Debra
11-29-2007, 03:48 PM
Hello Clarence,
Like so many other readers, I'm glad to see you back in print, and thanks to MAN for recognizing that.
I am about to break in a new OS .91FX and coincidentally opened an old RCM (August 1999) where you did a review on that same engine. The item that caught my eye was the range of props that you tested the 91 on, which ranged from 13x6 to 16x6, while the 91's instruction manual recommends a prop range of 15x8 to 17x6.
I understand that you tested the 13x6 as an extreme example of what the engine could do, and would not seriously recommend it as a worthwhile prop for that engine. But, I was curious why there was such a discrepancy between what the manual recommends and what you felt should be tested.
Has the engine technology improved enough in the past 8 years that the 91 can now swing that 17x6 properly? Or did you (with your real-world experience) feel that the 17x6 would not be a good combination for the engine, and thus did not test it?
I'm sure that there are other reviews where your recommended range of props disagrees with this or that manufacturer. Other areas would be why you choose this fuel while manufacturer's recommend 'that' fuel. I thought that it might be an interesting column sidebar to discuss why, how, or what you base your decisions on. I put a lot of stock in your opinion.
Thanks for bringing back Engine Clinic - I'm looking forward to many more columns from you. I've learned a helluva lot over the years from you.
Bob M.
Geesh Bob, I tested the engine with 9 different prop sizes and you wonder why I didn't include a 17 x 6. I thought that the prop sizes I ran pretty well covered those recommended by O.S. As the engine I tested turned a 16 x 6 8,300 rpm, which is about as low as you would want to lug the engine down, a 17
x 6 would have been too much prop. Maybe O.S. is as little optimistic regarding what the engine can do, or their make of 17 x 6 does not load the engine as much as the Zingers I used. I don't try to burn the engines up just to see what they can do. I try to stick with the same prop sizes for other makes
of engines for comparison purposes. I also do not use a mixture of prop manufacturers and odd ball sizes as others doing engine reviewers have done which makes it pretty difficult to make comparisons.
As far as fuel - you puzzle me. The majority of the engine manufacturers that I know of (with the exception of YS) recommend 5 - 15% nitro fuel with oil content usually in the 18 -20% range. How does the fuel I use (Omega 19%) differ?? It certainly falls with in the recommended range.
Thanks for taking the time to write and the kind words regarding the column.
Best regards,
Clarence Lee
Like so many other readers, I'm glad to see you back in print, and thanks to MAN for recognizing that.
I am about to break in a new OS .91FX and coincidentally opened an old RCM (August 1999) where you did a review on that same engine. The item that caught my eye was the range of props that you tested the 91 on, which ranged from 13x6 to 16x6, while the 91's instruction manual recommends a prop range of 15x8 to 17x6.
I understand that you tested the 13x6 as an extreme example of what the engine could do, and would not seriously recommend it as a worthwhile prop for that engine. But, I was curious why there was such a discrepancy between what the manual recommends and what you felt should be tested.
Has the engine technology improved enough in the past 8 years that the 91 can now swing that 17x6 properly? Or did you (with your real-world experience) feel that the 17x6 would not be a good combination for the engine, and thus did not test it?
I'm sure that there are other reviews where your recommended range of props disagrees with this or that manufacturer. Other areas would be why you choose this fuel while manufacturer's recommend 'that' fuel. I thought that it might be an interesting column sidebar to discuss why, how, or what you base your decisions on. I put a lot of stock in your opinion.
Thanks for bringing back Engine Clinic - I'm looking forward to many more columns from you. I've learned a helluva lot over the years from you.
Bob M.
Geesh Bob, I tested the engine with 9 different prop sizes and you wonder why I didn't include a 17 x 6. I thought that the prop sizes I ran pretty well covered those recommended by O.S. As the engine I tested turned a 16 x 6 8,300 rpm, which is about as low as you would want to lug the engine down, a 17
x 6 would have been too much prop. Maybe O.S. is as little optimistic regarding what the engine can do, or their make of 17 x 6 does not load the engine as much as the Zingers I used. I don't try to burn the engines up just to see what they can do. I try to stick with the same prop sizes for other makes
of engines for comparison purposes. I also do not use a mixture of prop manufacturers and odd ball sizes as others doing engine reviewers have done which makes it pretty difficult to make comparisons.
As far as fuel - you puzzle me. The majority of the engine manufacturers that I know of (with the exception of YS) recommend 5 - 15% nitro fuel with oil content usually in the 18 -20% range. How does the fuel I use (Omega 19%) differ?? It certainly falls with in the recommended range.
Thanks for taking the time to write and the kind words regarding the column.
Best regards,
Clarence Lee