This page is all about a story behind building say... a monocopter by me. Solid rocket motor powered monocopter to be precise... two of them, actually. So yes it's first of all about rocketry as a hobby, bolts & nuts, cutting composites, DIY in general and this sort of stuff. Whether you are a newbie in rocketry (like me) going to make your first monocopter OR perhaps a rocketry_master_Yoda I hope you may find this page quite helpful and useful (or at least -- entertaining) in some way.
Chapter I, Let's build something
The story began with Phil Charlesworth's idea of "monocopter competition" as a 2010'th special meeting of F.O.G. rocketry club. Honestly I'd never thought before about monocopter seriously... but because the competition was already in the calendar and I had some ideas about future machine design I decided why not to try.
My idea was quite simple: I was going to use one of main blades (25cm) of my MS Composit Hornet X-3D RC heli as a... blade for monocopter. And because I wasn't sure about which angle of attack (AOA) of the blade would be perfect I also decided to add say an ability to change it... as well as AOA of a motor -- just to see how if at all it would affect altitude.
And I made it. And showed not so bad time at the competition. Unfortunately I got no pic of a newborn but at the end of her "career" and tonnes of mods applied Monocopter Mk1 looks like this [click-click]:
Main material = carbon fibre (CF, www.robotmarketplace.com); main glue = epoxy (Z-Poxy 30min). I used a heli's blade grip as a joint between the blade and main frame and played with AOA by changing pushrod's length. Because I didn't have any idea about whether the construction would be strong enough to withdraw vibrations and forces during the flight I decided to start with A Class BP motor (Estes) but make Mk1 also able to flight on B and then on C motor as well. The issue here is that B motor twice heavier than A (and so on) therefore I made the joint between motor_tube and main frame to be able to turn and also slide to put motor close to monocopter CG. That was a plan... meanwhile in a real life there is no much space between motor_tube holder and launch_tube glued in a middle of main frame. So I launched it on A motor then applied no. of mods, launched again -- everything was looking good so I cut motor_tube holder, added CF reinforcement on motor_tube and launched it on B. Then added some more bits and pieces, cut motor_tube holder again and finally launched it on C motor many times //success rate = 100% ^___^
The results are:
a) it works i.e. yes you can use a heli blade for such an application
b) main blade AOA of 16° looks very good in terms of altitude and brings no visible problem with drag
c) there is no need to turn motor -- the best AOA of a motor is no angle at all
d) try to avoid to make a construction with CGs of quite heavy parts such as blade or motor out of a main frame plane -- centrifugal forces are strong enough to bend main frame quite seriously which adds even more stress to the joints and parts and changes shape of whole construction in flight.
But this is not the end of the story...
Chapter II, Bigger, longer and... Mk2
Because of the success of Mk1 and popular trend to make something BIG later I decided to make another one -- Mk2, yes slightly bigger and propelled by AP motor this time.
I made two early prototypes starting with one
No more changing angles (blade fixed @ 16°); motor and blade in the same plane as an main frame; 325mm blade (MS Composit MS-20325); Rouse-Tech 18/20 D Class AP RMS.
I launched it for the first time last 2011 EARS meeting and I should say that it was mainly success... except bunch of disintegrated and missed small support parts :)) Here some more detailed pics of Mk2:
All "yellow things" are (fiber glass-to-fiber glass nomex honeycomb) replacements for missed CF parts glued now on epoxy rather CA as before. The other very important mod is blade_stopper_at_start device to prevent hard impact between the blade and the main frame at the very first moment of start (4th pic; left to right, top to bottom).
Blade grip made of 2mm thick CF angle, stabiliser and launch_tube supports made of 1mm CF angle (both pre-preg); main frame made of 1.5mm thick CF (pre-preg); angles, tubes and sheet are from www.easycomposites.co.uk. I cut the other blade from the same pair to make stab surfaces. M3 bolts of blade grip are made of aluminium alloy (blade bolt and M2 bolts are steel) and bought from www.pro-bolt.com. Lock nuts made of aluminium by Ansmann. Motor tube connected to main frame by gluing (same Z-Poxy 30min epoxy) and wet lay-up of 2 layers of CF cloth. Two washers both sides of the blade (3rd pic) are actually TAMIYA 53572 TRF Damper Pistons made of PTFE.
Unfortunately I have no proper "blueprints" for whole machine, what I've got is this:
Blade grip at 1st pic (left to right), motor_tube at second and at least some info about stabilizer & launch_tube at 3rd picture of one of Mk2 prototype.
Plans: I'm going to launch updated Mk2 for the first time at the first 2012 season EARS meeting (04.03.2012) and hopefully by this time I'll also add some ~magic~ onboard which could help me to measure altitude and RPMs!.. //28.12.2011
P.S. If you have any questions/need more info/specs/data/etc. feel free to contact me as Alexander Kroll on Facebook, by flickr or Picasa and of course you can see me and Mk2 at EARS monthly meetings. Thank you.