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Old Jul 17, 2013, 09:20 PM
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Simple VTOL Build Thread

The idea behind the Simple VTOL Build Thread is to create the simplest possible VTOL and then document its construction so that anyone can make one in as little as a weekend. It should be relatively cheap and be both easy and fun to fly.

The design is based on the Plug-n-Fly Hobby King Wilga, $67.72

http://www.hobbyking.com/hobbyking/s...lug_n_Fly.html

The Wilga comes with floats which should make an easy mount location for quad-copter motors. The stock motor will remain for forward flight so transitions will be a matter of gracefully turning off the lift motors and turning on the forward thrust motor.

So far I have the Wilga in pieces and most of the necessary gear is left over from previous projects. Let the fun begin....
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Old Jul 18, 2013, 01:33 PM
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Newport News, Va
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Ran D. St. Clair,

About 23 years ago I built a fairly large tilt rotor, about 90" from blade tip to blade tip powered by a 120 OS, but I never finished it. Your sucess and this build project has inspired me to get back into VTOL.

Just this morning I have placed orders for most of your build. This is going to be fun! Many thanks for sharing.

Gene
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Old Jul 18, 2013, 03:02 PM
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YW Gene!

A word about the choice to use separate thrust and lift motors. Previously I have used lift motors that tilted, and that worked fine, but 4 motors churning with low pitch props burn up a lot of battery current even when flying level. One small forward thrust motor should give much extended flight times even if I am burning about 0.4A just keeping the 4 lift motor speed controllers at idle. It should also make for a simpler build as there is no need for tilting motor mounts or servo's to tilt them. The single thrust motor should be fine for normal flying, but I don't expect it will have the low speed grunt of the VTOL-Trainer. It will probably require some entry speed to do a decent loop.

The argument against this approach is that the lift motors become dead weight for normal flying. This is true, but a decent wing carries that weight very efficiently compared to a small spinning rotor. This particular design will have the lift motors exposed so they will create drag as well, but a more sophisticated design could place the lift motors in streamlined motor pods. Such a design could also stop a 2 bladed propeller in line with the airflow for minimum drag. In the interest of simplicity, this design won't bother with that detail either.
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Old Jul 18, 2013, 03:51 PM
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Nice build. I'll be interested in the flight time and speed of the aircraft.

A 4 min flight time on a faster, lighter ship might go around the park twice while a slower, heavier ship with an 8 minute flight time might only go around once.
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Old Jul 19, 2013, 12:09 AM
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Gene,

I hadn't seen the picture before. It looks pretty awesome, and complicated...

RCvertt,

I plan to use a 2.2Ah, 3S battery. In hover mode it should only last 5 minutes, but in forward flight it should be good for 15 minutes or more. We will see, and I will share success and failure alike. My biggest concern is that the wimpy cheap little motor that comes with the Wilga is only meant for 2S. I will trim the prop to run 3S, or possibly just buy a different prop. If the end result doesn't have reasonable power for decent flight performance I may have to upgrade the motor. Hopefully not, because I want to keep this project as simple and cheap as possible.
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Old Jul 19, 2013, 04:55 AM
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Gene, nice model. Does it have full collective and cyclic on both rotors? If you were to convert it to a T tail it would make a pretty good scale AW609 ( http://en.wikipedia.org/wiki/AgustaWestland_AW609 )
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Old Jul 19, 2013, 06:42 AM
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Newport News, Va
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Brandano,

Yes, it has almost 32 degrees of total collective, 0 to 12 degrees Plus the 20 added. The blades are twisted making them suitable for both hover and forward flight. The mono cyclic ( 15 of pitch only) is phased out as the nacells tilt and the collective is automatically increased by 20 degrees by the time it is in airplane mode.

I do not wish to hyjack this thread, the photo was only posted to show my enthusiasm for Ran D. St. Clair build.

Gene
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Old Jul 22, 2013, 04:22 PM
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The build is about 80% complete, but is not going well. The Wilga is turning out not to be the best platform for this project. I had to widen and brace the float mounting struts for my purposes and they are still not stiff enough. It is not that difficult for me to bend wire and make struts, but it is difficult to document in a manner that others can easily reproduce.

I am also having difficulty with the fuselage layout. The battery compartment is too small and can't easily be enlarged to accomodate a 2.2Ah 3S pack, which is the minimum I would use for a plane of this sort. As a consequence I will have to strap the battery under the belly of the fuselage.

The internal layout is also posing some challenges for wiring access, and a plane of this sort has lots of internal wires.

I think something like a Multiplex Fun-Cub with wing mounted motor pods would be a better choice.

Since I am getting close to being able to fly, I will go ahead and finish it, but I won't be documenting it at the level that I had planned. It just doesn't meet the mission requirement of being a Simple-VTOL.
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Old Jul 23, 2013, 09:01 PM
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The Wilga has flown. 20 seconds of hovering in my living room trying desperately not to hit the coffee table or the couch counts right? Now the tuning and testing can begin, but there isn't much to tune, just 3 pots on the flight controller.

In keeping with the simple/cheap mission I am using this flight controller, which is new to me.

http://www.hobbyking.com/hobbyking/s..._Edition_.html

It is cheap, and it does exactly what it promised to do, so I can't complain, but I would not recommend it. It has no concept of a safe mode or arming sequence so you have to be very careful with it. Even with the throttle full off, the motors can start up when you pick up the aircraft and the gyro tries to fight to hold it in position. This is also true even if the TX is turned off.

As near as I can tell, it has no "I" feedback loop (which is fine by me) and no "D" either, only "P". It also has no accelerometer so no auto level mode, which is also probably fine.

I will have to wait until the weekend before I can do any serious testing and report further. Most likely, once I learn what can be learned, it will go back to being a regular Wilga. Nothing I have done is completely irreversible. I have already ordered a Multiplex Fun Cub that I think might work better.
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Old Jul 25, 2013, 12:28 PM
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My Multiplex Fun Cub arrived last night. and I haven't even test flown the Wilga yet.

It seems a shame to modify what is already a pretty perfect airplane.
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Old Jul 27, 2013, 12:45 PM
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The Wilga has now flown (sort of) and is now done for this project. I never got into sustained forward flight as the forward thrust motor is just too weak to keep it airborne. I tried two transitions and both ended in a rough landing as it couldn't really fly.

The original Wilga is intended for a 2S battery, but I needed 3S for the hover motors. I measured the current on the motor with a 2S battery and the supplied 3 bladed prop, marked 8-6, at 8.5A at full throttle. When I upgraded to 3S the best prop I could find was a GWS 2 blade 7-6 which I had to cut down to 6-6 in order to keep the current down to 9A. The total thrust was pretty pathetic. I had hoped that it would wind up in the air and begin to work, but it never did.

the Wilga is essentially a throw away plane, and the cowl is glued on with the motor trapped inside, so I can't easily replace the motor. The motor is so cheap that you just touch the prop shaft and the motor bell housing just falls out the back. Surprisingly, it seems to run OK, aside from not making any real power. I don't know if I got a bad motor or what, but it doesn't matter because the project won't work for other reasons as well.

The mounting of the floats with piano wire is too flimsy and springy for this application. I tried to brace it but it didn't really work. The piano wire is also too soft and deforms on even a mildly bad landing. I am guessing that the landing gear wire that comes with the Wilga is bent soft and then heat treated, so it may be better than regular piano wire, but it was too short for my purposes.

The flight controller is also not so great. I was able to fly but it never felt really stable like I am used to with the KK2. Having the motors bounce around on the flimsy float mounts didn't help. I mentioned earlier that the flight controller is actively dangerous on the ground. Even at low throttle the motors can start whenever you move the aircraft, even with the TX turned off. It's an accident waiting to happen and I won't be using it again.

So, the next step is to build the Fun-Cub with proper motor pods. I have a good quality Axi forward flight motor for it so power should not be a problem. I am a little concerned about the total battery current during transition though. Having all 5 motors pulling hard will draw a lot of current even if only for a few seconds.

I will turn the Wilga back into its original form, possibly even by tomorrow. I am half curious to see how it flies when built as intended.
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Old Jul 27, 2013, 04:07 PM
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Good luck with the new biuld, to bad the first one did not work as intended.
I take it you will be using the KK2 for the new build.
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Old Jul 28, 2013, 08:04 PM
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Yes, I will probably use the KK2 again. It is certainly a known quantity and I already own a spare one so I might as well.

I flew the Wilga today in standard form with floats and a 2Ah 2S battery. It's a cute little airplane, but woefully underpowered. It couldn't get started on dry grass by itself so I gave it a hard shove. It staggered into the air and was only able to climb slowly at full throttle. I did several nice touch and go's on the grass and after I got used to it, it was pleasant to fly. I can see now that it never had a chance of flying with the extra weight and drag of the lift motors. I don't know if this particular motor is a weak one or if they are all like that. With a better motor it would be a reasonably nice little plane, but only for flying in lite winds. At this point I will pull my RX and see if I can get $40 for it.
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Old Aug 03, 2013, 08:44 PM
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The Simple VTOL-2, as I am calling it, based on the Multiplex Fun Cub is progressing nicely. I have completed the basic design and have started the build. Thus far I have completed all 5 motor mounts, 4 for the lift motors, and the 5th one because the Axi 2212/34 did not fit into the factory stock front motor mount. The Axi is probably a bit less powerful than the Multiplex power package but that's OK for my purposes.

I am using motor pods similar to the VTOL trainer, but the motors don't tilt. I made the motor mounts out of 1/8" thick aluminum, which is probably a bit overkill, but they are very strong.

The hardest part, so far, is figuring out where to mount everything. I am using the KK2 this time so I need access to the buttons for tuning. I will be mounting the KK2 under the front hatch, which will also be my access for installing the battery.

Putting the Flight controller on top of the wing, as I did with the VTOL Trainer is somewhat ideal because it mounts almost all the electronics in one place. The wing can hold the motors, ESC's, Flight controller, RX, aileron servo's and SBEC. The only connections to the fuselage were the main battery connector and two servo connectors for the rudder and elevator.

With the Fun Cub, I could mount the flight controller on top of the wing again, but it would look ugly, so I am putting it in the fuselage. That means the wing will still hold the motors, ESC's and aileron servo's. The connections between the wing and fuselage will be the main battery connection and instead of the elevator and rudder servo's, the two aileron servo's. I will also need to connect the 4 ESC control connectors. It's a fairly minor problem, but I will need to label all of the connectors and make sure that there is enough service loop in the wires. That will leave a nest of loose wires in the fuselage when the wing is installed. I don't usually take planes of this size apart for transport, but I could if I wanted to.

I will not be installing the flap servo's for this build. There is nothing about the design that prevents having flaps, I just don't need them.

I have attached some pictures and such for the progress thus far.
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Old Aug 06, 2013, 09:20 PM
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The motor pods are done. Now it is time to start assembly.
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