DSSS (Direct Sequence Spread Spectrum)

A 2.4GHz radio system which selects one (or two) of the available "free" frequencies and transmits only on the one(s) chosen. Like FHSS (Frequency Hopping Spread Spectrum) systems, it is resistant to electrical noise. See also: FHSS.

Wikipedia: In telecommunications, direct-sequence spread spectrum (DSSS) is a modulation technique. As with other spread spectrum technologies, the transmitted signal takes up more bandwidth than the information signal that modulates the carrier or broadcast frequency. The name 'spread spectrum' comes from the fact that the carrier signals occur over the full bandwidth (spectrum) of a device's transmitting frequency. Certain IEEE 802.11 standards use DSSS signaling.

---

DSSS - Direct Sequence Spread Spectrum
Direct Sequence Spread Spectrum (DSSS) is a spread spectrum technique whereby the original data signal is multiplied with a pseudo random noise spreading code. This spreading code has a higher chip rate (this the bitrate of the code), which results in a wideband time continiuous scrambled signal.

Direct Sequence Spread Spectrum
DSSS significantly improves protection against interfering (or jamming) signals, especially narrowband and makes the signal less noticeable. It also provides security of transmission if the code is not known to the public. These reasons make DSSS very popular by the military. In fact, DSSS was first used in the 1940s by the military.

DSSS can also be used as a multiple access technique, whereby several different pseudo random spreading codes are being used simultaneously. This multiple access technique is better known as Direct Sequence CDMA.
DSSS is e.g. used in IEEE 802.11b and Zigbee.

Read More

Down Thrust

Down Thrust: Downward angle of the engine relative to the centerline of the airplane. Down thrust helps overcome the normal climbing tendency of flat bottom wings.

Read More

Ding

Minor dent or damage to the structure. Also, a nick in a prop. Dinged props must be replaced.

Read More

DSC - Direct Servo Control

This radio feature permits you to check servo operation without broadcasting a radio signal. A cable connects the transmitter to the receiver. Direct servo control is very useful for on-the-ground control checks.

Futaba Description:
Direct Servo Control (DSC): High-end convenience feature which allows control/adjustment of servo function without sending signal through receiver. Requires optional DSC cord (FUTM4250) and DSC-compatible receiver such as R149DP and R113IP.

Read More

Dihedral, Dihedral (Aircraft) Angle

Image: Dihedral

Dihedral:

The V-shaped bend in the wing. Typically, more dihedral causes more aerodynamic stability in an airplane, and causes the rudder to control both the roll and yaw axis. This is why some trainers and sailplanes require only 3 channels of radio control--i.e., having no ailerons.

Image: Dihedral Angle

Dihedral Angle

In the illustration above, A and B are two separate planes lying perpendicular to another plane C. The dihedral angle equals zero between planes A and B.

To demonstrate a dihedral angle greater than zero, first let aA and aB equal 90 degrees. Second, let plane B rotate around the line where plane B and C intersect while letting plane A remain perpendicular to C. For example, let aB (the angle where plane B intersects plane C) equal 60 degrees.

The dihedral angle (represented by the symbol J) between A and B now equals 30 degrees. This can also be viewed as the illustration below.

Dihedral (Aircraft)

Dihedral angle is the upward angle from horizontal of the wings or tailplane of a fixed-wing aircraft. "Anhedral angle" is the name given to negative dihedral angle, that is, when there is a downward angle from horizontal of the wings or tailplane of a fixed-wing aircraft.

 Schematic of dihedral and anhedral angle of an aircraft wing.

Dihedral angle (or anhedral angle) has a strong influence on dihedral effect, which is named after it. Dihedral effect is the amount of roll moment produced per degree (or radian) of sideslip. Dihedral effect is a critical factor in the stability of an aircraft about the roll axis (the spiral mode). It is also pertinent to the nature of an aircraft's Dutch roll oscillation and to maneuverability about the roll axis.

 Measuring the dihedral angle.

Longitudinal dihedral is a comparatively obscure term related to the pitch axis of an airplane. It is the angle between the zero lift axis of the wing and horizontal tail. Longitudinal dihedral can influence the nature of controllability about the pitch axis and the nature of an aircraft's phugoid-mode oscillation.

When the term "dihedral" (of an aircraft) is used by itself it is usually intended to mean "dihedral angle". However, context may otherwise indicate that "dihedral effect" is the intended meaning.

Image: Anhedral angle

Source: Wiki

Read More

Differential Throw

Differential Throw Ailerons
Ailerons that are set up to deflect more in the upward direction than downward are said to have Differential Throw. The purpose is to counteract Adverse Yaw.

Radio controlled aircraft with ailerons can benefit from differential throws of ailerons. Aileron differential means that the aileron that moves upward needs to be deflected by a larger angle, and the one that moves downward is being deflected by a smaller angle. This results in a more coordinated roll of the aircraft because if the aileron throws were the same, the equal angle of downward deflection causes more drag than lift for the upward moving wing, slowing the wing down and causing the aircraft to yaw in the direction opposite to the desired direction of turn (if any).
     While desirable, differential aileron throws is not really a critical flight function and is not implemented in many lower-cost computer radios. And, of course, it is not at all available in simple, non-computer radios. And if you sensibly choose to drive both ailerons with one servo then transmitter programming is of no use at all.
     There is a simple way of accomplishing differential aileron throws mechanically, by positioning control horns away from the hinge of the control surface. On this page we provide simple charts that allow one to measure and position aileron control horns to get precise maximum throw angles while achieving the desired differential.

To use the charts, first make a note of the deflection angle you need and of what percentage of the upward deflection angle you want the downward deflection angle to be (the differential). Next critical parameter is servo arm travel. This parameter is what you can change by placing the aileron linkage in the different holes in the servo arm.
 Next, follow the links in the table below to find the servo arm travel that will enable you to select the horn offset and clevis height, while giving the desired deflection angle and percentage of differential. Make sure that you use charts for the same servo arm travel.
Source: http://www.rcmix.com/diff_ailerons.html

Read More

Dead Stick

A term used to describe unpowered flight (glide) when the engine quits running.

With the engine quiet and the plane ready for takeoff, Steve coaxes the Highlander into flight. The plane gains speed as it coasts down a steep hill and before long it is airborne. Now gliding through the air, the engine remains off; Steve brings the plane in, landing it just as he took off: completely deadstick. The shear excitement and joy from this maneuver is contagious. Not only do you easily feel Steve’s enthusiasm for the feat he is performing,
but you also feel his love for the air and for his plane. Without the Highlander this would be nearly impossible.  However, due to the unique qualities of the plane, Steve was able to master this act and share his joy with the world.

Read More

2 Wheel-Drive vs. 4 Wheel Drive

As in full-scale cars, there are two main drive types: two-wheel drive (2WD) where power is supplied to the two rear wheels, and four-wheel drive (4WD) where power is supplied to all four wheels. The 2WD vehicles are less expensive and require less overall assembly and maintenance than 4WD vehicles. Assembly and maintenance for 4WD vehicles tends to be more involved, though not necessarily more difficult; the trade-off is that 4WD vehicles offer better steering through turns.

Read More

Differential Throw

Ailerons that are set up to deflect more in the upward direction than downward are said to have Differential Throw. The purpose is to counteract Adverse Yaw.

Read More