This recent thread has been very interesting and I think it is one of the most useful purposes of a forum like this. I detect a few common elements in the various anecdotes:
1. There seems to be a tendency to keep going in spite of inflight problems. Is it because the pilot is intimately familiar with the workings of the machinery and knows it is okay. Or is it because he is intimately familiar and thinks it is okay? Maybe I'm overly conservative, but any deviation from the norm is probably a reason to divert to the nearest airport. I suppose none of us follows this rule completely (not even me), but we probably should. Murphy's law is at work here - any change is a bad change, at least 99% of the time. There also seems to be a tendency to
downplay problems found on the ground. If they will ALWAYS be found on the ground, okay, but is there any chance that failure would not be detectable before flight? Then it's just as serious.
2. Getting known good parts can be a problem - is the rebuilt water pump really a good one? How do we know? Yes, rebuilt or even new certified aircraft parts are not necessarily good either, but compared to some of the automotive parts we are forced to use (I don't think anyone deliberately uses substandard parts) they are much more likely to be good.
3. How carefully are the systems put together? It might take me 30 seconds to put together an electrical connection in my car, but it will take me 5 minutes to do the same connection in the airplane, including the number of inspections that come after. Should an engine be rebuilt in the field? In a hurry? I noticed design problems that encouraged
build errors - like the woodruff key that can be lost behind the sprocket and not seen. Is the car engine assembly process like an aircraft engine assembly process? Casual processes breed mistakes. Since non of us are perfect each assembly step should be followed by an independent inspection step, preferably with written documentation. That takes time.
4. Are the systems tested in every way before being used? I know this isn't always possible, but it should be done to the extent possible. Are the cooling systems pressure tested? Every time they are taken apart? I don't mean to normal operating pressure, but well beyond - probably to at least 2 and more like 3 times the maximum pressure. should the core plugs be replaced with something else? I noticed there was one core plug failure reported - one is enough to change the design from then on, at least in my opinion. How about the intake systems, especially
for boosted engines? Instead of counting on a bead to hold the hoses together how about welding a couple of tabs on the tubes and using a metal link to hold them together, eliminating the need for the hose to do the mechanical support. Are the exhaust systems pressure tested?
5. Is there anything except fuel and air that can get into the intake system? Are there any kind of nuts, bolts, compressor blades or other pieces that could possibly come loose? If not, is there a screen that can catch the big ones? An intercooler serves this function well.
5. Piston engines have hot exhaust systems, but rotary engines have HOT exhaust systems. Hundreds of degrees hotter. Are all the components up to the stress? Even stainless steel has probably lost 2/3 of its strength at that temperature. At that temperature a muffler isn't just a muffler - it has to be done really well - aricraft mufflers
are designed so that internal parts can't block the flow if they come loose (although I've heard of it happening). It looks like standard passenger car turbos are not up to the task. Should you use water-cooled turbos? They are not readily available and using one would further increase the complexity. What do the racing Mazdas use?
6. Rotary engine exhaust components are really HOT (repeating myself, eh?). To get an idea of how much potential heat imagine a blowtorch burning a gallon of gasoline every 2 minutes - that would be a huge fire. That much heat is being contained within the engine compartment. Obviously all the hot parts and all the parts nearby have to be carefully done. An effective heat shield can be just a shell, even of aluminum that is between the exhaust and sensitive components. A plastic fuel system component? No matter how well shielded I don't think I would put one in the engine
compartment. What if an exhaust system component cracks, especially with a system that is under pressure? Are all the nearby components protected from the blowtorch that would result?
7. I was told once that an airplane has only 2 moving parts - the engine and the fuel. Keeping a continuous flow of fuel is critical. Automotive fuel pumps, except the turbine variety, are very sensitive to contamination and a small particle can cause them to seize. Is there an adequate inlet filter? Not just the coarse screen we use in normal aircraft fuel tanks, but probably the nylon sock that is used in cars. That filter is there to protect the pump - nothing else. Automotive fuel injection systems require fuel that is much cleaner than typical aircraft systems, so standard aircraft gascolators, etc usually won't work except to separate water. Are the filters adequate? do they have adequate reserve capacity? Standard
automotive paper fuel filters have a large reserve capacity, but aftermarket sintered bronze filters typically don't. Should there be two filters in the system, the primary with a bypass valve? Is the filter able to be inspected? If not, how often should it be changed? I suspect the filters should be changed after the first hour of operation, then after 10 hours and then every 100 hours. Not because they are expected to collect that much dirt, but because they COULD collect that much dirt. You never know when that big slug of dirt gets purged out of the tank, but is more likely to happen early. All the systems I've seen use 2 fuel pumps and I would install a filter downstream from each pump. Should you be this paranoid of the fuel system? Yup.
A very carefully designed and built turbocharged 2-rotor at 300 hp (3-rotor 400 hp?) would be true thing of beauty. I'm sure such a thing is out there. Problem is to
thoroughly address all the issues listed above takes time and money. Experience is a poor teacher - it gives the test before the lesson. Other people's experience is, however, useful as then I can put the lesson before the test.
I hope this discussion has been useful.
Gary