircraft, the same problem may well kill you.
5) Handling - single engined piston fighters, particularly late war ones with big engines, had vicious handling characteristics on takeoff. Add in the long nose (to house the big engine) and they would regularly kill inexperienced or tired pilots. Jet engines don't have these problems, and adapt well to tricycle undercarriages.
6) Power to weight - if you a good power to weight ratio, you're better off building a light aircraft with a light, reliable engine. There are lots of aircraft out there by the likes of Pitts, Yak or Extra with a power to weight ratio in excess of unity. You also get all sorts of handling and manoeuvrability benefits.

breadbasketbomb
08-03-2012, 09:16 PM
Lots of issues here:
1) Engine cooling. As engines get bigger, they get harder to cool. Higher power densities compound this process. I know for certain that Rolls-Royce bench tested engines of pretty similar power densities to this (the Rolls-Royce Crecy, a two-stroke producing equivalent to 5,000 bhp from 1536 cubic inches in single-cylinder tests). The majority of problems were to do with extreme overheating, even using sleeve valves (less problematic than poppet valves).
2) Absorbing the power. It is next to impossible to drive a propeller aircraft through the sound barrier - all sorts of nasty things happen at the blade tips, essentially turning most of your power to noise and heat and unless you have very short, stubby propeller blades probably ripping them off too. It should be noted that even with enormously powerful turboprop engines available today (11,000 BHP per engine on the A400M for instance) the fastest propeller aircraft around are still WW2 warbirds racing at Reno. More power in this case does NOT equal more speed.
3) Jet engines exist, and have since the early 1940s. They are massively more reliable than piston engines, much more pleasant to fly with (next to no vibration), and much more fuel efficient at high speed.
4) Reliability - big powerful piston engines running at high specific powers have very low reliability. Not the end of the world in a car race - you'll accept losing the odd race in return for winning a lot more. In an aircraft, the same problem may well kill you.
5) Handling - single engined piston fighters, particularly late war ones with big engines, had vicious handling characteristics on takeoff. Add in the long nose (to house the big engine) and they would regularly kill inexperienced or tired pilots. Jet engines don't have these problems, and adapt well to tricycle undercarriage
6) Power to weight - if you a good power to weight ratio, you're better off building a light aircraft with a light, reliable engine. There are lots of aircraft out there by the likes of Pitts, Yak or Extra with a power to weight ratio in excess of unity. You also get all sorts of handling and manoeuvrability benefits.

Thanks for all the information, that's what I need to know. Except about the reliability, I know the aircraft would be a total wreck, except for the heating part. The engine is not bigger, it's just as efficient as modern engines, but is still inefficient compared to a modern car engine. Though I do think the heating is going to be a major problem because we are talking about a 50 liter engine that has a power density of a modern wankel engine.

If I had to commit suicide, I would do it by flying this aircraft fast and hard, not by crashing, but by catastrophic failure in mid air.

I just had a new idea this mourning BTW.

Use the same engine I made up that produces too much horsepower, and use it as a heater in a boiler, with it's drive shaft attached to a steam turbine. You get the image I'm seeing. This is how a hybrid engine should work dammit!

pdf27
08-05-2012, 11:30 AM
Been done:
http://en.wikipedia.org/wiki/Napier_Nomad

Doing it with a steam cycle is only really practical in very large ships and more commonly power stations as the steam plant is EXTREMELY heavy compared to the rest of the engine. Most commonly done with gas turbines as diesel engine exhaust can be made cool enough (with turbocharging) that the efficiency gain from an additional steam cycle is minimal.

breadbasketbomb
08-05-2012, 06:41 PM
Been done:
http://en.wikipedia.org/wiki/Napier_Nomad

Doing it with a steam cycle is only really practical in very large ships and more commonly power stations as the steam plant is EXTREMELY heavy compared to the rest of the engine. Most commonly done with gas turbines as diesel engine exhaust can be made cool enough (with turbocharging) that the efficiency gain from an additional steam cycle is minimal.

Well I have only one idea left for improving the performance of a propeller driven aircraft, two actually.

The first is a Ultra lean burn engine. I heard they went 40 miles to the gallon. If I had a B-36 peacemaker with lean burn engines of equivalent power to weight ratio, will that help the range by allot? It has too. I heard the only disadvantage was the complex catalytic converter to keep emissions low. Why do we need a even more complex (but gradually simplifying, so might as well not care) hybrid car. I don't hate hybrid cars, it's just... why the cant we just use lean burn engines with complex catalytic converters? Anyhow, back to the subject. Really how would a lean burn engine do.

The second is in regards to a non ww2 aircraft. The SR-71. What happens if we take the same engine pod with the spike, and instead of using a J58, what happens if we just used titanium counter rotating propellers making it a ducted fan, will the intake spike allows them to run for how fast and high?

pdf27
08-06-2012, 01:34 AM
OK, you've got some very mixed up ideas here@
1) Lean burn engines. They weren't deigned to increase fuel economy (that was a small side effect - can't actually remember if it was actually any more efficient, I have a feeling it wasn't), they were designed to have a low flame temperature inside the engine, achieved by using a leaner fuel mixture so the flame was diluted with air and burned cooler. This reduces NOx formation inside the engine, and gave you low emissions without the need for a catalytic converter. Also, they don't have the same power to weight ratio - burning lean means you need a bigger combustion chamber, and hence a bigger/heavier engine to burn the same amount of fuel and generate the same amount of power.
Hence, with a heavier engine cutting into your payload and roughly the same fuel efficiency, your range will be reduced.
2) SR-71: the engine inside the spike essentially runs as a ramjet at high speed. That more or less means that once you get to ~Mach 1.5 or so, you could take out everything but the afterburner section of that engine and it would still fly just fine. A ducted fan will probably get you up to this speed. You still run into the original problem though - the lightest and most efficient way of running this ducted fan is to attach it to the front end of a gas turbine engine! At that point, you've just reinvented the J58 ;)

breadbasketbomb
08-06-2012, 08:44 PM
OK, you've got some very mixed up ideas here@
1) Lean burn engines. They weren't deigned to increase fuel economy (that was a small side effect - can't actually remember if it was actually any more efficient, I have a feeling it wasn't), they were designed to have a low flame temperature inside the engine, achieved by using a leaner fuel mixture so the flame was diluted with air and burned cooler. This reduces NOx formation inside the engine, and gave you low emissions without the need for a catalytic converter. Also, they don't have the same power to weight ratio - burning lean means you need a bigger combustion chamber, and hence a bigger/heavier engine to burn the same amount of fuel and generate the same amount of power.
Hence, with a heavier engine cutting into your payload and roughly the same fuel efficiency, your range will be reduced.
2) SR-71: the engine inside the spike essentially runs as a ramjet at high speed. That more or less means that once you get to ~Mach 1.5 or so, you could take out everything but the afterburner section of that engine and it would still fly just fine. A ducted fan will probably get you up to this speed. You still run into the original problem though - the lightest and most efficient way of running this ducted fan is to attach it to the front end of a gas turbine engine! At that point, you've just reinvented the J58 ;)

Well I would have known that if someone made a simplified summary of it, which you have thankfully did and now I know.

And for the last part do you see what I am getting at? I'm trying to make a high altitude supersonic airplane that gives of minimal heat signatures, it's a science fiction thing I have going on that I am aware, is not suitable for this sight. And are you sure it is the lightest and most efficient way of getting a ducted fan to get me up to mach 1.5? because car engines can end up becoming insanely powerful these days compared to the last of the piston engines built for speed and power, and relatively cheap because I can make it out of cast aluminum, not machined superalloys. Remember, Nelson Racing Engines?. Just to tell you, I don't read books so that's why I'm clueless.

pdf27
08-07-2012, 01:48 AM
You're being a little harsh on yourself - I have a Masters degree in this stuff, I haven't just read a few books ;)

For Mach 1.5, aerodynamic heating will start to become significant. I can't remember what exact temperature they reach and my notes aren't to hand right now (might check tonight if I remember), but I do remember that the cruising speed for Concorde was set by aerodynamic heating limits at Mach 2. For what I remember of Aerospace aluminium grades, that equates to around 100 deg C. The US wanted to go to Mach 3 with their competing aircraft, which required a Titanium structure.

Supercruising is possible (not just for the F-22, the English Electric Lightning in the early 1950s was the first), and that means you don't need the very hot reheat. It also means exhaust gas temperatures aren't really any hotter than for a standard low-bypass turbofan at subsonic speeds. With a bit of care (designing it to fly at high altitude and having the engine exhausts on the top of the wing) and your wing leading edge becomes the hottest thing going.

The other issue is how much heat each engine will put out. Assuming they are set up for the same cruising speed, the exhaust gas speed and mass flow rate will be about the same (optimum propulsive efficiency). That means the compression ratio in reality - the higher the compression ratio, the cooler the exhaust and hence the higher the efficiency. Racing car engines have a problem here - one of the ways they get high specific powers is to use turbo or supercharging, which let them get high power to weight ratios. Unfortunately, they also limit the compression ratio inside the engine (and petrol engines are inherently limited anyway as petrol will self-ignite before top dead centre if the compression ratio is too high). Gas turbine engines don't have this problem - they use a heavier fuel and burn continuously around the injectors so could live with it anyway. Compression is instead limited by weight and diminishing returns for efficiency - if you add 1% to the weight of the aircraft to gain 1% in engine efficiency, that's a net loss.

breadbasketbomb
08-07-2012, 04:28 AM
You're being a little harsh on yourself - I have a Masters degree in this stuff, I haven't just read a few books ;)

For Mach 1.5, aerodynamic heating will start to become significant. I can't remember what exact temperature they reach and my notes aren't to hand right now (might check tonight if I remember), but I do remember that the cruising speed for Concorde was set by aerodynamic heating limits at Mach 2. For what I remember of Aerospace aluminium grades, that equates to around 100 deg C. The US wanted to go to Mach 3 with their competing aircraft, which required a Titanium structure.

Supercruising is possible (not just for the F-22, the English Electric Lightning in the early 1950s was the first), and that means you don't need the very hot reheat. It also means exhaust gas temperatures aren't really any hotter than for a standard low-bypass turbofan at subsonic speeds. With a bit of care (designing it to fly at high altitude and having the engine exhausts on the top of the wing) and your wing leading edge becomes the hottest thing going.

The other issue is how much heat each engine will put out. Assuming they are set up for the same cruising speed, the exhaust gas speed and mass flow rate will be about the same (optimum propulsive efficiency). That means the compression ratio in reality - the higher the compression ratio, the cooler the exhaust and hence the higher the efficiency. Racing car engines have a problem here - one of the ways they get high specific powers is to use turbo or supercharging, which let them get high power to weight ratios. Unfortunately, they also limit the compression ratio inside the engine (and petrol engines are inherently limited anyway as petrol will self-ignite before top dead centre if the compression ratio is too high). Gas turbine engines don't have this problem - they use a heavier fuel and burn continuously around the injectors so could live with it anyway. Compression is instead limited by weight and diminishing returns for efficiency - if you add 1% to the weight of the aircraft to gain 1% in engine efficiency, that's a net loss.

Well, here is what I am trying to do for the sake of science fiction and bad literature that litters the internet (my immortal... anyone?). I will leave out the plot and only give out some setting. A given civilization is staring at 1980's America, and said that they want an SR-71. At the time all they got is piston driven aircraft and a giant radio station to talk to humans. How will they get an SR-71 equivalent with only a propeller driven aircraft. I'm sure that all problems stated with the motor can be fixed with engineering (I heard the me 262 can run on diesel), and ignoring efficiency not by adding weight, just making the engine more modern. OK I'm changing the priority.

I dont care about heat, or efficiency anymore (unless it ends up being less efficient than a J58).

Is there a way to make a SR-71 competitor in a car factory is all I want in it's most basic form. The point is that gas turbines are much more complex than piston engines or wankel engines (which I want to use). Is it possible to use aviation fuel in any of the engines. I believe that just because we had a given technology in the past does not mean we can do it then. And for the temperature aah, just leave that there, fix the thing later. The only solution I have created is using diesel, and with engineering it can at high speeds and so and so. All I have is one question now that I scrapped all other wanted benefits that wont come: How do I make it go mach 1.5 or up. The original concern I had was with the ducted fan.

And about the last part, what do you mean by specific power? like power to weight ratio, or fuel efficiency. I just want the fan to spin fast enough now.

pdf27
08-07-2012, 08:17 AM
Well, here is what I am trying to do for the sake of science fiction and bad literature that litters the internet (my immortal... anyone?). I will leave out the plot and only give out some setting. A given civilization is staring at 1980's America, and said that they want an SR-71. At the time all they got is piston driven aircraft and a giant radio station to talk to humans. How will they get an SR-71 equivalent with only a propeller driven aircraft. I'm sure that all problems stated with the motor can be fixed with engineering (I heard the me 262 can run on diesel), and ignoring efficiency not by adding weight, just making the engine more modern. OK I'm changing the priority.

I dont care about heat, or efficiency anymore (unless it ends up being less efficient than a J58).

Is there a way to make a SR-71 competitor in a car factory is all I want in it's most basic form. The point is that gas turbines are much more complex than piston engines or wankel engines (which I want to use). Is it possible to use aviation fuel in any of the engines. I believe that just because we had a given technology in the past does not mean we can do it then. And for the temperature aah, just leave that there, fix the thing later. The only solution I have created is using diesel, and with engineering it can at high speeds and so and so. All I have is one question now that I scrapped all other wanted benefits that wont come: How do I make it go mach 1.5 or up. The original concern I had was with the ducted fan.

And about the last part, what do you mean by specific power? like power to weight ratio, or fuel efficiency. I just want the fan to spin fast enough now.
Hmmm…. Best bet I would say would be a composite aircraft, the mother aircraft having piston engines to get off the ground and the daughter aircraft only a ramjet for speed. Ramjets need a minimum speed to start (quite high, but achievable for WW2-era aircraft – exact speed depends on the design) and then if designed right can reach up to Mach 2-3. Conceptually they’re pretty simple (the first patents were about 5 years after the Wright brothers). This would have the mother aircraft climbing to altitude and reasonable speed, with the daughter aircraft then being dropped to dive steeply and start the engine. It would then run the mission on ramjet only, and glide into land (much like the Me-163 in WW2 in some ways). That’s actually a pretty simple aircraft, probably shaped something like a Bell X-1 or Miles Messenger (fuselage shaped like a bullet, which is known to be stable supersonically, and very thin straight wings which all the experience with piston engined aircraft suggested would cause the fewest problems).
Trying to replicate a jet engine with ducted fans and piston engines can be done, but the results are pretty awful – stick “Coanda engine” into google for details. It’s a nice concept, but the actual practicalities are horrible – you end up essentially having to reinvent the jet engine to get it to work.
Specific power is the power output of an engine per unit mass – it was only when I googled it to work out why I was unclear that I realised there are other uses for the term.

breadbasketbomb
08-07-2012, 04:09 PM
Hmmm…. Best bet I would say would be a composite aircraft, the mother aircraft having piston engines to get off the ground and the daughter aircraft only a ramjet for speed. Ramjets need a minimum speed to start (quite high, but achievable for WW2-era aircraft – exact speed depends on the design) and then if designed right can reach up to Mach 2-3. Conceptually they’re pretty simple (the first patents were about 5 years after the Wright brothers). This would have the mother aircraft climbing to altitude and reasonable speed, with the daughter aircraft then being dropped to dive steeply and start the engine. It would then run the mission on ramjet only, and glide into land (much like the Me-163 in WW2 in some ways). That’s actually a pretty simple aircraft, probably shaped something like a Bell X-1 or Miles Messenger (fuselage shaped like a bullet, which is known to be stable supersonically, and very thin straight wings which all the experience with piston engined aircraft suggested would cause the fewest problems).
Trying to replicate a jet engine with ducted fans and piston engines can be done, but the results are pretty awful – stick “Coanda engine” into google for details. It’s a nice concept, but the actual practicalities are horrible – you end up essentially having to reinvent the jet engine to get it to work.
Specific power is the power output of an engine per unit mass – it was only when I googled it to work out why I was unclear that I realised there are other uses for the term.

I do not know why I should compare the design to the the Coanda 1910. The Coanda is a jet powered aircraft, albeit a bad one. The aircraft I am using looks like a normal single engine jet (most comparable a mig 21). The design is best comparable to the Stipa-Caproni flying beer can, and at this point I hope you got the image. What I am about to state is a second problem other than just engine design (which I believe I may have fixed by using a twin turbocharged -and supercharged- diesel wankel engine producing some 10 thousand horsepower or far more.); and that issue is drag. The venturi tube of both designs should increase engine efficiency, but the Stipa caproni had an issue with aerodynamic drag. I do not know the source of the drag, is it the fact that the airplane is extremely stubby, or is it something else, like the mass flow rate of the vanturi tube being to small to fill an a vacuum, or something else. To states again, it's like a Mig 21 with the engine replaced with multiple supersonic propellers inside a longer, sleeker venturi tube.

pdf27
08-08-2012, 12:27 AM
OK, I've got the idea of what you're thinking of now. As always, there's good news and bad news.

Good news is that you can forget about having to invent a supersonic propeller - using the duct design you can fit a conventional shock cone or similar to slow the airflow down to subsonic speeds before it reaches the propeller (all current jet aircraft do this too - they require subsonic airflow at the engine inlet). Further good news is that doing this with a converging-diverging nozzle will give you supersonic airflow at the exhaust and potentially very high speeds.

Bad news is that you're limited to two bad options aerodynamically. The drag problem that Caproni had is most likely due to the very high wetted area of the aircraft - it had a lot more skin than a similarly sized conventional aircraft, and hence a lot more skin friction. At high speeds this gets worse - wave drag (from shockwaves) is a function of how fat the body you're pushing through the air and how fast the cross-sectional area changes. Anything with a large cross-sectional area (required unless you're going to be getting enormous thrust per unit mass of air) will have so much drag you won't be able to break the sound barrier without additional thrust (rockets).
The second option is to accept that you're going to be getting low propulsive efficiencies (i.e. the air leaving the engine will be at very high speed indeed to get the thrust needed). This enables you to run your shaft compressor at high pressure ratios (cutting down on your air mass flow needed and hence cross sectional area of the front of the aircraft). The high pressures can then be converted to extremely high exhaust velocities, and hence relatively large amounts of thrust per unit area.

For working out your thrust, this calculator should prove helpful - http://www.grc.nasa.gov/WWW/k-12/airplane/ienzl.html . If you look for an aircraft of similar size and performance to what you're looking for (so if it's a MiG-21 use that), that will give you required thrust for the performance you want. For a MiG-21 that's 70kN on a 1.1m diameter. That gives 70kg/sec of air at a compression ratio of 4.8:1 - conveniently with a much smaller diameter. Stealing somebody else's spreadsheet (because it's too early this morning to work it out by hand and the cat is lying on me!) gives a power requirement of ~22,000 hp. In reality you will probably need more like 15,000 hp or so as for engines this big the exhaust gas provides a very significant amount of thrust.
The NASA calculator doesn't seem to benefit from increasing the temperature of the gas flowing through the nozzle, which seems odd to me - I would have expected a significant thrust benefit from burning fuel in the compressed air before it hits the nozzle. I'll have to think about why that might be if I get around to it today.

breadbasketbomb
08-09-2012, 02:23 AM
OK, I've got the idea of what you're thinking of now. As always, there's good news and bad news.

Good news is that you can forget about having to invent a supersonic propeller - using the duct design you can fit a conventional shock cone or similar to slow the airflow down to subsonic speeds before it reaches the propeller (all current jet aircraft do this too - they require subsonic airflow at the engine inlet). Further good news is that doing this with a converging-diverging nozzle will give you supersonic airflow at the exhaust and potentially very high speeds.

Bad news is that you're limited to two bad options aerodynamically. The drag problem that Caproni had is most likely due to the very high wetted area of the aircraft - it had a lot more skin than a similarly sized conventional aircraft, and hence a lot more skin friction. At high speeds this gets worse - wave drag (from shockwaves) is a function of how fat the body you're pushing through the air and how fast the cross-sectional area changes. Anything with a large cross-sectional area (required unless you're going to be getting enormous thrust per unit mass of air) will have so much drag you won't be able to break the sound barrier without additional thrust (rockets).
The second option is to accept that you're going to be getting low propulsive efficiencies (i.e. the air leaving the engine will be at very high speed indeed to get the thrust needed). This enables you to run your shaft compressor at high pressure ratios (cutting down on your air mass flow needed and hence cross sectional area of the front of the aircraft). The high pressures can then be converted to extremely high exhaust velocities, and hence relatively large amounts of thrust per unit area.

For working out your thrust, this calculator should prove helpful - http://www.grc.nasa.gov/WWW/k-12/airplane/ienzl.html . If you look for an aircraft of similar size and performance to what you're looking for (so if it's a MiG-21 use that), that will give you required thrust for the performance you want. For a MiG-21 that's 70kN on a 1.1m diameter. That gives 70kg/sec of air at a compression ratio of 4.8:1 - conveniently with a much smaller diameter. Stealing somebody else's spreadsheet (because it's too early this morning to work it out by hand and the cat is lying on me!) gives a power requirement of ~22,000 hp. In reality you will probably need more like 15,000 hp or so as for engines this big the exhaust gas provides a very significant amount of thrust.
The NASA calculator doesn't seem to benefit from increasing the temperature of the gas flowing through the nozzle, which seems odd to me - I would have expected a significant thrust benefit from burning fuel in the compressed air before it hits the nozzle. I'll have to think about why that might be if I get around to it today.

OK so here is the design in my head:

A tube shaped, delta winged, relatively small sized fighter when compared to an F-15. It has a 46 liter, 24,000 horsepower diesel wankel engine to power 4 counter rotating propellers inside the long venturi tube, each becoming more oriented towards the front from the first to the last. And at high enough speeds, the wankel engine exhaust is producing enough thrust to go to mach 1.5 or up. Well, is it less efficient than a cold war turbojet? We got the speed, aerodynamics is fixed (because the airplane I am speaking of is not a flying beer can), is it efficient enough?

pdf27
08-09-2012, 09:00 AM
OK so here is the design in my head:A tube shaped, delta winged, relatively small sized fighter when compared to an F-15. It has a 46 liter, 24,000 horsepower diesel wankel engine to power 4 counter rotating propellers inside the long venturi tube, each becoming more oriented towards the front from the first to the last. And at high enough speeds, the wankel engine exhaust is producing enough thrust to go to mach 1.5 or up. Well, is it less efficient than a cold war turbojet? We got the speed, aerodynamics is fixed (because the airplane I am speaking of is not a flying beer can), is it efficient enough? OK, so a fairly simple UAV engine using current technology can do ~250 bhp/litre (Wankel-type engine). You’re looking at twice that per litre – really pushing it and would probably be more credible if you dropped it back a bit, but it certainly doesn’t need the intervention of Skippy the Alien Space Bat.You’ve got the wrong end of the stick with the propellers. I’ll try to explain - but it’s pretty complicated so bear with me.There is a concept in aerodynamics known as choking or choked flow. This is the concept that the maximum mass flow rate past a point will be at exactly the speed of sound. To get the air to go faster, you need to suck rather than blow, and this can practically only be done by using a converging – diverging nozzle. For the thrust and frontal area you’re after, that means the pressure upstream needs to be about 4.5 times the pressure downstream. A centrifugal compressor could to this in a single stage, you’re looking at 8 or 9 for an early axial compressor.One of the oddities of this is that it really doesn’t matter what speed the upstream air goes through the compressor at – you just change the converging part of the nozzle slightly. This makes life a LOT easier, since you don’t need to worry about transonic flow in the compressor and all the losses that will give you, but instead means you need to pay attention to the air inlets (that’s what all the weird and wonderful air inlet spikes do that you see in early supersonic jets).For that power and size, you’re looking at something with similar performance to a MiG-21, maybe a bit better but with shorter range/less payload. Fuel efficiency will be worse and empty weight will be a lot higher, but it should reach the speeds you need. Personally I think your biggest problem will be engine reliability and cooling – the rest of it will probably not be a big deal.

breadbasketbomb
08-09-2012, 08:20 PM
OK, so a fairly simple UAV engine using current technology can do ~250 bhp/litre (Wankel-type engine). You’re looking at twice that per litre – really pushing it and would probably be more credible if you dropped it back a bit, but it certainly doesn’t need the intervention of Skippy the Alien Space Bat.You’ve got the wrong end of the stick with the propellers. I’ll try to explain - but it’s pretty complicated so bear with me.There is a concept in aerodynamics known as choking or choked flow. This is the concept that the maximum mass flow rate past a point will be at exactly the speed of sound. To get the air to go faster, you need to suck rather than blow, and this can practically only be done by using a converging – diverging nozzle. For the thrust and frontal area you’re after, that means the pressure upstream needs to be about 4.5 times the pressure downstream. A centrifugal compressor could to this in a single stage, you’re looking at 8 or 9 for an early axial compressor.One of the oddities of this is that it really doesn’t matter what speed the upstream air goes through the compressor at – you just change the converging part of the nozzle slightly. This makes life a LOT easier, since you don’t need to worry about transonic flow in the compressor and all the losses that will give you, but instead means you need to pay attention to the air inlets (that’s what all the weird and wonderful air inlet spikes do that you see in early supersonic jets).For that power and size, you’re looking at something with similar performance to a MiG-21, maybe a bit better but with shorter range/less payload. Fuel efficiency will be worse and empty weight will be a lot higher, but it should reach the speeds you need. Personally I think your biggest problem will be engine reliability and cooling – the rest of it will probably not be a big deal.

We are almost at the finish line. With creativity, our alien friends (I did not create them, someone in Japan did) which I will not reveal may be able to fix the engine problem, and that is only up to me or someone else who finds an application in a wankel engine that works reliably 60,000 feet in the air and at mach 1.5. As for the efficiency how less efficient is it when compared to the MiG-21, which had a range of about 1000 miles. Does this airplane have 700 miles? 500 miles?
300 miles! DON'T TELL ME 100 MILES DON'T TELL ME IT'S A PLANE THAT GOES A HUNDRED MILES ON THAT MUCH FUEL.... nah you tell me how much range it has and we should be done. Unless you give me another idea... ;)

pdf27
08-10-2012, 01:41 AM
Working at altitude isn't a problem - provided it's mainly spending it's time at that height then you just fit a higher pressure supercharger on the engine (or even just use bleed air from the big compressor you're using to provide propulsion, which would be my favoured option.
Fuel efficiency is a bit of a grey area - it mostly depends on how light you can make everything else, the problem is weight not how much you can cram in. If you go for really lightweight engines (I saw a UAV engine the other day that does 1 hp/lb - look up cubewano) and don't require it to be able to pull lots of g-force, then you could probably reach the same range. Certainly it should be able to do 500 miles without major problems.

breadbasketbomb
08-10-2012, 03:13 AM
Working at altitude isn't a problem - provided it's mainly spending it's time at that height then you just fit a higher pressure supercharger on the engine (or even just use bleed air from the big compressor you're using to provide propulsion, which would be my favoured option.
Fuel efficiency is a bit of a grey area - it mostly depends on how light you can make everything else, the problem is weight not how much you can cram in. If you go for really lightweight engines (I saw a UAV engine the other day that does 1 hp/lb - look up cubewano) and don't require it to be able to pull lots of g-force, then you could probably reach the same range. Certainly it should be able to do 500 miles without major problems.

OK so the guys working in the other planet has an interim solution to getting a jet engine. 10 years later, they get a functioning jet engine. But for working out the kinks and some ingenuity (which will remain a mystery), they extend it's service life to 30 years. Hooray!

Actually I forgot, there is still one question left. Cost.

At the time, these guys are pre ww2 level tech. I think this airplane will be a cost effective solution to not having a viable jet engine YET.

pdf27
08-10-2012, 03:23 AM
Say it's roughly twice the cost of an equivalent propeller plane, all down to the highly strung/complex engine and the development work for the supersonic aerodynamics. Or ~50% more than the equivalent MiG-21, if that's easier.

Another route to this - if they see photos of an aircraft (say a MiG-21) and get an idea of performance but don't see how. This would leave them assuming it's some sort of ducted fan powered by a piston engine - which would then lead them to develop this. Someone has a bright idea, and this then develops into a jet engine ~10 years down the line...

breadbasketbomb
08-10-2012, 05:24 AM
Say it's roughly twice the cost of an equivalent propeller plane, all down to the highly strung/complex engine and the development work for the supersonic aerodynamics. Or ~50% more than the equivalent MiG-21, if that's easier.

Another route to this - if they see photos of an aircraft (say a MiG-21) and get an idea of performance but don't see how. This would leave them assuming it's some sort of ducted fan powered by a piston engine - which would then lead them to develop this. Someone has a bright idea, and this then develops into a jet engine ~10 years down the line...

Well we are finished with the design but here is the final thought:

It is 150% the cost of the MiG-21 , though I didn't see how. Machined nickel is different from cast aluminum, I expect it to be 20% less. It's probably the materials and labor of handling them that raises the cost. Though the MiG-21 is designed to be extremely cheap as it lack a radar and other avionics. If you are saying the aircraft cost twice as much as the equivalent propeller plane, my guess is the P-47 thunderbolt. This supersonic aircraft cost 2 million dollars.

Though considering that at the time they know what a jet engine is (they just cant stand the laughable fuel efficiency), I guess it is viable. The reason i made this was because the design was supposed to be cheaper. I thought axial compressor turbines are significantly more complex than a wankel engine made of cast aluminum.

I'll hitch you in on the story:

The race we are speaking of lives on a very complex and exceptionally rare system of planets in which there are two orbits very close to each other, each having two planets of there own. Earth's orbit remains the same, and behind is Verdeckt, Vilous, and Gaia, the latter one is the enemy). Take great notice that earth is on average 15+ years more advanced than they were in the real world. World War two is fought with jets and nukes.

In the case of this airplane, it was located in Vilous, made 1982 earth time. But before that they don't even know what firearms are. Well in this story , Apollo wasn't going to the moon, it was making second and even third America should the United States lose to The Soviet Union, Verdeckt and Vilous based nation were the Calvary that will wipe out what wasn't wiped out. They needed a vehicle to do it called the Sea Dragon, which can effectively put a one million pound spaceplane into orbit for a very low cost of 50 USD per pound, and is very reusable. In 1965, Apollo commissioned a series of rovers on a scaled down rocket, 5 Sea dragon rockets (4 are spares), 20 spaceplanes containing men, weapons, a farm, and medical equipment, this counts as a single fleet and separate project. Apollo 1 is a single fleet to Verdeckt. Apollo 2 is a single fleet to Vilous. Did I also mention the probe is a unarmed robotic extremely long range M113 APC?

The first phase in Apollo 2 (like Apollo 1) is just the rocket and probe, the result are different though. It resulted in a bunch of savages running from a M113 APC. But they had swords and buckboards and stuff. Also the only Vilous inhabitant to intentionally run towards it invented the suspension for carriages, a torsion bar. That was an extremely unlikely result to meet a civilization that advanced. He just wanted to see the damn thing.

The second phase was production (which was quick), and by 1967, there are over a thousand volunteers with different roles, none of which were expected to come back to earth and they knew it. The purpose of the medical facilities was vaccination. They went over to Vilous and took there germs and language, and in exchange interested them in a new subject: the Bessemer process, successfully accepted by norther tribes (did I mention savages). Success resulted in the production line and car by 1972. then the airplane by 1975. by 1979 the four stroke engine. By 1982 the airplane I was talking about, and they broke the sound barrier.

To the humans understandings, they cannot use jet engines because the steel they produced did not withstand temperatures and was not efficient enough to save the limited oil. The needed material came from a separate territory called Tonruz which was owned by a different species and for political reasons, it's not possible to trade. It turns out there is a cold war going on in Vilous. The humans used interesting ingenuity to get them to drive cars while meeting demands which are comparatively strict. So they made the airplanes use a wankel engine, but why?

While it was inefficient, humans told them to make it out of the strongest wood- steel composites, the Sound barrier is very much real, and also to stay in it for only a certain time. The airplane was put into production after a strange modification to make it run on "something else", and as a result is a very important aircraft in 1985. BUT if the aircraft cost 50% more than a mig21, why not make a mig 21. Easy, there is a resource problem on metals between the tribes and tribes in Tonruz. only steel and wood is viable. Aluminum is also kind of an issue. The only issue is the fuel. The thing about Vilous is that all the races are almost feral, and the planet is a desert with little oil reserves. The thing is that the resources used (and i did not mention this earlier) is planted wood as a renewable resource. Even by 1982 industry does exist, but is so limited. So the races are still savages all along. As a result Apollo 2's result is near questionable. Unlike Apollo 1 which does not have any resource problem, and met countries on verdeckt which are at a state of Tranquility.

For the last words: this is highly off topic, as i am now explaining this planes history which is highly fictitious. I recommend that you do not search up Vilous or the races that live in it. Those races and above location are not my responsibility or idea. The original race is made by a person in Japan, the work is left unfinished. But you can go hear: http://verdeckt.wikia.com/wiki/Verdeckt_Wiki

At this point, it is very much off topic.

pdf27
08-10-2012, 08:58 AM
It is 150% the cost of the MiG-21 , though I didn't see how. Machined nickel is different from cast aluminum, I expect it to be 20% less. It's probably the materials and labor of handling them that raises the cost.
Thing is, the turbines in a modern jet engine are only expensive because they’re operating at extremely high temperatures to get high efficiency. If you’re willing to accept lower efficiencies, you can use simple cast nickel turbine blades – not quite cheap as chips, but getting there. Furthermore, the power loadings on turbine blades are huge compared to compressors – off the top of my head, a single HP turbine blade the size of your thumb will produce about 100 horsepower and weigh a few tens of grams. This means they can get seriously expensive per blade before any other form of engine gets cost-competitive.
The problem here is that the speeds you’re requiring force you to go for a compressor + Convergent-Divergent nozzle. That’s the front half and most of the weight of a jet engine, with the rest being sheet metal work (jetpipe + combustors) and the turbine


Though the MiG-21 is designed to be extremely cheap as it lack a radar and other avionics. If you are saying the aircraft cost twice as much as the equivalent propeller plane, my guess is the P-47 thunderbolt. This supersonic aircraft cost 2 million dollars.
Rough guess – all the electronics will be the same price, the airframe will be significantly more expensive due to what is essentially a piston + jet propulsion system.


Though considering that at the time they know what a jet engine is (they just cant stand the laughable fuel efficiency), I guess it is viable. The reason i made this was because the design was supposed to be cheaper. I thought axial compressor turbines are significantly more complex than a wankel engine made of cast aluminum.
The turbines are pretty simple provided you keep the temperatures down – it’s only when you plan to operate in gas significantly above the melting point of the metal (as is routine nowadays) that it becomes a problem. With the early Whittle-type units they just turned the temperature down until it gave an acceptable turbine blade life (IIRC ~1000 hours) and replaced the blades regularly.


To the humans understandings, they cannot use jet engines because the steel they produced did not withstand temperatures and was not efficient enough to save the limited oil. The needed material came from a separate territory called Tonruz which was owned by a different species and for political reasons, it's not possible to trade.
Seems entirely reasonable. That being the case, this is about the only way you could exceed the speed of sound. The Germans did try using what were IIRC mild steel turbine blades with active cooling at the end of WW2 (nickel being unobtainable) and they did get a working engine. Problem was it had a life expectancy of about 10 hours – at the time they didn’t care as this was significantly longer than the life expectancy of their pilots, but unless you’re in the process of fighting a war you’ve already lost that isn’t a good way to go. You could possibly improve it with very modern technology to match the early Whittle-type engines, but that’s about your limit – it was a pretty awful design!

breadbasketbomb
09-11-2012, 03:14 AM
Yes I have been thinking for this long.

And that wooden airplane part- that's hard to explain, especially how they managed to get it to supersonic speeds. But I think I know why but that was not the production model.

So what are the main problems of this aircraft right now.

It needs an engine that last at least 250 hours. It's cooling of course.

we have the airframe down
we have the engine power down since the beginning...

then I notice I did something terribly wrong. If the Mighty Earbanger/ Thunderscreech has a design speed of around transonic with a massive 4000 horsepower engine. Why can't I just use the starting engine, 12 liter wankel with 6000 horsepower. What I am speaking of is sizes. The Merlin sueprblock of similar size to the engine is not even close to half the weight of the Allison T40, let alone half the size. I have room for 2 more of these, and I can still go mach 1.5 with a single engine.

I think.

Anyhow, you mentioned earlier that increasing the weight of a vehicle or engine by 1% to to increase efficiency by 1% is a net loss. What is it a net loss of? speed, efficiency range?

because I am having a thought of making the engine a compound engine.

What do you think I could do to increase fuel efficiency now.

pdf27
09-11-2012, 12:40 PM
Increasing total vehicle weight by 1% will increase fuel burn by 1% (the ratio of lift:drag is a function of the aerodynamics - so modifying the engine won't affect this). Drag will also be increased, slightly reducing top speed (although probably by an insignificant amount - drag can increase incredibly quickly with speed when you hit the design limits).
If you increase engine efficiency by 1% at the same time, the fuel burn per unit distance travelled is the same.

HOWEVER the maximum takeoff weight is unchanged. If the empty weight of the aircraft is increased by 1%, that same weight increase must be removed from the amount of fuel (or payload) it can lift off the runway.
Hence, you will lose ultimate range (can lift less fuel off the runway), payload (can lift less weight off the runway) and possibly a tiny bit of speed depending on the exact design - this can easily be handwaved away.

breadbasketbomb
09-11-2012, 05:41 PM
what this means is that my increase in efficiency by percentage has to be higher than the increase of weight by percentage. do you have a suggestion for modification, this thing has two massive turbochargers right now.

and if I have the 12 liter wankel in a Mig-21 -ish fighter and that's it, how does it compare to the mig 21, right now without your guessed modification?

in terms of speed and efficiency. I I could remember correctly it has half the efficiency, but it can achieve the same speed. How do we improve this? more turbos?

I am literally just starting to see how this is going.

pdf27
09-12-2012, 01:34 AM
In terms of short-term power, water or methanol injection between the turbocharger exhaust and the engine inlet. This cools the gas, which then contracts and then enables you to cram more into the same size of combustion chamber and hence burn more fuel for more power. This is the same thing an intercooler does, but I don't think you're going to have space or weight for one - this is a much lighter way of doing it, but the consumption of water/methanol is high.

Another option is hybrid jet/rocket power. This can be as simple as a couple of large fireworks on underwing pods. This is mostly of value for takeoff, which is when the aircraft is at it's heaviest and needs the power most, hence military jets normally taking off using reheat (afterburner). If fired at high altitude it gives you a LOT of extra potential height, and if you're higher you can also go faster. Good altitude/speed diagram giving you an idea of what the thrust gives you here: http://www.spaceuk.org/sr53/sr53%20research.htm

Finally, you could look at air-launching from a mother aircraft (like the B-52 used to launch the US X-planes). That saves a hell of a lot of weight in climbing to altitude, allows you to optimise for high-speed flight, and gives you a lot more effective endurance - the aircraft can be airbourne and ready to launch, as if on a standing patrol, and launched very fast when needed.

breadbasketbomb
09-12-2012, 05:31 AM
This is where I start to disagree with using a turbo jet or advanced air compression, or just accepting poor performance.
Throughout this entire discussion, I have been pretty confused, so I end up with a new idea every now and then. This is not about cooling.

Well, something just popped up in my mind. I will add an airplane: the XF-84H Thunderscreech, I like to call it the Witch (you will get it if you are in your 20's and play video games).
By the time it's engine was made, it had 5850 horsepower, and weighed in at over 2000 pounds.
The airplane itself I am speaking of weighs in at 18000 pounds

The airplane we are speaking of weighs the same.

The Wankel engine that it uses has twice that power density as that engine because it is a modern 12 liter with massive twin turbos, and the same power... on cast iron. Half the weight, same power, but it is a crap load less efficient. If I made it a tandem with another wankel (forming a compound engine), the engine would nearly double in weight, but power would be increased, and because of the shear power left in the exhaust I would get a great increase in efficiency, and it would still suck compared to the turbine. However, it will be more reliable and cheaper because at the time the most advanced available engine material looked like this:

http://www.castironcookware.com/lodge-dutch-oven-loop.jpg

This is unsuitable for a turbojet because they are flimsy with this material. Wankel engines are... chunky (it may be more important than you think).

To get to the point: you suggest using exhaust gas to drive more air into the compressor. If I do that, there will be more heat in the engine and the problems arise in cooling the engine. I use a standard cooling system in the simple Tandem Compound Wankel because I do not increase the efficiency of the first engine. Instead, I used the unburned fuel and hot exhaust to run a second non combustion engine. At the time of the country making this airplane time, this is better than a complex cooling system and an efficient first engine. This is also far different than the Napier Nomad you mentioned earlier because there is not extra power shaft, or gear box, it's just another set of somewhat wider expansion chambers. It's all in one engine block, in fact.

And that is only half the story. The X 84 came from a time where the most powerful engines had the fuel economy of a Bugatti Veyron, but had roughly twice the horsepower of a modern day 2007 Fiat 500. Yet the P-51 and Spitfire were impressive sights, and they went far enough. When we are talking about my idea I feel like that it will go 300 miles an hour and fly all the way to the next McDonalds. In other words, my side of the discussion is pessimistic but confusing.

Now that I have explained the concept, The goal is to have a range of 600 miles with no external tanks, and a top speed of mach 1.5.

I am very confident in this concept, but right now, you're the king.

pdf27
09-12-2012, 12:48 PM
Errr.... no, I'm not suggesting that at all. I'm suggesting intercooling the existing turbochargers that feed the Wankel engine using some sort of evaporative cooling (Water or Methanol). This reduces both charge temperature and work required by the compressor section of the turbocharger - in turn allowing you to fit either a bigger turbocharger for more boost or have higher exhaust energy for more thrust. The cost is a bit of weight and efficiency.

Intercooling the compressor you're using to generate the supersonic thrusting air is a BAD thing - it'll significantly cut down your thrust.

breadbasketbomb
09-12-2012, 11:52 PM
Sorry, my mistake, I was thinking about cooling the turbochargers not the rotor. I used the wrong word, referring to the turbocharger as the spool of compressor blades in a jet engine.

what about the engine design.

Oh yes, and thank you for all the information you gave out and sticking in the thread, I am going to use them in the concept.

J.A.W.
03-26-2013, 01:45 AM
As a matter of interest, I'd reckon you should be checking out the Flight Magazine Archives which show Napier aero-engines, they were right up there with the last hi-po big inch aircraft reciprocating mills..

Check out the Sabre, a 36 litre H-24 sleeve valve fighter mill type-tested giving 3000+ hp @ 4,000rpm at world beatingly competitive power-per-cc & hp/kg ratios.

Napier also developed the Nomad, a very efficient [& it's still more efficient on a SFC basis than today's gas-turbines] 2-stroke Diesel aicraft engine..

Napier also did the Deltic [also a 2-stroke Diesel] for high speed heavy vehicles - express locos & fast patrol boats, so good that even the USN used them in Vietnam...

pdf27
03-27-2013, 02:29 AM
Napier Sabre: 2kW/kg bare engine
Cubewano: 1.7 kW/kg bare engine - before turbocharging, etc. so more useable in the real world.

J.A.W.
03-27-2013, 02:44 AM
Cube-a-what-now?
& has IT passed a 100hour type-test at 3,000hp?-If not, See Napier Sabre Mk VII...

The last 2-stroke G.P. race motorcycles [sadly, now banned from competition..] were reliably putting out 55hp from each 125cc [non-turbo] cylinder...440hp/Ltr.

J.A.W.
03-27-2013, 03:29 AM
This mob have some high power to weight mills too... www.4x4tuff.com/ctsme8.html

pdf27
03-27-2013, 12:34 PM
Cubewano (http://www.cubewano.com/)- listed because they're typical of modern rotary engines intended for UAVs, and aren't too highly stressed. It'll burn just about any fuel, has no boost and about 2 moving parts. Something like Liquid Piston (http://liquidpiston.com/) would also be a possibility - that's more like what we'd end up with if we tried to design an internal combustion engine from scratch, rather than based on the first successful technology out there (steam engines).

Given the particular context of this thread (a non-earth based civilisation with only propeller driven aircraft) there is no reason to assume that they will have started out with piston engines. No jet engines is a given, and since a turbocharger is almost identical to a Jet engine in principle (and a supercharger is close behind) that implies little or no boost. Rotary engines make very high power to weight ratios easier, and are recognisably different from Earth technology which would be important in a book.

If I was going for extreme piston engines, I'd have either suggested a Rolls-Royce Crecy (bench tests gave potential for 5,000 BHP from 860kg before it was cancelled!) or a Formula 1 engine (about 6kW/kg)

J.A.W.
03-27-2013, 06:01 PM
Forget about F1 engines, they are ludicrously complex & expensive for what they make power-wise, in fact the RR Crecy would be a good basis for up-dating [with 21st century metallurgy/computer engine management],being a 2-stroke.

4-strokes are inherently 'lazy' & have to be revved very high [F1] or pressure boosted [ by pumps &/or chemically] to make power, but then have mass/complexity/cost issues.

Consider the chainsaw...

A chainsaw has to have a high power to weight ratio, be manually heft-able,capable of operating at various attitudes/angles, & cost effective..

Honda is an ideologically driven pro-4-stroke company, but even they haven`t been able to make a viable 4-stroke chainsaw, since a low mass,compact dry-sump,turbo 4-stroke is very difficult to make on a cost effective basis to compete with the current 2-strokes.

The Wankel [technically not a rotary -see Bentley BR 1] is interesting, & running on a 2-cycle does offer good power density, but - [ as can a high performance 2-stroke using a pulse-tuned exhaust system] may be seen as a mechanical 1/2-way stage between reciprocating mills & true turbines..

tankgeezer
03-27-2013, 06:40 PM
I prefer the Stirling closed cycle engine. The orbital rotary engine uses far too much fuel.

J.A.W.
03-27-2013, 07:31 PM
Alas, yes..Toyo Kogyo [Mazda] recently dropped their Wankel engines from production - after doing their best with them for decades..

SFC efficiency & max power density are hard to get in the same machine, the most fuel efficient are the [very] big 2-stroke ship Diesels...
... but the Napier Nomad [also 2T Diesel]-is likely still the most SFC efficient mill to fly..

What is the best Sterling cycle mill performance [in metal, -not in theory] achieved, power to weight-wise?

pdf27
03-28-2013, 02:24 AM
The Wankel [technically not a rotary -see Bentley BR 1] is interesting, & running on a 2-cycle does offer good power density, but - [ as can a high performance 2-stroke using a pulse-tuned exhaust system] may be seen as a mechanical 1/2-way stage between reciprocating mills & true turbines..
I'm well aware that rotating radial engines are (realistically were - nobody has made an engine like that for almost a century, for VERY good reasons) known as rotary engines. However, Wankel refers to a specific type of engine, and the derived versions of it running a slightly different cycle are known as Rotary engines nowadays. Liquid Piston isn't a Wankel cycle but is mechanically similar, and is known as a rotary engine (in much the same way as piston engines typically follow the Otto, Diesel or Rankine cycles).

pdf27
03-28-2013, 02:25 AM
I prefer the Stirling closed cycle engine. The orbital rotary engine uses far too much fuel.
Take a look at the Liquid Piston link I put in there - the problems aren't inherent to Rotary engines but to the particular implementation. Conceptually you can get pretty close to the Carnot limit, although how close you end up in practice is as yet unclear...

J.A.W.
03-28-2013, 04:00 AM
Wankel intended his unit to be a true rotary [ engine revolves around grounded crankshaft] to utilize air-cooling, but referred to his production units as being a rotating piston design..

If there is any merit in the 'Liquid Piston' set-up, I `d wonder if Toyo Kogyo hasn't checked it out..

Incidentally, Mazda pushed the technically improper 'rotary' nomenclature - as a way of avoiding paying royalties on the Wankel name..

J.A.W.
03-28-2013, 08:56 PM
Page 93, July 25th 1946 edition of Flight ; [available in on-line archive] ,
Has an interesting plan of a proposed 500+ mph Napier Sabre powered fighter using advanced ducting methods..

tankgeezer
03-28-2013, 11:07 PM
The citation of the Stirling engine was just a joke on my part,(and a rather obvious one I might add ) although they would be appreciative of the increase in power available in the lower temps at altitude, the Stirling of the 40's would be more at home in a river barge. They were used in shipping for awhile, but the room required for them took space needed to revenue producing cargo. The pistons and displacers moved slowly enough for people to ride on while in operation.
As to the Wankle, even after the the problems of uneven wear on the inner surface of the rotor, and the apex seals were finally resolved, it still used too much fuel. Mazda would have been better off getting a license to use John Marshall's Tri-Dyne rotary engine. Since the Tri-Dyne wasn't around in the 40's it wouldn't be much help in War time aviation.

Nickdfresh
03-29-2013, 01:38 AM
Alas, yes..Toyo Kogyo [Mazda] recently dropped their Wankel engines from production - after doing their best with them for decades..

SFC efficiency & max power density are hard to get in the same machine, the most fuel efficient are the [very] big 2-stroke ship Diesels...
... but the Napier Nomad [also 2T Diesel]-is likely still the most SFC efficient mill to fly..

What is the best Sterling cycle mill performance [in metal, -not in theory] achieved, power to weight-wise?

Mainly due to emissions in the U.S., but yes, fuel efficiency is a big problem despite the excellent power output to displacement ratio. The Wankel rotary also received a bad rap in the United States because the turbo-charged variant of the last gen of the RX-7 tended to destroy itself after about 60K. They pulled it out of North America yet solved the problem and continued to sell them in Japan for a while after. They had the RX-8 here, but the horsepower was dampened again by emissions whereas the car had about 20 more horsepower in Japan...

J.A.W.
03-29-2013, 02:10 AM
For some reason the automatic Rx8 was detuned too, - but I really liked that triple rotor howling sound made by the 20B Rolex championship sports-racing Rx8s..

Nickdfresh
03-29-2013, 12:06 PM
For some reason the automatic Rx8 was detuned too, - but I really liked that triple rotor howling sound made by the 20B Rolex championship sports-racing Rx8s..

They were fun to drive, I think Mazda was shying away from the super-car thing as the last of the RX-7's were virtually on par with Corvettes and more expensive Euro performance vehicles. The RX-8 was marketed as a nice, fun car to drive with real world performance. But it wasn't powerful enough for enthusiasts and the fuel economy was abysmal. Also, Mazda went to their MazdaSPEED entries for the turbocharged Mazda3 in the U.S. as their performance niche making the RX-8's obsolete. And many people who would have bought an RX-8 simply opted for the Miata. I think they're still working to comeback with a Rotary powered sports car in the future...

tankgeezer
03-29-2013, 02:39 PM
There were some Corvettes that had Wankel engines in them, though they never made it to a showroom. The XP-895,(1973) an outgrowth of the XP-882 program (a Corvette with a transverse V-8 Mid-Engine design) The 895 used a pair of joined 2 rotor engines from another Chevy product program. This was later changed to the XP-897GT which used a single 2 rotor engine, along with some other design changes. The entire program was tossed out as the fuel shortages of the early 70's made it unlikely to be a sales success.

pdf27
03-30-2013, 02:44 AM
If there is any merit in the 'Liquid Piston' set-up, I `d wonder if Toyo Kogyo hasn't checked it out..
They've probably taken a look and left it at that for now. As with any prototype engine, there are enormous hurdles to be overcome before you can even think about commercialisation. Far better to have them continue to work on it, and license the design if it ends up working moderately well in order to refine it for mass production.
Personally I suspect Mazda will never use it for a road car (or if they do, it'll be a niche model for remote areas) - given the trajectories of oil prices and battery performance, in 20 years or so I think cars will be overwhelmingly electric. It does have potential use in aviation though, where weight is critical.

J.A.W.
03-30-2013, 04:42 AM
Electrickery...nah..battery power is a dead-end,... heavy, limited range & long re-charge times..useless..

Unless maybe an electromotive type, with a high-efficiency liquid/gas fuelled ceramic 2-stroke turbo-diesel engine running at max torque - as generator to electric drive..

..& maybe with an electro-regenerative motor at each wheel, like Porsche drew up over a century ago..

Or a NASA surplus, deep-space probe, plutonium fuel-cell electro-drive..

tankgeezer
03-30-2013, 10:11 AM
Back to the Stirling engine we go, even Sears, and Roebuck sold them in the latter 1800, they did well for field engines on the farm, and in mining. Sears even sold a solar version having a cast iron collector at the top. modern incarnations of the Stirling might well do for a car. (as long as no one wants it to go very fast. )

pdf27
03-31-2013, 12:47 PM
Electrickery...nah..battery power is a dead-end,... heavy, limited range & long re-charge times..useless..
Recharge time has been demonstrated in the lab to be a product of microstructure, not chemistry. They've demonstrated on a benchtop scale the technology to recharge a car with ~300 miles of range in under a minute, for a total system weight very comparable to current petrol-based systems. Given the throttling losses IC engines experience, once you get the charge speed and cost right (which is now a matter of engineering, not science), electric cars will always be cheaper to run.

tankgeezer
03-31-2013, 02:27 PM
I wish they were cheaper to buy, for my general inclement weather needs, a battery only car would do a good job. The price is much too high at present to make a purchase worthwhile. I appreciate the technology, and all of the present troubles one may avoid by driving an all electric, (and can only wonder at what future troubles they may present us) but its still too costly. I have hopes that the GM Highwire will someday be available at something approaching a realistic price, would have one in a heart beat, fuel cell clean, but no range limitation.

pdf27
03-31-2013, 02:55 PM
Prices are coming down pretty rapidly, the likes of the Nissan Leaf are still pretty expensive but that's always the case for a first prototype. Give it another decade and they'll be on a par with combustion engines.

tankgeezer
03-31-2013, 04:12 PM
Prices are coming down pretty rapidly, the likes of the Nissan Leaf are still pretty expensive but that's always the case for a first prototype. Give it another decade and they'll be on a par with combustion engines.
The Leaf is available here in the mountains, I had given it a look over. Would be fun to have one someday.

J.A.W.
03-31-2013, 05:59 PM
Wonder what hill climbing power usage will do to battery endurance/car range?

I 've heard proposals that quick swap battery packs will become available, at gas stations, or maybe Hydrogen fuel cells..

How does running other power ancilliaries [ heating/aircon/lights/sound systems & etc] affect battery car range?

Maybe there is a Tesla wireless energy transfer system coming...kinda like a slot-car - but without the need for direct electrode [source-to-pickup] contact?

tankgeezer
03-31-2013, 10:48 PM
Like any other finite power source, the more you use, the faster it's depleted. They don't have a great deal of range to begin with, maybe 100 miles best conditions, start using hvac, wipers, lights, etc. and that would lessen the useful range considerably. The brakes should be regenerative, like dynamic brakes on a locomotive, and should recharge the battery pack as you go along. Just found a video about it, so if you like, have a look.
http://youtu.be/0_4fvEwXros

although when I think about it, one of these would be fun too.. http://youtu.be/ZFcanpNarEg