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  #1  
Old 04-09-2018, 08:40 AM
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JackinMichigan JackinMichigan is offline
 
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Location: Canton, MI
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Default Normal CHTs - should I stop worrying?

I've got just under 10 hours in my RV-10 as of yesterday, and since the first flight I've been fighting a battle with high CHTs. After much work this weekend sealing every leak and removing every flow obstacle, these are my CHT numbers; better than before but still widely varying. This is at level cruise, 24" MP and 2400 RPM, full rich mixture with break-in mineral oil, speed approx. 170 MPH, outside temp mid-30s F:

Cyl 1 - 335
Cyl 2 - 335
Cyl 3 - 315
Cyl 4 - 320
Cyl 5 - 364
Cyl 6 - 347

The numbers are all under my 380 limit, but #5 is way hotter. In fact my coolest and hottest cylinders are right next to each other. I want to think there's something that can be done about that.

Should I just stop fretting and call these numbers good? That #5 cylinder does creep up to 410 or so during climbout, so I'm not sure if I need to get more creative with my baffle layouts or just accept these numbers as normal. I'm curious what these numbers will look like on a 90 degree summer day.
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Build #41389, started Oct 2012
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  #2  
Old 04-09-2018, 08:49 AM
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Toobuilder Toobuilder is offline
 
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Does cyl 5 have the bypass duct mod or standard baffles?
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  #3  
Old 04-09-2018, 08:54 AM
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Jack, nothing wrong with those numbers.

#5 will need a bypass duct to get it even with the others. Same as the old "washer trick", only better, allows airflow through the top rear fins and feeds air to the lower fins inboard of the intake flange. Lots of info in the archives.
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  #4  
Old 04-09-2018, 10:48 AM
Ralph Inkster Ralph Inkster is offline
 
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The advice Iíve always followed from old time mechanics (& shops) is to run an engine hard & hot during break in, between 380 & 400, to insure the rings seat and not glaze the cylinders. Lycoming red line is 500, I set a 450 no go limit, so even with 400 is well below any thing serious.
With slippery RV airframes this is hard to do so I leave all gear fairings off during break in, try to make the engine work as hard as is sensible.
Your running mid to low 350 temps seem conservative for a 10hr break in engine.
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  #5  
Old 04-09-2018, 11:23 AM
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JackinMichigan JackinMichigan is offline
 
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Yes, I've heard that you're to run a new engine 'hard', but I haven't heard 'hot'. I've read that for the first 25 hours at least you should keep the power setting to 75%+ as much as possible at full rich, which is what I've been doing, but even with the leg farings off this thing is FAST. The structural speed limit of the RV-10 is around 178mph, and I find my self hitting 170mph in level flight rather easily.

I've also heard that using break-in mineral oil will cause the engine to run hotter than normal, but still the maximum temperatures do apply (it's a metallurgical thing).

If the temperatures I'm observing stay where they are when the outside temperature is 50 degrees warmer then I'm probably OK, but it would still be nice if I could get them all to even out a bit more.

I think I have something like 18 temperature probes all around the plane. The amount of info being thrown at me is rather overwhelming. Never had to worry about half of this stuff in my old 172.
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  #6  
Old 04-09-2018, 11:46 AM
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Auburntsts Auburntsts is offline
 
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Quote:
Originally Posted by JackinMichigan View Post
Yes, I've heard that you're to run a new engine 'hard', but I haven't heard 'hot'. I've read that for the first 25 hours at least you should keep the power setting to 75%+ as much as possible at full rich, which is what I've been doing, but even with the leg farings off this thing is FAST. The structural speed limit of the RV-10 is around 178mph, and I find my self hitting 170mph in level flight rather easily.

I've also heard that using break-in mineral oil will cause the engine to run hotter than normal, but still the maximum temperatures do apply (it's a metallurgical thing).

If the temperatures I'm observing stay where they are when the outside temperature is 50 degrees warmer then I'm probably OK, but it would still be nice if I could get them all to even out a bit more.

I think I have something like 18 temperature probes all around the plane. The amount of info being thrown at me is rather overwhelming. Never had to worry about half of this stuff in my old 172.
Just curious -- are you seeing 170mph IAS or TAS, at what altitude, and have you verified the indications with a GPS calibration run?
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Last edited by Auburntsts : 04-09-2018 at 12:57 PM.
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  #7  
Old 04-09-2018, 12:59 PM
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B Cunningham B Cunningham is offline
 
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RVĖ10 Performance
General InfoSpecificationsPerformance



Speed and ranges in statute mph.

*235 hp performance estimated.
Speeds and ranges in statute mph (sm)
Light Weight 2200 lbs * 235 hp 260 hp
Speed
Top Speed 204 mph 211 mph
Cruise [75% @ 8000 ft] 194 mph 201 mph
Cruise [55% @ 8000 ft] 174 mph 180 mph
Stall Speed 57 mph 57 mph
Ground Performance
Takeoff Distance 415 ft 360 ft
Landing Distance 500 ft 525 ft
Climb/Ceiling
Rate of Climb 1,669 fpm 1,950 fpm
Ceiling (est) 20,538 ft 24,000 ft
---------------------------------------------------------------------------------

Gross Weight 2700 lbs * 235 hp 260 hp
Empty Weight 1,585 lbs 1,600 lbs
Speed
Top Speed 201 mph 208 mph
Cruise [75% @ 8000 ft] 190 mph 197 mph
Cruise [55% @ 8000 ft] 170 mph 176 mph
Stall Speed 63 mph 63 mph
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  #8  
Old 04-09-2018, 01:06 PM
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Auburntsts Auburntsts is offline
 
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Quote:
Originally Posted by B Cunningham View Post
RV–10 Performance
General InfoSpecificationsPerformance



Speed and ranges in statute mph.

*235 hp performance estimated.
Speeds and ranges in statute mph (sm)
Light Weight 2200 lbs * 235 hp 260 hp
Speed
Top Speed 204 mph 211 mph
Cruise [75% @ 8000 ft] 194 mph 201 mph
Cruise [55% @ 8000 ft] 174 mph 180 mph
Stall Speed 57 mph 57 mph
Ground Performance
Takeoff Distance 415 ft 360 ft
Landing Distance 500 ft 525 ft
Climb/Ceiling
Rate of Climb 1,669 fpm 1,950 fpm
Ceiling (est) 20,538 ft 24,000 ft
---------------------------------------------------------------------------------

Gross Weight 2700 lbs * 235 hp 260 hp
Empty Weight 1,585 lbs 1,600 lbs
Speed
Top Speed 201 mph 208 mph
Cruise [75% @ 8000 ft] 190 mph 197 mph
Cruise [55% @ 8000 ft] 170 mph 176 mph
Stall Speed 63 mph 63 mph
Sigh, I know the specs - I built and fly an RV-10 after all. My question was specific to the OP's performance as his cruise speeds seems a bit fast to me for not having the gear fairings and wheel pants on, not the general performance specs for the model.
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Last edited by Auburntsts : 04-09-2018 at 01:24 PM.
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  #9  
Old 04-09-2018, 01:34 PM
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JackinMichigan JackinMichigan is offline
 
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The 178mph speed I was referring to is the maneuvering speed, or structural speed, not the top speed. And in Michigan, particularly in the early Spring, the turbulence is such that you should probably stay under that.

The altitude was around 4,000 ft. I did the four-compass-direction IAS calibration and compared it to ground speed, but I keep forgetting to take the numbers home and figure out where my calibration stands. So no, my IAS is not yet calibrated. I might be flying slower than I think.
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RV-10 N1861G
Build #41389, started Oct 2012
Current status: 1st Flight 11/10/17
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  #10  
Old 04-09-2018, 01:46 PM
togaflyer togaflyer is offline
 
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Having 50 hours on my -10 with a fresh engine, I have seen a good drop in the CHTs since it first started flying. I would not worry. Keep flying and see what the temps are 40 hours from now.
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