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Crash Test Hobbies - Gladiator XL

After the wing was glued, taped, and laminated, it was time to start laying out the electronics on the wing.  Moving servos, batteries, ESC, etc. around the wing changes the center of gravity (CG).  Wings have a narrow CG range and being off a bit will make it an ill mannered performer, no doubt about that.  Because so much of the wing is behind the COG, sometimes extra weight must be put in the nose to balance things.  No one likes to do this since it means dragging around dead weight which cuts performance and reduces flight time.  Reluctantly, I ended up adding 80 grams of lead to my wing in order to get the CG where it needed to be.

Locating the required components in the best possible location to maintain proper CG is essential.  I started this by placing the components on the wing and holding them in position using masking tape.  This allowed me to check CG, determine if it was nose or tail heavy, move a component a little bit, and then repeat the process.  Once I optimized the placement of the batteries, servos, etc., it was time to start mounting them.


battery cutout in foam wing

Once again I turned to my Weller soldering gun I had previously used.  With the outline of the component drawn on the laminant, I carefully cut the laminant (and tape if present) and removed it from the wing.  I then melted a grid pattern, about 3/8" square and a 1/4" deep, into the foam that was to be removed.  Using a small needle nose pliers, I removed the small square pieces of foam.  Squeezing the foam and twisting it resulted in it being ripped from the wing, leaving a fairly clean area behind that was easy to clean up using the pliers to take smaller "bites" of foam. 

I'll emphasize that it's important to keep the fit between the foam and the component very tight.  In doing so, you help maintain the structural integrity of the wing, essentially replacing foam with other objects.  Running the hot tip of the soldering gun along the edge of the cutout area helps seal the laminant to the foam.  Be careful and don't overdo it.  The cutout in the above pic is for one of the two 3S 5,000 mAH batteries I use.  The batteries are a very snug fit but not tight enough to trust flying without a battery strap to hold them in position.


servo cutout in foam wing

I'll also mention that it is important to make the cutout area deep enough so that it allows the components to fit flush to the wing surface.  Having components sitting above the wing surface disrupts airflow over the wing resulting in decreased performance.  Take time to make sure your cutout for an elevon servo, such as in the above pic, positions the servo correctly so the push rod is aligned properly with the elevon's control horn and it rotates in the correct direction.  With the tape and laminant already on the wing's surface, you don't get an easy do-over if you make your cutout in the wrong location. 


completed gladiator XL wing - top view

Here is top side view of my completed Gladiator XL wing.  During my next upgrade when I take this to an FPV platform, I'll do a bit of decorating on this side of the wing's surface too.

Here is a run down of what I am using after the initial build:

Motor:  RC Timer 3536 1450 KV
ESC:  Turnigy Trust 70 amp
Servo:  Blue Bird BMS-620MG Kg torque x 2
Battery:  Zippy Compact 3S 25C 5000 mAH x 2
Prop:  APC 9x7.5E & Crash Test Hobby prop saver
Rcvr: FrSky X8R full duplex telemetry
Trans:  FrSky Taranis X9D Plus 16 channel


completed gladiator XL wing - bottom view

The bottom side view of the Gladiator XL wing.  The red battery straps can be seen here.  The black and orange coloring was done with 3 mil tape.  It adds virtually nothing to the overall weight and is easy to apply.  It sticks very well to the laminant. 

Here is some more information regarding the build and weight of components:

Bare airframe, with everything taped and laminated, 790 grams
Lead added to the nose to correct CG, 80 grams
Battery pack, two 3S 5000 mAH batteries,  680 grams
RC Timer 3536 1450KV motor, 102 grams
Trust 70 amp ESC, 71 grams
Rcvr and voltage sensor, 22 grams
Servo, two 9 Kg torque,  102 grams
Prop, 20 grams
Misc (battery straps, push rods, servo leads, etc), 30 grams

All up weight is 1897 grams.

Motor performance is quite good.  The wing can go vertical easy enough.  If I put 4S batteries on it, I would need to upgrade the ESC for sure and most likely the motor as I'm near max power rating for the motor.  Here are the current draw numbers for the the motor:

50% throttle ~ 23.7 amps, 283 watts
100% throttle ~ 54.7 amps, 623 watts

After a number of satisfactory flights over one of my hay fields, it is currently on the project table again as winter cold and snow signals the end of the flying season.  As I mentioned previously, my next goal is to set this up for FPV flying.  I've acquired most of the extra components I'll need.  I'm using an Eagle Tree Vector flight controller (FC) and OSD.  This will be my first time using this FC. 

I've been spending a lot of time reading the Vector forums to ensure the first flight with it will be a good one.  Getting the new components positioned on the wing, without messing up my CG, will be the next challenge.  I'm hoping that I'll be able to remove some of the lead I previously added but not sure if that will happen.  If not, hopefully I'll be lucky enough to not need any additional lead to correct the CG. 

I'll provide a link in this write-up when I start the upgrade on the wing.  Here is some footage of the maiden flight.





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