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martynk

Mad Hatter F3-RES

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martynk

Thanks both.. I have regressed and revised and now have v4. Similar to v2 except with a slightly (10% area) bigger tailplane which has improved Vh and should have better pitch damping.

plan v4.jpg

stability4.jpg

Following Jon's suggestion the wing section is now AG35 > AG36 > AG37 > AG38. I am not sure this will work quite as Mark D intended, my outer panels are much shorter pro-rata than his which are more of a consistent size (in length). However, this isn't a $1000 mouldie, this is an £80 woodie so its not a huge financial gamble for me.

Personally, I feel quite comfortable with this now..

I'll get the 'Cat' finished and this will be next on the building board. Definitely not until September though.

Thanks for the feedback..Mad Hatter Wing Plan v4.pdf

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martynk

I have now made a start on this. The Carbon goodies arrived from Hyperflight last week and last weekend I built the fin and tailplane

There is not going to be a lot of detail in this blog, i may replicate it onto Aeromodellers and Model Flying forums to try and generate more interest,

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Tailplane is very simple again. I have simplified the original structure a little further to reduce the number of joints > less glue

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CF for the reinforcement - top and bottom around the Blaster DLG tail mount. Weight (without mount) is 8.4g

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The underside view. The mount sits on a slice of 0.014" carbon (I am learning from my previous builds) to add a bit of stiffness and toughness. Still a bit hairy..

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The fin and rudder while pinned down. unusually I haven't used my Kevlar hinges this time. I spoke to John O'Donnell a couple of months or so ago and seeking advice on using thin Mylar. He has given me some useful tips. Keeping the surfaces separate will hopefully make it easier for me.

My usual laser cutter hasn't been too well so BelAir are cutting the wing ribs this time. All the ribs fit easily (for a laser cutter) on 2 sheets of 36x4 1/16 including doubler ribs for the dihedral joints

More to come - but probably not for a few days

DSCN3211.JPG

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martynk

A bit of progress. While waiting for the wing ribs to arrive I have covered the Tailplane and Fin with 5 micron aluminised Mylar. I still haven't mastered this but have been given some useful tips from ex Free Flight Colleagues on Facebook. It does have its uses..

cover3.jpg

The Vladimar mount and fin attached to the boom. As its a not standard boom/mount combo (DLG bits), I had to pack the mount slightly..  It actually looks better than the photo :)

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The wing ribs arrived on Tuesday - yaay - from Belair - and very reasonably priced -  so started work on the wing. I am using a different (and probably the correct approach) with this one. The lower cap has a slice of 1/32 balsa temporarily glued to it (using a Pritt stick) - the thickness of the lower sheeting and each web/spar piece is cut to size before it is glued into place. Measurements from the ribs are transferred to the sheet balsa, marked and then cut allowing for the thickness of the razor saw.

DSCN3301.JPG

and very slowly moving outwards. Thicker wedge ribs will be used to delimit the dihedral break. This is the outer two panels.

Caps are 0.007" tips, 0.014" centre and 0.025" inner panels  (top and bottom). The inner caps are also tapered from 10mm at the root to 6mm at the break. However, the slots in the wing ribs aren't so I need to have a think about that one as well.

DSCN3305.JPG

Wing tips were made exactly like I did on the Cheshire Cat and due to some sensible planning for once, I can even reuse the original template/former

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More to come... but its going to be slow

Still trying to get this completed for the 1/1/2017 so I can have an entry in for the 1st of the Postal comps..

 

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martynk

Been a bit hectic since I last posted on this. In a moment of crass stupidity I committed to build 2 Kwik Fli Aerobatic models - also to be completed before Christmas. These were reduced to 40 size and fully CAD ready for laser cutting. It left me very short of time to get this finished. That 'other' commitment also instigated a couple of stupid errors which I had to fix as well

The wing construction followed basically that for the Cheshire Cat using Carbon caps on soft balsa spars/webs.Very photos - surprisingly - you will have to imagine a wing under construction - sorry.

IMG_1308.JPG

Batteries to make sure its flat and stays flat.

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You can just see the LE D box lifting on the middle panel :(

While the wing was almost built - waiting for the spoilers to be added -  I started work on the fus. F3-RES rules limit how far the boom can come forward under the wing (to prevent carbon pods being used)

 

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My pod is made from a sandwich of 2 x 1/2" balsa with a 1/16 ply sides and 1/32 ply top and bottom. The tow hook plate is from 6mm ply bevelled in front and back and then well glued to the sides. The observant will notice that it is undrilled :( for a tow hook

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First fit of the 1/16 ply sides.  Still no holes for a tow hook - its getting worse

 

DSCN3327.JPG 

This shot looks a bit odd. Basically I use laser alignment to get the fin and tailplane square with the wing dowel. It looks bent but as the light is not passing through water and the refractive index does not change over a metre in air I have to assume that its straight and the camera is wonky

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and you can see the laser line down the TE of the fin - just. The lights need to go out while do this

Lots of epoxy and micro balloons and allowed to dry for 24 hours

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Horns for the spoilers from 1/16 glass fibre sheet. I decided to use a pull chord to activate spoilers and gravity return. Works better than expected.

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This is the spoiler actuation servo recessed into a gap in the centre of the fus. The chord from the spoiler simply hooks over the screws in the servo arm

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Rudder horn

The second hole is for a spring if I couldn't get a reliable push rod action then I was going to use DLG practice. As it happens the push rod was fine.

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Radio installation. Following Jef Ott's recommendation I have gone for a LV setup using a 1000mAh 1S LiPo for power. Power switch in the top

The wing was covered in Black Lite-Tex (World Models - its film) over the D Box and a Polyester Tissue (red) over the TE of the wing. 

I had big problems with the D box though. To try and keep weight down I used 1/32 sheet balsa. As I sanded the LE profile, the sheet kept coming detached. When I build another I will definitely use a false LE to support the D box. As the time I feeling pretty fed up. I now try and get the LE profile as accurate as I can and because I seemed to be chasing my tail on this D box sheeting kept coming away it got slightly misshaped. In cold light of day, its not too bad but the shed was full of expletives last week.

DSCN3341.JPG

And it looks like this. With a bit of flare as well.

The tow line is an old F1A 50m line from the 1980's with the standard  6mm red HK bungee rubber for propulsion

This was cut to length - HK were 0.5m generous and the ends made up as follows:

Basically, I stuffed a length of fuel tube (about 75mm) inside the bungee at each end then crimped it into a length of 8mm brass tube like this

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and

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Quite pleased with that..

Final details

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Subfin

The tow hook. The second night of expletives.. After securing the push rod tubes I realised that I couldn't get into the fus to secure the tow hook.

The tow hook position was calculated (based on a 40% CG) and drilled. The hook was made from a length of M3 stainless steel bolt and is clamped between a captive nut on the inside then locked with a nut on the outside. I needed to make an access hatch to be able to do this which is now semi permanently glued into place

Not ideal but it does mean that I can move the hook if needed without too much surgery

DSCN3351.JPG.

Not very sharp and not very good woodwork either - sorry 

DSCN3352.JPG

To balance it, I had to add 40g of lead into the nose and an incision was made, balsa hollowed and molten lead added.

AUW of the model was now just over 400g - I need to measure it again..

So - it was basically finished. LiPo charged and a calm sunny day. What could possibly go wrong :) 

At the patch for 11:30. Quick function test - no elevator :(  Examination showed that I had somehow managed to fracture the signal line so I pulled out the spoiler servo and popped that into the elevator servo slot and realigned everything. Ho hum

Back to basics. Checking the glide from a hand launch into long grass. A bit of elevator tweaking and it was ready for a gentle bungee launch.

Now. today was calm - absolutely not a breath of wind. Nil zilch Zero nothing. Cant ever remember a day so calm.

Pegged out the bungee, attached the tow line - about 10m stretch and it was away. But it only got about 6m high but enough to test that the glide was OK.

First flight and it was obvious that I had far too much elevator response. So reduced that by 50% (on the transmitter) and this time with a bit more stretch I tried again. Getting better but only 10-15m high but good enough for 1 minute plus flights. Still too twitchy on elevator and I am losing a lot of height trying to gain height. Not getting a good transition.

More stretch and the model is going up like a missile - but only to about 15m and still jut over 1 minute  flights..

More stretch - and I break the bungee (aaaagh)

Repaired the bungee and I am now leaning back on the line - but getting slightly better transition by just letting the model glide off the line rather than trying to ping it.

By now I am doing quite a lot of walking. 

Next flight - looking better but managed to hit a telegraph pole which terminated that flight. No damage :)

One of our members turned up to fly a Heli so I had a rest while he had a flight. The faintest breeze then came up. 

Next flight - in slight sink was just under 2 minutes but getting much higher on the line although I lost the elevator setting some how and it was over elevated - lost a fair bit of height but definitely getting better

The final flight - I was already an hour late for lunch and the breeze (Beaufort 1) gave me just enough lift on the line - a perfect transition and down in 2:45 - which is what I have submitted for my first postal comp flight. I am still not getting max height. It was still very calm - the drift was about 150m in 2 minutes.

I noticed on the last launch that the wing was bending quite a bit. A nice curve but not unduly concerned. Models that bend are less likely to fracture

Until I took the joiner out..

DSCN3348.JPG

The 6mm carbon joiner had fractured. The question though is why? All the strands had clean fractures apart from the last 10% which held it together until I took it apart - than it broke..

Anyway, I need a new joiner..

 

Quite pleased with this. I'll fly it for a while than maybe make another later on this year..

DSCN3340.JPG

DSCN3352.JPG

 

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martynk

And the Kwik Flis got finished as well :) - Both maidened last week

DSCN3338.JPG

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mhodgson

Lucky on the joiner- it may well have cracked when you hit the post.

If I may suggest, a 6mm carbon joiner is not a lot for a 2m wing joined in the middle.

Also double check you don't have a burr on the tubes in the wing/fus. Even a small one can produce a weak spot that will develop into a crack in a bang.

Bungees do need a breeze to work properly. More breeze equals higher launch.

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mikef

Cracked joiner.  Where is the break relative to the wing/fuselage junction - right at the wing/ fus junction?  That kind of failure looks like the result of a shock load.

Pultruded Carbon varies a lot in quality - I have found the Martin Van Dyke material from Free Flight Supplies superior to the LHS stuff.

I would use a steel joiner.

 

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martynk

Thanks both

The fracture was right on the Wing/Fus joint. The rod sits in a CF Tube (in the fus and the wing) which I could (reluctantly) drill out to 6.25mm if needed. I cant remember where the rod came from. Its what I used on the Vintage Aquila 100S that I built a few years ago and that has survived 'proper' bungee launches to 100m plus. However, the wing on the Aquila is far more flexible (traditional wooden construction) .

The strange thing was that the fracture was circular and very clean. Never seen carbon break like that before. Mined ewes I don't have much experience of carbon breaking at all.

When the model hit the pole, it wasn't too vicious, the model just spun round and wrapped itself round the wires then just dropped vertically from about 6m.  I have had far worse, I was more concerned about the ground impact - the pointy nose got well buried in the very soft soil. It is more likely to have fractured then I think.

I was actually going to fabricate a steel joiner anyway - but that was a simple way of adding a little extra ballast. The models glide speed is quite reasonable, probably OK up to about a 10kt wind speed as it is

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mhodgson

Based on where the break was it was most likely done when you hit the pole.

It would have been the only place the joiner could flex due to the tubes in the wing so that is where it cracked.

Good quality carbon rod will be better but I would still go for a steel joiner, If only for piece of mind. You didn't spot the problem until you took the model apart and were lucky it held. One more may well have broken it

If you build a new one then enlarge the joiner or use 2.

Overall though the model sounds promising.

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martynk

I certainly wouldn't want it to break in flight. I think the Goddess of Aeromodelling was looking after me yesterday. I cant believe how it held together for the last 2 or 3 flights. I'll see if I can get a 6mm steel joiner or perhaps a hybrid carbon steel joiner.

It certainly wasn't obvious that it was broken when I picked the model up  or handled it.

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mhodgson

That's the problem with carbon and why joiners in commercial models look/are so oversized.

Steel may be heavy but it will bend.

Anyway, Luck for the next flight.

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PeteMitchell

I used to make my wing joiner rods using thin walled brass tube of a suitable o/d to fit into the joiner tube. I would then find a carbon rod which was a good fit inside the brass tube.

The carbon rod was epoxied into the brass tube which made it very strong and very resistant to the scissor/sheer effect caused by a sharp shock impact .

And a lot lighter than a solid steel rod.

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martynk

Thanks Pete. That may be easier. 6mm i/d on the wing joiner tube is a bit of a tricky size to fill with imperial materials. I was thinking of the the other way round, getting a 6mm O/D carbon tube (5mm i/d) and then stuffing that with a 6swg Piano wire rod (4.878mm dia) and epoxy to seal the minuscule gap.  Not sure how that would work as the Bending Modulus of the two materials is very different and I think that the tube will crack under load. 

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PeteMitchell

I am sure 

1 hour ago, martynk said:

 I was thinking of the the other way round, getting a 6mm O/D carbon tube (5mm i/d) and then stuffing that with a 6swg Piano wire rod (4.878mm dia) and epoxy to seal the minuscule gap.  Not sure how that would work as the Bending Modulus of the two materials is very different and I think that the tube will crack under load. 

I think that would work well. 

Any unseen damage in the carbon tube is most likely to fail on a bungey launch, even though you are not using that much power.

If the carbon part of the joiner did break, the steel rod would save a disaster. You will probably fly the model very easily with a bit more dihedral:rolleyes:

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martynk

Thanks - thats worth a try then... :)

 

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Whitmore

Nice to see this in the air Martyn! Look forward to hearing more about the handling and flying characteristics. Do you have an accurate all up weight figure yet?

I think 6mm carbon for a centre joiner is a little undersized too, 6mm is used on the mid panel joiners of most of the F3-RES designs where loads are reduced. At least you have a practical data point now :)

It will be a little while before we can join you in the Postal Challenge with a proper F3-RES as our Slites are delayed by a month and my Halo design is on hold until they are built.... but I might have a pop with a smaller model if the weather is good :)

Jon

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Jef Ott
19 hours ago, martynk said:

6mm i/d on the wing joiner tube is a bit of a tricky size to fill with imperial materials. I was thinking of the the other way round, getting a 6mm O/D carbon tube (5mm i/d) and then stuffing that with a 6swg Piano wire rod (4.878mm dia) and epoxy to seal the minuscule gap.  Not sure how that would work as the Bending Modulus of the two materials is very different and I think that the tube will crack under load. 

I did something very similar recently, when I had an identical perpendicular shear failure, on a vee-tail tail surface joiner. I was shocked at how little force had finished it off, and conjectured that it must have gone a little at a time over a long period. As it is such a rigid material, it is not obvious when half of the thickness is damaged.

The id of the carbon tube I had was 3.2mm and it was easy finding a steel rod to fit inside. A smear of Araldite Rapid on the rod before easing it into the tube. 

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martynk

Thanks both

As no-one has screamed 'No No No' about a sleeved steel/carbon joiner then I'll investigate that further. I need to keep the weight down.

BTW - there was a typo in the weight above. Not 400g but:

  • Tailplane 9.2g
  • L Wing 131.6g
  • R Wing 133.9g
  • Fus 320.0g (with 45g additional nose-weight)
  • New Joiner estimate 40g

Total 634.7g :cry:

A bit heavier than intended.

So where did the weight go?

The tailplane, fin and rudder - I couldn't have saved much weight there. 

Rear boom and tail mount - fixed although I could have used a shorter moment arm and that would have saved a bit of nose-weight

Wings are too strong and too heavy despite using light - perhaps too light - wood. Over engineered perhaps but they are not going to break in a hurry

Fus - A longer nose would have saved some nose-weight. I have kept the flight gear as light as possible and the pod 1" balsa core is hollowed and is very light wood. Reduce the 1/16 ply side to 1/32 is about the only saving I could make there, possibly 15g but in the wrong place.

The new Joiner will be somewhat heavier than the first one. 

I am not unduly worried :whistle:. This is meant to be a wooden model class and I have a model that is slightly larger than a F1A and is correspondingly heavier.  I would never attempt to get down to 400g, it simply wouldn't last more than 5 minutes in my hands although I would have been happier if it was nearer 500g which was my original target.

The wing loading is 178g/dm^2 if I have got my units correct

On the positive side:

The wing will fly at a higher Re because of the increased mass (glide speed) and also its quite low aspect ratio. It should be more efficient

It will fly in more typical British weather conditions without additional ballast although obviously some will be needed when it gets very breezy.

 

In summary, its a model designed for F3-RES in the UK - I would love to see what other people come up with :)

 

 

 

 

 

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mhodgson

Still a work in progress but here is what I am working on.

Still refining structure choices etc but all wood is the aim (minimal carbon).

2m esoarer print.jpg

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martynk

I like that - it looks great. What wing section are you going to use?

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