Re: Detonation in a Cont. 550

[Corky Scott]

On Wed, 25 Aug 2004 22:17:48 -0700, Richard Riley
> wrote:

>The #3 cyl has the piston crown pretty much gone, along with the
>rings. The other pistons show significant crown damage as well. The
>local A&P believes it's detonation.

I'm no expert Richard, but that kind of damage could be pre-ignition
rather than detonation.

>The mags were unchanged from their original factory timing, but it
>turns out they were set at 18 and 20 degrees.

One would think, with those timing settings which are conservative,
that detonation would be unlikely because they are promoting a delayed
Peak Pressure Point, which should reduce pressure and heat. It should
also reduce power a bit, but that should also mitigate against
detonation.

Corky Scott

[Tom S.]

"Richard Riley" > wrote in message
...
> A friend of mine has just had a Continental 550 destroy itself. He's
> asked for my advice, but all my experience is with Lycomings. If
> anyone has experience with 550's and can comment, I'd be thankful.
>
> The #3 cyl has the piston crown pretty much gone, along with the
> rings. The other pistons show significant crown damage as well. The
> local A&P believes it's detonation.
>
> The engine has about 60 hours since new. My friend was the pilot for
> the last 4 hours or so. As he's been flying it he's been getting much
> higher fuel burn than he expected - cruise lean was 18-20 GPH. He's
> also seen higher oil temps than expected - 220-240.
>
> The mags were unchanged from their original factory timing, but it
> turns out they were set at 18 and 20 degrees.
>
> Any ideas here? He was running it at no more than 25" and 2500 RPM.
> I'd have thought all that fuel would have kept it cool.
>
http://www.avweb.com/news/columns/182132-1.html
Pelican's Perch #43:
Detonation Myths

[[email protected]]

On Wed, 25 Aug 2004 22:17:48 -0700, Richard Riley
> wrote:

I have many questions.

Was the 550 installed in a type-certificated aircraft?

Was the 550 normally aspirated?

Was the 550 equipped with the auto-lean fuel pump? If so, was your
friend trying to lean the engine manually?

When the engine was installed, was the fuel system properly set-up
following TCM SID97-3B? BTW, this is NOT optional.

Was the ignition timing accurately set/verified when the engine was
installed? A 2 degree split on an out-of-the crate engine is not
unheard of.

Did the friend have accurate CHT indication/s? What were they in
cruise?

What % power does 25 squared equal according the power chart for the
aircraft? If no power chart exists, perhaps someone in the group
flying behind a similiar 550 install can help out.

Was the cruise fuel flow an actual measured fuel flow (a la totalizer)
or was it a metered fuel pressure gage indicating fuel flow?

Detonation to the point of destruction doesn't take an engineer to
identify it. If the #3 piston was damaged to the point that the rings
seized and a slot was burned down the side of the piston (through the
rings), it was subjected to severe/extreme detonation.

I've not taken the time to read Mr. Deakin or Mr. GAMI's treatises,
but am somewhat familiar with detonation in aircraft engines . High
power setting + high CHT + advanced ignition timing + 50-100 degrees
ROP fuel flow is worst case for detonation. Reducing power or CHT,
retarding ignition timing, and either leaning or enrichening the
mixture reduces the risk.

TC

>A friend of mine has just had a Continental 550 destroy itself. He's
>asked for my advice, but all my experience is with Lycomings. If
>anyone has experience with 550's and can comment, I'd be thankful.
>
>The #3 cyl has the piston crown pretty much gone, along with the
>rings. The other pistons show significant crown damage as well. The
>local A&P believes it's detonation.
>
>The engine has about 60 hours since new. My friend was the pilot for
>the last 4 hours or so. As he's been flying it he's been getting much
>higher fuel burn than he expected - cruise lean was 18-20 GPH. He's
>also seen higher oil temps than expected - 220-240.
>
>The mags were unchanged from their original factory timing, but it
>turns out they were set at 18 and 20 degrees.
>
>Any ideas here? He was running it at no more than 25" and 2500 RPM.
>I'd have thought all that fuel would have kept it cool.
>
>Richard Riley