Welcome! Becoming a registered user of ShortWingPipers.Org is free and easy! Click the "Register" link found in the upper right hand corner of this screen. It's easy and you can then join the fun posting and learning about Short Wing Pipers!
-
Re: Engine Cooling Fixes
# 3 is usually the hotter cylinder. what kind of probes do you have, bayonet or spark plug washer?
I had a #3 that ran 60-70 hotter that the next highest temp. Put a bayonet probe on it and it was
much more normal. The rule of thumb is the spark plug washer sensors run 50 degrees hotter than
the bayonet, but mine was much bigger delta.
Agree with most the other suggestions, don't think you'll do any damage to scat tube, I would cover up
and go fly to see if there is a diff. Seems like you don't have much exit in the aft bottom compared
to the normal cowl and the tab doesn't look all that big either for generating enough low pressure
to get air flow. Not sure how much affect it would have, but the RV cowl was probably designed
for having more dynamic pressure at the intake due to higher indicated airspeed.
"Progress is our most important problem"
-
Re: Engine Cooling Fixes
Originally Posted by
andya
# 3 is usually the hotter cylinder. what kind of probes do you have, bayonet or spark plug washer?
I had a #3 that ran 60-70 hotter that the next highest temp. Put a bayonet probe on it and it was
much more normal. The rule of thumb is the spark plug washer sensors run 50 degrees hotter than
the bayonet, but mine was much bigger delta.
Agree with most the other suggestions, don't think you'll do any damage to scat tube, I would cover up
and go fly to see if there is a diff. Seems like you don't have much exit in the aft bottom compared
to the normal cowl and the tab doesn't look all that big either for generating enough low pressure
to get air flow. Not sure how much affect it would have, but the RV cowl was probably designed
for having more dynamic pressure at the intake due to higher indicated airspeed.
I've got bayonet probes.
I agree there doesn't appear to be as much exit size as a standard pacer cowl. I think the intake size is smaller as well, but I need to compare with someone.
I can't maintain higher speeds to keep pressure above the baffles higher or the temps climb like crazy. My only current option is to throttle way back and accept what speed that gives me. Improving cooling should give me the ability to cruise fast again.
-
Re: Engine Cooling Fixes
Well FWIW,
Two of my neighbors have RV 6s. Their oil temps tend to run hot. One added a second cooler which helps some. The other has to do step climbs.
Your cowl is made for fast planes and even at that it has minimum air inlet.
If you have a tunnel at the firewall a lip isn't required. My Starduster Two doesn't have one. If you do a little research you can find the formula for the relation of inlet air and outlet air. It has been to long since I did my cowl and don't remember
What are your cyl. heads running that is more important than oil temp. They should not go above 380. 400 for a shot time max. Yea I know what the red line states. They will crack just when
As far as the oil breaking down at 230-240. From what a friend of mine with a Dr. Engr.that worked for Shell Oil in the research lab says not to worry about oil break down at temps below 300.
Also you need to have air flow inside the muffler shroud. If not you will cook some of the parts due to the high heat build up inside. Anyway I did, you might get lucky
Jim
-
Re: Engine Cooling Fixes
Generally the air inlet and outlet should be the same size. You don't want to create positive or negative pressure in the cowl.
-
-
Re: Engine Cooling Fixes
The top cowl is a plenum, not much air movement but a pressure increase. Basically you want to convert velocity pressure to static pressure to increase the pressure on the top of the engine, slow the air flow and gain static pressure then you want generate low pressure on the bottom. Hence the lip that generates a vacuum behind it. This aids in pulling air thru the cylinders with minimum friction loss.
As Steve pointed out, Lycoming says you need a pressure differential of at least 0.5 inches of water difference between the top and bottom of the cowl to properly cool the engine.
-
Re: Engine Cooling Fixes
I measured approximately 49 sq in of inlet and approximately 73 sq in of exit. I took a bunch of pics today and will post more findings after dinner.
Sent from my LG-D850 using Tapatalk
-
Re: Engine Cooling Fixes
It looks like two issues exist: 1) the inlet area is too small for the aircraft speed and 2) the exit area is too small. Generally, the exit area should be 1.5 times the inlet area. With such small inlets all bets are off, especially since the cowling was designed for an aircraft with almost twice the cruise speed. Adding a lip will create a pressure differential, but with a small exit area it's like adding a lip to an orifice.
Is your exit area accounting for the exhaust and other items of area obstructing the exit airflow?
-
Re: Engine Cooling Fixes
Originally Posted by
taildraggerpilot
It looks like two issues exist: 1) the inlet area is too small for the aircraft speed and 2) the exit area is too small. Generally, the exit area should be 1.5 times the inlet area. With such small inlets all bets are off, especially since the cowling was designed for an aircraft with almost twice the cruise speed. Adding a lip will create a pressure differential, but with a small exit area it's like adding a lip to an orifice.
Is your exit area accounting for the exhaust and other items of area obstructing the exit airflow?
Not accounting for exhaust pipes. Those and the gascolator are the only obstructions down there, though.
This plane will cruise around 140 mph around 2400 RPM.... if I can keep the temps down. Didn't have a problem with it in Alaska, even in the summer. I'm betting something changed in combination with the hotter weather down here.
Pictures to follow in my next post.
-
Posting Permissions
- You may not post new threads
- You may not post replies
- You may not post attachments
- You may not edit your posts
-
Forum Rules