Understanding Vess Propellers

     The unique shape, design, and size designations of the Vess Propellers did not come about by accident.  They are the result of many months of computation, prototyping, and testing.  And instead of simply recreating another version of existing designs or following conventional practice, this project began from a “clean sheet of paper” and proceeded in a direction that was guided by formal engineering analysis. The result is a prop design that truly sets a new standard for performance, efficiency, and noise reduction.

     The introduction of anything unconventional is sure to draw questions since it is not supported by conventional thinking.  It’s the nature of being different. Vess Propellers certainly fall into this category and thus a little simple education is warranted. So, by addressing a few common questions, some details of the design philosophy of these props is presented.

Q. Why are these props shaped like this?

A. Instead of just picking a shape and using a constant “helical” pitch along the blade, the geometry of Vess Props were computer defined as required by each specific application. This means that the combination of chord, thickness, blade angle, and airfoil were digitally optimized at several radial stations along each prop blade by applying advanced propeller theory. In each case, a “mission specific” non-linear twist distribution was defined by the optimization process.  The unique blade sweep was also included for noise considerations.

Q. Since the pitch is not constant, how do you know what it is?

A. It is not important to know what the pitch values are. It is only important to know how one prop relates to another so that you can select the proper one. The diameter of the prop is chosen to put you into a typical “class” of aircraft/engine. Remember, our extensive analysis and testing has optimized a blade shape and pitch distribution to work well for that combination.  Conventional pitch descriptions are simply incapable of describing this unique twist, so it is not appropriate to attempt to apply them here.  Instead, we have employed a simple alphabetic designation for pitch.  And we have also created a 3-4 prop “series” for each diameter that will allow you to adjust to your particular requirements.

     It will most likely give you the tremendous vertical performance, great acceleration, and low noise that it was designed to deliver. But all engines, airplanes, and even weather conditions are not alike. So, there may be a better choice for your particular situation.  If you have an aircraft that is heavier, has more drag, or is larger than a typical 33-35% aerobatic model or has less horsepower (either due to less displacement, higher field elevation, or higher air temperature), you may need to go down to a “27A”, which has less load. Conversely, if your airplane is lighter, has less drag, or is smaller than a typical 33-35% aerobatic model or has more horsepower (due to more displacement, lower field elevation, or lower air temperature), you may can use a higher loaded “27C” to properly absorb the power and keep the propeller quiet. Remember, the prop, engine, and airframe directly interact and affect each other so you need to think about that when choosing your prop.  See the prop selection info below for a summary of this methodology.

Q. What should my Vess Prop tach on the ground?

A. Don’t waste your time measuring ground RPM unless you are attempting to somehow quantify relative loads on the engine.  Vess Props will usually turn less on the ground and in the air.  It’s part of the design philosophy of properly loading the engine under real flight conditions. The benefit comes from the thrust that is produced at that lower RPM.  So judge these props against others through performance in the air. You will most likely be amazed!

Q. How quiet will my plane be with a Vess Prop?

A. Noise is driven by the loudest component is a system.  If you have a loud muffler, you will not realize the full potential of using a quieter propeller. But it will still help!  Vess Props were optimized to absorb the full power of each engine/airframe class at RPM’s below which the tips reach sonic conditions.  In almost every case that we have tested over the past year, the Vess Prop did not unload to the point of producing sonic tip noise. The in-flight noise was most often dominated by the exhaust sound.

     And recent sound testing by the organizers of the “Don Lowe Masters” competition have shown the true potential of Vess Propellers for controlling noise.  A 43 pound, 42% Hanger 9 Ultimate fitted with a DA150 engine and canister mufflers measured as low as 93db at 25 feet with a Vess 32D prop! And the in-flight performance of this combination was astonishing. Also, a 40% Carden Extra 300 with DA150 and Johnson-type mufflers measured 98db with the same Vess Prop and also showed fantastic performance in the air.  You don’t need to fly a loud airplane, even with stock mufflers.

Propeller Selection Principles

Step 1 - Choose a Diameter

     The one thing that is conventional about these props is the designation of the diameter.  It is described by the two-digit number printed on the side of the prop hub and has units of inches. In general, the choice of a diameter will put you into a “class” of engine and airframe. For example, our 32 inch diameter prop series was optimized for typical 150cc-powered aerobatic aircraft.  Of course, there are many different engine and airplane combinations that could utilize this same series, so the choice of diameter also serves as another tuning variable.  But, in general, the diameters that are currently chosen for different aerobatic setups are a good place to start here.

Step 2 - Choose a Pitch Series

   As discussed on the tech info page, the pitch is not defined by a constant helical value in inches as with conventional props, but by an alphabetic letter.  This is because the optimized pitch distribution for each prop is not constant or linear and, thus, cannot be described by a single value.  In actuality, the A-B-C pitch series concept provides an intuitive means of tuning the prop load. This process is driven by the simple understanding that the “B” series is intended to be the normal or baseline load and the “A” and “C” produce less and more load, respectively.  You could probably utilize the “B” prop and note increased performance compared to your normal prop.  But there are added performance and noise benefits to be gained from further adjustment.  The follow graphic describes some of the reasons why you might change from the baseline pitch series.

Step 3 - Adjust as Required

   As we have repeated many times, one objective of this prop sizing concept is to allow for the adjustment of performance to not only meet differences in aircraft and engines, but also to keep pace with weather changes.  This fine level of adjustability is quite useful and powerful!

     Even when you use the selection methods described here, you may find that you cannot meet your needs within a specific diameter series. In that case, you must more to a smaller or larger diameter as the situation dictates. The line of Vess Propellers is ever-expanding and will eventually include enough sizes meet virtually any requirement.