Go Big at Flite Fest

[Ran D. St. Clair]

The + Size VTOL has completed flight testing. It flies nice.

I did make an error in my statement above. It is not a good idea to fly it in forward flight when in hover mode with the autolevel turned off. Control is fine but the axes are mixed up. Yaw in hover mode is -roll in airplane mode, and roll in hover mode is yaw in airplane mode. This is because I set it up to hover like a multicopter and fly like an airplane. Open Aero VTOL (OAV) allows you to set it up to hover like an airplane if you want but most people don't like to do it that way. I have flown both ways and I find hovering like a multicopter more natural.

Bottom line, as it is now, flip the switch to hover mode and you are flying a + quad. Flip the switch to FFF (Fast Forward Flight) and you are flying an airplane.

It might seem odd, but it is even possible to flip the switch to the center position and fly comfortably there. You just move the aileron and rudders sticks left or right together. If you were to hover in airplane mode then the aileron stick and rudder stick would have to move in opposite directions. If you have good 3D visualization skills, you can figure out why. Otherwise, I could bore you with pages of explanation and it still would not make sense.

Now that flight testing is complete I just have to write It up and get some video. I really need a good 3D pilot to better show what it can do.

 

[Ran D. St. Clair]

Lots of flying this weekend. A couple of other pilots have flown it now. Kasra took a short I-phone video which might show up shortly. Adam was doing some nice looking flat spins. Bob says it flies "majestic" and would make a good first tail sitter. I flew it in almost a 10 MPH wind and it did fine.

 

[Ran D. St. Clair]

The + Size VTOL project is essentially complete. The video is in post processing, and the build instructions are complete, just waiting to add a link to the video. I modified it to make it more transportable. It now fits into a space approximately 51" x 27" x 8" with a little padding prevent damage. Since it turns out to be quite fun to fly, it is not just suitable for Flite Fest but everyday flying, therefore it had to fit in my Honda Accord, and now it does.

 

[Ran D. St. Clair]

Module-Air

The “Module-Air” is the 3rd and possibly last in the “Go Big at Flite Fest” series. It is envisioned as a 32 ft. span flying wing consisting of 4 each 8 ft. x 2 ft, modules joined wing tip to wing tip. Each module will include its own Battery, ESC, Motor, Receiver, BEC, Flight Controller, and servo controlling a single elevator surface. All of the receivers will be bound to one transmitter and the aircraft will be flown by 1 pilot. More than 4 modules are theoretically possible. The Module-Air will be a BIG, slow, BIG, gentle, BIG, light weight, BIG wing that won’t handle much wind or turbulence. It is nothing more than silly good fun in a BIG way.

Assuming a kit of parts, each module can be built at FliteFest in just a few hours, and multiple modules can be built by different people as part of a team build. Each module consists of about $5 worth of foam, and another $10 of various disposable materials, all available from a home improvement store near the event. The radio gear per module is no more expensive than the typical regular size electric plane and is all reusable for other projects.

The technology of the Module-Air is based on a combination of the “Flying Barn Door” discussed earlier in this thread, and the “Twofer”.

https://www.youtube.com/watch?v=MKJNE2slGPs

https://www.youtube.com/watch?v=WDIEJIrgROc

The un-braced wing of the Module-air will be too long and floppy to support itself except in the air. Each of the modules will essentially fly itself in formation with the others. The multiple Flight Controllers (FC) are what makes this possible. Each module will be properly balanced for pitch stability, and the FC will use AutoLevel to hold them at the proper angle of attack.

The FCs will also monitor their individual roll angles and use AutoLevel and the individual elevators to fly the composite aircraft to wings level. Due to the lack of torsional stiffness the aileron functionality is reversed compared to a normal wing. If, for example, the right module applies down elevator, it will twist the wing so the right side of the composite aircraft will go down. This is similar to the Twofer as the string that connected the 2 planes had no torsional strength at all.

This only works because the modules are weakly connected in roll. In order for one module to roll to the left, then all the modules have to roll to the left, or the composite wing has to bend. If the composite wing bends, and it will to some degree, then the FCs will act to straighten it out. If, for example, the right module were to bend up then its FC will detect the left bank and apply down elevator, bringing it back down to level and straight in alignment with the rest of the composite wing.

Yaw control is via differential motor thrust among the 4 motors. The flight controller will also monitor yaw rates and modulate throttle to dampen any rotation in yaw.

Since the Module-air has no vertical surfaces, it can slide down hill sideways in a “slip”. The FC will counter this by applying ailerons to level the wings, and also by applying additional power to the high side motors to match the yaw rate to the bank angle and create a coordinated turn. This is the same technology as used on the flying barn door, which is also a flying wing with no vertical surfaces.

The pilots role is to disturb the aircraft stability and make it turn. All maneuvers will be a balance between the pilot telling the aircraft to do something, and the flight controllers trying to bring it back to straight and level.

The interesting technical challenge, at least for me, is to find the balance of all the various flight controller parameters that will make this possible without oscillations or other unwanted dynamic behavior. Success is NOT guaranteed.

 

[Ran D. St. Clair]

The Module-Air is complete and ready to fly. Now it is just a matter of finding a weekend weather window.

Specifications:

Span: 32ft
Area: 72 sq. ft.
Weight: 14.24 lbs. with batteries.
CG: 25.9%
Batteries: 4 each 3.3Ah, 3S
Motors: 4 each, Emax GT2215 1100kv
Props: 10 x 4.5, approximately 2.5 lbs. static thrust each at 24A

The picture shows each of the 4 modules stacked one in front of the other. The flying barn door is in the back. The + Size VTOL is up against the wall to the left.

Each module has its own RX and FC (Flight Controller). The FC programming is fairly simple, mostly because there is only 1 motor and 1 servo per module. The combination of parameters that will hopefully make it stable in the air is what is interesting. I have yet to assemble all 4 modules as there isn't room inside the house, but putting two modules together, which is one wing half, suggests that up to 10 degrees wing twist in flight is to be expected.

Each assembly joint, of which there are 3, is just Velcro and a splice spar with 4 sacrificial cable ties. There should not be a lot of stress on these joints, but we will see.

All four elevons will control pitch. Only the outer elevons will control roll, and in reverse by twisting the wing. With luck it won’t be hard to fly. I have set it up with a strong autolevel in pitch and roll, and also automatic turn coordination. I expect it will never bank more than about 15 degrees, and that it will be flown mostly with rudder and throttle. I need to make sure the inside wing doesn’t stall in a turn. It should never be flown at zero throttle except possibly in a straight line due to the lack of yaw stabilization when the motors are not running.

The first flight of these things often ends in some un-interesting failure, but we will see.

I have a plan for launching. After joining the module flat on the ground, I will tilt it upright on the tail stands with its belly into the wind. With the motors running at full power, they will lift well over half its weight. I will then lift it up by the leading edge in the center and walk backwards while it "kites up" over my head. Once it reaches near level I will just let it go. The challenge will be to get it up and wings level in roll. I think it will fly as slow as about 10 MPH so it wont be necessary to throw it hard.

 

[Hai-Lee]

Ran D. St. Clair.
Whilst it is far too late now it would have been good to have a couple of profile, (KFM winged?), P47s or P51s to fly escort for the B17.

I hope it all goes well!

Have fun!

 

[Ran D. St. Clair]

+ Size VTOL Video Link

The flight video for the + Size VTOL is now available.

The build instruction are available here:

https://www.dropbox.com/s/zq48ilzl7zzsczc/%2B%20Size%20VTOL%20Build%20Instructions%20Combined.pdf?dl=0

 

[Ran D. St. Clair]

Another Video with multiple VTOLs.

Another Video with multiple VTOLs.

 

[DamoRC]

What great flying machines. It's been a real treat to see these fly in person. Will we see the module air up this weekend?

DamoRC

 

[Liam B]

I’ve loved watching this thread. When do you guys fly at Baylands? Love to come by some day.

 

[Ran D. St. Clair]

Module-Air Maiden

What great flying machines. It's been a real treat to see these fly in person. Will we see the module air up this weekend?

DamoRC

The Module-Air might make a maiden flight early Saturday morning. I am not advertising since these sorts of things often result in uninteresting failures.

 

[Ran D. St. Clair]

The Module-Air has flown

The Module-Air has flown.

The flight was about 6 minutes and all batteries still had about 63% capacity left on landing. It was not easy to fly but I am working on modifications to improve that. The wind was under 5 MPH but there were some thermals coming through. All control systems worked as expected including the "backwards" ailerons. The flight characteristics are such that it is all about the rudder, which is actually differential throttle. It banks into turns naturally due to the differential airspeed. Ailerons and roll autolevel are used to try to keep it from banking too much. At the slow speeds that it flies it can turn fairly sharply without a lot of bank, but at some point the inside wing is flying too slow and begins to stall. The solution is more power and airspeed.

The rate of climb was quite good, much better that the B-17, which used the same motors and propellers. This makes sense when you understand the reduction in induced drag is in proportion to wing span squared. The parasite drag is high, but that goes up (or down) with the square of airspeed, and since it flies quite slowly, it is not that bad. It turns out that a flat plate airfoil with a square leading edge is not a bad fit for this application.

Pitch trim and pitch stability were good, or at least a non-issue with pitch autolevel applied. The main issue at this point is yaw stability, it has none. It will happily fly through the air at a 45 degree angle, however at some extreme angle it won't be happy any more. One simple solution to this problem will be the addition of streamers, not to make it more festive, but to make it easier for the pilot to recognize when it is flying sideways and correct. Left to its own devices it would probably correct itself eventually, but when maneuvering it is easy to get it out of sorts in yaw. This is why a capable pilot is currently needed.

 

[Ran D. St. Clair]

The Module-Air has flown a 2nd time, this time in near no wind conditions. Between the better weather and the modifications I made, it is now easy to fly, at least up to the point where the batteries start to die. We were having a bit too much fun and after about 16 minutes the left side motors were down to about 6% battery capacity and it developed a definite desire to turn left. Never the less, we got it down safely. High quality video including air to air video should be available in a few days.

Wind limits aside, this is now a very viable "Flite Fest" project. I will publish the build instructions in due time.

 

[Ran D. St. Clair]

Module-Air Ground Camera View

With real time commentary from your truly.

 

[Ran D. St. Clair]

Module-Air Build Instructions

Detailed build instructions for the Module-Air are available here:

https://www.dropbox.com/sh/b5z524y7lfrhsrg/AABnCqbFe0PJC_4xshZV2Lv_a?dl=0