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  #51  
Old 10-17-2017, 07:32 AM
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snopercod snopercod is offline
 
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I may remove that carb temp sensor once I've learned what I want to know. I may not need to use carb heat ever. So far, I've never seen my carb temp lower than 6C under any conditions. Before I remove the sensor, though, I want to see what it shows this winter. But OTOH, that sensor obviously doesn't mess up the air flow at cruise.
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Last edited by snopercod : 10-17-2017 at 07:36 AM.
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  #52  
Old 03-05-2018, 05:36 PM
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Default The saga continues

I watched the carb temperature all winter and never once saw the temperature get down into the icing zone, even during an idle power descent on a cold day. Enough heat is transferred from the oil sump to keep the carb warm. So I'm confident that my particular engine just doesn't need carb heat on descent. (Of course it's there if I ever need it.) I'm still debating the wisdom of removing the temp sensor that sticks out into the throat of the carb. Several commenters have recommended that and they're probably right. What I have found over the last six months is that the rearmost cylinders 3 & 4 run lean at WOT on takeoff with the mixture full rich. That's probably not a good thing, but to compensate, I pull back on the throttle a little when reaching 500' and the EGTs even out. You can see that in the graph below. It's curious because I would have expected that with the throttle fly vertical, more fuel would reach the rear cylinders than when the fly was aimed more toward the front. I think my next step will be to drill out the "peppermill" holes I drilled in the nozzle years ago to provide more fuel to the rear cylinders. IIRC, they're only #57 now, and in the photos of the Marvel nozzles, they look much bigger. "It's Experimental"

Full Throttle--------Throttle back------------- Leaned out for Cruise
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Last edited by snopercod : 03-06-2018 at 01:55 PM.
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  #53  
Old 03-06-2018, 08:30 AM
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Default Suggestion on pulling power back

Quote:
Originally Posted by snopercod View Post
I watched the carb temperature all winter and never once saw the temperature get down into the icing zone, even during an idle power descent on a cold day. Enough heat is transferred from the oil sump to keep the carb warm. So I'm confident that my particular engine just doesn't need carb heat on descent. (Of course it's there if I ever need it.) I'm still debating the wisdom of removing the temp sensor that sticks out into the throat of the carb. Several commenters have recommended that and they're probably right. What I have found over the last six months is that the rearmost cylinders 3 & 4 run lean at WOT on takeoff with the mixture full rich. That's probably not a good thing, but to compensate, I pull back on the throttle a little when reaching 500' and the EGTs even out. You can see that in the graph below. It's curious because I would have expected that with the throttle fly vertical, more fuel would reach the rear cylinders than when the fly was aimed more toward the front. I think my next step will be to drill out the "peppermill" holes I drilled in the nozzle years ago to provide more fuel to the rear cylinders. IIRC, they're only #57 now, and in the photos of the Marvel nozzles, they look much bigger. "It's Experimental"

Full Throttle Throttle back Leaned out for Cruise
Snopercod,
Your post mentions pulling the power back at 500 agl.
I'd suggest you practice an engine out at 500 (equivalent at a higher altitude) to see if you could return to base and land.
After extensive practice, I was not able to RTB until 850 agl. That is where I first make power changes.

You may be much more experienced and skilled than me, but just a suggestion.
Daddyman
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  #54  
Old 03-06-2018, 09:45 AM
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Bob Martin Bob Martin is offline
 
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Quote:
Originally Posted by snopercod View Post
It's curious because I would have expected that with the throttle fly vertical, more fuel would reach the rear cylinders than when the fly was aimed more toward the front. I think my next step will be to drill out the "peppermill" holes I drilled in the nozzle years ago to provide more fuel to the rear cylinders.
It is well known that closing the throttle a "little" from WOT will disturb the airflow just enough to promote better fuel atomization.
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  #55  
Old 03-06-2018, 10:30 AM
EXflyer EXflyer is offline
 
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Default Drilling things

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Originally Posted by snopercod View Post
I may remove that carb temp sensor once I've learned what I want to know. I may not need to use carb heat ever. So far, I've never seen my carb temp lower than 6C under any conditions. Before I remove the sensor, though, I want to see what it shows this winter. But OTOH, that sensor obviously doesn't mess up the air flow at cruise.
I doubt if you know better than those who designed the carb to randomly drill out things. They did that for a reason. Also on your engine way back when no one ran much more than oil temp, oil pressure and RPM for engine feed back. Very few ran more than one cht probe if any. All this new tech engine feedback was never there and they ran fine for years with no problems. I find that having any spalling on either the cam or lifter would be ok. Some wear is ok but any dishing of the lifter or wear on the cam is not. Another item, solid lifters always have clearance more cold than hot so that is not a problem. What is when you have it with a hydraulic lifter, and no there never should be any. If there is the lifter is bad or push rod and or rocker is worn beyond the lifters ablity to compensate for it. Hopefully not the cam but have seen that happen on auto engines.
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  #56  
Old 03-06-2018, 01:40 PM
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Quote:
Originally Posted by Bob Martin View Post
It is well known that closing the throttle a "little" from WOT will disturb the airflow just enough to promote better fuel atomization.
I'm learning a lot of things lately that seemingly everybody else knew
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  #57  
Old 03-06-2018, 01:53 PM
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Originally Posted by EXflyer View Post
I doubt if you know better than those who designed the carb to randomly drill out things. They did that for a reason.
Actually, it was Marvel-Schebler who came up with the idea of a perforated [AKA "peppermill"] nozzle to provide better fuel atomization and distribution. See: SB-22. My engine is so old (1946) that they didn't bother to make a peppermill nozzle for my carb, so I copied what they did as best I could. You can see a photo of the nozzle they came up with here. I'm not "randomly" drilling out things. I drilled out the main nozzle to obtain adequate fuel flow on takeoff. I drilled a couple aeration holes on the diameter and they helped, but I believe they need to be bigger. I'm being very meticulous and taking data after each modification.
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  #58  
Old 03-06-2018, 01:59 PM
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Originally Posted by daddyman View Post
I'd suggest you practice an engine out at 500 (equivalent at a higher altitude) to see if you could return to base and land.
That's an excellent suggestion and it's on my list of things to do. I have an AOA so I feel pretty safe in making a 45 deg banked turn with idle power and see how much altitude I lose. (I'll do it at altitude, of course.)
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  #59  
Old 03-06-2018, 04:37 PM
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Default It's all relative...

John,
I wouldn't sweat the CHT's too much, if they're not exceeding 425F, lower the nose on climb-out rather than reducing power, accelerate to 120 and climb at a shallower angle, higher RPM and airflow over the cylinders. I'm sure you've already checked your baffling by placing a light in the oil door at night and look for gaps. You can always build a plenum which works very well. I advise against reducing power in the climb below 1000' AGL at less than best glide speed, ever.

As you well know, the 0-290 has been around a long time (WW2) and was built to sustain abuse. In the 80's my Dad had a Korean War vintage surplus GPU with the XO-290-5 installed. Dad decided to fire it up one day so we started un-crating and cleaning. It had been preserved in cosmoline and after what seemed like an eternity of flushing goop, Dad was able to attempt a start. After several attempts and with smoke belching it fired right up and surprisingly (to me) showed positive power output after (at that time) 30 years. The operating RPM listed was 3000 and Dad told me of thousands of hours in all weather conditions these little gems operated in Korea without missing a beat. Before I left for AF pilot training in the early 80's, I flew a friend's Thorp T-18 with a modified GPU installed. (no EGT or CHT gauge). When I retired from the military in 2008 it was still flying with the original 0-290G still growling...

GPU stands for Great Power Unit.
V/R
Smokey

PS: My Mom and Dad grew up in Mars Hill, not too far away from you...
PSS: Before I went in the USAF, I towed banners behind an 0-360 powered Scout, six hours a day, seven days a week in the summer. I rarely saw less than 425F all day long with 450F being the norm. Both of our Scouts 0-360's went to TBO...

Last edited by smokyray : 03-06-2018 at 05:13 PM.
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  #60  
Old 03-06-2018, 06:17 PM
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Quote:
Originally Posted by smokyray View Post
I wouldn't sweat the CHT's too much...
Thanks, Smoky. The graph I posted was EGT, not CHT. My CHTs are fine - running around 380 or so on climbout (closer to 400 in the summer). I'm very pleased with my high-compression Don George O-290-D2. Supposedly that engine has the highest HP-to-weight ratio of any of the Lycomings, so it's perfect for my Lancair. I'm not pulling the power back a lot during climb - about 2" MP - just enough to lower the high EGTs on #3 and #4. I recall that when I was training in an Arrow, we would always pull the power back to 25/25 at about 500', so I feel like I'm doing the same.

Edit: Small world. My son-in-law's parents lived in Mars Hill - Wolf Laurel, IIRC.
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Last edited by snopercod : 03-06-2018 at 06:19 PM.
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