Semi-Scale VTOL V-22 Osprey

by hoiberg42 | May 14, 2016 | (16) Posted in Projects

I started this project one and a half years ago, when I built the V22 version 1. It was great at hovering, however in fast forward flight (FFF) it flew terrible. But now, after a lot of tweaking and experimenting, the version 2 has become a very nice plane to fly! It is a great compromise between "scaleness" and simplicity. And it's cheap to build too!

Overview

The construction is as I said rather simplistic: it is built out of 6 and 3mm depron and a single wooden spar. The wing is of one piece and can be rotated 90° around the top-axis (as the real V-22 does on aircraft carriers) for easy transport and storage.

The motors are mounted on a simple tilt mechanism (like the one from David's tricopter v2, but modified for >90° rotation), each of which are driven by one servo. The flightcontroller is a KK2.1.5 flashed with OpenAeroVTOL.

The wings have a Jedelsky-inspired airfoil: the front part is made of 6mm ribs and 3mm cover, and the back is simply one 6mm piece that is also the flaperon. I have chosen this construction to make 90° downward deflection possible.

That's all very nice, but how does it actually work?

In hover flight mode (HF) it's controlled just like any helicopter or multirotor, the flightcontroller does all the mixing for you.

  • To go forward it tilts both motors forward
  • To yaw it tilts them in opposite direction
  • To roll it will use differential thrust (increase the thrust of one motor and decrease that of the other)

Then when you engage slow forward flight mode (SFF), both motors will gradually tilt forwards and the flaperons will slowly go up. They will stop at about 50% inbetween HF and FFF.

In SFF it's literally a mix of a bicopter and a conventional airplane, it will fly at about half the speed of that of FFF. Thus the flightcontroller will halve the control throws it had in HF, and add 50% of those it will use in FFF.

Then when you transition to FFF, the motors will tilt to their most forward position and you'll fly the V22 like any normal airplane. Only, because it has no rudder, it uses differential thrust to yaw.

The build

 

Specs

  • Wingspan: 106,5cm
  • Length: 115cm
  • Scale: ± 1:15
  • Fuselage weight: 243g (incl. one servo)
  • Wing set weight: 715g (incl. motors + electronics)
  • Battery weight: 191g
  • Total: 1149g
  • Motors: Hextronik DT750 (not the ideal choice - KV too low)
  • Tilt servo’s: Aerostar AS-170MG modded with two 2.2KΩ resistors for bigger throw
  • ESC: HobbyKing 20A
  • Prop: 10×4.5 SF
  • Battery: Turnigy 2200mAh 3S 25C
  • Other servo’s: HXT900
  • Flight controller: KK2.1.5

The plans

The build plans can be downloaded off of my website

There are no build instructions, but it should be “figureoutable”. And if you need any more clarifications or detail photographs, just leave a comment here or on my website! (A lot of questions have already been answered on my website). Note that this is not meant to be a build-and-fly model. It’s more of a buid-and-experiment-tune-and-maybe-fly model.

OpenAeroVTOL settings

I know I'll be asked about this. They're on my website (I did not feel like duplicating all the tables etc).

Flying characteristics

Hovering: It is quite stable and flyable in hover mode. However, sometimes it will suddenly point the nose vertically downwards and starts falling. With enough height, it will recover automatically but I've already had a couple of close calls. I'm not yet sure what causes this. Maybe it’s the PID’s, maybe it’s actually some sort of a stall, or maybe it’s preventable. I’m not sure. It, by the way, does not like to fly backwards or with the tail in the wind. That’s because the horizontal stabilizer will then act like a horizontal destabilizer.

Transitioning: The transition to fast forward flight is very uneventful, you have more than enough control authority the whole time.

Slow Forward Flight: The Osprey actually flies best in between hover flight and fast forward flight. It feels very responsive and predictable.

Forward flight: It has plenty of power during hover flight, yet it feels very underpowered in forward flight. This is because the DT750 (with the propeller I use) has a low maximum airspeed. This can only be fixed by using another motor setup (which I don't want to spend my money on). It's however stable enough for me to try some low-level maneuvering - that's something I could never have done with the first version.

So far, there are 6 flight video’s, 3 of which I've put below.

Conclusion

After a lot of tweaking and practice, it has become a very nice plane to fly. And because it fits in our car in 1 piece, it’s also very fast to set up at the flying field. I first thought this would never be more than an hard-to-fly experimental plane, but it now is a favourite of mine.

Its only real shortcomings are the low KV motors and the unpredictable nose-down tendency in HF. The latter could probably be fixed with a movable-battery, like the first version had. Also, scale motor pods would be really nice. Though these are things for antother time.

Note: This is a summary of the full article on Hangar42. There's also a RCGropus thread.

COMMENTS

FlipCrash on May 24, 2016
Nice build! Should make for a nice summer project on those rainy days... Grats!
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MikeRobey on May 24, 2016
Utterly brilliant. Well thought out and implemented.
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julezflies on May 22, 2016
That thing is awesome!
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Gryf on May 28, 2016
Really impressive!
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jrvalentin62 on May 22, 2016
FANTASTIC!! Hope to follow your progress.
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d2it4me on May 23, 2016
How does elevator control work with only two motors and no elevator?
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hoiberg42 on May 24, 2016
It does have an elevator, which it uses in forward flight (I forgot to mention that).
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d2it4me on May 24, 2016
I mainly mean while in hover mode. You don't have a third motor like a tricopter.
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hoiberg42 on May 26, 2016
Oh, right.
That's correct! In HF both motors tilt forward if you give DOWN input, or backward for UP. While not the most stable solution, it's good enough to be flyable.
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Kurt0326 on May 25, 2016
Thinking of trying your build, since I have most of the electric parts but the kk2. Now, is there a FCB out there that utilizes a SBUS impute with this VTOL mix?
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hoiberg42 on May 26, 2016
OpenAeroVTOL supports Sbus input (it's the recommended input type, actually). Though it does, like other FC's, require an inverter.
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Flyingninja on May 23, 2016
How many channels doses my transmitter need to operate this?
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hoiberg42 on May 24, 2016
Five: throttle, aileron, elevator, rudder plus an extra one to control the flight mode (which should be either a 2 or 3 position switch).
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flyingsquirrelrc on May 24, 2016
thats cool. both of my parents worked on the first couple of versions of the osprey, and this looks very accurate. I really like how you had the wing swivel so that it folds up nicely. that is actually a scale feature on the real osprey, allowing it to fit onto carrier decks and minimize the space needed.
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hoiberg42 on May 26, 2016
Indeed! It's a really handy feature, space in hobby workshops is often even more limited than on carrier decks (you probably know what I mean).
Thank you for your comment, it's very cool to hear someone here has actual 'connections' with the real V22.
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TurtlesThatFly on May 21, 2016
My VTOL works somewhat like this, but it turns the two front motors left and right (yaw), and the tail motor up and down (elevator). Nice project though!
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hoiberg42 on May 22, 2016
Thanks :D
Do you have a project log (or something the like) of your VTOL?
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TriTriAgain on May 26, 2016
There are a few more details here, it looks like: http://www.hangar42.nl/v22v2
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Unkle Bilge on May 24, 2016
Way Cool! A lot of thinking went into this!
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shavenwookie on February 4, 2017
This is one of the coolest things I've ever seen. Fantastic job man!
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Semi-Scale VTOL V-22 Osprey