Your virtual propeller design can be analyzed at off-design conditions, i.e. at a different speed or a different velocity of rotation. The analysis is a so called "Blade Element Method" and uses the same airfoil polars as the design procedure. The influence of blade number and tip loss are take into account by the "Prandtl Tip-Loss Factor". More details can be found in references [10] and [11]. It should be noted, that the analysis does not work accurately for high thrust loadings as they occur under static conditions.

*JavaProp* offers two ways to use the analysis procedure:

- First, it is possible to analyze the propeller for its
__full operating range__, from static to the beginning of the windmilling range. The results of this "Multi Analysis" are presented a a table and a graph showing the thrust and power coefficient depending on the advance ratio*v/(nD)*. The only detail about the flow conditions on the blade is the number of blade sections where the airfoil has stalled, which is given as a "percentage stalled" number. When 100% of the blade are stalled, all airfoils operate beyond their maximum lift, which is usually the case al low speed. Due to the definition of the efficiency the efficiency at larger advance ratios may be higher than at the design point; this does not mean the efficiency in the design point is not maximized. The results also show the maximum possible efficiency for each advance ratio, labeled*eta**. This efficiency could only be reached with a propeller without any frictional losses.

- A second way to use the analysis method is to perform an analysis for
__one advance ratio only__. This "Single Analysis" gives you more details for the aerodynamic conditions along the radius. A plot shows the distribution of lift and drag coefficient and a table lists all data of interest. These include the additional local flow velocity induced by the propeller wake in terms of the so called "interference factors". These factors are labeled*a*and*a'*, where*a*is the ratio of the additional axial velocity to the onset flow velocity. A value of 0.05 for*a*means that an aircraft propeller adds 5% of the flight velocity*v*to its jet. The total axial flow velocity in the propeller plane will be*(1+a)*v*. In a similar way, the factor*a'*defines the ratio of the additional swirl component at the propeller in relation to the local circumferential velocity*Omega*r*. The total circumferential velocity seen by the airfoil section is*(1-a')*Omega*r*. Also, it is possible to calculate the local flow direction immediately behind the propeller in terms of a swirl angle*delta*.

As the previously given total velocities, this angle is again valid in the propeller plane only or__immediately behind the propeller__. The slipstream extends downstream from this point, which makes a point far behind the propeller feel twice the induced velocity components (here the slipstream extends downstream as well as upstream). So the additional axial velocity far behind the propeller is*2*a*v*and the additional rotational velocity in the slipstream is*2*a'*Omega*r*. I have named the resulting swirl angle*delta_ff*(far field)*.*

*Last modification of this page:
24.12.06*

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