REFLECTOR: Engine RPM Troubleshooting / Loaner Prop?

[Al Gietzen]

Brett;

My sense of this is that the engine is not putting out its advertised power.
Possibly some issue with timing or mixture.

What is the rpm for the rated 306 hp?  I'd assume about 2900.  My 20B rotary
gives 265 hp at a prop speed of 2900.  It would spin a Catto 66" x 85" pitch
to around 2450 static at airport elevation of 1400'. I don't recall max rpm
in the air, but I think it was maybe 2600.

 The 68" x 82 pitch would absorb similar power; maybe a bit more, but I
think your engine should spin that to 2500 static if it was performing
properly.  Since one major change since the dyno run was the ignition, that
might be something to check. Late timing might also give low EGT and
incomplete burn (soot).

We have since reduced pitch to 80" with a smaller blade root, and I now get
over 2500 static and bit over 2900 WOT in the air.  The lower pitch gave
some improvement in takeoff and climb performance, and maybe a bit more top
end.

Al

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Brett Ferrell
Sent: Thursday, April 10, 2008 9:43 AM
To: reflector
Subject: REFLECTOR: Engine RPM Troubleshooting / Loaner Prop?

OK, I guess it's my week for hogging the reflector.  If you've been
following our progress at all you know we've had Dave Bertram fly our plane
a couple of times, and we've been fighting engine RPM the whole time.  I've
been getting some really good advice, but since I think I need to find a
smaller prop at least to break the engine in with, I thought I'd come to the
collective wisdom.

As background, we've got a zero time rebuilt IO540D from Magnum engines with
high compression pistons.  It was dynoed at 306 HP by Lycon, but I believe
the dyno was done with mags, and then Magnum installed my dual LSE plasma
III ignition.  The dyno information was given to Catto, who built us a
68x82" 3 blade fixed pitch prop, which for some reason we can't swing better
than 2150 RPM static.  On the second flight Dave got off the ground in about
800 ft, and had to throttle back to hold under 160 kts, so there is power
there, but the RPM in flight never exceeded 2335.  The RPM is coming off of
the LSE, and we've prop tach'ed it, so I think it's accurate, which my fuel
flow gauge isn't (a Floscan 231, once the engine starts it's readings go
nutty).  Also, on the last flight, the EGTs never exceeded 1083 on the
hottest cylinder and 990 on the coldest (EFIS/one tracked).

So, what I'm looking to do is try to eliminate possible issues with the
installation in as logical fashion as possible.  Catto mentioned that when
Berkut couldn't develop >500 RPM from static to in-flight they found the
intake was choking the engine, so tonight I'll run it without any hosing
attached to the intake and see if we get better RPM from that.

I'm also going to ship my servo back to Airflow and have them readjust it,
since we've diddled with it, and I think (based on the EGTs, which should be
I'm told 1250 or better) that we've got it way out of adjustment.  We had
soot on the blades after the second flight, so I think it's over rich, but
it could be too lean I suppose.

Meanwhile, I'm looking to borrow or buy a shorter prop, so if anybody has
one they can loan or sell me, let me know.  We really need to get 2750 RPM
to break the engine in, and I wouldn't expect to get more than 2450 static
with our prop, and don't expect Dave to make 190 kt circles over the airport
till it's broken in!

Brett
www.velocityxl.com
www.n44vf.com

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