Indy GT
Yea, I got one...too
Kingman, this may be correct but unlikely the “airport” makes the call to close due to density altitude. It is really up to the air carrier and ultimately the Pilot In Command (PIC) as he is the individual responsible for the flight’s safety. This issue comes up (or use to) at Las Vegas and Denver which both get very high ambient temperatures in the summer and Denver has high physical altitude as well. They have longgggg runways to help with this issue.
The density altitude issue did effectively close the Denver commercial airport years ago as the ambient temperature was higher than the temperatures in the aircraft operating manual charts used to calculate takeoff distance. In that take off distance was off the aircraft manual charts, the PIC was not able to calculate the necessary distance for takeoff (usually an internal corporate requirement) and thus could not take off on a revenue flight. Again this was a PIC decision (and corporate requirement) which grounded the air carrier equipment which did not have high temperature takeoff charts in their manuals. Manuals now have much higher ambient temperatures for the takeoff calculations and thus the problem goes away.
Jbyrnes, I guess I misunderstood your earlier question “The higher horse increase for a SC engine vs a turbo'd motor as temps decrease is an interesting phenomenon. Why is this?” This was the explanation I presented in my post. I take it you now understand and recognize charge density and its relationship with power.(?) So your next question (as I understand it) it two fold. You are asking 1) why does the SC engine have a cooler (induction air) charge relative to a turbo equipped engine and 2) engine “reaction” time to both systems.
Well for No. 1 anytime you compress a gas (like air) there is associated with the action, heat. You are doing work on the air which results in a temperature change. Reference again to the perfect gas law. But, too, the effectiveness of the system you use to compress the gas has a bearing on the final gas temperature as well. Compression systems are not 100% efficient and thus these compression system inefficiencies also result in heat added to the final compressed gas state.
A positive displacement mechanical air compression system (like a Roots http://en.wikipedia.org/wiki/Roots-type_supercharger or Lysholm as our GT has http://en.wikipedia.org/wiki/Rotary_screw_compressor) have an associated compression efficiency associated with each. The Lysholm type supercharger is generally more efficient at compressing air relative to the roots style because it has lower internal leakage levels and lower parasitic (horsepower) losses. Thus, being more efficient in converting mechanical rotational work from the engine crankshaft to compressed gas, there is less heat imparted to the working or compressed gas. (Relative to a roots type system).
A centrifugal impeller/compressor system (http://en.wikipedia.org/wiki/Centrifugal_compressor) is not considered a positive displacement pump and provides gas compression “by adding kinetic energy/velocity to a continuous flow of fluid through the rotor or impeller. This kinetic energy is then converted to an increase in potential energy/static pressure by slowing the flow through a diffuser.” Using Bernoulli’s Law as you slow the gas velocity through the diffuser part of the turbo, the pressure increases. This compression system too has an associated efficiency and thus an influence on the final gas temperature after compression and upstream of the intercooler.
Compression efficiencies vary greatly and depend on many, many variables. I have no idea of the relative efficiencies of a Lysholm supercharger relative to a centrifugal compressor both designed for similar mass flow rates to supply our 5.4L engine. But it is certainly reasonable to assume they very likely ARE different values. Thus it is reasonable to conclude that if each system has a different compression efficiency, for a given mass flow rate of air, the output gas temperature is likely different as well. So to answer your question 1, I never stated that one compression system would deliver cooler output gas temperatures. But I certainly would not be surprised if the output temperatures were different between the two systems. And for power you want the coolest compression system output temperature. (charge density, remember)
To answer question 2, I already answered that one in my earlier post on turbo lag vs. direct response to crankshaft rpm.
Hope this better answers your questions.:thumbsup
