Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Skyguns MKII on September 05, 2013, 01:20:26 AM
-
Going to school for my FAA certificate and though I know the basics I still have the "gotta know it all" feeling. SO! pros and cons of the following
opposed
V block
In-line
reciprocating
-
Going to school for my FAA certificate and though I know the basics I still have the "gotta know it all" feeling. SO! pros and cons of the following
opposed
V block
In-line
reciprocating
:airplane: Not quite sure what your question is regarding your list of engines, but assuming they are asking you to evaluate each of the engines, here is my comment:
#1- Opposed engines are engines which have there cylinders on opposite sides of the crankcase and is the engine of choice of many manufactors of light aircraft such as Cessna, Piper and Beechcraft-Raytron. First appeared on the aviation sence in the forties, with the Cessna 120, Luschome 8A, Ercoupe, Stinson, Taylorcraft and probaley some others that I have forgotten about. Good reliable engine, no heat problems that I ever heard about with would warrant an AD from the FAA.
#2- There were a couple of different aircraft which tried the V-block engine, such as those in a car, but because of weight, due to liquid cooling and weight of the engine, as far as I know, neither one ever went to production.
#3- Inline engines have a long history in aviation, starting back in the mid or early 1900's, used almost on ever aircraft in WW1 and the in-line design went on to power a whole host of aircraft, Fairchild PT-19', 26's, P-51's, Spitfires and some of the Geman and Japanese aircraft also used the inline engine. Some were cooled in flight with a coolant liquid, and some were cooled with forced air thur the cylinder arrangement. Top end speed with the in-lines were good to excellent, but not much climbing power when pitted against the more powerful Radial engines.
#4- Radial engines are probabley the best all around design for a number of reasons. Power output vs weight, ease of cooling, simple design, ease of maintaince. Untill the on slaught of jet engines, ever aircraft which carried more than 3 people, since the late 30's, were powered with Radial engines, the smallest being a "Kinner", 5 cylinder on the PT-22 Rayans which trained a lot of pilots in the 30's and 40's to the biggest radial ever built, the Pratt & Whitney R-4360 engine which powered the giant B-36, XC-99, Boeing 377 Stratocruisers which the airlines used, the KC-97's, B-50's just to list a few of the aircraft which used this engine. Serveral of these aircraft had heat problems with the rear bank of cylinders, such as the B-36, B-29, B-50 and the Boeing 377. Even the Lockheed 1049G "Constellation", i.e. C-69 had cooling problems.
(http://i1346.photobucket.com/albums/p684/earl1937/220px-ULPower_UL260iopposedengine_zps5f720be2.jpg) A opposed engine.
(http://i1346.photobucket.com/albums/p684/earl1937/220px-Ranger_L-440_zps9f96ceb6.jpg) A inline, inverted engine.
(http://i1346.photobucket.com/albums/p684/earl1937/800px-Pratt_amp_Whitney_R-4360_Wasp_Major_1_zps35929bd4.jpg) The largest radial engine ever mass produced, had 28 total cylinders, arranged in 4 banks of 7 cylinders in each bank.
I hope this might of help to you, if not, be more specific about your question and I might could help you! :salute
-
#2- There were a couple of different aircraft which tried the V-block engine, such as those in a car, but because of weight, due to liquid cooling and weight of the engine, as far as I know, neither one ever went to production.
Except all those aircraft that did use V-blocks, because they give the same power but in a much shorter design.
Spitfires, Mustangs, Hurricanes, 109s, Yak 9, Pe-2, Mig 7, Beaufighter, Hawker Tempest, Bf110, He111 etc. The air in WW2 was full of V12s.
#3- Inline engines have a long history in aviation, starting back in the mid or early 1900's, used almost on ever aircraft in WW1 and the in-line design went on to power a whole host of aircraft, Fairchild PT-19', 26's, P-51's, Spitfires and some of the Geman and Japanese aircraft also used the inline engine. Some were cooled in flight with a coolant liquid, and some were cooled with forced air thur the cylinder arrangement. Top end speed with the in-lines were good to excellent, but not much climbing power when pitted against the more powerful Radial engines.
Most WW1 aircraft used the Rotary Engine.
Inline motors work just as well as a V but as the motor gets longer (More/larger cylinders), the strain on the Crank gets a lot higher. You then have to bulk it up which in turn saps some of the power gained. V-blocks keep the run shorter which reduces the spinning mass of the motor.
-
What was the advantage to having an inverted V design?
-
What was the advantage to having an inverted V design?
It allowed better views for single seat fighters of the time.
-
The question is a bit vague, but some issues are addressed in what has become the following wall of text. Hope it's useful.
There's a little ambiguity in the world of aircraft about what an inline engine is as the term seems to be interchanged quite freely with V engines. The history of this might be to distinguish them from radial engines, while in the automotive industry they are distinctly different things. A V engine has essentially two banks of inline engines sharing a common crankshaft.
One thing you notice about many V engines is that the same angle keeps suspiciously popping up. The Rolls Royce Merlin and the Griffon, the Allison V-1710, Daimler-Benz DB 601 and 605 and many others all use a 60° angle between the banks. This is not insignificant, for a V12 engine the 60° bank gives a theoretically perfect primary and secondary balance: in other words the reciprocation of the pisons, con rods and the rotation of the crank cancel each other out harmoniously (A straight six also has this attribute and many WWI aircraft employed this format). This is a very different situation from a (Ford, I think it is) 90° V8 with a flat plane crank which produces a vertical oscillation twice the frequency of the revolutions, so the engine literally wants to bob up and down in its mountings. This has an obvious advantage in terms of reducing vibration and stress on the engine, and hence increasing reliability.
One restriction of the 60° bank is that it does limit the space available for the fuelling system. This is why many Ferarri engines have a bank of 72°, the needs to improve aspiration overode the balance issue.
Additionally regarding perfect primary and secondary balance with twelve cylinder engines, there is another bank angle which also has this benefit: 180°. The Hawker Typhoon and Tempest essentially have two 180° V12s on top of each other in a shared casing. These engines are called horizontally opposed engines but not necessarily boxer engines. The way to distinguish is that in V engines (of any angle) two connecting rods typically share a big end bearing while in a true boxer engine each connecting rod has its own bearing.
Any boxer engine with six cylinders or more will also have perfect primary and secondary balance (VW Beetle for example does not, it has the same secondary balance characteristics as an inline 4). Many post war civil aircraft use a six cylinder boxer unit, which has an additional advantage regarding cooling which we will address later. Porsche has stood by the boxer engine from the first 356 right through all models of 911 and many of their racing cars including their 8-cylinder Grand Prix cars, however an interesting example is the vaunted Porsche 917 which in fact employed an air-ccoled 180° V12 and NOT a boxer engine.
This brings us to another interesting point about engines: positive net torque output. If you imagine a cyclist doing his thing, only part of the revolution of his pedals is delivering torque to the bicycle (and hence the road). As his pedal comes over the top only at about 20 degrees or so does the lever of the crank begin to deliver rotational force, at the top and bottom of the pedal rotation and all the way back up there is no positive torgque contribution, infact a negative or a subtraction from the torque is the situation. Only the momentum of the crank and his other leg keeps the whole thing rotating smoothly.
With a four-stroke engine this positive and negative torque is exasperated because each piston is only making a power stroke every other rotation. The magic number with piston engines is 7. 7 pistons never have a negative torque phase and are thus always making positive torque. Although a six cylinder engine comes very close!
All of the aircraft in Aces High have a positive torque output (including the Storch) but again consider what more firing strokes means. At low altitudes the Nakajima Homare engine with a displacement of only 32 litres and two valves per cylinder nearly matches the output of the Daimler Benz DB605 with over 35 litres of displacement and four valves per cylinder (and a superior supercharger). The 18 cylinder engine simply has 50% more power pulses per 720 degrees of revolution this explains the outputs (here is another difference between air and liquid-cooling: it is very difficult to employ a 4-valce head with an air-cooled engine and a bigger valve area makes for a more efficient output. This also weighs into the selection).
This brings us to a discussion about engine cooling. Of course a radial lends itself very well to air cooling while an inline or V engine does not. There is some merit to the famous quote that a liquid-cooled aircraft engine makes as much sense as an air-cooled submarine however it is not as simple as that. In a dive an air-cooled radial engine can actually become over-cooled which leads to temporary fuelling problems.
The biggest penalty for liquid cooling is of course the radiator which can produce an awful lot of drag. Arguably the P-51D had the best wartime solution for this in single engine aircraft. With a twin engine such as the Mosquito or the Whirlwind you have the opportunity to nest the rads in the inner wing section which is as close to an optimal solution you can find. This opportunity was missed by the Me410 design team who essentialy doubled the drag of a single engined fighter's radiators!
Many modern civil piston craft use a boxer-six which has many advantages of both the radial (air-cooled, good access) and of the V / inline: perfect primary and secondary balance.
In the end all design solutions have compromises and especially with aircraft it is often only at the flight testing phase that the true measure of the design as a holistic entity announces. The relative advantages and disadvantages of the different formats are core to these design choices.
In closing there are two interesting aircraft which switched between air-cooled radials and liquid-cooled V engines throughout their production run:
The Fw190 started as an air-cooled radial and employed a liquid-cooled V12 in the later stages of its development and the Ki-61 did the opposite, being adapted to carry a radial when the supply of V12s ran out!
-
"This opportunity was missed by the Me410 design team who essentialy doubled the drag of a single engined fighter's radiators!"
Not really. Two engines, two radiators, the Mossie and Whirlie had two radiators as well, there is no way around the required cooling area, unless you use higher engine temperatures to make a smaller radiator more efficient which to my knowledge Merlin did not use but DB did. The 410 used the standard MT recessed radiator design and not the much draggier surface mounted design e.g. Spitty used.
http://109lair.hobbyvista.com/techref/systems/cooling/f_flaps.htm
http://www.britmodeller.com/forums/index.php?/topic/234907504-messerschmitt-me-410-hornisse-hornet/
-C+
-
What was the advantage to having an inverted V design?
There was enough space for the cowl guns.
Also, Fish, most of the the Tempests had a H engine (Napier Sabre), as far as i know. Some had Bistrol Centaurus radials though.
-
Power to weight, reliability and simplicity of operation make the turbine a clear winner. Engage starter, fuel condition lever forward at specified percentage of rpm and Whoomp the turbine is running.
But for manly man airplanes you want a radial. Crack the throttle, engage starter and count 6 blades, primer on for 3 more blades where the mags are switched on. 3 more blades and she fires Bark, snort, cough...great clouds of smokr. Keep tickling the primer as you move the mixture to auto rich ( using your third arm) and if you did things right she continue to run.
Jets (turbines) are for kids.
-
Except all those aircraft that did use V-blocks, because they give the same power but in a much shorter design.
Spitfires, Mustangs, Hurricanes, 109s, Yak 9, Pe-2, Mig 7, Beaufighter, Hawker Tempest, Bf110, He111 etc. The air in WW2 was full of V12s.
Most WW1 aircraft used the Rotary Engine.
Inline motors work just as well as a V but as the motor gets longer (More/larger cylinders), the strain on the Crank gets a lot higher. You then have to bulk it up which in turn saps some of the power gained. V-blocks keep the run shorter which reduces the spinning mass of the motor.
:airplane: Not for sure what the questions are that the FAA test requires, but from what I understand, the V block engine was about automobile type engines and how they would work in aircraft. That is why I did not include all the V-block engines of WW2 era. I wish he would be more specific, then I am sure someone could answer him with something that would help.
I am certainly no expert on WW1 aircraft and engines, but, the air war was not dominated by the rotary engine.
The albatross D.I. was one of the best German and Austrian air force aircraft of the last two years of the war and was powered by a 6 cylinder, in line, water cooled engine. The Nieuport16, was a French built aircraft which did use a rotary engine, The Curtiss Jenny trainer had a 8 cylinder V-block engine.
A lot of experts which have made statements as to the best fighter of WW1, say that the German Fokker D.V11, powered by a Meacedes D-III, 6 cylinder liquid cooled, in line engine of 160HP, was the best all around fighter of the first World War.
-
Not really. Two engines, two radiators, the Mossie and Whirlie had two radiators as well, there is no way around the required cooling area, unless you use higher engine temperatures to make a smaller radiator more efficient which to my knowledge Merlin did not use but DB did. The 410 used the standard MT recessed radiator design and not the much draggier surface mounted design e.g. Spitty used.
Respectfully, I think you have missed the point.
Power to weight, reliability and simplicity of operation make the turbine a clear winner.
But you do have to factor in the fuel consumption!
-
:airplane: Not for sure what the questions are that the FAA test requires, but from what I understand, the V block engine was about automobile type engines and how they would work in aircraft. That is why I did not include all the V-block engines of WW2 era. I wish he would be more specific, then I am sure someone could answer him with something that would help.
Erm what are you smoking cos it seems like good stuff . The Rolls Royce merlin was a V block , so was the WWI RR Eagle , RR kestrel , Alison V1710, RR peregrine . These were not developed from auto-mobile engines but from the ground up for aero use.
-
This brings us to another interesting point about engines: positive net torque output. If you imagine a cyclist doing his thing, only part of the revolution of his pedals is delivering torque to the bicycle (and hence the road). As his pedal comes over the top only at about 20 degrees or so does the lever of the crank begin to deliver rotational force, at the top and bottom of the pedal rotation and all the way back up there is no positive torgque contribution, infact a negative or a subtraction from the torque is the situation. Only the momentum of the crank and his other leg keeps the whole thing rotating smoothly.
Sir, if you are describing a casual bicycle rider your statement is true. If you are described a trained bicycle racer you have completely missed the mark. The professional cyclist has shoes that clip into the peddles. This allows him to pull up, push forward, and pull back along with pushing down on the peddles. He will maintain a high rpm, 70 rpm or better and he will not have a "stroke" as you have described it but will be a "spin". There is nothing in common with a professional bicycle racer's ability to produce power and a reciprocating engine of any type. The professional cyclist using this "spin" method is also able to use more of the muscles in the upper and lower portion of the leg greatly enhancing his ability to produce more power.
-
Sir, if you are describing a casual bicycle rider your statement is true. If you are described a trained bicycle racer you have completely missed the mark. The professional cyclist has shoes that clip into the peddles. This allows him to pull up, push forward, and pull back along with pushing down on the peddles. He will maintain a high rpm, 70 rpm or better and he will not have a "stroke" as you have described it but will be a "spin". There is nothing in common with a professional bicycle racer's ability to produce power and a reciprocating engine of any type. The professional cyclist using this "spin" method is also able to use more of the muscles in the upper and lower portion of the leg greatly enhancing his ability to produce more power.
It's just an analogy Zoney. Not that type of cyclist no, just an ordinary one.
-
Sir, if you are describing a casual bicycle rider your statement is true. If you are described a trained bicycle racer you have completely missed the mark. The professional cyclist has shoes that clip into the peddles. This allows him to pull up, push forward, and pull back along with pushing down on the peddles. He will maintain a high rpm, 70 rpm or better and he will not have a "stroke" as you have described it but will be a "spin". There is nothing in common with a professional bicycle racer's ability to produce power and a reciprocating engine of any type. The professional cyclist using this "spin" method is also able to use more of the muscles in the upper and lower portion of the leg greatly enhancing his ability to produce more power.
It's not just pro cyclists either . I use clipless (not using toe clips but the type you describe) and so do most cyclists. though you still get dead spots (11-1 and 5-7 o'clock positions) in fact you don't even need clips to achieve that , if you tilt your foot forward on the upstroke you can pull up on the pedals .
-
:rolleyes: You pair have completely ruined my awesome analogy to explain positive torque output :furious
If you don't pack it in I'm rolling out the graphs and the equations, then you'll be sorry :mad:
Think Douglas Windsock going to the corner shop for tobacco on his old clunking 1920s Granddad Flyer™ and we'll be fine! :old:
-
:rolleyes: You pair have completely ruined my awesome analogy to explain positive torque output :furious
If you don't pack it in I'm rolling out the graphs and the equations, then you'll be sorry :mad:
Think Douglas Windsock going to the corner shop for tobacco on his old clunking 1920s Granddad Flyer™ and we'll be fine! :old:
Can't help it , i run a bike repair business and my own brand of bikes .
-
Shida I think your explanation was outstanding. The only issue I had was trying to visualize a 180* V.
My favorite aircraft piston engine of all time is the radial. I love all redials but especially the R-2800's. I love the way they look, sound and smell.
-
Shida I think your explanation was outstanding. The only issue I had was trying to visualize a 180* V.
My favorite aircraft piston engine of all time is the radial. I love all redials but especially the R-2800's. I love the way they look, sound and smell.
I wonder if the water cooled v12s had lower maintenance costs. I remember reading somewhere that the radials on the p-47 had a 'life expectancy' of 50 hours and after 50 hours they would just toss them and put on a new one (not exactly cost effective).
-
According to my grand farther a hurricanes Merlin was about 2 days to service after 30 hours flight time .
-
I wonder if the water cooled v12s had lower maintenance costs. I remember reading somewhere that the radials on the p-47 had a 'life expectancy' of 50 hours and after 50 hours they would just toss them and put on a new one (not exactly cost effective).
Not sure I would believe that as just about every commercial airliner before the proliferation of jets was a radial.
-
I wonder if the water cooled v12s had lower maintenance costs. I remember reading somewhere that the radials on the p-47 had a 'life expectancy' of 50 hours and after 50 hours they would just toss them and put on a new one (not exactly cost effective).
It was war, more expedient to just do an engine change than overhaul. I bet the used engines were recycled however.
If I was flying behind one of those engines knowing that my life may depend on it's performance and knowing that the engines are being abused by combat flying I'd want the engine changed on a short service cycle as well.
When I was flying the B-17 and B-24 we were getting anywhere from 200 hours to 1200 hours on an engine....with several cylinder changes along the way. The PW 1830s on the B-24 went through more cylinders than the Wright 1820s on the -17....don't know why. The biggest difference between the two is that we used the turbos on the B-24 while the B-17 didn't have the turbos operational so maybe the slight extra boost used on the B-24 had an effect. Usually we'd just notice a performance loss/rough engine and find low compression on a cylinder but sometimes they were more dramatic in their demise. On both airplanes experienced the loss of cylinder heads...on the B-17 very rough engine, big ball of fire and smoke. On the B-24 the only indication we had was some smoke that diminished with throttle reduction.
-
Not sure I would believe that as just about every commercial airliner before the proliferation of jets was a radial.
:airplane: You are correct! The first multi-engine commercial aircraft was the Ford Tri-motor in 1925, which had 3 Pratt & Whitney C-9 "Wasp" engine of 9 cylinders. Then the Boeing 247 was the next "big" airliner with 2 P & W S1H1-G Wasp engine which came in with 550 horse power. Then Douglas came onto the commercial airline business in 1934 with their DC-2, with a P & W GR-1820, a 9 cylinder engine, the fore runner of the famed DC-3/C-47/RD-1 aircraft. All these engines had their good and bad points, but overall, they were the ones which led the way for development of the more powerfull engines such as those used in WW2 on bombers and fighters. The largest engine ever mass produced was the P & W R-4360, which 4 of them powered the Boeing Stratocruiser, a international carrier aircraft, which was quite popular with the traveling public back in the 50's.
-
Don't forget the Lockheed Constellation, and the Douglas DC-7.
I don't remember it, (because I was like a year old) but I'm told that my first commercial flight was on a four engine piston powered plane.
-
Shida I think your explanation was outstanding. The only issue I had was trying to visualize a 180* V.
My favorite aircraft piston engine of all time is the radial. I love all redials but especially the R-2800's. I love the way they look, sound and smell.
You are very welcome. I have done a lot of research for a long time into piston engine design. Sorry there are no references but it is easy to check what I've said and of course read further.
A 180° V12 looks externally the same as a boxer engine. These are Porsche racing car engines but they will suffice for explanation.
Here is the crank from a 911 six-cylinder boxer engine. You can count the big end bearings, six in number (plus seven mains):
(http://i1114.photobucket.com/albums/k526/rwrk2/39807129My910906CrankaftOlliesFeb05Photo02_zps0ed2a5b1.jpg) (http://s1114.photobucket.com/user/rwrk2/media/39807129My910906CrankaftOlliesFeb05Photo02_zps0ed2a5b1.jpg.html)
and a close up of the crank:
(http://i1114.photobucket.com/albums/k526/rwrk2/39807132My910906CrankaftOlliesFeb05Photo05_zpsa69471e9.jpg) (http://s1114.photobucket.com/user/rwrk2/media/39807132My910906CrankaftOlliesFeb05Photo05_zpsa69471e9.jpg.html)
As you can see from the hole which supplies oil to the big end and the width of the bearing only one con rod attaches to each bearing
Now the famous Porsche 917's engine, here it is assembled, sans fan shroud and so on:
(http://i1114.photobucket.com/albums/k526/rwrk2/21933404MVC044S-2_zps9f6aabbb.jpg) (http://s1114.photobucket.com/user/rwrk2/media/21933404MVC044S-2_zps9f6aabbb.jpg.html)
(http://i1114.photobucket.com/albums/k526/rwrk2/21933322MVC040S_zps63eec5c1.jpg) (http://s1114.photobucket.com/user/rwrk2/media/21933322MVC040S_zps63eec5c1.jpg.html)
Looks no different externally from a boxer engine, however the crank is fundamentally different:
(http://i1114.photobucket.com/albums/k526/rwrk2/21844550Casewithdistshaftdriveshaftandfandriveinstalled_zps55ade0f3.jpg) (http://s1114.photobucket.com/user/rwrk2/media/21844550Casewithdistshaftdriveshaftandfandriveinstalled_zps55ade0f3.jpg.html)
(http://i1114.photobucket.com/albums/k526/rwrk2/21849380Crankinstalled2_zps3bb0b188.jpg) (http://s1114.photobucket.com/user/rwrk2/media/21849380Crankinstalled2_zps3bb0b188.jpg.html)
Each main bearing carries two connecting rods. This makes this engine a 180° V12 and not a boxer engine. This is significant because as stated earlier, only a 60° or 180° V12 has perfect primary and secondary balance, while any boxer engine (with an even number of cylinders) above six have this attribute. Why did Porsche then make their engine a 180°? Well it's a practicality issue basically. A high performance boxer engine usually has big end +1 number of main bearings, and the webs want to be as thin as possible. This raises crank flexing issues. I believe no one has built a boxer unit with more than 8-cylinders.
Just an addendum, the Rolls Royce and the Daimler Benz V12s have what is now an unusual con rod arrangement, instead of identical con rods which sit side by side, they have two different types one of which inserts into the other. These are often referred to as fork and blade rods:
(http://i1114.photobucket.com/albums/k526/rwrk2/MerlinConrods-2resize_zps1d0a544f.jpg) (http://s1114.photobucket.com/user/rwrk2/media/MerlinConrods-2resize_zps1d0a544f.jpg.html)
This means each bank of cylinders aligns when you view the engine from above, whereas with the Porsche 180° V12 in the 917 and many automotive engines each bank is offset slightly. This is very apparent when peering into the engine bay of some Ferraris.
About radials, if you sit down and try to design one and pay attention to an even firing order you will see why a single bank radial has to have an odd number of cylinders. Of course two banks makes it even again. Staggering the banks allows the rear bank to be cooled through the gaps of the first but after that you have problems. Increasing the number of cylinders does make maintenance very difficult but the quest for compact power generally negates those concerns.
Regarding cooling it is interesting to note that 40% of a piston engine's heat escapes through the exhaust, regardless of whether the rest of the engine is air / oil-cooled or liquid cooled.
I wrote an article over at the Bristol Beaufighter Wishlist thread which used the Bristol Hercules radial engine. This engine used sleeve valves and apparently had three times the service interval of a conventional pushrod engine. Additionally because of the porting the engine became more fuel efficient at maximum power, something which cannot be achieved with poppet valves.
Take a look at the article and please support the Bristol Beaufighter Wishlist thread, those guys have worked very hard to gather informaiton.
Here is the thread:
http://bbs.hitechcreations.com/smf/index.php/topic,255408.885.html
Here is a preiew of the remarkable crankcase and valve gear:
(http://i1114.photobucket.com/albums/k526/rwrk2/Crankcase.jpg)
I'll stop boring you all now :old:
:salute
-
You are very welcome. I have done a lot of research for a long time into piston engine design. Sorry there are no references but it is easy to check what I've said and of course read further.
A 180° V12 looks externally the same as a boxer engine. These are Porsche racing car engines but they will suffice for explanation.
Here is the crank from a 911 six-cylinder boxer engine. You can count the big end bearings, six in number (plus seven mains):
(http://i1114.photobucket.com/albums/k526/rwrk2/39807129My910906CrankaftOlliesFeb05Photo02_zps0ed2a5b1.jpg) (http://s1114.photobucket.com/user/rwrk2/media/39807129My910906CrankaftOlliesFeb05Photo02_zps0ed2a5b1.jpg.html)
and a close up of the crank:
(http://i1114.photobucket.com/albums/k526/rwrk2/39807132My910906CrankaftOlliesFeb05Photo05_zpsa69471e9.jpg) (http://s1114.photobucket.com/user/rwrk2/media/39807132My910906CrankaftOlliesFeb05Photo05_zpsa69471e9.jpg.html)
As you can see from the hole which supplies oil to the big end and the width of the bearing only one con rod attaches to each bearing
Now the famous Porsche 917's engine, here it is assembled, sans fan shroud and so on:
(http://i1114.photobucket.com/albums/k526/rwrk2/21933404MVC044S-2_zps9f6aabbb.jpg) (http://s1114.photobucket.com/user/rwrk2/media/21933404MVC044S-2_zps9f6aabbb.jpg.html)
(http://i1114.photobucket.com/albums/k526/rwrk2/21933322MVC040S_zps63eec5c1.jpg) (http://s1114.photobucket.com/user/rwrk2/media/21933322MVC040S_zps63eec5c1.jpg.html)
Looks no different externally from a boxer engine, however the crank is fundamentally different:
(http://i1114.photobucket.com/albums/k526/rwrk2/21844550Casewithdistshaftdriveshaftandfandriveinstalled_zps55ade0f3.jpg) (http://s1114.photobucket.com/user/rwrk2/media/21844550Casewithdistshaftdriveshaftandfandriveinstalled_zps55ade0f3.jpg.html)
(http://i1114.photobucket.com/albums/k526/rwrk2/21849380Crankinstalled2_zps3bb0b188.jpg) (http://s1114.photobucket.com/user/rwrk2/media/21849380Crankinstalled2_zps3bb0b188.jpg.html)
Each main bearing carries two connecting rods. This makes this engine a 180° V12 and not a boxer engine. This is significant because as stated earlier, only a 60° or 180° V12 has perfect primary and secondary balance, while any boxer engine (with an even number of cylinders) above six have this attribute. Why did Porsche then make their engine a 180°? Well it's a practicality issue basically. A high performance boxer engine usually has big end +1 number of main bearings, and the webs want to be as thin as possible. This raises crank flexing issues. I believe no one has built a boxer unit with more than 8-cylinders.
Just an addendum, the Rolls Royce and the Daimler Benz V12s have what is now an unusual con rod arrangement, instead of identical con rods which sit side by side, they have two different types one of which inserts into the other. These are often referred to as fork and blade rods:
(http://i1114.photobucket.com/albums/k526/rwrk2/MerlinConrods-2resize_zps1d0a544f.jpg) (http://s1114.photobucket.com/user/rwrk2/media/MerlinConrods-2resize_zps1d0a544f.jpg.html)
This means each bank of cylinders aligns when you view the engine from above, whereas with the Porsche 180° V12 in the 917 and many automotive engines each bank is offset slightly. This is very apparent when peering into the engine bay of some Ferraris.
About radials, if you sit down and try to design one and pay attention to an even firing order you will see why a single bank radial has to have an odd number of cylinders. Of course two banks makes it even again. Staggering the banks allows the rear bank to be cooled through the gaps of the first but after that you have problems. Increasing the number of cylinders does make maintenance very difficult but the quest for compact power generally negates those concerns.
Regarding cooling it is interesting to note that 40% of a piston engine's heat escapes through the exhaust, regardless of whether the rest of the engine is air / oil-cooled or liquid cooled.
I wrote an article over at the Bristol Beaufighter Wishlist thread which used the Bristol Hercules radial engine. This engine used sleeve valves and apparently had three times the service interval of a conventional pushrod engine. Additionally because of the porting the engine became more fuel efficient at maximum power, something which cannot be achieved with poppet valves.
Take a look at the article and please support the Bristol Beaufighter Wishlist thread, those guys have worked very hard to gather informaiton.
Here is the thread:
http://bbs.hitechcreations.com/smf/index.php/topic,255408.885.html
Here is a preiew of the remarkable crankcase and valve gear:
(http://i1114.photobucket.com/albums/k526/rwrk2/Crankcase.jpg)
I'll stop boring you all now :old:
:salute
:airplane: :banana: What an outstanding post!!! I knew that somewhere in here, we had some engine experts that could explain things better than an old throttle pusher like me! Thanks again for a great, great post!! :salute
-
I believe no one has built a boxer unit with more than 8-cylinders.
Subaru made a boxer 12 for an F1 car. If I remember right it was for Coloni, who found it to have a terrible power to weight, they decided to scrap it for v8 Fords.
-
:airplane: :banana: What an outstanding post!!! I knew that somewhere in here, we had some engine experts that could explain things better than an old throttle pusher like me! Thanks again for a great, great post!! :salute
:cheers: :salute
Subaru made a boxer 12 for an F1 car. If I remember right it was for Coloni, who found it to have a terrible power to weight, they decided to scrap it for v8 Fords.
I'm fairly sure that one was also a 180° V12 Dolby. Take a look at the small offset between the banks. With a boxer the centreline of one cylinder usually aligns exactly with the gap between two on the opposing bank. This is the problem when people (not necessarily you Dolby) see a flat engine and automatically think it's a boxer. Another interesting flat 12 was the Mercedes-Benz C291 engine. They put the induction system between the cams and the exhaust out of the top allowing the engine to sit very low in the car (normally the exhaust system needs a lot of clearance).
Boxers and flat 12s are pretty wide. When the aerodynamics became a big thing in F1 it was more advantageous you use narrower Vs.
-
This has been a very interesting and informative thread. Thank you Shida for your research and insights.
What I haven't seen discussed yet is the differences in torque and power curves among the various engine types and how that plays into aircraft design.
From a very high level both are affected by displacement which is a combination of piston size (diameter) and stroke. Inline engines typically produce maximum torque at very low RPM where V types typically produce torque at much higher RPMs. The reason is that an inline engine can, by it's design, allow fo a much longer piston stroke. I suspect though am not sure that both flat and radial engines would also produce tourque at higher RPMs due to stroke limitations.
That makes an inline engine an odd choice for an aircraft where it would seem moving the tourque curve up the rpm spectrum would be a better choice.
I've also not seen any discusson of valve design and am curious what types of valving were used in the various aircraft engines of WWII. I suspect it was kept very simple in the radial engines but am curious as the v types were introduced.
-
More good stuff Shida. :aok
I get the 180* V now thanks to your explanation. It's basically an opposed arrangement but the opposing cylinders share a common crank journal. Where a true opposed design each cylinder has it's own crank journal.
-
This has been a very interesting and informative thread. Thank you Shida for your research and insights.
What I haven't seen discussed yet is the differences in torque and power curves among the various engine types and how that plays into aircraft design.
From a very high level both are affected by displacement which is a combination of piston size (diameter) and stroke. Inline engines typically produce maximum torque at very low RPM where V types typically produce torque at much higher RPMs. The reason is that an inline engine can, by it's design, allow fo a much longer piston stroke. I suspect though am not sure that both flat and radial engines would also produce torque at higher RPMs due to stroke limitations.
That makes an inline engine an odd choice for an aircraft where it would seem moving the torque curve up the rpm spectrum would be a better choice.
I've also not seen any discusson of valve design and am curious what types of valving were used in the various aircraft engines of WWII. I suspect it was kept very simple in the radial engines but am curious as the v types were introduced.
:airplane: In the radial engines of the 40's and 50's, the valve stems were filled with "sodium" to better cool the valve. Not sure if they are still doing that now are not. Interesting quote about the in line and torque out put. I had always thought the radial engine produced more torque because of the ability to carry a larger prop. Not sure though, but other considerations had to be taken into account. Wonder how the F6F would have fared with the same engine as the P-51? Might have been faster than with the radial, but the fuseledge would have to be lengthen and I suspect that overall size played a part in using the radial because of deck space on carriers. I would think also that exposing the whole radial engine by removing all the cowling had some bearing on design, as they were a lot easier to work on from what I have been told, than in line engines. Working from carriers, I would think that acceleration created by different engine designs also played a part in it.
-
It would very much change the centre of gravity quite a bit . I wouldn't thnk it would change the length of the F4u though .
-
It would very much change the centre of gravity quite a bit . I wouldn't thnk it would change the length of the F4u though .
It probably would change the F4U quite a bit. Much of the noses length is taken up by the main fuel tank which is in front of the cockpit. Just look at how long the nose is in the super corsair with the R-4360, which I believe is shorter than a Merlin.
-
ahhh I thought the tank was behind the pilot .
-
Excellent posts nrshida! thanks.
You made some nerds very happy. :aok
-
valve stems were filled with "sodium" to better cool the valve. Not sure if they are still doing that now are not.
my car's engine has sodium filled valves. so at least in cars they still do it. (it is a flat 4 btw)
-
:cheers: :salute
I'm fairly sure that one was also a 180° V12 Dolby. Take a look at the small offset between the banks. With a boxer the centreline of one cylinder usually aligns exactly with the gap between two on the opposing bank. This is the problem when people (not necessarily you Dolby) see a flat engine and automatically think it's a boxer. Another interesting flat 12 was the Mercedes-Benz C291 engine. They put the induction system between the cams and the exhaust out of the top allowing the engine to sit very low in the car (normally the exhaust system needs a lot of clearance).
Boxers and flat 12s are pretty wide. When the aerodynamics became a big thing in F1 it was more advantageous you use narrower Vs.
Was working from memory
-
Was working from memory
No disrespect intended Mr. Dolbeh :salute
-
What was the advantage to having an inverted V design?
It allows the reduction gear to be placed lower on the engine, which in turn lowers the thrust line. This is considered aerodynamically preferable in single-engined low-wing monoplanes.
Junkers Jumo 213
(http://upload.wikimedia.org/wikipedia/commons/thumb/8/89/Jumo_213.jpg/788px-Jumo_213.jpg)
Rolls-Royce Merlin
(http://upload.wikimedia.org/wikipedia/commons/thumb/7/7d/Rolls-Royce_Merlin.jpg/800px-Rolls-Royce_Merlin.jpg)
-
It allows the reduction gear to be placed lower on the engine, which in turn lowers the thrust line. This is considered aerodynamically preferable in single-engined low-wing monoplanes.
Junkers Jumo 213
(http://upload.wikimedia.org/wikipedia/commons/thumb/8/89/Jumo_213.jpg/788px-Jumo_213.jpg)
Rolls-Royce Merlin
(http://upload.wikimedia.org/wikipedia/commons/thumb/7/7d/Rolls-Royce_Merlin.jpg/800px-Rolls-Royce_Merlin.jpg)
ahh make sense... thanks for the info :salute
-
NP :)
-
NP :)
:airplane: I just wanted you to know that I appreciate your posts and information concerning German Aircraft and engines! Each time, it generates interest on my part and I always have to go research on the subject and I always learn something! :salute
-
IIRC JUMO made a diesel areo engine that used 2 pistons per cylinder! 1 piston at the top of the bore and another at the bottom,each had it's own crank. I think the JUMO 222 but I could be mistaken.
There's also the 24 cylinder double opposed 180 degree V 12,not sure if it was successful or not but I think the Tiffie/tempest was supposed to be fitted with them.
:salute
-
Going to school for my FAA certificate and though I know the basics I still have the "gotta know it all" feeling. SO! pros and cons of the following
opposed
V block
In-line
reciprocating
*facepalm*
I started my own pursuit of an AMT certificate last year (advanced to AMT16/powerplants so I didn't have to sit around until this year), congrats. I've been staying after class til' 1am and helping all my classmates with questions lately in 19/20 (recips OH, IO-540s), and if I can pull a new/good carb (or a mixture needle and seat) for a R985 outa my arse I can get into it with the one in the test cells. Im in Reno this week, my current prof (new one I haven't had before) asked if I'd at least work 20hrs on engines.... 25hr maint alone on the stang on Saturday before I left town on Sunday stuck that fork.
Work, school and volunteering kill all my AH time lately.
-
:airplane: I just wanted you to know that I appreciate your posts and information concerning German Aircraft and engines! Each time, it generates interest on my part and I always have to go research on the subject and I always learn something! :salute
You're welcome. I thoroughly enjoy your posts on aircraft here in this small corner of the bbs. :salute
-
The question is a bit vague, but some issues are addressed in what has become the following wall of text. Hope it's useful.
There's a little ambiguity in the world of aircraft about what an inline engine is as the term seems to be interchanged quite freely with V engines. The history of this might be to distinguish them from radial engines, while in the automotive industry they are distinctly different things. A V engine has essentially two banks of inline engines sharing a common crankshaft.
One thing you notice about many V engines is that the same angle keeps suspiciously popping up. The Rolls Royce Merlin and the Griffon, the Allison V-1710, Daimler-Benz DB 601 and 605 and many others all use a 60° angle between the banks. This is not insignificant, for a V12 engine the 60° bank gives a theoretically perfect primary and secondary balance: in other words the reciprocation of the pisons, con rods and the rotation of the crank cancel each other out harmoniously (A straight six also has this attribute and many WWI aircraft employed this format). This is a very different situation from a (Ford, I think it is) 90° V8 with a flat plane crank which produces a vertical oscillation twice the frequency of the revolutions, so the engine literally wants to bob up and down in its mountings. This has an obvious advantage in terms of reducing vibration and stress on the engine, and hence increasing reliability.
One restriction of the 60° bank is that it does limit the space available for the fuelling system. This is why many Ferarri engines have a bank of 72°, the needs to improve aspiration overode the balance issue.
Additionally regarding perfect primary and secondary balance with twelve cylinder engines, there is another bank angle which also has this benefit: 180°. The Hawker Typhoon and Tempest essentially have two 180° V12s on top of each other in a shared casing. These engines are called horizontally opposed engines but not necessarily boxer engines. The way to distinguish is that in V engines (of any angle) two connecting rods typically share a big end bearing while in a true boxer engine each connecting rod has its own bearing.
Any boxer engine with six cylinders or more will also have perfect primary and secondary balance (VW Beetle for example does not, it has the same secondary balance characteristics as an inline 4). Many post war civil aircraft use a six cylinder boxer unit, which has an additional advantage regarding cooling which we will address later. Porsche has stood by the boxer engine from the first 356 right through all models of 911 and many of their racing cars including their 8-cylinder Grand Prix cars, however an interesting example is the vaunted Porsche 917 which in fact employed an air-ccoled 180° V12 and NOT a boxer engine.
This brings us to another interesting point about engines: positive net torque output. If you imagine a cyclist doing his thing, only part of the revolution of his pedals is delivering torque to the bicycle (and hence the road). As his pedal comes over the top only at about 20 degrees or so does the lever of the crank begin to deliver rotational force, at the top and bottom of the pedal rotation and all the way back up there is no positive torgque contribution, infact a negative or a subtraction from the torque is the situation. Only the momentum of the crank and his other leg keeps the whole thing rotating smoothly.
With a four-stroke engine this positive and negative torque is exasperated because each piston is only making a power stroke every other rotation. The magic number with piston engines is 7. 7 pistons never have a negative torque phase and are thus always making positive torque. Although a six cylinder engine comes very close!
All of the aircraft in Aces High have a positive torque output (including the Storch) but again consider what more firing strokes means. At low altitudes the Nakajima Homare engine with a displacement of only 32 litres and two valves per cylinder nearly matches the output of the Daimler Benz DB605 with over 35 litres of displacement and four valves per cylinder (and a superior supercharger). The 18 cylinder engine simply has 50% more power pulses per 720 degrees of revolution this explains the outputs (here is another difference between air and liquid-cooling: it is very difficult to employ a 4-valce head with an air-cooled engine and a bigger valve area makes for a more efficient output. This also weighs into the selection).
This brings us to a discussion about engine cooling. Of course a radial lends itself very well to air cooling while an inline or V engine does not. There is some merit to the famous quote that a liquid-cooled aircraft engine makes as much sense as an air-cooled submarine however it is not as simple as that. In a dive an air-cooled radial engine can actually become over-cooled which leads to temporary fuelling problems.
The biggest penalty for liquid cooling is of course the radiator which can produce an awful lot of drag. Arguably the P-51D had the best wartime solution for this in single engine aircraft. With a twin engine such as the Mosquito or the Whirlwind you have the opportunity to nest the rads in the inner wing section which is as close to an optimal solution you can find. This opportunity was missed by the Me410 design team who essentialy doubled the drag of a single engined fighter's radiators!
Many modern civil piston craft use a boxer-six which has many advantages of both the radial (air-cooled, good access) and of the V / inline: perfect primary and secondary balance.
In the end all design solutions have compromises and especially with aircraft it is often only at the flight testing phase that the true measure of the design as a holistic entity announces. The relative advantages and disadvantages of the different formats are core to these design choices.
In closing there are two interesting aircraft which switched between air-cooled radials and liquid-cooled V engines throughout their production run:
The Fw190 started as an air-cooled radial and employed a liquid-cooled V12 in the later stages of its development and the Ki-61 did the opposite, being adapted to carry a radial when the supply of V12s ran out!
This is an excellent post with excellent information, thank you.