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

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AVSIG Discussion Sections >> Training & Proficiency

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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: Nigel Thompson(1D2)]
      #249221 - 05/28/09 09:28 AM

Quote:

Dave, you are correct, if you increase throttle and concurrently move the mixture control to maintain the same fuel flow then the engine will go progressively leaner. I am not at all familiar with the P Baron, but I think it has Lycomings, not Continentals'. Is that right, and if so, are they intercooled?

I have never even been in one, but they seem to have a reputation as very nice airplanes.

Nigel.




Nigel: The P-Baron has TSIO-520 WBs. Earlier models have the L I believe. They generate 325 HP on the WB. Yes, they have small intercoolers.

Very nice plane Nigel. It was my dream plane when I was younger. Much smoother than my A-36 because of higher wing loading and more weight. Very stable plane; it's like a little tank in many regards. I fly in much more challenging weather in this than I would in my TN A-36. Partially because of the above, but also because of the second engine, redundant systems and K-ice certification.

We'll just have to get you up in one sometime if we are ever near one another or link up. Very good handling and all the features that distinguish a Beechcraft plane.

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: Dave Siciliano (ADS)]
      #249223 - 05/28/09 10:24 AM

Dave, I know my confusion, is it the BE 56 (Baron TC) that has the TSIO 540's (Lycoming)?

Obviously the P baron is powered by proper engines...

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: Nigel Thompson(1D2)]
      #249224 - 05/28/09 10:34 AM

Quote:

Dave, I know my confusion, is it the BE 56 (Baron TC) that has the TSIO 540's (Lycoming)?

Obviously the P baron is powered by proper engines...

Nigel.




Yep <VBG>

Best,

Dave


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Flight Test [Re: Stan Prevost]
      #249567 - 05/30/09 09:10 PM

Today I did a limited flight test of something touched on in this thread.

I set up for LOP cruise at 8500, per usual settings - 30"/2400RPM/13.2GPH. #2 cyl EGT 1431, CHT 387 (and increasing), TIT 1574. Then I increased MAP to 35", keeping fuel flow at 13.1 GPH (as close as I could get after much fiddling). EGT 1400, CHT 369, TIT 1560.

Got quite a bit of cooling from the increased MAP. But the mixture was so lean that the engine was running pretty rough, and I lost 3-4 kts of airspeed. This makes me lean (no pun) toward getting the GAMIjectors to balance the fuel/air ratios better and smooth out the engine when running very lean.

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

Stan


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Timing Procedure Difficulties [Re: Stan Prevost]
      #249568 - 05/30/09 09:25 PM

Just some things I have encountered so far, not saying I can't overcome them.

My son loaned me a digital angle gauge from his workplace, reads out to 0.1 degree. SmartTool

I took it out to the airplane to see about how to affix it to the prop or spinner. First thing I discovered about the tool is that it is sensitive to how it is oriented in the orthogonal axis. The face of the tool must be vertical, meaning parallel to gravity. This is not mentioned in any of the literature. I sort of expected a cosine response or something like that, but this is different, and worse. Next I discovered that there is not a flat surface anywhere on the prop/spinner assembly. Then I realized that there is no reason to expect that the propellor axis of rotation, presumably colinear with the crankshaft axis, is horizontal, or perpendicular to gravity, thus the cross-axis error of the gauge would vary as the prop rotates.

Lots of sources of error here that must be tamed. Just because the device reads out in 0.1 deg increments doesn't mean much about the actual angular position we want it to be indicating.

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

Stan


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Joe Budge (W29)
Top Gun


Reged: 04/30/04
Posts: 7423
Re: Flight Test [Re: Stan Prevost]
      #249608 - 05/31/09 09:26 AM

Good! APS doesn't really cover what happens to the power curve when you get waaay out there LOP. My experience suggests that the nice linear relationship between fuel flow and power output begins to break down. That could explain why you're seeing some power loss (lower airspeed) even though fuel flow is constant. Not sure, though. I haven't done rigorous testing.

Regards,
Joe


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Re: Flight Test [Re: Joe Budge (W29)]
      #249615 - 05/31/09 10:24 AM

Joe -

I remember that with the -S1AD engine with Gamis, leaning way out would cause TIT to start increasing again. Some theories that the mixture burns so slow that it is still burning when the exhaust valve opens.

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

Stan


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Nigel Thompson(1D2)
AVSIG Member


Reged: 04/30/04
Posts: 610
Loc: Ann Arbor, MI
Re: Flight Test [Re: Stan Prevost]
      #249629 - 05/31/09 11:50 AM

Very lean burn does slow combustion sufficiently that the egt's/TIT go up if you can get it run that lean (mostly because the timing is too retarded). CHT's will drop, and the BSFC gets a lot worse. No point to operating at that end of the combustion envelope with these engines.

A lot of this odd behaviour is all because we have to operate with fixed ignition timing. If we could get the timing right for a wide variety of operating conditions the BSFC gets a lot better. As it happens the fixed timing we have, usually around 22 BTDC, works very well WOTLOP and high power as well as very rich WOT max RPM. It is not optimal for just about all other operating conditions.

Anyone remember an idea called PRISM.....


Nigel.


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Joe Budge (W29)
Top Gun


Reged: 04/30/04
Posts: 7423
Re: Flight Test [Re: Nigel Thompson(1D2)]
      #249634 - 05/31/09 12:40 PM

Quote:

Very lean burn does slow combustion sufficiently that the egt's/TIT go up if you can get it run that lean (mostly because the timing is too retarded). CHT's will drop, and the BSFC gets a lot worse. No point to operating at that end of the combustion envelope with these engines.




Yes, I've seen that myself. EGT's go up ... then go down again as the engine starts to shut down. This gives a second "Peak EGT" which is really quite useless. When I was first learning the "Big Mixture Pull" I'd pull too hard and end up on the wrong peak. Setting the engine there is a good way to fall out of the sky - no power!

I don't think that's what Stan saw, though. His EGT's were (apparently) still declining, suggesting he was somewhere on the back of the first peak still. The slight power drop-off (4kts or so) also suggests this.

Quote:

Anyone remember an idea called PRISM.....




LOL!

Regards,
Joe


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Re: Flight Test [Re: Nigel Thompson(1D2)]
      #249667 - 05/31/09 06:42 PM

Quote:

Anyone remember an idea called PRISM.....





Yeah, whatever happened to that?

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

Stan


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