REFLECTOR: Back in the air.

Mon May 28 11:24:30 CDT 2007

Hiroo,

My #6 runs the hottest on my IO540 but I always attributed that to the
oil cooler tapping off NACA air right in front of it.  I have the
pressure box on top of the engine with CHT in the 340F-360F common and
#6 about 400F.   

Something you might want to check is the casting flashing between the
fins on the cylinder head.  It is well documented that if the flashing
between the fin, from where the two halves of the mold met, isn't
thoroughly removed, that it will block air flow.  The better fit the
baffling, the worse the problem.  With real tight fitting baffling
against the fins, the blockage between the fins form a dam, essentially
cutting off all cooling air flow.

I looked at your numbers and see that you climbed at 2430 rpm and
cruised at 2650 rpm?  Are those numbers reversed?  You cruise at a
higher rpm than you climb at, or were they just sample settings that you
happened to note.  

On a different, but related, subject, Aviation Consumer had an
interesting article a year or two ago about the optimum combination of
rpm and mp.  There was thought afoot that running lower rpm at the same
mp (for instance 2300 x 24") would reduce piston travel and thus wear of
the rings and cylinders.  Interestingly, the outcome of the
investigation was that the reverse was better for the engine (2500 x
24").  Even though the pistons travel a longer distance and reverse
directions more times because of the higher rpm, the peak pressure in
the cylinder was lower and later.  In other words, the gas was expanding
later in the ignition cycle as the piston was on its downward power
movement.  At a lower rpm, the flame front had a chance to propagate
further while the piston was still near the top of its stroke, thus a
higher pressure was generated.  Pressure is the enemy of engine life--as
any turbo, or 10:1 piston, fliers.  In short, lugging the engine at high
power settings is not a good idea (if their investigation and research
is to be believed).

One thing I have noticed is oil temps go up about 5% at 2500 rpm versus
2400, which I assume if greater friction from greater piston travel et
al.  I haven't noticed a corresponding change in CHT because the
influence of leaning can overwhelm the minor temp change, if any, from
higher rpm ops.  

Chuck Jensen 

 -----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Hiroo Umeno
Sent: Monday, May 28, 2007 11:22 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Back in the air.

Good thoughts on the mixture.  I didn't mention it in the original post
but I did suspect something like that and I kept an eye on the EGT
through the flight.  The EGT was generally in line with the rest so I
definitely think it is an airflow issue.  I'll have to see if the
"rubber seal" under the cowl is leaking or not.

My plane does not have the conventional fiberglass box over the top of
the engine.  Instead, the whole upper cowl area is pressurized through
ram air from the top NACA and I have metal baffles around the entire top
with rubber flaps sealing the gaps between the baffles and the cowl.  If
it isn't leaking, I might need an additional arrangement to direct more
air over to that corner.  It is interesting that the #5 on the other
side has no problems.

Hiroo

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Chuck Jensen
Sent: Monday, May 28, 2007 7:27 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Back in the air.

Hiroo,

It sounds like you are getting some quality time on the bird.  Regarding
the hot C#6, of course, it may be a cooling/baffling (well, actually its
always baffling, but of a differently type) issue.  However, another
possible cause is if you are running rich of peak, #6 by be way leaner
than the other cylinders so while they are running ROP, #6 is running
right at peak EGT/CHT temps.  Or, if you have engine instrumentation for
each cylinder and you are running lean of peak, then perhaps #6 fuel
mixture is way too rich.  In this case, as you bring the other cylinders
to LOP, it leaves #6 right at peak temperatures.

Air flow/cooling may be the most obvious cause of hot temps, but since
its isolated to a single cylinder, there are a couple other possible
causes, such as fuel/air mixture to that cylinder.  Just another thought
to noodle over.

Chuck Jensen 

 -----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Hiroo Umeno
Sent: Sunday, May 27, 2007 9:36 PM
To: Velocity Aircraft Owners and Builders list
Subject: REFLECTOR: Back in the air.

Yesterday, after many thwarted attempts and frustrating weekends staring
at the sky, I was able to bring N21HV back in the air.

Take off was at 1:10pm.  After staying close to Paine to verify that all
systems were running temps were in the reasonable range, I took the
plane through some "cruise" configuration tests over Puget Sound.  The
flight prior to this in September was with the Mid-CG configuration with
60lb ballast on the co-pilot seat and the additional 30lb of lead-shot
in the nose.  Yesterday was a aft-CG test without the 60lb ballast
keeping the 30lb in the nose, full tank of gas.  This simulates the
single-pilot X/C load-out.

Some numbers in case anyone cares<g>.  (Performance data based on data
capture from the EFIS)

Take-off Weight: 2011lb (2400 Gross)

Take-off CG: 121 (115 - 121 allowable)

Initial Climb:  1800fpm at 2424ft DA, 2430rpm, 27.5in/Hg on the MAP,
100Kts

Cruise: At 6000ft DA, 2650rpm, 20.6in/Hg MAP, 152Kts TAS, 8.0Gph burn
rate.

The plane is currently in the "Dirty, no-pants" configuration where all
the aerodynamic trims, fairings, and wheel covers are still off which, I
am told, will add another 15Kts or so.  At this point, I haven't been
able to test the wide open throttle since the CHT is still running
hotter than I would like.  I have 13 hours on the engine so far and my
engine guy tells me that it will run hot until all the rings break in.
It does bother me a bit that #6 CHT stays consistently hotter than the
rest, though.

I did a somewhat rectangular leg of W10 - BVS - FHR - 0S9 - W10
including some dodging of occasional wispy layers here and there.  Over
South Whidbey, I did some low-speed work like MCA, Pitch-Buck, etc.  On
pitch-buck, with the CG fairly close to the aft limit, I ran out of the
elevator travel at 75Kts and the aircraft settled onto steady, mushy
descent.  Noticeable pitch buck never occurred.

Back at Paine, I did a few touch-and-go's, all were fairly good.  On the
last landing, (full-stop) I was able to slow the plane down to taxi
speed a bit past A6.  If I can consistently nail this one, I can bring
my personal minimum runway length to 3,000 from my current 4,000.

Overall, very good flight.  2.5 hours on Hobbs.  13.9 TT airframe
cumulative to date.  It's a nice flying machine!

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