Firebird--Allows you to fly in high and gusty winds

L Edge

Master member
As the winds get higher and more gusty, fewer fly. The 2 keys to this type of flying relies on the plane as well as the skill of the pilot. Looking at the plane, the more stable it is, the higher the winds and turbulence it can handle.

So looking at the design of the bird, I chose to explore Sponz's "wonder series" with his approval and adapt it with devices. I also wanted it to fly low and near me rather than high and far distances within an enclosed tree area that causes wind havoc (unseen turbulence) and crosswinds. You can learn a lot more when the model is up close. Grant it, the closer to the ground, the odds go up in favor to the ground gods. I still do test myself and have paid the price at times.

1) Use of 4 large end caps to slow the roll rate down and help control the airflow.
2) I am adding the "UDDER RUDDER" just behind the prop which adds yaw control of crosswinds and high resolution at very high AOA at slow speeds and counteracting wing roll overs. Since the end caps essentially are a good length of the plane, the udder rudder was added at the nose for a quicker response time in yaw.
3) I am adding a modified leading edge slot found in early NACA videos that is used to increase stabilization of the wing.

Specs of my avain bird:
Eflite 370 motor Outrunner 920KV 3S 1300 lipo
APC 9x3/8SF prop with 20Amp ESC
L= 24"
Width = 33"
Fuse is 2" square
CG is 1" from leading edge.
5 servos with rudder, and 2 sets of elevons in wing and tail
Weight with battery 415.6 grams
Using just one layer of flat plate foam (no airfoil or k stuff)

I am being hampered by the fact I am running out of foam. So it is using 2 types of foam to finish it off. So far I have used 4 bundles of FFF (each 50 ft long by 4 ft high), 1 FFF bundle given to me (that is 1 sided re-enforced-same dimensions) and a 10 pack of dupron of different thicknesses and 28" wide by 42. That is a lot of models I have made.

This controlled my dimensions, so I eyed Sponz's and being old school, made my cuts out of paper until I felt "it looks good".

So cut the wing out and the back plate and hot glued them together. Again, going for a light weight plane.


Notice the small dimension between back plate and front wing and ailerons. That is for the end plates. Ailerons are 1 1/2" wide by 12" long. Elevator is 8 1/4" wide by (modified) 2 1/2" long.

Turning it over:


The strength of the wing is increased by using a carbon hollow rod(31" long) and notching out a groove in the foam and hot gluing it in place at 3 1/2 ' from LE. The rest of black crap is ink added by Dow, hard to get off,

Fuse is designed 2" wide by 2 3/8 down. At 2nd plate glue joint, it is narrowed down to 1 1/4 exit.
An opening behind motor mount is added so there is an airflow to remove heat from battery and ESC and flow out end. Added two servos to bottom of wing to be 1/2 the control surfaces which will be programmed as 2 sets of elevons. Reason that the 2 sets of end plates(large in size) slow the roll of the plane, so to overcome and gain rotational speed, 2 surfaces are better than one. Motor is 5" from leading edge of wing.


Position of 2nd set of elevons servos is using outer tube to eliminate bowing of wire.
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L Edge

Master member
Now that you have 2 elevons (don't forget to cut the elevon in half), you need to set up your radio. Depending on your radio, you may have to set up mixes to get the sets to work in unison. My DX9 allows you to assign the second set by going into the system setup, select channel assign and go to the assigned channel and toggle in ral and lal and when you go to model, it's assigned. So mine is channel 2 and 3 for front set of elevons and channel 5 and 6 for the second.


Remember, aileron deflection needs to be much more than elevator due to endplates. Total deflection is controlled by ATV. You can add expo if you want.

Next, the motor is mounted in front by using a thin bass piece so threaded screws hold the motor frame and then glued to blue foam. No right or down thrust. To have cooling to battery and ESC where it exhaust out at rear fuse, the wires are brought in from the motor in an enlargend hole between motor mount segment.


It ended up to get CG, battery, receiver, ESC were all pushed forward.

wonder battery.JPG

Rudder is really needed in gusty or windy weather especially to handle crosswind landings. Another reason it is necessary is when the plane ends up in high angles of attack in gusty conditions, no airflow can block the rear rudder, so no yaw. I built an "UDDER RUDDER" that can be placed in front or behind the rudder guaranteeing airflow to induce yaw.

Design is simple, you mount servo in either front or rear of prop. Take a very large servo arm and center it on the servo. Now you shape the foam rudder so it as high as the tip of the prop and about 3-4 inches in width. I average about 1/2" distance to the prop. Take the large servo arm off, position it so it is the right height and distance from the prop. Then, hot glue the foam (it better be perpendicular) to the servo arm and make small hole so you can insert servo screw into rudder to hook to servo. I am using a Hitec 55 servo where you can see the glue between foam and servo.

Actually, it is a very simple build and nothing very complicated. End plates are just shaped the way you want. I left 1/2" under wing plate and 1" under back plate so it allows clearance for elevrons.
Here is what it looks like so far. Notice the prop is vertical to show the gap between prop and UDDER RUDDER.


In my test flights, I found that with low throttles, the reaction to the rudder is slow(all those endplates), so to accelerate the process, I did this.

We tend to add expo to our control to slow servo movement around the center point. Spektrum call it positive expo. Negative expo is just reverse where it give a lot of servo movement with a small deflection of the rudder stick.

This is what I did with Firebird rudder. Flying in high and gusty winds, concentration and quick control movements are required to keep it upright. It now requires adjustment to your normal style of flying and provides yaw when turbulence is strong.


So I use -30% expo on the rudder. It works real nice especially when you are making a crosswind landing.
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L Edge

Master member
This is Firebird all put together.
I added the stabilizer and checked it out in the wind.
It met my expectations.
Tomorrow will add the video.

Side view:


Rear View:


A flat plate weighing in with battery at 418 grams, less than a pound to do battle with gusty, swirly winds that can be flown at low altitudes.


Well-known member
This is Firebird all put together.
I added the stabilizer and checked it out in the wind.
It met my expectations.
Tomorrow will add the video.

Side view:

View attachment 232993

Rear View:

View attachment 232994

A flat plate weighing in with battery at 418 grams, less than a pound to do battle with gusty, swirly winds that can be flown at low altitudes.
What is the function of the orange piece on the leading edge?

Thank you.

L Edge

Master member
End plates, dual elevons and the orange stabilizer are the right ticket that make flying in gusty and swirling winds.

I used my trusting windsurfing meter to measure the wind speed that went from very low winds to gusts up to 25 mph. I fly in an enclosed area with trees about 100+ ft high all around me. Behind me to the right about 50ft are trees and to my left is a parking lot about 100 ft back. So the downwind airflow hits the behind right trees quicker than the left so the pattern includes a cross flow to the left. Especially the landing, a gust hit me from the right wing area, so by kicking in hard right rudder(good flow from the prop) kept me from flipping it.

The video shows tree branches moving and others very little, indicating swirly winds as well as in the audio. Notice flying above the tree line and below and how this model can wind surf to forging ahead with no sweat. Especially, I almost meet the ground gods near the end at very low altitudes due to a down draft. Notice the high AOA at times with wind and no problems.

What makes it possible is the end plates, dual elevons, rudder in front using negative expo, and the "stabilator" that insures it not rolling over.

Now, all I need is someone to make a design of SPONZ's "wonder series" with the above modification's and tested out so that FF community can build it.

I will do a separate thread showing the evolution and working variations of my "stabilator" models and what they can do. My motto is "build things that don't exist".

Thank you SPONZ.!!!!!