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Geoff's Rite of Spring


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As the sub-title suggests, this is not going to be a detailed build thread but a series of comments on a build that may, or may not, result in a flying model. I'm just hoping that when the rites take place there's a model to take them

I made my first mistake. Having been inspired to laminate the tail plane leading edge, elevator trailing edges and the rudder trailing edge, I cut the outline for the jig for the tailplane. I made it accurately to the drawing before realising it had to allow for the 1/4" wide laminations and be inside the outline rather than on it! At least I noticed before actually making the part so all I need to do is cut 1/4" off all round.

Be warned

Geoff

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I've been making and cutting out parts for the wing and laminating the tailplane leading edge and thinking about how I'm going to modify the front of the fuselage for an electric motor and a hatch for battery access. I think it would be an advantage to extend the sides forward of the existing F1, but 36" isn't quite enough and I don't have any 48" lengths (I'm tight and they cost more in postage). So how about I make the sides with 2mm liteply, because I have a 48" sheet of that from a batch I bought to deck my sailing barge in one piece.

I think it might be lighter but would it be adequately strong without doublers? I'd perhaps have to allow a little in the fuselage formers. It would save having to extend the 3/32" balsa sides.

btw I found it perfectly OK simply to spray the 1.5mm balsa strips for the tailplane l/e laminations and leave them for only about 15 minutes. They bent round the former easily and I just held them in place with clamps as my former is only about 15mm wide. Hope it's OK in the morning when I aim to take it off.

Geoff

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  • 2 weeks later...

As I said at the start I don't intend this to be a blow by blow build thread. I'm too shy for that and not always proud of what I make

The laminated leading edge of my built-up tail plane came out OK and I've made the whole thing now. Nothing very special and much like those others have made. Not done the elevators or fin and rudder yet.

I've moved onto the wing and cut out most of the parts. I did a dummy dry run of the starboard wing and it looks like my method will be OK. My method? Well I don't build over the plan but over a piece of lining paper protected by some cling film. That means I can see the drawing without its being obscured by inconvenient pieces of wood.

I glued the bottom main spar to the bottom 1.5mm sheeting and pinned it to the board then used the 3mm plywood patterns I used to make the ribs to position the trailing edge capping strip and the rear main spar and its capping strip at the aileron. As Peter suggests I packed up the rest of the rear spar with scrap 1.5mm sheet.

Where I deviate slightly is that I space the ribs by making a full set of sheer webs and use them to position each rib in turn. This also has the advantage that they fit well and it's a lot quicker than making each one individually. These are 60mm wide and 38mm for the narrow bay at the root. That makes it easy to build the wing without using the drawing as a jig yet ending up with an accurate build. I use a square to ensure the ribs remain parallel but it's not a problem anyway.

I've ended up with a wing half 5mm longer than the drawing so mine will be a long wing span Ballerina by 10mm At least the wing loading will be slightly less!  This is the first time I've put a wing together like Peter  recommends and I really like it. 

I've also marked on the outermost ribs the line for the sheet tip to make aligning it easier. I think I may glue a then strip of 2mm balsa sheet to locate the tip. Hopefully it'll ensure the tips at each end are identical - almost.

I'll try and post some pictures tomorrow.

Geoff

Edited By Geoff Sleath on 12/01/2016 22:46:54

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Not a blow by blow build but here's a brief update. I've built one wing just about completely and I'll probably have the whole wing finished this week built more or less to Peter's drawing including his building method.

One little problem I found was that after planing the chamfer for the aileron l/e there wasn't much of the top capping strip left, so I replaced it after glueing some 1.5mm x 1.5mm strip between the ribs to support it better. The problem is that the aileron is so thick and the leading edge material so slim at 6mm there isn't enough meat for a 90 degree angled chamfer so you just have to judge the optimum angle with the material available. That's a pity as my plane has a nifty attachment that allows you to plane at 45 deg accurately which makes perfect control surface chamfers with narrower material easy to achieve. It's not a serious problem at all but when I build the second aileron I'll set the top capping strip a further back and fit the support pieces right from the start.

However, I needed to get the servos for the ailerons to complete the wings and I've opted for these from Airtek. They're metal gear, ball bearing and are specified to have 3.3kg cm torque (about the same as a standard Futaba 148). They weigh only 20 grams and are much smaller than 148s. They have brass(?) servo arm splines and secure the arm with a 2.5mm machine screw (though one of the 4 I bought had a 3mm screw which I've replaced from my stock). They take standard Futaba servo arms from what I can tell - they have 25 splines and the Futaba arms seem to slide on OK. They look quite good.

I tested them using the servo test facility on my iCharger. They all centred very consistently and moved smoothly over =/- 45 degrees with 1mS to 2 mS pulse width (1.5mS centre) but could be pushed much further to +/- 60 degrees without a problem. They would go to +/- 90 degrees but they weren't too keen on the last 5 degrees so I didn't push it. This was all off-load testing so how they'll behave in real life is still unknown but they seem to be really good so far.

What servos are others using?

Geoff

Edited By Geoff Sleath on 19/01/2016 15:01:21

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  • 7 months later...

Well, my Rite of Spring has turned into late summer. The Ballerina got started with enthusiasm but got laid aside for a month or two when other things took priority. It's now very nearly finished and was intended for a test flight today but I had CoG problems as will be explained.

I didn't buy the wood pack but cut everything out myself. A first for me.

It's an electric version and the current spec (pun intended) is as follows:

Motor: Turnigy SK3 4240, 740 rpm/volt 50 amp maximum current

esc: Turnigy PLush 60 amp

(both those were suggested by BEB back in the winter and seem to be ideal)

weight including a 4S 4AH LiPO is 2.3kg- a smidge over 5lbs. So a bit heavier than Peter's but I'm not sure why.

Prop: APCe 12x6 draws 30 amps and 450 to 500 watts. APCe 13x6.5 draws 42 amps and consumes 600 to 650 watts. I intend to use the latter for the test flight (always good to have a bit of power to spare) but I think I may opt for the 12x6 afterwards (assuming there IS an afterwardfs).

Starting at the front:

ballerina motor.jpg

This is the motor installation. I made the stand-offs from some 12mm aluminium bar drilled in my bench press with 4mm holes. They were cut very slightly under size to allow adjustment using washers. Notice I cut the firewall with a hole big enough to allow a flight battery to pass through just in case it was needed to get the CoG right. Just as well because it was!

ballerina cowl 1.jpg

I'd never made a cowl before and I'm quite pleased with this one. I made the back plate first with 3 x 4mm dowel locating pegs and 2 x 3mm fixing bolts then just knife and forked the rest in a similar way to Peter's . The sides and top are 2.5mm balsa sheet end the bottom and front soft 6mm balsa. The cowl rings immediately behind the spinner were made using the off cuts from a hole cutter.

Here's the completed cowl

ballerina cowl 2.jpg

... and here it is fitted:

ballerina cowl 3.jpg

Those aluminium back plate spinners are very good and I'm pleased it blends in with the cowl. Their only fault is that it's a bit of a fiddle to get the prop in the right place for the front fixing screws to line up with the holes in the back plate.

ballerina open hatch.jpg

I decided to make the whole of the top fuselage from the fire wall to the turtle deck removable for access. I was expecting the battery to sit in this area but, as you can see, it has to be as far forward as possible to get the CoG right. Never the less the ease of access for the receiver and aileron connections, etc made it a good choice for me.

Here's the hatch fitted. The pilot will have to go. He's very porky at a whole 40 grams and behind the CoG, too! It's secured at the front by the top motor fixing bolts which protrude back into the hatch area and at the rear by magnets. It's a very tight fit anyway so I don't think it's going anywhere in normal flight.ballerina cowl and hatch.jpg

You can see the cockpit edging I asked about a few days ago. The screen is made to the same pattern as my Tiger Moth. It worked very well and looked OK until I distorted the rhs with my covering iron. It fixes with tabs let into slots and Cyanoed.

Here's a quick view of the top. My workshop's a bit cramped and I''l take a better shot on the runway before the test flight for the Completed Ballerina thread.

btw the boat hull in the background is a Thames sailing barge I built winter before last. I'm finding the complicated rigging a bit daunting. I built the Easy Street years ago and never got round to test flying it!

That's the story so far.

Geoff

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I forgot to mention the servos I'm using. They're all from Airtek. MO170s ballbearing metal gear for the ailerons (one in each wing) and PO200s for rudder and elevator. The PO200 have ball bearings but plastic gears. I wish I'd bought the MO200s which have both ballbearings and metal gears and may replace them.

Geoff

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Looks like I forgot to add the picture of the whole model. It was late

Here it is:

ballerina top view.jpg

I think one of the reasons I had problems with CoG is this tail wheel:

ballerina tail wheel.jpg

I didn't have one so I made this from scrap. The main bracket is dural from an old undercarriage. Both tillers (the one on the tail wheel itself and the one on the rudder) are made from old fibre glass printed circuit board. The wheel support is brass and the springs came from an assortment bought from one of the tool stands at a show.

I was very conscious that I was putting weight in the worst possible place but assumed the heavy battery would more than compensate for its 24 grams. It did - but only by pushing as far forward as possible through the firewall.

The irony is that when I was looking to see if I had a lighter pilot anywhere I found a brand new HK plastic scale-like tailwheel tucked away. My Dad was hoarder of international scale and I always told him that if you had something but were unaware, then it was the same as not having it. How I take after him. Anyway, I quite like my homemade tailwheel so it stays for now.

Geoff

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Managed to maiden my Ballerina today and it flew brilliantly with just small trim adjustments.

There are one or two minor issues. The first is that it has a tendency to nose over on landing which can easily be corrected by angling the undercarriage legs a bit further forward.

Also it seems to need quite a lot of up elevator which may be because I've somehow got the wing seat wrong and the incidence between it and the tail plane needs to be adjusted. Currently I have about 0.5 degrees of downthrust but it can be easily corrected by the number of washers on the motor mount spacers. It would be a pity to have to change that because as it is the spinner blends perfectly with the cowl.

I did the test flight with a 13x6.5 prop which gives me about 650 watts on this 5lb model. There was power to spare but the nose over tendency damaged the tip on our hard runway so I fitted a 12x6 which gives a power output of 450 watts. Surprisingly there is ample power for aerobatics - stall turns, easy axial rolls in either direction and big loops. In this configuration the motor draws only 30 amps flat out so energy consumption is very low (less than 50% of a 4000 mAH 4S battery after 7 minuted). So much for 100 watts/lb needed for aerobatics. It would be great to fit a lighter battery but I need the weight to get the CoG in the right place - the battery is as far forward as I can get it.

The 60 amp esc gets to about 35 degrees - measured with my calibrated finger. The ventilator hole I cut in the cowl doesn't do much for the cooling as the battery covers it. I'll probably fir an airscoop in the fuselage side and an air exit underneath near the back.

I checked the stall at a good height and it was a non-event. The model just mushed about and showed no tendency to drop a wing. I was tempted to put the rudder over and try a spin but chickened out. That's for another day.

post tesr flight.jpg

Post flight smile.

 

ballerina and tiger moth.jpg

Hangar mates.  DB Tiger Moth and Peter Miller Ballerina. Both new builds test flown this year and both flown today.

Geoff

Edited By Geoff Sleath on 30/08/2016 22:01:11

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