More Winter baffle questions...

[DavidBlom]

Hello All - I've had a look through previous posts & though there are quite a few posts about winterization kits haven't found found the information I'm looking for. First, some background to the question(s).

I flew to Kelowna today from Langley (about 1 hr drive east of Vancouver) and because it was -7 Celcius (about 20 Farenheit) at the airport I decided to fashion some cooling inlet restrictors for my 1950 170A. I covered the hole in front of the oil pan with duct tape, and blocked about 1/2 of each cowl inlet from the spinner out. Took off after a quick ground run & tape integrity check, and soon realised that the cabin heat inlet was nicely covered. Oh well - put on scarf, toque & winter survival kit gloves & kept climbing. Oil temps continued to climb, and by the time I was ready to level off at 9500 feet the needle was a couple of mm from redline. Not great, but I thought since it was a little below 0 Farenheit outside the temp should drop a bit after cruising for a while. At that point I glanced at the CHT (single cylinder probe) and was alarmed to see it reading 460 F. I've never managed to bring it above 380 on a hot summer day. Not being sure that this was a healthy number I elected to land at a nearby airport (all the way back down to 38ft asl) and remove the tape from the cowl inlets. I left the oil pan inlet blocked. Put on some snow pants, took off & climbed back to 9500. This time oil temp maxed at about the 1/2 way point and CHT barely broke 300 F. In cruise oil temp needle stayed at about the 1/3 point & CHT was 290 to 300.

I've searched the forums about the Cessna restrictor plates and what others have done re. taping the inlets, etc., and it seems like the Cessna plates cover about 1/2 of the inlet width. Checking the CHT limits for O-300's I find that 525 F is the redline, so apparently 460 isn't going to melt anything.

It seems to me that if i shorten the amount of cowl inlet blocked and un-block the cabin heater inlet then all should work well. Has anyone out there measured the width of the Cessna restrictors, or does anyone have a measurement for the duct tape solution that works? Is 450F on a single probe CHT a reasonable number? I'm guessing that covering 1/2 the inlet is the most you would want to do, and then back off that amount as OAT approaches 30F. What is the best metric to check to ensure the setup is good - a target cruise CHT reading perhaps?

I'll stop rambling now - any insights would be appreciated!

Dave Blom
1950 170A
C-FNIE

[Bruce Fenstermacher]

Here is a link to discussion and some pictures of the plates I made which are duplicates of the early Cessna plates. Looking back is realize I need to fill in a bit with dimensions and a drawing of the upper plate. I'll get those dimensions later today.

http://www.cessna170.org/forums/viewtop ... e&start=15

As for your experience. I've come to realize there can be a wide difference of the cooling from the '48 to the '56. From '48 through most of the A models if memory serves the lip was 2 1/2" deep which really draws air through the engine and for the most part these air frames run cold. This lip on later years is called the seaplane lip. Somewhere in the late A model but by the the 52 B model time frame the lip was reduced to 3/4" standard. Then of course in '53 the cowl was changed to a pressure cowl an the inlet design changed as well. These later models primarily I believe because of the small lip, run much hotter.

Bottom line. When you compare cooling from one 170 to another, you have to be pretty specific what lip and cowl it has in order to compare apples to apples.

Generally it has been my experience that if you have the early cowl with a 2 1/2" lip, you can close all the area the Cessna plates cover and not get the temperatures anywhere near as hot as you did. This leads me to think perhaps your lip is smaller. With the smaller lip you can experience the temperatures you did and knowledge is key here. As you later discovered you did not exceed any limits.

I personally would uncover the heater air intake. I might slightly reduce the upper intake block to bring the oil temp down slightly. But be advised on many 170s in the summer months the oil temperature runs a s you describe all the time.

[sfarringer]

Did you cover the half of the intake that is closest to the valve covers, or the half closest to the center of the engine?

If you covered the half closest to the valve covers, that would explain your high cylinder head temperature.
Always start covering area near the engine centerline. Probably best to start small and work up, until you find what works for your installation.

[N2255D]

by DavidBlom » Dec 8th, '13, 04:09
I covered the hole in front of the oil pan with duct tape, and blocked about 1/2 of each cowl inlet from the spinner out.

Looks like he closed the half closest to center of the engine.

[DavidBlom]

Thanks Bruce,

I do indeed have the shorter cowl lip. I'm going to make a set of plates something like the ones in your photo & will try to make them adjustable over a couple of inches as well. Will leave a gap for the heat inlet too - that tiny little outlet near my left shin is so much better than nothing!

Dave Blom
1950 170A
C- FNIE

[HA]

David, when I made up my winter fronts I cut the RH one up from the bottom where it was in front of my heater inlet and bent the flap back about 45 degrees-ish, so it's basically a ramp directing airflow down into the heater duct. sorry I don't have any pictures or measurements handy, but it gives you the idea.

[bagarre]

Have a look at this link:
http://cessna170.org/forums/viewtopic.php?f=24&t=10951

The simple heat duct made a world of difference in my '52 for cabin heat.

[DavidBlom]

Thanks David - Great idea - I will make one of those along with the restrictor plates. Will make my wife *somewhat* happier. Actual happiness would require a cabin temp around 80F.

Have a look at this link:
http://cessna170.org/forums/viewtopic.php?f=24&t=10951

The simple heat duct made a world of difference in my '52 for cabin heat.

[Bruce Fenstermacher]

David,

This link will take you to a picture of my first winter baffles. these were shorter than the Cessna solution. My cowl had the 3/4" lip. They worked fine. At this link you will see how I addressed the heater intake. Basically slit the opening and bent the aluminum back creating tabs. To these tabs I riveted some silicone baffle strip which sealed around the intake scoop. You might think this would help airflow but I did not notice a difference over having no baffle but it was better than having the intake blocked by the baffle.

You probably don't have a scoop as shown as that seemed to be a '52 year improvement.

http://www.cessna170.org/forums/viewtop ... ate#p90135