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#1
06-08-2011, 08:34 PM
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28 mm Hg is a pretty severe vacuum... I suspect that you mean 28" Hg, which would be almost atmospheric pressure, roughly what you'd expect for a naturally aspirated engine running WOT at sea level on a standard day. Actually, you'll find that because something like an O-360 is naturally aspirated, it's more likely to tolerate WOT operation than a supercharged or turbocharged engine because the manifold pressure (and therefore the power) simply lapses away as you climb. (Of course, a lot of GA aeroplanes don't climb very well, so YMMV, especially if you subscribe to the old-fashioned view that takeoff = 1 minute unless something has gone wrong.) Equally, you risk engine failure at all times. Even before you start the engine (which is why you should treat all props as live, because magnetos can fail ON). You should never fly an aeroplane into a situation in which losing an engine will leave you with no options, because as Chuck Yeager wisely advises: Always leave yourself a way out. So I would modify your first statement to say that "Otherwise you increase risk having the engine fail beyond that assumed during certification". This increase might well be pretty small, especially if the engine has a long overhaul life and you only misbehave very infrequently. Indeed, if you're prepared get the engine overhauled more frequently than the nominal TBO then you may actually be able to charge about the sky WOT all the time and still have a very safe engine. Does this mean that you can ignore the limits? Of course not. But it's important to understand what the limits are about. They're intended to deliver acceptably high reliability at the end of the certified overhaul life of the average engine, based upon a set of usage assumptions. This means that the same engine might have very different ratings for different applications. For example, given the same total number of flying hours, if you were going to fly lots of short sorties, you'd spend a higher proportion of each flying hour at takeoff power than if you were going to fly a smaller number of longer sorties. You'd therefore feel comfortable in allowing a more aggressive takeoff rating in the latter case than in the former. If you've got a short duration manifold pressure limit, a naturally aspirated engine, and a reasonably good power:weight ratio, you may well find that you can actually operate the aeroplane WOT from takeoff to top of descent, without exceeding the limits, because the aeroplane climbs fast enough that the manifold pressure has lapsed to less than or equal to the maximum continuous rating before the time limit is exceeded. Something like a GTSIO-520 might be a bit less forgiving, but if you look at the TCDS, you'll find that the manufacturer helpfully just flatrated it such that the takeoff power = max continuous. Engineers do this because it is generally assumed that pilots can't be trusted to obey the limits in the Pilot's Notes. Sad but true. Now, actually AFAIK these engines didn't have the best reliability record in the world, but that was more due to how people operated them in the cruise than due to people charging around with all the levers rammed into the firewall. If you go to the average flying school in the UK, at least in my experience, most people will have no idea what the actual limits for the engines in their knackered old Cessna 150s and 152s are. They'll almost all be flying the aircraft outside of their certified weight & balance envelope (indeed, when I did my skill test, the examiner from the CAA, who was 6 ft tall and not exactly thin, looked over my shoulder as I performed the weight & balance calculations and told me that he weighed 4 stone - which made us "legal" - to which the response was of course "yes sir", given that I wanted my PPL). Very few of them will perform as well as the book says they should, and a lot of the time they'll be "cruising" with the throttle crammed into the firewall (for the first few weeks of my PPL I actually had the Cessna throttle shape embossed into my hand...). None of this is good, but it is reality. People get away with it because the engines are pretty much agricultural (and the airframes are forgiving). They drink fuel and oil at a prodigious rate, they have a pretty low piston speed, are naturally aspirated and actually quite heavily built. That O-360 makes about 180 bhp, which is only 0.5 bhp/cubic inch. The O-360 has a stroke of 4.375 inches and turns at a maximum of 2700 rpm. This gives a mean piston speed of 1968 feet per minute. The TBO is about 2000 hours. An early Merlin on 100 octane fuel had a combat rating of about 1300 bhp from its nominal 1650 cubic inches, which is 0.78 bhp/cubic inch. Late war engines on 150 grade were putting out about 2050 bhp for war emergency, which is almost 1.25 bhp/cubic inch. The Merlin has a stroke of 6 inches, and turns at a maximum of 3000 rpm, giving a mean piston speed of 3000 feet per minute. The nominal overhall life of a a fighter Merlin was 240 hours at the start of WWII, increasing to 300 hours (360 for twins) at the end. A substantial proportion of engines didn't make it to their nominal life. [I've left power:weight out of this equation because otherwise we risk a chart war over different engine dash numbers and mod states for different power ratings, resulting in rather different weights, not to mention the secondary argument about the weight of the Merlin's cooling system. But I think it's probably fair to say that the Merlin's installed power:weight was also a bit better than that of the O-360.] The military would accept rather higher accident rates in wartime than anybody (regulator, manufacturers, pilots) would accept for GA flying in peacetime. So if you wanted to match the engine failure rates without de-rating or changing the usage schedule you'd probably end up with considerably shorter overhaul lives. The fact is that the margins in GA are sometimes pretty generous. A couple of renewals ago, I had to fly off some hours, so I bashed the circuit in a PA-38. It was a beautiful sunny day, about 15ºC with some reasonably strong thermals and quite large cumulus development; I rather regretted not being in a glider. The engine was sometimes a little sluggish when I opened up to touch & go, but nothing dramatic. The next day I went in to the flying school to do some more hours and got asked all manner of pointed questions about whether I had checked the carb heat before I flew, which of course I had. It turned out that some time after I checked it, the cable broke, and I'd been flying touch & goes for probably the best part of an hour without it in almost perfect carb-ice conditions. Does this mean that you can get away without using carb heat? Certainly not. But it illustrates the fact that failure to do so doesn't cause instant/rapid, guaranteed engine failure (as it does in some flightsims, such as X-Plane). It just increases your exposure to risk. The point here is that IRL there is no re-fly button. This dramatically changes the way in which the average person will behave. If you've got a 1% chance of having to hit re-fly because of questionable decision, most people will shrug their shoulders and press on. Swap that out for a 1% chance of actually being killed, and a lot of people would change their behaviour. For example, it's a legal requirement in most places that you wear a seat belt when travelling by car. But even in places with really bad road traffic accident rates, most people would expect to manage more than 100 journeys between even minor crashes. To put it another way, imagine for a moment that 1c make the Wellington flyable in a future expansion. IRL, RAF bomber command sometimes suffered a 10% loss rate. This was unsustainable, both for reasons of morale (given that the probability of surviving a tour was therefore pretty low) and also for the simple practical reason that it was difficult for the training organisation to produce sufficient crew to replace those losses. Very few people would want to step into a bomber pilot's shoes IRL. But if you look at the way most people fly online, they'd consider a 10% loss rate per sortie to be somewhere between good and excellent (though they'd find the actual flying to Germany and back very very boring, given that almost 90% of the time nothing much would happen, and they'd probably bomb an empty field due to the limitations of their navigational abilities). Quote:
It seems to me that this document is largely aimed at lawsuit avoidance. I'm not saying that the information it contains isn't valid & important, but we're really talking about different orders of magnitude of safety margin from those associated with WWII aircraft and engines; compare and contrast with the nominal overhaul life of a Merlin. Quote:
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I get the strong sense from reading accident reports that quite often people get themselves killed after putting their head into the tiger's mouth dozens or even hundreds of times, probably without even knowing that was what they were doing. Some people smoke for a lifetime and don't get lung cancer. Some people never smoke and do. Likewise, some people do stupid things with aeroplanes for a lifetime and get away with it, and some people are just downright unlucky, and get killed through no fault of their own. The latter group are thankfully in a tiny minority, and the size of that minority is subject to reduction via the application of what may broadly be termed "engineering methods". But it's very hard to prevent people from killing themselves through stupidity, because idiots are both persistent and ingenious. I'm at an entirely post graduate university. At a minimum, everybody here has at least a BSc; a substantial proportion have enough degrees to make a rudimentary thermometer, and most speak multiple languages. So these are clever, well educated people. But an amazing proportion of them smoke. Wandering around the place, you'll see them clustered outside doorways sucking on their cancer sticks. Even outside the healthcare building, where there are so many smokers that they've had to put up signs to remind them not to litter the place with cigarette butts. Not that they seem to take much notice. That basically sums up the general problem with risk. Once things get safe enough that people don't see their peers dying around them as a consequence of questionable risk management, they tend to just go with the flow and get into bad habits, even if they objectively understand that they're taking risks. By the time the population of post-graduate smokers start to suffer an increased cancer rate, not only has the damage been done, but a lot of them will have become so habituated to smoking that they'll have real difficulty stopping, because of course by then their friends will contain a disproportionate number of smokers, and if they quit then they'll be left alone whilst the smokers all go outside to suck their cancer sticks. I've watched this happen to several of my friends. They start smoking, then all their friends smoke, their girlfriend smokes, and so when they quit they suddenly find their whole peergroup basically ostracises them for a large amount of the time whilst they all go outside to smoke. So unless a majority of the group decides to quit, they can't make it stick. Also, people are generally happy to take a large number of small risks (for the same total risk exposure) than a small number of big risks. So the smokers will happily gradually erode their life expectancy one cigarette at a time, but if you could arrange to lump even about a year's worth of smoking risk into one event, they'd probably feel much less comfortable. I suppose this is due to perceived variance. In a similar way, some pilots will happily take lots of small risks (e.g. pushing decision heights a little), despite the fact that if you re-arrange the overall risk into one big hit (e.g. by saying, "if you guarantee never to take this small risk again, I'll give you a one-time-only get-out-of-jail-free-card to fly under/through Tower Bridge, the Eiffel Tower or some other suitably dramatic landmark of your choice - you can even do it upside down if you want!") they'd feel very uncomfortably about taking it. Overall, aviation safety has now reached a point where a lot of people do questionable things without seeing consequences, and so they build up bad habits, and don't feel uncomfortable about them. I've seen people at some gliding clubs move powered aeroplanes by pushing or pulling on the prop. It makes me feel extremely uncomfortable. Especially when I challenge them and they say things like "It's OK because I checked that the switches in the cockpit were off". In fact, the people who do behave sensibly are made to feel uncomfortable because they're abnormal. Walk out to a club aeroplane wearing a flying suit, flying boots, gloves and a parachute, and people will make snide comments. I think that at some level it reminds them of their own mortality. Personally, I've never used my parachute, and I hope I never will. The flying gloves are a pain most of the time. But if the aeroplane were to catch fire, the gloves would protect my hands, giving me much more time to get out, and if I used my parachute then the boots greatly reduce the chances that I'll break an ankle on landing. Therefore I'll gladly suffer the inconvenience 99.999999% of the time, just in case one day I find myself on the 0.000001% flight. I'll also actually wait 2-3 minutes after a jet airliner has landed before using the same runway to takeoff, even if the controller moans at me, because clearance to takeoff does not magically guarantee that it's safe or sensible. But I'm not your average GA pilot. TL;DR
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#2
06-08-2011, 09:54 PM
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I don't mind them reacting to in-game risk by treating their ride in a rough manner.
I just want them to have consequences for it when flying under higher difficulty settings. What the consequences should be within the frame of a computer game is what this thread is about. We're not here to discuss how long it takes for a particular engine to fail. We're here to discuss how to integrate consequences for reckless operation of the airframe into a new game mechanic/feature. This following part is not directed to anyone in particular, it's just a very visible trend lately on these here forums. There seems too many people whose sole purpose seems to be running their preferred warbird at top performance for no cost. This is not a problem. What is a problem is the apparent desire of some to have this happen across the board, regardless of realism/difficulty settings, so that they can fly on full real servers with their preferred easy-mode button enabled by default, while everyone else flies with limitations in place. Sure, let's have a constant +12lbs Merlin in the sim. Let's have a constant 1.45 Ata DB601 too and whatever the Me-110s used to run with their better performing DB601Ns (which are not even modeled currently), something which would suddenly make the 110 the fastest one of them all. Fun times and varied gameplay, huh? Well, not so much. For a sim that's been so criticized for sharing a lot of commonalities with the previous IL2 series, there's an awful lot of people who expect to carry their IL2 flying habits into the new series without any need to adapt their tactics and without any cost whatsoever to their preferred way of flying and fighting. Sure, they should have the option to do it. Keyword here is option. Turn down CEM and temp effects if you want and red-line the thing all day long. Just don't force me to play the same way. It's not a social stigma to fly on less that full difficulty you know  I'm with Kurfurst on this one. There needs to be a way to limit such behaviour by the player if they choose to fly under such difficulty settings, because otherwise a) we have a repeat of IL2:1946 where everyone flies on full boost all the time just because we can and b) this greatly skews the historical balance of things No matter the accuracy of the FM, if i'm tooting around with a constant 30% more horsepower than the real guys did, then all the variables that govern the fight take a jump for the historically inaccurate: i climb higher at an earlier point in time, i have the jump on the enemy with less effort, i don't need to look into the cockpit and suffer reduced SA because i know the engine can take it even if i don't look at the gauges, i can pull more G's during a fight, last longer in a zoom climb or vertical scissors and so on and on and on. Meanwhile, what really happened is that the extra 30% was only used when absolutely essential to someone's survival. Otherwise, they were milling around with lower power settings and relied on interesting stuff like the element of surprise, proper tactics and getting a kill in one pass before scooting off to reposition for another pass from a favorable location. This is leaps and bounds away from what we had in IL2:1946, where people could either furball it on the deck at low airspeeds and full throttle with no penalty whatsoever, or boom and zoom like rocket-ships without worrying about all the nasty stuff that can happen in a high speed dive and a subsequent zoom climb, like freezing your carbs, shock cooling, tearing off your cowl flaps or run the engine rough for any number of reasons and be left wallowing during the zoom back up like a sitting duck. CoD gives us a way to get one step closer to how these battles were really fought. If that's not glamorous enough for some then it's ok, there are difficulty settings they can adjust to tailor it to their taste. Better yet, let's get a "IL2:1946 mode" in the realism options that automatically disables all the cool new stuff so people can fly without having to learn anything new or change their habits. I'm perfectly fine with it, as long as they don't try to impose it on everyone else. I want my engine to fail and i want your engine to fail if we don't know what we're doing. If you don't want it like that, fly on a different server with different settings, problem solved  In summary, i don't care what each engine could run and for how long. All i care about is that the real pilots back then didn't fly like that for a host of different reasons. I want a set of restrictions in place that will force the player to do the same if he enables the relevant difficulty settings. This is what this thread is all about, not technical specs and charts. Last edited by Blackdog_kt; 06-08-2011 at 09:56 PM.
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#3
06-08-2011, 10:30 PM
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12lb boost for more than 5 mins
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 from: http://www.wwiiaircraftperformance.o...on-1july40.pdf In real life pilots would risk all for a kill or to stay alive. Last edited by Seadog; 06-08-2011 at 10:34 PM.
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#4
06-08-2011, 10:48 PM
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Seadog no matter how many charts you produce the fact remains that there WAS a limit imposed on the use of +12lbs boost. Even the charts you produce sate that use of +12lbs boost MAY shorten engine life. The fact that an engineer was to assess for potential damage after +12lbs boost was used is a bloody good indicator that potential damage could occur. Not definately damaged but MAYBE damaged, after eventual inspection it may be found that engine is perfect but it didn't mean the potential for damage wasn't there. It doesn't matter if an inspection was mandatory or recommended or even to be contemplated, the fact remains that use of +12lbs boost EVEN FOR A FEW SECONDS, DID require the pilot to make a note in the flight log. It was then up to the engineer to determine if the engine needed overhauled based on the fact that +12 boost INCREASED THE RISK OF DAMAGE. He would not be under orders to do this if there was not some good bloody reason for it.
Not one single person replying to your posts is saying a Merlin will break as soon as 5 minutes at +12lbs boost has passed. We are saying the potential for damage was increased the longer it was used. If you don't want to damage your Merlin then turn off CEM. The rest of us will keep it as close to real as possible. Last edited by ICDP; 06-08-2011 at 11:00 PM.
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#5
06-08-2011, 11:45 PM
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There is a poster who is claiming that any use of 12lb/3000rpm will result in grounding till a mandatory inspection is done, and I'm glad to see that you disagree with this. Again, this is exactly what I've been saying. Keep your gauges in the black and 5min+ at 12lb/3000rpm results in increased but still minimal ("low probability") risk, but it is completely ahistorical to claim that pilots did not use 12lb/3000rpm repeatedly or for more than 5 mins as the situation warranted. We know that in the real battle pilots weighed the risks and then "pulled the plug" and some were willing to keep it pulled for more than 5 mins and the game should allow this even with CEM, because that's the way things were. RAFFC went to 100 octane fuel precisely because it allowed the use of 12lb boost and this gave RAFFC a vital edge in performance when it was needed, and some even state that this was the difference between defeat and victory: Quote:
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#6
06-09-2011, 07:53 AM
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WE ALL AGREE THAT USING +12LBS BOOST COULD BE AND WAS USED LONGER THAN 5 MINUTES BUT IT WAS NOT A RISK FREE ACTION. Quote:
Last edited by ICDP; 06-09-2011 at 02:23 PM.
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#7
06-09-2011, 07:59 PM
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Let's be very clear on this point.:  Quote:
I have read through every source on the Merlin engine that I have, and all the combat reports at: http://www.wwiiaircraftperformance.org/ From what I can gather, Merlin engine failures, were primarily random events and the main culprit was manufacturing defects/design faults that eventually break the engine. The 50 hour 12lb/3000rpm test is an example of this, where the engine was cycled 100 times at 5min/20min at 12/4.5lb boost and eventually developed a coolant leak from a defect that plagued service engines that were not being run past 6.25lb. The Merlin in Perspective states that fighters had a higher propensity for coolant leaks than bombers because fighters were cycling engine power from very low to very high much more frequently, but this was still not a common occurrence. The next greatest problem was bearing failure from oil starvation, and again 12lb boost had little to do with this except for prolonged steep climbs, as per Dowding's memo, but probably the greatest cause was inverted flying and prolonged dives that caused excessive (~3600) RPM. 1939 Merlin TBO: Fighters: 240 hrs Bombers: 300 hrs repair depots: 1942 onward: 35% of engines were there due to time expiry. 1942 onward: average engine under repair had 60% of nominal life, or 144 hrs for a fighter engine and 180 hrs for a bomber engine. I would propose the following: Any engine has a 65% probability of random major engine failure, during 240 hrs of operation, or about 160 sorties. Another way to express that would be a 6.5% probability of one aircraft out of 16 having major engine failure on a typical mission. I don't know how to model the use of 12lb/3000 rpm for more than 5mins, but a simple way would be be multiply the failure probability by, say 1.15, to simulate the increased RPM and stress on the engine.
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#8
06-09-2011, 01:10 PM
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__________________
Il-2Bugtracker: Feature #200: Missing 100 octane subtypes of Bf 109E and Bf 110C http://www.il2bugtracker.com/issues/200 Il-2Bugtracker: Bug #415: Spitfire Mk I, Ia, and Mk II: Stability and Control http://www.il2bugtracker.com/issues/415 Kurfürst - Your resource site on Bf 109 performance! http://kurfurst.org 
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#10
06-09-2011, 12:18 AM
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A Lycoming O-360 is take off rated and you don't use it except for take off. That is an engine limitation. The Hartzell bulletin is talking about specific O-360A1A's equipped with a specific hub/blade combination AND using Lightspeed's Engineering electronic ignition. Your next point, of course I meant inches of mercury. It does not matter though...you don't exceed the 28 on the EFIS!!   Quote:
Many times manufacturer's set them very low at first and then raise them as field experience is gained. Rotax 912 is a modern example. Everyone is expecting the Centurion Diesels to see a TBO raise too. They did the same thing. http://www.centurion-engines.com/typ...x.php?id=2&L=1 What is important and seems to get covered up in your reply Viper is the following: Pilot's fly airplanes IAW the Operating Instructions published by the manufacturer. End of message. Anything else is baloney and thinking like a gamer, not a pilot. Quote:
I certainly don't know any licensed A&P's who think that way or do not follow publications. That is good way to kill somebody, lose your rating, and even go to prison. There are shady folks in aviation. One owner and he FBO are in the process of suing one such individual right now. That is if the sheriff does not get to him first. In reality, not following published procedures can and will kill you. The FAA statistics show this quite nicely. The reality is only a tiny fraction of the community knowingly violate procedures. Most understand the importance and the consequences of not following it. I knew this pilot. He was VERY professional and flew his aircraft by the numbers. Nothing he did in an airplane was unplanned or "seat of your pants". He died because he did not change his altimeter setting. He made a simple mistake and did not follow procedure to monitor ATIS and adjust the altimeter accordingly. He entered a loop and end up with CFIT. You should know the old axiom, "There are Old Pilots and there are Bold Pilots but there are not any Old and Bold Pilots!" It got to be a axiom because it spells out the truth. Quote:
Of course there are almost 20,000 airports to land at in the United States. I can find a convenient airport at almost any destination I choose. In the EU, you have just over 2500 airports to land at..... It is impossible to compare the General Aviation community as GA is a completely different animal in the EU. Perhaps when the EU GA community matures, it can begin to keep statistics to help make the pilot community safer. Maybe then your civil pilot population will become more educated and not act so recklessly. Quote:
Continental did that because they did not test or design the engine for any higher rating. When the O-520 first came out, the crankcase was too light even at maximum continuous and there were many failures as a result. Subsequently Conti went to steel on steel for their rings and now very few of them make it to TBO without a top end. In short, the engine has had too troubles at it's current rating to even think about a manifold pressure increase. It is also not tolerant at all of improper procedures. Feel free to invest your money in an O-520 and then not follow the book. :p If the installation has plenty of power, there is no need for a Take Off rating. The Lycoming O-360 has been adopted to so many installation that including many heavy twins. That little 180 hp engine pulls some weighty airplanes around now. The O-360 series is a close to bullet proof as you can get in a light aircraft engine. I wouldn't trade mine for all the tea in china. Last edited by Crumpp; 06-09-2011 at 02:35 AM.
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