Minimum inspired 4 blade pre-rotate Autogyro
I have long been fascinated by autogyros and recently took the plunge and bought the HK Cierva C30, with more or less disastrous results. Undeterred, I followed this forum and came upon Jochen's Minimum. I built the minimum, using the HK C30 blades, and found instant success. Old Jochen sure knew how to design them, bless him.
I have been flying the minimum for a while now and thought it would be nice to have a pre rotate feature rather than doing the autogyro shuffle down the strip or risking it getting off too early and having it do the funky chicken on its side.
I am a great believer in sticking to what you know and making slight adjustments to it. That's why my 'creation' has a minimum tail section and HK blades, I know they work.
I also thought that 4 blades would give me more lift than three. Ok , so now I have a design brief . But, how to achieve it all?
the First step was to buy a 4 blade flybarless head from ebay for £20 and a basic HK450 heli from HK for £23
Bearing in mind that I wanted to use a 300W motor driving a 9X6 for propulsion the first job was to replace the way-too-short heli main shaft with one that would allow prop clearance. Then I turned the rotor drive gear over so that the sprag clutch worked the right way for the HK blade rotation.
Keeping the same angles as on the minimum I angled the entire heli frame backwards to give me 8 degs lean back on the shaft. Then built a frame to mount this lot onto a tricycle undercarriage ( just like the minimum), a basic cruciform for wheel positions and a CF tube out the back to mount the tail on.
Rather than me bang on let me know if this thread is of interest and I'll give a blow by blow account of the build
Keep it coming
Nice to see you Joe, here goes,
One problem that needed sorting fairly early on was the TX I was going to use. I have 2 x Spektrum DX6i’s and they have a flap ‘switch’ rather than a rotary knob and I wanted to use the flap channel for rotor spin up.
The answer was to convert an old Futaba Skysport 6a to 2.4 Ghz using a FR sky 2.4 TX hack module. Now I have a 6 channel TX that I can proportionally control the spin up motor with.
Oh wait a minute the Skysport 6a is not a heli radio and I need to operate the swash plate, like a heli.
The solution was to have one servo for forward and back cyclic and one servo for left and right. I don’t need them to work together as collective is not going to be used, the swash plate is fixed on the shaft between two collets.
On the 4 blade heli head there are 3 ball links at 120 degs. The rear one was ok but I needed the left/right cyclic control to be a t 90 degrees to the fore /aft. To overcome this I fitted a steel band between the front ball links extending to a 90 degree position and put another ball link on it. Now it all works in the right sense. The picture should explain it.
I suppose before I go much further I should give some weights and measures
Rotor disc = 40”
Weight = 900g
Propulsion motor = 300w
Spin up motor = cheapo 450 size heli motor
Prop = 9X6 APC slowfly
Lipo = 1 X 1800mAh 3s
ESC = 2X 30A
Now, where was I, oh yes, as a result of making a longer main shaft the swashplate anti rotation fitting had to be lengthened (also in picture), but this wasn't much of a task.
As I mentioned the tail is pure minimum, the only difference being that the fin and rudder are built up balsa 6mm sq and tissue covered. There is on servo slung low on the U/C which has a CF pushrod going back to the rudder and forward to the nosewheel for better ground handling
The propulsion motor is offset to the right just as the motor on the minimum. you can see the amount of offset in the picture.To mount the motor i removed the heli boom holder and bent the side frames out 90 degs with a bit of a twist to give me 8 degs upthust compared to the shaft. This is in fact parallel with the tail plane .
I fly out to the RC Hotel early tomorrow for a few weeks to do some fixed wing and helicopter instructing and hope to continue with my similar experiments using heli parts for autogyros
I will watch your progress and will post any success or failure I have
Awe the best Joe
Ok Joe, Have a good time ( PM sent)
Obviously no interest in this so I will not continue posting
You can't get away with that for an excuse :p, some of us have only just seen the thread, and there are probably several who haven't seen it yet, with one or two saddos :eek: who look in dozens of times a day.
I'm afraid you will have to climb out and collect your toys and throw them back in the pram. Some of lead a sad existence called (sorry guys) "work":censored: so get back to posting and continue the exciting series now you have got the pilot study out of the way. :D
How far have you got with the test flying.?
All toys now collected an stowed in pram :D
First test flight was quite short and proved one thing. With a swashplate you don't need as much movement:eek:
Wind was about 8 mph and the spin up worked perfectly at what I estimated to be enough rpm I shut down the spin up motor and opened the tap on the drive motor.
Off it went like a scalded cat and rose into the air in about 20 feet. At about 10 feet up I put in some left cyclic and BAM 90 degree roll to the left. Whacked in some correction and BAM 180 degree roll to the right. Shut throttle in panic and tumble into long grass.....and breathe again. Mininal damage but repairs completed at home and try N0.2
This time it was flat calm. I reduced the throws on cyclic down to about 25% of what I had before and tried again. Again the beast shot off down the strip and got off in about 30 feet this time ( no wind I guess). This time I GENTLY put in some left cyclic and it was better but still quite twitchy, tried some right and yes the thing was controllable, Unfortunately it was also about 200 yards away and getting VERY small. Now I have a problem with orientation ( which is why the port side is red and the starboard green) and at that distance it was all grey and I panicked (again) and shut the throttle. This time tailplane and two blades busted :mad:
To cut a long story short I guess I should have put in some back cyclic to slow it up a bit (and possibly throttled back a bit) but I didn't. This bird flies , and a lot better than I can fly it:o
But, the system WORKS :D:D There is enough power, enough lift and all the angles seem right, it just scares the bejeebers out of me. But I will learn to fly it as it deserves to be flown:)
Need to place another order with HK for more blades before I can progress
The heli you linked was the right one. I ordered it from the UK warehouse and it came in 48hrs for £23 Pounds Sterling the head I got from ebay. I'll find the link hang on.
I this picture is my method of giving the blades the ability to cone. the hinge material is 2 Laminations of glow fuel container plastic( 5 litre) sandwiched between 1.5mm fiberglass sheet. This gives a nice snug fit between the blade grips.
On the HK cierva three blade head there is a 15 degree 'hinge line' I have incorporated this in the blade holder as shown.
Pic 1 shows the general layout of equipment. The glass fibre board frames attach to the metal heli side frames using existing holes in the metal. This view shows the rake angle of the shaft in relation to the keel tube (datum) 8 degrees.
Halfway up the GF frames 6mm holes were drilled, 6mm CF tube cyanoed in to provide a base for another horizontal GF board between the sides. This board houses the 2 ESC's and the RX (underneath) also seen here is the butchery to fit the motor mount
The bottom of the GF side frames are drilled to take the 8mm axle support. The 6mm axle slides into that and is cyanoed. the two cyclic servos can be seen in this pic too
Pic 2 shows the minimum heritage tailplane
Pic 3 shows the motor and amount of offset
Link for 4 blade head
Thanks for the links. Does the UK warehouse have the blades? I'll have to try navigating the HK system, I haven't used it yet as I refused to pay the shipping costs and may as well buy from UK suppliers when that is factored in.
One thing that will have to go is the heli canopy :D doesn't have the autogyro appeal. (And it covers up some, what looks like, luxury cnc machined FG sheet ;))
I think with the swash plate it is much more sensitive as you are actively altering the incidence angle of the blades. I might be wrong. A very short servo arm might help and allow you to have better resolution of control movement.
I believe that one of your problems "may" be in the fact that you attempted the ROG like "a scalded cat ". I have found over the years that these models can be very twitchy at a higher speed, in fact my two blade Minimum flipped on its back several times as I was testing it.only to find that it was stable at a lower speed,
And yes I have been watching with interest ,but only make a comment when I think it is applicable.
Chris, I don't have enough experience with Autogyros yet but I will take on board what you say in the next trial. I think I may have had too much forward trim on in the first place.
My main fears with this model were that:
a) it wouldn't have enough power and:
b) the blades wouldn't have enough lift
Both of these fears have evaporated. I guess I just need to learn to fly it
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