What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Winter Ops

Simon Hitchen

Well Known Member
Thought I’d share my cold weather mod.

Up here in cold Canada I was having issues running too cold. The engine has always run cool but with an OAT of 5F I was running at 280 CHT at cruise.

First I made a baffle to reduce the exhaust area and that helped so I made a couple of inlet baffles this morning to reduce the inlet area by 25 percent. I was concerned that It may interfere with the airflow into the snorkel but it seems to be fine. I’m now running 2400 rpm with CHT’s around 340F and oil temp at 180F with the help of an anti splat oil cooler shutter (mandatory for up here). I used existing screw/bolt holes in the front cowl so didn’t do any damage. If anyone knows of any problems with this design, please let me know.

474-C45-BD-448-B-4-E82-A360-0-D2999-FD5-F5-D.jpg

F231471-D-4-BD8-4-F44-91-C1-B09-F67-A694-DC.jpg

B3-B1-D8-DC-0-E9-B-45-D6-82-C0-7-EB57-AC4-BE8-B.jpg
 
Last edited:
Great idea, I was just thinking about making something similar after briefly hitting 200deg CHT during my descent from 9k yesterday.
 
Last edited:
Simon - if you need more warmth you can go to a larger surface area on your front inlet fillers, then if it's too much, just poke some holes in them.

On my non-RV I was having a difficult time regulating temperatures in the cold winters here in the Ottawa Valley. Finally in frustration i poked a bunch of 3/4" holes in my inlet fillers. Miraculously they changed from being suitable for a very narrow band of temperatures to being suitable for a broad band of temperatures, up to and even slightly above freezing. Surprised the heck outta me!
 
Simon,
I?m confused about why you are worried about low CHT?s. Isn?t that the goal? As long as your engine is producing the power you expect to get and the oil temp is within a normal range, what is wrong with CHT?s below what is your upper limit? Seems like that would be a good thing. CHT is an indication of your cylinder?s ability to dissipate wasted combustion heat. Reducing that efficiency by blocking airflow over your cylinders, while at the same time not gaining anything in reduced cooling drag, and in fact maybe increasing it, seems counterproductive. Reducing the inlet and exit areas of your cowling for reduced cooling drag, that enables you to operate your engine at higher temps that you are still comfortable with, may give you a net benefit if these changes are designed in a way that reduces drag, thereby increasing your TAS for a given fuel flow. Putting a barn door in the inlet, and the exhaust is of no benefit to you. It doesn?t reduce drag and increases CHT for no reason. Control your oil temperature with the barn door, not the CHT.
 
Cooling

Thanks guys,

Scott, thanks for your reply. I had many chats with the guys at the continental booth/Oshkosh this year about LOP ops. I was quite proud of the fact that at 50 degrees LOP my CHT’s we’re running around 280-300F and the engine runs smoothly at 7-8 GPH, even on a hot day. They all told me that was too cold for long engine life. 340-360 would be much better. I’ve got 25 years on Rolls Royce turbo-fans but I’m still learning this recip business!

Now that it’s colder up here in Toronto the engine is running colder and I had issues keeping it warm especially in cruise descents. To the point that I saw sub 200F on approach and I select flap early and keep the power up. I felt uneasy about the possibility of applying go around power...

The baffles change all that, 330F-340F in the cruise stabilising at 290F in the descent and 270F on approach. Makes me much happier :).

I may we’ll be wrong here, just going by the guidance given to me by continental,..What’s the general consensus on optimal CHT’s??
 
Last edited:
I?m interested in the answer to this one too. I didn?t think a low CHT would be bad. My RV8 runs at normal 340-360 in cruise, but the RV4 I used to own ran cool - similar to what you are experiencing. I figured that if I could keep the oil temp in a normal range (170-200) then everything would be fine. I struggled to do that in the winter in the -4, but the engine always ran strong. Using a cooler spark plug that fits in accordance with your engine manual should increase your CHT?s a little, and making sure your mag timing isn?t retarded below specs may help too if it?s off.
 
From what I've read here and elsewhere, cylinder head temperatures need to be kept up within a certain range (as already mentioned in this thread) in order to encourage the efficient scavenging of lead. Long-term low temp operations are very problematic. After recently reading the story of Voyager it became clear that one of their greatest challenges was with fouling resulting from their prolonged low power / cool engine operations.
 
Engines have optimal wall/head temperatures to achieve efficient combustion and generally speaking, the warmer the better at least up to a point. However, at certain temps other bad things happen and that is usually the limiting factor. Cooler temps also mean tighter Piston/wall clearances. The designers had expectations of certain temps at max power and designed the cold clearances accordingly. Run max power and too cool of a barrel temp and it will accelerate cyl wall and piston wear. I can't tell you what the temp is, though I suspect it is a good bit lower than 280 CHT. However, this is the reason you do warm ups. You don't want to run an aircooled engine at max load until the barrels temps come up to a reasonable level.

I am guessing that Lyc/Cont are recommending temps in the 300's because they know how this translates into temps inside the combustion chamber to achieve efficiency.

There is more than enough heat inside the combustion chamber at 50% + power to effectively scavenge lead, regardless of the CHTs. The real problem there is the reduced heat at RPMs below 1000 or so.

Larry
 
Last edited:
49clipper

That's interesting.
A year ago, I was trying to make my O-320 run a little warmer in cool weather (specifically the Oil). I called Lycoming tech rep and described the temps and he said, "lucky you!". Your cylinders will go to TBO or beyond. He said, you have the opposite problem of most and if you cylinders go below 150f, then call me. Yesterday I flew at 25f OAT and my cylinders ranged from 225 to 275f. According to Lycoming, no problem at all. My typical cruise summer CHTs range from 310-345f (90f OAT).
RV-6 O-320-D2A
 
Back
Top