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AVSIG Discussion Sections >> Training & Proficiency

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Sean Franklin
Top Gun


Reged: 08/15/04
Posts: 2566
Loc: Eureka Springs, Arkansas
Re: High CHT @ High Altitude [Re: Stan Prevost]
      #249673 - 05/31/09 07:16 PM

Quote:

I am TIT limited when LOP. I watch TIT and FF, and if TIT gets high, I reduce FF. Now that I think of it, that's another funny thing. Say I level out in cruise, get up to speed, then set 30/2400/13.6GPH. TIT will be 1550-1570. But it will soon start creeping up with no change in FF, and I have to back down on FF to maybe 13.2.



Stan, just out of curiosity today I tried running LOP for about 15 minutes. 11,000', 35", 2,200RPM, and about 23GPH got me about 177kt true with hottest CHT of 380F and cool TIT (<1,500F). I pulled back to LOP, and gave it plenty of time (10min+) to stabilize and get a good setting - ended up at about 14.1GPH, still 35"/2,200RPM, low EGT's (370's) but TIT was 1,590 or so, and TAS of only 156kt.

Obviously LOP is much more efficient - 11nm/gal vs less than 8 - but a 21kt hit is too much. My engine runs a little rough LOP so GAMIs would certainly smooth things out - question is, would they allow me to run a little higher FF (more speed) without taking TIT over 1,600?

--------------------
Eureka Springs, Arkansas


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Dave Siciliano (ADS)
Top Gun


Reged: 05/17/04
Posts: 8469
Loc: ADS (Dallas, TX)
Re: Flight Test [Re: Stan Prevost]
      #249680 - 05/31/09 08:37 PM

Stan: APS has a graph of the power curve: the ROP side is pretty flat you you get richer; the LOP side trails off much more markedly. Take a look at it if you get a chance.

PRISM has been pending a long time. I sure hope they get it done, but it seems to just drag on.

The GAMI lean spread test would clearly show how far apart your cylinders are peaking. That should drive the GAMI/no GAMI decision IMO.

Best,

Dave


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Re: Flight Test [Re: Dave Siciliano (ADS)]
      #249682 - 05/31/09 09:23 PM

Quote:

APS has a graph of the power curve: the ROP side is pretty flat you you get richer; the LOP side trails off much more markedly. Take a look at it if you get a chance.




Yep, I have looked at that many times, and recently.

Quote:


The GAMI lean spread test would clearly show how far apart your cylinders are peaking. That should drive the GAMI/no GAMI decision IMO.




I posted my results a few days ago in this thread.

--------------------
Best Regards,

Stan


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Re: High CHT @ High Altitude [Re: Sean Franklin]
      #249684 - 05/31/09 09:43 PM

Sean -

You might gain a little, but I think you are close to your limit. I can't run 14GPH at 30", but might can at 35". You can gain some power back by running 2400RPM and see how the other temps react. You might gain 5 kts that way.

But aren't you selling your 'Toga?

--------------------
Best Regards,

Stan


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Dave Siciliano (ADS)
Top Gun


Reged: 05/17/04
Posts: 8469
Loc: ADS (Dallas, TX)
Re: Flight Test [Re: Stan Prevost]
      #249687 - 05/31/09 10:10 PM

I thought those results were from a previous test done some time ago. I was thinking you might want to retest after timing and other issues are checked and reset.

I have to say, GAMI has probably helped me more than any other party apart from my mechanic at getting things straightened out. From an over all and engine theory standpoint, they are ahead of my mechanic. One can send them info from their engine analyzer and get truly unbiased, informed feed back. Of course, my mechanic does the actual repair work for the most part.

Best,

Dave

Edited by Dave Siciliano (ADS) (05/31/09 10:11 PM)


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Re: Flight Test [Re: Dave Siciliano (ADS)]
      #249693 - 05/31/09 11:30 PM

Quote:

I thought those results were from a previous test done some time ago. I was thinking you might want to retest after timing and other issues are checked and reset.




Yes, those data were from 2007, sorry, I misunderstood you. If we make any changes to timing or any other relevant thing, I will sure rerun the test. Will probably do it anyway. I hope to do a timing check before the annual, will post if I get it done. My son is making me a piston stop and I borrowed an angle gauge, but have several issues to work through to get an accurate procedure worked out.

Maybe the GAMIjectors will be on sale at Oskosh!

--------------------
Best Regards,

Stan


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Sean Franklin
Top Gun


Reged: 08/15/04
Posts: 2566
Loc: Eureka Springs, Arkansas
Re: High CHT @ High Altitude [Re: Stan Prevost]
      #249701 - 06/01/09 07:17 AM

Quote:

But aren't you selling your 'Toga?



Pulled it off the market, nothing's moving in this price range.

--------------------
Eureka Springs, Arkansas


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Re: Question for Dave (or others) [Re: Dave Siciliano (ADS)]
      #251216 - 06/14/09 04:07 PM

Dave -

Quote:

Let's say one puts a digital protractor on the prop and puts an aluminum plug in the cylinder to stop it from hitting TDC.




What kind of plug do you use in the cylinder? Is it threaded, or just a nonthreaded rod small enough to go down through the spark plug hole? What I have is not long enough, although I might be able to get a piece of all-thread rod and make a longer one, and also it is steel. Already gouged the piston a little with it.

--------------------
Best Regards,

Stan


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Tom Tyson [SUW]
Glider Guider


Reged: 05/27/04
Posts: 4691
Loc: KSUW
Re: Question for Dave (or others) [Re: Stan Prevost]
      #251237 - 06/14/09 07:46 PM

I'd really advise against anything likely to scratch the piston, the head or the cylinder bore.

I have a dial indicator (with a small ball bearing on the end of the plunger) which slides into a collar threaded into the plug hole I occasionally use. But most often I simply plug the #1 spark plug holes with my thumb and index finger and feel for compression. Let the pressure leak out as you approach TDC and when it changes to suck you're there.

You normally don't need to locate TDC that precisely. All you're trying to do is verify that the timing marks are in the correct orientation relative to #1 TDC. The ring gear support plate (that hat shaped aluminum disk the steel ring gear is shrunk around) will either be in the correct location or else it will be an increment of forty five or sixty degrees off. In addition to the TDC mark on the plate, there should also be a firing mark located at the point BTDC where Lycomming wants the engine to be timed to. Find approximate #1 TDC and then back up to the firing mark. Line that up with the case split and then time the mags.

Use the engine side timing marks, sight down the case seam from the front of the engine and use a small inspection mirror to show the reflection of both the case split and the timing marks. You can get within a half a degree or so after only one or two tries.

Anything closer than a half a degree on the crank is meaningless, but you do want both mags to be timed within a degree of each other at the firing mark on the support plate.

Maybe it's time to turn it over to the pros.

- TT

--------------------
Tom Tyson-A&P

Pilots without Mechanics are just Pedestrians with fancy watches.

Edited by Tom Tyson [KGSO] (06/14/09 07:48 PM)


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Re: Question for Dave (or others) [Re: Tom Tyson [SUW]]
      #251241 - 06/14/09 08:38 PM

Quote:


I have a dial indicator (with a small ball bearing on the end of the plunger) which slides into a collar threaded into the plug hole I occasionally use.




I have a dial indicator but don't have a rig made up to use it through a spark plug hole. Just haven't gotten to that yet.

Quote:


You normally don't need to locate TDC that precisely. All you're trying to do is verify that the timing marks are in the correct orientation relative to #1 TDC.





I am trying to locate it that precisely. Others in this thread have strongly pointed out the importance of accurate timing and having found benefits of knowing, and setting, the timing to tolerances of better than half a degree. It was a surprise to me, but I'm not going to dismiss that advice just yet. I know that others will, but I want to see for myself. Increased accuracy doesn't do any harm.

Quote:


The ring gear support plate (that hat shaped aluminum disk the steel ring gear is shrunk around) will either be in the correct location or else it will be an increment of forty five or sixty degrees off. In addition to the TDC mark on the plate, there should also be a firing mark located at the point BTDC where Lycomming wants the engine to be timed to. Find approximate #1 TDC and then back up to the firing mark. Line that up with the case split and then time the mags.





Again, others have pointed out that engine timing marks (TDC and firing) are notoriously inaccurate, so I want to verify for myself how accurate the marks on MY engine are.

Quote:


Use the engine side timing marks, sight down the case seam from the front of the engine and use a small inspection mirror to show the reflection of both the case split and the timing marks. You can get within a half a degree or so after only one or two tries.




That's another one of those things I want to verify, using an independent accurate method. Thanks for the tip on a way to do it. I tried sighting but didn't think of the mirror trick.

Quote:


Anything closer than a half a degree on the crank is meaningless,




Others disagree. Some say anything within a couple of degrees is OK, others say 0.2 degrees. I'm going to try for the best accuracy I can get with a reasonable procedure. I want an accurately known adjustment, so I can make accurate changes and evaluate any changes in performance. If I can get another 0,5 GPH within my temperature limits, that is worthwhile to me.

Quote:

but you do want both mags to be timed within a degree of each other at the firing mark on the support plate.




Mine are now about a half degree apart, but about one degree retarded relative to the specified timing.


Quote:


Maybe it's time to turn it over to the pros.





Not quite sure what you are getting at here. Trust but verify. Know what can be reasonably done. Understand what is being done and how accurate it is. "Leaving it to the pros" left my timing a degree retarded, and previously has left me with one set of pros telling me that the previous set of pros set the timing all wrong. I'm in the learning process now, and when I am done I will know as much or more about how to time the engine and how that system works and how accurate the procedure can be done than they do, for MY engine, not all the engines they know how to work on. Tomorrow morning I start working with them in a joint effort to get it right as well as I want it.

--------------------
Best Regards,

Stan


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