REFLECTOR: Running LOP -- Climbing or Cruising

Brian Michalk michalk at awpi.com
Thu Nov 11 11:14:33 CST 2010


There's lots of very technical literature on detonation.
Detonation occurs during normal operations, because it's a random 
event.  We just want to minimize the probability of it happening, 
causing a sympathetic feedback.

There's a few things we can do to prevent detonation.  Not all of them 
are reasonable as a matter of operational parameters.
* lower the (cylinder) charge temperature
* increase RPM
* decrease cylinder volume
* decrease (cylinder) manifold pressure
* increase the octane of the fuel

If one has a runaway CHT on a cylinder, it's probably detonation.  The 
event scrubs the cylinder walls of a thin layer of insulating gasses, 
causing a feedback loop exacerbating the problem.  If this is happening, 
try a cooler spark plug.  This is a plug with less reach into the 
cylinder.  Plugs present nice sharp edges that are hot, causing 
preignition leading to detonation.  Another thing to try is to retard 
timing.  During first flights, if oil or engine cooling is problematic, 
back off on the timing to try to reduce temps.  Fix baffling and add 
back your timing if possible.

I know this doesn't directly answer the LOP operation.  We can either go 
LOP or ROP.  To run at peak EGT is to run at peak combustion temps, 
heating up the cylinders, raising the charge temps.  If one is able to 
get all of the cylinder temperature profiles to line up exactly, then 
there's no thermodynamic operating difference if one runs 25 ROP or 25 
LOP.  They are identical ... or almost identical in that the ROP regime 
makes an almost insignificant more power.

On 11/11/2010 10:36 AM, Bob Jackson (Jax Tech) wrote:
>
> Thanks Scott & Brett,
>
> I think Brett answered the question, and the answer is there is 
> nothing wrong with running LOP at any altitude, provided you're not at 
> too high of a power setting (generally accepted in the Tornado Alley 
> (Turbo Cirrus) community as 75 to 85% power.  So if you want to climb 
> WOT (and you're not turbocharged) once you get above 5-6000' there is 
> only enough air to get 75-85% power, so you may as well be LOP 
> (assuming you can still keep your CHTs down).
>
> But that doesn't mean that you can't run LOP at any altitude, as long 
> as you're below 75-85% power where detonation shouldn't be a problem 
> -- which was my question.  I think Brett's answer (which applies only 
> to full power ops) has been turned around inadvertently by some to 
> mean you can't run LOP safely below 5-6000', which I don't believe is 
> the case, provided (as in all LOP operations) that you're not at a 
> power setting above 75-85% (and you're temps are OK) in order to 
> minimize the detonation risk.
>
> We've studied the Deakin/Tornado Alley articles a lot over the years 
> because that's how we want to operate.  I think these guys have 
> re-opened a whole new dimension to efficient, safe and 
> good-for-your-engine operations for general aviation.  The Turbo 
> Cirrus, for one, is designed around LOP operation.  I was just 
> wondering whether there was something we had missed concerning 
> cruising LOP at low altitudes...
>
> Thanks,
>
> Bob
>
> ------------------------------------------------------------------------
>
> *From:*reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] 
> *On Behalf Of *Scott Derrick
> *Sent:* Thursday, November 11, 2010 9:59 AM
> *To:* Velocity Aircraft Owners and Builders list
> *Subject:* REFLECTOR: Running LOP in the climb
>
> Here's a link to JOhn's article with instructions on how to run LOP in 
> teh climb to altitude.
>
> http://www.avweb.com/news/pelican/182085-1.html
>
> Scott
>
> -------- Original Message --------
> Subject: Re: REFLECTOR: Auto engine installed 172
> From: Brett Ferrell <reflector at velocityxl.com> 
> <mailto:reflector at velocityxl.com>
> To: reflector <reflector at tvbf.org> <mailto:reflector at tvbf.org>
> Date: 11/11/2010 06:49 AM
>
> Bob,
>
> I'm not an expert, so I'll probalby get part of it wrong, but as I 
> understand it:
>
>     * Running LOP at "Full Power" risks detonation
>     * "Full Power" is only possible below something like 5-6,000',
>       above that the air is so thin, you cannot generate over 75% power
>     * Thus leaning above that altitude is safe, because you can't
>       generate //enough power// to risk detonation.
>
> But here is an article that is probably much, much more useful.
>
> http://www.avweb.com/news/pelican/182132-1.html
>
>
> Brett
>
>   
>
>   
>
> ------------------------------------------------------------------------
>
> *From:*reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] 
> *On Behalf Of *Bob Jackson
> *Sent:* Wednesday, November 10, 2010 10:36 PM
> *To:* 'Velocity Aircraft Owners and Builders list'
> *Subject:* Re: REFLECTOR: Auto engine installed 172
>
> You're right, Scott and Sid!
>
> I said "electronic ignition" -- I meant "electronic fuel injection".  
> With Gami injectors and the already-well-balanced airflow of the 
> IO-550N, LOP is a piece of cake and the standard operating mode for us 
> in cruise at any altitude.  What we need is better fuel injection.  
> I'm hoping Sid will have an availability list for that, too!
>
> A while back there was some talk of it being bad or dangerous to run 
> LOP at low altitudes, but I never heard anyone explain their "why".  
> Other than wanting to be back set up ROP in the pattern for any 
> required WOT go-around, can someone explain to me the above concern?  
> We routinely cruise LOP at all altitudes without distinction.
>
> Thanks,
>
> Bob
>
>   
>
>
> _______________________________________________
> To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector
>
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.tvbf.org/mailman/private/reflector/attachments/20101111/30b16b51/attachment-0001.htm>


More information about the Reflector mailing list