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Jerry Harold Spinner/Scoopless cowling

Aden Rich

Well Known Member
Jerry Harold has had a number of medical issues so his production has stopped. He was also working out of a small shed and could only work when the temps were up to allow for curing.
My friend Bill Drake has spoken with Jerry and is trying to get him to bring all of his stuff out to Bill's heated hanger in Battle Ground, WA.
I will talk to Bill and see what the status is and if they are producing I will ask Bill if it's OK to give out his number.
I got the last Harold spinner and I gave it to Bill so he could complete his RV-10 :(. Now I don't have one. Hopefully he'll have something cookin.....

The scoopless cowling (at least in my opinion) from my results may be a little faster than the stock cowling. My friend had a 180hp RV-6 with the stock cowling and I could slowly walk away from his. His airplane was also extremely clean as well.

There is talk about loss of MP due to not having ram air. However, your cowling chamber is getting rammed with air. And lots of it! I paid very close attention to the snorkel and the inside of it. I made sure everything was sanded smooth and the transition to the servo was blended. I also sealed up EVERY gap in my baffling so I did not let any air leak out. It either went into the induction or over my cylinders and oil cooler. I also used a Setrab oil cooler which is smaller and lighter. I smoothed out the air going into the cooler and my temps stayed right at 180 degrees. Even on hot summer days. I have had people tell me that it's not possible and that my gauge was reading off. However, Bill from above has the same cooler on his airplane with a more accurate digital gauge and he is getting the same readings.
I really think the big difference is the tuned induction. If you look at a normal updraft engine and then at the tuned induction, you can see how the air flow is going to be more even and increased as the cylinder is drawing air down the bore. I wouldn't think that taking the air and ramming it into a split spider line and trying to distrubute to 4 cylinders is going to increase your MP. My mind tells me that is more about flowing the air to the cylinders then working your way back up the system to the inlet is more important than just ramming a whole bunch of air in the holes. Hence the advent of porting/polishing.

I think all of these little things added up to more speed gains.
I am sure the engine was making more than 180 hp with the tuned induction and exhaust. Factor in the lower cooling temps, better air flow in the cowling, tight intersection fairings (and I mean TIGHT), attention paid to thrust line, tail wheel fairings, rigged straight, harold spinner (????) and WAXING THE HECK OUT OF THE PLANE has given the speed increases.
Now again, I am sure I'll get some flak but it's hard to argue with RESULTS.
When I had the airplane and the engine was brand new I could get 219mph.
When I sold it and let the new owner fly it around and the engine was really broke in, he was turning in speeds of 224. He goes out on calm, cool days with no wind and runs TWO (2) gps and 4-way runs and gets 224. And again has repeated this many times over.

I am hoping to repeat this again on my new RV-6 with a Sam James cowling. I've heard of 7-10mph gains just from the cowling system. I am also going to work on exit air out of the cowling as the RV-6 has room for improvement here. I will be using the same 180hp engine (stock), however, I will have 4-1 exhaust. My ultimate goal is to kick butt on my Dad in his Rocket. I want to see his face when I can hang with him!!!
 
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