Fixed Wing + Tail Rotor Giant Scale Aerobatics

News: Super Honey Badger should be at FliteFest 2015!

Anyways, I wrote this article when I first built the tail rotor but regretfully the model destroyed itself. Since then it has been rebuilt, but this is the process that was used to build it. For what it's worth, I hope people enjoy the process...

There was a FliteTest episode that featured my previous work on a crazy plane which had air brakes on the wing tips, can view that episode at the bottom of this article. The idea was to try and spin it around and do other high drag and 3D maneuvers. I was the guy that built that airplane. It was not, however, much of a success which the episode pretty much showed.

The problem was, it didn't work all that well for flipping the plane at all. There were things that I could try to improve it, but during the build I had the idea to mount a powerful tail rotor into the plane to do it that way instead. This idea became all consuming, so that is what work started on.

This is the outline of the building the plane come to be known as the "Super Honey Badger", and cutting its tail off, replacing it with booms and adding the tail rotor. The plane is still the 3DHobbyShop 87" Extra 300SHP (though now the SHP is "SHB" to be the Super Honey Badger), the booms are from Rock West Composites, and all the rest of the tail rotor equipment being various helicopter parts (essentially Align TRex 700 upgrade parts, a few RC car parts and high discharge lipos) from amain.com ...those three vendors have pretty much everything needed.

NOTE:Before we get into the build, just want people to know that this is all hand tools, mostly the work of a dremel and sanding blocks. The most complex tool I own is a drill press. I only mention this because you don't need a complex set of tools to get into some engineering fun!

THE BUILD

This is how the tail was before the work on the tail rotor started. This is how it was for the air brake project from 2012...

1) The initial idea and motivation. Holding the 14" prop from one of my 3D planes against the tail, this is roughly the power (1kw+) and the size of the rotor diameter I was aiming for.

2) Still getting the general feel for how I wanted it to end up...

3) Bit the bullet and ordered the tail rotor components of an Align TRex 700 with 800 upgrade torque tube. Following photos getting an idea for how I will place it...

4) Worried about the rotor being too far above the thrust line, modofications happening to drop it down...

5) And naturally I had to spin the rotor as soon as was humanly possible, even though it was just taped in :)

6) Cutting the cross members in the photo above, the ply box lost all strength, was decided to move to a boom configuration for strength as well as improved airflow to the rotor. The photo below is the big moment when I took the dremel to the fuselage of the 50cc plane and literally cut the tail off, taping it back together to see how it would look at this point (apparently rather ugly)...

7) The width of the booms with room for the rotor, I had to move the inside rib of the stabs over. Hacked it off with a hand saw, and then repaired the damage I just inflicted on it. Actually most of the build reflects this pattern; damage the plane in some horrific way and then repair it in a new configuration.

8) Setting the booms in place. This is a critical structure point as the leverage of the booms against the fuselage use this as the point of cantilever.

9) Carbon tube joinery. To add surface area to the inside of the joint, the tubes were filled with end grain balsa before shaping.

10) Direct motor coupling for powering the rotor's torque tube.

11) Measuring and positioning the horizontal stab. Pretty close in position to the original airframe, plus slight change based on an intended improvement.

12) Making the joints captive by wrapping them with kevlar thread, soaking the thread in super thin CA.

13) Making the boom mount for the rotor tail case. During flight, this piece has proven to be the only piece that wanted to come apart... so this has seen a few revisions since.

14) Binding rotor case to the mount. Lack of metal milling machines meant that most of this crazy creation was kevlar bound and CA'd... the best answer I had on hand that could be done with hand tools. All carbon cut and shaped by dremel, scroll saw or various other hand building techniques.

15) With the tail removed, the rudder servo had to be relocated up to the booms.

16) ...with new structure for mounting the control horn for the new location...

17) Rotor motor mount made from laminated ply and carbon plate.

18) Balance! ...was always going to be tough with this plane. To get it all to balance, the tank for the petrol/gasser engine was but underneath in the canister area, this was to free up the main area to be able to slide a battery tray all the way to the firewall. The battery tray was made so that it keyed into some structure at the firewall to stop it moving around. Batteries for the radio equipment and the rotor both as far forward as possible. Happily (Luckily?) this balanced the plane out perfectly, I was relieved to not need dead weight or to do more exotic things like extending the engine standoffs, etc.

19) The wad of batteries strapped to the battery tray. Two 2S 2200mah packs for the radio equipment, and two 2S 3000mah 100C Protek packs wired in series (4S 3000mah) for the rotor power. All sits perfectly behind the firewall...

20) Setting the pitch of the rotor. Tied it down, connected a watt meter to the rotor and increased the pitch until the power draw was 1.2kw...

21) Almost ready for flying...

22) Now ready for flying...

23) Flown! ...at this point I'm a happy camper, plane proved it flew great and the rotor was working perfectly. Next was to make it look nicer and refine flight characteristics (the changes introduced some problems with some maneuvers, though interestingly knife edge performance even in this configuration was still excellent)...

24) Radio setup/clean up... 

25) Testing a stub fuselage, to clean up the airflow to the rotor, made from depron and masking tape...

26) Depron test scoop to cool the rotor equipment...

27) Test fuselage worked great, swapping it out for permanent balsa structure to be covered with ultracote...

28) Permanent cooling scoop...

29) Need to be time efficient, which includes eating while still working...

30) All cleaned up and structures in final form...

31) Adding stickers...

32) Project ready for the big reveal at the Ohio Huckfest...

33) Performance of the plane continues to bring me much joy. the Super Honey Badger also taking home the "Bad Ass Plane" award from the event...

34) Next setup, upgrades! ...will have a fresh set of Protek servos in it real soon, looking forward to reducing some of the harmonic issues with flutter that can happen from time to time with the tail boom configuration.

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THE FLITE TEST EPISODE OF THE PREVIOUS AIR BRAKES VERSION