More about downdraft cooling

[Waiter]

Post Cure:

My plenum's are not part of the cowling, but little shells that fit over the top of the cylinders. They are small enough so I  could post cured these in the Kitchen oven. I started out at 250, let sit for 10 minutes. then raised it 25 degrees, let sit for about ten minutes, I repeated this until I had it up to 350.

Cowls - DO NOT POST CURE COWLS. When you post cure, it softens the epoxy a tiny bit, then recurse at the new higher temperature. The epoxy will not re soften again until you reach the new higher temperature.
This process makes the epoxy much harder than if you let air cure at room temperature.

The cowls will maintain a better fit if they are allowed to post cure while mounted on the plane. The heat from the engine will be more than enough to do the post cure.

For other parts, its EZ to post cure.

Set them out in the direct sun. Be very carefully when doing this as its easy to over heat the part and damage the underlying foam.  Generally, if there is blue Styrofoam, I use the "Rule of Hand".  It may get hot to touch, but if I cannot leave my hand on the surface, then its getting to hot (About 140 deg is just about the max pain threshold).

If there is no foam, I usually don't worry about it, Unless the part is painted black its not going to get over 200 deg.

I've post cured wings, canards, and just about every part I built in this manner.

Post curing stabilizes the epoxy at the higher post cure temperature.

Waiter

[Lowlevldevl]

Post Cure:

  "I started out at 250, let sit for 10 minutes. then raised it 25 degrees, let sit for about ten minutes, I repeated this until I had it up to 350."
Waiter,
Is your epoxy cooling for the 10 minute sit? Or is it remaining at the oven temp and just ramping up 25degrees every 10 mins or so?

[Waiter]

Leave it in the oven, no cool down

Waiter

[GlennBob]

Drew,

Thanks for the pics of George's bird.  This was immensely helpful ! !

I'm not sure I'd leave the exhaust stacks shootin' straigh out the bottom, . .but to each his own.

The pics were very informative ! !   Lot's of scat there but the rear end is very clean and EZ to work on the alt, starter, cooler etc ! !    I LIKE IT  ! !

Waiter :  Thanks for the informative comments !

Glennbob

[ezeguy440ez]

Well If you must.
yes you can feed them from your old NACA but then if your going to do that why do it at all?
If you must then reduce the size of the NACA make a small plenum using the old portion of the NACA one side will feed your oil cooler and the other is your RAM air for the carb. Carb ram air is connected using 3 in scat .At this point your naca will be way ahead of the original inlet probably at the area where you will have 6 sqin of inlet. Is that kinda clear its just a fast way of reducing the size of the NACA and creating a plenum. then go ahead and make your down draft intakes remember to project the intake well ahead of where they are attached to the cowel 2 to 3 inches or more is best. This gets them away from the boundry layer. T. So if you want to you can make a flat sheet of bid and glue up some angles on the inside of the existing NACA and use nut plates and screw it to fill the old NACA opening it makes it easy to play with to adjust the opening.Now you are going to have to figure out how to get  to the dip stick? you can cut the dip stick tube and route it where you want it with any ruber hose and hose clamps that will stand the temp and oil. attach it at your best location. take the old dip stick head measure your oil before you do this cut off the stem leave enough to attach a 1/8 in 7X9 cable that will reach far enough into the oil tank duplicate your oil maks on the cable using the known reference and swage on cable stops at say the 7 qt level and and 5 qt level or where ever you want as long as you understand the markings. Have fun. Hope I havent confused you to much. My only other comment is if you have a cool running engine. Dont do any of this its alot of work and there are no gaurantees.

[GlennBob]

Thanks for all the pointers.

Agreed, . . if the engine were cooling well . . .why would anyone try it ?  It's because many of us have problems cooling these things.  I'm up over 400 degrees before I can get to the runway for take - off ! !

I think you're trying to make a silk purse from the proverbial sow's ear with the dip stick tube, not to mention the problems with making the new one accurate.  I think I'll just find me a way to get to the stock one.

One side note.  You might want to proof read your post before sending. Quite difficult to read without proper punctuation.

Thanks for your input !  

Glennbob

[Charles Davis]

On a related topic; location of the oil cooler.

Does anyone know of a reason why the oil cooler should or must be mounted aft of the oil pan?

I had planned on mounting the oil cooler close to the firewall for two reasons:
1. Better CG
2. Better connection of the oil cooler heat lines to the "main" engine oil cooler

So a small Naca duct to the oil cooler, then 3" scat tubing to route the hot air to the aft section of the cowling.

Here is an image of the work as it is right now:
http://www.thesolacegroup.com/Downloads/oil_cooler.pdf

Notes about this pic:
I was trial fitting some things in this pic.  I've decided since to move the fuel filter and fuel flow meter under the seat pan.

[Drew]

I mounted mine aft of the oil pan because that was the best place I could find at the time.  I fed the oil cooler from the Naca like you are (just aft of the pan though).  The oil cooler then just dumped out the back end (no pressurizing the lower cowl, and no dumping heat into the lower cowl.  You may need to do the opposite of me----run a line to dump the air out the back.  I would not run the line until you test your configuration as is---you might not need to run some hose.  Looks pretty cool.

[GlennBob]

Many builders have tried other locations for the oil cooler.  Some use the pressure from the underside of the strake to enter (naca ? ) and then pass through the oil cooler and just dump into the lower cowl.   When I bought mine, . .the oil cooler was mounted above the engine up in front and incoming air from the main naca was diverted up the forward side of the engine.  Then there was this large wedge shaped ( almost a reverse naca ) void built into the upper cowl.   The idea was to have the laminar flow suck air through the oil cooler.  I don't really know how well that system worked, . .but I took it off right away ! !

I'll see if I can attach some pics.





Glennbob

[GlennBob]

Here's a shot of the upper cowl.

Glennbob