REFLECTOR: Oil cooler VG photo
Dave Nelson
davenali at charter.net
Sun Jul 16 16:09:35 CDT 2006
Thanks again, Scott - much appreciate your input. I've embedded some
answers below.
----- Original Message -----
From: "Scott Derrick" <scott at tnstaafl.net>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Sunday, July 16, 2006 3:40 PM
Subject: Re: REFLECTOR: Oil cooler VG photo
> Dave,
>
> There has to be things that are different as we are driving the basic
> same machine.
>
> 400 degrees isn't really hot but my CHTs in the summer in cruise were
> very close to 330-360 range. So I wonder about your overall engine
> cooling. You say your taking some of your armpit cooling air and using
> it for induction? I do not. I have a separate ram scoop and use all the
> arm pit air for cooling.
I'm basing my "comfort" factor only on the history of having not made the
CHTs worse with this mod (in fact, slightly better). As I said,. the scoop
from which I take the induction air was sized bigger than the other scoop to
account for the cooling air loss. It is also separated internally so that I
don't loose the ram air effect for my induction air.
>
> You also didn't mention:
>
> Are you running LOP or ROP, makes a big difference in your temperatures?
I've been taking data at full rich. because on data generation flights I
only climb to 2500 MSL (around 1500 AGL) and keep the power high (26
squared).
>
> How unobstructed is your oil cooler duct? If you also use that for
> cabin heat how tightly does the diverter flap come up against the side
> when cabin heat is turned off? Are their bumps and angles near the
> outlet that the air has to negotiate or is it a smooth all the way out?
I've looked at this before, and it seems pretty smooth to me - but I'll look
at it harder. Thanks for the tip.
>
> Is your baffling really tight, I mean really really tight or do you have
> big gaping 1/2 inch or inch wide holes where the baffling meets the case?
I'd have to say yes, I believe the baffling is tight. I've even gone over
it with a flashlight in a dark room looking for light leaks. As I
mentioned, I'm somewhat familiar with cooling problems like this... this
isn't my first canard pusher.
But, on another note... I've discussed the correlation between CHT and oil
temp repeatedly and at length with several Lycoming engineers - all of whom
have consistently told me that there should only be a very weak relationship
if any at all. In fact, most will initially deny any relationship at all.
I've had this discussion because one of the reasons I modified the armpit
scoops in the firstplace was to eliminate air leakage from the armpit scoop
to the lower cowl area (which dropped the differential pressure from the
plenium to the lower cowl, thereby lowering cooling efficency. But, the
leakage air DID mean that there was quite a bit of air circulation (blow by)
passing around the oil sump. When I made the mod, and oil temps became a
problem, my first guess is that this was the reason - not enough air moving
around the oil sump. The Lycoming team absolutely disagreed, & told me that
oil cooling from that mode was very limited. This is a very meaty
discussion for endless debate in my book... but for now I'm going with the
"professionals" advice.
>
> Each of these things won't make a big difference, but added up together
> they can.
Couldn't agree more - and thanks for taking the time to give me input!
>
> Scott
>
>
> Dave Nelson wrote:
>> Thanks much for the tips, Scott - and for the speedy response. Here's
>> more
>> background...
>>
>> I have been going after drag reduction to ensure that I remain faster
>> than
>> my hangermate (Doug Solinger in his beautiful Cozy Classic). One of the
>> things I've done is to tighten up air leakage that was occuring between
>> the
>> old stock armpit scoops and the lower cowl. I did this by engineering
>> new
>> armpit scoops that are a bit smaller. I also created an airbox to use
>> armpit scoop ram air for induction air (and yes, I did size the scoop for
>> this mod). More recently I designed & had built a new exhaust system
>> that
>> keeps the entire exhaust internal to the cowl and exits the exhaust
>> behind
>> the prop (similar to what you see on alot of long-ezs these days). The
>> exhaust this new one replaced was purchased from Velocity - the exhaust
>> gas
>> exited the lower cowl pointing straight down (and created quite a bit of
>> drag).
>>
>> I've always been focused on ensuring that every molecule of cooling air I
>> take in gets used - my plenum is very tight. On a 90 degree day, I
>> seldom
>> see any cylinder reach 400 deg. F., which I consider acceptable.
>>
>> I am having a BEAR of a time with oil temps, however. I've been working
>> on
>> this problem for two years now and I'm about at wits end. I've had
>> extensive discussions with Lycoming (and others), and I've done all of
>> the
>> obvious things (detailed measurements of the vernatherm per Lycoming
>> specs
>> to ensure it's working correctly, flushed the entire oil cooling system
>> to
>> ensure no "gunk" build up, inverted the oil cooler to put the connections
>> at
>> the top (to eliminate any chance of a bubble), various "scoop"
>> modifications
>> to the nose NACA for the oil cooler, MANY test flights (standardized so I
>> could gather data)... I even added a bilge fan under the pilot seat to
>> blow
>> air into the wiring duct containing the oil lines)... all to no avail.
>> Where I'm at right now is, a short flight at 25 squared on a 85 degree
>> day
>> quickly results in oil temps that have exceeded 225 degrees F.
>>
>> I'm at the point of giving in. My current theory is that the oil pump on
>> my
>> engine is no longer as capable of pushing the oil through the approx. 30
>> feet of tubing as it was when I installed it about 750 hours ago.
>> Lycoming
>> tells me that the system is designed for around 4 feet of tubing, and
>> that
>> this installation is completely nuts (my words... they are more
>> diplomatic).
>>
>> Sooo... to avoid loosing another summer of flying... I'm now willing to
>> consider installing a second cooler.
>>
>> Any thoughts are welcome - and thanks for the good suggestions!
>>
>> Dave
>> ----- Original Message -----
>> From: "Scott Derrick" <scott at tnstaafl.net>
>> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
>> Sent: Saturday, July 15, 2006 8:57 PM
>> Subject: Re: REFLECTOR: Oil cooler VG photo
>>
>>
>>
>>> Dave,
>>>
>>> I have Std RG, and had an IO360 200 HP engine in it. Standard oil
>>> cooler. When I bought the plane I had temp problems. Bad ones. Couldn't
>>> run any where near 75% power without over heating.
>>>
>>> I did the following which allowed me to run 75% any time of year and
>>> normal cruise temps were 190, I even had to cover up some of the oil
>>> cooler in the winter to get the temps above 180.
>>>
>>> 1.) Put turning vanes in the oil cooler duct and smoothed out the duct,
>>> especially the exit. You don't want turbulent air downstream of the
>>> cooler.
>>>
>>> 2.) Got very anal about air leaks in the engine cowl/baffling. Any
>>> hole larger than 1/4 inch must be plugged. Also be sure the silicone
>>> baffles are pressed against the engine so that the air pressure will
>>> tighten them against the heads. Lowering your CHT's will have a
>>> dramatic effect on your oil temps.
>>>
>>> 3.) Run LOP. I installed a Lightspeed Ignition that provided such good
>>> complete fuel burn I could run 75 degrees LOP which dropped my oil temps
>>> 5-10 degrees from a similar ROP power setting.
>>>
>>> Scott
>>>
>>>
>>> Dave Nelson wrote:
>>>
>>>> Wow is this both interesting and pertinent to me... I've been battling
>>>> oil temp issues for the past two summers on my std rg - I'll try the
>>>> VGs tomorrow.
>>>>
>>>> In the meantime, since I'm getting desperate - for those of you that
>>>> have succumbed and added a second oil cooler - where did you mount
>>>> it? Where do you get intake air?
>>>>
>>>> Thanks.
>>>>
>>>> Dave
>>>>
>>>> ----- Original Message -----
>>>> *From:* Laurence Coen <mailto:lwcoen at hotmail.com>
>>>> *To:* reflector at tvbf.org <mailto:reflector at tvbf.org>
>>>> *Sent:* Saturday, July 15, 2006 12:46 PM
>>>> *Subject:* REFLECTOR: Oil cooler VG photo
>>>>
>>>>
>>>> Mike,
>>>>
>>>> Here is an attached photo of the VG's. The top VG should produce
>>>> a clockwise vortex and the bottom one should be counter
>>>> clockwise. I have no idea as to why you felt a "flutter". The
>>>> only effect I experienced was cooler oil and nothing else. I felt
>>>> that my arrangement should stuff air into the oil cooler
>>>> opening. A 20 degree drop in temperature would logically tend to
>>>> support the theory.
>>>>
>>>> I hope this is of some help.
>>>>
>>>> Larry Coen
>>>> N136LC
>>>> SE/RG Franklin/IVO
>>>>
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>>
>>
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