Sonex Trials

From time to time I have folks contact me about cooling issues on a Sonex. Tom Huebbe from Missouri has a Sonex and has experienced high chts for some time. This past winter he pulled his heads and added some fin extensions, his email with the results:  

Hi Wayne,   Tried to download the pictures I have from my wife's digital camera, but something is screwed up with her camera so I will try to take some more pictures and get them to you.   In the meantime here are my results:  To begin with I have been flying my Sonex since 2006 and have about 350 hours on it total time.   Have been having problems with high CHT's and oil temps. since day one.   I had been flying behind VW's since early 80s' but all in single place, small engine airplanes,  1600 cc and 1835 cc and never had any problems with high CHT's or oil temps.   Had about 1300 hours in those two planes---no issues.  I am sure because they were small engines and not hauling around much weight.  With the Sonex is it quite different especially with two people aboard.    My engine is a 2276,  94 mm cylinders, and 82 mm crankshaft using an Aerocarb.   I also tuned the engine using my son's wide band fuel/air meter and verified the timing on both ignition systems.   I also verified my CHT sensors using two other digital thermometers so my CHT temps I read are quite accurate.  My sons and I also measured the pressure in the cowl using a manometer.   We tried just about everything to try and bring the temps down to no avail.   I have always measured the CHT the same:  under the spark plug right up against the head so I am always comparing apples to apples.  Typical flying day is:  start up cold and taxi to take off which can be 1/4 to 1/2 mile depending on which runway to use.   CHT's will be up to 350F by the time I do runup and ready to fly.   Take off and climb at 90 MPH and by the time I am turning downwind the CHT's are already above 400F heading for 450F.   I cannot get to pattern altitude without the temps going above 450F.   I then have to level off and reduce power and wait until the temps get down below 400 F and then try to climb some more.   Have to do step climbing to reach cruise altitude.   Oh, also my airport is here in Missouri,  440 MSL.   I usually end up cruising at at 2500 to 3000 ft. altitude because it takes so long to climb.  After I reach cruise altitude I then pull the power back to cruise at about 22-23 inches M.P. and then my CHT will very sssssslllllllooooooooowwwwwwllllly  fall to 360-370 F.   I know this is too hot because my old planes never did this and the VW's I raced years ago never ran over 280F cruising and 310F racing very hard.  We always thought anything over 360F was getting hot and never wanted to run over 380F.

Now, new results with the fat fins we welded on:   Taxi forever and never get above 280F.    Takeoff and climb at 80 mph W.O.T. till reaching pattern altitude and do not get above 376 F tops.   Also, left and right heads are now ALWAYS within a couple of degrees of each other.   Never did that before either.   When I pull back to 22-23 inches of M.P., and go into cruise flight,   CHT's will pretty quickly fall to 290-300F and stay there.
This is with two people aboard and near gross weight.   As I said before this is measured under the spark plugs not way out on the fins someplace which will make you THINK you are running cool all the while you are toasting your heads.    The engine now runs just as cool as my little engines did.   Just need more fin area to dissipate the extra heat the bigger engine makes.   It is well worth the effort to not cook the heads with all the associated problems a person will run into running such high temps.---regardless of what some "experts" may tell you  is acceptable to run.

This may not be as good as your results, but each plane is very different.   And, I had to work within the confines of the cowl I already have.
I am now a happy camper.

Regards,
Tom

Congratulations Tom! When we get some pictures I'll post them for folks to see.
Wayne

Slow News Day

I wanted to let everyone know I was still alive. I apologize for not starting on the dual plug demonstration but I have been very busy at work to support my habit. A trip out of the country, the condition inspection on my plane and flying has also consumed many hours.
 Several people are working on their own fat fin heads and I want to share some pictures. Dane Smith, M.D. from down in South Carolina was kind enough to send some pictures and talk about his progress. It looks like he has a good start.

He took his heads to a professional welder and had them tigged, the price sounded good to me all things considered. I won't say how much here, it is not my place but I think those who are wanting this mod  could get it done for less than you think. Time to shop around. As soon as he knows how much it helped I'll let everone know. In the mean time enjoy some more pictures.    

I also want to let everyone know the condition inspection went very well. I inspected the cylinders, combustion chambers and valves with a borescope and run a compression test. The engine checked out fine.  I have not been able to fly as much as I would like due to work and weather conditions but the hobbs meter is ticking off the time.
 One last thing, it appears Kitplanes may do a follow up article, look for it in the near future.   

Kitplanes

Just wanted to let everyone know that Kitplanes did an article on my airplane and me and it will be in the April 2011 issue. Apparently they saw my pictures in Zenith's photo albums and asked to contact me. The interview was done the latter part of May 2010 right after the 1st generation fat fin heads developed a crack between the valves in the number two cylinder that let the seat move around. I mentoned this event in an earlier post. I was a little less than optimistic about the vw at this time and the article copy reflects my my mood at that time.
 I'm a " the glass is half full" kind of guy and I just call things like I see it. It's either back or white, I don't see things in shades of gray. I figured out that there are more people who stretch the truth in the homebuilt community than anywhere else on the planet. At first I believed all the hype people were spewing, the performance, weight, temperature, fuel consumption claims because I WANTED it to be true and in the end I found out the truth. Thats about the time when I decided to take matters into my own hands and fix it. I also came to the conclusion that I had to tell the truth, how many times have you heard about experimental planes not meeting published performance figures?
 I promised from this point on that I would always tell the truth, be honest and open with my experience and data, and for that I have caught the most hell. Like I said earlier, if you don't tell people what they WANT to hear then you are an idiot. I have had some tell me that the "expert" says you need to do this or that after thay didn't get the expected response from me in regards to performance. Guys, I just tell the truth. I've just about tried it all.
 The important thing to remember when you read the article is the time when the interview was done. I just told the truth. Since the interview a lot has happened, 9 months has elasped, hours have been flown. I have flown the plane a total of 35.5 hours since the installation of the Generation Two heads, this includes flying through the summer (and winter) as well as a total of 54 full power takeoffs and climbs........ with no issues what so ever.  What does this mean? Nothing really. Only extensive testing will prove the viability of the heads. When, or rather if I get a couple hundred trouble free hours on this thing then I'll have to say Bob and I are on to something, so I guess I'll just have to keep flying.
 I flew this evening for another hour and had a wonderful time, I just get in the plane after a preflight and go at full power with no special handling. That throttle is tight against the panel while I climb to whatever altitude I want and thats it, tonight was a 3000 foot climb in excess of 8 gph and the cht never got over 320. I'm finally happy and hope this thing holds together. When I logged the trip tonight I took the time to actually go back total everything up, I've been estimating the times in some of my other communications. 
 The condition inspection is due the end of the month and I intend to take pictures of the combustion chambers if possible when I borescope the cylinders. I'll post them here if they work out.
 I have the steel to build the jigs for the dual plug conversion and 'll get on that after I get the inspection done.
 
     

Nice flight

The weather finally gave us enough of a break to allow for some flying today. So, I took advantage of Mother Nature and went for a spin. I have had several requests for updates but there has been nothing to report. Until today.

 I took some pictures of the panel so folks can see what is going on with the plane and engine to reinforce what I have been saying about my testing. Remember, when you look at the photos I have the sensors under the head stud by the exhaust port. I'll keep it short and let the pictures do the talking.  I apologize for the fuzz, it was pretty bumpy, enough so I couldn't get a good one in the climb.





My scratch built creation waiting to go.





 

The cht was 310 in the climb, about 45 degrees ambient on takeoff.

The switches are set to show the maximum temp, or hottest cylinder on both instruments. In this case number two is 275 and the egt is 1338. Just about at the limit I'll allow.



Those of you who know what a Ch701 is probably realize it is a high drag airframe. Mine has all the high drag stuff just like the factory plans (slats)  except I installed strut fairings. This picture shows that the vw pulls it through the air pretty well. You have to watch it in rough air and not throw it around.

Here is a good shot of my cruise power setting, I have it 1" lower than usual because of the rough air. It would normally be 5.5 to 6" and 3900 to 3925 rpm. It is worth noting that wide open throttle is 3", before I advanced the camshaft 4 degrees W.O.T. would result in a indication of atmospheric pressure, or 0 inches.  The fuel flow has settled down to 7.3 gph which means I don't go far, about 1.5 hours. That's about as long as I can sit still anyway. The gps is showing ground speed in knots. 

8 minutes after the shot above the engine has settled down and all the cylinders have stabilized at this point.  I run a ellison throttle body injector which I think is a fine piece but I have a slight imbalance with my induction system that I need to work on. I think it would improve my fuel efficiency slightly if I could get the right bank a little leaner.  



Number 1 numbers. As you can see, by comparing the pictures the cht is pretty even, I have to work on the egt. Unfortunately I didn't get a shot of number four ( the right front) , it runs cooler by about 30 degrees

I go back and reread these postings when nothing is going on and see things I want to add, today is one of those days. Relocating the sensor to the center head stud from where I have it ( under the head stud by the exhaust port) would result in a reading about 20 degrees cooler than those in the pictures. In the earlier posts I address this, but I still have folks asking why I run the heads so "cool".  To me, they are not cool. I am sure there are places in that head that are much hotter than what the sensor is showing. If there were a way to get the sesors mounted down under the head under the sparkplugs I'd do that just to see what is going on down there. I also feel that the sensors are getting a little cooling effect from being on top in the air stream. Look at the pictures in some of the earlier posts to see what  mean.
  I have folks asking about the summer temps, they generally run a little hotter but not much more. In hot weather the engine makes less power until you get up to altitude so the heat rejection is lower. I have flown with the temps in the middle 80's and the CHT will run about 320 in the initial climb. I usually climb at 65 to 70 when it's hot getting about 500 fpm and the cooling holds it own.
  If anyone has any questions let me know. I think the next posts will be how I did my own dual plug heads, anyone interested?    

I

More Thoughts.

I have wanted to get to the local Vw shop since I saw the article in Hot Vws magazine about the different heads on the market. I needed to buy a carburetor for my sawmill so I figured I wouldn't put it off any longer. While I was there I took the time to look at some heads on the shelf, unfortunately he didn't have exactly what I wanted in stock ( they will be in next week) but what was available will do for today's thoughts.

 Bob Hoover always told me to use stock head castings, they would cool better than the aftermarket types. I wouldn't listen and bought the dune buggy heads the first go around. After I saw the magazine article I knew where Bob was coming from and so I wanted to get my hands on a few different examples for the blog. Here is what I found.    

The head casting that I originally started with and flew for the first 60 hours. I later modified these heads with the fat fin extensions.







The picture above is a well known 042 casting with 40 mm intake and 35.5 mm exhaust valves. I tried to open up the passages where possible but the thickness and shape of the casting prevented much improvement. The fins on the end of the head were nearly completely blocked due to mold shift and I did take the time to open those passages. As I said earlier, I tried unsuccessfully to add fin extensions to this head and just gave up because I was in a hurry and everyone told me it was not needed. Big mistake. I flew these heads for 60 something hours when the issue with the bottom plugs came up. See the earlier text. I went back to them later adding the fins and putting them back in service, that is where the fun began, literally. 



Here is a different casting that is like the original Vw, the difference between the two heads is clearly visible. 



When the two heads are compared you can see the wide open passages in the photo above that are filled in on most heads. How much better would this head cool ? I don't know, I would expect some improvement and in a aero application you need all the help you can get. I'm thinking that there is not a great amount of surface area added but the most important issue is the exhaust valve. Just above and to the right of the screw boss you can see the exhaust valve guide between the two port castings. More accurately I should say the valve guide is in the casting under the fin. Now look again at the top picture. Which guide is going to be cooler? The guide that is buried in the casting and getting heat soaked from the exhaust gasses passing through the head or the one that has air flowing all around it. The only way a exhaust valve is cooled is by heat transfer through the seat when the valve is closed and also up the stem into the guide where the heat is then transferred to the head. A little cooling is accomplished with oil bathing the stem. I have had folks argue that the stem will in effect be cooled better in a solid head because of more mass to absorb the heat. I  just don't buy it and neither did Bob, or Hot Vws.    



Here is what I'm talking about. How much air will get through this head?

Looking at the head above you can see how the two halves of the casting mold were not in alignment. There isn't alot of room for air to get through if this is perfect so with this kind of issue you can imagine how restrictive it will be. This MUST be corrected even if you do the fin extensions. I used a slitting saw in my mill but you can use anything that works, grinder, file etc. This head is the one with better passages down around the valve guide in the middle picture but they blew it on the ends. No free lunch. I would love to have the resources to buy a set of these and try them naked and then try the fat fin mod for comparison to my other data. I have been  tooling with the idea of building a test stand to measure engine performance and start trying different things to see what works best, but money is an issue..... maybe I could just build a MONSTER size motor and use these heads with the fat fin extensions, hmmmmmmmm.


I had to add this for inspiration, I hate winter and needed a pick me up. I flew over 4 hours this weekend on a cross country and doing a photo shoot for Kitplanes magazine. The work, effort and expense of the fat fin engine has paid off. I now just get in and go with much less worry than before.  

 I'd have to come up with a better redrive though. Maybe that will be my next project, I'm getting pretty bored this winter.

My Thoughts



Taking off from Crazy Horse International.



 The snow is flying and it's to cold to do much, my daughter is watching a chick flick on tv which means I am also so it's as good a time as any to post a few thoughts.

 The drawbacks of the fat fins:



 The extensions will keep the heads from fitting in many tools and machines used currently for repair. My engine machinist has no issues with the extensions at this time but problems may crop up later.

  The fins will be fragile, this means extra care in handling and they most certainly will have to be bolted to plywood for shipping.

 I'm sure there are other issues but I can't think of any at this time.

 Some of the frequently asked questions:

 I have have a buddy who knows somebody who doesn't have a cooling issue. Why did you?



 There are many reasons. One is the application. I'm using a Vw with a 1.6 to 1 redrive spinning a 70" Powerfin 3 blade prop. My engine is on a high drag slow speed airframe which requires much more power at a slower airspeed. Now look at the Sonex. They probably climb at an airspeed faster than I cruise and turn around 3000 rpm. I'm turning 37 to 3800 in climb and 3900 in cruise burning 7.2 gph so I'm making more power which means more heat. Apples and oranges.

  400 to 410 doesn't seem that high. Well opinions vary. I know when I was hot rodding these things early in life 350  was about all I wanted to see.  See the text above about what Pratt and Limbach has to say.

  So and so says 450 is ok. Oh, really? How did they determine that 450 wouldn't hurt anything? Like I say, see the text above. The problem is nobody knows how hot is to hot on a vw engine. Who has done the testing? What was the power setting and how much power was produced and for how long?,  Where is the cht sensor? How many hundreds of hours did they get out of it? Did they fly it continuously at this temp????? I'll take Limbach and Pratts word for it though, I have a feeling they know more about what they are talking about. Since they have more at stake than a guy selling chinese heads over the counter I feel they have spent a little more on testing. I know what problems I had with the cht getting above 400.

 What about heat transfer across the joint?  What about it? Look, heat travels to less heat or cold. So what if heat doesn't transfer across the weld joint as well as a solid fin? Big deal! Any heat transfer at all is better than nothing isn't it?

 What about just doing every other fin? I don't know, I didn't try it. I am of the opinion to do them all. It's a lot easier to reduce the amount of cooling versus trying to increase it later. You see, to do this mod requires you to start on the bottom fin and work up one fin at a time, so if you do every other one and find out later you need more you have to remove the head, break off the fins you already have on down to the first one and start over. If you just go ahead and do them all and it proves to much cooling just cut down on the air flow through the fins. Think what it will take to pull the head and redo it.

 Is this mod needed on all conversions? I don't know about this either. To find out one would have to test each application with and without a fat fin mod. Right? In my opinion I would think it would be advantageous, like I said before, if it proves to much then cut down on the airflow which would reduce the cooling drag. I think this would be desirable for the go fast guys who want all the speed they can get. Ever heard of cowl flaps? I know I have had a bunch of the go fast guys talk to me about having to limit taxi time and step climbing to keep from exceeding redline.

  Why is your fuel burn so high?  Ummmm.... I'm making horsepower? I haven't been able to develop a carb that will make 100 hp on 2 gph. Kinda like the 300 hp 100 mpg car carburetor we all heard about back in the 70's that the oil companies supposedly stopped. Look at the claims made by some of these vendors. 100 hp and cruise fuel consumption of 3.5 to 4 gph.  Research brake specific fuel consumption. Ain't that about 45 hp? I could get about 90 to 95 hp for takeoff before the fat fin mod but had to limit it to 30 seconds or less then pull the power back. I interpret their claims to be just that, blast off for a few seconds and then run 45 hp which is about what a stock head fin is capable of cooling.  One other thing to remember, I have a egt sensor on each pipe so I know if I'm running rich or not. 

 Why isn't your climb better if you are making the power claimed? Maybe because I'm honest? Apples and oranges again guys, load up a 701 to 1075 lbs with a Rotax 912 and see what happens. I have static pull tested the plane and it produced 420 lbs of thrust BEFORE I hopped it up a little. With the high lift high drag wing on the 701 pulling the nose up just seems to increase the drag. It seems that my plane will climb at the same rate whether it is 55 or 65 mph.   Watch the youtube videos and see what you think. Search for "wclagg". There will be three short videos..... be sure to watch the end.
 What would happen if you turned more rpm for takeoff?  It would accelerate faster, climb somewhat better, and get hotter while climbing. I tried many, many, different settings of prop pitch all through out testing. At one point I had the takeoff roll about two thirds what it is now, it would get to rotation speed faster than I could think. Climb was a little better with the engine screaming at 4000 rpm and 55 to 60 mph. What really hurt was the cruise, it was down in the mid to upper 70's at 4100 to 4200 rpm. This is just to hard on the engine and prop and I only flew it  a couple of flights before I started setting it back the the way. Interestingly, I have guys tell me I had my prop set wrong, with the redrive I should be getting 4200 for takeoff and 3400 for cruise. Now, think about what I just said. HOW can you get more rpm for takeoff and climb than in cruise without a constant speed or in flight adjustable prop? Ever heard of static rpm? My plane will barely stay in the air at 3400 rpm, 2400 rpm is 500 fpm DOWN. I'm just stupid I guess, I haven't been able to figure out how to make my rpm go down as the plane accelerates into cruise configuration. The rpm on mine, and every other plane I have flown with a fixed pitch prop goes up as the plane speed increases.
 If you don't agree with me the next time you fly do a static rpm test and write it down. Then when you get to cruise write that down also. Sure you can make the rpm go down below static rpm but it will NOT be optimum cruise settings. I cruise my engine at 75 to 80 percent power continuously.        

 We'll cover some more later!

    

A Positive Test

I finally managed to get the engine on the plane without suffering frostbite and waited for a few weeks to test. One factor was the weather but another was my nerves. I was so worried that that this fat fin thing wouldn't work and I would be disappointed yet again. As usually happens I got up the nerve one day that I was in a good mood so I cranked it up to start breaking it in. I was not disappointed.
 Immediately I could see a difference, I thought the cylinder head temperature gauge was broken but I watched all the other instruments and all seemed well. I taxied up and down the runway and had trouble getting the temperature up. This was in March and the ambient temp was in the 40's but I at last got the cht up enough to do a full power ground test. I taxied around until I had the nose pointed uphill and the main wheels in a low spot so I could see what happened. My brakes wouldn't hold the plane before and I could tell the engine was more powerful so I knew I'd have trouble holding it........


Instrument panel showing the tach at the top, intake manifold vacuum gauge to the right and the fuel flow meter added after Oshkosh 2010 under that. 

 From the beginning of the design and layout of the panel a manifold pressure gauge, cylinder head and exhaust gas temperatures for all four cylinders were a must. I fully expected to have some trouble and I wanted to be able to see what each was doing to aid in troubleshooting but I had no idea how much trouble.
I wanted to use good instruments and I liked the features of Aerospace Logic, a Cherokee 180 I had been flying had a full compliment of them and watching ebay for over a year finally paid off. I had some new gauges at a really good price. I decided to install a vacuum gauge instead of a manifold pressure gauge after reading what Steve Bennett had to say about .
 Before I get into the testing I want people to understand something. This entire test program was done by a simple country boy who built a airplane in his shop with what was available or could be scrounged up. The testing was recorded by writing what I saw on the gauges on a piece of paper on a knee board with an ink pin. If you have a problem with that don't read any further.
 I have had calls asking if my instruments were calibrated, temperature compensated, if the data was corrected for atmospheric conditions, the same fuel used for all testing and on and on. The general answer.....no. Then they say the data isn't worth the paper it is written on. Just for the record, the Aerospace logic instruments are certified and they are "mathematically compensated over the entire temperature range".  You know, I don't give a _ _ _ _..... Here is what I do know. I had temperatures that I felt were above safe limits and I took it upon myself to correct that. The point here? The readings are a comparison, they show a difference from a baseline I had developed. There have been volumes written on Temp. compensated instruments and I won't pretend to cover it here but I didn't care if the ACTUAL compensated temperature was 410 or 420. What I wanted to know was what difference I could achieve between the original heads and the modified ones. The instruments are in the cabin and the temperature was close all through out the test. I have a heater ya know. Not being a complete idiot I had the good sense to establish a baseline ( about 75 hours of flying) and then make a change ( fin extension and camshaft) and keep all other things the same to see what effect it had. Here are the results using the same instruments, same sensors in the same location, same prop setting, same octane rating of fuel, timing, oil, and so forth.
 Before the mods:
1. Taxi time was very limited.
2. Full power for less than a minute no matter what airspeed.
3. Cht would be to 410 in 30 seconds after application of power, the manifold pressure would be at atmospheric pressure. Climb would be at best 600 fpm.
4. 65 to 70 in the climb and 4" of manifold vacuum resulted in 410 to 390 cht and about 400 fpm.
5. Cruise power setting of 6" of vacuum would result in a cht of 350 to 370 and 82 mph cruise.
6. Average fuel burn was 5.8 gph.

After the mods:

1. Unlimited taxi time. Full power runs on the ground were possible.
2. Full power can be maintained indefinitely.

3.  Cht at 300 or less with full power in the climb, manifold at 3" of vacuum with wide open throttle. The engine is really pulling harder on the injector and a larger TBI could be used. Climb at least 600 fpm usually over 700 fpm.

4. 65 mph in the climb, again at full power, 550 fpm. Cht less than 300.
5. Cruise power at 6" , 84 mph with cht of 270, some cylinders about 210 to 220 .
6. Average fuel burn undetermined but I know it was higher.

Cruise power, 7.2gph. 272 degrees.

332 degrees in the descent, reduced power.

  










These two pictures are somewhat comparative. The one on the right is with the Generation Two version of heads with the smaller fins. There is a video on Youtube that shows me taking off with a heat soaked engine and climbing 2000 feet. I'll let the video speak for itself. The heads in the video are the original developmental " Generation One" version and they performed much better than expected other than the crack that showed up between the intake and exhaust valve on number two cylinder. I contribute this crack to the heads having been cooked for 60 some hours before the plug holes pulled out. From the beginning of the fat fin test the number two exhaust valve required adjustment every 1.5 hours and it had always tightened up when checked. I flew these heads for a little over 11 hours to obtain good data but it became obvious that the valve was not going to settle in and closer investigation was required. I pulled the head and discovered the crack. I was actually relieved because I worried about the bottom plugs blowing out due to failure of the Helicoil inserts I used to repair the threads.
 I used the data from the original test to come up with a redesigned fin extension. I eliminated one fin by the exhaust port due to interference problems with the exhaust pipe and made the fins all the same length but slightly shorter than the short genertion one fins. The Generation Two heads have been on the engine for about 32 hours with zero difficulties, no valve adjustments or loose head studs, nothing. I put the heads on the engine and flew it one time, cooled it off and adjusted the valves again. So far I have had no issues, but only extensive testing will tell!! 

 The Generation Two head stats with slightly more prop pitch:

1. Unlimited taxi.

2. I have to watch full power runs on the ground.

3. Unlimited full power climbs, 320 max cht. All other statistics about the same.

4. 65 in the climb is about 300 to 290 and the climb rate is about the same.

5. Cruise at 6", 270 to 280, 230 to 240 on the cooler ones, 88 to 90 indicated.

6. Fuel burn is 8.5 to 9 gph in climb, 7.2 in cruise. Based on my calculations using the formula for brake specific fuel consumption I think I'm getting about 100 hp once established in the climb and about 86 in cruise.
 The difference in the two sets of heads are small. I used the "new" $1000.00 heads mentioned before that failed at just over 10 hours. Remember, I took them to my local engine builder and he "rebuilt" them using silicone bronze guides, new exhaust valves and a 3 angle valve seat cut. Both sets were 042 designs with 40 mm intake and 35.5 exhaust but were by different manufacturers. The intake ports appear to be the same between the two manufacturers but the exhaust ports were slightly smaller on the current heads. I also went down to about 8.2 or 8.3 with the compression but this does not seem to effect performance.

The factory fin to the left  didn't get an extension on round two.

The original baffle extends below the extension in this picture showing how much shorter the current version is.

 The reason I went with fewer fins on the new design? Like I said before, I had trouble getting the pipes on and off and testing showed me that I didn't need that much cooling.  I  had a few fins crack off on one head due to the Durafix failing and I noticed no reduction in cooling in those cylinders. I am confident that I am responsible for the Durafix joint failing since the fins that came loose were on the first head I started working on. The second head I did with this material had no loss of fins. I am sure it was due to the fact I had not developed the proper procedure for success early on. I decided to try and tig weld the fins on this time as I fully expected these new heads to be on the plane for some time, and I was told that it couldn't be done. Look below, what do you think? 

These fins were tig welded on. Another thing that I was told " can't be done" 

 Is this Fat Fin Mod necessary? You have to be the judge of that but for me it was essential. Just the piece of mind was worth the effort and for sure my reliability has gone up. We'll talk about the drawbacks of the fat fin mod and answer some frequently asked questions the next time.           

Changes

Changes. What did I change from the original engine to the second engine that had the fat fin heads? Not much. I would have to write a book to itemize all the changes and their effects I have done since I first test flew the plane but I changed very little from the 40 hour mark up to when the engine came off  the firewall for the power loss, at about 80 hours, I think.
  Here are those changes...and why I did it.
Camshaft timing advanced 4 degrees. Why? I was disappointed by the climb rate of my 701 on the original engine and I had done several tests trying to improve that, but the problem had ALWAYS been heat. I could not sustain full power long enough to get good data but I knew the engine could do better. My fuel burn showed that. So when I decided to put the engine back on the airframe I gave up all hopes of just getting in the plane and zipping off to a fly-in, I changed to developmental, see what happens if I do this mode. I began looking for ways to improve low end torque with exactly the same parts as before to put to rest some of the myths I had heard over the years. One of those myths is changing the camshaft timing in relation to the crankshaft would alter the powerband, or rpm that the engine makes the most torque. The problem was I couldn't get two people to agree on which way to go. So I experimented. My engine machinist said for lower torque to advance it and others said to retard it. So I looked on the net.
http://www.compcams.com/technical/FAQ/LSAproperties.asp
I looked at a bunch of stuff but I figured these dudes had a better than average chance of knowing what they were talking about.
  My camshaft gears are adjustable, 4 degrees advance, straight up and 4 degrees retarded. When I set the engine up the first time I assembled it straight up. The second time I decided to try and make more bottom end torque and advanced it based on what I saw on the Comp Cams site, and on advice of my buddy Vic Dawson. I figured if it didn't work out I'd just pull the oil pump and go the other way, which I'm sure is easier said than done. The results later.

 Another change I made was to the cylinder baffling, I removed, or I should say I chose not to install the cool tin baffling on the bottom. This was going to save some weight but meant new block off baffles would be required. This time instead of putting the baffles on top of the cylinders I chose to put them on the bottom, just like the real engines have it. The holes you can see in the aluminum plates are to hold them in place. I used a piece of heavy steel wire to go up through the fins to a bracket or fin on top to haold it in place, again, like on many certified installations.
 Compression ratio is the second thing, I raised it abou .4 to around 8.6 to 1. Every change  made was expected to increase the power output of the engine and therefore the amount of heat to be rejected. I was very confident that the fin extensions would help if they stayed on, I just didn't know how much or how little the effect would be.  All that was left was to hang it back on the plane and see what I had.
 One statistic most are interested in is weight. I completely assembled the engine and weighed it on an engine hoist. I had heard that the redrive engine would weigh about 185 lbs, and I wanted to know. My 701 came in at 742 lbs empty and I knew I didn't add that much junk to it. I figured the biggest weight penalty was in the engine but I was shocked at what I found. With everything on it that would be there when it was on the plane except the prop the package came in at 223 lbs. This includes all the baffling, exhaust, intake system, dual ignition which includes a 4216 mag setup, oil cooler with brackets etc. Like I said, everything as it would hang on the plane. Oh well......a little more than than 185.

  Then, the weather hit. On the day I planned to mount it up I got out of bed and the outdoor temperature was 6, yea 6, as in 6 degrees fahrenheit. This meant that my hanger, which is unheated was also 6 degrees inside since the snow was blowing in the cracks of the siding. I put on my work clothes and insulated coveralls and went to work. Global warming my butt, you can't prove it by me. I had the engine hanging pretty quick and began hooking up all the sytems and controls until I froze out. Warmer weather was coming though........

This shot is before the fat fin mod, the reason I included it here is to show the hanger, not much more than a barn but at least I'm dry! 

Experimenting

I had talked to many people about my flight testing with this power package on the 701 by this time and many, many, folks were asking me not to give up. I think if it had not been for all the individuals from around the world thanking me for trying and letting me know I was giving them hope for affordable flying I wouldn't be where I am now.......

 I looked up at the durafix and it hit me lick a brick! I knew the fin extensions had to help but how would a common man without a $3500.00 Tig welder get them on? Durafix! If I could make it work. Just for the record I have a Miller Dynasty 200 tig machine but I wanted to try to develop something that EVERYBODY could do.

 I came up with a fin pattern the hard way, I laid the head down on a piece of cardboard and traced the inside radius that would be brazed to the head fin. Then I used the header pipe to check the clearance and made the biggest extension I could, 1 3/8". I had a good idea that I would just add it on the end because I wanted the modification to be used on all engines or at least as many as possible. I studied all the intakes and accessories I could and found some of the intakes go right over the top of the head and would hit the extension if it was carried up and over the top. The certified engines had the longest fins by the exhaust port but I felt I needed to try a few different lengths to get a comparison of how much fin area to add or subtract after testing. Looking around the shop I found  some .050 6061 left over from another project and using my cardboard patterns I traced out enough blanks to do the job. Then I cut them out with snips..... in a couple of hours I had a good start.
 A side note, within hours of my initial publication of the test results guys were talking about how to get the fins drawn up in some form of CAD and cutting them out on cnc machinery etc. I did it with snips in less than two hours from the time I had the brain wave until  the fins were on the table. Folks this ain't rocket science. Over the years I have come to notice that most people work harder at getting out of work. Remember, the dread of a job is almost always worse than the job itself.

I mounted the head on the table with the rocker arm studs through a 2x6. Oh, by the way, I had removed all the casting flash from between  the factory fins with a slitting saw in my mill. You just use a grinder or file or whatever works. Then I started on the fin by the exhaust port ( bottom). I just picked up a piece of .080 4130 steel I had in the scrap pile that matched the curve of the head and stuck it in between the fins after sanding it clean. Then I clamped the fin to the steel and fired up the oxy actylene torch. With a stainless brush I heated the head fin and scrubbed it good and then tried to get the brazing to work. The first head went pretty slowly, I had trouble getting the braze to take and the fins would crack off but I kept at it. In the picture above you can see the joint, to the left it looks good, in the middle it looks cold and to the right it looks, well, like crap. You want it to look like it does on the left.
 I finally figured out that heat was the issue, I wasn't getting it hot enough. Aluminum is an enormous heat sink, about as fast as I heated it, it seemed to wick away and I couldn't get the rod to stick right. On the last few fins of the first head I had a better grasp of what was going on and had better luck.
 I went home and checked the groups and Bob Hoover was on there shouting about Durafix, I thought what a coincidence it was that I had just started on this and Bob found out about it at the same time. I made a post on the group that I was doing a fin extension using Durafix and said to "stay tuned". That is where our relationship began, Bob and I. It was worth the effort just to get to talk to him by email ..... I miss you bud.
 I changed the game plane on head two. I installed the plugs and filled the chamber with water. I then started on the bottom again but this time I turned the torch up and as soon as the head finned showed evidence of  accepting the rod I began to move around the fin like before but I concentrated the heat on the head and the filler would just flow around the joint like solder. It takes a lot of heat guys and done properly it only takes a few minutes. I could do two complete fins in about five minutes if all went well and then I would take a break and refill the chamber with water. I did the second head in about four hours.
 When you glue these on it doesn't have to be pretty. Only one joint will be seen but you need to keep the slot open for airflow. How? Just get a grinding wheel for non ferrous metals or a file and clean it with a wire brush when the grooves get clogged. A rough surface will cool better than a smooth one anyway.



Finished product

After getting the fins on cut wood strips to go in between them all and lay the head down like above. Use a sander to dress up the outside of the fin to remove burrs and make them all even. I didn't spend all day fitting each individual one perfectly, just cram something in for support to keep from breaking the fin off. The top four fins are under the exhaust port and I eliminated them before I mounted the heads on the engine.

 Change of subject now. Back up, back up, back up! Computers are nice but when a drive crashes it is a bad day.  About a month ago I had a real real bad day. My computer crashed and with it all my pictures. I have come up with these from all over where I have published them before, if I had only backed up. I'll try to locate more pictures tomorrow.   

 Wood spacers used for support to shape fins to the final form. The top 4 fins were removed before the heads were put in service. Thanks to Kevin McCune for finding my picture in his files.

I reground the exhaust valves, just touching them up in my grinder . DO NOT REUSE EXHAUST VALVES. I knew these heads would be on the plane just a few hours as a test base to see where to go with the fin experiment so I took a chance and reused the old valves. Not a good idea.  The fixture for drilling the heads for bottom plugs is visible in the foreground on the mill. I reused it to insert helicoils in the stripped plug holes. 

Starting over

 I set the engine on the shelf in the fall of 2009 and began hoping to hit the lottery so I could buy a Rotax 912.  I pouted all through the Holidays and worked on finishing the shop at the farm. After the first of January I moved all my equipment there which included a lathe, vertical mill, valve grinder, seat grinder, mig and tig welder and a couple of truck loads of misc junk. I began looking around for something to build and everyone said to work on the engine.

 I didn't see the point in wasting the money, I wasn't having fun anymore. I finally gave in and tore the engine down just to see what happened. To say I was shocked when I took the heads apart would be an understatement and then I got really REALLY mad. The valve seats had a ridge or lip around the base that prevented the valves from sealing and the guides had way to much slop. I took the heads to my local engine builder and he nearly laughed me out of the shop. " You paid how much, a THOUSAND dollars for this junk? !!!!!!" I can't print the convesation from that point on. I asked what it would take to make them right and he said a complete rebuild. This meant all new silicone bronze valve guides ( the originals appeared to be plain brass) a three angle cut on the seats and while he had them apart just put new exhaust valves in them.  After all the problems I had with the engine I took it all the way down to the crank and started over. I found a few other problems that I should have checked but didn't the first time and corrected those. I reassembled the bottom of the engine and took down my old original cooked heads and began dreaming.

 My son in law was up early one Saturday and stumbled across some aluminum brazing alloy on one of those paid advertisement tv shows, so he ordered some and promtly decided it wasn't worth a nickle. He gave it to me. It was in a  box of junk that we hauled out to the farm and I threw it on the shelf forgetting about it.
 I had thought of adding fin extensions to the heads on the original build but didn't put forth much effort. I tried to tig weld one on that was not successful so I just forgot about it. I wanted to fly. I had been doing research on the Vw all along the build of the airplane and that is when I discovered Bob Hoover's blog about the Fat Fin Head mod. I had come up with the idea on my own and started looking around for examples of someone doing it. His mod wasn't quite what I had in mind and he made some good points against it, one was the modified head would likely not fit in existing tooling for repair. So I moved on without it, afterall, everybody else was flying without doing the extensions.
 One day I was thinking about adding some surface area to the head fins again and began to exam the old heads I had begun with. I happened to look up and there was this stuff called Durafix that my son in law had bought just laying on the shelf. The lights came on.    

         

Progress

I continued testing throughout the winter of 2008 and I had the cooling to the point I could spend a little time in the air but I was SURE that I was still cooking the heads. I had to adjust valves on a regular basis and I had trouble with head stud torque. I kept a record of the previous adjustment to track what each valve was doing and I was not happy. More work was needed before summer.

 I had been reading the late Bob Hoover's blog for quite sometime and in it he stated the cylinders only accounted for 15 to 17 percent of the heat rejection of the engine.  I looked at the airflow paths through my engine and suddenly remembered that air is like water, it follows the path of least resistance. This path was down and out around the cylinders, not through the head fins. I had used cool tin under the cylinders like everyone else used but what I finally realized is the path around  the cylinders was shorter and therefore offered less resistance, basically a cowling leak. I needed to make the air go where it was going to do the most good, which is what I had been trying to do all along. I just couldn't see the forest for the trees. I figured that blocking off all the air down through this area wouldn't hurt for a test flight just to see what happened.
 The picture above shows my original head and baffle configuration but of particular interest is the small piece of metal visible in the lower left corner and then the piece between the cylinders. There is another one in the back but it is not visible here.
 I was just blown away when I flew, the cht was down about 50 degrees average. Oh boy! We were going to start traveling now!  I stepped up flying and when I began gaining confidence in the engine I would find some issue that scared me and destroyed that confidence.  All along the way I had other problems, things like oil temp, uneven egt, oil leaks etc. and I would just keep chipping away at it.
 Two things of interest I want to point out about this test. When Continental put the 0200 on a weight reduction program recently they realized that the fins on the barrels were basically worthless for cooling. So they removed them and then discovered that the barrels would not stay round. They added material to the barrel wall to increase it's thickness but found that it was heavier than the old finned barrel. The fins actaully act like a brace and give the cylinder it's strength so they went back to the finned barrel for lightweight strength, not cooling. The second thing is I learned a lot about trying my own ideas. Bob Hoover told me all the time "you are your own best mechanic". After this success I began to realize more than ever I needed to quit listening to the same old song and develop my own package. Bob always said "every installation is different".  
 In August of 2009 I decided I was going to fly it to the Zenith Aircraft Open Hanger Day in the middle of September. I was going to have to fly at least 16 hours round trip without major problems but I felt like I could handle any of the little things that would crop up if I was prepared.  About 4 weeks before the departure I decided to tune it up and when I pulled the bottom plugs, well they wouldn't come out. Three of them stripped out the threads and the forth broke off, in the head.  What a blow.
 I had about all of this I could take, this was supposed to be fun, right?  So I gave up. Three weeks later I got the itch again and decided to just abandon the heads I was using and order a brand new set ready to bolt on. I had cooked them and they were constantly requiring attention, and after all, I had the cht under control, I thought. The heads came in and I bolted them on using copper head gaskets for setting the compression ratio. The first flight was a disappointment since these didn't cool quite as well as the others. I took a couple of short test flights and at about 1.2 hours I noticed  number two would hiss out the exhaust pipe when I pulled the prop through. It would seal when the engine was hot though. I made a few calls and was told the guides were probably tight and the valve was sticking due to the colder weather. Uh huh. Well, I'll just fly it and see what happens. And I did, but the valve never got better. This is probably one of my best stupid moments, I KNEW it wasn't going to get better in my heart. I flew the plane to the local airport to work for my friends at the fbo with between 12 or 14 hours on the new heads. When I departed for home I knew I was in real trouble, the takeoff roll was longer and it didn't climb at all. About 250 to 300 fpm. I turned for home after climbing around the airport for enough altitude to make a safe landing either at home or the departure airport.
 Disgusted, I pulled the engine and gave up for good.......      

How hot is to hot???

  Ask 10 different experts what the limits are and I bet you will get 20 different answers. I did. When I tried to get a cylinder head temperature limit I received figures from 350 to 475 degrees. Doing a little research, wait, that's a lie, doing a LOT of research on the web I began to get some numbers to shoot for. According to Pratt and Whitney aluminum becomes brittle at 450 degrees for a casting and about 550 for a forging. This varies some with the alloy used. I was a little confused by Limbach, they have a service bulletin out that says aluminum begins to change on a molecular level at 200 degrees C ( about 390 F) yet they advertise maximum cht in their literature of 250 C ( around 480). At this stage of the game I decided I would shoot for the low end since we used to think 350 was to hot when driving down the interstate during my hot rodding days. Dune Buggies and Hot Vw's magazine has a very good article in the August 2010 edition that backs me up on this. You really need to get a copy and read this.
 On more than one occasion I was told I was sensing the temperature in the wrong location and to get the proper temperature I needed to relocate the sensor. Basically, move it until you get the reading that makes you feel good? Now...., I have a different opinion here, I feel you should sense the cht at it's hottest point since that is where the damage is going to be. I looked at several " certified " aircraft engines in the last four years while working on my A/P rating and all of them had the sensor on the bottom, some between the plug and head while others do it with a sensor screwed into the head. From what I can tell this is the hottest point on a certified head / cylinder assembly as the cooling will have picked up a large amount of heat coming down through the fins and it is also near the exhaust ports.
 I looked at where the Vw engineers put the cht sensor on the fuel injected engines and it was near the exhaust port also. I tried it in three different locations, under the plug, under one of the center head studs and under the head stud over the exhaust port. As for the plug location my testing showed the plug has an effect on the reading, a cooler plug gave a few degrees cooler cht reading. The center head stud location is the coolest part of the head as far as I can tell.  So, based on what I was seeing on the Continentals and the stock Vw head sensor location I chose the head stud over the exhaust port. All of my development work has been done with the sensors in this location so as to have a solid comparison.

The picture above shows the cht about 20 min after takeoff on a day in the forties. This is early in the test program before the fat fin mod with about 30 hours on the Hobbs. This is a cooler than normal cruise reading and it is one of the cooler running cylinders of the 4. It is below normal cruise temp because I have the power pulled way back. I was trying to get to a landing area since I have no oil pressure indicated on the gauge. Yes it was a gauge issue, the engine stayed together! I flew the plane about 60 hours with stock type heads and had constant issues with valve adjustments and head stud torque among other things. I saw it as a sure sign of overheating and I worked between every flight to get the cht lower.
 I tried all the gimmicks in the book after talking to all the experts and locals. Several told me I had to slow the air down to allow it "to pick up heat" and other wild ideas. I finally got serious and went back to my Hvac roots. I installed a air pressure manometer in the cabin with the probes in various locations in the cowling to make sure I had a pressure differential to make the air move. I found out the best I could get was about 2.5 inches and that was about all I could expect with the speed a 701 flies. Armed with that info I began looking at ways to move a larger volume of air through the head fins. I knew that heat travels from hot to cold and the larger the temperature differential the greater the heat transfer will be. Next time we'll talk about having some success!
           

Who am I ?

I'll give a brief background on who I am to help folks make a determination on whether or not to take me seriously. I am a country boy who grew up around machinery from a early age. My father rebuilt Vw engines part time for several years and I'm sure this is where my interest in the Vw engine began. At the age of 13 I started working in a garage owned by neighbors while still working on the farms around home.
 When I entered the 11th grade in high school I chose to enter the heating and air conditioning trade in Vocational Technical school. How I wound up in this business is a story in itself, maybe to be told at a later time. Five months into my first year of training I was called to the office where two men in work uniforms were waiting with the Diversified Cooperative Education instructor. I found out that my instructors felt I was wasting my time in class and would be better served by moving to the next level, on the job training.
 The two men were from Marshal University in Huntington, West Virginia and needed a replacement set of hands in housing maintenance. The next week I started the next phase of my life, working on all types of refrigeration equipment,  150 ton chillers, 32 ton rooftop ac units, hot water heaters for an entire dormitory, steam boilers and believe it or not, Brunswick bowling pinsetters among other trivial things. I learned a bunch pretty quick. The pinsetters were in the basement of the Memorial Student Center, named in memory of the football team, coaches, boosters and doctors who lost their lives in the 1970 plane crash on approach to Huntington Tristate Airport in bad weather. The movie, WE ARE MARSHALL, tells the heart wrenching story of this tragedy. Most of the movie was actually shot on campus and in a few of the scenes the Memorial Fountain in back of the Student Center is shown. Maintaining this fountain was also one of my responsibilities, one which I recall as my least favorite. Now, looking back, I'm proud to have done it realizing it was an honor that I could not recognize at my young age.
 I stayed at Marshall for two and a half years then I took a job at a private HVAC company for more money. At the age of 22 I purchased the Company after my employer passed away and over the next few years we struggled along. We finally relocated, changed our company name and we have been at it since. All along the way I have been in continuing education and have been able to accumulate quite a collection of tools and test equipment but most importantly, I have 31 years of experience in heat transfer. I have also learned the proper way to troubleshoot and analyze problems from a mechanics point of view, something that has really paid off with the plane.
 When you are in business for yourself you are forced to do things out of desperation, like working on a truck all night for the next day. I have done most of my own truck maintenance over the years because we couldn't afford to have it done rebuilding three automatic transmissions, untold numbers of engines, rear differentials and the list goes on. Along the way I have become a self taught machinist and welder.
 Now many of you who have read this will by now think am bragging about my life, my experience, I am. I'm proud of where I am, who I am and how I got here but most importantly I want my readers to understand that I have a little bit more experience than your average shade tree weekend mechanic. That is the only point I want to make.
 Next time we'll talk about airplanes, I promise. 

Welcome!

I want to welcome all who are interested in my Vw powered experimental aircraft engine cooling experiments. Over the next few weeks I will be posting information on my experiences with a Vw powered Zenith CH701, the issues I have encountered, how I over came them and my plans for the future development of my Vw aero engine.  Stay tuned!