Oil Temp during Pattern Work / Taxi
 

Hi all,

I?ve never had a problem with oil temps or CHT?s. My typical mission profile is takeoff, climb at 110kts (CHT: 370 Oil: 200-210) level off at cruise (CHT: 320 Oil: 190) and descend to land (CHT: 300 Oil: 190).

Today however I tried doing pattern work for the first time, and my oil was getting up around 210 degrees in the pattern, and once I landed, the temps kept going up. The long downwind taxi back to the hangar yielded a shut down temp of 230 degrees F.

The temps during a long taxi at OSH got warm too, but not as quickly; I?m guessing the denser sea level air was the reason? I?m in the Mojave Desert, so field elevation is 2300? and OAT can be up to 120 in the summer. Today was about 85 degrees OAT however. I believe I have the standard Vans oil cooler, baffles, and an O-360-A1A with AFP Fuel Injection. 180HP.

Here are my questions;

1. Is it normal for an RV-8 to heat up during pattern work? I was using 25?/2500 on the takeoffs, then immediately coming back to 12? MP at pattern altitude. The oil would heat up during the takeoff, but didn?t cool back off during the rest of the pattern, so each touch and go added heat to the oil; I had to stop after #3.

2. During extended taxi?s my oil gets pretty warm. Not an issue pre-flight as I need to warm the oil anyway, but post landing the oil immediately starts climbing above 190 which is what I typically land with it at. If this is normal what optimizes cooling on the ground? I?ve heard about 1000 rpm to try and keep air through the cooler?

3. Am I just seeing normal oil temps for operating Hot / High? I ask this because on a normal mission profile I don?t have any cooling issues, just on a dedicated pattern flight. When I?m low, slow, high power.

I'm guessing you are running a Hartzell BA CS prop. If so, as this prop goes flat (pattern work) it becomes more of a solid disk and reduces engine cooling. While CHTs are manageable because of the reduced power, the oil still heats up.

When I upgraded my RV-8A from FP to this prop I was amazed at the improvement in performance of the plane. The first time I saw increasing oil temp on landing I was surprised - then I figured it out.

Parallel or angle head engine?

If you are running the recommended Van's cooler your options are to manage it via operating technique, or get a better cooler.

Carl

Carl,

I?ve got a Hartzell non-BA Prop. But I think your theory still applies. It?s a parallel valve motor.

Your "problem" is common.
 

I fly out of FFZ in the low Arizona desert. Any time you operate at lower airspeeds in the heat, you are going to see high oil temps. Airflow is the key - it's just physics. I climb in the summertime at 120 KIAS.
Just two or three practice stalls with OAT's at altitude in the 90's will quickly send the CHT's up past 400 and the oil temp past 210, especially if you don't speed up past 120 for some time between them.
It is normal for me to enter the downwind at 130 KIAS at 185? oil temp, and even though I reduce power to nearly nothing, by the time I roll off the runway I'm 20? hotter. Flat pitching the prop and low airspeed does it every time.
FWIW,
Andy

Guess I was asking for it. OAT was high 80?s. Took off, climbed at 80kts to 6500 feet (from 2500?), did 2 power off stalls, then returned for the 3 touch and goes. Pretty tough flight profile on a hot day for the ole girl...

Evan, that oil cooling performance can be improved. Exactly what to do depends on installation details.

Not very likely, for several reasons.

Mass flow (air) through the oil cooler is a function of pressure delta. Set aside the minuscule increase in area due to flat blade pitch, and consider that propeller outflow increases deltaP by raising upper plenum pressure above that available due to freestream dynamic pressure alone. Sample data here; coefficient of pressure (as defined in CR3405) pushed to 1.17:

http://www.vansairforce.com/communit...&postcount=198

The typical fixed pitch prop has much better airfoil shape near the hub, as compared to most constant speed props, which for structural reasons tend to be more rounded near the root (look at a Catto, then, at the other end of the scale, look at a Whirlwind). Given an inboard inlet close to the spinner (i.e. a standard Vans cowl), I'd suggest the fixed pitch blade root shape improves Cp.

The cowl in the above measurements is optimized with inlets moved outboard, where the BA Hartzell has excellent airfoil shape.

Fixed pitch also reduces climb RPM. Cooling load is a function of combustion air mass flow, i.e. RPM.

I spoke with a Hartzell guy at Sun and Fun. He said they started the current aluminum prop line with smaller roots, but added meat there to beef Up strength to gain structural margins with modified engines.

Evan, RPM is a big factor, my climb temps right off the runway, and CHT will drop 15-20F with a drop from 2700 to 2500 at 400' AGL. Since you already do this, look to airflow issues.

I would submit: RPM was the variable for Carl too.

Listen to Dan - upper cowl pressure-lower cowl pressure = available Pressure for cooling. If there is excessive lower cowl pressure, it is likely because the baffles are leaky and too much air bypasses the fins. Vans design works quite well.

I'm fairly early in my RV8 build process. (I'm somewhere between the empennage and the wing kit...). Thinking ahead all the time though. As I also live in the desert (right up the road from A39), I was wondering if adding a motorized cowl flap to the bottom half for use during climbs only would be the answer for a desert bird?

Climbed at 80kts?? Yikes. I generally climb at 120mph mostly to give me a decent look ahead of me in the climb.. heh.