I certainly agree with George in his comments in that a well-designed intercooler will offer significant performance benefits at altitudes like 18,000. When I said "marginal benefit" I was referring to benefit in a more global sense. It all depends on how much of the operation is conducted at 18,000 feet. From my experience I would guess it would be very, very rare for someone
to spend 50% of of the total hours at or near 18,000. A 4-hour flight will spend maybe 30 minutes in climb and 3 minutes in descent from 18,000 for 50% spent at 18,000. A serious cross-country flier might be there for, what, 20%? And then how much of that time is spent at 30 inches manifold pressure, burning close to 30 GPH? At lower manifold pressures the higher inlet temperatures are not as detrimental as they are at full power, where they limit the power output. In other words, 25 inches with a 150F inlet might be equivalent in power - and nearly equivalent in efficiency - to 24 inches at 100F inlet. Another thing to be aware of - the inlet air temperature does not exactly match the temperature of the inlet charge as it is trapped in the cylinder, which is, after all, what counts. Tests I have seen show that the charge is heated about halfway to the cylinder temperature. If the cylinder temp is 300F and
the incoming charge is 100 the resulting charge temperature is about 200. Increase the inlet temp from 100 to 200 and the trapped charge will be at 250, only 50 higher. While no one is truly an average operator, my point was that chasing the optimum performance at 18,000 feet may not be worth the cost and development expense. Depends on your goals. All flights involve operation below 10,000 feet while a limited number involve operation above 18,000. When flying my TR182 on a lot of cross-countries I flew between 12 and 15 a lot, but flew above 18,000 only a couple of times in 5 years. Like in the drug commercials, these comments are directed only at turbonormalized nonpressurized oxygen-equipped aircraft operated in non-commercial environments. Oh, yeah - and by "average" resource-limited owners :-)
I'm not sure I agree with George when he says that "Intercoolers have large benefits - - - even at sea level." In this case the turbo is producing negligible pressure, so the temperature rise is dependent only on the heat picked up going through the turbo and the small compression heating when the turbo has to overcome its own flow restriction. This is also true when cruising at less than 10,000 feet at reduced manifold pressure. Is the added weight, cost and aerodynamic drag more of a detriment
than the cooling is a benefit?
Gary
>>Here's another thought: A lot of it might depend on your intended usage. If you want to go really high (over 20K) and have maximum performance you might want
to consider getting the extra power of the TSIO-550. But if you, like me, might limit altitudes to less than 20K and are more cost and fuel economy sensitive, then a lower tech solution might be in order. I flew for many years behind a Lycoming O-540 that was turbonormalized (C-TR-182) and it worked quite well. It didn't have an intercooler or automatic waste gate - the waste gate was connected to the throttle linkage so there were no extra levers. It was fed by a pressurized carburetor, so that doesn't apply with a Continental. So the question is, what's wrong with using a standard IO-550 with a turbo and manual waste gate? The Lycomings don't bother with a sniffle valve, so there isn't any difference between turbo, fuel injected, or naturally aspirated engines in that regard. At 18,000 feet the use of an aftercooler has real, but marginal benefit, as the extra aerodynamic drag and pressure loss negate most of
the charge-cooling benefit. Just a thought, suggesting a KISS methodology.
Gary<<
Gary,
Some comments.
I think new designed high compression engines with compressors of any kind should use our present state of knowledge and incorporate intercoolers - - good intercoolers.
The engine you are discussing had lower compression ratios. As someone else said in this same thread of messages, unless you really know what you are doing, you can screw up and have a very unhappy installation.
Intercoolers have large benefits - -
- even at sea level. I do not think it is accurate to claim that intercoolers only have “marginal benefit” below 18,000 feet.
Here is why I think they are important: At 18,000 feet, the compressor discharge temperature on a warm day can easily exceed 200dF. Without an intercooler, 200dF air goes straight to your cylinders.
With the TN IO-550, the induction air temperature at 30” at 18,000 feet on a hot day will be less than 105dF. Typically 95 to 100. There is a large difference in performance and detonation margins between 200+dF air and < 105dF air.
The O-540 “solution” does not really provide more fuel economy. Rather, likely just the opposite.
The TN IO-550N engine that Tornado Alley delivers to Cirrus will produce horsepower at 0.38 to 0.39 BHp/lb-fuel/hr across an altitude and power range that spans anywhere from sea level to 29000 feet and do so at 200 Hp or at 310 Hp, or anywhere in between. [The real world numbers for the Thielert diesel was about 0.36 to 0.37 BHP/lb-fuel/hr.] There is no other general aviation engine installed in any fleet of aircraft that works anywhere near that well across that broad range of operating requirements and environment.
90% of the hours flown with those engines are flown between 11,000 and 18,000 feet.
There is a reason why Cirrus has sold ~ 900+
turbonormalized SR22 aircraft in the last 35 months, including 15 months of some of the worst times in general aviation history.
The reason is - - the systems consistently exceed the expectations of the owners.
During that period of time TAT continued to improve and refine those systems. They are, today, about 15 lbs lighter than they were in 2007. They run cooler. They are simpler to maintain. That comes from a passion for continuous improvement.
And those systems are going to become still more efficient and versatile when the electronic density controllers are installed.
Regards, George