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Down Draft Cooling


niceez

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I want to start a thread about Down draft cooling.

 

The intent will be to better equip builders with the information on what has been tried, results, and what works and what doesn't.

 

I have begun the process and have the center exit exhaust done. I would send a photo but have not figured out how to do it on the forum yet.:confused:

 

I would like to be able to get a duplicatable system completed that anyone can build himself and list the suppliers of the materials as things progress..... So jump in when you fancy.

 

I plan on building a set of cowling molds for the LEZ after I make the system work carving up what I now have.

 

- Dale

--

Dale Martin, 509-780-7320

LEZ

Lewiston, ID

EAA Technical Counselor

Owl Eagle Aerial Composites

=====================>

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I am really REALLY interested in downdraft cooling. I have a Long-EZ that is laid up with airframe damage that, when fixed, will be given an O-320 engine that I hope to downdraft. Some of the fast-fliers have done this, and I will generally follow their "proven" methods.

 

My immediate problem is a (flying) Velocity that doesn't cool worth a flip. It has these pisant armpit scoops and updraft cooling. I have sent for the Velocity downdraft templates (which should work just fine on a Cozy). I feel that one LAAAARRGE advantage of downdraft cooling is the reduction in baffling to practically nothing. You build a little fence around the top of the engine and that's it. You make a fiberglass plenum that screws onto the top of the "fence" and connects to the inlet ducting. It seems MUCH simpler to make and offers way better access to the engine than conventional baffling.

 

I'm looking for ideas on the details. It seems that retrofit is a bit tougher than putting it in original, but not much.

 

Jim Sower

...Destiny's Plaything...

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I read Jim Sowers wants and comments.

 

First, I sure wish Jim was absolutely correct about how little baffling we need. True there will be less but I would like to stress that the better the baffling job is, the less cooling air required.

 

Secondly, I first thought I could do this so well as to not require an oil cooler (engineers often think they can pole vault over anything<grin>) but a quick note from Gary Hertzler made me recheck flow velocities, CFM flow, and heat transfer rates. He is right. An oiler cooler is a must.

 

If you now suffer from poor cooling I can almost (ALMOST) gaurantee it is do to poor baffling arrangement. Burt is a great airplane designer but the plans suffered greatly in engine baffling area.

 

I rebuilt mine around 500 hours and now my engine is always to cool.

 

The entry on top will be a matter of good sealing. The pass through the cylinders will need to be baffled tightly with either aluminum or the silone/fiberglass method. I personally will also be building a shield under the cylinders to force the air aft and not let it go down and heat the case or intake tubes.

 

In addition, the exiting air will be ramped out the back similar to what the inlet of many tractor engine have. By this I mean incased in an aluminum tunnel with the exhaust pipes inside adding to augmentation.

 

The lower part of the engine, Oil sump and intake for carburetor will be in a separated area from above. I feel any excess cool air can be used better to keep things cool. A completely new intake box is being designed for a "drop in" rectangular K&N filter with hot air supply for those of us that still use carburetors.

 

I still haven't figured out where to include pictures yet. It only refers to adding links to web pages.

I can send Jim one personally but I don't know fellow from OZ's email address.

 

My personal email address is: niceez@cableone.net

 

- Dale

--

Dale Martin, 509-780-7320

LEZ

Lewiston, ID

EAA Technical Counselor

Owl Eagle Aerial Composites

=====================>

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I agree that baffling is always required. I further agree that most cooling problems can be traced to poor baffling. I am a case in point. I bought both my airplanes. My EZ had cooling problems caused by baffling that had gaps in it you could throw a cat through. It took me a LONG time to fix that (no plans, just trying to figure out how to fix the design and fabrication problems I found). I did all the sheet metal and silicone over and added glass-RTV head/barrel wraps. When it was all done, I had much better cooling, but still hated the design. Like sealing off the exhaust. Damned if you do (the exhaust now pre- heats the cooling air) and damned if you don't (the cooling air all squirts out around the exhaust pipes). Also, baffling the starter and alternator, and that HUGE area below the cylinders (and putting an oil cooler in the bulkhead formed) all adds up to rendering updraft cooling a lot more trouble than it's worth.

 

Downdraft OTOH starts with the short "fences" around the top of the engine on three sides (that you had on your downdraft system) and add another short fence to the aft face (#1,3 cylinders). You're done. All the lower baffling (most difficult to fabricate, maintain and most apt to leak)is eliminated. Lay up a glass plenum that screws to the "fences". The fences are easier to make since they don't include any silicone seals. Access to everything in the engine compartment is VASTLY improved. Since we're not pre-heating the cooling air going to the cylinders, we need less air ~ smaller inlets ~ lower cooling drag.

 

Downdraft minimizes plenum size, air volume needs, silicone sealing and the structure (weight and complexity) on the engine associated with baffling. It maximizes cooling efficiency, simplicity and ease of construction and maintenance.

 

Looks to me like all plus's and no minus's. The only downside I can see is that downdraft, not having been widely done, requires you to do some development yourself. Even that is minimal since that part of the process has been done enough times to minimize what you have to actually DESIGN yourself.

 

Just a theory .... Jim S.

...Destiny's Plaything...

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Jim,

 

Very true. If you have ever built up the old beetle VW's engine you can get a very good idea's of how the air was "channeled" below the cylinders.

 

I am wanting extreme speed from my Long-EZ so when the time comes to upgrade to more HP it will be as good as it gets. I feel we have suffered from cooling drag and poor in-flow dynamics long enough.

 

I am sure we will all have or own idea's. I just want to make what I am doing duplicatable so if the timing is right I could sell plans or whole baffling and cowl systems. (Then I can get to more EZ flyin's and airshows) <Big Grin>

 

By now you have seen my current engine and understand the quality i am willing to accept as a minimum.

--

Dale Martin, 509-780-7320

LEZ

Lewiston, ID

EAA Technical Counselor

Owl Eagle Aerial Composites

=====================>

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Check the webpage www.geocities.com/~kleb/homebuilt/shell to see how George Shell implemented DD cooling on N10LZ. He put 4-inch inlet scoops onto the top cowl in front of the cyliner bumps. These inlets feed directly into aluminum plenum boxes mounted over the cylinders and baffled against top cowl. Same arrangement normally seen on DD factory planes. Air exited below the engine. Yes, he did have a NACA scoop, but used scat tubing to directly cool the oil cooler, alternator, and fuel pump. N10LZ runs a stock 0-320 with dual Lightspeed ignition, prop, spinner, and wheel pants. It runs at 227 MPH at sea level and we routinely cruise at 205 MPH at 2500 RPM. Oil temps were always in the 190 range and cylinder temps were all within 20 degrees of each other. Once did an extended climb from sea level to 11,000 feet on a hot day. The CHT warning went off once during long, extended taxi. But once airborne, we never redlined anything.

 

Wayne Hicks

Wayne Hicks

Cozy IV Plans #678

http://www.ez.org/pages/waynehicks

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I saw two interesting designs at air shows.

1. DD cooling buy using the bottom NACA scoop. The owner took two 4 in dryer hoses, routed it in the engine compartment (from the bottom to the top), filled it with expanding foam, removed it from the plane, bondo'd the outside and sanded smooth and the 2 layers of carbon. He then split the tube, removed the form and installed in the plane with a traditional plentum box on the top. He ran "too cool" and was in the process of reducing the NACA scoop size.

 

2. Saw the E-racer at OSH this year. He was using DD cooling...worked "OK" but wasnt gettting enough air out the back of the cowl. He then sealed off the cowl and used 12"x6" augmentation tubes on each side for the exaust (the only outlet for engine cooling). Now it works "GREAT" and he can sit for 20 minutes on the runway without overheating... and the plane is quieter! Nice.

 

I think the bottom line is: updraft cooling works, but I primarily hear of the engine running too hot. DD cooling work, but I typically hear the engine is running too cool. Doent take a rocket scientist to figure out which way I am going on my new plane...

Regards, Nick

___________________________________

Charleston, SC LongEZ, N29TM, 2400 hrs

http://www.canardzone.com/members/nickugolini/

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All,

 

Have pictures of George's nice set up in my data base so i can refer to them.

As a note: Using one foot of aero-scat tubing is equal to 10 of smooth wall aluminum.

 

Georges uses to much scat tube for me. In Georges defense, it was quicker and he is flying.

 

I wish to be an ultimate system.

 

I do plan on a top cowl inlet but they will not look like George's LEZ. I want less drag and this is not a simple task. (Well for me it isn't) Far to many varibles and one will affect the other.

 

More later.

--

Dale Martin, 509-780-7320

LEZ

Lewiston, ID

EAA Technical Counselor

Owl Eagle Aerial Composites

=====================>

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All,

 

I will trying to keep track of all the design idea's we come up with and maybe repost it once every two weeks so we can see where we are going. You in turn can adjust your own personal list. This way we can get some mileage out of this.

 

Some reasons to do it a little different is the many types of airplanes we have. For example a Cozy has much more firewall room then a Long-EZ and so on.

 

We should really be able to have some great advice for the builder who decides to make the change.

 

I have some pictures of many installations so far. As Tony said it would be great if we could post them (and catagorize) since the old adage is so true, "A picture is worth a thousand words." Recently Terry Schubert sent a mass of photo's of his well design system.

 

One other comment about Wayne Hicks post. He stated George used 4 inlet inch scoops. I think he meant 4 inch diameter inlet scoops - (Hope I am correct) and that's a little over 12.5 square inches of air intake per side. And I am not sure if George has done away with his NACA scoop or made it smaller.

 

We will gain more speed for a given RPM if we do away with the NACA inlet but I really don't know how much. Gary Hertzler tells me it is a bunch. Terry also designed a much smaller carburetor box and it has a smaller shroud on the bottom cowl.

 

- Dale

--

Dale Martin, 509-780-7320

LEZ

Lewiston, ID

EAA Technical Counselor

Owl Eagle Aerial Composites

=====================>

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Mike,

 

You are correct in your assumption however, (don't you just love the however word)- when this is applied to a LEZ or the VE we tend to forget about the sharp up-curve it has to make in order to make a close close out with the spinner.

 

If you have ever seen Gary Hertzler's bottom cowl you will understand.

 

I have already been told that a new cowling is a must for maximum speed. Making new cowls will be one of the last things I do - (that's the lie I want you to believe now anyway) - as I finish this retrofit.

 

And in fairness to the bottom mounted NACA scoop it will work okay, but it is not the best for cooling an engine that was designed to be cooled from the top down. As a fact, the top of the case needs to have a cool air supply and this is due to many factors. One of which is that the cam is above the crank shaft it rides in aluminum journals formed by the case halves without any bearings what-so-ever.

 

And I further believe that a well thought out DD system will not only cool the engine better, it will also allow us to shape the rear of the airplane to create less drag and better airflow to the prop.

 

I have already found that dd will allow easier access to the engine for MX.

 

That's enough of my oppinion for now : )

--

Dale Martin, 509-780-7320

LEZ

Lewiston, ID

EAA Technical Counselor

Owl Eagle Aerial Composites

=====================>

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John,

 

While working at Scaled I have learned a couple of other ways to build a cowl that would appear to be a little easier.

--

Dale Martin, 509-780-7320

LEZ

Lewiston, ID

EAA Technical Counselor

Owl Eagle Aerial Composites

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Well, well, well.......

 

I must say that everyone wants to know how. I wrote John a personal email explaining that these are some of the ways I produce income.

 

It is more timely (easier for me) to tell someone or show and let them some how experience the task rather them try to write a manual online. Perhaps time will lend itself in the fall months.

 

Since I will be doing this later I could surely take pictures but that in of itself will not explain every thing. Hopefully I can put something together in a small pamphlet form.

 

You see it all depends what your making and even the materials you feel the most comfortable using. I will be making a mold for the LEZ and perhaps I could also make one for the Cozy as well. A person could make the money to pay for it faster with a pert-time job then do all the work himself. Besides I still have to finish the canard offset elevator modification first. :(

 

Here is a shot of the newer pipes. I had to remove all the rear baffling and the alternator. Much to our suprise the DD baffling will not be using this metal and will look much like this in the long run.

post-17-14109015169_thumb.jpg

--

Dale Martin, 509-780-7320

LEZ

Lewiston, ID

EAA Technical Counselor

Owl Eagle Aerial Composites

=====================>

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I learned early on in my engineering career that if you are trying to solve a problem, you should define what the problem is before you start thinking of solutions.

If the problem is engine overheating, you can have that with either updraft cooling or downdraft cooling. So you need to look a little farther. Before giving up on updraft cooling, you should first of all consider the advantages. The flush NACA scoop is a low-drag scoop. Translated, that means faster speed. Secondly, when climbing you need better cooling than in cruise, because you are at a slower speed. With the NACA scoop on the bottom, it is in a higher pressure area, so you are getting more efficient air intake. A scoop on the top would be in low pressure air and less efficient. Thirdly, when taxiing or idling at the end of the runway waiting for clearance, updraft cooling is more efficient because convective airflow is aiding, rather than impeding cooling. And lastly, when parked with the engine off, natural convection will cool the engine and reduce its cooking.

I have investigated cooling problems in both Long EZs and Cozys. In all cases the problem has not been updraft cooling, but rather a very poor baffling job. For example, some builders think that there should be 1/4 inch of clearance around the exhaust pipes. That thoroughly destroys the pressure gradient, so there is little pressure drop to force air through the cylinder fins. Also, some builders never caulk between the baffling and the engine.

We have an 0-360 Lycoming (180 hp) and in high-speed cruise at altitude my hottest 2 cylinders do not exceed 350 deg F, measured with probes at the bottom, and my coolest 2 cylinders rarely get over 300 deg. F. My hottest cylinder (#1) has a probe at the bottom and a thermocouple under the top plug. The thermocouple runs about 40 deg. hotter than the probe. But since a thermocouple under a plug alongside a probe always runs 40 degrees hotter, this means that there is very little temperature difference, if any, across the cylinder, which is remarkable.

I have a 13 row oil cooler using cowling air (no extra scoop) exiting under the strake, and my oil temperature runs 170 - 180 deg F at altitude in the summer time.

My installations are per plans, or per newsletter, in the case of the oil cooler. I haven't used any magic. You should get the same results if you do the job properly, and there will be no incentive to go to downdraft cooling, which has fewer benefits. On the other hand, if you do a poor job at downdraft cooling, it will be worse.

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Nat,

 

While your mind seems to be made up, mine is not. In my engineering days (which are still current) we were taught to use systems as they were intended. Hence, the need for down draft cooling. I too have made updraft work however, it is not better.

Let's examine your claims;

1.) The NACA scoop is low drag - not NO drag. The scoops on top can be smaller and the air on top is not in compression so they do not creat as much drag. The required shape of the lower cowl is real draggy. The penalty for frontal area verses induced drag are less so the theory about speed is inaccurate.

2.) The pressure of the air is the same whether induction is on top or the bottom. Ram pressure could be greater but only if a poorly designed system is used for DD. Angle of attack in a climb will not affect a well designed system. Since the drag is less on the DD system the speed would be greater using the same BTU's for power thus it will subject to greater airflow.

3.) The cooling on the ground with dd could be poor however with augmentation and superior baffling that has not been a problem.

 

Rather then change your mind about downdraft cooling, I would challenge you to think of all the benefits of down draft.

1.) Less baffling

2.) Easier to work on engine

3.) Greater access to starter, alternater

4.) Cooling air to the top of the case were it is needed.

5.) Cooling air to the bottom is easily doable

 

These are only a few.....

 

It sure is amazing what cleaning up that bottom cowl can do. Gary Hertzler's lower cowl is a perfect example of the the correct lines that we can achieve easily with down draft. I am not willing to use a modified engine sump just yet or re-route and fabricate all new intake tubes to use updraft as Gary has.

 

Like yours, my own CHT temperatures using up draft are now to low. Keep in mind that to produce 75% power you require 365F cylinder head temperature. Under that you require more fuel to achieve the same power results.

 

We may disagree but one thing is for sure to me, and that is that updraft cooling is a greater compromise and does cause greater internal engine wear.

--

Dale Martin, 509-780-7320

LEZ

Lewiston, ID

EAA Technical Counselor

Owl Eagle Aerial Composites

=====================>

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Nat,

 

Your jab at my current profession I would have thought below you. (I guess I still make mistakes in character).

 

To answer your question directly, trying to reduce drag, reduce weight and have a simple system with easier access to engine componets. As smart as you are I'm sure you knew that. I would also guess you think since I have left engineering and found a new profession that my little peon brain is not up to the task.

 

- You may be right!

 

-- Oh, one last thing, I don't rely upon luck when it comes to systems design.

 

Good Luck in your furture endeavors as well,

--

Dale Martin, 509-780-7320

LEZ

Lewiston, ID

EAA Technical Counselor

Owl Eagle Aerial Composites

=====================>

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Dear Dale,

I will apologize for my jab at you, but it was a reaction to what you said about me. Remember, that your engineering was more current than mine? That was completely uncalled for. I have worked in engineering all my life! I thought my comments were factual, and presented much data in support of updraft cooling as shown in the Cozy Mark IV plans. Apparently your interest in downdraft cooling has nothing to do with cooling, but rather that you believe the cowling design would be better. That could well be with the Long EZ, which is quite cramped, but not necessarilly true of the Cozy Mark IV. I believe Lycoming supplies engines for updraft cooling as well as downdraft, so it really doesn't seem to make a whole lot of difference to Lycoming which way the air flows. And the data I have shows that there is very little temperature difference across the engine anyway. So cooling isn't really the issue, is it? It is a scientific fact that air tends to rise as it is heated, so updraft cooling will always have that advantage over downdraft cooling. This can be very important in ground operations. It would be especially hard on an engine to climb at high power and low airspeed after it has overheated on the ground. If you find that there is some huge advantage in downdraft cooling (after you have demonstrated it), I am sure we would all be glad to hear about it.

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