Flea Fli Build Blog

[Martyn K]

I have continued working on the Fuselage and tailplane and fin. (I hate the description "tail feathers" - just when did people start using that?)

First job was to glue the triangle section along the upper fuselage, Then I noticed that I had managed to buy different triangle sections. Never seen the equilateral triangle stock before - fortunately, I had another spare strip of the proper stuff.

Added the two middle formers. Although this balsa former was cut with the grain shown as per the plan, it actually started to buckle when I added and pulled the second side in - I had to add braces to support it. If you are following along, I recommend that you cut this and the other formers with the grain running cross ways (or be prepared to add additional braces).

Onto the jig - making sure that what is vertical stays vertical, and no bananas lengthways. Leave it for 24 hours in the jig for any stresses to relieve and the glue to dry thoroughly. Note that the rear formers have the grain crossways.. and the additional supports (very soft balsa) for F3

The front former added. One thing that I hadn't allowed for was the taper of the fuselage when I cut the hardwood block. I couldn't undo it so added some tapered ply wedges at the side - not ideal, but it should be OK.

Note the thrust line is zero side and down thrust. The datum is parallel with the fuselage upper decking - always worth establishing this before you start glueing the engine mount in place.

And with the prop fitted to make sure it wont bind and it really IS no up/down thrust.

The nose leg with the stop soldered into place and the heat shrink sleeve added over the motor wires. I have also put a bit of heat shrink over the top of the nose leg.

Which brings us nicely onto the tail assembly..

Martyn

Edited By Martyn K on 18/11/2013 10:05:01

[Martyn K]

Tail plane and Fin

I am still using the Kevlar cloth hinge material.. So the decision is to either make the hinges separately or laminate the fin and tail plane from 1/8" sheet. Looking at my balsa stocks, I decided to make up separate hinges as the balsa density I had available was better for 1/4" sheet.

So making up the hinges. Using my new balsa stripper, I stripped 4 lengths of 5/8 x 1/8 light balsa. One corner was lightly bevelled and then using the cyano technique, a strip of 1/2" wide kevlar sheet was sandwiched between two strips. Note the use of a straight edge to make sure that the strips are ABSOLUTELY straight.

After 5 seconds (when dry), add 3 pins to act as a spacer - centre and at each end, then add the other 2 strips to form the hinge. When done, remove the pins. The whole process takes about 1 minute...

It should look like this...

A perfect hinge joint

Butt joint the 1/4" sheet. I make sure that I have got a perfect contact area, use PVA and pin down over a sheet of polythene (where the glue will run out underneath). Let it dry for a few hours..

Lay the plan over the tail plane, pin through the hinge line and through the real hinge at each end then pin prick around the outline.

Join the dots and cut it out... Note when you cut the elevators out, only cut up to and not through the hinge.

Sand to shape and check that the elevator actually moves OK. Note, I haven't added any further bracing in the centre. The Kevlar adds a certain amount of toughness to the joint, however, if the model was any bigger I would have supplemented the centre with additional bracing of hardwood or piano wire

Repeat for the fin. Remember to allow for the fact that the rudder is somewhat longer than the fin though..

The rudder is oversized at the stage - it will be cut down later. I also used thicker diameter pins as the hinge spacers as the rudder will have more deflection than the elevators.

Adding the tail plane and fin.. You will need to cut slots in the fuselage side (just below the triangle section) for the tail plane and a slot through the triangle section for the fin. It took a few attempts to get this right and I ended up using 1/32 ply shims to get everything aligned correctly (using BEB's triangulation system described in his Tiffie build blog).

A shot from underneath - you can see where I have added Shims.

That's about it for the weekend - the wing ribs have arrived for the 'Magic' so I can also get cracking on that as well now.

 

More to come.

 

Martyn

 

Edited By Martyn K on 18/11/2013 11:18:27

[Martyn K]

The Magic build is now getting in n the way of this at the moment, mainly due to lack of space. A major family crisis has also slowed things down quite a bit as well

 

Anyway...

Top decking added and started planing and sanding to shape. One of the nice things about using longerons is when you sand through you can check progress by the width if the line. If its wavy, like this is, then obviously there is more sanding to do.

 

At the rear of the fuselage, the upper decking has lifted marginally - probably because the longerons had twisted slightly when the slot for the fin was cut and were no longer horizontal. It will probably need a bit of filler.

At the front end, 2 triangle blocks have been added upper and lower around the motor - but still leaving enough space to get access to the mounting screws and the lower sheet block glued into place. The plan shows a ply nose ring, I won't be adding that - I want as much cooling air flowing though as possible.

I have also added a lite-ply battery box base - supported by 2 x 3/16" square beams. As the nose area curves in quite a lot, I have sanded the curve into the beams rather than try and bend it. Keeps the stresses down.

A shot from the front showing the triangle section pieces.

Finally - for the moment - a 3mm ply plate and 3/16" square beams inserted. This will be where the ESC will be located, the cover pinned at the front and secured by a screw at the rear. (You can also see the Magic wing in progress in the background).

More to come..

Any guesses on the RTF weight (including 2200 3S battery? Clue - the LiPo is the heaviest component so far..

 

Martyn

Edited By Martyn K on 25/11/2013 09:43:07

[kc]

1 kilo fully covered with Lipo & radio gear?

Anyway a great build thread Martyn, makes me want to start building one right away! Trouble is it's a bit too small - our flying site requires us to fly a long way out- but there was a Flea Fli plus 10 so maybe a Flea Fli plus 20 or 30 percent would be nice.......

[Martyn K]

Thanks kc

It is small, but Phil Kraft  managed it OK - and in at least one comp as well. Not sure just where the edges of the box were though.

I think if it was scaled up by 25% - say 48" span, it would be perfect for a modern 25..

Martyn

Edited By Martyn K on 25/11/2013 16:07:34

[Martyn K]

A bit more progress. I have got a major family problem I am having to deal with which is slowing things down for both this and the Magic.

Anyway, I have managed to steal some time in the shed. Most of the progress has been on this while waiting for the glue to dry and complete the other wing half on the Magic. That update will have to wait..

The liteply battery base was added and a velcro strap to hold the LiPo in place. There is also a Velcro Pad at the front. This is to prevent the LiPo sliding backwards (all my 2200 3S packs have a matching pad on the battery). You can also see the front 'bumper' bad to allow a little bit of forward movement of the pack in case (or when) the model stops faster the planned

Battery installed and now build a hatch around it. I used 1/2" x 3/16" as a frame. Note that the front part of the decking has also been fitted - this will be laminated from two pieces - the idea is that the whole lot will be sanded down to keep the lines nice and smooth.

And here it is... 1/2" sheet added to the frame and sand to your hearts content..

The lower hatch (which hides the ESC will be held be an aluminium pin at the front and small wood screw at the rear (screwed into a 3mm birch ply plate. The screw is supported by an inlaid piece of 1/32" ply. as the balsa is very light = soft = potentially fragile

Inside view of the upper hatch. A little bit of easing was required as the battery had lifted slightly after the Velcro pads were glued in... (Planning!)

The lower hatch showing the aluminium pin fitted. Note that 1/32" ply facing plates have been added and a cut away in place for the nose leg spring.

More to come.

Martyn

[Martyn K]

 

Starting on the radio gear installation. This is quite simple and I think always best assembled before it is glued in. I tend to follow a standard pattern that works for me. Cut a 1/8" lite ply tray. Add 1/8" x 3/8" lite ply doublers across the tray where the servo screws will fit. Then glue in side rails and allow to dry. When happy, glue the assembly into place

I have taken the easy option and used goldenrods. An additional slot in the rear former to support the rods and they are glued at the rear end and held at the front in a 1/8" lite ply plate.

Note that the upper sheeting has been added between these two photos being taken..

The grain runs across the fuselage and is cut well oversize - at least 6mm all round. When dry, leave the pins in place (which go into the fuselage sides) and using a very sharp scalpel blade slice off the excess using the pins as a guide. Sand it square, not too rounded as there are no longerons supporting the sheet here.

I have trimmed the rear of the tubes flush with the fuselage. I normally support them externally, but as the distance to the respective moving surface is fairly short, this time I have simply added epoxy fillets on the inside to support them

Finally (for the moment) the front hatch is secured with a small magnet inlaid into the ply facing plate. Note the front ply facing (above the sponge bumper) and the hole for thee pin.

This attaches to a small tin plate bracket epoxied to a 3/32 lite ply spacer which is glued to the base of the upper deck. Leave it all in place while the glue hardens.

And it looks like this. The front edge of the hatch is faced with 1/32" ply and pinned (like the lower hatch) with a short length of aluminium tube. As this is cosmetic only, this is amply strong enough to retain the hatch, no matter how hard I crash it..

More to come

Martyn

[kc]

Looking good Martyn. I like your magnetic hatch catch setup.

I found that not all 'tinplate' was magnetic when I tried it!

[Martyn K]

Thanks kc

the tinplate I use is 'proper' tin rolled onto steel. I bought a couple of small sheets of it a few years ago to make RF proof boxes for some microwave radio gear that I was making. Other "tinplate" is very often stainless sheet which as you know isn't magnetic..

BW

Martyn

[kc]

Well some stainless steel is magnetic some is not. Some 'tinplate' seems to be resin coated instead of tinned, it might be magnetic but not solderable.
A quick trip to the kitchen cupboard with a magnet found that most tin cans are magnetic but some are not. So there should not be a problem finding some scrap to suit our purpose.
I like your idea of having the magnet slide past the tinplate as compared to some hatches which rely on the magnet being pulled up off the steel. Have you found that the sliding past action is sufficent to hold the hatch on and not get pulled off in the slipstream?

[Martyn K]

Agreed - there is no problem finding magnetic tin plate in the kitchen. The problem I find is that the plate from cans is a bit on the thick side for small parts. The stuff I use for RF boxes is very thin - probably about 20 thou thick and can be bent into very sharp angles.

I have never tried a sliding "catch" before. I think it should be OK as there is no load on this. The magnet is placed so that it gets maximum contact - hopefully this should be sufficient. I wanted to keep the area as clear as possible as this is where the battery will be located. Any other beams etc. would just get in the way.

BW

Martyn

[Martyn K]

Apologies for the delay with the update. Sadly, I have had a bereavement in the family which has upset the flow somewhat.

Anyway - still got some progress with the Flea Fli..

The airframe was just about finished - now simply a case of fitting it all out.

The ESC goes in the front lower compartment. I have opted for a 60A Hobby Wing device - they seem to be reliable (and cheap) and this one is well over-rated - by about 50% - I think a 40A unit would probably suffice.As it is quite a tight fit, it doesn't need securing.

The servos are installed and wired up. The wing mounting plate is screwed (not glued) to 2 hardwood blocks. Just in case I have to remove a servo or change a linkage. The linkages at the servo end are 20swg wires araldited into the yellow inners and 'Z' bent. A single Nylon M6 bolt hold the wing in place.

The model has been covered - in LighTex (from SWM) - this is really nice stuff - similar to Profilm but about half the weight. It does stick and shrink at a much lower temperature though.

The undercarriage legs were bent up on the Wirebender - I now wonder how I managed without that now.

The hardwood u/c mounting blocks are narrower than the saddle clamps so holes were drilled through at 45 degrees and all held in place using long servo screws. The technique works OK.

The 'collets' are created by wrapping the axle (inside and outside) with copper wire and soldering up. A steel washer separates the wheel from the 'collet'.

And here it is completed..

Canopy from Vortex Canopies - excellent service as usual but painted on the inside with acrylic metallic blue car paint.

The dark gunmetal stripes are from a pin striping job that I did on my last motor-home. Bought from an eBay supplier a few years ago. The check tips are profilm - the mistake I made was putting this on last as it needs a much higher temp to make it stick.shrink which upset the silver and black

I had problems applying the silver again - however, a coat of adhesive kept it down.

One from the rear...

And a contrasting scheme underneath..

A few more details.

Aileron linkages are simple wire rods with a 'Z' at the servo and adjusters on the ailerons

Rudder and elevator are conventional Goldenrod ends with normal clevis and horns.

Servos are Tower Pro MG-90S

And the AUW with a 30C 2200 3S is.....

2.29lbs - just over a kilo - which is about 6 ozs less than Phils Krafts Original

However the CG is a little far forward - not too bad, but it may need some tail weight.

I may also need to cut cooling vents - I'll weigh that up after the first flights - see how hot it is getting

Now I'll crack on with the Magic

Hopefully this will get a maiden in the next few weeks if it is calm enough. I should get one decent day over the Christmas break.

Not much more to come.

Thanks for following this

Martyn

[Bob Cotsford]

Very nice scheme Martyn, I quite like the Worlds Models films in fact the Tornado is covered in their Toughlon and still looks pretty good after a fair bit of abuse.

Could you move the Esc or battery back to help with the balance? There doesn't look to be any shortage of space above the wing.

[Martyn K]

Hi Bob,

Thanks.. Plan A will be to move the battery back. I will need to extend the box shelf area back a bit to support it. The CG is about 25% chord at the moment, the plan shows is about 35% from memory. I'll give it a thorough check over in the next day or so. The ESC will have to stay where it is because lead length are too short to move it back and these is no logical 'place' to put it.

Martyn

[kc]

So my guess at 1 kilo was pretty close!
I look forward to hearing how the castoring nose wheel works.......

[Martyn K]

Hi kc

Yep - near as could be. IOU 1 beer for 1st prize. I came second so I get 2 beers

Quite pleased with the outcome, I am also intrigued as to how well that noseleg works. At the moment its a little stiff, I need to loosen it up a bit before I think it will become totally effective.

Cheers (hic)

Martyn

[kc]

Thanks Martyn!

I also would like to know how well that hatch catch works in the air.

[Martyn K]

I maidened the Flea Fli on Saturday morning. The field conditions were very poor, very boggy and some surface water. Ideologically (and idiotically) I actually tried a take off. The model tracked straight for all of 3m then the front wheel dug in and if it was IC the engine would have stopped when the prop dug in. Because it was electric, it totally churned up the mud and covered the model in a thick ooze...

So I cleaned it up and hand launched it.

She flew beautifully but a little underpowered. Nonetheless, loops bunts, rolls, spins and stall turns all ok (for a maiden). However, vertical performance was non existent - the best I could get was a gentle climb at about 15 degrees.

I have checked the power input to the motor and at full tilt she is spinning at 9000rpm and using 100W (less than 10A peak with a 3S) with a 9x6 prop.

I have ordered a higher KV motor of the same type.

A very nice easy to fly model. I moved the CG back for the next 2 flights (slid the battery back be about 10mm) and this made her more responsive, I don't think it needs any more.

I'll try and get some photos next time I am out, but I am really very pleased.. delighted in fact..

Martyn

[Martyn K]

Forgot to mention.

The hatch stayed in place...

Martyn

[kc]

Do you think the motor was damaged by running in the mud?
It's difficult choosing motors so I tend to buy BRC own brand motors which give full details of props to use and the watts.

So the sliding contact magnetic hatch catch worked OK but how did the castoring steering work?

[Martyn K]

Hi kc

The motor didn't actually get covered, everything else did - spectacularly so, but the motor stayed dry.

I simply under-rated the motor, its only 870kV, I must have ordered the wrong one and its obviously powerful enough to spin the prop, I just need one that spins it faster.. I have got a Keda ThumRun 2837/10 Outrunner Brushless Motor - KED0089 from GiantShark on order. Same case - just different windings. This has a 50% higher kV - that will sort it...

 

Regarding the steering, it tracked OK until the nose dug in, but I cant pretend that there was any scientific value to the test, it didn't last long enough...

Martyn

 

 

Edited By Martyn K on 13/01/2014 12:25:19

[kc]

My reasoning was the motor got a lot of resistance when churning mud ( same as an extra large prop) which might have damaged it. I have at least one motor (unmarked brand ) which did not achieve anything like the Kv marked on it!

I also wondered if the castoring nosewheel went a bit sideways and caused the model to dig into the mud. I suppose you will have to wait for dry surface conditions to prove it works.

[Martyn K]

I noticed before I let it go that it seemed to be lacking thrust, in fact I was more concerned that there would have been insufficient thrust to get it off the ground.

The nosewheel didn't budge, I was watching it closely - you have made me paranoid. The amount of travel is now restricted to about 30 degrees each way, even if it veered, it wouldn't have stopped it the way it did. I think it simply fell into a hole and made things a lot worse for itself.

TBH, I wont really be able to test it properly for a few months until the strip dries out sufficiently or perhaps find a tarmac strip - the M6 runs pretty close - that would do.. (I only need 1 lane)

Martyn

[Martyn K]

I have now replaced the 870kV motor with a 1480kV of the same type. Static tests show that the motor is now drawing just over 40A with a 9x6 prop - approximately 450W.

Keda ThumRun 2837/10 Outrunner Brushless Motor from GiantShark

Its also much harder to hang on to!

Looking forward to the next test

Martyn

[kc]

Isn't that 4.5 times the power?
Will be balistic!

My Mini Frantic was about that size and weight .....when I did the maiden flight on 300 watt motor it went up more than vertical and almost went straight up and behind my head!
Very tricky situation but the model survived and it only took a day or two for my heart to recover too! I reduced the motor to a 200watt version and still had more than enough excitement.

Best of luck with the extra power.