I just got a Cox 049 with a Davis Diesel head running.  It runs a bit
inconsistently; I'm still trying to sort out the best tuning that'll
give me a good flight.  It tunes well on the ground, but in the air it
definitely unloads and starts to 'cackle' like it's under-compressed,
although it could be too rich; I suspect not enough compression because
usually an engine leans out a bit in the air.

It also puts out a lot of black gunk in the exhaust.  I don't remember
this happening the last time I had that head on an engine, but Jimmy
Carter was president then so it may have spewed ink all over everything
for all I can remember.

Does any one know what the black stuff in the exhaust may be?  And
should I expect the think to need a bit more compression in the air than
on the ground?

It's running a 7-4 prop, on a control-line trainer.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

news:JbadnQk-8fqeh_rVnZ2dnUVZ_qfinZ2d@web-ster.com...
| I just got a Cox 049 with a Davis Diesel head running.  It runs a bit
| inconsistently; I'm still trying to sort out the best tuning that'll
| give me a good flight.  It tunes well on the ground, but in the air it
| definitely unloads and starts to 'cackle' like it's under-compressed,
| although it could be too rich; I suspect not enough compression
because
| usually an engine leans out a bit in the air.
|
| It also puts out a lot of black gunk in the exhaust.  I don't remember
| this happening the last time I had that head on an engine, but Jimmy
| Carter was president then so it may have spewed ink all over
everything
| for all I can remember.
|
| Does any one know what the black stuff in the exhaust may be?  And
| should I expect the think to need a bit more compression in the air
than
| on the ground?
|
| It's running a 7-4 prop, on a control-line trainer.
|
| --
|
| Tim Wescott
| Wescott Design Services
| http://www.wescottdesign.com
|
| Do you need to implement control loops in software?
| "Applied Control Theory for Embedded Systems" gives you just what it
says.
| See details at http://www.wescottdesign.com/actfes/actfes.html

The most recent experience I have is with an OS 40FP with the Mecoa
conversion head. It has the right angle compression adjuster with a
stamped steel locking wrench.

It has always had  black gunk in the exhaust. I ran Tygon tubing to the
tail of the airplane to keep as much off as possible. The last fuel I
bought from Davis Diesel had synthetic lube instead of castor lube. If
anything the black exhaust gunk was worse. I did break the engine in on
glow fuel before installing the diesel head as recommended.

I always start the FP40 with the compression reduced and using an
electric starter. (not recommended) Then I increase the compression and
adjust the needle valve and airbleed for the best transition from idle
to high speed as well as a little on the rich side from peak rpm. When I
get the pre-ignition frying or crackling sound I know that it has too
much compression. I back off on the compression and readjust the needle
valve.

If Davis Diesel is no help you might try Dr. Diesel at this site-
http://www.cafes.net/doctordiesel/default.htm

--
Anyolmouse

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