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.