---------------------------------------------------------- KIS-List Digest Archive --- Total Messages Posted Sat 03/12/11: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 01:12 PM - Re: KIS TR-1 Propeller (BlueSkyFlier) 2. 08:55 PM - Re: Re: KIS TR-1 Propeller (Galin Hernandez) ________________________________ Message 1 _____________________________________ Time: 01:12:06 PM PST US Subject: KIS-List: Re: KIS TR-1 Propeller From: "BlueSkyFlier" Light a the end of the tunnel! ... and about time too :o) In late January I started exploring to find the best replacement propeller configuration for the recently acquired KIS TR-1. The objective is to replace the old 2blade 68 x 69 inch cruise prop with a new prop which will markedly improve low speed climb performance after take-off at full weight. It turns out that the new prop should be a 3blade 61 x 64 inch climb propeller. The insights gained from these studies have turned upside down all notions I previously held regarding what may or may not constitute an optimal propeller. Initially I was quite ambivalent about 3-bladed props, but results of the comprehensive performance modeling exercise showed conclusively that a 3-blade prop offers significant comparative performance gains at low speed and also at high altitude (i.e. high density altitudes) with only a small sacrifice in top end speed. This follows from the fact that an 8-fold increase in power is required for a given speed increase. Trading power for top end speed is therefore not a very effective use of power unless you have oodles to spare thinking of Scott here ;o). For us lesser mortals with engines cranking out 130hp or less (at best) it may be sensible to forgo a few knots at the top end (~ 5 knots ) in order to gain a bucketload of spare power to support much improved acceleration and climb performance at the lower end of the speed range in combination with better performance at high density altitudes. For general interest, and for others who also have a problem with sluggish takeoffs, the findings are described below with reference to the attached diagram. From previous communications about propeller performance it seems that many KIS TR-1 planes are fitted with 68 or 69 inch pitch props. Those owners my find the information below particularly relevant. For actual propellers the choice is still between Prince P-tip, Catto and Idrovario. Kind regards, Alfred The old (61 x 69) and the new (61 x 64) propellers are compared for three typical operating points: A) Climbing after take-off nominal MSL B) Level flight at low altitude (nominal MSL) C) Flight at 7500 feet (or equivalent altitude where only 75% of engine power remains) Notes: (i) Green arrowhead lines connect the tips of the three pairs of old vs new performance comparison lines on the diagram. (ii) Full throttle B.H.P. curve information supplied by OC Baker was instrumental in making it possible to complete the analysis. (iii) Although I refer to the new prop as a climb prop it cruises perfectly well the distinction is merely in name, not in application. (iv) Brake specific fuel consumption does not vary by much over the RPM range of interest. Refer http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption A) Climbing after takeoff. With the old prop, engine rpm tops out at less than 2750 in level flight at low level. Upon starting to climb the rpm then drops to just below 2400 rpm for climbing at 400 ft/min. When operating at this point, only 91% of the available engine power can be accessed. The rpm drops despite WOT and the operating point slides to the left and downward on the full throttle b.h.p. curve for MSL shedding power along the way. [Refer to the uppermost bhp curve in the diagram.] Because it is so important to retain access to all of the power that the engine can deliver, the new prop has smaller diameter (less torque) and finer pitch (lower blade loading). It allows 2800 rpm to be maintained whilst climbing at 400 ft/min. For the O-240 engine this produces an extra 12hp in the climb compared to the old prop and 12 horses can give the TR-1 a goodly lift. With the new prop one can truly cruise and climb well at the same time. If WOT is used, the climb rate must exceed 400 ft/min to avoid over-revving. Correct handling of the throttle to prevent over-revving is essential. (A rpm monitor and alarming device will be installed.) The climb rate can of course be increased so that the rpm drops to ~2400 as for the old prop. The resultant climb rate is then just about double that of the old prop. At MSL and 2400 rpm, the new prop will apparently sustain a cruise + climb combination of 122 kt + 780 ft/min. As altitude increases the climb rate could be steadily relaxed to maintain the speed. B) Level flight at low altitude. In level flight at low altitude the old prop could not achieve maximum rpm of 2800 and dropped to 2400 rpm and below when climbing at 400 ft/min. In stark contrast, the new prop could be over-revved in level flight up to altitude of ~8000 feet. This is an unavoidable side-effect if one desires to have the option to extract all the power the engine can deliver essential for operating at hot & high fields where density altitude routinely exceeds 8000 feet. During the cruise climb, rpm must be maintained at 2800 or preferably a little less. (If cooled properly, the Rolls Royce O-240-E is rated for continuous operation at 2800 rpm not that one would do that all the time.) C) Flight at 7500 feet. At this higher altitude, only 75% of the original engine power remains and that only if 2800 rpm can be maintained. Reduction of rpm below 2800 results in less power being accessible. [Refer the middle tier full throttle curve in diagram below.] It can be seen that the maximum power available to the old prop with WOT in level flight was a mere 70%. The effect of climbing is to further decrease the rpm despite the WOT. The resulting loss of power seriously inhibits climb performance at this altitude. The new prop enables access to all the power still available at this level and provides the freedom to operate at any chosen point on that full throttle bhp curve. In particular, climb performance is markedly improved. The same applies to all altitudes below ~8000 feet. -------- _________________________________________ Read this topic online here: http://forums.matronics.com/viewtopic.php?p=333641#333641 Attachments: http://forums.matronics.com//files/climb_vs_cruise_propeller_comparison_for_kis_tr_1_173.jpg ________________________________ Message 2 _____________________________________ Time: 08:55:17 PM PST US From: Galin Hernandez Subject: Re: KIS-List: Re: KIS TR-1 Propeller THANKS for the write-up. Now I can use this to justify to my wife me getting the 3-bladed prop I want.. :o) On Sat, Mar 12, 2011 at 3:10 PM, BlueSkyFlier w rote: m > > > > Light a the end of the tunnel! ... and about time too :o) > > In late January I started exploring to find the best replacement propelle r > configuration for the recently acquired KIS TR-1. The objective is to > replace the old 2'blade 68 x 69 inch =91cruise=92 prop with a new prop which > will markedly improve low speed climb performance after take-off at full > weight. It turns out that the new prop should be a 3'blade 61 x 64 inc h > =91climb=92 propeller. The insights gained from these studies have turned upside > down all notions I previously held regarding what may or may not constitu te > an optimal propeller. > > Initially I was quite ambivalent about 3-bladed props, but results of the > comprehensive performance modeling exercise showed conclusively that a > 3-blade prop offers significant comparative performance gains at low spee d > and also at high altitude (i.e. high density altitudes) ' with only a s mall > sacrifice in top end speed. This follows from the fact that an 8-fold > increase in power is required for a given speed increase. Trading power f or > top end speed is therefore not a very effective use of power unless you h ave > oodles to spare =85 thinking of Scott here ;o). For us lesser mortals wit h > engines cranking out 130hp or less (at best) it may be sensible to forgo a > few knots at the top end (~ 5 knots ) in order to gain a bucketload of sp are > power to support much improved acceleration and climb performance at the > lower end of the speed range in combination with better performance at hi gh > density altitudes. > > For general interest, and for others who also have a problem with sluggis h > takeoffs, the findings are described below with reference to the attached > diagram. From previous communications about propeller performance it seem s > that many KIS TR-1 planes are fitted with 68 or 69 inch pitch props. Tho se > owners my find the information below particularly relevant. > > For actual propellers the choice is still between Prince P-tip, Catto and > Idrovario. > > Kind regards, > Alfred > > > The old (61 x 69=94) and the new (61 x 64=94) propellers are compared for three > typical operating points: > A) Climbing after take-off nominal MSL > B) Level flight at low altitude (nominal MSL) > C) Flight at 7500 feet (or equivalent altitude where only 75% of > engine power remains) > > Notes: (i) Green arrowhead lines connect the tips of the three pairs of > old vs new performance comparison lines on the diagram. > (ii) Full throttle B.H.P. curve information supplied by OC Baker was > instrumental in making it possible to complete the analysis. > (iii) Although I refer to the new prop as a =91climb=92 prop it cruises > perfectly well ' the distinction is merely in name, not in application. > (iv) Brake specific fuel consumption does not vary by much over the RPM > range of interest. Refer > http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption > > A) Climbing after takeoff. > With the old prop, engine rpm tops out at less than 2750 in level flight at > low level. Upon starting to climb the rpm then drops ' to just below 24 00 > rpm for climbing at 400 ft/min. When operating at this point, only 91% of > the available engine power can be accessed. The rpm drops despite WOT and > the operating point slides to the left and downward on the =91full thrott le=92 > b.h.p. curve for MSL ' shedding power along the way. [Refer to the > uppermost bhp curve in the diagram.] > Because it is so important to retain access to all of the power that the > engine can deliver, the new prop has smaller diameter (less torque) and > finer pitch (lower blade loading). It allows 2800 rpm to be maintained > whilst climbing at 400 ft/min. For the O-240 engine this produces an ext ra > 12hp in the climb compared to the old prop ' and 12 horses can give the TR-1 > a goodly lift. > With the new prop one can truly cruise and climb well at the same time. If > WOT is used, the climb rate must exceed 400 ft/min to avoid over-revving .. > Correct handling of the throttle to prevent over-revving is essential. (A > rpm monitor and alarming device will be installed.) The climb rate can of > course be increased so that the rpm drops to ~2400 ' as for the old pro p. > The resultant climb rate is then just about double that of the old prop. At > MSL and 2400 rpm, the new prop will apparently sustain a cruise + climb > combination of 122 kt + 780 ft/min. As altitude increases the climb rate > could be steadily relaxed to maintain the speed. > > B) Level flight at low altitude. > In level flight at low altitude the old prop could not achieve maximum rp m > of 2800 and dropped to 2400 rpm and below when climbing at 400 ft/min. In > stark contrast, the new prop could be over-revved in level flight up to > altitude of ~8000 feet. This is an unavoidable side-effect if one desire s > to have the option to extract all the power the engine can deliver ' > essential for operating at =91hot & high=92 fields where density altitude > routinely exceeds 8000 feet. During the cruise climb, rpm must be maintai ned > at 2800 or preferably a little less. (If cooled properly, the Rolls Royce > O-240-E is rated for continuous operation at 2800 rpm ' not that one wo uld > do that all the time.) > > C) Flight at 7500 feet. > At this higher altitude, only 75% of the original engine power remains ' > and that only if 2800 rpm can be maintained. Reduction of rpm below 2800 > results in less power being accessible. [Refer the middle tier =91full > throttle=92 curve in diagram below.] It can be seen that the maximum pow er > available to the old prop with WOT in level flight was a mere 70%. The > effect of climbing is to further decrease the rpm despite the WOT. The > resulting loss of power seriously inhibits climb performance at this > altitude. The new prop enables access to all the power still available at > this level and provides the freedom to operate at any chosen point on tha t > =91full throttle=92 bhp curve. In particular, climb performance is marked ly > improved. The same applies to all altitudes below ~8000 feet. > > -------- > _________________________________________ > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=333641#333641 > > > Attachments: > > > http://forums.matronics.com//files/climb_vs_cruise_propeller_comparison_f or_kis_tr_1_173.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.