Elevon Gyros.
This tutorial will go over the installation of 2 gyros (Label Up style) onto an Elevon controlled airplane. This method will NOT use an external V-tail Mixer but will require V-tail mixing in your Transmitter. The method of using 2 gyros will stabilize both pitch and Roll of the plane. Because a single elevon will affect both the pitch and roll of the plane, the gyro will need to be installed at an offset angle. In my example I am showing a Gy48V from HobbyPartz. These are Piezo sensor gyros that are inexpensive, built well and have a nice flat surface to mount on each side of it's cube type enclosure.  Both gyro's gain wires will be connected through a splitter to a single channel to adjust the gain. I will show you how to set the gain switch for OFF(low rate gain) and ON (Rate gain) which is how I recommend you set it up for initial flying.   

IMPORTANT: You should install the gyros onto a plane that has been test flown and trimmed out FIRST before installing the gyros. You should MECHANICALLY adjust the trims on your airplane using linkages or repositioning the servo arms to be centered.  Remove all Subtrim and trim from your airplane and keep mechanically trimming the airplane before moving further. PLEASE refer to RCGROUPS or RCUNIVERSE or just google "ELEVON SETUP <insert your radio>" to figure out how to setup Elevon mixing. It is typicall that swapping the aileron/elevator channel and/or servo reversing is needed to get this done. Once again FLY THE PLANE w/o the gyro installed first to validate your setup.

1) Choose and purchase a gyro.  I recommend the Detrum GY48V gyro from Hobbypartz. This gyro is easy to mount because it is square with flat sides. It also requires no modifications because the gyro is held well inside the case and the cables are strain relieved.

2) Follow the drawing below for Gyro connections.  You will need a servo Y splitter to connect up the gain.  Note that the label of the gyro faces FORWARD AND RIGHT for the Right servo's gyro and FORWARD and LEFT for the LEFT servo's gyro. (This is valid for a LABEL UP style gyro like the GY48V)

3) Power the TX on first, then the RX. Let the airplane stabilize for about 10 seconds before moving.  With all the connections shown above, you should be able to flip your gain channel and both GYRO LEDs should go on and off (both should be on at the same time or off at the same time).  With LED off, this is RATE mode. With LED on, this is Heading Hold (HH) mode.  Flip switch so that LED is off (Rate mode) At this time, travel adjust for Gear Channel should be 100% on each direction.  
4) Pitch the plane up/down.  When you pitch the plane's TAIL down, BOTH Elevons should move down. When you pitch the plane's TAIL up, the elevons should both move UP. If either elevon does not do this, change the reverse switch on the cooresponding gyro.  
5) Roll the plane left (lift the right wing up). The right Elevon should move UP and the left should move DOWN.
6) Move your aileron stick right, Right elevon should move up and left elevon should move down
7) Move your elevator stick back (towards you). Both Elevons should move up.
8) If after performing STEP 4 above, Step 5,6,7 is not correct, then you are going to have to play with servo reversing, gyro reversing and possibly swapping the Aileron/Elevator channels.  YOU MUST be able to pass the test in steps 4-7 before flying.

Adjusting Gain in Tx
9) Rember how one gear switch setting turned the LED on? Well set the switch to where the LED is on. That's Heading Hold mode, we don't want to fly in that mode. Now, adjust the Travel adjust for Gear channel all the way to zero. (One or both LEDs on the gyro may turn off at this point).
10) If either of the Gyro LEDs are lit, then adjust the Gear subtrim until both Gyro LEDs are off.  Go about 2-3 clicks beyond the point where the gyro LED turns off. This is now your gyro OFF switch position.
11) Verify now that moving the airplane does NOT move the elevons.  Also verify that moving the sticks still yield the correct elevon movement.
12) Flip the gyro switch in the other direction.  Now adjust the travel adjust for the gear channel to about 30%. This will be our initial setting for flying.  

Adjusting Travel Adjust
12) With gyro switch in RATE mode, adjust the travel range of the Elevator movement per the instructions of the manual for your airplane.  You will NOT use the Tx for this, the TX should be set to 100% travel adjust already for aileron and elevator.  Pull full back then turn the LIMIT dial on both gyros to get the desired elevator movement.  
13) Since the gyro's limit dial affects both aileron and elevator movement, you can now test aileron movement.  If you think there is too much, you can turn down the aileron dual rates or travel adjust in the TX. note that, you may not see the movement in the elevons, but when the airplane is in the air, the roll rate will be reduced whenever you have the travel adjust/dual rates for either the elevator or aileron set below 100%.

Initial test flight and adjustments
Now for the moment of truth. Before EACH flight, make sure you power up the plane AFTER the TX. Also to let the gyro sit for 10 seconds before moveing it. Do a control surface test. Then move the airplane and verify the elevons are moving corretly (steps 4-5 above).  Do your first flight at 30% gain.  If the plane wobbles/oscillates at any time (especially in a high speed dive) then turn down the gain.  You can also adjust the angle of the gyros to compensate for oscillation in one direction or the other.  For example if it's oscillating in the roll axis but you want more pitch stability, instead of turning down the gain, angle the label of both gyros more towards the sides. If it's oscillating in the pitch axis but you want more roll stability, then angle the label of both gyros more forward. Move about 5 degrees each time you try as a recommendation.

Video of Flying Dog House with 2 gyros on an Elevon setup.
This was my first venture into elevon gyros in 2011. Before adding the gyros, this plane was a real pain to fly and even worse to land.  I really lost aileron controllability on landings and almost always flipped it over. With the gyro, only my nose wheel became my issue.  Flying it was like it was a totally new plane.