yes HighPlains,
There are SO many misconceptions in this thread, but let me elaborate on this one.
I too have seen prop efficiencies of 80-85% quoted, but that's for full size props, carefully designed for a specific purpose. And that will be their peak efficiency, at the particular airspeed for which they were optimised.
On models I'd advise using a prop efficiency of 50%, unless you go to great trouble calculating and experimenting to find the exact prop which will perfectly suit your model, and engine, and its intended purpose. The speed freaks do it, and get efficient props, but let's face it most of us fit the one in our box whose hole fits the shaft and whose numbers seem about right.

<div style="margin: 0in 0in 0pt">Now, who thinksa model can never reach its theoretical "pitch speed" (the product of prop pitch and RPM)?
I copied thefollowing table out of anold American magazine 20 or maybe 30 years ago.
The writer (sorry I forget who, but if you are reading please chip in) performed experiments with a 60 two-stroke in an aerobatic model using a wide range ofprops.
</div><table border="0" cellspacing="0" cellpadding="0" style="border-collapse: collapse"> <tbody> <tr style="page-break-inside: avoid"> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: windowtext 1.5pt solid; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: windowtext 1.5pt solid; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">1</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: windowtext 1.5pt solid; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">2</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: windowtext 1.5pt solid; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">3</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: windowtext 1.5pt solid; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">4</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: windowtext 1.5pt solid; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">5</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: windowtext 1.5pt solid; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">6</div> </td> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: windowtext 1.5pt solid; border-right: windowtext 1.5pt solid; padding-top: 0in"> <div style="text-align: center; margin: 0in 0in 0pt" align="center">7</div> </td> </tr> <tr style="page-break-inside: avoid"> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: windowtext 1.5pt solid; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">.Prop</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">static</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">static</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">RPM</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">mph</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">%max</div> </td> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1.5pt solid; padding-top: 0in"> <div style="text-align: center; margin: 0in 0in 0pt" align="center">% max theory</div> </td> </tr> <tr style="page-break-inside: avoid"> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: windowtext 1.5pt solid; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">dia x pitch</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">RPM</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">thrust</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">level</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">level</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">theory</div> </td> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1.5pt solid; padding-top: 0in"> <div style="text-align: center; margin: 0in 0in 0pt" align="center">(static rpm)</div> </td> </tr> <tr style="page-break-inside: avoid"> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: windowtext 1.5pt solid; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">APC 11x7</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">13100</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">7.5</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">13500</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">87.1</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">97.3</div> </td> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1.5pt solid; padding-top: 0in"> <div style="text-align: center; margin: 0in 0in 0pt" align="center">104</div> </td> </tr> <tr style="page-break-inside: avoid"> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: windowtext 1.5pt solid; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">APC 11x8</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">12500</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">7.75</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">12920</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">91.7</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">93.7</div> </td> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1.5pt solid; padding-top: 0in"> <div style="text-align: center; margin: 0in 0in 0pt" align="center">97</div> </td> </tr> <tr style="page-break-inside: avoid"> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: windowtext 1.5pt solid; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">APC 11x9</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">11500</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">6.25</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">11550</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">85.3</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">86.7</div> </td> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1.5pt solid; padding-top: 0in"> <div style="text-align: center; margin: 0in 0in 0pt" align="center">88</div> </td> </tr> <tr style="page-break-inside: avoid"> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: windowtext 1.5pt solid; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">APC 11x10</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">10500</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">5.13</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">11000</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">78.9</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">75.8</div> </td> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1.5pt solid; padding-top: 0in"> <div style="text-align: center; margin: 0in 0in 0pt" align="center">80</div> </td> </tr> <tr style="page-break-inside: avoid"> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: windowtext 1.5pt solid; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">APC 11x11</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">10000</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">5.25</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">10750</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">83.4</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">74.5</div> </td> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1.5pt solid; padding-top: 0in"> <div style="text-align: center; margin: 0in 0in 0pt" align="center">79</div> </td> </tr> <tr style="page-break-inside: avoid"> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: windowtext 1.5pt solid; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">APC 12x10</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">9250</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">5.75</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">9500</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">77.9</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">86.6</div> </td> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1.5pt solid; padding-top: 0in"> <div style="text-align: center; margin: 0in 0in 0pt" align="center">90</div> </td> </tr> <tr style="page-break-inside: avoid"> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: windowtext 1.5pt solid; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">Revup 11x7.5</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">12800</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">7.00</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">13500</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">86.2</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">89.9</div> </td> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1.5pt solid; padding-top: 0in"> <div style="text-align: center; margin: 0in 0in 0pt" align="center">96</div> </td> </tr> <tr style="page-break-inside: avoid"> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: windowtext 1.5pt solid; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">Revup 11x8</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">12000</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">6.63</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">12830</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">86.2</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">88.7</div> </td> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1.5pt solid; padding-top: 0in"> <div style="text-align: center; margin: 0in 0in 0pt" align="center">96</div> </td> </tr> <tr style="page-break-inside: avoid"> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: windowtext 1.5pt solid; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">Revup 12x6</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">12250</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">7.75</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">12750</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">75.2</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">103.9</div> </td> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1.5pt solid; padding-top: 0in"> <div style="text-align: center; margin: 0in 0in 0pt" align="center">107</div> </td> </tr> <tr style="page-break-inside: avoid"> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: windowtext 1.5pt solid; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">Revup 13x6</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">10500</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">7.88</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">12000</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">72.4</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">106.2</div> </td> <td valign="top" width="106" style="border-bottom: windowtext 1pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1.5pt solid; padding-top: 0in"> <div style="text-align: center; margin: 0in 0in 0pt" align="center">121</div> </td> </tr> <tr style="page-break-inside: avoid"> <td valign="top" width="106" style="border-bottom: windowtext 1.5pt solid; border-left: windowtext 1.5pt solid; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">Revup 14x6</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1.5pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">9500</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1.5pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">8.88</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1.5pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">11000</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1.5pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">69.7</div> </td> <td valign="top" width="67" style="border-bottom: windowtext 1.5pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 0.7in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1pt solid; padding-top: 0in"> <div style="margin: 0in 0in 0pt">111.5</div> </td> <td valign="top" width="106" style="border-bottom: windowtext 1.5pt solid; border-left: #ebe9ed; padding-bottom: 0in; background-color: transparent; padding-left: 5.4pt; width: 1.1in; padding-right: 5.4pt; border-top: #ebe9ed; border-right: windowtext 1.5pt solid; padding-top: 0in"> <div style="text-align: center; margin: 0in 0in 0pt" align="center">120</div> </td> </tr> </tbody></table><div style="margin: 0in 0in 0pt"></div>This table shows that using static RPM andprop pitch gives an accurate estimate of the potential top speed of the model, as long as the prop was chosen sensibly.
the table also shows clearly that this model will fly at 120% of its pitch speed (based on static rpm column 7), or 111% based on in flight RPM (column 6).
That is because the pitch marked on a prop is a pretty arbitrary number, whose main purpose is to compare it to other props in the range.
The pitch is generally measured using the flat bottom of the airfoil, NOT its zero lift line or chord line. That is in no way a criticism of manufacturers. I like simple, easily checked numbers.
This model can exceed its pitch speed on a 6" pitch prop because that is the WRONG prop for the model. Those fine props are suited to slow flying models, old biplanes or vintage types.
The very coarse props are wrong too, for performance. They yield only 80% of pitch speed, and were used just to satisfy the noise regulations.
Note also that the prop for highest static thrust produces the lowest flight speed!!! This is no way to choose a prop (see below).

Right, who said you cannot get zero thrust? Of course you can, if you fly fast enough.
check out the website www.drivecalc.de/PropCalc/
and download the program Propcalc. If you input a specific prop and RPM it will draw you a graph of thrust andefficiencyagainst airspeed. Note that thrust drops to zero as speed increases.
Note also that efficiency reaches a maximum at just about the airspeed that corresponds to "pitch speed"

<u>Choosing a Prop
</u>To choose a prop you want to know the stalling speed of the model, and my rule of thumb for this kind of model is 5 times the square root of the wing loading (in oz/sq.ft)
Say your loading is 30 oz/sq.ft, (the sq root is 5.5) times 5 = 27.5 miles per hour
You want a general purpose sport/scale/slow model to fly at double that, let's say 60 mph, which is 88 ft/s
Work out a prop pitch and RPM that produces the necessary pitch speed. At 7500 RPM you want 8.5 inches pitch, so an 8" or 9" pitch is called for.. Then choose the diameter that goes with this pitch AND suits the engines. What about a 17x8? or a 16x8, or a 16x9

Anyone know how much powerthose OS 160 FS engines produced? I can't find a test report.
My guess 1.5, at most 2 HP at 7500 rpm.
That is equivalent to a brushless electric model fed with 1500 to 2000 watts input, giving a power rating froma conservative 68 watts/lb to a generous 90 watts/lb. The electric fliers consider 50 watts/lb adequate for a big slow model, so I think the OS has plenty of power if given the correct prop.

forget static thrust, work out how much Power you need