Phantom FX-61 Flying Wing 114 km Flight


Hello all,

I just wanted to detail my small triumph this past weekend with this - my first blog. I have been building up to a 100 km flight for the past few weeks (months?) It's just something I've been wanting to do - and do it with budget friendly parts.  Data analysis and design optimization are things I enjoy almost as much as flying. Aero design and controls are not my expertise though, so this has been a trying but enjoyable learning process. Thanks to the knowledgeable folks here, and other forums, I gleaned enough tips to go for my own 100 km attempt.  Enough about me - on to the plane and flight!

Airframe: Phantom FX-61 flying wing by Zeta Science
WS: 1550 mm (61")


I chose this airframe because I have some experience with wings (DIY foamies), they are generally durable, and I was just tired of fiddling with/fixing my Skywalkers.  Failed launch attempts on my SWs (V6 and 2013) usually meant my day was done and time to get out the hot water and glue.  The Phantom has survived several rough launches and hard landings with very little damage to show.  The worse is to the canopy when it came loose during a cart wheel and was chewed up by the prop.  I also had a motor mount fail on the day of the attempt.  (more on that later)  The Phantom does not appear to be the sleekest of wing designs.  It has fat dual vertical stabs, upturned tips, and a lot of reflex in the airfoil.  It does make for a slow and steady FPV platform, which is what it was designed for.


Printed motor mount extension to move the light motor rearwards and help balance the batteries.  This, along with shaving down the curious horn shaped fuselage end, also considerably reduced the noise of the prop.


No additional spars other than bracing the top and bottom with lots of fiber strapping tape.
The ailerons were cut free and tape hinges were applied.  The hinge line was also sealed top and bottom with Blenderm.


Motor: Turnigy Multistar 4225-390Kv 16Pole Multi-Rotor Outrunner

Prop:  APC 10 x 10
ESC: Hobbyking YEP 40A (2~6S) SBEC

Batteries:  6S 7200mAh (2 X 3S 5000 mAh 20C + 2 X 3S 2200 mAh 20C) lipos

Control:  9x with er9x, FrSky 2.4Ghz tx module, D8R-XP rx

FC:  APM 2.5 (2.77 firmware)

Sensors & misc:  NEO-6M GPS, Airspeed (disabled for flight - not by choice), 90A RCTimer-style power module (needed for 6S I believe), and 915 mhz 3DR telemetry


On the ground, I ran the latest version of MP with the 3DR ground radio zip tied to a fiberglass driveway marker rod on a 10ft usb cord - very simple and cheap.

I designed the power system based roughly on a discussion here on DIYD.  (Wayne Garris' 170 min Techpod flight)  It was some time ago, and when I went back to check, I realized it was Reto Buettner advising Moglos - who just joined the 100 km club as well!  Well done Reto.  You should start charging a fee, or perhaps deserve a "100 km master" badge.


I will include the testing/tuning flights leading up to this, but felt this blog entry was getting long.  I'll add the preflights below.


The Flight
The winds were mild last Saturday so I decided to go for it.  There was a window in the morning with the afternoon bringing more wind and rain.  To make certain of the distance I decided to go to 7200 mAh of lipos.  This took some foam removal and a few frustrating hours of getting wires to fit.  I hesitate to cut the heavy gage wires and make a custom power harness, but that is really what should have been done.

My first launch attempt at the heavy weight (relatively) ended in a premature belly landing and flip.  Since I was still on the throttle trying to eek out the launch, the prop hit the ground and tore the motor and mount out.  My AS sensor pitot was also ripped out.  Desperate to fly with no end to crummy weather in the extended forcast, I performed field surgery with superglue and kicker.  I also disabled the airspeed sensor.  The second launch was not much better.  This time I cut the throttle to avoid snapping the motor mounton the ground, but the plane skipped up like a rock!  I hit the throttle and away she went.  Everything appeared to be working properly so I started the WP pattern.  Fast forward a couple of hours and here are the results!


Flight time:  2 hrs 37 mins

Total flying distance:  114 km

Battery consumed:  60% 68%

Ave current during Auto:  3.7 A  1.9A*

Ave power during Auto:  87 W  44 W*

Ave airspeed during Auto:  13 m/s

AUW: 2145 g

I am not sure how to attach the tlog.  It is 15Mb.

*I have edited the originally reported current valves (and subsequent calculated power values) to the correct values.  Thank you to frederic reblewski for catching the error.


It is strange to be able to photograph your own plane in flight.


Two of the guys flying FPV quads actually chased the plane around its circuit.  I got to experience a chase plane view of my Phantom as it navigated to WPs through a spare set of goggles!  One even advised me that my plane seems to be speeding up and slowing down throughout the flight - which was later confirmed in the tlog.  This was an unexpected treat to have a full scale flight instructor giving feedback from a chase "plane" like a real prototype flight.


Due to the early launch issues, the tail end of my flight missed the target window and the last 20 km of the flight were in gustier winds and light rain.  I still had plenty of juice left, but the conditions were worsening, so I brought her in.  After a 114 km flight, I greased the landing within 10 ft but still broke the motor mount off.  Resting voltage was still 3.75 V per cell.


All in all, it was a spectacular day in my book - one of the best days of flying in a long time even though I was on the sticks for about 3 total minutes!

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  • Trung, I'm curious now at Frederic's comment and did some calcs for my own edification.

    If I understand correctly you had 4 batteries aboard, 2 x 2.2Ah and 2 x 3Ah for a total of 10.4Ah of 3S, equivalent to approximately 10.4Ah * 11.1V * 3.6 = 415.6kJ of electrickery.  If you were cruising at 87W for 157 mins (round figures!) that would be 87W * 9420s = 819.5kJ which is an impressive 200% efficiency, assuming you consumed all your battery - but you didn't either!  

    Frederic's estimation of 50W average is still a bit pessimistic too, I fear, as this uses 471kJ - also more than the battery capacity.

    If you assume that you wound up at 20% capacity remaining, this yields an average flight power of 35.3W or 2.92kJ/km

    This is quite a pleasing number to me, because if I can achieve that kind of efficiency and whack a 4S 5800mAh battery in my Skyfun - currently recording 4.3kJ/km on it's maiden flight - I can theoretically get 100km out of 95% capacity.  If the airspeed really is varying as much as your graphs suggest, then tuning it for a more constant control should yield some more efficiency gains as well to top the landed reserve margin up a little further.

  • 3692942339?profile=originalphantom with 5500 Lipo. APM2.0 in a glassfiber case. only flown in FBW-A mode and manual mode. will soon do autonomous flight. but a fantastic bird. i am using airspeed sensor. have kept the cruise speed as 13m/sec. needs folding prop. normal prop flips the aircraft at touchdown.

  • Never mind, I just realiZed that you did so on page 2.
  • Very nice, I have the same airplane, I'm curious to see how you mount the apm inside.
    May I ask you post some photo of your setup ?

    Thank you.
  • 100KM

    @Austin, wow, 4 frequencies on board! Sounds like you'll be using up all of that real estate on the X8. Funny you link to that catapult. I've been thinking about how I would adapt that exact one to the Phantom. The wedge trailing edge holder won't work on the Phantom. Good luck with your competition.

  • @Nguyen - It's a lot of tech to complete the objectives of the competition :) It's AUVSI's SUAS competition:


    If you look at some of the previous years, you can see videos and details on what the competition entails. It's fairly broad and complex in requirements.

    Actually, the 5.8GHz is long range wifi with custom antennas on an antenna tracker, and even then we might not get more than a mile. It should allow us to stream pictures back from the camera and let us process them live, but it's really hard to get that range. We're using 900MHz telemetry, 1.3GHz video, 2.4GHz for multiple things, and 5.8GHz. I think the only thing we haven't used is 72MHz. We're also using a catapult launcher for our X-8, and I don't want to risk hand launching it and cutting into someone's hand, so it hasn't flown yet. Here's a link to the catapult we're building, you should be able to make something similar:


    I can't wait to see how long your plane will stay up in more ideal conditions! It's always exciting when someone hits 100KM!

  • 100KM

    @Austin, I definitely plan to get it back in the air. Yes a bungee or catapult would take much of the stress out of launching - especially chasing longer distance goals with more batteries. Wow, that sounds like quite a techno-payload. Will the 5.8 data link replace the need for 3DR telemetry? Range?

    @Moglos, It was probably the most exciting day at the field that I can remember. Lots of interesting things happening - from long distance auto flight, to a work-of-art wooden FPV ground station w/ antenna tracking, to a micro FPV proximity speed quad. The gentleman with the long range FPV GC station also has a Phantom and was really excited to make his own attempt. He lives ~20 miles from the field and can turn on his GC station and watch FPV video feed from the the field at home!

    I wonder if some of the swarm behavior from multis can be adopted by fixed wing. I am imagining a master/slave arrangement where only one plane is operated/monitored from a ground station while the slave(s) would only focus on holding a preset relative position to the master or its neighbor. I can see where multiple low cost UAVs could benefit most of the emerging applications like geomapping, crop monitoring, conservation, and perhaps SAR. I'm getting way ahead of myself. A tandem long range flight could be cool. I think this will be a good summer. Stay tuned!

  • 100KM

    @Frederic, Thanks for your calculations.  I agree the error is in the power number.  I simply calculated this from the measured I & V.  Since the V measurements tend to agree with my charger and lipo monitors, I think it's my current reading that is off.

    Would you or anyone know if APM does any scaling to the current reading, or if it simply records what is output from the power module?  Is there a calibration process to follow?

  • Fantastic work. Thank you for posting your 100+km efforts.
  • 300km

    Well done Trung.

    Especially well done that you pushed on even though things didn't start off well. Imagine if you had perfect conditions.

    I had regular speed variation on my 100km flight too but it wasn't as extreme as yours.

    Awesome to have some company for your flight (I read a book during mine) and even more awesome to have a chase vehicle.

    I bet the ASW28 would do 200km

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