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FX-79 Buffalo QuadPlane Conversion

Thanks Greg.

I made some progress today. Need to trim the canopy in a few places and do the final CG adjustments. Have to head out of town for a few days tomorrow morning, but hoping to do my first hover test next weekend.

Wondering what you think of the following: I am thinking about doing my intiail quad testing with copter instead of q plane. Thinking I could auto tune the plane with quad autotune to dial in the PIDs. And I understand the landing algorithms are much better in copter than plane. Once I dial in the PIDs, I’ll load plane and set the q Copter PIDS. Good idea? Bad idea? Or waste of time? I don’t have a great understanding of PIDs so I thought this would be a useful exercise.



I’m not sure if it will be a useful exercise or not. I might save it as an alternative if you have QP hover problems. The most critical tuning parameters are Q_A_RAT_RLL_P and Q_A_RAT_PIT_P. Other than that, the yaw authority setting is largely based on personal preference.

In my previous QP autonomous testing with v3.6.0, the Bix3 landed nicely once the final phase transition bug was worked around. On v3.8.0, there should be no issues with autonomous QP landings. I will test this in the summer.

The main thing that you need to take away from your FF6 experience is that a hovering wing is not like a hovering copter. The roll and pitch PIDs may need to differ and the wind is not pushing on a symmetrical airframe. In the video above, when I tried to move from the right back to the left, the wind spun it clockwise and I didn’t fight it until things settled down. I will, however, enable active weathervaning for my next larger field test.

I graphed the vibrations, ThrOut, Voltage and Current from the first hover test. The vibrations were very low due to the mount that the Pixhawk lies on. The ThrOut setting of 42% and 33amp average hover current were much lower than when this power system was on my Ranger EX. I suspect the overall plane weight is less as I am using the same batteries. It looks like I have plenty of room for payload!

Hi Greg
Where did you end up placing the ESCs?

Ned Clark
Mobile 0419399201

Hi Ned,

Just look up at post 27 and you’ll see all 5 ESCs.

Winter persists in Upstate NY (and the rest of New England) in March 2018 so I decided to add the new Open Source Frsky Telemetry Script by Alex Yaapu. The LUA script works for newer versions of APM Copter and Plane.

A few prerequisites were needed. Both my Taranis X9D+ radios were upgraded to OpenTX v2.2.1. Using the FrSky Telemetry page in the Wiki, I added the appropriate Craft & Theory cable between the Pixhawk and X8R receiver. Lastly, the Serial 4/5 port needed to be set to protocol 10 for Passthrough.

What a fantastic telemetry script! I can’t wait to try it in flight this summer.

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That look´s too cool Greg…BRRRR!!!, If you didn´t your first transition yet, be carefull with your incidence, I had to change in reference the cuad, my first transition fails with the FX64, then it flies.

I am your advancement with a lot of interests, because it’s been a long time since I hesitated to turn my FX 79 into VTOL.
But my knowledge of arduplane is very limited …
So I confess that I would surely imitate you, if you allow me.
And of course I dare deep within me, hope you share your firmware setting …

Hi Eric,

Here is my param file from my initial hover test. The only change I have made since then is to set Serial 4 Protocol to 10 for Passthrough telemetry.


FX79_Hover1.param (16.1 KB)

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Hey Greg -

I’m purchasing the power system for my FX-79, and had a question. Was there a reason you have went with a smaller prop / higher KV motor combo than most others? I see a lot of 12.6 props with lower KV power plant being used on this wing, Just curious!

Hi Bill,

The combination was proven on several Ranger EX setups, including mine, and provides 746 watts at 51 amps using an APC 10x6 e-prop with a 4s Lipo pack. No reason to swing a 12" prop if you don’t need to.


Looking good! I did consider the FX-79 at one point but did run into some claims as @count74 mentioned. That’s when I decided to go with the RVJet. Now, if I can only get my lazy behind to go flying again, I’ll dust her off.

By the way, have you seen Marco Robustin’s FX-79 conversion? He’s got that thing well tuned to reliably and comfortably recover from a flat spin!

Anyway, good luck with the build and will be following the progress.


No, I haven’t seen that video before so thanks for the link. Marco is my hero! It’s too bad that he never seems to post power system setups or details on his projects.

The FX-79 performed as I would have expected. I have plenty of large wing experience and the videos I have seen of the FX-79 all show it performing well so I hope to have a good maiden transition soon.

I did a search and found more FX-79 videos from Marco. It looks like he had it all tested out in 2017 before I even started my project. I see that he also uses a Taranis X9D. I’ll see if I can find a list of components he used. There should no longer be doubt that the FX-79 makes a good QuadPlane and has plenty of payload capacity for batteries and cameras.

Ardupilot QuadPlane - Flight mode demonstration
VTOL (Buffalo FX-79) - First transition tests
Buffalo FX-79 VTOL - Full automatic mission
FX-79 Buffalo - Auto-landing (“3DR Pixhawk” with “APM:Plane V3.2.2”)
Ardupilot Quadplane - Recover a forced plane stall (flat-spin) with the copter

Yes, it is a shame that he won’t share his build specs and params. I think he’s avoiding any liability or being publicly blamed for problems when others copy his settings and the build fails or whatever. I had been following his videos for a couple of years now; since my re-introduction to the hobby after a quarter century hiatus. If he was more forthcoming and demonstrated some willingness to participate more in assisting the community forums, I may have gone ArduPilot instead of PX4 Pro. He just seem to make things look so simple and stable.

Interesting that Marco has the quad “bars” mounted so far forward on the wings. Wouldn’t they be far forward of the wings CG?

@Wmacky I actually experienced the same thing with my RVJet conversion. Even with a 10000 mAh 4S shoved all the way up front and a 2-axis gimbal and a GoPro Hero 3 in the nose, I had to move the rear quad motors with only about 1/2" clearance between its props and the pusher, then get the front motors forward enough to balance. I think you’ll find, when you look at other flying wing quadplanes, to be the same.

As far as I understand, the plane CG must be at the same spot than the multirrotor CG. Correct me if I am not right

Yes, that is correct.

I finally have this project on my testing radar so by mid or end of June it should be tested. This got me thinking about the next step, which would be converting the application to a mapping plane. For FPV, it is fine to have the cameras on the top since you use them for flying. For a mapping plane, it is typically an autonomous flight with cameras on the bottom. Some plane designs have landing gear like the Ranger EX. The FireFLY6 wing uses retracts and this has worked well. I’m not thrilled with the stick legs added to the Nimbus 1800 Mapping Version as it seems quite the afterthought for a $2200 design.

I came across this 3D printed design below for the 2-meter E-flight Opterra and it looked perfect for the FX-79 as well. So this will be my next step after transition testing later this month. I’m having them printed now.

Project Build and 3D Parts:
Electric retracts trays E-flight Opterra FPV wing 2meter

Retracts, Struts, and Wheels:
Servoless Retract with Metal Trunion 44mm x 41mm mount (2pcs)
Servoless Nose Wheel Retract with Steering
Alloy Straight Oleo Struts 115mm (2pcs)
Alloy Oleo Nose Strut with Wheel
Light Foam Wheel 5 Spoke (2pcs)
Emax ES3154 17g Metal Digital servo

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