REFLECTOR: IFR Flight

nmflyer1 at aol.com nmflyer1 at aol.com
Sat Oct 29 13:05:56 CDT 2011


Could be the density of the cold air. Colder air requires more fuel, so bumping up the carb temp a bit may put the mixture and atomization of the fuel in the sweet spot. 


Kurt 



-----Original Message-----
From: Laurence Coen <lwcoen at hotmail.com>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Sent: Sat, Oct 29, 2011 7:22 am
Subject: Re: REFLECTOR: IFR Flight


John,
 
The temperature probe port in a MA 4-5 carb is part of the design so I don't see how it could be in the wrong place.  Since you actually experienced carb ice the temperature had to be below freezing.  The probe could be at fault.  My carb temperature shows a temp of 25F or more drop from OAT.
 
Something that you may find interesting is a Dekins trick that I tried while cruising at 9500ft with an OAT of 6C.  I added carb heat to raise the temp in the carb to match OAT.  I got a 30 RPM increase (2630).  EGT and CHT remained stable. I'm not sure why that works.
 
Larry Coen
N136LC




From: aminetech at bluefrog.com 
Sent: Friday, October 28, 2011 12:54 PM
To: Velocity Aircraft Owners and Builders list 
Subject: Re: REFLECTOR: IFR Flight




Larry,
 
11C was a joke.  Guess I should have included (haha).  What I don't understand is why my carb temp probe didn't detect a freezing temp.  Is the probe in the wrong place?
 
John

--- lwcoen at hotmail.com wrote:

From: "Laurence Coen" <lwcoen at hotmail.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Subject: Re: REFLECTOR: IFR Flight
Date: Fri, 28 Oct 2011 12:26:06 -0500


John,
 
Water doesn't freeze at 11C.  If it did you'd have ice on the wings, not in the carb.  The vaporizing of fuel drops the temperature in the carb and causes two things to happen.  Since you were flying in rain it's pretty safe to assume that the humidity was high.  The cooling from the fuel vaporizing  condenses water vapor into super cooled droplets which freeze instantly when they come into contact with the internals of the carb.  Cool dry air, no problem.  Cool damp air, carb ice.
 
Larry Coen
N136LC




From: aminetech at bluefrog.com 
Sent: Thursday, October 27, 2011 4:34 PM
To: Velocity Aircraft Owners and Builders list 
Subject: REFLECTOR: IFR Flight




Today I did my first real IFR flight direct from McPherson, KS to Ocean Springs, MS.  There was VFR weather at both ends and IFR in the middle.  I learned a few things.  In the clouds my speed decreased by 5 kn.  Is this typical?  My IVO prop performed flawlessly and helped a lot with the speed variations.  I replaced the motor brush torsion springs with stronger ones and that seems to keep the motor working, so far.  In rain the plane pitched up and down a lot.  In moderate to heavy rain the A/P couldn't maintain altitude within 100 feet and I had to assist it.  The rain showers lasted only 10-15 min, each.  I was happy about that as I didn't want to have to fight it for an hour.  Also, water dripped on my feet during the heavy rain.  I'll have to seal the canard joints somehow.  The OAT and carb temps were both 6 C initially and gradually increased to 11 C as I progressed farther south.  I was wondering about carb icing, but it was raining, so I figured I was ok.  My MAP began at 20.5", and slowly decreased over 1 1/2 hours.  When it go to 19", I knew something was wrong because I've never seen it that low at 9000'.  So I applied carb heat and the MAP immediately dropped 1/2".  Then it slowly increased for several seconds.  Then the engine stumbled for 1/2 sec and then the MAP jumped to 21".  So there was some ice there.  Now I know that water freezes at 11 C in OK and AR.  My understanding is that you can't fly IFR through MOAs, yet I went through 2.  The last hour I was out of the rain and could have climbed and went VFR, but I decided to continue going in and out of cloud tops for experience.  It was quite bumpy and next time I'll climb and go VFR.
 
I met a guy at the McPherson airport who knows someone who just bought a Velocity with a rotary engine.  Is that your's, Al?
 
John



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