Need help getting quadplane off the ground

I am building a quadplane for an engineering senior design project. We had a break from class recently and threw together a prototype that we could learn some things from.

It is a modified SkySurfer trainer plane. We put aluminum spars through the wings to support the aluminum channels used to hold the quad motors.

Current specs:
Pixhawk Cube Black
2-4s 30A Simonk escs
4S 4500mAH LiPo
2212-920kv quad motors
14" carbon fiber propellers
7.66 in prop pitch (measured, so probably not super accurate)
Push motor that comes with the plane originally (we’ll have to change this eventually, but for now we’re just trying to get the quadplane to hover)
Weight without battery: 1700g
Center of gravity slightly forward from the middle of the wing (battery being strapped on top for now)

This version of the plane could not get off the ground at all. We reduced the battery to a 4S 1500mAH and we could get it off the ground, but it couldn’t go any higher than ~1ft and it was uncontrollable (yaw issues, drifting one way or another). The control issues are almost certainly due to a misalignment of the quad motors, so we’ll have to do some adjustments to fix that. But first we need to make sure it can even get off the ground.

My first thought is that we need higher power, lower kv motors. 920 is too high for a 14" prop. At my school we have an extra set of 4 Tarot 4114-11 320kv motors, so I’m thinking we can use those.

I used the ecalc prop kv wizard to find a configuration that would result in a recommended kv around 320. I determined that we would have to increase our battery voltage to 6S to get the recommend kv down to our desired 320. Sticking with 4S would result in a higher kv.

Is that a good course of action for getting the quadplane off the ground? Or is there something else we’re doing wrong?

In this thread, I found someone who claims to have a working quadplane with the specs listed in the picture:

His quadplane is a similar weight, has a similar battery, has higher kv motors, and has smaller props. Yet his flies and ours doesn’t. That makes me think we’re missing something here.

Here are some log files from our first few unsuccessful hover attempts:
2023-10-28 10-26-26.bin - Google Drive,,,

Neither of those motors is well suited for the application. If you use the 920kV motors and 10" props (typical for that kV) on 4S power the take-off weight (w/ battery) should not exceed 1.7kg. If you use the Tarot 320kV motors (~150g each in weight) with the 14" props on 6S power the take-off weight should not exceed ~2kg.

How do you know what the max take-off weight should be for a given configuration? Is that shown on ecalc somewhere?

Also, could you explain how that other builder was able to achieve flight with 1050kv motors and 10" props on 4S power with a take-off weight of 2320g?

Sure it’s in Ecalc, just plug the components and weight into the Multcopter calculator. You want a linear hover throttle ~50%. It could be a bit higher for a QuadPlane.


So I’m guessing our best option is to buy some ~620kv motors like these.

Then we’ll need to also buy 45A ESCs. Do they have to be opto ESCs like this? Or can they be blheli_s ESCs like these?

And if we do that it should have enough thrust to get off the ground?

Those RCtimer motors are junk, that’s why they are so cheap. That motor kV and prop could work but not sure it’s a good choice for a Quadplane. You might be better off with good 1200-1300kV motors and 9" props. Those ESC’s you linked too are poor quality too, get a decent BLHeli_32 4-in-1.
All that heavy aluminum on there isn’t helping much.
Use the eCalc Multicopter calculator.

Hi, we are getting ready to build our next (much improved) iteration of the quadplane. Could you take a look at our eCalc and make sure we’re not missing something crucial?

eCalc - xcopterCalc - the most reliable Multicopter Calculator on the Web

We will be modifying this kit: RMRC Skyhunter FPV Plane - Get Yours Today! - RMRC

In this link you have a VTOL TILT modification of the airplane that you are going to modify in case it is a guide.


If you want to share an eCalc configuration you have to share a screenshot, it is not possible to share a configuration with a link.

The link works fine if you have a subscription to eCalc. Click the link, Login and it’s populated.

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Lol, yes it does now…
never seen it work before though xD

Regarding your question for an opinion @vandjac, here are my thoughts about your config:

  • Is the weight of the additional structure for the VTOL conversion included in the 1725 g?
  • if you use 14" props, the hover throttle comes from 64% down to 57%, still not perfect but better
    • that is scraping at the limit of the ESC though, if you plan on doing long hover phases you might want to upgrade the ESC as well (or discard my suggestion for 14")

That’s all I see for now

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Yes, the VTOL conversion materials are included. Also, we plan on using a 55A 4-in-1 BLheli-32 ESC. Unfortunately, there isn’t quite enough room for 14" props, which is why we have to use the 13" ones.

For those who don’t have an eCalc subscription, here’s our xcopter calcs:

Also, if you’re willing to look at it, we just finished the fixed wing eCalc for the quadplane: eCalc - propCalc - the most reliable Propeller Calculator on the Web

Edit: I just realized the ESC in this is way oversized, you can ignore that.

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