Hi Tracy,

Haven't heard any more news since the marriage license purchase. Did y'all make it official?

I'm still struggling with how to configure my radiator setup for the Renesis. Tentative plan is still to use 2 of the 30 row oil coolers (same as your 20B oil cooler), but I can't decide whether to go with them stacked (4" deep, ~9" x 10" face) & a straight K&W duct feeding it, or to emulate your setup with them end-to-end making a 2" thick, ~9" x 20" face, with a wedge fed by a modified K&W streamline duct like your 20B. Either configuration would be fed from one round 17 sq in inlet on the James cowl, similar to your intake (my inlet area would be about 70% of yours, IIRC).

The data in K&W for streamline vs wedge seems to be conflicting (& seems far more conservative than what's actually flying). If K&W are to be believed, the wedge is less efficient than the straight streamline, but there seems to be other evidence that low speed cooler efficiency is actually better with the wedge & the same inlet area (meaning more flow through the thinner, bigger faced core). If that's the case, it would seem that throttling the exit should keep high speed drag down to similar levels as the thick core with a straight duct.

My question is this: What's your max *sustained* climb rate in the -8, without overheating?

If you (in the 20B RV-8) can sustain anywhere near the max climb rate of your Renesis-powered -4, then I'll be very tempted to use the wedge, thin core setup.

What do you think?

Thanks,

Charlie
(feel free to post your answer on the list, if desired)



On 10/15/2011 11:36 AM, Tracy wrote:

The oil cooler diffuser was more seat of the pants sculpting, no math involved.  Didn't do any tuft testing but did blow air with a leaf blower and dangled a tuft in back of the cooler to see if I was getting relatively even airflow across the face of the cooler.  It did look good.    The rad was less so.  More air at the back end so I was not aggressive enough in pinching down the wedge at that end.  Compensated by stuffing some ridge vent material at the back.   Worked pretty good.

Thanks!  Count us in for the weekend!

Tracy

On Fri, Oct 14, 2011 at 4:23 PM, Charlie England <ceengland@bellsouth.net> wrote:

Sounds great; are y'all coming for the whole weekend? If so, we'll hold one of the bedrooms for you.

Thanks for the mold pics. Did you try any tuft testing with the wedge on the wedge/rad assembly before actually flying it? I'm wondering if I can do anything to verify whether my attempts to copy 'what works' are successful short of actually flying it.

The success that the Lyc guys are having with exit ducts is making me look for ways to position the rad/cooler where I can try exit ducts, & that will mean moving them farther back in the cowl where there is more width to play with. Does the oil cooler duct design follow the K&W design guidelines, or is it shortened a bit?

Charlie



On 10/14/2011 10:54 AM, Tracy wrote:

I'm assuming it is internal diffusion but you know how that goes.  Could be some of each.   Here are a couple of pix showing the oil and rad diffusers.  I did try to gradually increase the cross sectional area from inlet on but the transition to the acute angled rad makes this non obvious in the aft section. The pictures won't show the subtle shapes on the rad 'wedge'  but gives you an idea. 

Best info Ive heard on long vs 'pinched' diffusers is that the short version can be 85% as effective as the ideal 7 degree long ones but only if done properly. 

On rad thickness, i think thicker is better on 200 mph planes but the diffuser and inlet becomes more & more important.  With a large face & thin core rad, even  sloppy duct work will do but you pay for it in cooling drag.

Looking forward to the Pumpkin Drop.  I'll have my new partner (Diana) with me.

Tracy

On Fri, Oct 14, 2011 at 11:16 AM, Charlie England <ceengland@bellsouth.net> wrote:

Many thanks for the input!

Interesting info on the wedge. Makes one wonder how much hard science there really is on this stuff. :-) Is the air flow slowing inside the wedge, or is it all 'external diffusion?

On the issue of inlets/diffusers, as I've struggled through some of K&W & other info on streamline diffusers, they all seem to point toward much longer ducts than what most RV guys are fitting. If I use a narrower & thicker (around 4") core & have room to fit a much longer duct on the -7 (core would be as much as 24" behind inlet), do you see the pressure recovery efficiency improving significantly?

I'm toying with the idea of 2each 2" cores the size of an oil cooler back to back with dual  pass back to front instead of the Scirocco style side to side dual pass. The face would be ~9" wide & 12-16" tall, depending on what I can find. The oil cooler would be on the other side of the engine, again with a longer streamline diffuser because of the extra room available in the -7's cowl. The cowl does have the standard Lyc updraft carb 'chin' with inlet, so it's tempting to go there with the oil cooler, but I have serious doubts on the inlet size being adequate (inlet is around 2 7/8").

Again, thanks for the help, and I hope that you can make it up for the Pumpkin Drop.

Charlie

On 10/14/2011 9:02 AM, Tracy wrote:

Hi Charlie,
   The radiator you mentioned sounds like the same one I'm using on the 20B and I think it's a good choice.   Core measures 12x18x2.65.  I used the "X" option which has 1.25" tubes instead of 1" tubes.   Got it at Summit, Griffin brand.   With tanks and all it is the same as the numbers you mentioned.  Never had any water cooling problems with it.   I don't really know how critical the wedge diffuser on it is.   I'll try to find some pictures I took of the foam mold for it.   It is not a simple wedge but an elaborately sculpted shape without any straight lines anywhere.   No formulas were used, I just tried to imagine the flow, volume and velocity at various points and shaped it accordingly.

Its hard to imagine too large an oil cooler on a rotary so I would go with the largest one you have room for.   The 30 row cooler I used is just adequate for the 20b IF the diffuser and inlet is right.  I was surprised at the difference a proper inlet made.

I'm itching to do a cross country in the -8 so would like to make it to the pumpkin drop on Nov 5.  Thanks for the invite!

Tracy

Sent from my iPad

On Oct 12, 2011, at 8:25 PM, Charlie England<ceengland@bellsouth.net>  wrote:

Hi Tracy,

It looks like I can't put off my cooling system design much longer, so I'm looking for info on what is known to work. I've got the Lyc-style James cowl on the -7 (Renesis). It looks like I can fit a fairly large rad on the plug side of the motor, if I use a wedge diffuser like your 20-B on the -8. I can fit one of the Scirocco style 22x13 inch radiators (same size that Dennis Haverlah is using), but don't know whether I'll need that much area if I can get a proper duct feeding it.

Do you have length/width/thickness numbers for your radiator? Also, any formulas/techniques on designing the diffuser&  wedge? Did you do a K&W type streamline diffuser to feed the wedge, or just transition the area of the round inlet to a rectangular cross section at the start of the wedge?

(I found an email that says you're using a CR Racing 30 row for oil; I located that,&  proportionately smaller ones, on their site.)

And last, if you're up for a road trip, the Slobovia Outernational Pumpkin Drop is Nov 5. Flyer is attached,&  we have plenty of sleeping space.

Thanks for the help,

Charlie
<slobovia11.jpg>