Prima Ballerina

[kc]

When thinking about electrifying an IC design I always want to get the Lipo well forward and that means moving the firewall forward. Means a fair bit of modifications to the fuselage front. So I thought a slightly different name is apropriate too. ( someone had to use it)

My preliminary rough drawings are as follows - comment if you have some opinions

[kc]

Because the original IC plan has a straight section in front of F2 and then goes to a steeply curved part it would not be possible to have the fuselage side extend to the more forward position of F!. Therefore I have drawn it as a straight taper from F2 to Nose Ring as you can see from my plan view. This also allows a rolled balsa hatch to follow the line of the roled balsa turtledeck. Should look much the same as the original I hope yet allow a long hatch to change Lipo and also to get to the motor.

In my models the ESC goes underneath the ply battery tray and gets some cooling air through.

Edited By kc on 30/11/2015 19:17:45

Edited By kc on 30/11/2015 19:18:34

[Biggles' Elder Brother - Moderator]

Hi KC,

can you give us an estimate of the length, height and width of the battery space so we can work out what might fit in there?

BEB

[Geoff S]

I built a Skyshark Fantasy from a kit last Spring. It's intended for up to a 60 size glow and I built it from the start as an electric model. I moved the firewall forward exactly as suggested for the Ballerina and made a similar hatch (incidentally it took ages ). I ended up having to push the battery right back over the wing in a battery box because it was so nose heavy. I keep meaning to move the elevator and rudder servos to the back but haven't done it yet.

So all I'm saying is that having the battery so far forward may not be its best position, so make allowances for either a shorter nose or for a more rearward battery position.

As you can see it has quite a long nose and battery is pushed back over the wing rather than just behind the motor where the hatch is.

Geoff

Edited By Geoff Sleath on 01/12/2015 00:01:59

[kc]

As drawn the space for the Lipo is 2 3/8 inch (about 60mm) minimum by 6 inches( say 150mm) but the length could extend all the way back to servos if the hole in F2 is lowered slightly. Limiting factor is WIDTH of hole in F2. Height avail is 2 3/8 ( say 60mm) up to the fus sides but the lipo tray could be lowered another 1/2 inch or so if desired. It is at that height in order to get handy access for fingers! Hatch would be hollow in middle section so could allow a Lipo to go a little above fus side height. So I think a 4S 5000 might fit OK.

The drawing and the slots shown for Velcro straps was based around a Zippy 4S3000

Motor is intended to be the Turnigy 3536/9 which produces 500 watts at 33 amps on the Zippy 4S3000 20C and has done 561 flights in an Avicraft Moronic after the OS 46 was removed. ( Moronic is equivalent to kit built balsa Wot4 and is fully aerobatic on this Lipo & motor but only for 6 minutes at full throttle)

Note that with the forward mounted F1 the motor will slightly protrude up into the hatch. This is no problem but bigger chunkier motors might not work without lowering the thrustline.

[kc]

Geoff you are right -hatches take ages to make. Actually usually take about twice the time to make hatches as it takes to build the fuselage. It is fitting between two fixed points and making a neat fit. My designs try to avoid this by building right onto the fuselage which will be covered in thin polythene to stop glue sticking. Hatch catch & dowel are best done at the pre skinning stage ( or pre sanding to shape stage if solid balsa)

Hatches sometimes come off in the air and experience has shown that it's better not to waste an hour searching the long grass at the outer perimeters of the field when you can make a new hatch in 30 minutes. Simple is better!

As for Lipos needing to go further back, my latest own design called Rapido was made with a long front and eventually proved tail light! I cannot get the Lipo any further back without moving servos back! Hence it won't take more than a 3S2200 and very short flights occur. If only I hadn't moved the servos well forward! At the design stage I didnt allow enough for the fairly short taill moment.

[kc]

We don't always realise quite how much skill goes into Peter's designs until we try to modify them! Lots of tricky bits and details have been worked out for us. Changing them reveals the cunning details of the original design. One little example is the fuselage side can just be made from a 36 inch sheet.

When I decided to move F1 further I found it would need a 37.25 inch sheet! I dont think this will actually be a problem as the joint will be beyond F1 and is partly covered by a 1/2 inch doubler . Not a structural strngth problem. The join could alternatively be made at the tail end , normally not a good idea but in this case it would be covered by the ( unusual ) rear ply doubler under the tail.

[kc]

The Ballerina is already fairly long in the nose so no need to alter that at all for electric.

Comparison with Oodalally is interesting.

Ballerina has spinner 11.5 inch in front of CG while Oodalally is only 10.5

Length behind CG is 29.5 on Ballerina and Oodalally is 32.25.

Many other differences too of course but the shorter tail model -Ballerina- has a longer nose so better for electric where the main weight is the Lipo which has to go further back

[Peter Miller]

Posted by kc on 01/12/2015 12:50:01:

The join could alternatively be made at the tail end , normally not a good idea but in this case it would be covered by the ( unusual ) rear ply doubler under the tail.

The rear doubler s a recent idea. If you look at it, on most models the tailplane is stuck on the the fuselage sides at the rear. If you knock the tailplane or the model tumbles on landing it will oftencrack the fuselage sides under the tailplane.

For many years I have fitted a sheet tailplane platform which provides more gluing area for the tailplane. Now the side can crack under the platform

The rear ply doubler prevents this and spreads the load over the whole side at the rear. This can save a flying session for a minimum of extra work.

[john stones 1 - Moderator]

Electric motors leave you well short of getting the prop clearance as you say K.C, standoffs is another way to go or build a small box onto existing F1 as in artf's, or you could simply shorten the nose a little.

John

Adds a bit of meat for snakes or push rod exit as well Peter

Edited By john stones 1 on 01/12/2015 14:11:34

[kc]

Probably we should reserve the term "prop clearance" for the amount the prop misses the ground! But I know what you mean here. My reasoning is that standoffs or a box just move the motor forward but don't allow the Lipo to go forward too. Whilst a Lipo & electric motor weigh about the same as an equivalent glow the Lipo puts the weight further back. Hence the probable need for lead to get CG correct.

Same with shortening the nose but that would also make the model look ugly as well. Not what we want surely, it's the nice looks that attract us to this model.

[kc]

Peter.

Thats interesting about the rear ply doubler. Do you advise cutting a hole in the ply before gluing in place? ( Hole for the snakes to pass thro is what I mean. )

[Peter Miller]

Yes, that is a good idea.

To be honest I tend to forget and then cut a slot with a cutting disc but then I do tend to go to fast for my own good!!!

[Dave Hopkin]

Moving F1 forwards would indeed create enough space between F1 and F2 - I quite like that solution KC

[Gary Vinten 1]

that will work kc

[kc]

Hatch catches are always a problem. Putting them in at the hatch construction stage seems best. I thought I might have the catch operated from the cockpit like this ......

[Dave Hopkin]

You could be artistic and bend the exposed end of the piano wire into a control yoke shape......

[kc]

A few extra bends could form a reasonable control yoke. If the wire comes further back for a control yoke then it will need a limit stop to keep a bit of compression in the spring. Therefore another washer soldered on by the guide block.

[Geoff S]

I just used location dowels at the front and magnets at the back to hold the hatch on the Fantasy. It hasn't fallen off yet but it is a close fit. Open cockpits allow more options than closed, of course.

Geoff

[kc]

I have decided to fit a Turnigy 3548/6 ( instead of the 3536/9 ) which is just a little longer and heavier.

[McG 6969]

Hi kc,

Just a question, please.

Is your 'Yoke-Hatch-Retaining-System' internationally patented & if yes, what could be the legal terms to make it possible to obtain a 'long term production license agreement'... ?

Happy yoking & Merry Christmas

Chris

Brussels, Belgium

[kc]

I published the hatch catch just so that nobody could patent it!

[kc]

Having decided on the motor I could now cut out the fuselage parts.

The fuselage sides on my electric version are extended right up to the nose to form the cowl, so this means extending the balsa to 38 inches. I chose to glue on a couple of inches at the front end where it's not structural. So just a butt joint done in the traditional way - balsa pushed tightly together and held by masking tape, then opened using the tape as a hinge whilst PVA glue is inserted. Finally hing closed, pressed flat and covered by another piece of tape whilst glue dries. Result 38 inch balsa sheet.

There are many ways to transfer the plan to balsa- carbon paper, tracing paper etc etc but my favourite is to photocopy the parts and stick onto balsa with small bits of double sided sellotape. Then I cut right through the photocopy and into the balsa or even thin ply. On thick ply I just score the ply and run a pencil around the scored groove for clarity.

All the smaller parts can be photocopied onto A4 paper. The fuselage can also be done with A4 paper but several overlapping copies need to be made and sheets taped together. A convenient place to join is the former positions. One sheet is cut right on the join line and the other left overlapping ( well underlapping! ) and sellotaped. Then I aligned the straight top edges wih the balsa sheet and secured with small pieces of double sided sellotape. Then cut right through the photocopy and through balsa with a scalpel. That made one fuselage side which was used to mark out the second side.

When both sides were cut out and sanded to precise shape they were checked against the plan to ensure the critical areas of wing seat and tailplane seat were absolutely accurate.

[kc]

Next came the 1/32 birch ply doubler. This was marked out from fuselage side taking care to minimise wastage of expensive ply. The ply doubler extends up to the new F1 position ( i.e. longer than the standard IC version ) and of course back to a rounded shape past F6. But it does not go right down the fuselage sides at front because its cut back where the thick 1/2 balsa doublers are located. This means the balsa can be sanded & planed back to a nice rounded shape without having hard ply in the way.

So the ply was marked out from a fuselage side with a very fine marker pen. ( Wilko set of 4 for around a pound ) Ply of 1/32 or even 1/16 can be cut with repeated cuts with a Stanley knife ( new good quality blade! ) and also up to 4mm Liteply too. The straight edges were cut using a steel straight edge and Stanley knife in about 3 strokes. Curves were done freehand following the marked line but didnt quite cut through so I ran the fretsaw around to separate. A scalpel would work to cut ply but the pressure needed is so great that blade will likely snap which is an eye hazard.

After making the first ply doubler and checking accuracy a second was marked out and cut.

[WolstonFlyer]

Does cutting parts out count as starting to build?