X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from access.aic-fl.com ([204.49.76.2] verified) by logan.com (CommuniGate Pro SMTP 5.1c.4) with ESMTP id 1407715 for flyrotary@lancaironline.net; Sun, 17 Sep 2006 23:19:50 -0400 Received-SPF: none receiver=logan.com; client-ip=204.49.76.2; envelope-from=unicorn@gdsys.net Received: from b9k4u9 (unverified [204.49.76.26]) by access.aic-fl.com (Rockliffe SMTPRA 4.5.6) with SMTP id for ; Sun, 17 Sep 2006 22:16:42 -0500 Message-ID: <003201c6dae1$fee86e20$1a4c31cc@b9k4u9> From: "Richard Sohn" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: ducted fan questions Date: Sun, 17 Sep 2006 22:13:16 -0700 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_001F_01C6DAA6.798B5AC0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2869 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2962 This is a multi-part message in MIME format. ------=_NextPart_000_001F_01C6DAA6.798B5AC0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message ----- Original Message -----=20 From: Russell Duffy=20 To: Rotary motors in aircraft=20 Sent: Sunday, September 17, 2006 6:12 PM Subject: [FlyRotary] Re: ducted fan questions ing a ducted fan(not a shrouded propeller). =20 Now that's just way too cool Richard :-) =20 Was the fan running directly off the engine, with no redrive? Did you = feel that the performance was better than it would have been with a = traditional redrive and prop? If I get serious about trying this, I'll = certainly take you up on your offer to share info. =20 Cheers, Rusty There are plenty of ducted fans, look at the bypass stage of every = turbofan engine. The difference between a ducted fan and a shrouded = propeller is the blade solidity. This is the ratio of the fan cross = section to the total blade area. A turbofan is around "1" and a shrouded = propeller, I have seen, may be as low as .1 or less.=20 My fan with the KAWA engine was running reduced at 3400RPM, in order = to allow for more solidity with the benefit of lower noise. When I = changed to direct drive with adjusted solidity at the same HP, the fan = efficiency went from 70% down to less then 50%, and the noise was almost = unbearable.=20 The fan I flew had six blades, and the test fan on direct drive had = three blades, which were smaller too.=20 BTW the diameter was 26".=20 The conclusion is, if you aim for a solidity of 1, or close to 1, for = a given hp, there is only one fan size and RPM. Now, what compromises = can be made to arrive at a practical design? Your imagination, and = expectations, are the only limits. My 90+hp design has nine blades at 26", giving a solidity of .6 . This = is not very good, however, I do not want to make a new shroud and I also = have a given max RPM, which locks me in. Nevertheless, the data would be = as good as any, knowing the deficiencies. So much for now.=20 Should we discuss this on another E-Mail? I don't want to bore our = rotor head friends. Richard Sohn N-2071U ------=_NextPart_000_001F_01C6DAA6.798B5AC0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message
 
----- Original Message -----
From:=20 Russell=20 Duffy
Sent: Sunday, September 17, = 2006 6:12=20 PM
Subject: [FlyRotary] Re: ducted = fan=20 questions

ing a ducted fan(not a shrouded = propeller).  
 
Now that's just way too cool Richard=20 :-)  
 
Was the fan running directly off the = engine, with no=20 redrive?  Did you feel that the performance was better than it = would have=20 been with a traditional redrive and prop?  If I get = serious=20 about trying this, I'll certainly take you up on your offer to share=20 info.   
 
Cheers,
Rusty
 
 
There are plenty=20 of ducted fans, look at the bypass stage of every turbofan engine. The = difference between a ducted fan and a shrouded propeller is the blade=20 solidity. This is the ratio of the fan cross section to the total = blade area.=20 A turbofan is around "1" and a shrouded propeller, I have seen, may = be as=20 low as .1 or less.
My = fan with the=20 KAWA engine was running reduced at 3400RPM, in order to allow for more = solidity with the benefit of lower noise. When I changed to direct = drive with=20 adjusted solidity at the same HP, the fan efficiency went from 70% = down to=20 less then 50%, and the noise was almost unbearable. =
The = fan I flew had=20 six blades, and the test fan on direct drive had three blades, which = were=20 smaller too.
BTW = the diameter=20 was 26".
The conclusion is, if you aim for = a=20 solidity of 1, or close to 1, for a given hp, there is only one fan = size and=20 RPM. Now, what compromises can be made to arrive at a practical = design? Your=20 imagination, and expectations,  are the only=20 limits.
My = 90+hp design=20 has nine blades at 26", giving a solidity of .6 . This is not very = good,=20 however, I do not want to make a new shroud and I also have a given = max RPM,=20 which locks me in. Nevertheless, the data would be as good as any, = knowing the=20 deficiencies.
 
So = much for now.=20
 
Should we discuss=20 this on another E-Mail? I don't want to bore our rotor head=20 friends.
 
Richard=20 Sohn
N-2071U
 
 
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