The tail of the Ultrasport 254 can drag sometimes on a flare. It is approximately 30" above the ground, when sitting on the ground, and is approximately 19'-6" behind the back end of the skids. This is an angle of 14.5 degrees from back of skid to tail. The Synchropter is currently 17.2 degrees. 

IDEA; The larger the controllable tail surfaces are (ruddervator only since rudder is fixed?) the less cyclic has to go to the rotor disks to achieve the same results. This will result in more minimum clearance between blades.

Consider having length of tail assembly about the same as a blade assembly. This way 1/ they will store in the same space & 2/ the boom will extend back beyond the blades because it is mounted to the engine mounting plate. 

The Ultrasport tailboom uses cables and they have some means of quick disconnect. 

The rudder at the end of the boom may have to be removable because the overall length of the tail will probably exceed the blade lengths. 

Consider making as 8-H-12 and reversing airfoils if upward lift is desired instead of a downward force as speed increases.

NO. Make 0012. This way 1 mold does both airfoils. 

When one rotor's blades are at azimuths of 90 and 180 degrees the other's are at 90 and 270 degrees. This means that the downwash striking the ruddervator from one rotor is very closed to being midway between the downwash pulses from the other rotor. This could cause a vertical vibration of 4P on the tail. There could also be an oscillatory rotational force on the tail at 2P since the downwash from the two disks will probably have some rotation and the port disk will have more impact on the port ruddervator there by causing a CCW torque on the tail. The starboard disk and ruddervator will then give a CW torque. As the forward speed increases the downwash will decrease and so will the vibration from this source. In fact it might totally disappear.

The tailboom must be built to take this loading and/or preferably to dampen it.

Question: How do they establish the airfoil and angle of attack on the horizontal stabilizer on a helicopter?

Answer 1 by Jim Burt: First, they calculate the requirement, second, they fabricate a test article according to their calculations, and third, they test it (wind tunnel and flights) until they have it right. The calculation considers the rotor design (articulated, semirigid, bearingless, etc.), the weight/balance/size of the airframe, and the intended performance envelope. Consideration of these factors gives the amount of rotor disk tilt that will be necessary to produce cruise and maximum airspeeds and the degree to which the airframe
will be inclined (no pun intended) to tilt with the rotor disk. The horizontal stabilizer is intended to counteract this tilt and level the fuselage in forward flight, which is why it is an inverted airfoil. The testing is required because theory practically never seems to translate into reality without some tweaking.
Answer 2 by Nick Lappos: Jim Burt's post was right on for the static trim part of a horizontal tail's job, where the tail airfoil and incidence (and area) are chosen to keep the pitch attitude in cruise at the right angle. It is a balance between keeping the nose up for less drag (since nose down means that the fuselage is developing negative lift) and the need for forward stick, which flaps the rotor, and induces continuous bending stresses. Shaft tilt is selected in conjunction with stabilizer incidence to balance the need.

The horizontal stab is also very important for dynamic pitch stability, so that the aircraft doesn't go wildly instable and pitch up or pitch down after a disturbance. The tail is larger than that needed for static trim to cover this case. In a maneuver, the lift on the tail switches from download to upload. What we hope is that the tail always has enough "lift" to counter the rotor's wish to just keep digging in and flipping the helicopter. Usually aft cg is the worst case, and we test for positive maneuvering stability, looking for the tail to keep the nose in place in a high G pullout. The way we can tell is to note if we need to push forward on the stick as we hold the G in a turn. If we have to use cyclic to keep the nose from accelerating its pitch rate, then the tail is not big enough yet. We then make it bigger, or reduce the aft cg, or add a Gurney flap to make it more effective.

" NACA investigated the problem and concluded that a horizontal stabilizer volume equal to 10% of the rotor volume would provide a solution. Modern helicopters generally follow this rule.

C.B., Rotorcraft Conference:~ Horizontal stabilizer ought to be located in "clean air" because it can't work in the propeller slipstream: This is one of Tom Milton's claims as well as many other people who ought to know better. I suppose it never occurred to them that the same laws of aerodynamics apply to the vertical stabilizer which works very will centered in the slip stream.

A plans built Bensen vertical stabilizer tracks the airstream very well as long as the engine is running; the pilot doesn't have to do anything to keep turns coordinated, but tracking becomes marginal when the engine quits.

This is due to the energizing effect of the propeller slipstream. Lets say, for example, that a gyro is flying at 50 mph with a 100 mph propeller slipstream, typical for a daggy gyro with a small propeller. Then, a horizontal gust produces a yaw angle of 10º. The angle of the propeller slipstream shifts, being the vector sum of the freestream (airstream) velocity and the propeller induced velocity, to 5º. But aerodynamic lift varies as the square of airspeed, the result being that a stabilizer surface in the propeller slipstream is 2 times as effective. The conditions given in the example aren't fixed, they depend on airspeed, propeller diameter and the thrust necessary to propel the machine, but fortunately, the stabilizer effectiveness is most improved at the low end of the speed envelope where the freestream velocity is too low for stabilizer surfaces to have much effect otherwise..  

D.J., Rotorcraft Conference :~ Would it be correct to agree with your position in that the 'aerodynamic lift' of the empennage's airfoil varies as the square of the resultant airspeed, up to the point where the resultant angle of attack exceeds the stall angle. Should the resultant angle exceed this stall angle then the stabilizing force would no longer be 'aerodynamic lift' but be that of vector summing only?

Assume the above scenario with the vertical fin in the propeller's slipstream. If the angle of attack were to increase from the 5 degrees to around 16 degrees or beyond then the vertical fin will 'stall' and the 'aerodynamic lift' portion of yaw correcting force will lost. Basically ~ no more power of 2.

I believe that this is the thinking that applies to the Bell's stabilizer since in autorotation the airstream will be 'hitting' the wrong side of an asymmetrical airfoil and the 'aerodynamic lift' will be lost.

Experimental verification of a simplified vee-tail theory and analysis of available data on complete models with vee tails