Kanga - Fun Flier

[Martyn K]

I have been following the posts on the Facebook Inter Club FunFlier Competitions group with interest. These contests seem to take part (mainly and at the moment) in the North west of England and look to be a lot of fun. I fancied taking part but did not have a suitable model that I was prepared to destroy!

Being a builder, an ARTF didn't appeal and neither did any of the kits. I found a plan on Aerofred for the Joey Funflier and I used this as the basis for my humble efforts. Now, the next contest is on the 31st October 2016 and I want it finished trimmed and with enough time remaining for some practice flights.

The original was IC powered, I wanted electric, a 4S source and use the cheapest reliable hardware (read Hobbyking) that I could find. I don't expect this aeroplane to have along and happy life, especially with me flying it.

I am also fortunate that Andy Ellison has been secretly (oops - let that slip) coaching me with lots of sensible ideas on improving (I hope) the breed. This will be a dedicated contest model - so things like a maximum power on time of 3 minutes will be the target and power source selected to suit. Think Frantic rather than relaxed.

The last Nationals event in 2015 had a healthy number of flyers - I'll bet other events wished they had this volume of competitors:

(Photo - Andy Ellison)

So - Let the race/challenge begin....

So my working plan looks like this today.

A bit more detail to go on but the wing and tail outline and sections are Joey - not taking any credit for this. The fus has been modified and simplified to accommodate an electric motor and batteries and the u/c has been moved even further forward. Ground looping may be a problem I have to live with.

Remembering that I need this completed quickly, I made a start Monday evening on the tailplane and fin while I was still working on the plan.

The Elevators and rudder hinged with Kevlar strip - that I tend to use for all my models now. The clamps are holding a strip of 0.014" Carbon Fibre with an additional doubler along the main tailplane spar - effectively the other side of the hinge..

..and clamped while the epoxy dries.

This was completed very early Tuesday morning...

and the fin assembled as well -

again using a carbon reinforcement along the fin post

Wing ribs cut while I was waiting for the glue to dry

You don't get many of those from a sheet of 36x4 balsa.

With tailplane and Fin parked, on Wednesday night I made a start on the wing. The outline and rib spacing was drawn directly on the board, lower main spar pinned down and the wing assembled

The servos will be housed in LaserCraft Servo boxes sandwiched between 2 ribs like this. Servos located on the upper surface of the wing

The LE and two front spars are laminated from 2 x 1/8 sq spruce with 1/4 /18 spruce doublers across the 3 centre bays.

Last night (photos to follow), the D box LE sheeting was added and webs inserted.

More to come

Martyn

[kc]

Are you expecting to extend the nose compared to an ic version?

[john stones 1 - Moderator]

Looks like fun Martyn, tried to get an inter club thing going in our neck of the woods sadly no joy, lecky's the way to go no deadstick if you mess up.
John

[Martyn K]

Hi kc

Yes - I am using the principles of moment to calculate the new nose length.

Basically weight of a 35 ic (OS35 = 363g) x existing nose moment = (weight of D3548/6 (159g) x new moment) plus (weight of 2200 4S (235g)) x moment to pack centre of mass) = constant (I think!). Haven't allowed for the fuel content as CG is normally dry but going for a rearward (30%) CG anyway.

Surprisingly, the nose firewall only went forward about 12mm

Martyn

[Martyn K]

John

The event looks like great fun - I am not sure where you are based but I am sure you would be welcome as a team of 1 - much like I will be as well for my club.

The next event is at Sleap Airfield - near Wem in Shropshire - 30/10

 

Martyn

Edited By Martyn K on 23/09/2016 16:10:41

[kc]

Well Martyn i mentioned this because when i electrified an existing and nearly comparable model I found the motor needed to go much further forward than i expected. I replaced an OS 46FX in an Avicraft Moronic with a 3536/9 motor and 4S 3000 which weighed much the same and found the motor needed to go about 100mm further forward to avoid using lead.. Reason is the OS 46 has all the heavy bits like bearing right at the front while much of the electric setup like the Lipo goes much further back. in fact the heaviest bit ( half the Lipo ) is right near the back.

I hesitate to show you my crude lashup to determine this but it may just help. here a piece of wood is balanced on the points of two screws resting on a hard Formica surface. With the engine and tank one side and on the other the motor with Lipo positioned as far out as needed to equal the weight. ( visually the photo doesn't seem to show the actual difference that I report - this was actually a separate test for another model )

By all means have the Mods remove this photo when you have seen it as it spoils your nice thread!

[kc]

Actually I have just realised I have a Turnigy 3548/6 handy and an OS 40 SF which weighs just about 360 g without silencer. So I simulated a 4S2200 ( actually a 3S2200 plus a PP3 which together weigh 235g ) and balanced them on my crude balance. Result is to balance without lead the 3548 needs to have the prop driver about 50mm further forward than the OS40. (using a SLEC engine mount and 6oz tank on the glow side and a 'cross mount' and alloy prop adaptor with Lipo just behind bulkhead on the electric side. )

However if the glow version used the Rx Nicad under the tank to achieve balance then the electric version ( if BEC used) would need to be about 70mm further forward at the prop driver ( rather than 50mm ) All by practical experiment with a crude lash up but food for thought perhaps?   Bearing in mind if the front is too long it's easy to move the lipo back but if its too short you have to add lead.

Edited By kc on 23/09/2016 18:41:49

[Bob Cotsford]

Posted by kc on 23/09/2016 18:37:24: Bearing in mind if the front is too long it's easy to move the lipo back but if its too short you have to add lead.

Edited By kc on 23/09/2016 18:41:49

or push the motor further out with stud in tube stand-offs?

[Richard Harris]

Watching with interest Martyn,

 

I can confirm that the inter club fun fly comps are good fun, all very light hearted with everyone being made welcome. I compete with a foamie WOT 4 and have stood my own up against the bespoke fun fly type models. You would be surprised just how hard it is to drop an egg from 50ft onto a target, not easy at all.

We could do with a few extra pilots on our 'made up' team to show those Northerns we can drop an egg in the same field!

 

 

Rich

 

Edited By Richard Harris on 23/09/2016 19:09:51

[john stones 1 - Moderator]

Aye lad you can tell the Northerners in the photo line up....still got their pit helmets on

[Martyn K]

Ha ha.. And there trouble down't mill.

Back to kc's comments.

I will go back and check. The difference may be due to the rearward CG and I have moved the LiPo much further forward. You do not have me a little worried though. Bobs idea about using standoffs may be realised.

Moving the LiPo wont be that easy - its going in a dedicated box so its not going to be easy to move...

Thanks all

Martyn

[kc]

I only mentioned the balance because I thought Martyn had not started the fuselage yet.....but it seems you probably have! If it's too late I wish I hadn't mentioned it!

Bobs idea of stand offs might work in this instance because the 3548 seems a long and heavy motor, while the proposed lipo is quite light. Normally the lipo is the really heavy part and the motor needs moving forward an awful lot to compensate. The problem seems to get worse with higher wattages - the motors are not a lot heavier but the lipos are much heavier so moving just the motor a little does not achieve much.

[Martyn K]

Thanks kc

i haven't started the fus yet so I am very grateful for your thoughts. I'll post my calculations on here later. The original was powered by a west 36. This is designed for a tuned pipe and is actually lighter than the os engine I quoted earlier. Assuming that a pipe was used then I didn't count the weight of that as it would be hung under the fus with its mass spaced faiy evenly forward and aft of the CG. Including the header of course.

I'll add a littler extra for the mount but I am really unsure just how far forward the original motor was mounted which I guess is the real crux of the problem.

So. Some more thinking to do.

martyn

[Martyn K]

I have redone the calculations and allowed a 10% safety factor.

On the original Joey, the engine is a piped 36 with Tuned pipe, The mass of the pipe and header appears to be split fairly evenly around the CG so I have discounted it. My 'replacement' engine is an OS36 with standard exhaust and for the example weighs 363g. This should be reasonable allowance for the weight of a Nylon mount and other hardware. However, this is somewhat heavier than a West 36 without silencer. The distance from my CG (30%) to the front edge of the cylinder is 147.5mm which gives a calculated mas moment of 53564

My derivative has the centre of the motor at 203mm from the CG with mass of 159g (with hardware) giving a mass moment of 32277 plus the LiPo is mounted(centre) 116.5mm from the CG with a mass of 235g giving a mass moment of 27260. Combined, these give a mass moment of 59537 which is 11% larger than the original. I can move the ESC to compensate if necessary

How does that sound? I have effectively now moved the motor forwards by 56mm. I feel that I may have overdone it...

Martyn

[Martyn K]

A little bit more progress. as mentioned, the D box on the wing has been completed and webs and cap strips added. I have selected slightly harder wood than I normally would for this and unfortunately, I can feel the weight

The wing tips are cut from 3/16 light balsa with a single 1/16 ply doubler across the TE part to add a bit of toughness.

And glued in place with a 2mm lite ply end rib - which will get hollowed out shortly.

Finally, the first aileron has been built.

with a 1/8 x 1/4 TE. The 'ribs' are simple pieces of oversized strip then sanded down to size. Quicker and easier and probably more accurate than cutting dedicated parts.

to help keep it stiff and then test fitted. This is quite a big wing now...

The second aileron is currently being built on top of this aileron - with the original upside down

More to come

Martyn

[kc]

Martyn, I would suggest a mock up of the part built fuselage together with fully built wing & tailplane would be worthwhile. When I electrified the Moronic I used a lash up of motor & lipo on a bit of ply rubber banded to the fus front. Motor & lipo were then moved to a balance point which avoided lead. The motor and 4S300 was far further forward than the OS46FX had been and quite a bit further forward than I expected. This was well worthwhile - the model only weighs about 4 pounds ( despite being oil soaked from it's previous glow powered life) and has today completed 879 electric flights. Very satisfying.

Rubber bands, bits of sticky tape and ten minutes of experiment equals or exceeds calculations!

 

P.S. it is, of course, easier to saw a little off the fus front than it is to put a bit extra on.....

Edited By kc on 26/09/2016 12:19:32

[Martyn K]

Thanks kc. Yes - I think that would be a good idea. Quite easy to achieve as well. I'll simply cut the fus sides about (another) 50mm to long, fasten the motor and prop to the bulkhead and adjust to suit. Not really rocket science

I'm planning to start the fuselage tonight. My HK parts should arrive tomorrow so should be able to fit out fairly soon as well

Martyn

[kc]

Looking at the ailerons it would seem the fuselage must be very narrow at that point to avoid clashing. Or is it an illusion? ( sorry I cannot get into the original Joey plan so I don't know the design)

Very nice balsa workmanship - it inspired me to get on with some balsa work!

[Martyn K]

Thanks - you are embarrasing me.. ..

The fus is 50mm wide at the start of the ailerons. I only need 40mm to get the LiPo to fit but these are from the original plans. If anyone wants a full size pdf of either the original Joey or my variant, please PM me. I can also supply Joey as a DXF as wll

Martyn

[Martyn K]

I had a very nice PM last night from a fellow forumite who asked me a few questions and provided some suggestions (in italics) after reviewing my WIP plan. It was too useful not to publish here ..

<snip>

u/c I would have thought the original location under LE was OK. 10SWG ( 3.2mm) would seem sufficient for a double type u/c rather than 4mm. My Moronic uses two struts each of 10SWG and was perfectly OK for the first 500 landings, then it started to bend out of shape! Still going at 879 landings though. The design uses a couple of thin wire hooks for rubber bands as a spring. I removed them because being too low down they caught the long grass in winter. Probably caused the loss of shape. I suggest a similar one with band clear of grass. Personally I prefer torque rod type u/c on all my other models.

I moved the uc forward to help protect the prop. Andy Ellison is adamant that I don't under spec the uc legs. They get a lot of abuse with lots of fast touch and gos and he thinks 8swg is about right. The wheels are actually forward of the prop arc. If it does nose over it should rest on the spinner and wheels and hopefully save the prop (edit. Not sure that will be true now if the nose gets extended further)

With ailerons very close to fuselage any slight misalignment of wing could cause an aileron to catch the fuselage and jam. Even touching a wing on ground during takeoff might cause this misalignment despite wing bolt.

Yes. Another Ellison point. He says design to allow for a 30 degree skew. I am going to put a foam block where the ailerons meet the fus. Allowing for 30 degree aileron deflection if the wing does skew, the foam will shear and hopefully the ailerons will be protected. I will try and do something similar at the LE as well but that is more tricky as it will need to support the LE of the wing. I am using bands to hold the wing in place not bolts or pegs

Doubler. If doubler is to be ply for electric it could be much smaller than shown. A diagonal line from u/c to just behind wing works OK for my models and saves ply ( cost & weight!)

The structural aspects of the fus will be a little narrower to accommodate the foam. Need to keep sufficient material for the motor bulkhead though.

Lipo. such a small lipo might even fit in vertical behind motor bulkhead keeping all the weight forward. Seen this used on vintage , scale SE5's etc. Or a bit diagonal.

I am going to use the uc legs to hold the LiPo in place. No hatch. A real crazy thought. That idea may get changed though

Just my crazy thoughts........

The best ideas are always a little bit crazy.

</snip>

Thanks for the ideas and suggestions - appreciated

Martyn

[Martyn K]

I have been pondering the fuselage detail for a few days now and with some additional off line conversations with a friendly forumite I have decided on this approach.

The objectives are:

1. Easy access to the LiPo. I don't want hatches or screws or anything like that

2. The u/c must be able to survive a 45 degree approach and bounce

3. If the wing skews by up to 30 degrees it mustn't damage the wing

4. It doesn't have to be pretty

Here is a bit of detail for the front fuselage

• 3mm sides, 1.5 mm ply doublers
• The fus has been narrowed from the original Joey by about 15mm
• There are 3mm ply braces/supports around the U/C legs
• The main legs are 8swg. The last 12mm of the leg are bent backwards by 90 degrees to take away the shock of a straight on landing
• The front torsion bar U/C support legs are 16swg, extended outwards by about 12mm each side to allow the u/c to spring backwards
• Behind the wing - in line with the ailerons (deflected), the fuselage is cut away and replaced with a foam block. If the wing skews the foam block will get crushed, not the wing.
• The LiPo is placed in a 'box' in a slot in the lower fuselage - supported at the front by a Lite Ply plate (25mm). The box has foam padding to protect the LiPo
• The u/c leg has a fuel tube across the horizontal part that sits in a slot under the LiPo.
• The u/c is swivelled into place after the Lipo has been fitted and held in place by bands to the peg just above the LiPo. The u/c cross member supports the LiPo.
• The wings are held in place by bands
• The LE of the wing has a 2mm carbon rod (75mm wide) which rests against the 3mm ply former. This should protect the LE if the wing skews

This is what is looks like so far.

3mm ply former with slot for LiPo

Slot cut for U/C leg to sit in. The 3mm ply supports have not been added yet (I may use aluminium instead of ply)

Rear former, you can see the cut away for the foam block nearest to you

Thoughts please, but I am probably not going to change my mind too much on this. I am running out of time

Martyn

Edited By Martyn K on 28/09/2016 15:46:52

[john stones 1 - Moderator]

I think you have number 4 covered Martyn

John

[Martyn K]

Ha ha.. Functionality is my middle name (sounds better than Ugly)

[kc]

Playing "Devils Advocate" my comments are

The fuselage would be very strong.....fuselages often use 3/32 ( 2.4mm) balsa with 1/32 ( .8mm) ply doubler.

Presumably as the wing is banded on the fuselage has been narrowed to clear the wing bands at the ailerons?

If the Lipo is in a 'box' will it cool enough or overheat and would it remove if it 'puffs' at all?

I couldn't see quite how the u/c works. Normally in a torsion bar type the torsion bar part goes across the fuselage and is restrained on the far side so that it twists along it's width and provides springing.

Putting the ESC behind the lipo means the motor wires need to be long enough to reach.

ESC cooling may be more important on a funfly where the motor is often at part throttle which causes the ESC to work harder.

 

Edited By kc on 28/09/2016 16:57:20

[Martyn K]

Thanks kc

I did wonder about the fuselage. The wood is medium soft quite straight grained. Doesn't feel too heavy. I am planning on drilling some lightning holes under the wing that will provide some ventilation for the ESC. The exact location will depend on how short the nose ends up to be honest. If its very short, then it will have to go rearwards as there will not be enough space and I want to keep it in the open as much as possible.

The undercarriage. I am not sure it will work either but if it doesn't its easy to replace or change.

I am looking at two scenarios.

The 45 degree approach and bounce.

The legs are raked forward. If i hit the ground straight on then the impact gets transmitted straight into the fuselage. Bending the last 15mm or so of the leg backwards will cause a torsion effect (I hope) that will twist the main legs forward.

If I just have a normal heavy landing, the legs will be pushed backwards. The idea for the 16g torsion spring/front legs is to allow this to happen, then pull the main legs forward again when the pressure is released. I may wind a coil into this leg at each side rather than just extend it. wide of the fuselage. I may need to draw this up as I am having trouble explaining it.

Regarding the LiPo. it's mainly going to be in fresh air with foam pads supporting it at the top. There are no sides to the box. I think it will stay cool. As you suggest, I need to make the slot wide enough for a slightly swollen LiPo

Martyn