REFLECTOR: Still test flying...battling high CHT's

[Geoff Gerhardt]

Darrell,

There was some reassuring and educational info in that article as Duane was
speaking generally about leaning procedure, EGT's and CHT's.  While it
sounds like nobody wants to run routinely a cylinder at 425F, I may be
freaking out a bit too much when my cylinder hits 420F as Duane indicates
he had people with 450F cylinders who have been trying to cool them down.
 My #4 is unusually high, tho.  I think I'll go back and look at which
injectors I swapped as it used to be my #2 was the unusually high one.

I do have VG's just before the NACA.  I may try different locations.  My
gut tells me that, because its mostly a problem on climb out that putting
one set of VG's more fore (say just behind the door, to keep the air
attached to the roof), and one set inside the NACA (to keep the air
attached to the runner and help turn the corner to cool the fore cylinders)
might help (this from a scientist, but a scientist who knows nothing about
aerodynamics).

Thanks for pointing out that article.

Geoff

On Sun, Sep 9, 2012 at 11:08 PM, Darrell & Nora Kufalk <kufalk at wi.rr.com>wrote:

> How many hours on your engine?  New cylinders run hot during break in.
>
> Also read this starting on page 4 third column halfway down.  Duane Swing
> talks about VGs and CHTs.
> http://www.velocityaircraft.com/views/v29.pdf
>
> For what it's worth, I tested 1/4" tall VGs in front of my NACAs and got
> exactly ZERO degrees in cooling reduction.
>
> Darrell
>
>
> -----Original Message-----
> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
> Behalf Of Richard J. Gentil
> Sent: Sunday, September 09, 2012 8:40 PM
> To: geoff.gerhardt at gmail.com; Velocity Aircraft Owners and Builders list
> Subject: Re: REFLECTOR: Still test flying...battling high CHT's
>
> Hi Geoff,
>
> My deflectors inside the plenum did nothing but the VG's in front of the
> NACA's helped. I have not tried inside the runners.
>
> Richard
>
> Sent from my iPhone 4 Classic
>
> On Sep 9, 2012, at 8:08 PM, Geoff Gerhardt <geoff.gerhardt at gmail.com>
> wrote:
>
> > 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
> >
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