---------------------------------------------------------- KIS-List Digest Archive --- Total Messages Posted Sat 03/26/11: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 02:29 PM - Re: KIS TR-1 Propeller (BlueSkyFlier) ________________________________ Message 1 _____________________________________ Time: 02:29:25 PM PST US Subject: KIS-List: Re: KIS TR-1 Propeller From: "BlueSkyFlier" 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). -------- _________________________________________ 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 ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message kis-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/KIS-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/kis-list Browse Digests http://www.matronics.com/digest/kis-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.