When you command a quad to go forward, it tilts forward, and that creates a forward "thrust".
What would happen if I attached a horizontal motor/prop onto the quad, and provided a horizontal thrust that way? Would the quad maintain level?

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• I fly one of these for work, without the turbine of course. Its a Riegl RiCOPTER and it is made to carry a Lidar sustem. Just scale those are 30" props.
• That's an encouraging video, James. Thanks.

• Developer

There are a few videos of this kind of thing on YouTube including this one.

This idea has come up a few times and there was even a pull request to add support into Copter.  It wasn't accepted because we're not ready to break the assumption that the thrust is always vertical (i.e. it made the position control code extremely messy).  Also the general consensus on the dev team was that although it's kinda fun and cool, it doesn't actually add much value (at least in the scenarios that we could think of).  If someone is looking for a faster copter, it's better just to increase the power of the existing motors rather than add a new one.

• What you are describing is very similar to what was just introduced by Tridge as "quadplane". Look it up in the wiki. Perhaps you could set the min speed so high that the aircraft never achieves it, then the quad motors would always be active.
• @Azobe: What do you mean by "spaz out"?

Suppose I pulled the quad with a string 10m away from its GPS position, would it be at a constant tilt trying to get back to its original position?

Actually what I'm thinking of doing is using a quad to launch a fixed wing plane that would be carried on top of the quad. The quad would hover at a GPS position and the plane would gradually provide horizontal thrust. When the plane's speed is near flying speed, it would separate from the quad and the quad would return to home.

Is that feasible?

@iskess: How does the quad measure speed, with a Pitot tube?

• Developer

Sorry, my other reply was before I read all the other comments here.  Insitu did something similar to what you're talking abuot here.  My understanding is that the test was using ardupilot (aka Copter, aka APM:Copter, aka ArduCopter) on the multicopter that was doing the lifting.

• By Spaz Out I mean it will go haywire. Anyway, if you have GPS lock on, then yes it will try and maintain its coordinates. If you just keep your quad in auto stabilise, and have the rear thrust on, then it should be fine if everything manages to be balanced with the thrust from the rear.

However, I dont know why you would want to top mount the plane and launch as you described. Why not bottom mount the plane, drop it from altitude, and as soon as the plane has broken away from the quad turn the plane motors on and fly away? Your method seems unnecessarily cumbersome. After all, RC planes don't need to travel very far or fast with speed to create significant lift.

• A lot of planes won't be controllable without any forward speed. Dropping the plane might work if it started with a nose down attitude. Some planes might just spiral down due to control surfaces not having enough air across them.

I want to treat the quad like it was an airborne carriage. It would be like the plane was on a runway in the air.

• If your quad creates more thrust per motor at hover then the plane can around 60-70% throttle (im assuming) then I think the quad might only be a little phased if not at all and might still hold decent handling.

What size quad and plane are you using? This would be interesting to see how it would play out