ENGINE AND PROP TESTING FOR SPORTSMAN PROFILE CARRIER Bill Bischoff
Recently I tested three different engines, a few different carburetors, and a handful of props to see how they would perform for Sportsman Carrier. I tested these particular engines simply because I already owned them. Also, they all have the same mounting pattern and the same size hole for the carburetor. This made it possible to switch things around easily. Even though some of these engines and carbs are no longer in production, they were all standard hobby shop fare; nothing custom or exotic. All flight testing was done with my 323 sq. in. Hellcat, weighing 36-38 oz. depending on the engine. Fuel was 10% nitro/ 5% castor/ 15% synthetic unless noted otherwise. Static RPM figures were measured using an APC 9x6 prop.
OS 32F, stock 3H carb weight 8.3 oz 15,180 RPM (15,240 RPM, Evolution 9x6 prop)
OS 32F, OS 4BK carb 15,600 RPM
OS 32SX, OS 4BK carb weight 9.5 oz 16,100 RPM (16,500 RPM, Wildcat 30% nitro)
EVOLUTION 36 CL, Evo. carb weight 10.0 oz 15,900 RPM
EVOLUTION 36 CL, OS 4BK carb 15,800 RPM
PROP TESTS
All prop test times were for seven laps from a standing start, per normal Navy Carrier procedures.
Times are in seconds.
OS 32F, 3H carb
APC 8x6 22.50 22.60 22.75
APC 9x6 22.50 22.56 22.59 (different day 22.44 22.57 22.61)
Evolution 9x6 22.85 22.97 23.06
APC 9x7 22.58 22.58 22.76
OS 32F, 4BK carb
APC 9x6 22.29 22.32 22.42
OS 32SX, 4BK carb
APC 8x6 21.71 21.71 21.90
APC 8x7 21.83 21.95 22.01
APC 9x6 21.47 21.74 21.77
APC 9x6.5 21.59 21.77 21.92
APC 9x7 21.64 21.77 22.11
EVOLUTION 36 CL, 4BK carb
APC 8x6 21.71 21.95
APC 8x7 21.82 21.89
APC 9x6 21.21 21.56 21.69
APC 9x6.5 21.38 21.42 21.45
APC 9x7 21.15 21.42 21.56
OBSERVATIONS AND ANALYSIS
I had high hopes for the Evolution carburetor, since it is readily available and inexpensive. It is very similar in appearance to the OS 4BK, and has a slightly larger bore through the barrel, which yielded an extra 100 RPM. The carburetor comes set up for a remote needle valve, but the needle valve assembly can also be installed directly on the carb body. Although there isn't an adjustable idle stop, I found that the carb gave a very usable low end RPM. Unfortunately, the bore may be a bit too big, as I was unable to get off the ground without the engine faltering or quitting. Perhaps the barrel could have been sleeved down to reduce the intake size, but I did not try.
The OS 3H carburetor has a smaller bore than the 4BK, which represented a difference of over 400 rpm on the OS 32F. This also resulted in a speed difference. However, for the sportsman competitor, the 32F with the stock 3H carb is such a good running and reliable setup, there is no need to bother with trying to get a 4BK carb. Although the 32F has been out of production for over 15 years, they are not hard to find at swap meets or online. This is the setup I will continue to use on this Hellcat, and would recommend to anyone looking to get into carrier.
I am currently working on an advanced carrier trainer Hellcat with a slider. On this airplane, I plan to use the Evolution 36 with the OS carb. The Evolution and the OS 32SX are very similar in performance, but the Evolution is available, parts are inexpensive, and quite frankly I want to show that this engine is a viable choice for carrier. Note that mine is actually the CL version. The RC version may be a bit faster, but I don't have one to compare.
As for props, note that all the props tested were fairly close in speed, but the APC 9x6 looks to be the prop of choice. Of all the props tested, it seemed to get off the deck the strongest. Other props may be faster in the air, but are slower off the ground. Some novices may find this easier to deal with. The 8" props make the airplane less "floaty" at idle than the 9" props. Again, this may make it easier for novices to get a landing, as the airplane will stop flying when they want it to. Since there is not a lot of performance difference between props, the novice may want to choose a prop to tailor the flying qualities of the airplane to his personal preference.
Now for the disclaimers. These tests were carried out over several different weekends, but weather conditions were similar. The second set of times for the OS 32F/ APC 9x6 were done to make sure nothing had drastically changed during the course of testing. I make no claims, promises, or guarantees in reference to these performance figures. Your results may vary. I invite questions and comments.
A big thank you goes to Phil Dunlap for his help with these tests. His assistance was invaluable.