The BE-Shape (Backwards Electric - Shape)

The BE-Shape is no-more.   It suffered from an "aero-dynamic problem" that caused it to pitch up and down if the airspeed was too high.  Eventually this happened going into a turn and it went out of control and crashed badly breaking many parts.  I've not tried to rebuild it.



After I had got reasonably proficient at flying my Rotorshape, I decided to to try something a bit more challenging.  I had been reading the Autogyro Forum on RC Groups where I had read about the BEGi (Backwards Engined Girocopter).

I ordered the kit initially without the pre-rotation drive.
The BEGII added the extra nose wheel in an attempt to stop it nosing over on the grass, but the high thrust line and high CofG meant it was never 100% successful.  The later addition of the pre-rotation drive helped but I still had great difficulty in actually getting the thing to fly.

To cut a long story short I only ever got it to fly a couple of times before it was destroyed.



A plan....However, it wasn't totally destroyed, and I had an idea.....

Due to a "building mistake" with my Rotorshape, I now had a spare head assembly and set of blades, so I set about working how to attach these to the remains of the BEGi.   This picture is of the first "mock-up".  As you can see  the main undercarriage and tail wheel, the main  boom, the vertical fin and rudder all survived and now became the basis of the BE-Shape. "BE" from the BEGi and "Shape" from the Rotorshape.

I showed my idea to JochenK who had produced the Micromum and the Minimum designs.  He was very helpful and encouraged me to continue with my idea.   We exchanged several e-mails where he helped me to determine the correct the rotor angle and motor position/thrust line,  based on his experiences.
After a few weeks of work the BE-Shape emerged ready for it's maiden flight.



Motor MountHere's a close up of the motor mount I built.  The slotted plate is angled to the mast with washers, such that the thrust line is level relative to the horizontal stabiliser.  The slots allowed me to offset the motor to produce the same result as "side thrust" on a conventional model. The model's CofG came out just above the arms on the servos, and I set the motor's vertical position so that the thrust line passed 25mm above the CofG (Jochen's suggested starting point).  The rotor support mast is clamped between two pieces of ply wood so it's position could be adjusted by loosening off the bolts.  The initial position wasn't far from correct, but on the first few flights it did tend to pitch up and down as it flew along.  Dropping the motor by 5mm cured that behaviour.


After a few flights (see below) the epoxy holding the plywood triangles to the boom and mast came unglued, luckily not while it was airborne !  I took it all apart, cleared off the old epoxy and added some binding threads.  These have helped to produce a much stronger joint as they helped to keep the epoxy in the right place while it was setting, and the epoxy flowed along them to produce a much greater glued area onto the main boom.

Although I rudder servo is much further back on the BE-Shape I had retained the pull-pull  control via thin thread.  However this proved to be hard to keep tensioned correctly, and eventually one side of the horn broke so I replaced it with a simple push rod.

To start with I had fitted a GWS motor that I had lying about.  While it performed well for the first few flights it seemed to develop a fault that made it fail to spin when the throttle was opened.  It may have been that I damaged the bearings when I reversed the shaft to use it in a pusher configuration, but eventually it stopped while in mid-air!  I can't claim that I controlled it's decent but the only damage was the epoxy joints between the plywood and carbon fiber tubes failed. 

I had used the GWS motor rather than the Hacker I had used in the BEGi as it had a higher Kv rating and because I was using a 9" prop (rather than the 10" on the BEGi) I wanted to spin it a bit faster.  However when the GWS motor failed I replaced it with the Hacker as it hadn't needed full throttle at any point with the GWS. 

Since I had got used to hand launching my Rotorshape I started off using the same technique with the BE-Shape.  Until one evening I was faced with trying to launch with no head wind to spin up the rotor.  As you can see below I ended up running across the field before tossing it into the air.  Not very dignified!


(Not) spinning up the rotors
Running across the field
Off it goes




Here's a link to a video that starts with a hand launch in a reasonable breeze.
However here's a video where the  hand launch didn't quite to go plan.

When I was next faced with the prospect of having to run with the BE-Shape because there was no wind I decided to try and take off from the grass.  Luckily the grass had been cut  and compared to the BEGi the BE-Shape has a lower  CofG and  more rearward position for the prop which meant it didn't suffer from the same nose-over tenancies.  The first takeoff from the grass went so well I've not done a hand launch since then.

Here's another video which starts with a takeoff where if you look closely you can just see that I'm holding the elevator stick back at the start of the run to get maximum air flowing through the rotors.  Once they start to accelerate I released the stick and let it take off when it was ready. 

I've set up my transmitter (Futaba FF7) with a switch selected mix which allows me to adjust the rotor angle via means of the "channel 6 knob".  I've found this useful on the Rotorshape to reduce the rotor angle when flying in stronger winds.  This increases the airspeed required to spin the rotor at the rate needed for level flight and means it can be flown into wind with a reasonable ground speed without it gaining altitude.   I've also used it (as shown in the video above) to increase the rotor angle to allow for slower ground speed on approach to a zero roll out "spot"  landing.   The same results can be archived by holding the elevator stick  up  or  down,  but I find using the switched mix easier as it doesn't feel like the model is out of trim.