[RV8R999]

Questions raised during a recent CHT thread about the affects of oil temperature on CHT during climbs encouraged a test to determine the relationship between the two.

Results: Oil Temp has little or no influence on CHT during climb

Test: Two runs from Take-off to 6000PA, Vy climb @ WOT/Full rich. Each T/O was commenced with #2 CHT at 350 deg F to keep data consistent. Rate of throttle application, rotation speed and initial acceleration to Vy (110mias) were consistent between the two runs. Data was taken just prior to throttle application, 300ft, and every 1000ft to 6000ft via Dynon Skyview screenshot.
The first run was conducted with Oil temp at 100deg F at Take-off while the 2nd run Oil Temp was 159 deg F at T/0. OAT was within 1 deg at each altitude for each run. A/S was maintained +- 1 mias throughout. Ball centered during all phases of flight. Aircraft configuration was constant between runs.

Data: (note configuration and test conditions in upper corners)

Next test is to investigate the influence of heat soak on CHTs during initial climb.

 

[RV8R999]

Plots are a little small so...

see if this is better

of note:
1. #1 & 2 cht begin to decrease consistently sooner than 3 and 4 but each pair tend to track shortly after t/o.
2. OT increase is linear until 180 at which it levels off - probably due to vernatherm action.
3. #2 is always hottest on the ground but the steepest cooling gradient while airborne - If I run the engine with the cowl off #2 is coolest on the ground all day long. cowl on = #2 hottest. Wonder if the prop rotated the opposite direction 4. if #1 would be hottest on ground?
5. CHT behavior is predictable and consistent

I suppose I should repeat this exact test at a cruise climb speed.

 

[Wayne Gillispie]

A very small amount of oil flows to the valve/rocker area on Lycomings which is one of the reasons for sticking exhaust valves. I am assuming that is also the reason for them not affecting each other much.

 

[RV8R999]

Plot of Oil Temp Delta from T/O to Max for each run

not surprising they are consistent but I do find it interesting my #2 which is ALWAYS the hottest on the ground has the lowest delta. From the data all CHT's are pretty close after 2000ft so how is it CHT #2 can start so high and end up the same and cooler than the others in flight? Well, I removed the baffle **** from the #2 cyl which probably had little affect on ground CHTs but aids in rapid cooling during flight. #1 has steel SS tape in exact same size as it's baffle **** (I removed it too).

Typically I focus on #2 during taxi and run-up but noticing #3 has exactly twice the CHT delta maybe #3 should be the cyl which dictates climbout A/S and power. I'll run the test again at 130mph and again 150mph and create a CHT Delta vs A/S plot.

 

[Mike S]

Think about it

so how is it CHT #2 can start so high and end up the same and cooler than the others in flight? Well, I removed the baffle **** from the #2 cyl which probably had little affect on ground CHTs but aids in rapid cooling during flight. #1 has steel SS tape in exact same size as it's baffle **** (I removed it too).

Cyl 1, and 2, both receive similar blasts of cooling air from the inlets, but one of them has the exhaust side to the inlet, and the other has the intake side of the head toward the inlet.

Methinks this may have something to do with the answer

 

[RV8R999]

Added a cooling flow augmenter

Decided to try an experiment and fabricated a flow augmenter attached directly under my louvers at the rear of the cowl exit area. The idea is to create a low pressure area at the louver exit, entrain this in the faster moving flow from the inlet of the augmenter and accelerate through a converging nozzle back to freestream.

Inlet face, inlet nozzle, diffuser section and exit nozzle area ratios are all guestimates since a bunch of data is needed to properly design this thing. Tried to account for the Mass flow through the louvers and reduced density through the larger diffuser section prior to accelerating through the exit nozzle. Its all just an experiment.

here is a hand drawing:

I have not fabricated the exit nozzle yet as I'm trying to decide if I should capture a portion of the cooling flow which does not pass through the louvers.

here is a pictured as installed. I did not modify the cowl in any way and simply used the existing louver installation points:

Flew the same profile I flew at the beginning of this post under very similar test conditions. Ground OAT was 3 deg cooler however OAT at altitude from 1000ft PA to 6000ft PA was within 1 deg of previous tests. Starting CHT on #2 cyl (the control cyl) was a little hotter than previous tests at 358 deg vice 350 deg. Accelerated to Vy (110mph), at WOT/Full rich to 6000ft PA and recorded data at T/O, 300ft, and 1000ft increments to 6000ft as previously.

Results: Peak CHTs were cooler from 5-10 deg, CHT at 6000ft were 10 deg cooler. Delta CHT (from T/O to Max) were all reduced by 7-12 deg.

Data:

wanting to capture the affect to A/S I conducted a max speed run using the Weight over Sigma method (to account for GW and DA) and compared to previous Vmax data - result - no change to Vmax. 1000ft PA, 2700ft DA, 93%pwr, 2700rpm = 186mias (previous data = 187mias).

I'll refly the profile once I install the exit nozzle.

 

[John Clark]

Missing data?

This would much more interesting if fuel flow/mixture/egt was included in the data. Fuel flow can make a big difference in climb CHT. "WOT, full rich" doesn't mean much without fuel flow numbers. A slightly richer main jet might provide some interesting information.

John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA

 

[RV8R999]

John - I could include that data easily however this a relative test with a constant configuration. WOT/Full rich with other environmental conditions equal is the same for my airplane from test to test. Once we try to compare my results to someone else's we lose configuration control and results are compromised.

Looking at the data for all the runs to include FF and EGT

FF ranged from 16.0 gal/hr to 13.8 gal/hr from T/O to 6000ftPA with fixed throttle and mixture, and was consistently within .1 gal/hr between all runs at each check point. EGTs for all runs ranged from 1210-1270 deg F from T/O to 6000ft PA.

I agree a richer carb jet would be interesting. I'm assuming making this change would only affect the "relative" position of the mixture lever for a given power setting and FF? AT WOT/Full rich I'd expect CHTs to be lower.

 

[DanH]

..wanting to capture the affect to A/S I conducted a max speed run using the Weight over Sigma method (to account for GW and DA) and compared to previous Vmax data - result - no change to Vmax. 1000ft PA, 2700ft DA, 93%pwr, 2700rpm = 186mias (previous data = 187mias).

Interesting...I would have assumed a greater speed loss.

Question...."mias" is indicated air speed in miles per hour, about 189 mph true?

 

[RV8R999]

Interesting...I would have assumed a greater speed loss.

Question...."mias" is indicated air speed in miles per hour, about 189 mph true?

I too am surprised. I'm going to re-run the power/speed test with and without the augmenter. I realized I've done a bunch of stuff to the plane, since the data was collected in Phase I so Apples-Apples isn't quite right.

yes - MIAS = indicated in MPH. TAS was showing 192

 

[RV8R999]

Flow Augmenter Drag

Needed to verify affects of the flow augmenter on power required. conducted a full power required run with both flow augmenter installed and not-installed under the same GW, CG and environmental conditions

Results: negligible drag