AVSIG: High CHT @ High Altitude wwswsigarch.jpg (7236 bytes)

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Dave Siciliano (ADS)
Top Gun


Reged: 05/17/04
Posts: 8469
Loc: ADS (Dallas, TX)
Re: High CHT @ High Altitude [Re: Stan Prevost]
      #248670 - 05/24/09 12:03 PM

Quote:

Dave -

OK, I thought the Baron would have Lycomings. I wasn't referring to the power setting tables in the POH, rather the more detailed graphical data in the engine manual, presenting %power versus MAP and altitude for specific RPMs and mixture settings. One can infer from those data the maximum recommended MAP for the given RPM. But they don't show any LOP data.

What is the mechanism for TIT changing with cowl flap setting? Is it cooling of the exhaust manifold, or cylinder heads, or both?

And I'm curious about

Quote:

MP really doesn't matter as I'm LOP and power roughly equates to just under 15 HP per gallon burned




I haven't seen data of power or temps vs MP for fixed FF. So say I am operating at a LOP setting, then I increase MP but maintain constant FF, meaning more airflow through the engine for the same fuel, thus a leaner mixture. Your comment suggests that power doesn't change significantly. So what happens to TIT (or EGT), CHT, ICT, ICP, and timing of peak pressure? I would expect TIT to decrease and the pressure peak to be delayed, dunno about the others. What I'm getting at is, is there a strategy here for me to safely cool my engine by increasing MAP while maintaining fuel flow (if the engine will run OK at the leaner setting)? If power is maintained, then airflow will be maintained. There was an earlier suggestion in this thread to consider higher power for better airflow, which I don't think I can do, but if I can run leaner at the same power, maybe it will work out.

Good on the family, keep it first.




I don't know that I can address this all at once. May respond in pieces. Nigel has some great insight and some others as well as the TAT folks.

In simple terms, LOP fuel flow is limiting the burn; ROP it's air flow. Therefore, when LOP, no matter how much air (MP) we add, it's fuel that limits power generation. That said, the power curve drop off more quickly on the lean side of peak than ROP. So, if you stay within reason, say within 50 degrees or so, what I'm saying applies. What one can to with higher MP is burn more fuel and stay on the lean side of peak within that 50 degrees temps allowing. On my plane, about 16.5 to 17 gph higher up limits me because CHTs get up to 380 and TITs get near 1650. Lower, where the air is denser, I can burn slightly higher fuel flows.

I don't know why the cowl flaps being slightly open can keep TITs lower; just a pilot here and know they do on my plane. I assume it improves cooling in some manner, but have never investigated to see what actually occurs and haven't asked the experts. I do have intercoolers which would make a difference.

If you look at the TAT materials, they show where power is for different settings. If within the range I stated, LOP power is pretty close to 14.9 times fuel flow on the higher compression engines. 13.7 I believe on the lower compression engines like mine. I don't know your engine.

The trick is to check what has been suggested including accurate timing. I find many mechanics don't think one can get closer than one degree and than may not matter much ROP at lower power settings. But, when we are running 75% power, LOP at higher altitudes, it makes a material difference.

Best,

Dave


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Nigel Thompson(1D2)
AVSIG Member


Reged: 04/30/04
Posts: 610
Loc: Ann Arbor, MI
Re: High CHT @ High Altitude [Re: Stan Prevost]
      #248722 - 05/24/09 07:44 PM

This really sounds very odd. I am not at all familiar with this specific engine, but the physics and engineering doesn't change.

Your TIT sounds too high in the climb as well.

I think a timing check is definitely worth doing.


NIgel.


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Dave Siciliano (ADS)
Top Gun


Reged: 05/17/04
Posts: 8469
Loc: ADS (Dallas, TX)
Re: High CHT @ High Altitude [Re: Stan Prevost]
      #248728 - 05/24/09 08:44 PM

Quote:

Dave -

Wow! That is precise! Is this procedure defined somewhere, or is it your own creation? And how did you come up with 22.2 degrees? Experiment? My TIT peaks higher than 1650 at cruise power, and I don't really know at what temp, since I didn't take it that high. I did the lean test at lower power, don't remember offhand what it was. Is that a timing issue, or just the nature of the beast?

I have noticed that under certain conditions, I can see a difference between EGTs on the left and right sides of the engine. This is at power settings lower than the cruise setting at which I set the engine monitor normalize function.




This is a procedure Bill Cunningham uses at Power Masters. We have discussed rebuilding our engines with him. When we related our woes to him, he talked my mechanic through this. It made a significant difference. Your TITs simply shouldn't be peaking before you get more fuel flow through the engine as Nigel said. Sounds like you need to have that checked by someone very picky <g>. 22 degrees advanced is normal for my engine. Bill find that just a bit more advanced seemed to help a bit.

We can chat on the phone sometime after my family leaves town if you like, but I'm not at the forefront of things. I tip my had to George, Tim and Walter at TAT there and Bill at Powermasters. Really would be get to the source if you continue to have issues. I find most mechanics are just not used to these very close tolerances and have had my share of mentoring and wallet pains getting my folks to do it.

Best,

Dave


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Re: High CHT @ High Altitude [Re: Dave Siciliano (ADS)]
      #248950 - 05/26/09 10:00 AM

Dave -

It sounds like the procedure is a refinement of the manufacturer's procedure, with a more precise method of locating compression stroke TDC and more precise setting of the advance angle. I have Lycoming's procedure (not from the maintenance manual, which I don't have, but from the engine operator's manual), but I don't have a digital protractor. I can get a device to measure and display tilt angle good to 0.1 deg (displays to 0.05 deg) much more reasonably than a good digital protractor good to 0.1 deg. It can be used to measure prop angular position and rotation angle.

My annual starts June 15, and I would like to use precision techniques to check the current timing setting and to set it accurately to the proper value (Lycoming says 20 deg for my engine, and I think all the TIO540 variants).

If you could kindly explain the procedure to me in sufficient detail, I can get the equipment and talk with the shop beforehand.

The first thing that happens on this annual is to pull the prop and send it off for overhaul (it's ten years into a six-year overhaul recommendation, but below the hour limit).

I have also been rereading all the TAT and GAMI material that I can find on the web. This has helped some, clearing up a few issues that were murky. I know that I have been doing one thing wrong, and that is treating TIT too absolutely and not considering the effects of ambient temperature. If I run 1550 at 50F, then run 1550 at 0F, I am probably 50 deg closer to peak when cold than hot. But I'm quite sure I have kept all cylinders LOP. I have also not been using my analyzer's lean function, and I probably should learn to use it.

One thing this airplane really really needs is a mixture vernier, but I have never been able to find one. At least, it could use a smoother and easier mixture adjustment. I can't set mixture much closer than 0.5 GPH, without a lot of trial and error, just moving it back and forth and seeing where it ends up. Seems to be a well-known problem with the Saratoga or maybe all Pipers.

--------------------
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]
      #249020 - 05/26/09 07:20 PM

Quote:

One thing this airplane really really needs is a mixture vernier, but I have never been able to find one. At least, it could use a smoother and easier mixture adjustment.



Amen, brother!

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


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Nigel Thompson(1D2)
AVSIG Member


Reged: 04/30/04
Posts: 610
Loc: Ann Arbor, MI
Re: High CHT @ High Altitude [Re: Stan Prevost]
      #249027 - 05/26/09 07:59 PM

Stan, can you check if there is any lost motion in the mixture controls, from cockpit control to fuel servo. If that is a bit sloppy, that may also be a factor. It is a long time since I looked at the system diagram for the Lycoming fuel injection system, but are there any springs that tie mixture and throttle linkages together, like in the Continental system, for the express purpose of eliminating linkage wear as a factor in uncontrolled variation of air fuel ratio. If so, worth a check at the annual too.

I would work down a little check list during the annual.

1. Check mag timing and clean the distributor caps inside. Check the filters and the plumbing integrity of the mag pressurisation.
2. Check the mixture and throttle linkages for any wear. I think you may be operating much closer to peak than you might think, and any small changes in FF will have a large impact on TIT and CHT.
3. Reconsider your decision on GAMI's. It is not clear (to me anyway) that you really have a tight pattern of peaks on all cylinders.

I believe TAT recognises some oddities about the Lycoming TSIO 540 which make if difficult to run nicely LOP, do you know any Turbo Saratoga operators who routinely run high power LOP with no CHT or other issues? If all the above checks out OK it may just be a problem with the way this installation was "engineered". Certainly with no intercooler you will not be able to make as much power at altitude or ISA ++ days as the air mass flow is so much lower (and hence fuel flows LOP).


Good luck.

Let us know what you find in the annual please.

NIgel.


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Joe Budge (W29)
Top Gun


Reged: 04/30/04
Posts: 7423
Re: High CHT @ High Altitude [Re: Sean Franklin]
      #249042 - 05/26/09 09:29 PM

Quote:

Quote:

One thing this airplane really really needs is a mixture vernier, but I have never been able to find one. At least, it could use a smoother and easier mixture adjustment.



Amen, brother!




+1

Regards,
Joe


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Dave Siciliano (ADS)
Top Gun


Reged: 05/17/04
Posts: 8469
Loc: ADS (Dallas, TX)
Re: High CHT @ High Altitude [Re: Joe Budge (W29)]
      #249054 - 05/26/09 10:52 PM



I'm going to take a quick stab at explaining this and hope I give folks some insight. If you can take it from here, great! If not, I may just have to show you here in Dallas sometime <g>.

Let's say one puts a digital protractor on the prop and puts an aluminum plug in the cylinder to stop in from hitting TDC. One moves the prop one way until the cylinder hits the plug and all slack is out of the gears, etc. (not hard, just reducing the slack). Take that reading on the digital protractor.
Now, rotate the prop in the other direction until it hits the plug the other way and take out slack. Lets say, it travels 260 degrees (or what ever it actually is). One now knows the difference between actual travel and a full turn of the prop 360 minus 260 is 100 degrees. Now, TDC is a known point because you have each side of it and it's in the exact middle.

Take out the cylinder plug and turn the prop to TDC using the digital protractor or to whatever point you want: 20.3 [edited] advanced for instance is what we use in the P-Baron. The timing marks on the engine are notoriously inaccurate. Using this method, one doesn't need to use them and the digital protractor can get you within one tenth of a degree <g>.

Best,

Dave


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Re: High CHT @ High Altitude [Re: Nigel Thompson(1D2)]
      #249059 - 05/26/09 11:35 PM Attachment (142 downloads)

Nigel Ė

The mixture adjustment is difficult to move, with a lot of stiction. When you apply increasing force to move it, it suddenly breaks loose and jumps to a new position, usually a half GPH or more away. Tapping it has little effect, it does about the same thing. Itís not just mine, look at Seanís and Joe Budgeís comments. Previous (1980) Saratoga was the same. GAMI acknowledges the problem, says to just do the best you can. With several up and down adjustments you can eventually get close to what you want, but it is a hit and miss proposition and a real hassle. I have had it looked at on this airplane by a couple of shops, no progress. I have tried jury-rigging verniers for lean testing, using C-clamps and other threaded arrangements, with no luck.

I donít remember about the springs and linkages, Iíll have to look.

Thanks for the annual checklist items, Iíll certainly work them in.

When I did the lean test, I sent the results to GAMI, then called to order the nozzles. The response was basically, why do you want to by GAMIs? Are you sure you need them? Does the engine run OK LOP? I was surprised, but it does run OK, except for the problem under discussion. The peak spreads are not great, but could be worse. I have reconsidered but am trying to defer some of the expenses, especially after installing the oil cooler mod. First I want to understand the problem. That was my approach to the oil cooler issue also, and never succeeded. <ng>



--------------------
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: Dave Siciliano (ADS)]
      #249063 - 05/27/09 12:21 AM

Thanks, Dave, that makes sense. I can handle that.

Now gotta get my son (mech engr) to make me a threaded plug, or to make one out of an old spark plug.

Here is what I was thinking of using to measure prop blade tilt angle.

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

Stan


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