More Winter baffle questions...
Posted: Sun Dec 08, 2013 8:09 am
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
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