REFLECTOR:Oil temps and heating

Scott reflector@tvbf.org
Thu, 23 Oct 2003 21:10:13 -0600


Dave,

Are you sure your CHT's aren't a bit higher now than they were before the 
mods you made?

I slight rise in CHT's can make a huge difference in your oil temps, I'd 
say 80+% of your oil temps come from cooling the cylinder-head assemblies.

Its possible a 10 degree rise in cyl head temps can give you a lot more 
than a corresponding 10 degree rise in oil temps.

I just went though(well I'm not totally done, are we ever?)  a cowl 
modification which included tightening up the air leaks in the engine 
compartment.  I also have the standard single nose mounted oil cooler, and 
updraft cooling from armpit scoops. I used to be in the cooling-challenged 
position you are in now.  I could get my oil in the 240's pretty easy, and 
during the summer could not run at max RPM or I would over heat.

Now  with 80% of the air leaks fixed I haven't seen oil temps above 220 
after a 10,000 ft steady climb and I cruise at max rpm with oil temp around 
205F.

I've been told that most cooling problems are a direct result of poor 
baffling, and in my case it was completely true.

Scott

At 08:23 PM 10/23/2003, you wrote:
>I'm fairly new to the reflector,  so I apologise if this subject has been 
>covered before.  I guess I'd be a bit surprised if it hadn't...
>
>I've just passed 600 hours on my STD-RG, which I built.  I live in 
>Minnesota, and winters are long up here, so I always search for good 
>projects to upgrade my aircraft over those long winter months.  Last 
>winter I decided to clean up the lower cowl in order to improve speed & 
>performance.... you see, my hangar mate is a beautiful Cozy 3 place.  With 
>his 150 horses, he's close (way too close) to keeping up with me in my 
>IO-360 powered, 200 HP velocity RG.  It's always a race when we go flying...
>
>My plan was to do drag reduction to the lower cowl by reworking the armpit 
>scoops I use for cooling air and eliminating the induction air scoop.  My 
>airplane's been flying for quite awhile now, so I'm sure you guys and the 
>factory have come up with 50 better solutions than what use to have... 
>which was the factory standard scoops mounted on the cowl, and separate 
>"inner" scoops that were mounted to the sides of the fuselage and ducted 
>cooling air to the plenum.  I orignally made the inner/outer scoop 
>combination to make it easy to remove the lower cowl without having to 
>muck with anything.  It worked well, but there was quite a gap required 
>between the inner fuselage mounted scoops and the cowling.
>
>I figured I could reduce the total scoop size by about 25% and improve 
>cooling in the process by getting rid of the gap.  Cooling would be 
>improved given that high pressure air was leaking into the lower engine 
>area through the gap... by tightening up the outer scoop I would actually 
>increase the differential pressure between the plenum and the lower engine 
>area, and also reduce overall drag.  At least that was the theory.  So, I 
>reworked the whole system - I made smaller armpit scoops that are mounted 
>to the fuselage, and reformed the cowl to fit tight against the new 
>scoops.  I faired the new scoops into the cowl so that the airflow stays 
>attached as long as possible.  Additionally, I made a small plenum that 
>provides both engine induction air and cooling air from the right hand 
>armpit scoop, thereby eliminating the drag from the separate induction air 
>scoop.
>
>Results from all this work are very mixed... my speed didn't increase at 
>all despite the drag reductions.  You may laugh at my stupidity on this, 
>but I neglected the fact that by not separating the air in the new small 
>cooling/induction air plenum, I lost the ram air effect on the induction 
>air side.  I lost about 1.5 inches of maximum manifold pressure because I 
>didn't separate the induction air from the cooling air on the right 
>scoop.  Alas, a project for this winter.  The real problem, though, has 
>been that with this new setup, my oil temps have become very difficult to 
>manage.
>
> From a cooling perspective, I've got the standard nose mounted oil cooler 
> and cabin heat system.  Before the modification, my oil temps rarely got 
> up to 100 C (212 F), and my CHTs were all around 350 F +/- 25 degrees. 
> Now, in a climb I can easily heat the oil to redline (242 F) if I'm not 
> careful.  After much thought and work, it appears that the leakage air 
> that was slipping between the inner and outer armpit scoops and 
> pressurizing the lower cowl also had a cooling effect on the accessory 
> case, oil sump, and the oil temperature transducer.  Tightening up the 
> cowl, eliminating the "blow by". Reducing the size of the armpit scoops 
> did not change the CHTs, but because I lost the airflow over the bottom 
> engine and accessory case, my oil temps are now a problem.
>
>So, here are two questions for the reflector crowd:
>
>1) How much, if any, cooling air is required for the accessory case and 
>oil sump?  It's logical that you'd want some, but, OTOH any air down there 
>reduces the differential pressure from the plenum / top of the engine to 
>the bottom... thereby potentially increasing CHTs.  Thoughts?  BTW, just 
>to get the discussion going, I discussed this extensively with the 
>Lycoming rep at OSH, who told me that he didn't think I needed any airflow 
>over the sump/accessory case...
>
>2) My cabin heat box is the original, and I've always been unhappy with 
>the push/pull cable for the babin heat flapper valve.  Anyone put in a 
>electrically actuated flapper valve?
>
>To anyone who's acutally read this far... THANKS!
>
>Dave
>600+ hours STD-RG N22DN
>
>----- Original Message -----
>From: <mailto:romott@adelphia.net>Ronnie Brown
>To: <mailto:reflector@tvbf.org>reflector@tvbf.org
>Sent: Thursday, October 23, 2003 2:02 PM
>Subject: Re: REFLECTOR:Heating
>
>I was considering installing electric seat heaters but I decided to try a 
>google search for 12vdc electric blankets and look what I 
>found! 
><http://www.baproducts.com/rphb1101.htm>http://www.baproducts.com/rphb1101.htm
>
>Ronnie
>----- Original Message -----
>From: <mailto:cdwoolston@earthlink.net>Craig and/or Denise Woolston
>To: <mailto:reflector@tvbf.org>reflector@tvbf.org
>Sent: Wednesday, October 22, 2003 1:20 AM
>Subject: RE: REFLECTOR:Heating
>
>Well I went way overboard but it was one of those great ideas that quickly 
>multipled in to lots of hours and it's still not done...
>
>I made two plenums that will mount on canard bulkhead.  They each have a 
>hot and a cold source coming from front oil cooler and fresh air NACA 
>respectively.  Since the wife and I are never the same temperature a small 
>diverter flap inside each plenum allows for individual temperature 
>control.  I plan to drill two holes in canard bulkhead that each plenum 
>sits over the top.  One hole will just allow the output to blow down on 
>feet and the other will be routed to the instrument panel eyeball 
>vent.  Time will only tell if it will work.  As for the rear seats I'm 
>thinking seriously about electric seat warmers and/or electric blanket outlet.
>
>Craig
>
>!----------------------------!
>! Craig Woolston             !
>! XL-FG in Palmdale, CA      !
>! cdwoolston@earthlink.net   !
>!----------------------------!
>-----Original Message-----
>From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On Behalf 
>Of velocityxlfg
>Sent: Monday, October 20, 2003 9:07 AM
>To: reflector@tvbf.org
>Subject: REFLECTOR:Heating
>
>Can some one send me some pictures of what they did on there heating 
>system. ducts, Heat exchanger routing of the
>heat ducts.   Ect.
>Ron
><mailto:velocityxl@fastmail.fm>velocityxl@fastmail.fm