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Update on Jim's Rocket

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jrstone(at)insightbb.com
Guest

Posted: Thu Oct 04, 2007 5:07 am Post subject: Update on Jim's Rocket

Rocketteers,

 To update you on the rapid battery drain and high CHTs:

  

 I did some  starter circuit troubleshooting and found a couple of wire segments with  slightly high resistance and will work on those very soon.  I changed the  timing to 20 deg bftdc and yesterday, all temps were below 390, even in the  climb.  Leaning still causes #6 to run on up towards 410 not sure  why.  Oil pressure adjusted up from 60 to 70 with two washers.  Oil  temp still good at 190-200.  The #4 cylinder runs cool, 80 deg or so cooler  than the hottest #6, I cleaned the injector with an ultrasonic cleaner with no  improvement.  After flying to three different fields to do a touch and go,  and test work at altitude I am starting to get more confident in the engine and  actually did a few rolls yesterday.  I've got about 12 hours  now.  Following shutdown and a 15-20 minutes simulated fuel stop,   I did a restart using the technique that most guys recommended in the last  few days.  The trick is to get it started quickly and with the right  technique, that is possible now.  Thanks for all the advice  guys.

 Jim Stone

 Louisville

  [quote][b]

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James Baldwin

Joined: 16 Jan 2006
Posts: 23

Posted: Thu Oct 04, 2007 6:23 am Post subject: Update on Jim's Rocket

Jim -

Has any one spoken to you about or have you read about the whole subject 

of injector balance and its relation to an individual cylinder's 

EGT/CHT?  If not, say so and I'll get you started on an education which 

most of the guys with an injection system are beginning to understand is 

infinitely tunable.   JBB



Jim Stone wrote:

 	  Quote: 	
		   Rocketteers,

 To update you on the rapid battery drain and high CHTs:

  

 I did some starter circuit troubleshooting and found a couple of wire 

 segments with slightly high resistance and will work on those very 

 soon.  I changed the timing to 20 deg bftdc and yesterday, all temps 

 were below 390, even in the climb.  Leaning still causes #6 to run on 

 up towards 410 not sure why.  Oil pressure adjusted up from 60 to 70 

 with two washers.  Oil temp still good at 190-200.  The #4 cylinder 

 runs cool, 80 deg or so cooler than the hottest #6, I cleaned the 

 injector with an ultrasonic cleaner with no improvement.  After flying 

 to three different fields to do a touch and go, and test work at 

 altitude I am starting to get more confident in the engine and 

 actually did a few rolls yesterday.  I've got about 12 hours 

 now.  Following shutdown and a 15-20 minutes simulated fuel stop,  I 

 did a restart using the technique that most guys recommended in the 

 last few days.  The trick is to get it started quickly and with the 

 right technique, that is possible now.  Thanks for all the advice guys.

 Jim Stone

 Louisville

 *

 *

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nico(at)cybersuperstore.c
Guest

Posted: Thu Oct 04, 2007 8:46 am Post subject: Update on Jim's Rocket

Wow, I guess we could all benefit from that, JBB, so would you consider this

"say so" as sufficient motive to go ahead?

--

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James Baldwin

Joined: 16 Jan 2006
Posts: 23

Posted: Thu Oct 04, 2007 9:50 am Post subject: Update on Jim's Rocket

Hi Nico,

I will certainly share my knowledge with all the listers and this will 

probably start a good general discussion on the subject.  Having said 

that, my basis of understanding is from my personal experience with 

aircraft, my engineering background and, most importantly from people 

like GAMI and Barrett Aircraft Engines as they really are the experts 

with respect to internal combustion in these very simple normally 

aspirated aircraft engines.  Anyone who has used a dyno like these 

people have are the ones who have documented the behavior we are 

observing.  I won;t have an rebuilt/new engine on my airplane that 

hasn't been on a dyno/test cell.

All of the progress made in the last decade is mostly a result of the 

vastly increased amount of digital information available through the 

many different data acquisition systems available.  Lean of peak 

operation was never even considered in my experience before GAMI or with 

carburetors.  Others began teaching that each cylinder is really an 

independent little expansion device all by itself (an internal 

combustion engine is nothing more than a device which uses hydrocarbons 

to create an expansion in the volume of a fluid which is mechanically 

converted to rotational energy, i.e. torque).  The inefficiencies were a 

result of uneven airflow distribution which led to (AND HERE'S THE BIG 

ONE!) each cylinder reaching its peak temperature during leaning 

(increased efficiency) at different times.  The number (EGT) 

wasn't/isn't important, it's WHEN it happens.   Who cares if one 

cylinder doesn't get as much air as another or if its exhaust tract is 

less efficient, it is contributing to the overall output of the engine 

at the best level it can given its intake/exhaust tract efficiency with 

an ideal amount of fuel for that cylinder.  But, if it reaches its peak 

of efficiency at a significantly different time than its brother or 

sister cylinder then one or more of them will not be as efficient as the 

reference cylinder.  So, what we do is accept the fact that all are not 

equal for whatever reason and match the fuel requirement to the specific 

airflow capability of that cylinder.  GAMI does this with a matched set 

of injectors and Airflow Injection does it by supplying injectors with 

different sized orifices in a similar way. 

Jim Stone is noting that one cylinder is running at a higher CHT than 

another and, all other things being equal, is really suffering from the 

probable reality that all of his little engines aren't in lock step 

mixture wise.  We could take this to extremes by flow matching all of 

the individual intake tract/cylinder head/exhaust tracts but the more 

practical approach for us is usually to match the peak temp EGT point by 

matching the flow nozzle to how much air is really going into each 

cylinder.  My guess is once he really ascertains his baffling is as 

close to perfect as he can get it he will find he needs to log the 

temperature peak for each cylinder with respect to overall fuel flow and 

then adjust the nozzle for that cylinder until he can standardize it to, 

probably somewhere around  the .1 to .2 GPH flow rate.  I am betting the 

CHTs will be close and if not then there are other mechanical issues 

(improper cyl/piston clearance, leaky valve seat, ignition issue,etc) 

that might be looked at once the cooling airflow is assured.  A new 

engine during breakin complicates this whole process and should be 

completed before embarking on an efficiency quest. 

What is really wrong is needing to retard an already retarded ignition 

event.   The electronic ignitions show us at the higher altitudes the 

factory fixed setting of 25 deg BTDC is way late and efficiencies are 

easy to get by moving it to somewhere (variable) around 10-12 degress 

earlier.  Operation lean of peak requires even more time to get the 

combustion event completed (or nearly so) with fewer molecules of fuel 

to combust.  Even at the low speeds we're talking about here (2000-3000 

RPM) the ignition/combustion event is in the millisecond range and is 

pretty darn quick.

I could say a lot more but this is a pretty basic and well known intro 

to the subject and anyone who feels like it can jump in and 

add/refute/ridicule or whatever.  If the guys from Barrett chime in 

you'll hear from the real experts.  I haven't asked them a question they 

didn't have an excellent answer for based on quite a bit of experience.  

GAMI has classes you can attend.   JBB



nico css wrote:

[quote] 



 Wow, I guess we could all benefit from that, JBB, so would you consider this

 "say so" as sufficient motive to go ahead?

 --

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jrstone(at)insightbb.com
Guest

Posted: Thu Oct 04, 2007 5:22 pm Post subject: Update on Jim's Rocket

Hi James,

Randy Pflanzer has documented his experience on his website but I have not 

yet had a close look at it.

I'll take any help I can get.  I'm ready so fire away.

Jim

---

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Don

Joined: 18 Jan 2006
Posts: 13

Posted: Fri Oct 05, 2007 1:58 pm Post subject: Re: Update on Jim's Rocket

To chime in here, Jim’s comment/dissertation on nozzle tuning is mostly correct.  At peak EGT the engine is not necessarily running at peak efficiency.  If you talk to people that have the equipment to actually measure efficiency, that is outfits that have dynos that measure air flow, fuel flow, torque, etc; not just a prop stand, BSFC and BSAC will give the efficiency of the engine.  The point at which the EGT peaks is a specific fuel air ratio.  This is what we’re trying to match.  There are curves that show (Lycoming data) that even with different engines, naturally aspirated and turbo charge, the point at which EGT peaked was the same F/A for each engine and the F/A changed a specific amount to the change from peak EGT.  This was again true of any engine they tested.  Obviously the EGT number was different for the turbo charged engines and the naturally aspirated engines at peak EGT, but the F/A was the same.  So a given change form peak EGT results in a specific F/A.  For instance running 200 rich of peak EGT results in a F/A of .086.  Peak EGT is a F/A of .065.  This is pretty much true for any Lycoming engine, and probably most engines.  So what Jim said is we’re adjusting the fuel flow to the cylinder’s air flow so that all the cylinders run at the same F/A.



An important consideration when gathering the data is to not exceed 25”MAP, keep the fuel flow above the point where the flow divider influences the flow division and let the EGT stabilize before changing fuel flow to get a new line of data.  This means that if you use a data logger to capture data, slowing leaning the mixture control while gathering data will result in mostly worthless data, as the EGT does not respond as fast as the fuel flow indication.



If you need more instruction on this process give me a call or email me off line.



Don

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