Wednesday, 30 November 2016

Kanga Fun Flyer

This is a Joey Fun Flyer derivative, the original was designed by Johan Smit. The Joey plan was downloaded from Aerofred and modified extensively for an electric conversion.

The purpose of this particular build was to give me a model for the Inter Club Fun Fly series of events which appear to be gaining in momentum - particularly in the NW of England where I live.

This is my derivative from the original plan, named Kanga, hopefully, it will bounce just as well.




The biggest change to the original design was to extend the fuselage to accommodate the lighter electric motor and LiPo. Mounting the elevator and rudder servos in the rear necessitated a further extension.

Following discussions with Andy Ellison, a few other tweaks were made to make it more rugged and help it survive the rough and tumble of a Fun Fly contest.

Tailplane and Fin
These were built almost exactly as per the original Joey but with 0.014" Carbon Fibre bracing doubler along the tailplane spar and the front of the fin post. Hinges are carbon fibre sheet which also add additional toughness.


The fin and rudder. Looking carefully, you can see the carbon fibre doubler on the front edge of the fin post


Tailplane construction starts with the pre-hinged spar and elevator joiner. 1.5 mm spruce doublers are inlaid into the joiner that links the two tailplane halved together



The almost completed tailplane. Hard points for the horns are yet to be added


Wing
The LE and front spars were laminated from 2 x 3 mm sq spruce, the main spar is 6 mm square balsa with a spruce doubler, top and bottom as shown on the original plan. The gap between the ailerons has been increased by 30 mm  and the wing is now retained by bands, rather than bolts as per the original.  A 2 mm carbon fibre rod brace has been embedded into the LE at the centre section (approx 30 mm each side of centre) to prevent dings from forming in the LE if the wing swivels around the fuselage former. Wing tips are 5 mm balsa with lightning holes. The main spar is extended to the tip along with the upper of the rear spars.


Wing ribs are cut using a ply template. Note the use of building tabs to prevent twists (warps) being built into the wing

Wing construction is quite simple. No plan is needed, simply mark a line for the Trailing Edge of the wing, then mark out the positions of each wing rib. Pin down the lower spar and then add the ribs, making sure they are upright and square. Add the TE, upper spars and leading edge. 


There are two ribs that are close together that  have the aileron servo tray sandwiched between them. Adjust the height so that the top of the servo turret is about 3 mm above the top of the rib. I mounted my servos on the top of the wing for protection, convention dictates that they are located under the wing.

The wing D box is sheeted with 1.5 mm balsa and with 1.5 x 8 mm cap strips behind the D box. The TE has a 1.5 mm x 8 mm false TE, top and bottom that sits over the real TE.


Wing tips are 5 mm light balsa with lightning holes. Note that I have also added lightning holes in the external wing ribs. Every gram counts. A short length of triangle stock to keep the tip square and the spars are extended to the top. At the very rear of the tip, there is a tapered strip of 1/16" ply to add a little extra local strength


 The ailerons are conventionally built. The TE of the Aileron is L shaped with the vertical part made from 3mm x 5mm spruce. Because of the method of construction, I have used conventional hinges for the ailerons, 4 per panel. To ensure that they are secure, 6mm soft balsa blocks have been added at the wing and aileron side to ensure a good glue contact area


Fuselage
Basically a simple box construction, 2.5 mm balsa sides, 1.5 mm balsa top and bottom. 1/16" ply doubler from the front former back to behind the aileron clearance cut out and 1/32" ply doubler around the tail. 3 mm longerons top and bottom between the ply doublers. The 1/16" ply doublers have 26 mm lightning holes cut in them down the full length

A 2.5 mm Lite ply deck sits from behind the front former to half way down the wing and is used to locate the ESC (top behind the motor), LiPo, underneath and Receiver - under the wing.

The former in front of the wing is 3 mm birch ply which interlocks with the deck and also the small 6 mm undercarriage mounting plate.

The engine mount former is also 3 mm birch ply. a third former located at the TE of the wing is made from 2.5 mm Lite ply.

The unusual part of the fuselage is the cut away behind the main part of the wing. This allow the wing to skew without impact the ailerons or risking damaging the aileron servos. It was originally intended to fill this 'gap' with a soft foam block but that was purely for aesthetics.

The fuselage was designed around the components that I wishes to use. Trying to save money, I opted for budget end for everything - I wasn't sure that this model was gong to last


Fuselage construction is the traditional simple box. The cut out to clear the ailerons if the wing got skewed looks quite odd but I have to admit I quite like it. It has Character.. :)


Any Ellison advised me to make the undercarriage strong. It will take a battering. I admit I underestimated strong but I decided to slot the main legs into the fuselage to transfer the impact into the main structure. Where I went wrong was that the front bracing legs were too thin and needed to be reinforced to the same level


Bare bones


You can see the wing mounted and the slot for the ailerons - to allow the wing to twist on impact and hopefully not rip the ailerons off.


ESC located above the battery in a screwed down hatch


Another shot of the undercarriage main mounting. The legs are screwed to a 3mm ply plate which is integrated into the former above. All locked together


The rear skid is stitched using Kevlar thread to a 3mm plate and epoxied into place.

It looked like this before its maiden.




Contrasting colours - probably not needed on this model..



With the model completed, I only managed to get 3 flights in before the InterClub Competion



The first flight ended prematurely  when the motor mount broke. Looks like it failed because I hadn't balanced the prop correctly. The replacement is cut from the next gauge up dural. That will not break..

My Inter Club comp flights were great fun but made me realise I had a lot to learn.

1. I had to fly a lot closer in than I normally do. I had problem keeping the model on track and judging the distance away from me. My 4th round Limbo flight ended after I 'took out' the far limbo pole which damaged the firewall but the rest of the model was unmarked... I can see this flying close and judging distance being a problem to me. Practice, practice, practice

2. Its very draggy - but adding more drag showed that I had insufficient power. In the water carry task, the take off was long and I could barely build up enough speed to perform the loop. I have subsequently fitted a larger prop which is within the power capacity of the power train.

3. The undercarriage wasn't strong enough. On the triple thrash (3 Touch and Go, 3 Rolls, 3 Loops) my second T&G removed the front u/c mounting. Easily fixed but it failed far too easily. This has now been replaced with a 12g leg and this is now bolted to the Firewall

After the comp, I replaced the Firewall with 6mm ply (was 3mm ply) and added Carbon Fibre reinforcement.


I have had a few more flights including some targeted hard touch and go's and it hasn't failed yet.

My thoughts on the model is that its a bit on the heavy side now - Although not dreadfully heavy, it could do with being 0.5kg lighter. Something to think about for the next version. Its great fun and dead easy to fly though

Roll on the next comp. That was really enjoyable.

School Visit

I was invited to a local school to talk about Model Aeroplanes.

Their current topic is aviation. The age group is Year 1 (5-6 year old Children)

I wasn't given much time as the room I was given is in fairly constant use. 20 minutes to prepare, 30 minutes to talk, 2 minutes to dismantle and the opportunity to fly from the school playground - which on Google Maps looked quite large.

I agreed with the teacher that I would show a few model related videos (from YouTube) and bring some aeroplanes to show them. The children are multi cultural/lingual and had probably never even seen a model aeroplane before.

I took along a mix of things to show them.

1. A BMFA Dart which I flew in the hall - much to the children's delight
2. 3 Peanut Scale models plus one under construction which I walked around and showed them so they could see how they were made
3. A 2.5m span glider with transparent Solarfilm covering - again so they could see the construction link.
4. A Fun Flier - which is what I flew but with a Mobius Camera attached
5. A 2.1m span aerobatic model.




There were about 60 children (2 classes) and they were really well behaved.

Taking lots of cues from the teacher - who wanted the children to learn and repeat hard words - like 'pro-pell-or' the session went really well

The four videos I chose were:
https://youtu.be/RriKI7u72Xs



Wright Brothers early flight. I explained that 100 years ago real aeroplanes were just big models because no one knew how to build full size. I talked about the construction and compared the Wright 'Flyer' with my peanut models - basically sticks covered in tissue/cloth



The second Video showed Aeromodelling in the 1930's. Explained how popular it was because Aviation was still very exciting. Again talked about how models were made and flown.






A short video of an indoor scale model from last years Nationals







Finally, a fairly modern MAN video showing a Free Style aerobatic model in flight.  Didn't quite get time to show all this video but it set the flavour and the oohs and ahhs indicated I had got that right

Some of the children were invited to come and pick the models up so they can see how heavy/light they were and invited to ask questions..

We then told the children that I would give them a demo flight and we reassembled in the play ground/field 30 minutes later.

I had agreed where I would fly from and that I wouldn't overfly the school or the Children. Just 2 flights of about 4 minutes each and some aerial photography. It was a perfect flying day, calm and sunny.


You can see the Children behind me and my no fly zone was from about 10 yards in front of me. Kept the model high and safe and nothing too adventurous.

Apparently the little people were chanting 'Martyn, Martyn' when I was flying but unfortunately I couldn't hear them

A very worthwhile 3 hours of my day. Happily do that again.



Thursday, 8 September 2016

White Rabbit - F5J






This is my first attempt at a full function Thermal Soaring Glider designed for F5J (Electric Powered) FAI class.

I have used Sailplane Calc extensively with this model, Profili for the wing design and Draftsight to pull it all together. There is no rush, this is going to be a winter build and I have the Mad Hatter F3-RES to build first.


So v2 is here - still some tweaking to do but its a starter for 10.




Some salient details based on a target AUW of 1500g (whether that target is achievable is debatable - I have a feeling that 1800g AUW will be a more realistic target).


Total Span 3770.00mm
Total Area 84.60dm2
Wing Loading 17.73gr/dm2
Mean Chord (area/span) 227.42mm
Mean Aerodynamic Chord (length) 231.32mm
Wing Aspect Ratio 16.36

Effective Wing Results (Projected)
Total Span 3734.31mm
Total Area 83.95dm2
Mean Chord (area/span) 227.86mm
Wing Loading 17.87gr/dm2
Aspect Ratio 16.17


Wing section is an RG-15 and tail HT-21

RG-15

Flaps on the inner panel and ailerons on the middle panels. How these get engineered I have yet to decide.

Wing will be constructed with C/F caps over solid balsa web/spars. I am also going to use a strip C/F TE as well. The LE D box will (possibly) be skinned with 0.2mm proskin (Jury is still out on this) and C/F cap strips over the wing ribs.

6 panel polyhedral wing. My very limited experience with Aileron Thermal Soarer Glider wings is that the models seem to use Ailerons for roll control rather than steering, but then again that could be the wings that I saw. EDA is therefore at the bottom end of Mark Drelas design guide at 6.13 degrees

Sailplane Calc threw out these numbers:






More to come...

Thursday, 4 August 2016

Cheshire Cat - 100S Glider

The glider bug is quite infective. After not building a Glider for several years, this is my 3rd in fairly rapid succession.

This is a 100S contest glider, the class rules dictate that Rudder Elevator and Spoilers are the only flight controls permitted, i.e. no ailerons and wing span restricted to 100". This class of model is also eligible for the 'OPEN' class events as well - F3J and F5J if electric powered.

There are very few 'modern' designs around that are suitable for home scratch building, so this is my own design with a great deal of help from Jef Ott on the BARCS forum.

The full build blog is available here on BARCS:

To add a little extra, this model will be an 'E' version with an electric motor, height limiter etc. so that it will qualify for the Bartlett's league - if I ever manage to get down there.

Our local field isn't particularly brilliant for tow or bungee launching so I need to have an alternative method of launching models.

There have been several iterations of the design, starting from a simple 'Vee' dihedral aircraft in imperial units and ending up as 6 panel wing in metric units... Wing section is Mark Drela's AG35 at the root tapering to AG37 at the tip.

I used a spreadsheet to calculate the various stability values, that in itself was a very interesting exercise..


These are the 3 key stability values, I need a model that can fly by itself if I ever need to rest my eyes momentarily.

The latest iteration looks a little like this:


The construction follows that of a 'Bubble Dancer' that I built late last year, in fact the tailplane is scaled directly from the BC plan. Boom, tail mount and spars are all Carbon Fibre or CF Composite - again following the same type of construction method used on the BD.


Tailplane - a little heavier than hoped for at 16gms


 The covered tail assembly showing the Carbon boom and Vladimir tail mount - from Hyperflight


Wing construction (inner right panel) in progress. Lasercraft produced the wing ribs for me - beautifully cut as usual.

Updated: 2016-08-04

The wing went together in a similar manner to the Bubble Dancer, the spars are actually thick soft balsa webs capped with carbon fibre caps that go down the length of the panel. Thinner caps are used in the tip sections to reduce moments of inertia (weight!)

This shows the spar (web), lower carbon cap and a carbon strip reinforcement that goes over the dihedral break


The top cap is added (and in the centre panels) bound with Kevlar. Probably not needed for an Electric model, but I'll be able to use these wings on a winch launched towline glider version if needed


The spoilers were a bit tricky. I originally wanted to use wing mounted direct drive servos but I couldn't get them to fit so resorted to a bell-crank and fuselage mounted servo driving snakes through the holes originally intended for the servo lead.


 Like this.. The horn was bent (downwards - this is upside down) to clear the push-rod.

Next job was to get the fuselage pod made.


 Manufactured from Lite-ply with balsa triangle section corners, it looks very uninspiring


 But with a bit of work it can be made to look quite attractive


 I can never resist a dry assembly shot :)


The Front end - a 40mm Aluminium spinner and a reasonable fit, 5 degrees of downthrust, no side thrust


Servo's are mounted at 45 degrees so that the arms don't interfere with each other (the spindles are on the fuselage centre line. The 3mm Carbon wing alignment rod passes through the fuselage as you can see

A bit of work finishing the fuselage, making some nice curved hatches and covering the wing


And it weighs this much with batteries.



And a shot of the Cheshire Cat modelled by my beautiful No. 2 daughter :)



Just a maiden to come..

Thursday, 14 July 2016

Mad Hatter F3-RES

F3-RES is a new low technology class thermal soaring class. It's well established and popular - in German and USA making good use of modern wing sections, limited Carbon or Glass Fibre components. Models tend to very light and have excellent performance if built accurately.

A small group of us in BARCS are trying to get the class introduced into the UK, initially as a class for a postal event - and if this grows then we hope to encourage local, regional and national events.

Flights are flown in 9 minute 'slots' with a 6 minute maximum and spot landing bonus. Launch is via a standard bungee and towline which should get the model to about 80-90 metres before release. Models must be built from wood (predominantly) with composite materials allowed for the boom, tail and wing mounts, wing spars and wing joiner. EPP, other foam or moulded flying surfaces are excluded.

I am planning to build an own design glider, named 'Mad Hatter'.


 It's basically a condensed version of my Cheshire Cat 100S design - which at the time of writing is still being built. There is misplaced coincidence for you.



The wing section is the well proven Mark Drela AG35. This uses 10x0.5mm Carbon Fibre caps over 10mm wide balsa 'webs' (in reality the spar) and 6x0.6mm caps in the tip panels. No Kevlar thread spar winding will be needed in this model, it does not have to carry the load of a winch launch.


This is sheeted as far as the 'flat' sections of the airfoil with covering support spars at the rear

I am getting quite interested in carrying out stability predictions and using my spreadsheet I have the following:


The model will undoubtedly change as my thoughts develop over the next few weeks but this is my starter for 10.