X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao105.cox.net ([68.230.241.41] verified) by logan.com (CommuniGate Pro SMTP 5.2.0) with ESMTP id 2722549 for flyrotary@lancaironline.net; Sat, 09 Feb 2008 14:23:48 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.41; envelope-from=alventures@cox.net Received: from fed1rmimpo03.cox.net ([70.169.32.75]) by fed1rmmtao105.cox.net (InterMail vM.7.08.02.01 201-2186-121-102-20070209) with ESMTP id <20080209192307.DJGN9710.fed1rmmtao105.cox.net@fed1rmimpo03.cox.net> for ; Sat, 9 Feb 2008 14:23:07 -0500 Received: from BigAl ([72.192.137.74]) by fed1rmimpo03.cox.net with bizsmtp id nXP21Y00E1cVYgg0000000; Sat, 09 Feb 2008 14:23:02 -0500 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: Fuel burn Date: Sat, 9 Feb 2008 11:24:16 -0800 Message-ID: <000001c86b51$5c37e870$6401a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C86B0E.4E14A870" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3198 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C86B0E.4E14A870 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Let's see, I think it was Bob mentioned assuming .6 #/hp-hr (BSFC) for = fuel burn. Based on what I measured on the dyno on my 20B, that seems a bit = high to me. My numbers ranged from 0.49 for lean cruise settings to 0.54 for = WOT 5000 rpm, lambda of about 0.93 (max power mixture). =20 So-o-o . . , when I'm cruising at 7500' at 170 KTAS and 9.3 gph, I'll = assume a BSFC of about .5 which means a power of about 115 hp (mogas weighs = 6.18 #/gal). That's a believable number.=20 =20 When I'm taking off at WOT and about 5400 rpm I see about 19 gph. My = dyno hp curve shows about 230 sea level, standard day hp for that rpm. = Adjust that for 1500' elevation and using a BSFC of .54 says I should burn 18.7 gph. That's very consistent. =20 My dyno curve also says 270 hp @ 6200 rpm. Adjust that to 7500' (about = 80%) and varying the speed as the cube root of hp says if I get 170 KTAS at = 115 hp, I should get 210 KTAS at WOT and 6200 rpm. Guess what - when I did = that I saw 208 KTAS readout on my GRT EFIS. =20 It all hangs together. (Don't forget that SAE rated hp is normalized to = sea level, 60F day.) =20 These BSFC numbers should be fairly consistent with what a Lycoming = could get. The fact that I get better fuel economy than the Lyc powered = Velocitys suggests that I have a bit lower drag. =20 This also suggests that the 20B on my Velocity doesn't ever have to = really work very hard. =20 Al ------=_NextPart_000_0001_01C86B0E.4E14A870 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Let’s see, I think it was = Bob mentioned assuming .6 #/hp-hr (BSFC) for fuel burn. Based on what = I measured on the dyno on my 20B, that seems a bit high to me. My = numbers ranged from 0.49 for lean cruise settings to 0.54 for WOT 5000 rpm, = lambda of about 0.93 (max power mixture).

So-o-o . . , when I’m = cruising at 7500’ at 170 KTAS and 9.3 gph, I’ll assume a BSFC of about .5 which = means a power of about 115 hp (mogas weighs 6.18 #/gal). That’s a = believable number.

When I’m taking off at WOT = and about 5400 rpm I see about 19 gph. My dyno hp curve shows about = 230 sea level, standard day hp for that rpm. Adjust that for 1500’ = elevation and using a BSFC of .54 says I should burn 18.7 gph. That’s very = consistent.

My dyno curve also says 270 hp @ = 6200 rpm. Adjust that to 7500’ (about 80%) and varying the speed as the = cube root of hp says if I get 170 KTAS at 115 hp, I should get 210 KTAS at = WOT and 6200 rpm. Guess what – when I did that I saw 208 KTAS = readout on my GRT EFIS.

It all hangs together. = (Don’t forget that SAE rated hp is normalized to sea level, 60F = day.)

These BSFC numbers should be = fairly consistent with what a Lycoming could get. The fact that I get = better fuel economy than the Lyc powered Velocity= s suggests that I have a bit lower drag.

This also suggests that the 20B = on my Velocity doesn’t = ever have to really work very hard.

Al

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