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Cooling Poll

My climb to 10,000 ft, WOT, 100 knots IAS, is limited by:

  • Excessive CHT (more than 400F)

    Votes: 49 33.6%

  • Excessive oil temperature (more than 210F)

    Votes: 17 11.6%

  • Both CHT and oil temperature

    Votes: 14 9.6%

  • I am not limited by temperatures at this airspeed.

    Votes: 66 45.2%
  • Total voters
    146
DanH

DanH

Legacy Member
Mentor
Assume extended climb to 10,000 feet at WOT.

If you maintain a climb speed near 100 knots indicated, are you limited by

1. Excessive CHT (more than 400F)

2. Excessive oil temperature (more than 210F)

3. Both CHT and oil temperature

4. I am not limited by temperatures at this airspeed.
 
Too slow for me

100 Knots = 115.2 MPH.

If I dont climb at 140 MPH or so, my CHTs go up excessively----not sure where the oil gets to, because I am already dealing with the CHT issue, but I know the oil will get way above my normal cruise temp.

I checked "both"...........
 
I was having an oil temp problem this past summer until I removed an air restrictor plate in front of the oil cooler. Now that the OAT is much lower, I need to re-install it as my oil temp never gets above 160F now. I will plan to add this to my seasonal checklist.
 
DanH said:
Assume extended climb to 10,000 feet at WOT.

If you maintain a climb speed near 100 knots indicated, are you limited by

1. Excessive CHT (more than 400F)

2. Excessive oil temperature (more than 210F)

3. Both CHT and oil temperature

4. I am not limited by temperatures at this airspeed.
Click to expand...

Hey Dan - what was your vote, if we can ask?
 
Definitely, high CHT's prior to installation of louvers. Now in your scenario much more reasonable but still over 400 (a little).
 
Initially I was oil temp limited. Then went to a larger cooler and now I'm CHT limited. On a hot day (above 90F on the ramp at sea level) at 120kts I have to push over after 3000'. If I climb at 130kts, I can go much longer before pushing. I tried various power settings and the primary control is airspeed. Doesn't matter if I'm full MP/RPM or 25 squared, airspeed is king for CHT temps in mine. I have read everything I can find in the forums and tried everything I have read, short of extra louvers. I have ECI cylinders.

Jeremy Constant
 
I dont no how to answer the poll.
I do not consider over 400 excessive or limiting, nor over 210 excessive or limiting.
Tough choices.
 
Kahuna said:
I dont no how to answer the poll.
I do not consider over 400 excessive or limiting, nor over 210 excessive or limiting.
Tough choices.
Click to expand...

That is because your plane gets to 10,000' in less time than it takes for the CHT and OT gauges to react:D
 
I wouldn't climb at such a low airspeed for that length of time, but the point is still valid - CHT is the limfac by a wide margin. Generally controled by going LOP.
 
I have no issues with CHT or Oil temps. This picture shows a climb out in October from 1300' MSL on the way to 9500'. The snapshot is at 7700' MSL. I had been climbing for approximately 5 or so minutes at this point.
10-15-2011%252520climbout2.jpg

As you can see my oil temp is 182, CHT's 346, 343, 344, 346. Posted this on another thread about leaning during climb out here.
 
JonJay said:
Hey Dan - what was your vote, if we can ask?
Click to expand...

Oil would hit 215 when flying the smallest exit (roughly half of stock), departing a 90+ runway at 200 MSL with temperature already at 185F. CHT has always been a non-issue. Heck, oil is a non-issue right now with ground temps at 60-70F here in Alabama. Experimenting and modeling in progress with thoughts toward next summer.

As our Kuhuna says, 400 and 210 are not horrors; the Lycoming limits are higher. I had to pick something to define the questions. Most pilots get interested in temperature control above 400 and 200.

The poll is not rigorous. Mostly I'm curious to see how what percentage of the fleet has their climb performance compromised by cooling, notably the ability to maintain Vy for an extended period.
 
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This summer (OAT 95 on the ground) I saw 415-420 CHTs and oil 215-220 a few times. Climbing at 120kts things heat up, but 140kts everything goes flat or dips a little. This was before I sliced 3/8 off the cowl outlet to even things up with the firewall. Haven't really tested it since, but looks like CHT's are now 385-395, oil 195
 
DanH said:
Oil would hit 215 when flying the smallest exit (roughly half of stock), departing a 90+ runway at 200 MSL with temperature already at 185F. CHT has always been a non-issue. Heck, oil is a non-issue right now with ground temps at 60-70F here in Alabama. Experimenting and modeling in progress with thoughts toward next summer.

As our Kuhuna says, 400 and 210 are not horrors; the Lycoming limits are higher. I had to pick something to define the questions. Most pilots get interested in temperature control above 400 and 200.

The poll is not rigorous. Mostly I'm curious to see how what percentage of the fleet has their climb performance compromised by cooling, notably the ability to maintain Vy for an extended period.
Click to expand...


Roger that.

The reason for my initial question is that I would expect a large percentage of the RV's flying to exceed at least one if not both of these temps in hot summer conditions if an extended climb was done at Vy.
The CHT's and oil temp. in my own airplane (O-360, fixed pitch Sensenich) would go above your threshold temps if an extended climbed was done at Vy, but only slightly.

If they didn't, the engine and oil would likely be over cooled in most other phases of flight (possibly even cruise, in hot conditions).

Since the cooling system on RV's is simple (no adjustable cowl flaps, etc.), it is a compromise. Because of this and already mentioned, a change in climb speed of only 10 or 20 knots can have a large effect on CHT's and oil temp.

I think the testing and modifications you are great, and have been very interesting, but my guess is that you will never be able to find a configuration that will work for all airspeeds in all temps, with out making it in some way adjustable.

But maybe that is the direction you are headed?
 
DanH said:
Oil would hit 215 when flying the smallest exit (roughly half of stock), departing a 90+ runway at 200 MSL with temperature already at 185F. CHT has always been a non-issue. Heck, oil is a non-issue right now with ground temps at 60-70F here in Alabama. Experimenting and modeling in progress with thoughts toward next summer.

As our Kuhuna says, 400 and 210 are not horrors; the Lycoming limits are higher. I had to pick something to define the questions. Most pilots get interested in temperature control above 400 and 200.

The poll is not rigorous. Mostly I'm curious to see how what percentage of the fleet has their climb performance compromised by cooling, notably the ability to maintain Vy for an extended period.
Click to expand...

Sorry Dan. Didnt mean to detract from the poll. I understand better what your after now. I dont start paying attention until 430/235. Its nearly impossibly for me to hit those #'s in any condition with the exception of a hot start air show going straight into the box. (start heat soaked then fly in a limited air flow/high power condition with very high surface temps >95degF)
 
Starting on a normal summer day in Houston (whatever that is) with a cool engine, I generally won't hit either limit to 10K if I climb at 110 knots - I rarely climb slower because best rate changes so little between 100 and 120 in my -8, so I am not giving anything away in climb to go a little faster over the ground and get better cooling.

Paul
 
Under those condition and relatively warm OAT (90+) my CHT will go over 400 (near 410) but I don?t like it so I usually either speed up or turn the RPM down.
 
Would be an interesting comparison of angle-valve vs. parallel-valve engines... since the angle-valvers have piston cooling jets and seem to favor higher oil temps while also having more fin area on the cylinders keeping CHT lower.
 
fixed vs. C/S prop!

This post is very illuminating. The picture shows a climb while only turning 2330 rpm. The fixed pitch prop is not able to allow the engine to develop full HP by turning up to full rpm! so naturally, heating will be less. With a C/S prop, climbing at 2650 rpm at WOT, is about 13% more power, more waste heat. Either that, or the engine is sufficiently leaned to reduce power. Either way, it's not a full-power climb. Anyone can reduce power to control heating.

I get to about 215F oil temp under the conditions Dan prescribed. So, while I don't consider it limiting, it did exceed the limit he set. But with fixed pitch, or severely leaned, non issue!

RVbySDI said:
I have no issues with CHT or Oil temps. This picture shows a climb out in October from 1300' MSL on the way to 9500'. The snapshot is at 7700' MSL. I had been climbing for approximately 5 or so minutes at this point.
10-15-2011%252520climbout2.jpg

As you can see my oil temp is 182, CHT's 346, 343, 344, 346. Posted this on another thread about leaning during climb out here.
Click to expand...
 
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RVbySDI said:
I have no issues with CHT or Oil temps. This picture shows a climb out in October from 1300' MSL on the way to 9500'.
Click to expand...
23 squared is around 75% power? We generally don't have a problem at that power setting. At 90-100% we do (did).
 
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Don't know.

I never climb that slow, so I can't answer....I have no temp problems at 140-160 MPH climbs in the -10, WOT.

Best,
 
fixed pitch

Steve and Dave,
Yes my climb is not at full power due to the fixed pitch prop. I guess because I am unable to produce max HP my performance is not necessarily comparing apples to oranges. So I guess DanH's question ultimately should be asked of those who are flying with CS props.

Without a constant speed prop I am not going to gain ultimate climb performance. However, even though this particular snapshot does not show it, I am still usually climbing at this power setting around 900-1000 fpm. I consider that an acceptable performance at altitude.

I guess I can consider this protection from overheating as one of the benefits of running a fixed pitch prop.

p.s. Steve, you mentioned "severely leaned". Although I do lean beyond FULL RICH, during this flight and most others, I climb out somewhere around 150-200 deg ROP in order to gain the most power I can. At FULL RICH I cannot get near the power I can when I climb at the mixture setting that the above picture is displaying.
 
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FP like mine definitely still must watch the CHT during hard climbs or the temp will go over 400.

Is there any difference in the air entering the inlets on a FP at WOT vs a CS at max power/ rpm? My gut sez there is.... How does the different shape and pitch of the blades effect the cooling air at the inlets?

So many variables!!!

Steve, what was your fuel flow in the pic above?
 
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Good poll everyone. If you haven't already, please participate.

rvbuilder2002 said:
...my guess is that you will never be able to find a configuration that will work for all airspeeds in all temps, with out making it in some way adjustable.
Click to expand...

My own fixed exit system has conventional inlet and exit locations, so the response to velocity change is conventional; more V = more mass flow. And like a fixed pitch prop, any one outlet size is indeed a compromise.

Which is not to say you can't make significant differences with configuration changes. As a radical example, consider the inlet and exit locations on Garrison's Melmoth II referenced in another thread; the velocity response was flatlined or reversed.

But maybe that is the direction you are headed?
Click to expand...

An adjustable outlet? Probably....which brings up another example about configuration change. The low Vi/Vo system is exhibiting excellent drag response to exit size, while reports for various adjustable outlets on the conventional cowl all seem to suggest a mass flow change but little drag reduction. The RV-8 exhaust ramp was intended to be movable but the idea got dropped in production. Can you share the story?
 
I checked the not limited box, but it is only true at WOT and full rich mixture. I typically climb at 24/2400, leaned to about 8.5 gph or so. On a hot summer day, I'm pretty sure I'd go over 400 with that slow airspeed with the 24/24 setting. I typically climb at 120 kias, 24/24, and then might occasionally go just over 400.

Another poll might be level flight at 70 kias - the oil and cylinders will get hot on mine.
 
DanH said:
The low Vi/Vo system is exhibiting excellent drag response to exit size, while reports for various adjustable outlets on the conventional cowl all seem to suggest a mass flow change but little drag reduction.
Click to expand...

Concur. On the standard -8 cowl and baffles as well as a completely sealed cowl perimeter an adjustable exit area through use of a cowl flap had significant impact on CHTs during climb and steady state level flight. However when Ai/Ao was adjusted to as low as .45 I only saw approx. 3-4mph gain. I'll post more on the Cowl Flap thread with my latest results.
 
DanH said:
The RV-8 exhaust ramp was intended to be movable but the idea got dropped in production. Can you share the story?
Click to expand...

It is hard to believe that the final design work of the RV-8 fuselage was being finished up more than 14 years ago, but what I remember is that a movable ramp was never intended for production. There were too many variables with all the different engine choices, and there just wasn't enough resources to properly test all the possible combinations.
Even so, Van new that there might be some true home builders that would be interested in experimenting with a controllable cooling outlet, so he requested that the design incorporate an easily modifiable outlet into the fuselage design.
I don't know if any RV-8 builder has ever utilized it.
 
Fixed pitch , plenum

I dont know if I should worry about my CHT's or not. I hear a lot of conflicting info....

Example of my last flight it was a very hot day.
CHT 425F max, on climb out, with OAT 37C on the ground. oil always around 184F +/- 2 deg. Stock vans oil cooler. I climb out at 100KIAS.

When I leveled at 9500ft, this is how it ran. LOP.

temoracustom.jpg


On cooler days I see cht at 8500ft around 375F.

I have an "A" model, I do have a very large slot in the lower cowl, for the nose gear leg. I need to make a removable plate here to see if that helps.
 
I climb out at 100KIAS.
Click to expand...

Jamie Jamie Jamie, you climb out to about 700' at 100 knots then it is more like 120+ so the CHT's stop going past 430F

On Sunday we climbed out at 300FPM for quite a while coz it was so hot.

We need to fix that CHT problem. ;)
 
Too hot

Since buying the plane in the spring, our temps were too high this summer. We are in the process of replacing the oil cooler and addressing the baffling in November/December. Would love to be able to climb out at less than 140 mph indicated next summer! We will see.
 
I don't climb that slow as I can't think of a good reason to. However, prior to rejetting my carb, on a 110-115 kt climb with 2500 rpm, wot, mixture full rich, I would routinely see 420 or thereabouts on 1 and 3 on a hot day, 2 and 4 always under 400. I consider 420 too hot and like to stay under 400. I rejetted my carb one drill size larger which produced about 18 gph at t/o. With the rejetted carb I MIGHT see 400 CHT on 1 or 3 on a hot day. Just for grins after I rejetted the carb I did do a 90-95 kt climb and never saw 400, but then that was on a 65 deg ambient day. Oil temp has never been a problem with either jet or any climb angle or on an extra hot day. This is on an O-360-A1A swinging a Whirlwind 200 RV prop.

With the reworked jet, after climbing a bit and the HP and temps have been reduced by ambient conditions, CHT's start dropping and I lean accordingly, adjusting mixture to maintain 380 in the climb.

As an aside, I tried everything I could think of short of whittlng up my painted cowl in an effort to reduce climb CHT's with the original jet. Rejetting fixed the problem and I no longer worry about climb temps. YMMV
 
These are my parameters for an injected 320 FADEC Lycoming. RV9A Fixed pitch Catto 3 blade.

CHT: Min 150F-Max 500F in flight
Best Performance keep below 400F
Climb & Cruise range 350F-435F
Economy cruise Less than or equal to 400F
Normal variation between cylinders 100F Range

Oil Temperature:
In Flight Min 165F- Desired 180F - Max 245F

Oil Pressure:
Max 90psi-Min 60psi - Idle 25psi

Fuel Pressure:
Max 45psi - Min 14psi - Normal 42psi
 
Our oil is generally between 180-190 are rarely over 200.

At 90-100% power CHTs would go sailing past 450 if power wasn't reduced.:eek:
Unable to clime below 100 kts for any length of time.
So to improve that significantly:

Step 1: Drilled the carb jet from #42 to #41. Could now climb at 100-110 kts to 8000' and CHTs would stay below 450.

Step 2: Opened the cowl exit 5/8 inch. Could now climb at 100-110 kts to 8000' and CHTs would stay below 430-435. :)

Step 3: Drilled the jet to #40. Could now climb at 85-110 kts to 6000' and CHTs would stay below 430, usually below 410. :D

EGT on cylinders #3 & #1 on initial climb hit 1418 & 1390. They are also the ones with the higher CHTs (393 & 403) So, those cylinders may still be a little lean. May decide to drill the jet to #39 to bring those down..
 
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