REFLECTOR: Fuel Consumption Performance

Wed Aug 5 08:39:29 CDT 2009

Terry,

running the first cylinder LOP can put some of the richer cylinders
right in the BAD zone. Thats well... bad!  Thats why you always lean to
the last cylinder when running LOP.  Thats also why you lean to the
first cylinder when running ROP, so all the other cylinders are rich of
that point.

you said

"I was afraid my coolest cyl could be 150 LOP before the last cly peaked and that I could burn that exhaust valve."

Thats exactly backwards. Once a cylinder reaches peak EGT and goes on
the LOP side it will run cooler and cooler the leaner you run it. The
absoluter worst mixture is about 25-50 degrees ROP in terms of
detonation and the timing of peak power pulses.  If your coolest
cylinder was running at 150 degrees leaner than the last cylinder to
reach 75 LOP it would probably not be firing due to the too lean mixture.

How to operate your engine is a complex topic.  Here is a great set of
articles by John Deacon, I consider a must for any recip operator,
whether you run LOP or ROP.

part 1
http://www.avweb.com/news/pelican/182179-1.html
part 2
http://www.avweb.com/news/pelican/182176-1.html
part 3
http://www.avweb.com/news/pelican/182583-1.html
part 4
http://www.avweb.com/news/pelican/183094-1.html

Here's GAMI's lean test,  a great thing for anybody to do, to see how
balanced their injectors are.

http://www.gami.com/gamijectors/leantest.php

Scott

Terry Miles wrote:
> Scott,
> No I didn't know that.  Thanks.  Remember I am the rookie with no recip
> time.  I was afraid my coolest cyl could be 150 LOP before the last cly
> peaked and that I could burn that exhaust valve.  As it is, some cyl never
> get to peak.  That's why the fast TAS probably, and I could get the FF below
> 11 when I was up over 10,000 and only loose a few knots.  
> Thanks
> Terry
>
> -----Original Message-----
> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
> Behalf Of Scott Derrick
> Sent: Tuesday, August 04, 2009 08:05
> To: Velocity Aircraft Owners and Builders list
> Subject: Re: REFLECTOR: Fuel Consumption Performance
>
> Terry,
>
> You probably already know this.
>
> at that altitude you could run any mixture without fear of detonation,
> however that is not how LOP operation is usually done.
>
> For LOP you always lean to the last cylinder, not the first as you do for
> ROP.
>
> GAMI, recommends 75 LOP as the richest mixture now. Especially in a full
> power climb.
>
> nice numbers...
>
> Scott
>
> Terry Miles wrote:
>   
>> Tom,
>> I've got an XLRG-5 IO-540K 300 HP with a 3-blade constant speed ACI prop.
>> These numbers are about 2 weeks old.  Same day taken only an hour or so
>> apart on the xc from PA to IN.    
>>
>> Altitude  10000       12000
>> OAT C	    +16		+12
>> TAS       193		195
>> IAS       160		157
>> FF        11.5		11.5
>> RPM       2330		2390
>> % pwr      64  		62           wide open throttle
>> Oil T      192
>> Oil P       66
>> Cyl ave    300          25 hotter
>> EGT        1230         same
>>
>> I lean until my first cyl is 50 lop and quit there.  I can likely go 
>> to 11 gal.
>> I was about 2600 gross wgt at the time.    
>>
>> Terry Miles
>>
>> -----Original Message-----
>> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] 
>> On Behalf Of Tom Tolton
>> Sent: Monday, August 03, 2009 19:39
>> To: 'Velocity Aircraft Owners and Builders list'
>> Subject: Re: REFLECTOR: Fuel Consumption Performance
>>
>> Thanks Brian.  I'll start looking for BSFC numbers. After posting my 
>> last message I found an article where a LANCAIR with a 550N was tested 
>> to determine the Vbc or velocity for best CAFÉ or best Comparative 
>> Aircraft Flight Efficiency.  At 12.5 K density altitude 2300 rpm and 
>> 248.3 smph they were able to reduce fuel consumption to 10.4 gph LOP.  
>> Do you know if Velocity has entered the CAFÉ competition?
>>
>> -----Original Message-----
>> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] 
>> On Behalf Of Brian Michalk
>> Sent: Monday, August 03, 2009 8:16 PM
>> To: Velocity Aircraft Owners and Builders list
>> Subject: Re: REFLECTOR: Fuel Consumption Performance
>>
>> You want the BSFC number.  Brake Specific Fuel Consumption.  The 
>> smaller the number, the better.
>>
>> Typically, the following lower the BSFC:
>> large displacement
>> high compression ratio
>> low RPM
>>
>> Tom Tolton wrote:
>>   
>>     
>>> I recently traveled to Oshkosh with a friend who owns a Velocity 173 
>>> with fixed gear and a 200 HP fuel injected Lycoming.  He was able to 
>>> reduce gas consumption to 6.2 gallons per hour at 10500 feet and 
>>> maintain a speed of about 125 nm/hr using LOP techniques.
>>>
>>>  
>>>
>>> I am building a XLFG -5 with constant speed propeller.  I am looking 
>>> for what one might expect in minimum gas consumption using LOP 
>>> techniques at a density altitude of 10000  feet.  I am considering 
>>> the Lycoming IO540 260 and 300 HP, as well as, the 310 HP Continental 
>>> 550N.  It has been suggested that if I buy one of the more powerful 
>>> 300 HP engines  I will just be able to run with less throttle and 
>>> bring the fuel consumption to a reasonable level.
>>>
>>>  
>>>
>>> I would appreciate any comments / experience of the builders and owners
>>> with a similar XLFG configuration.    
>>>
>>>  
>>>
>>>  
>>>
>>>  
>>>
>>> Tom Tolton
>>>
>>> 989-835-5828 (Home)
>>>
>>> 989-750-8567 (Cell)
>>>
>>>  
>>>
>>>
>>> ---------------------------------------------------------------------
>>> -
>>> --
>>>
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>>   
>>     
>
>
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