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!