Do you really need V-tail differential on a Monarch ?

From Joe Hahn

Hi Mike.

Differential ruddervator travel is VERY MUCH an individual pilot preference. Most Monarch guiders prefer it (including me!) as it tends to help eliminate the nose-up tendency/airspeed loss(and possible tip stall) that is induced when entering a turn. A properly executed turn is one in which the airspeed- from wings level to wings at desired bank angle-either stays the same as the cruise speed or is slightly higher, as stall speed increases with bank angle. Differential helps to "automatically" create this situation with minimal or no pilot input, or at least it creates a more "manageable" or "natural" feel on the sticks.

The differential typically desired is that which gives you about 2 "parts" of up to 3 "parts" of down travel in the control surfaces. On the Monarch series(and Wizard), this can be achieved mechanically very easily by angling the servo arm towards the tail approx. 30 degrees with the tail surfaces and transmitter controls at neutral. This automatically induces more down elevator travel than up. Experiment with the servo arm angle until the handling suits YOU(the YOU part is important, as this adjustment is very dependant on the individual pilots preferred "feel" on the sticks!!). How about that--differential without a computer radio!!!

Hope this helps. Please let us know if you have any other questions.

Joe
DJ Aerotech

An additional response from Don Stackhouse follows...

Mike, I have just a few additional comments. What Joe says is quite true, and it definitely is a matter of personal preference. Unlike Joe, I personally prefer to set mine up for neutral response; i.e.: no change in pitch when making a pure rudder input. Just my personal preference. My setup is enough different from Joe's preferred setup that if he lets me fly one of his models I usually end up crashing it! (I honestly don't understand why he still lets me anywhere near his transmitter anymore!)

However, even getting neutral response frequently requires a small amount of differential. The reason is because the fuselage and adjacent tail surfaces create "end-plate effects". Because the geometry of this is not the same for both sides, and because the pressure fields around the two tail surfaces interact unequally, the force generated by the down-going ruddervator is usually not the same as for the up-going one with equal deflection. This difference causes a change in pitch whenever you make a rudder input if you have the travel equal for the two ruddervators (i.e.: no differential).

The exact amount of differential required to counteract this effect depends on a large number of factors, and will probably be different for each different model design and setup.

To see where you stand with your current setup, get the model in flight, not too high, and flying directly away from you so that you have a good, reasonably straight-on view of the tail. Give the model a strong rudder input, then watch to see if the tail rises or falls as it yaws to one side. When there is no change in pitch as the model yaws, you are at the differential setting that results in neutral behavior. You may or may not like it this way, in which case adjust the amount of differential and repeat this test until the model flies in a manner that is most comfortable for you. Then be careful not to let your friends fly your model, unless they like the same setup as you, or unless you really like to fix things!

Don Stackhouse @ DJ Aerotech