REFLECTOR: Still test flying...battling high CHT's (Geoff Gerhardt)

Mon Sep 10 15:08:45 CDT 2012

Geoff,

Great info!  Do you have any pics?  Gap in the plenum?  It's not clear to me where, what that looks like.  Cowl flap where?  Just on the bottom of the cowl to help with "suction."  Also, any pics of your cooling vanes would be very helpful.  I have a similar problem and would be completely thrilled to conquer it.

Leslie Huttunen

On Sep 10, 2012, at 9:27 AM, Scott Derrick wrote:

> Geoff,
> 
>     I felt like my battle of the CHT's was legend!  
> 
>     I have 5/8 VG's about 4 inches forward of the roof NACA, I thought I got 5-10 degrees better cooling from them.
> 
>     I have turning vanes in my plenum for #1 & #2 cylinders, those are the forward as in nearest to the firewall cylinders.  Normally I've been told those are the warmest because the air has to make a dramatic turn to go through them.  I have two vanes for each cylinder, one ends halfway across the cylinder, the other right between the cylinder and the next cylinder.   I think that dropped the temps on those two cylinders about 5-10  degrees.
> 
>     I opened a gap in the plenum in front of #2(right front).  That helped #2 about 5-10 degrees. 
> 
>     I installed a cowl flap(which I didn't need when I had the IO360, that helped about 15-20 degrees.
> 
>     Now I can climb out full power and not hit 400 unless the oat is above 90F.  In the winter I have trouble keeping the temps up, range is 290-320 in the coldest days.
> 
>     I cruise max throttle LOP 360-330, near max throttle ROP 390-360 in the summer.  Max throttle ROP exceeds RPM redline, so I don't do that much.
> 
> Scott
> 
> -------- Original Message --------
> Subject: Re: REFLECTOR: Still test flying...battling high CHT's (Geoff Gerhardt)
> From: Geoff Gerhardt <geoff.gerhardt at gmail.com>
> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
> Date: 09/10/2012 07:52 AM
>> Fred,
>> 
>> Yes, this is a new engine, so I'm guessing that's part of the reason, but I don't like having one cylinder being that much higher than the other three.  I have VG's about where you suggested putting them, an inch or so ahead of the NACA entrance.  Because I'm having problems primarily on climb out, I'm thinking I should move them fore a few inches.  Also, the VG's I'm using are relatively low profile (<1/2" high).  I think I'll make some taller ones and see if that helps, too.
>> 
>> Thanks for the suggestions.
>> 
>> Geoff
>> 
>> On Mon, Sep 10, 2012 at 9:23 AM, Fred Anderka <fred at holohil.com> wrote:
>> Geoff:
>> 
>> Had similar CHT problems with the IO-550, particularly cylinder #2.  There are deflector plates between the cylinders that can be bent to change the air flow, have not messed with them though.  Trying to put deflectors on top of that engine would be a nightmare with all the plumbing that is on top of that engine.  Is this is a new engine?  I have been told that the CHT's will decrease as the engine breaks in.  This is also a scary portion of your flight testing if you follow engine manufacturers reccommendations.  The engine manufacturers recommend that for proper break in of the engine it should be operated near maximum power for the first 20-25 hours.  Continued low power operation will glaze the cylinders resulting in high oil consumption.  I suppose 25 hours of touch and go's might qualify.
>> 
>> Place a pair of VG's 1 1/2" ahead of the start of the slope of the NACAs.  You will see a dramatic decrease in the CHT's to the point where I am trying to figure out a way to reduce the air flow in the winter or when flying at very cold altitudes.  Scott suggested making the ramp of the NACAs adjustable to reduce the size of the air intake.  The VG's pressurize the plenum to a point where I have also noticed an increase in manifold pressures during climb out.  The Continental gets it's combustion air from the back of the engine plenum.
>> 
>> Fred
>> XL-RG (620 hrs.)
>> 
>> 
>> Date: Sun, 9 Sep 2012 20:08:51 -0400
>> From: Geoff Gerhardt <geoff.gerhardt at gmail.com>
>> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
>> Subject: REFLECTOR: Still test flying...battling high CHT's
>> 
>> All,
>> 
>> Just an update on my test flying.  I've got just over 9hrs in now.  I have been battling high CHT's, making a few changes.  I had a fuel flow imbalance that was causing some problems (hot #2) - I think it was a partially blocked injector.  I took all the injectors/lines out and cleaned them and balanced the flows (mixed and matched injectors until all injectors were putting out the same flow.  Now, in cruise, all cylinders are pretty close and reasonably cool (or, I guess, not overly hot).  Once I get to cruise, they all sit <380F.  But, on climb out, #3 gets way too hot
>> (420F) forcing me to reduce power and bring the nose down so I'm climbing at <500FPM at ~60% power, 100kts.  But, once I get to cruise and can bring the nose down and get the speed up, it behaves.  Still the hottest, but it'll sit around 380F.  So, I'm thinking I have to work on my cooling plenums.  #4 will get hot too, but it doesn't get much over 400F.
>> 
>> Has anyone had success putting deflectors in the plenums to direct air flow to cyls 3/4?  Or, maybe VG's in the entrance of the runners to keep the airflow better attached to the bottom of the runner so it can turn the corner down to cool 3/4 (I have VG's before the NACAs)?
>> 
>> Part of the issue may be my cruise prop - I need to keep full power on to get a decent climb rate.
>> 
>> Thanks.
>> 
>> Geoff
>> 
>> _______________________________________________
>> To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector
>> 
>> Visit the gallery!  www.tvbf.org/gallery
>> user:pw = tvbf:jamaicangoose
>> Check new archives: www.tvbf.org/pipermail
>> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>> 
>> 
>> 
>> _______________________________________________
>> To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector
>> 
>> Visit the gallery!  www.tvbf.org/gallery
>> user:pw = tvbf:jamaicangoose
>> Check new archives: www.tvbf.org/pipermail
>> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
> 
> -- 
> What the superior man seeks is in himself; what the small man seeks is in others.
> Confucius
> _______________________________________________
> To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector
> 
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.tvbf.org/mailman/private/reflector/attachments/20120910/e83e120e/attachment.html>