QuadPlane Pitches Up using v3.8.0 beta 5

Lol Alexander, we wrote the same thing. I really think that’s the problem!

It’s compounded in forward flight in that during the transition there’s lift on the wing as well.
The easy test would be to place a camera facing along the wing and then fly around in hover and yaw and climb at WOT.


I think you guys may have nailed it! I took a snapshot of the video below. I can certainly believe a structural issue on this larger Ranger EX frame when compared to the Bix3…thanks!

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Looks like the entire wing is loose: see sec 6-8 of your above film


NP Greg.
I just saw your post now and watched the video, and said to myself, wait a minute that doesn’t look right!
The picture confirms it 100%. I’d try mounting the boom across the fuselage, they don’t have to be that wide btw. but that would completely get rid of the problem. Most wings, especially foam ones aren’t designed to take torsional moments.

Greg one other thing. Looking at it from the side in the last video it looks like you quad arms are too long in front of the wing. Do the quad and plane COG/COL match at all? The lever of the longer front arm means the loads between the motors aren’t balanced across the wing, so any quad lift will cause the wing to twist. To me it looks like the center of the arms is well forward of the plane COG. I’m not sure exactly where the Ranger CoG is though. I’d definitely check that. A QP will fly in quad mode even if the COG/COL is out.

Also your quad arms are quite far apart, you could try moving them much closer to the fuselage in as this should reduce the twisting. You can actually put them about 1.5 times the prop diameter from the fuselage. We do this all the time, typically QP don’t have any roll authority problems so moving them in is fine. Just test it carefully in hover to see if there’ any roll control issues before transitioning. It might need to be re-tuned as well.

Thank´s Greg for share all your unvaluable experiences; perhaps it´s usefull too reinforcing wings with CF cloth as I did with my flying wing First Phantom FX 61 VTOL but enlarge them up to fuselaje, that´s looks to give more rigid to the wings too. After your videos and Iskees advertise I´m waiting new motors before try to fly, good quad looks mandatory not to crash :slight_smile: . Anxious to give a try .

@JeffBloggs I guess great minds think alike! Lol. That is exactly what the issue issue after further evaluating. Taking it further, I’ve also tried building an Octa quadplane out of the ranger but noticed there is a significant amount of torsion (impossible to even maneuver properly in hover mode). I as well have my booms under the main wings. Seems we are going to have to find an alternative. That’s why I was thinking of an additional cf reinforcement to address the torsion. Another idea would be to maybe encase the wings with some type of fiber glass? This way we significantly increase the strength and ability to resist torsion forces. Thoughts?

The quad arms are placed to maintain CG with the standard wing. I try to design my QuadPlanes so that I can easily change to a spare normal wing and use APM Plane when a landing strip is available.

I think I will try some struts, first only on the back quad motors to the fuselage and then near the front quad motors, only if needed. In this manner, I can still easily connect/disconnect the QuadPlane wing or use the normal wing.

Time will tell…thanks for the help!

Lol yeah! :slight_smile:

I just checked the first video again and it’s really hard to see the twisting there.
I don’t have a Ranger, but I so have a Skywalker 1880…and that thing was as twisty as a curly fry!
It’s been stuck on top of a cupboard for the last 5 years.

As mentioned in one of the posts to Greg, quad arms structurally just don’t belong on the wings at all. Just because most other QPs are built like that doesn’t mean it’s right. The only “perceived” advantage of having the arms parallel to the fuselage is that one would think it reduces drag. But it’s not as simple as that because there’s a bunch of other factors at play.

It really depends on why you want a QP. If you want to hover around and look at things close range it’s better to use a quad. If you want to go further, faster and for longer then a plane is better. IMHO a QP should only give the aircraft VTOL capability, but for most of it’s flight it should use it’s really efficient wings, not it’s inefficient motors. You can’t have an efficient hover on a QP because there’s just too much “plane weight”, but you can reduce the quad weight substantially while actually improving the plane performance from stock after a QP conversion. Birds have wings and not props for a reason!

So if the above goal of “only VTOL” and then fly with the wings is the goal, all the design parameters change. The biggest differences are 1) you can nearly neglect hover efficiency and go for the smallest possible quad propulsion setup that gives you enough lift and control 2) you don’t have to configure your forward motor to produce static thrust for takeoff, and can completely optimise the forward motor and prop for best forward cruise. If done like this, in our experience a QP conversion results in a platform VTOL, carry more batteries/payload and fly further and faster than a stock plane can.

If you like you can take a look at what we use on our “Mozzie” QP the beta docs are here.
We’re going to be releasing the docs publicly once we finally finish the flying section.

No problems. I’m actually pretty glad it wasn’t a AP bug…I don’t like those at all, because they tend to be platform independent and I might catch it too! :slight_smile:

Although I can see the reason to have a quick way to convert it back to a normal non-QP, I think you’ll only get the most out of it if you configure it to always work as a QP. What are your mission goals with these platforms, or is it just for fun and try it out? I’m not sure if reinforcing the wings will completely solve the issue, so depending on what you want to achieve I’d maybe look at another airframe. Structurally that Ranger just doesn’t look up to the QP challenge in my opinion, and adding structural elements to compensate might end up being counter productive.


I like the Mozzie…thanks for sharing! I can see on some of the designs like the Mozzie and Darrell’s X8 QuadPlane wing that by eliminating some of the normal plane capabilities you can alleviate some complexities. My Ranger EX can still take-off using a normal wing but can also become a QuadPlane. This creates additional trade-offs.

On the medical transport subject, my standard gimbal mount from the FireFLY6 is mounted twice on my Ranger EX since it can carry more weight. Here are some images from my OpenGrab EPM dump of a FirstAid kit.

Nice! I like the delivery method.

One of the guys in our group also has a Firefly but we are yet to fly it.
Really need to give it a go, it has a bunch of nice running gear on it.

Are you trying to create a medical delivery platform? What range/payload is required?


I don’t have any requirements other than hobby fun and interest. I do have a second FireFLY6 that I will likely convert to Plane tiltrotor during the winter.

What is the base model for the Mozzie? Is it hobby based or proprietary?

Edit: I see now that it is a XUAV Mini Talon.

Here are a couple videos of the same Ranger EX QuadPlane conversion as mine but using the PX4 stack. His was copied from mine using the same boom length and offset but mounted closer to the fuselage. I’ll admit that his don’t wobble as bad as mine but it seems to work fine. It will be interesting to see the result after my strut installation. Perhaps I need to tweak my gain PIDs as well.

Hi Greg.

I’m quite passionate about designing stuff to meet goals, so sometimes I spoil the fun! :slight_smile:

That 360 video of the other Ranger QP is also quite revealing, in that it still has a lot of arm movement albeit less wing contortion. I’m pretty sure that the wings/structure will fatigue over time. After watching that I really think the ranger is better off being hand thrown or bungee launched and land it with reverse thrust for STOL rather than being run as a QP if you want to keep the arms on the wing.

How much do you think your Ranger weighs without the QP components? The spec says it’s about 1.5kg without batteries? If its under 2.5kg or so I’d recommend building the Mozzie quad arms and propulsion system that can be found here and attach them to the Ranger instead. Parts are listed here. They can still be dismounted with just two screws for normal non-QP flight, but only weigh 150g per arm and still produce 4kg of thrust which would be ample for the Ranger 2.5kg airframe. The only thing I’d possibly change is increase the width of the arms by about 50mm as it looks like the Ranger is a bit wider than the Talon and you might have to bush the mounting method to fit the Ranger fuselage curvature better. I’m 100% confident that it will not only fix all wing twisting but also improve quad hover control, will hover at around 40A, and will reduce the forward current draw if you optimise the forward prop for cruise.

The biggest problem with most RC aircraft is that propeller efficiency is so low. Most RC aircraft only operate in the 10-20% with around 40% being the high end. So in simple numbers this means that if you improve your prop/motor efficiency by just 1% on a 10% efficient setup, you’d increase your range by 10%. If you go from 10% to 20% or beyond you get twice the range just by optimising your prop/motor and without changing anything else. This is why aircraft are designed from the propeller backwards for efficiency, Most RC planes don’t do that because they a designed to either imitate a larger aircraft or be more aesthetically pleasing or easier to construct. Prop optimisation works especially well with QP’s because one can completely ignore specifying props for static thrust for takeoff and have a prop that is only optimised for the best cruise. (which is another thing that needs to be tested to find out where it is on that particular airframe at that weight)

Let us know how you go.

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Although I am in agreement with all the feedback provided in regards to locating the boom under wings, I’ve still seen many successful Ranger conversions work this way. For another quad conversion, I would definitely go with a “mozzie” setup. But in an effort to complete a successful conversion for the ranger, I strongly believe the “sweet spot” to its stability is bringing the booms closer to the fuselage. The farther from its main support, the more succeptible you are to higher levels of deflection and torsion. This will also allow you to avoid having to retrofit any struts or secondary framing which may lead do additional issues. I’m considering doing the same on my end. Is the person in the video an ardupilot member we can reach out to? I think it would be beneficial to bring him in to this discussion. I would invite him to hear his thoughts and feedback.

Sam (who I keep calling Jeff),

I agree with and appreciate your feedback. I’ll admit that the Mozzie mounting technique is a better approach to eliminate wing torsion. I missed the wing torsion issue on the Ranger EX since I had not seen it on the smaller Bix3 conversion. The Ranger EX (like a Skywalker) is a great flying FPV plane for long distances. Since parts are available from multiple vendors, it seemed like good candidate to convert to a quadplane with little effort. My goal of keeping the stock plane frame, so that it can be converted to a quadplane with just a wing change, has created additional trade-offs.

I will still try mounting some struts (or thin braces) to see if it fixes the torsion issue. These can be easily connected or disconnected while not losing the normal plane functionality. I will also glue some flat carbon rods across the wing chord to help reduce its ability to twist. You can see from my videos that the Beacon Foam Tac really creates a tough bond between the square carbon tube and the foam wing. With all the torsion and crashes, they are still bonded, so it would be a difficult task to remove them without destroying the wing.

I also plan to build a Mozzie as I now see the benefit of a dedicated quadplane design. A frame like the Skywalker X8 wing that Darrell converted is another good example. Many of us would love to have his machine shop! :slight_smile:

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He is RC Groups member, rollys, who posts on my RCG APM thread here. He is using the PX4 stack with QGC.


I have a few off-topic questions on the Mozzie.

  1. Will someone be selling the 3D printed parts as a kit?
  2. What is the purpose of the Companion Pi?


Hey Greg
I don’t really have any plans in selling the 3D printed parts, but I could if you want me too. Not sure what the freight to USA is but I can find out. Alternatively there’s the option of printing them at a local maker group or store, or an online producer like 3dhubs or shapeways etc. If you don’t need the CC or avionics enclosure/camera gimbal etc, you only really need to print the quad arm 3D parts and can use the timber parts that come with the mini talon instead to build a QP. (In fact that’s an idea I’ll add to the instructions as well!)

The CC Pi is for imaging using the picamera and to georefence images to find Joe in the OBC/MEC. It also runs 4G modem and/or wifi, which you can stream as well if you want. we’re currently working on a updated CC image using fnoops Maverick.

The idea is to provide a reference platform for everyone that is capable of completing the Medical Express Challenge.