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

[Fred Anderka]

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