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1. 02:29 PM - Re: KIS TR-1 Propeller (BlueSkyFlier)
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Subject: | Re: KIS TR-1 Propeller |
So how does one determine at what power level the aircraft is operating at any
given time?
Most of us fly around with basic instrumentation, so the answer is not immediately
obvious (be that for flight with WOT or not). Whilst investigating the question
I collated information which may be of general interest to KIS TR-1 owners.
The diagram below illustrates in general how to estimate with reasonable accuracy
the amount of engine power used at any given RPM and altitude (with %
of power on the right hand scale). For some readers this may be old news but
being relatively new to the game I found the exercise quite interesting and though
it worth sharing the results. (The normal disclaimers apply of course :o)
For the example depicted in the diagram, 65% of rated power is used in level flight
at 5000 feet with the throttle backed off to 2400 RPM. When the throttle
is pushed wide open (in level flight only) the operating point jumps immediately
to the intersection of the 2400 RPM line with the full throttle bhp curve for
5000 feet. Then the operating point moves to the right along that full throttle
bhp curve as RPM increases up to the maximum of approx 2630 (at the yellow
star for 5000 feet).
As a 2nd example, to operate at 75% of rated power (94 hp) with WOT one would look
for ~2600 RPM which should be possible at ~6250 feet. (this spot is marked
on the diagram and is easily found by tracking leftward at the 75% power level)
When climbing with WOT, the solid red line (and yellow stars) shift to the left
along the full throttle bhp curves as RPM decreases until the stability point
for that climb rate is reached. When throttle is closed in level flight the
operating point tracks down to the left along the engine load curve for that particular
altitude until it aligns with the selected RPM setting. The engine load
curves would change for a different propeller and changes in aircraft weight,
but the principles remain the same.
The earlier part of this thread described the performance effect of reducing the
propeller pitch. The diagram attached herewith illustrates performance derived
from the integrated airframe and propeller model for a KIS TR-1 with a 68 x
69 propeller. As can be seen from the slope of the solid red line, such a cruise
propeller will steadily diminish ones ability access to residual engine power
as altitude increases. This makes it easy to control cruise power levels by
simply flying with WOT at a suitable altitude.
However, for those of us who sometimes need to operate fully loaded from hot &
high airfields this is not a suitable performance profile. When taking off from
an airfield with a higher density altitude it is evidently desirable to be able
to access every last drop of available power the engine can still crank out
at that level. So, in that case one would instead want to use a propeller configuration
for which the solid red line in the diagram below drops down vertically
at the maximum rated RPM. As previously described a 61 x 64 propeller would
enable this objective to be met up to density altitudes in excess of 8000
feet (with ~6 kts sacrifice in top speed).
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Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=335114#335114
Attachments:
http://forums.matronics.com//files/power_at_given_rpm_and_altitude_174.jpg
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