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Mark,

The speed vs. altitude curve represents wide open throttle (WOT) cruise speed. While the actual values are unique to the airframe drag and induction pressure recovery of N91CZ, the trends are universal.

The curve is set by the weight, rpm and OAT (standard atmos. +/- xx deg) called out in the legend. Weight, rpm and OAT, combined with engine, propeller and airframe data, produce the cruise performance curve of interest -or series of curves for sensitivity studies.

The 55, 65, and 75% power lines are added as a reference. These are not necessarily tied to a specific rpm, but simply represent percentage of rated engine power, 99, 117, and 135.

The indicated air speed curve and fuel economy were added as a curiosity given the current LML discussion. The fuel economy curve uses actual flow data from my carbureted engine. Injected, even ROP, will be much better. Headwinds or tailwinds are also incorporated in the fuel economy output, but none are shown. The best range or L/D point can be seen where the fuel economy line rolls over at about 120 KIAS in the first chart. Engine speed was reduced to 2300 rpm to help move this point to the left. Reducing throttle is another means of pulling this point to the left, or to a lower altitude.

hope that helps clarify,

Chris

Chris Zavatson

N91CZ

360std

http://www.n91cz.net/

On Tuesday, December 24, 2013 11:06 AM, Mark Sletten <mwsletten@gmail.com> wrote:

Chris,

Can you give an example of chart use? Where do I enter and which way do I proceed to find performance?

Thanks,

--Mark

On Tue, Dec 24, 2013 at 6:42 AM, Chris Zavatson <chris_zavatson@yahoo.com> wrote:

not sure the attachments made it last time.
Chris Zavatson

On Monday, December 23, 2013 10:33 AM, Chris Zavatson <chris_zavatson@yahoo.com> wrote:

The section on range in “Handbook for Naval Aviators” does a good job comparing the various propulsion types with respect to achieving maximum range. While discussing propeller driven aircraft with reciprocating engines, it mentions that engine operating limitations may actually drive achievable range. This is indeed the case given the speed at best L/D for the 360, for example, is about 120 KIAS (weight dependent) and it only requires about 50 hp at low altitudes. At such low power and low altitude, engine efficiency is rather poor. And as Gary mentioned, we tend to place a relatively high value on speed. We can extract a good compromise by flying at higher altitudes. As the indicated air speed reduces with altitude, range continues to increase. At WOT, reaching best L/D may still not be practical due to the very high altitude required – unless we are really, really heavy, as in carrying an extra 350 gallons of gas. Throttling back on power or pulling back engine speed is an option. Since power has already reduced naturally at altitude, less power reduction is needed. One can also simply satisfy the need for speed and accept reduced range.

I superimposed fuel economy (fuel flow taken from a carburetor with poor mixture distribution – about a 20% hit) and indicated air speed on performance charts for the stated conditions. Peak economy occurs very near the 120 KIAS mark. Further reductions in power or increase in weight will pull this point to lower altitudes.

Given all this I tend to fly high so I can save gas and still go fast.

Chris Zavatson

N91CZ

360std

http://www.n91cz.net/

On Monday, December 16, 2013 6:45 AM, Mark Sletten <mwsletten@gmail.com> wrote:

Check Aerodynamics for Naval Aviators. The figure on page 169 and the accompanying text on page 170 will answer your question.

http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/00-80T-80.pdf

--Mark

On Mon, Dec 16, 2013 at 7:00 AM, George Wehrung <gw5@me.com> wrote:

Hey guys,

On long range flights I always fly a Max range profile no matter the wind direction. Case in point I logged a 7.5 in a king air 200 flying from Lajes Azores to St Johns Newfoundland today. The winds got up to 122 knots in the face. But with the internal ferry tank we made it with 800 lbs to spare.

Anyhow the guy next to me wanted to push it up saying we would spend less time bucking the wind but I owned the plane today and flew what I perceived a Max range AOA (no AOA installed) of about 3 degrees nose up and kept pulling the throttles back to keep her their. This attitude comes from 7 yrs in king airs and knowing the charts. But I don't have the aero background to counter his argument.

Can anyone help me out with research or otherwise?

I know their is a number of TPS grads and much smarter aviators than I.

George

Sent from my iPhone
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