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I really suggest ya´ll head to A2A site

I've heard normally aspirated engines gain about 1% power from every 10 degree(F) drop in temp, while forced induction engines gain about 2%.

I'd say that's true as my supercharged car certainly seems to gain a solid 40hp on a 0 degree winter day compared to a 70 degree summer day. I'm familiar with how an additional 40hp feels on my car because going from my stock boost of 7lb up to 11lb along with intake and exhaust upgrades gives me about 40hp and 50ft-lb.
 
The Cessna caravan uses a flat rated engine, in otherwords, it artificially restricts the output up to a certain altitude where the max available power meets the design output limit for the aircraft, and then decreases thereafter with altitude. Very similar to a supercharged engine limited to a certain MP, which can be provided to some critical altiude.

In aircraft super/turbocharged engines, an intercooler is quite important in being able to use full rated "Dry" MP without geting into the detonation range.

Cheers; T.
 
Hey Solar Eagle,
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You are feeling the same thing in your car that a plane feels in the air. The main difference with flying is it’s a matter of safety, as you may have to clear some trees or a hill at the end of a runway.
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I am not sure if you have our Accu-Sim Boeing 377, but it has torque meters that measure the actual twisting force from each engine. As you can see in your car, the PSI (manifold pressure) does not equal power. So with torque meters, you dial in all your engine settings as you normally would (mixture, prop, manifold pressure), which gets you in the ball park. You then fine tune each engine with the torque meters to insure you are dialing in the exact power in every situation.
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Also, on a very cold morning, you will notice it’s much easier to over-torque the engines than on a hot day. If you are on hot tarmac, it’s compounded even worse.
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I enjoyed building automobile engines when I was a teenager. My favorite engine back then was the <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:eek:ffice:smarttags" /><st1:place w:st="on"><st1:City w:st="on">Pontiac</st1:City></st1:place> 455. It produced about 370 horsepower but it was a very long stroke, so its power curve was almost flat. That thing felt like it could climb up the side of a building in a 2 ton vehicle. I would have been obsessed with a torque-meter if I had one, it sounds like you would too. The nice thing when we make an Accu-Sim aircraft, we built an engine diagnostics panel that measures various internal factors, and includes a torque meter that we use all the time.
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Scott.
 
Thanks for the post Scott. While I know how horsepower and lb-ft of torque interrelate through RPM I was never able to figure out how to translate PSI of torque from the torquemeter into ft-lb or horsepower, so I never really understood what I was looking at on the torquemeter. Is there anything you can share about that?

Just for fun I plotted a torque curve on the Allison 1710 since that's the only aero engine I have horsepower curves on and I was surprised it actually slants entirely down. With 32" Manifold pressure it shows 1955 ft-lb @ 1800 RPM and 1675 ft-lb @ 2950 RPM.
 
A lot of factors enter into the relationship between MP, Torque, RPM and THRUST delivered in aero engines. An interesting example of an internal improvment in the R2800 "C" series engines had to do with the lubrication system. Several hundred extra useable HP were "found" through reducing drastically the amount of oil being sloshed around in the crankcase! It was then possible to increase the max RPM from 2700 to 2800 withoug getting into a serious internal friction loss situation.
 
Solar Eagle,
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Since torque is a relationship of force and distance, and PSI is pressure, there isn’t a universal conversion for this, however, the PSI indicators in the Boeing 377 are measuring pressure based on the twisting force of each motor. So in the cockpit you are seeing an exact measure of the twisting force in PSI which is what you want to dial in the exact power setting. What we did is create the R4360 engine then tune the torque meters based on readings taken under specific power settings and carb air temp.
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As for that Allison, I actually think these readings are quite nice:
1955 ft-lb @ 1800 RPM and 1675 ft-lb @ 2950 RPM.<o:p></o:p>
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Assuming its peak torque occurs at 1800RPM, then at 2950RPM its well over 80% efficiency. If you plot the horsepower curve, it should look quite nice all the way up. This is a testament to the engineering that went into these old warbirds, especially when you consider this engine was built before computer optimization.
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I remember my grandfather used to make cider with this old engine, that just had a single piston traveling so slowly. I was so young I can’t remember much about it except for that ‘pop pop pop’ sound it used to make. It’s amazing how you think the technology is based on the same basic principal – suck, squeeze, bang, blow.
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Scott.
 
The Witte One Lung Diesel was a common feature in many rural areas before electrification (post war!!). They were also found in many oil fields in the Midwest to run the well pumps. Such low speed engines are still found in many fishing boats. I had a Lister Diesel for many years for electricity but it was a high speed engine running at 1800 RPM to produce 60 cycle power. Not nearly the cool Pocka, Pocka, Pocka....
 
I just read this bit in my amazing new book "Vee's for Victory: The Story of the Allison V-1710", which is a much cooler book than America's Hundred Thousand. :kilroy:

Vee's for Victory said:
The Allison’s went to work on farms and factories around the country, often pumping water or doing other mundane tasks. As of the late 1980’s, one of the hydroplane teams tells of stopping at a freeway rest stop in Nebraska and in the quiet of the prairie hearing the distinct note of a V-1710. Taking the next exit, and following the sound they found a farmer using a V-1710 for pumping water. He had two more still in their crates as spares. A deal was struck, and the hydroplane team picked up the three engines on their way home. The farmer then switched to diesel power.
Click to expand...
 
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