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Jul 08, 2003, 10:40 PM
Registered User

Which hyper drive prop for stock GWS 300C and P-51?

To expand on the thread title - which hyper drive (Direct drive) prop gives good performance for the gws 300C drive on the P-51? Or in general on the 300C drive for that matter. It has been said to move up a "size" from the reduction series. Currently I'm using the 10x8 reduction series prop and I can find 10x6, 11x7 and 12x8 direct drive props but not a 10x9 or 11x8 or 11x9 depending on what up a "size" is to mean.
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Jul 10, 2003, 10:13 AM
Registered User
Since I'm the one who first mentioned the concept of moving up a size from Reduction Series to Hyper Drive props, I'll try to explain. I first became aware of the efficiencies of the HD props by comparing their performance to the RS props in the EPS-400 table on the GWS site. In general, if you went up one size in diameter, you'd get more thrust at less current. So I thought it was obvious that the HD props were more efficient, and this proved true when I tested them in the real world.

The major weakness of the HD props is that in all of the sizes above 5 inches, they are only available in one pitch speed per diameter (6x3, 7x3.5, 8x4, 9x5, 10x6, 11x7 and 12x8). So you don't have any flexibility. If you want to go up from a 10x8 RS prop, you sacrifice a little prop pitch speed with the 11x7 HD. The only way to know for sure if this or any other prop design and size will work for you is to try it yourself in your application. There are too many different combos and too many different individual flying styles to predict what will be the "best" prop for all combos and all people.

One thing you might want to do is to check the new EPS-350 chart at the GWS site, as it has both the HD and RS props in it. Unfortunately, GWS has not updated its earlier tables, such as the EPS-300, to include the HD props, and the 350 motor is different from the 300. But at least you can get directional data. On the 350, the 10x8 RS and 11x7 HD are both recommeded for the D gearing (6.6:1) at 8.4V, with data as follows:

8.4V * 8.8A * 12.15 oz. static thrust = 10x8 Reduction Series
8.4V * 9.1A * 16.17 oz. static thrust = 11x7 Hyper Drive

So with this specific motor at this specific gearing, you can get a ~33% increase in static thrust for only a ~3% increase in current. The absolute numbers will vary depending on the combo. But you are always going to get more thrust per amp in every case. How the aircraft will fly is a different question. The loss of a little prop pitch speed may or may not negatively impact your flying experience. Likewise, the significant increase in thrust may or may not offset that loss of prop pitch speed, depending on the aircraft and the individual. I hope this helps answer your questions.