Received-SPF: none
 receiver=logan.com; client-ip=64.202.165.230; envelope-from=nospam@avamail.net
Message-ID: <450E4D80.7030504@avamail.net>
Date: Mon, 18 Sep 2006 09:40:48 +0200
From: Donald Willard Garrett <nospam@avamail.net>
User-Agent: Thunderbird 1.5.0.7 (Windows/20060909)
MIME-Version: 1.0
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: ducted fan questions
References: <list-1407717@logan.com>
In-Reply-To: <list-1407717@logan.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Hey! If you are taking this offline, please cc me!

Donald Garrett     flyrotaryNOspam@avamail.net

Richard Sohn wrote:
>  
>
>     ----- Original Message -----
>     *From:* Russell Duffy <mailto:russell.duffy@gmail.com>
>     *To:* Rotary motors in aircraft <mailto:flyrotary@lancaironline.net>
>     *Sent:* Sunday, September 17, 2006 6:12 PM
>     *Subject:* [FlyRotary] Re: ducted fan questions
>
>     ing a ducted fan(not a shrouded propeller).  
>      
>     Now that's just way too cool Richard :-)  
>      
>     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.   
>      
>     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.
>     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.
>     The fan I flew had six blades, and the test fan on direct drive
>     had three blades, which were smaller too.
>     BTW the diameter was 26".
>     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.
>      
>     Should we discuss this on another E-Mail? I don't want to bore our
>     rotor head friends.
>      
>     Richard Sohn
>     N-2071U
>      
>      
>