ShoestringRacer
Posts: 643
Joined: 3/25/2002
From: NY,
NY, USA
Status: offline
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You are right you did not say anything about convective weather. But you did say “bad weather” so that is just one logical type of “bad weather” one would associate with flying. So is icing, windshear, clear air turbulence, and a few others I can’t think of right now; at least with respect to operating airplanes in. And getting out of “bad weather” is the reason you cite for all airplanes needing a minimum of 1500 FPM climb. So now you are adding by saying 1500 FPM is needed to get above an overcast. So that must mean overcast weather is also “bad”. And if you think it is mandatory that all airplanes have this 1500 climb in order to get above the overcast it must mean you think that flying in the overcast (IMC) should be prohibited as well; otherwise there would be no reason to be required to climb above it when one could otherwise fly through it.
Well there can be IMC conditions (cloud) at any altitude, say 4000 feet, FL 260, or FL 450, etc. or whatever. So having 1500 fpm climb possibility doesn’t do any good when IMC conditions can exist right up into the high flight levels. IFR airplanes are not operated with the idea to get out of cloud that is otherwise not convective or ice laden. Not to mention normally aspirated singles and twins can’t get much higher than the mid teens or so where much weather is located. So we should retire all those airplanes to the scrap heap if they can’t fly at FL 450 to get above clouds? You are right, IFR flying wrecks do happen and mostly to GA pilots. But crashes happen every day on the highway. So should all cars be limited to 35 mph which would put the same operational restriction on them as to preventing aircraft that can't climb 1500 FPM from flying IFR in cloud?? I don’t mean to be hard on you, but you are just saying flippant, unsophisticated, and very impractical comments without much practical flying, or at least IFR, experience and knowledge. I am only pointing out these things to really address what I think are the issues at hand overall.
“If they lasted over 1000 as they do in a car, then they would be more reliable.” With that statement you are commingling two different things: reliability and service life. If something is reliable it means it has a low failure rate/occurrence. So to say mags would be more reliable if they lasted 1000hrs makes no sense. Consumables, like spark plugs, (and mags but they can be rebuilt) have an estimated service life (which can and does vary a lot actually), and a failure rate which are two totally different things. So a mag or spark plug would be no more reliable regardless of how long it is capable of lasting. If it fails often before the expected/planned service life is a reliability issue, not a service life length issue. High service life and high reliability is obviously ideal.
Modern day aircraft engines (which means they are not really modern at all) were designed to be simple and reliable. They are air-cooled for simplicity and low weight. For one an electric fan would not help all that much because cowl flaps are usually spec’d, and just adding an electric fan would not allow any significant change in tolerances. That could only come with precise, thermostat controlled liquid cooling. Even if one was used to supplement ground cooling, which is pretty much impractical and unnecessary given all the deficiencies of air-cooling as it is, it would add complexity. The very slight benefit of one would be a waste of time and money. Once the airplane moves to fly you have the best natural ram air fan going for cooling. An electric fan, especially in the operating environment of an aircraft piston engine, would have a high failure rate, add unnecessary and impractical complexity; at least if it was the quality that existed 50 years ago when our present day aircraft engines were born. Anything that adds weight, complexity, and extra systems was avoided as much as practical. Engineers didn’t pace up and down saying that if only they could add a fan they could really tighten up an air-cooled engine. A fan isn’t the solution to tolerances with an air-cooled engine. ( I will note that liquid cooling is superior for many reasons like shock cooling and tighter tolerances, etc. but an often over looked benefit is one of cooling drag: air-cooling creates drag; most of which can be eliminated with a sealed cowling when using liquid cooling)
The same complexity (and cost too) reason goes for liquid cooling. Up until maybe 20 or 25 years ago the cooling system on a car was one of the most failure prone systems it had. Water pumps quit, hoses burst, radiators leaked, thermostats stuck, etc. Only in the last 2 decades, and more like 10 years, did auto engines become much more reliable to the point that the cooling system as a whole is just as reliable as the engine as a whole. Look back to the 50’s, 60’s, and 70’s how often cars broke down. (and I wasn’t even around 50’s and 60’s) Can you imagine how many airplane engines would have quit in flight if they had water cooling and electronic ignition back then?? Today it is much more practical because of design/engineering and manufacturing advancements. Those complex items can be made to be much more reliable today. And being that those advancements come slowly in aviation powerplant options is another, yet valid, argument.
I am not defending current old technology aircraft engines. I would love to fly behind a liquid cooled, full FADEC aircraft engine for sure. I practically fantasize about it. Just variable ignition would be leaps and bounds ahead of fixed ignition we have now. (and the lead fuels we use are primarily designed to prevent detonation and preignition with the fixed timing and especially turbocharged engines) Better yet, a diesel, which is superior in so many ways, and are just becoming certified now for light singles and twins. There is certainly better technology available than what exists in current old tech aircraft piston engines, but the tried and true is also proven, and was the most reliable thing in its day.
New technology is becoming available with the aforementioned diesels from Thielert (which is liquid cooled), and true FADEC from Continental in some applications and Lycoming’s EPiC FADEC. Each has comparable or better specific fuel consumptions with as good or better reliability. And parts like plugs can last even longer because of the precise computer controlled mixture in each cylinder, and the oil becomes less contaminated from precise mixture control and variable ignition thwarts detonation and preignition. So those and various other things in the certification/approval stage are on the way. Better late than never…
“Flying at 2500 RPM is the same duty as driving on the freeway.” No it is not. 2500 RPM represents 92% of the redline speed of an airplane engine that redlines at 2700 RPM. (and also about 60-100% of the engine power depending on such things like temp and altitude: anytime you operate an engine above a temp of 59F and 29.92 baro and above sea level it won’t be able to make the 100% power that it was rated for on the ground) So no, your car engine isn’t putting out 75% or whatever of its total power when strolling down the highway. That is probably pulling somewhere around 30% total power. Those low power of autos also mean much lower cylinder pressures, so when run at higher power setting, nearly all things, but especially cylinders, take a beating. And except for a few minutes during descent and landing an airplane engine is usually at or above 65% power whereas your auto engine is loafing; meaning the aircraft engine cylinders are taking a constant and unrelenting beating.
It is really pointless to compare RPM range between car and airplane engines because they are so fundamentally different: the crank speed is so low (but not low stress) compared to auto engines which have higher crank speeds with much smaller displacements to get approximately comparable power. (like the previously linked articles state that aircraft engine speed was deliberately made slow to prevent near sonic prop tip speeds without the use of more complicated (failure prone) gearing boxes) I can almost guarantee you that unless an auto engine is specifically designed for such, the typical luxury sedan engine wont last 2000 hours when run at a constant 5000 RPM. And look at high performance race engines; they are only capable of lasting a few hours of racing if they are lucky; not one would last 2000 hrs flat out.
If you are so confident about your car, then just keep it downshifted whenever you drive (you can do this with an automatic or manual) so that the RPM stays up about 90% plus of its redline value. That should give roughly 75% or more of its rated power which is comparable duty. Drive it all the time everywhere you go at that engine speed/power and report back to us after 2000hrs. One or more of your engine parts may protest before 2000hrs.
< Message edited by wantsaneagle -- 8/28/2006 9:28:09 PM >
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RE: How safe are homebuilt planes? - 
