Hi,

I've been posting on the "Anyone building the RCM&E plan this month?" thread, but to keep it on topic I've started this new one for Minitwirl

Minitwirl is a 50% scale version of my Twirl, and first flew on Saturday 16 September.

It's made from 2 mm depron and follows the plan except that there are no carbon wing spars, and no forward fuselage doublers.

The rotor blades are 2 mm depron without paper reinforcement, with 22swg rotor axles and bearins/retaining bushes from a WD40 spray tube.

The radio is a Falconmodels set-up with an 8 gram brushless motor driving a GWS 6 x 3 propeller. The battery is a 2 cell 250mAh LiPo.

Ready to fly, Minitwirl weighs 46 grams, and so the rotor loading is about the same as Twirl.

Here's a link to a video of the first flight (18Mb):-

http://media.putfile.com/Minitwirl

You can see some ground shots in the other thread, but I've attached a couple of airborne shots from the movie. To give some idea ov the scale, the aerial (which I left dangling untidily below the aircraft ) is 8 inches long.

It is fun to fly, just like the bigger one so far, but I haven't explored the full envelope yet.

Al

Al,
The Minitwirl is a sweetheart! From the video it looks as if it's good outdoors too. Grey skies in England? Oh say not so!

I guess that I'll have to get a small motor and some 2mm Depron - this is too neat to pass up.

Dennis

Hi,

I've just flown Minitwirl again - this time in the sunshine . I flew it for 10 minutes, and found that the battery took 120mA to get it back to full again after the flight, so I had about a 50% reserve.

I did a hand launch again (must get the grass cutter out ), and l did a vertical landing back on the strip this time. It coped well with a 10 mph wind, but it's now up to 15 mph with gusts above that.

One interesting thing is that it needed quite a lot of left trim throughout the speed range. I wonder if this is the same effect that is alluded to in this thread:-

http://www.rcgroups.com/forums/showthread.php?t=559069

I had no lift or control problems at all, but the rotors are more in the propwash than the bigger Twirl. After the initial adrenalin rush of the first flight, I'm settling down with it, and hope to try it indoors next Friday.

I'm looking at the plan again, with an Aeroace/X-Twin airborne radioand motor pack in my hand. Maybe it can go even smaller......

Al

Hi,

Another flight today, this time with the wind at 13 knots (a bit over 15 mph).

The little thing coped very well. The only thing to watch is it getting blown over when on the ground . I was lucky - the wind died a bit just after it landed so I was able to grab it quickly.

It thus seems that you can fly the Minitwirl in the same conditions as the Twirl.

So, for those who might have been concerned that this would be a fair weather flyer only, don't worry, it took the wind in its stride. Might persuade a few others to build it?

Cheers,

Al

Hows about posting some plans? I think I have all the radio components and motor/battery. Just need to get some 2mm depron now.

Mark.

Hi Mark,

I just used the original Twirl plan, scaled down by 50% when I printed it.

You can find a pdf file of the Twirl plan in reply #63 of this thread:-

http://www.rcgroups.com/forums/showt...=450021&page=5

Hope this helps,

Al

Thanks Al. I found them and printed them at 50%. Now all I need is the Depron. I believe my local hobby shop has some - guess where I will be tomorrow!

Mark.

OK so all I could get was 3mm depron. Al - what do you think of using 3mm for the mini twirl? I guess it will be a little heavier but should still fly?

Hmm,

That's a difficult one. My 2 mm depron bare airframe weighed about 10 grams. Simplistically therefore, a 3 mm depron airframe would weigh about 15 grams assuming that the density was the same. I know that 5 grams doesn't sound much, but that's about a 10% increase in the total finished weight with everything on board. Having said that, some builders of the bigger Twirl had weights 50% greater than the prototypes, and they flew OK.

The thickness/chord ratio of the blades might be a factor too.

I have heard that people have sanded depron sheet down to the desired thickness but I have not tried it myself - would that be an option?

On the other hand, why not just try it with 3 mm depron and let us know how you get on ? I think that I would try to thin the blades down a bit if I was doing this, however.

Hope this helps,

Al

ive seen this thing go and its awesome. the only thing left to do is fly it
ill get some video for y'all to see.

Al; I could not figure a way to print the plans out at 50% so I printed them out fulsize and used the photocopier at work to reduce them. This mini-twirl is really small! it makes the 3mm depron look like decking planks! I think I will goahead with the 3mm stuff for the fuse, tail and wing but will see if I can thin it down a bit for the rotors. I will see if I can make a hot wire cutter and a jig to thin the rotors. I am reluctaant to sand the rotors and that may introduce some variability into the thickness of the blades and the weight distribution.

I intend to install a Falcon Breeze Block and power it with a Mighty Midget brushless motor on a 2 cell Lipo. I was thinking about leaving off the landing gear to save weight and just land in the grass.

BTW this is my first attempt with the really small stuff. I bought the Falcon gear for a Falcon DH Moth I bought but have not had the courage to build yet.

Wish me luck!!

Mark.

Hi,

It is pretty small, I agree - you can see how small at the beginning of the movie when I'm holding it prior to launch.

This was also my first attempt at a "small" R/C autogyro. Sounds like your radio/motor is almost identical to mine, except I chose a separate rx and servos.

When suggesting sanding, I had envisaged taking a sheet of depron and sanding with a large block with, say, some 2mm ply at the edges so that you got a consistent thickness. Only then would I cut out the components. I would have thought that the blades would be easier to do that way, since they are just rectangular planks.

As I say, I have not done this myself - might be worth searching RCgroups to see if there is better advice.

Removing the undercarriage will certainly save some weight.

Good luck, and let us know how it goes.

Al

Well I bit the bullet last night and started cutting foam. I thought I would start witht he rotors as they are probably the most critical components. As we discussed earlier I made a jig from some scrap wood and cut some foam to the width of the rotor blades and started sanding. I was surprised at how quickly and easily I got the foam to the correct 2 mm thickness. With that done it was a snap to complete the rotors themselves. I now have two handed rotors - yes I did remember to make a cw and ccw version!. My main problem here was the size of my fingers in relation to the components. Getting all the rotors lined up, overlapping each other and staying put while the glue set was the most critical stage.

Next I started on the fuselage. I wasnt sure about the 1/8 dowel (or 1/16 in this case) running the length of the fuselage. So I thought briefly about makeing the fuselage a "shocky" type but eventually ended up with two 1/4" wide strips of 3 mm foam running the length of the fuselage. I ran it so that it also provided the support for the tailplane and ran to the centre of the motor mount. I fugure that this will stiffen up the fuselage sufficiently for such a small model (I hope it is not overkill).

Tonight I will start on the wings and tail and see how I get on with those. They seem to be straightforward enough.

Will post more later.

Mark.

Hi,

Flew Minitwirl indoors for the first time tonight. I did a take-off from the smooth floor, and it was just like the bigger Twirl; the speeds were similar.

I just missed a basketball hoop on the side of the hall that I had forgotten about , but apart from that it all went very well. When the nose was pulled up to do some slow flying, I had the impression that it wanted to pitch up of its own accord so maybe the C of G is slightly too far aft - I didn't notice this outside but maybe the windy conditions masked this effect.

It was a really enjoyable indoor session .

Al

I made some more progress this weekend. I now have a - more or less - fully assembled Mini-Twirl airframe. For the rotor bearing I used the plastic sheathing from the Dubro mini pushrod assembly and used a large T pin, with the head cut off, as the shaft. The fit is good enough to allow the rotors to turn freely without binding and close enough not to have any rotor wobble.

I still need to hinge the rudder and install the radio/motor. I ran into problems with the Falcon radio as I discovered that I had got the wrong connectors for the battery to speed control connection. I have just contacted Falcon and hopefully I should have the correct stuff soon.

Now that the model is almost complete I am looking forward to the first flight. It should be interesting.

Mark.