Cowl pressure delta

[N661DJ]

I have a new , 30hrs., ECI Titan 0-360- A1AN and experiencing high CHT's. 390* at 75% power, over 400*F at WOT. 75* OAT.
Searched the threads?? My question, I think Dan H. addressed in a previous thread. What sort of differential pressure should I be seeing??
The differential I am seeing, measured with a manometer, top and bottom of the cowling is, @ 145mph indicated, 2500', 8.5" of H2o top., 3.5" of H2o bottom for a 5" of water difference. The airplane is an 8A. 3 blade CATTO PROP. I have installed louvers on the bottom of the cowling. ECI says these temps. are not too high, but I would like to see them down around 350* or so. I have spent a lot of time on the baffling and really don't think there is an issue there. Dan, is a 5" > adequate?
Dick

[crabandy]

I'm definitely not an expert, but here's my pressures (post 55):

http://www.vansairforce.com/communit...it+bump&page=6

8.5 " H20 in the upper cowling sounds reasonable. I had about 1.5" H2O in the lower cowling at 130 knts, 160 knts only increased it to 2" H2O with No Louvers. 3.5" H2O especially with Louvers sounds really high, how are you taking these measurements?

Google "Lycoming Cooling Pressure Differential Chart," 5" H2O is right in the ballpark of your CHT's.

[NDrv8r]

right off hand I can't find the chart, but I remember seeing a Lycoming chart that indicated that you need about 6" delta pressure to cool 200HP. Looks like your getting 5??

Google N91CZ. He has good data on plenum pressure.


I found some of my own data. IO360 200hp, 4055DA, 184ktas, 2780rpm
top pressure 14.7 inh2o, lower pressure taken near the exit 4.3, both referenced to static pressure. hottest cht is 335.

cruise: DA7957, 168KTAS, top pressures 11.0, bottom 3.1 hottest cht = 308.

[BillL]

Here is a dynamic head calculator. It needs altitude, speed, and temperature.

http://www.aerospaceweb.org/design/scripts/atmosphere/

If the temp was "normal" then your pressure recovery is 87%, pretty good.

[Weasel]

Originally Posted by N661DJ

I have a new , 30hrs., ECI Titan 0-360- A1AN and experiencing high CHT's. 390* at 75% power, over 400*F at WOT. 75* OAT.

ECI will tell you that your temperatures are normal. At SnF several years back they verbally told me that it will not hurt there cyl's to operate at 435F all day in cruise. By the way they do sell cyl's. I think you should go fly another 75 hrs. My experience is that the temps will drop a little more with time although most of the cyl break in is already complete.

Also few things to check would be ensure you are ~150-200 deg rich of peak EGT when WOT. I had to have my Bendix servo modified to achieve enough fuel flow to make 150 ROP. Check that your timing is per manufacture recommendation.

[DanH]

Originally Posted by N661DJ

I have a new , 30hrs., ECI Titan 0-360- A1AN and experiencing high CHT's. 390* at 75% power, over 400*F at WOT. 75* OAT.

The differential I am seeing, measured with a manometer, top and bottom of the cowling is, @ 145mph indicated, 2500', 8.5" of H2o top., 3.5" of H2o bottom for a 5" of water difference.

There are a few additional parameters you need to know if you wish to compare your cooling performance to a Lycoming cooling air demand chart. First is altitude and temperature, really meaning air density. In bubba terms, thicker air can carry away more heat. Second is mixture state, as the charts assume 0.5 BSFC (fuel lbs per hour/HP). In rough terms, that's a ROP best power mixture. Makes sense; high cooling demand.

I don't have an ECI chart, but here's the Lyc chart:



Assume a standard day temperature (60F at the engine face), and 5000 feet. Power is 75% (135/180) and mixture is 0.5 BSFC. The green line predicts a 435F CHT with a 5" baffle drop. At 2500 ft, a 5" baffle drop nets pretty much the same result.

The unspoken assumption here is typical GA quality baffling, which is pretty awful. Better-than-GA baffle quality is probably why your cooling performance is beating the charts (390F at 75% rather than 435F, at a higher OAT). Chances are good that you can improve further, but a bit more break-in time is in order before direct comparison with known installations.

An excellent indicator of heat transfer efficiency (maximum heat being carried away by the cooling air mass flow) is found by measuring outlet temperature. Since you're actually measuring important parameters (my compliments sir!), you may wish to install a temperature measurement probe or two. You want a probe on the end of a wire which can be re-located anywhere under the cowl as desired.

The output of a National Semiconductor LM34AH-ND (try DigiKey) is read with an ordinary hand-held digital multimeter or a digital voltage display. The voltage corresponds to temperature, 10mV = 1 degree F. Example: Meter says 2.5 volts. 2.5V is 2500mV. 2500/10 = 250F. Whatever the meter says, just move the decimal point two spaces to the right and you have temperature.

Only three connections, aircraft power, ground, and sense. Connecting to the avionics bus so the sensor is “on” with flight instruments is fine. Meter negative and probe ground should both be connected to the aircraft single point ground bus.

You’ll need a way of routing the probe wire through or around your firewall. Some have run it through the heater duct. Installing a screw-type terminal block on the firewall wired to another screw terminal block in the cockpit is a nice, permanent way to make temporary connections in the future.

Solder the LM34 to the ends of the three-conductor tefzel shielded aircraft wire. Insulate each lead connection carefully as you go, the cover the entire end with a short length of ¼” adhesive heat shrink. Leave the cap of the LM34’s can uncovered.

The cockpit end will connect to aircraft power and the aircraft ground bus, with the third wire routed to a convenient location for meter connection. Run a single wire from the ground bus to the same location. The latter two wires are for the voltmeter.

You’ll find a great many temperatures of interest, but the primary in this investigation is cooling air exit temperature. The probe is mounted just inside the cowl exit. It is critical to shield the probe from radiant heating, the primary source being the exhaust pipe(s). Fabricate a radiant heat shield as necessary. Make sure the heat shield itself cannot transmit heat to the probe via conduction.

[Randy]

Here is my data to compare to:

Differential between top engine center area at the lifting eye measured with 1/4" OD tube with aquarium stone to get static pressure versus the same at the back side of the engine. Used my Magnehelic 0" to 15" guuge.

At cruise speed and EZ Cool flaps closed I always see more than 10" differential. Open the cowl flaps and it goes up to betweeen 13" and 14".

I did attempt to get a very good seal on my baffles but it is mostly stock.

My CHTs will still get up to 400F if I run it at best power mixture for extended periods in warm OATs.

I like the idea of getting set up with a method to check temperatures in various areas, like the mechanical fuel pump, exit air versus OAT would be nice. I will look into the LMXXXXXX that Dan mentioned, thanks Dan.

[DanH]

Dick, BTW, I assume your upper and lower pressure measurements are differential with aircraft static. If so (setting aside any aircraft static error), your dynamic pressure capture is pretty good. The total available standard day dynamic pressure at 2500 ft and 145 MPH is about 9.7" H2O, so 8.5" is 87~88%. This is not a surprise; previous measurement says the stock RV-8 cowl inlet is quite good. Note that 100% is impossible, as cooling flow never comes to a full stop like an airspeed pitot. Anyway, in terms of moving mass flow through the system, you already have all the motive power you're going to get. After full break-in (whenever that is), lower CHT will require better heat transfer...heating the air more as it passes through the fins.

Originally Posted by Randy

Differential between top engine center area at the lifting eye measured with 1/4" OD tube with aquarium stone to get static pressure versus the same at the back side of the engine.

Note that this method (direct measurement of upper and lower differential pressure) works fine for baffle drop, but doesn't tell anything about dynamic pressure.

I like the idea of getting set up with a method to check temperatures in various areas, like the mechanical fuel pump, exit air versus OAT would be nice.

A good cooling yardstick is:

(Exit - OAT)/(Avg CHT - OAT) = epsilon

...a decimal value. Work to push that value as high as possible; maximum heat transfer means less mass flow is required for the same cooling.

[Bavafa]

Do you guys have a picture of your home made a manometer as how you built it and routed the hoses.
I was picturing in my head a U shape clear plastic/glass-type pipe connected to two hoses on each end and perhaps run them thru the heat scat connection in the firewall to the engine compartment. Do you I have this pictured correctly? Do you have any info as where I can get the clear plastic tubing so I am not re-inventing the wheel?

Much appreciate any info

[rv6ejguy]

Originally Posted by Bavafa

Do you guys have a picture of your home made a manometer as how you built it and routed the hoses.
I was picturing in my head a U shape clear plastic/glass-type pipe connected to two hoses on each end and perhaps run them thru the heat scat connection in the firewall to the engine compartment. Do you I have this pictured correctly? Do you have any info as where I can get the clear plastic tubing so I am not re-inventing the wheel?

Much appreciate any info

Forget water manometers, just a pain to mount and read. http://www.dwyer-inst.com/Product/Pr...ges/Series2000