SLOPING OFF...
...the Newsletter of Christchurch and District Model Flying Club for...March 2025
A10 Thunderbolt 11 “Warthog” EDF build from the Flite Test kit - a tale of three first flights
by David Bicker
A10 maiden flight at Win Green on 2nd Feb 2025
In conversation with Frank Bayes at one of the indoor flying sessions at Broadstone sports hall, Frank mentioned that he had a spare Flite Test depron A10 flat-pack kit that was available to buy as he had bought 2 kits. Having then watched the Flite Test build video (some 3+ hours long!) and some videos of it in flight, I thought that it might be fun to see if I could build one aimed at slope soaring.
The base kit was £50. What you got in it was a shrink-wrapped stack of waxed paper-coated sheets of pre-laser cut and marked Depron, some light ply, a fairly sparse bag of bits that included 3 wheels, BBQ sticks a few metal rods and a cover sheet with a picture of the built plane with a link to the build video online.
The videos showed that, although when built (if unpainted) it looked like it was made of cardboard, it had a great size and presence in the air, mainly due to the size and height of the side profile of the fuselage. It also flew very well too. Various builds were demonstrated using up to a 6S 3000 mAh flight pack. The kit is minus all of the power train and servos, so there is huge scope to build to your own requirements.
Having said that, the original Flite Test build is designed for 2x outrunners mounted in the front of the undercarriage pods so that they sit in front of the leading edge of the wing. I took an instant dislike of the look of it with props on the wings. Luckily, during the build video, he shows you that there are 2 ply mounting rings that are used to form and mount the ducts on top of the fuselage. With some future-proofing in mind, they had included 4 mounting points on each ring that they suggested could be used by builders who wanted to experiment with building it with in-duct props or in-duct EDFs.
I found several videos of builds with in-duct props and initially decided to try building it with my own take on the idea. Not being at all technical and not doing my research properly, I ended up with an interesting looking design with 3 bladed carbon fibre contra-rotating props mounted on each ring. This took a lot of time and hand crafting and resulted in a set-up that was totally inadequate and produced way too little thrust.
So that idea was junked and, after some research on EDF thrust and power ratings, I opted for 2x 64mm EDF. This set-up proved to work very well and is fairly quiet because the EDFs are recessed deeply inside the ducts, so there is little noise unless you are directly behind the plane
The EDFs are mounted to ply duct support rings with a strong 7mm ply 4 spoke mounting plate on the front ring and a 3mm Depron 4 spoke mounting plate on the back ring. The back ring mount is only acting as an alignment for the end of the 3mm Depron duct tube off the back of the EDF. This also helped to keep the weight in the ducts as far forwards as possible. There is plenty of air flow around the EDF as well as through it. The EDF duct tapers down to 85% of the FSA (Fan Swept Area). This was calculated excluding the surface area taken up in the duct by the outrunner. The duct length is just under 3x the diameter of the fan intake. The EDF is recessed 50mm into the front of the A10 duct and the rear of the EDF duct is 75mm recessed into the rear of the A10 duct.
The EDFs draw 27A & are rated at 278w each. The ESCs are 40A with 45A surge. . I mounted the ESCs outboard, between the duct mounts. This gives easy acces for changing them out and minimises the cabling lengths to the motors. They also get optimum cooling there.
Each EDF is powered by its own 3s 2200 35c Li-Po on separate power leads, with 3 RX channels used to produce differential thrust on the Throttle/rudder stick. TX used is a Radiomaster TX16S.
RX used is an 8 channel Corona CR8D. Differential thrust used Ch 3,4,5. Throttle cut on Ch3 on the Inputs screen to have global effect. ESC feeds on Ch 4 & 5. Differential throttle gives +30% on one motor and -30% on the other motor for steering as the model doesn’t have rudders.
In the Win Green flight video (YouTube link at the bottom), when I was making close passes in front of Andrew taking the video, the motors were just idling so that I could spool them up quickly if needed and I made the tight turns without using any thrust steering. Just ailerons and elevator. It turned out to be very stable and manoeuverable.
I went for the 3 wheels otpion as the original FT build had a design flaw in that, with the 2 wing mounted wheels only installed as per plan, the tail is always going to drag on the ground as the wheels are in front of the CoG. Being made of Depron, if you were flying off hard ground, I could see the underside of the tail wearing unless a tail drager wire is fitted.
The wheel pods include the motor mounts on the original build. I fitted the motor mounts for strength, but cut the front off the pods and shaped them to look more like drop tanks. So, having built it as per plan, I later on cut off the wheel pods and turned them around 180 degrees so that the wheels moved to behind the CoG, thus allowing me to add a nose wheel mounted on a ply base plate to reinforce the floor.
It now lands and sits with the tail well clear of the ground.
To balance it with the weight of EDFs and their heavy power leads fitted way behind the CoG, my battery packs are mounted about 300mm forwards of the original battery mounting position / velcro straps. It only required 39g of lead in the nose to balance with there being 2x 3S 2200’s in the nose section.
I added 2 extra Depron box sections in the nose section to slide the batteries into. A sliding Depron twin “ram” assembly pushes the batteries forwards & is then pinned in place by a BBQ stick across & through the assembly (side-to-side)
If you decide to build the plane with the motors on the wings as per plan, I would still suggest extending the rear end of the engine/undercarriage pods to be able to move the wheel mounts back behind the CoG if you want the ticycle undercarriage set-up.
QD Wing mounting
I devised a quick detach reinforced wing mounting with a reinforced floor at the leadng edge. I noted that when the wing was being fitted, the floor section in front of the leading edge bowed outwards. So I added a thin ply sheet to the underside of the floor. So now, the wing has a tongue that fits above the floor and the wing now fits over the extra ply tongue under the floor. On the underside of the wing’s trailing edge I added another ply plate. The plan method of attaching the wing is with rubber bands off dowels. I tried that and found that it quickly started to damage the trailing edge of the wing. So I added ply mounts over the end of the wing dowels and exetended them to allow a D-shaped cross-section 6mm dowel to to span the width of the fuz, under the new ply plate. Just withdraw the D-shaped dowel & the wing can be popped out.
As a side note, I also built up the wing tips with multiple strips of Depron so that the tips can withstand slope landings better. They looked a bit exposed and fragile without it.
The tailplane has been reinforced each side with 2x BBQ sticks on top & 1x underneath. Without these I found that when in storage and the fuz was sitting on the tail fins, the Derpon tailplane started to warp upwards quite quickly. I have also made a small removable tail stand now that keeps the tail fins off the worktop.
Non-standard barn door flaps were added in-board of the wheel nacelles, deployed with a switch on a 3 second delay so that they drop slowly & smoothly. The plane doesn’t change attitude when they are deployed, just slows up & flies normally.
Finally, some initial build advice:
If you opt for the EDF route, leave gluing the A10’s front and rear duct cones off until you have completed adding your EDF mounts, EDFs, EDF ducts and cabling. I cut mine off twice due to design changes!
Leave the nose cone off until you have completed the rest of the build and reached the point where you need to balance it. I also found access through the nose helped when fitting the 2 battery housings in the nose. Experiment with your fine tuning weights. Hold the weights and nose cone onto the fuz with tape until you are happy to bond it on with hot glue. I cut the nose off mine 3x before I got it right!
Tech and Spec notes:
The AuW came to 2,2kg - 4.85 Lbs
Wing loading is 16.95 oz/Sq foot
CoG is 64mm (2.5") back from the wing leading edge
Throws: Ail: 16 degrees up (32mm), 8 degrees down (16mm)
Elev: 16 degrees both ways
Expo: 30%
Weight: Fuselage with 2x 3S 2200 fitted: 1550g
Wing: 650g
Balance weight needed: 39g
Maiden flight duration (with a fair number of full throttle climbs) was 7.5 minutes. The fully charged batteries were down to 40% after the flight.
YouTube video link: https://youtu.be/zEBH8WW-aBs
Some more pictures taken on the day - by Andy Slightam
Subsequently, David was persuaded by the Ed of RCM&E to see if it would take off grass. During a rare visit to Oldfield, he did try but three cells just were not enough to gain decent airspeed and a small arrival took off the nose and disloged the wing (Maiden #2)
He then rebuilt the nose, took out the fans and SCs and replaced the big Lipo with a smaller battery, saving 500g. He then flew it again at Wing Green as a pure glider, where it performed well in a 12 -15 mph breeze. (Maiden #3)