Item 1105
DESIGN:
UniCopter ~ Fuselage - Tail - Stabilizer - Horizontal
Initial Consideration:
Note: It is appearing that a single boom, coming from the center of the propeller, might be the best. This is because there appears to be no reason for a horizontal stabilizer. See the bottom of this web page.
Consider this for the vertical stabilizer; OTHER: Flight Dynamics - Control - Twin Vertical Stabilizers
Note: The Horizontal Stabilizer may not be necessary. See UniCopter ~ Trim, Stability & Control - Stability - Angle of Attack Stability - Decalage.
Drawing:
xxx
Notes:
Consider mounting all or partially on top of the VS. The drag during forward flight will help (a little) in offsetting the drag of the body. It could be an inverted asymmetrical airfoil and will have approximately 8º negative pitch. Could the two sides have inverted dihedral (the free air is coming from above and the airfoil probably has a downward pitch also) and help (a little) with lateral static stability? With increased forward speed, they will come more into the downdraft of the rotor disks, maybe.
The dynamic pressure ratio on the horizontal stabilizer should be greater (approximately 1.0) with an elevated HS since it is out of the rotors' and fuselage's wake. In autorotation, it may be in the wake.
If the horizontal stabilizer is above the rotors and as far forward as possible it will be in the downdraft of the rotor during hover, climb and very slow forward flight. Is this an advantage or not?
The horizontal stabilizer should possibly be linked to the collective, so that its pitch goes down with the collective. It may have to be linked to the forward air speed as well, otherwise at high speed a lowering of the collective for autorotation may cause a severe pitch up of the nose. See graph on
[RWP5 p.70] Try to negate any need for this.Consider the Wortmann FX 74-CL5-140 Airfoil:
It has a maximum coefficient of lift of 2.4. The extreme camber should also provide good drag if it stalls.
Additional information: Wortmann FX 74-CL5-140 Airfoil , [Text RWP1 p.386], NVFoil program, Airfoil Browser program, UIUC Airfoil Coordinates Data Site, Airfoil Database
This blade is intended for sailplanes, and possibly other aircraft. I wonder what its maximum recommended speed is.
It looks like the Cl Max. might be around 10º. If this is the case and the craft was to exceed a nose down pitch of 10º could the downward force on the tail be quickly lost and the craft tumble forward?
Stabilator:
See
Ailerons:
The two sides of the H.S. could operate independently and be controlled by a gyroscope to assist with lateral static stability. The gyro would be overridden by all other control activity. This would only be beneficial during forward flight and be detrimental during reverse flight.
Outside Report:
Investigation of Aerodynamic Interactions between a Rotor and a T-tail Empennage by Erwin Moedersheim and Dr. J. Gordon Leishman
Descent:
The vertical and the horizontal stabilizer will probably be subjected to rotor vortices during descending flight and autorotation.
Consideration re Placing the H.S. in the Plane of the Rotors:
During hover and even more so during reverse flight, would the downdraft from the rotors attempt to draw the tail of the craft downward? Of course, lowering the HS will decrease its ability to assist with nose up drag in forward flight.
Investigation of Aerodynamic Interactions Between a Rotor and a T-tail Empennage The HS is in the plan of the (single) rotor disk and its center is 1.5R behind the mast. On figure 7 it is interesting to note that the induced velocity from the rotor appears to be exerting a downward force on the HS. Perhaps this downward force has a stronger CW moment arm about the craft's Y-axis then the drag of a high T-tail. In addition the empennage might be less weight and operate better in reverse velocity. ~ July 19, 2003 Consider this empennage configuration
Effect of Slipstream on H.S.:
The elevated H.S. is not in the
slipstream. Therefore, it does not have as much authority as it would if it was in it. Since the H.S. is imparting a downward pitch on the craft during forward flight, being out of the slipstream is probably good. If it was in the slipstream, the retraction of forward cyclic or the loss of power would result in the craft's nose pitching down.The HS will have to be larger if it is located outside the slipstream but the air velocity on it will be less. Therefore, the drag of the a HS inside the slipstream or outside the slipstream should be about the same.
Notes:
Gurney Flap:
Part 1 by Prouty: http://www.avtoday.com/reports/rotorwing/previous/0200/02rwaero.htm
Part 2 by Prouty:
http://www.avtoday.com/reports/rotorwing/previous/0300/03rwaero.htm
Concern re Use of Inverted Airfoil:
"Once a stabilizer stalls, either in descent or in climb, it loses its effectiveness as a stabilizing surface, since the changes in angle of attack are not accompanied by corresponding changes in lift. This has resulted in degraded flying qualities for some helicopters." ~
[Source ~ RWP5 p.70]
A Thought re Absolutely Rigid Rotors and the Need for a Horizontal Stabilizer:
The preamble:
The flight-control actuators on an airplane, such as the rudder, elevator (or stabilator), and ailerons are attached directly to the fuselage. They therefore give a rapid response to input.
The flight-control actuators on a helicopter are the pitches of the blades on the rotor, with the exception of the tail-rotor on single-rotor craft. The rotor(s) is loosely coupled to the fuselage and this results in a delay between the input and desired result.
It is obvious that greater rotor rigidity results in faster responses. This implies that a helicopter with 'absolutely' rigid rotors will respond to inputs at a rate that is similar to that of an airplane. Pitch change of the blades, when at the sides, will impart roll, just as ailerons do, and pitch change of the blades, when at the front and back, will impart pitch, just as a stabilator does.
The assumption;
Assuming 'absolutely' rigid rotors (or the closes thing to absolutely rigid), when the blades are at the back they will act as if they are stabilators. Since they act as stabilators there should not be any requirement for this helicopter to have a horizontal stabilizer.
In addition, when these blades are at the front they will act as if they are a canard and this pseudo canard will also contribute to the fast pitch response.
Further thoughts:
On a fixed wing craft, does the elevator combined with the stabilizer give a displacement [fixed amount of pitch] where as the stabilator give a rate of pitch [continual change of pitch]? Since the blades will probably act as stabilators, perhaps a horizontal stabilizer, perhaps a small one may be required.
From Sikorsky ABC Report 'Stability and Control Characteristics', page 1045-4 upper left corner:
"Figure 13. At 100 knots, the longitudinal control position moves 48 percent between steady maximum climb [+80%] and autorotation [+32%]. The aircraft is being modified with elevator boost and collective to elevator coupling to reduce the longitudinal control position change between climb and descent"
My preliminary thought: The high HS on the UniCopter and/or the elimination or reduction of the HS might negate this problem.
The 4º
precone should compensate for the flapbackConsider this for the vertical stabilizer; OTHER: Flight Dynamics - Control - Twin Vertical Stabilizers
Previous examples of rigid rotors and no horizontal stabilizer:
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Last Revised: March 4, 2007