Hangar Flying => Hangar Flying => Topic started by: Charles Davis on April 22, 2007, 09:12:23 AM
Title: More about downdraft cooling
Post by: Charles Davis on April 22, 2007, 09:12:23 AM
Currently, my plane still has the large NACA belly scoop used for updraft cooling.
I plan to convert to downdraft cooling with a plenum arrangement.
Now, what to do about feeding the carb and oil cooler?
I'd prefer to use the Hal Hunt Ram air box.
A few questions: 1. Does everyone agree that the oil cooler should be mounted aft of the carb? Or, has anyone mounted it close to the firewall? 2. Since the engine floats, I assume the Ram Air box is not connected to the firewall, but that the inlet "floats" inside the underbelly Naca inlet. 3. Does anyone have pics or can you share with me how you've configured your carb and oil cooler when using downdraft cooling?
One idea I had was to reduce the size of the belly Naca inlet and use it just to feed the carb and oil cooler.
Thanks for any guidance or pics if you have them.
Title: More about downdraft cooling
Post by: Waiter on April 22, 2007, 10:45:26 AM
CD;
I'm working on cowling mounting this week, so Hopefully, This problem will be solved by next week this time!
When I made my cowl, I included two small "armpit" scoops into the lower cowl, one for combustion air, the other for oil cooler.
HOWEVER,
I did see a couple on the Internet that did what your thinking; close off the old NACA scoop and build in a smaller scoop for combustion and oil cooler.
I chose the armpits for a couple reasons;
1) My sump tank now occupies most of the area that used to be the NACA scoop. I cut the NACA scoop out and now have a straight belly. I installed a 5/8 sheet of plywood in this area just in case I have a belly landing. it protects the passengers behind and also the sump tank.
2) The lower cowl does a downward transition in order to clear the exhaust pipes. Airflow must compress and move down about three inches (drag) to go around this transition
Having the small intakes gets rid of the transition. The drag is still there, but its now cooling drag.
My plan right now is to have a SCAT hose for the combustion air. The SCAT will need to be disconnected to remove the lower cowl.
I plan on forming a duct that the bottom of the oil cooler will mount to (cool air in from the intake), The Upper cowl will have a mating duct that will fit over the top of the oil cooler, the top duct will route the hot air out the back of the cowl.
Waiter
Title: downdraft
Post by: Charles Davis on April 23, 2007, 10:36:09 AM
[My only concern about scat tube feeding the carb is if the tube collapsed or if it came off at the joints.]
I'm no expert, but imagine this: 1. You make the belly intake so its area is equal to the area of the Hal Hunt intake plus the area of the oil cooler. 2. Place the oil cooler aft of the carb like a lot of the updraft installs. 3. Build fences in the lower cowl to channel the air around the the carb box and through the oil cooler.
I like the Hal Hunt intake because it's a proven design, and I'd rather than buy than build when I can.... I know that is contrarian to the opinion of many excellent builders.
I wanted to mount the oil cooler on the firewall (to shift the weight forward), but that firewall is so small on an EZ and the cooler takes up a lot of space.
Title: More about downdraft cooling
Post by: Drew on April 25, 2007, 07:49:07 AM
I did downdraft cooling and for simplicity, sealed off the lower NACA scoop. I put 3 SCAT flanged connectors on the sealed off naca wall and built 1 rectangular flanged aluminum connector. The biggest SCAT connector (3in?) went to an oil cooler box that I built that mounted behind the carb. The 2 smaller connectors went to go cool other stuff. I built a fiberglass extension on the hal hunt ram box to fit over the rectangular flange slip joint. Don't have any other pictures that is not already posted on my web page.
Title: downdraft
Post by: Charles Davis on April 25, 2007, 03:10:43 PM
Drew,
Interesting. What did you cool off with the extra hoses? (Mag, Alternator?)
What is the size of the opening for the carb inlet?
Thanks for the info.
Title: Downdraft cooling
Post by: Charles Davis on April 26, 2007, 06:13:04 AM
Drew,
Did the downdraft cooling meet your expectations?
Title: More about downdraft cooling
Post by: Drew on April 26, 2007, 06:51:00 PM
I based the downdraft cooling based on what George Shell did with his Longez (4 inch diameter round scoops and a sealed off Naca). Unlike George, I really opened up the exit area. If I were a speed freak (and willing to put in more construction time), I would have cut off the Naca scoop----and build a more appropriate size naca scoop for the oil cooler----and ram air to the carb (similar to the lower scoop on the berkut).
Since I kept the big naca scoop, I tried to fill up as much of the scoop as possible with flanges for scat---otherwise you just have a miniature speedbrake out there. At the same time, you will want to avoid unnecessarily pressurizing the lower cowl. For my oil cooler, no problem---it was pointed out the back end anyway. My additional cooling went to the mags and the electronics on the back of the alternator.
On my Cozy, I am considering adding a small naca scoop on the cowl to feed separate air into the oil cooler. Currently, the oil cooler is stealing cooling air from the engine.
The carb inlet was just a straight run extension from the hal hunt box. Carved a block of foam to extend from the hal hunt box all the way to the firewall. Glassed over the box and foam extension---then removed the foam. Then made a rectangular aluminum slip joint to mount the the firewall. The metal slip joint fit inside the hal hunt extension. Had no issues with any kind of cracking.
Title: Downdraft cooling
Post by: GlennBob on April 27, 2007, 01:07:25 AM
Drew,
Other things to consider cooling : if you have a vacuum pump, . .their life is extended dramatically if cooled. Fuel pumps, manual and electric. Back of the alt is good (as you mentioned).
Where do you get your smaller naca scoops ? Do you order from Spruce ? or just make 'em yourself ?
Glennbob
Title: downdraft cooling
Post by: Charles Davis on April 27, 2007, 01:51:20 PM
Just a quick word of appreciation for all the comments here.
I can see there is many ways to do this and they all work well.
This thread has really been very educational and has helped me solidify my ideas.
Thanks, guys.
Title: your pictures
Post by: mwilli7119 on April 27, 2007, 02:16:41 PM
Charles,
Thanks for your pictures. they are very good and you sure did a good job. I am going to do something similar. You should post those somewhere so people can see them.
Mike Williams
Title: downdraft cooling files
Post by: Charles Davis on April 27, 2007, 07:20:28 PM
Great idea. I should have thought of that earlier. I have the webspace to host the files now.
Here they are: http://www.thesolacegroup.com/Downloads/DowndraftCooling.pdf
Title: More about downdraft cooling
Post by: Drew on April 27, 2007, 09:00:35 PM
Glennbob, Glad you mentioned the vac pump---I was cooling that too.
For my Longez, the original large naca scoop was used for oil cooling, carb ram air, and accessory cooling. The downdraft scoops were not naca scoops.
On my Cozy, I am considering using a small naca scoop for oil cooling. If I go this route, I would buy the scoop.
Charles, Your pix look great! I'll be very interested in how it cools. I built ram scoops (non-naca) because I was afraid that there may be some separation off the top of the strake---and that there may not be enough air actually going in them. Nacas on the bottom or sides of the plane are much easier to feed. Not many people were building downdraft cooling when I did mine---so I made sure that the scoops were well into the airstream. Terry S (naca) has had trouble with his---but Bill James has not. George Shell and myself had no issues either.
And I am sure that you have found that the greatest thing about downdraft cooling is not having to baffle around all the crap on the back of the engine (starter, alternator, oil cooler, etc). Cool!! Sorry, couldn't help that one. :D
Title: Downdraft cooling
Post by: GlennBob on April 27, 2007, 11:23:16 PM
Charles.
I remember seeing these pics before. I too would like to know how well this system performs. Bill James said somthing about " heat treating " the plenums to avoid distortion. Did you do that ? How is that done ?
Drew,
Your pics look like you just cut a hole in the forward side of you upper cowl. You said you " built " the inlets. How much more was involved ?
I am seriously considering downdraft cooling. After looking at how small my underside naca scoop is and then all the junk in the way before the air ever gets to the cylinders, . .it only makes a lot more sense to see the fins right inside the upper openings ! !
:wink: Glennbob
Title: downdraft
Post by: Charles Davis on April 28, 2007, 08:40:27 AM
Can't say how it works because I'm not flying yet, and probably won't be for another year, as I'm building a house and that seems to be taking all my time and money.
The inlets were made by taking a naca template and scaling it up on a copier.
I have not heat treated the plenums.
I read something about heat treating (curing) composites before. Build a heat chamber; an box made from plywood and wrap with insulation. Feed it with an electric or gas heater, and use a fan to circulate the air. Monitor closely with a temp gauge.
Bring the temp up slowly, and keep it there for several hours. then bring it back down.
The idea is to raise the temp above what the part will encounter in service.
I do not know what those temps are, or how high you can raise the kevlar temp before damaging it.
Title: More about downdraft cooling
Post by: Drew on April 28, 2007, 09:40:05 AM
George Shells pix are better than the ones I have posted. My upper cowl pretty much looked like his.
http://www.geocities.com/~kleb/homebuilt/shell/
Similar to Charles, I cut a rectangular hole in the front part of the cowl. I then nailed a couple of blocks of foam together to get the approximate size of the inlet. I cut a for and aft template out of thin aluminum. Both templates were the same. The template's purposes was to get me the circular shape of the inlet----and hot wire the inside of the inlet. At this point you have a shoebox looking inlet with a big hole in the middle. The next thing to do is to put the inlets into the cowl holes and align them to the proper angles. Then you need to "glue in" a bunch of transition foam pieces-----very similar to how you see people making their own cowls from scratch. Once everything is pretty much in place, you can knock down the edges of the inlets with foam sanding blocks----pretty easy to get to the shape that you want. The harder part is getting the transition to look nice. Spend all of your time making it look good in foam---fixing in fiberglass is much harder. When it is all done and glassed in, you can dremel out the old portion of the cowl (some of the glass and all the foam)that is not longer needed. The only foam that was left in the inlet was the leading edge shape of the inlet---all other foam was removed.
One difference my upper cowl had from George's was I had an oil door in the left inlet. I used the old hinge mechanism from the portion of cowl that I cut out.
Title: More about downdraft cooling
Post by: Waiter on April 28, 2007, 11:52:28 AM
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
Title: More about downdraft cooling
Post by: Lowlevldevl on April 28, 2007, 07:35:49 PM
Quote from: Waiter
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?
Title: More about downdraft cooling
Post by: Waiter on April 28, 2007, 07:57:39 PM
Leave it in the oven, no cool down
Waiter
Title: Downdraft cooling
Post by: GlennBob on April 29, 2007, 02:17:10 AM
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
Title: down draft cooling
Post by: ezeguy440ez on May 05, 2007, 05:05:46 PM
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.
Title: Downdraft cooling
Post by: GlennBob on May 06, 2007, 12:30:51 AM
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
Title: downdraft cooling
Post by: Charles Davis on May 06, 2007, 12:23:31 PM
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.
Title: More about downdraft cooling
Post by: Drew on May 06, 2007, 09:09:45 PM
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.
Title: Downdraft cooling
Post by: GlennBob on May 07, 2007, 12:22:47 AM
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
Title: Oil cooler
Post by: GlennBob on May 07, 2007, 12:25:43 AM