X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from aspensprings.uwyo.edu ([129.72.10.32] verified) by logan.com (CommuniGate Pro SMTP 5.4.5) with ESMTPS id 5548580 for flyrotary@lancaironline.net; Fri, 18 May 2012 10:45:39 -0400 Received-SPF: none receiver=logan.com; client-ip=129.72.10.32; envelope-from=SBoese@uwyo.edu Received: from ponyexpress-ht5.uwyo.edu (extlb.uwyo.edu [172.26.4.4]) by aspensprings.uwyo.edu (8.14.4/8.14.4) with ESMTP id q4IEiw71003288 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=FAIL) for ; Fri, 18 May 2012 08:45:00 -0600 (MDT) (envelope-from SBoese@uwyo.edu) Received: from ponyexpress-m10.uwyo.edu ([fe80::60dd:cb9e:6f71:3d48]) by ponyexpress-ht5.uwyo.edu ([fe80::addc:5ab0:b0f8:ab9e%13]) with mapi id 14.01.0339.001; Fri, 18 May 2012 08:45:00 -0600 From: "Steven W. Boese" To: Rotary motors in aircraft Subject: Re: BSFC and EGT Thread-Topic: BSFC and EGT Thread-Index: AQHNNQTNKlJeW96jF0yMHoJ1kxEUAQ== Date: Fri, 18 May 2012 14:45:00 +0000 Message-ID: <3E8191F276108F4481AB0721BBA9269E05C4AE78@ponyexpress-m10.uwyo.edu> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [75.228.140.227] Content-Type: multipart/alternative; boundary="_000_3E8191F276108F4481AB0721BBA9269E05C4AE78ponyexpressm10u_" MIME-Version: 1.0 --_000_3E8191F276108F4481AB0721BBA9269E05C4AE78ponyexpressm10u_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Doug Dempsey wrote the following response to the BSFC and EGT plot that I p= osted recently: As we discussed at Paducah, the operating condition around 50 deg F LOP was= not used as a test point and while we indicated we were planning to do so,= it has not yet been performed. Steve, I believe you have confirmed this ap= proximate value in many hours of flying with your RV-6? From a study of gas dynamics and combustion, it is expected that the "minim= um peak" BSFC (that which produces the most power for the least fuel consum= ption.....and most MPG at that specific power condition and resultant veloc= ity) will be in the -30 to -70 deg F lean of Peak EGT. This depends very sl= ightly on engine design, but is fundamentally related to the physics of gas= combustion and mixture ratios of fuel and air. Note also that the operating condition of the graph was at 22.7" Hg MAP and= WOT due to our testing density altitude. It is possible that at some other= test condition, ie...-50 deg Lean of Peak, the BSFC could be lower (better= ie.. less fuel per hr per HP produced-lb/HP-hr.). Data from WWII engines p= roves that on those large radials, slower and heavier loads produced better= BSFC and resulted in greater range. The story of Lindbergh's instructions = to new pilots on this condition is legend for most pilots (unfortunately th= ose conditions require constant speed props)! My data on some of those engi= nes indicates a best BSFC of 0.58 in cruise condition! Lots better than the= .75-.80 at takeoff power!! While it is equally possible that our HP readings may be in error in magnit= ude, we suspect that the myth of Huge HP expectations is more the case. Our= plots of HP vs. MAP show minimal hysteresis, that is... the data retraces = the curve both up and down the MAP excursion within +/-3%, which should ind= icate reasonable error (<+/- 3%). Corrections for Density Altitude on numer= ous testing occasions have indicated that the engine would produce 165 +/- = 5 HP @6,500 RPM at sea level, which we consider probable. If one is propeller limited to 5,200 rpm instead of 6,500 rpm.....165 HP ca= nnot be generated. If one is N.A. and at 10,000' Density Altitude, 165 cann= ot be generated! No magic....just God's rules as we know them. The book "Internal Combustion Engine Fundamentals" by John B. Heywood, ISBN= 0-07-028637-X, McGraw-Hill, 1988 is a wonderful and readable book with in-= detail discussions of this area of interest. Heywood lists the minimum BSFC= of the Wankel rotary as 0.51. We believe this is possible under the most a= dvantageous conditions and have experienced 0.52-0.54 BSFC during several t= est conditions. Note of caution: the highest rate of heat transfer from gas to combustion c= hamber to coolant (NOT peak power) is -25 to -75 deg F RICH of peak......ev= en though PEAK POWER is nearby at -90 to -160 RICH of PEAK, the transfer to= coolant goes down, not up. If one wants to go fast...a "little rich" is NO= T an advised operating condition. Got to -100 to -125 deg F RICH of peak...= .more power, less heat to coolant. Bottom-line: Leaning more lean than -70 deg F of Peak EGT does NOTHING but = lower power faster than fuel consumption. If you want to fly slow set the M= AP, lean to find PEAK and then lean to -50 deg F from that point. Will it r= un super lean?? Perhaps, but who wants an even greater loss of power?? Each installation is slightly different and the absolute value will vary. P= rocedure: lean to find your Peak EGT, then ....either richen to -120 deg F = Rich of Peak for maximum power....or lean to -50 deg F for maximum fuel eff= iciency (minimum BSFC/maximum MPG) at that MAP. Do not then increase MAP to= recover the lost velocity.......you just upset your tuning for max MPG app= le cart! Regards, Doug Steve Boese RV6A, 1986 13B NA, RD1A, EC2 --_000_3E8191F276108F4481AB0721BBA9269E05C4AE78ponyexpressm10u_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Doug Dempsey wrote the following response to the BSFC= and EGT plot that I posted recently:
 
As we discussed at Paducah, the operating condition a= round 50 deg F LOP was not used as a test point and while we indicated= we were planning to do so, it has not yet been performed. Steve, I believe= you have confirmed this approximate value in many hours of flying with you= r RV-6?
From a study of gas dynamics and combustion, it is ex= pected that the "minimum peak" BSFC (that which produces the most= power for the least fuel consumption.....and most MPG at that specific pow= er condition and resultant velocity) will be in the -30 to -70 deg F lean of Peak EGT. This depends very slightl= y on engine design, but is fundamentally related to the physics of gas comb= ustion and mixture ratios of fuel and air.
Note also that the operating condition of the graph w= as at 22.7" Hg MAP and WOT due to our testing density altitude. It is = possible that at some other test condition, ie...-50 deg Lean of Peak, the = BSFC could be lower (better ie.. less fuel per hr per HP produced-lb/HP-hr.). Data from WWII engines proves that on t= hose large radials, slower and heavier loads produced better BSFC and resul= ted in greater range. The story of Lindbergh's instructions to new pilots o= n this condition is legend for most pilots (unfortunately those conditions require constant speed props)! My d= ata on some of those engines indicates a best BSFC of 0.58 in cruise condit= ion! Lots better than the .75-.80 at takeoff power!!
While it is equally possible that our HP readings may= be in error in magnitude, we suspect that the myth of Huge HP expectations= is more the case. Our plots of HP vs. MAP show minimal hysteresis, that is= ... the data retraces the curve both up and down the MAP excursion within +/-3%, which should indicate reas= onable error (<+/- 3%). Corrections for Density Altitude on numerous= testing occasions have indicated that the engine would produce 165 +/-= 5 HP @6,500 RPM at sea level, which we consider probable.
If one is propeller limited to 5,200 rpm instead of 6= ,500 rpm.....165 HP cannot be generated. If one is N.A. and at 10,000' Dens= ity Altitude, 165 cannot be generated! No magic....just God's rules as we k= now them.
The book "Internal Combustion Engine Fundamen= tals" by John B. Heywood, ISBN 0-07-028637-X, McGraw-Hill, 1988 is= a wonderful and readable book with in-detail discussions of this area of i= nterest. Heywood lists the minimum BSFC of the Wankel rotary as 0.51. We believe this is possible under the most advantag= eous conditions and have experienced 0.52-0.54 BSFC during several test con= ditions.
Note of caution: the highest rate of heat t= ransfer from gas to combustion chamber to coolant (NOT peak power) is -= 25 to -75 deg F RICH of peak......even though PEAK POWER is nearby at -90 t= o -160 RICH of PEAK, the transfer to coolant goes down, not up. If one wants to go fast...a "little ric= h" is NOT an advised operating condition. Got to -100 to -125 deg F RI= CH of peak....more power, less heat to coolant.
Bottom-line: Leaning more lean than -70 deg F of Peak EGT does = NOTHING but lower power faster than fuel consumption. If you want to fly sl= ow set the MAP, lean to find PEAK and then lean to -50 deg F from that poin= t. Will it run super lean?? Perhaps, but who wants an even greater loss of power??
Each installation is slightly different and the absolute value will va= ry. Procedure: lean to find your Peak EGT, then ....either richen to -120 d= eg F Rich of Peak for maximum power....or lean to -50 deg F for maximum fue= l efficiency (minimum BSFC/maximum MPG) at that MAP. Do not then increase MAP to recover the lost velocity...= ....you just upset your tuning for max MPG apple cart!
Regards,
Doug
 
Steve Boese
RV6A, 1986 13B NA, RD1A, EC2
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