Here is a list of all the postings Simon Chaddock has made in our forums. Click on a thread name to jump to the thread.
|Thread: Show Us Your 3D Prints|
I needed to test a small (9.5 g) out runner (5x3 prop) and could not find my home made wooden test stand but in any case the motor is so small none of the pre drilled holes would have been usable.
So I designed & printed one.
Basically hollow boxes with 8% infill. The most complex bit was creating the top plate to match the motor mounting holes. It includes 3 small holes that allows the screws to 'self tap' into the plastic.
It used 2.75 m of filament and took 48 minutes to print.
Not very sophisticated but with the current 'lock down' it seemed a reasonable (and cheap) way to pass the time.
On a 3s it confirmed the motor/prop combination would produce a more than adequate thrust for the intended application.
|Thread: Flap / down elevator mix|
The drag of a flap is only one of the forces involved. The change to the wing camber as the flap deploys also alters the wings centre of pressure which can result in a significant pitch change force.
The full span wing in about its correct relation to the fuselage and tail.
It now has some serious wing area.
The aileron servos lie flush withe the wing underside with short link rods to the printed horns.
A light and simple installation. The servo wire is buried into a grove cut in the foam but is carried internally in the hollow centre section.
The tail plane and fin 'fine trailing edge' extensions.
The problem is the elevators do not lie on the same axis so cannot be simply connected. After much thought the neatest solution was to connect via a printed 'ball and socket' universal joint.
This type of universal has limited angular capability but would handle the 10 degree angle of the elevator joint lines.
The joint installed.
Edited By Simon Chaddock on 01/04/2020 22:30:46
|Thread: Scratch Build Twin|
Ooops! Should have spotted that UBEC is powering the rx, servos as well as the lights.
I was not querying the power itself but only if for any reason one battery runs down before the other you will have asymmetric thrust. Not a problem as long as you spot it is happening.
That wiring diagram looks sound enough to me. The only query is the UBEC providing power to the lighting when it appear the power is also connected via the red wire from channel 7.
Is there a reason for using a battery for each motor?
There is an argument that a reducing power on one motor in a twin can be more serious than both failing.
I have a twin set up like this for structural reasons. I specifically keep the flight time shorter than necessary to avoid the risk of taking a battery down too low and not being able to spot it in time.
In hind sight I would have added a battery cross connection.
|Thread: Round the pole|
I first did indoor round the pole in the early 1960s using 3V early Japanese motors. Marginal flight and the motors did not last long with 12V transformer supply.
Much more success with later proper 12V motors which allowed more realistic planes to be built.
Given there were always two wires my big step was utilise them as a control line function as well. The centre pylon gets a bit more complex to not only move the wires but also to lead the control to the pilot outside the circle.
With elevator control RTP flying became rather more gentle allowing for very intricate models to be flown successfully.
Always a keen scale builder there was attraction in building small and very light yet with a reasonable prospect of it actually surviving. First a Sopwith Pup built late 1968 in classic balsa and tissue style.
20" span with a geared slot car motor driving a hand carved balsa prop. Just under 2 oz (40 g) but the motor alone accounts for nearly half of that!
Even on short 6' lines it flew well and at almost a true scale speed!
It prompted me to build a matching Fokker Triplane.
18" span and modelled on one of the planes flown by ace Wernher Von Voss. It weighs 2.25 oz (64 g).
Built in 1969 to almost perfect scale inside and out. This is the only picture I have of it under construction.
The fuselage with full internal bracing (cotton thread) is made from medium 1/32 round balsa to simulate the steel tube of the original.
A similar geared slot car motor and the Oberursel URII rotary actually goes round with the prop.
Just to confirm that control line RTP can be quite 'gentle' I still have the Triplane in the loft although at 50 years old it is firmly retired. .
That's quite enough of my reminiscing!
Edited By Simon Chaddock on 29/03/2020 19:00:54
|Thread: Composite wing ribs|
You only have to looks at a full size rib to get an idea of how 'spindly' they are when compared to the massive proportions of a spar.
This is a Tiger Moth wing.
It would be virtually impossible to reproduce this at a small size in wood and the geometric scale effects would actually make it impossibly weak to resist any compression forces.
The accuracy of 3D printing means you can technically create a small size scale wing rib and although the structure would be plenty strong enough in tension the members would need to be supported in some way to prevent them buckling under compression. The trick is to find ways to do this but only adding the minimum of extra material.
It took some experimentation to produced 3D printed ribs that were even close to the weight of a comparable wing rib cut from the same thickness balsa.
How light you want the rib to be really comes down to how much time and effort you want to spend designing it and how ingenious you become in using the 'features' of the slicer programme to give the result you want.
I have been printing wing ribs for some of my Depron planes.
I general the issue is not strength but weight. It is quite difficult to achieve a similar strength to weight as balsa and much harder to match Depron.
I have found that for real light weight at small sizes just a rib outline with a very thin web inside is quite acceptable.
This rib weighs 0.5 g
Even bigger ribs can have thicker elements and do away with the intervening web.
The rib set for the inner wing panel on my Depron 2700 mm span EDF Antonov AN 124.
I would not claim 3D printed ribs create the lightest or are the quickest to create but they are very accurate and exactly repeatable which makes them ideal for a 'plank' wing.
Edited By Simon Chaddock on 28/03/2020 20:50:32
As the aileron servo wires will have to run inside the centre section only the top skin as far as the shear web is glued on. This make the centre section rigid enough to handle.
The RH foam wing added to the centre section.
Although the Cheetah wing trailing edge is reasonable with Depron it is possible to get much finer so trailing edge extensions made from two 2 mm Depron layers which are sanded down on their inner sides before being glued together. This leaves the smooth stronger Depron skin intact right down to the very edge.
A 'before and after' comparison.
There is an argument that a 'cut off' trailing edge has little or no penalty as any loss in aerodynamic efficiency is countered by the reduction in skin drag. I am not so sure for a glider. Anyway in this case the extra wing area will be useful.
The trailing edge extensions with the aileron cut out.
Aileron servos next.
|Thread: 2 or 3 questions please, need some wise advice|
If you are fighting weight don't under estimate tissue. For such a small plane use lightweight Model Span if you can get it. With one coat of thinned dope it is about the lightest of all 'outdoor' coverings.
It can even be used with an all Depron structure to save still more weight.
.Rather important if you are trying to build a scale twin EDF under 250 g.
My experience using thin Depron suggested the Cheetah wing centre section would be strong enough without any spar just relying on the 2mm skin. All it would need would fairly close spaced ribs and a shear web.
As my supply of 2 mm Depron is limited, irreplaceable and cutting ribs tends to wasteful of sheet I decided to 'print' the ribs as well as the intervening shear web sections.
Each unit weighs 0.6,g.and is simply repeated for as many ribs as required
They are glued one at a time to the Depron skin under surface.
Although only intended to take the shear forces when all the webs are glued together in a line they will also act as a 'spar' hopefully adding further stiffness.
Each foam wing panel will be trimmed to plug into the centre section so when glued in place the bending loads are transferred directly into the Depron skin.
So far so good. .
|Thread: Folland Gnat|
Of course I could build a TN Gnat but it would likely need a cheat hole to work well and not needing one yet keeping scale inlets and exhaust was my target for this building.
The Gnat has had a rather chequed career so far and all of it my fault.
First attempt result.
Still turned right, too much wind so it went in fast at a shallow angle..Although the nose is completely destroyed the crumpling absorbed the energy so the rest of the air frame is undamaged. To make matters worse I had forgotten to switch on the gyro which would probably have saved it.
A completely rebuilt nose.
A week later complete and ready to go again.
Nearly this time except it 'sank' after the launch still banking right touched a wing tip and cartwheeled. This time the impact snapped off the nose although there was quite a bit of crushing damage at the break. I had forgotten to switch on the gyro again! Once is forgetful, twice is a seriously distracted mind.
3 days later.
After a bit of cutting and gluing to remove the wing warp it actually flew today and with the gyro on. Still a bit of a right turn tendency but within trim limits. Nothing special just 5 minutes of gentle flying as with all the rebuilds it really was another maiden.
Unfortunately given Boris's latest edicts I am not sure when it will be able to fly again to find out more about how it flies but at least it has.
Edited By Simon Chaddock on 23/03/2020 23:14:29
Looking through various forums it seem the Bolt glider has indeed been successfully converted to powered RC. Your comment on the strength of the Cheetah wings has also been repeated and even brought into question the practicality of doing so as apart from the control surfaces being market out everything else requires 'digging out' of foam to fit.
These observations and potential difficulty immediately attracted my interest!
The strength of the wing brought to mind the Antonov 225. It uses the wings from the AN124 with a centre section added (and 2 more engines) which enables the 225 be 50% heavier yet with only a 2% increase in wing loading.
So a centre section with 1/3 more area would allow the Cheetah's weight to rise to 160 g without increasing the wing loading. Furthermore some of the bending arises from its centre clip together joint which a one piece wing centre section would not, so my hope is the existing foam wings without specific reinforcement will be able to handle at least a 200 g all up weight.
Now I just have to put the theory into practise.
Edited By Simon Chaddock on 23/03/2020 13:24:25
|Thread: I never thought it would come to this....|
My own opinion is it is not much the physical space as the wind or rather the turbulence caused from surrounding tress that will effectively limit how often you can fly. In a true zero wind it is like flying indoors so your garden with its unlimited ceiling height (within airspace rules!) is 'big' provided your plane flies slowly enough.
If you can build yourself it does not even have to be that tough as it can always be repaired and it helps to pass the time.
I converted a Lidl 'hand throwing' glider to powered RC last year and with some aerodynamic 'improvements' it flies and glides really quite well. It weighs 225 g.
Although reasonably efficient it does not exactly look like a glider with rather 'chunky' wings.
I then noticed the Cheetah hand throwing glider. Similar in concept to the Lidl, slightly smaller and cheaper but with a rather more 'glider like' appearance.
At 890 mm span it looks to have a limited wing area for a electric RC conversion.
Quite nicely moulded, actually slightly better than the Lidl, but the 'clip together' two piece wing could present a strength issue as the glider only weighs 119 g so a conversion close to 250 g would double the wing loading.
Not really in the 'spirit' of a conversion but one solution would be to add a substantial wing centre section. This would increase the wing area and aspect ratio yet without adding significantly to the load on the existing foam wings.
That's very impressive.
I do wonder if you might loose quite a bit of air pressure directing the air through all those channels. It might be better to simply make the inside basically hollow with just the minimum of support structure and let the air find its own way out of the holes in the bottom plate.
It will be interesting to see how you get on..
|Thread: Twister 40, anybody know anything about one of these old motors.|
I think your motor is a Cyclon Twister 29 of 2000 vintage
Full spec here
If so the Twister 29 is considered a '40' equivalent at a max continuous current of 30 A and was considered capable of easily flying a basic plane up to 5 kg on 20 cell NiMh (6s LiPo) delivering 600 W.
On a 3s LiPo you could only get 300 W at 30 A.
That absolutely amazing!
I too built a hovercraft in 1960 out of 1/4" and 1/16" balsa also powered by a Mills 75 (the only engine I had!) swinging a 8x4 plastic prop. The tips were trimmed to just clear the duct that had been built around an 8" cake baking tin.
Being an inveterate hoarder I still have it 60 years on!
It quickly had a clear polythene skirt added to create a deep plenum chamber which worked very well. Of course the vertical component of the engine thrust was probably a significant proportion of its weight.
I not unreasonably assumed that by taking air from the front of the duct and directing it to rear would drive it forward but I had completely misjudged the effect of engine torque on such a free running thing. The end result was it did hover, simply rotated about it axis and quickly started to travel down wind at what ever the wind speed was.
I did build another but with the Mills driving a 4 blade 6x4 prop facing forward with a duct diverting the air 90 degrees down into the plenum. It sort of worked and it did travel forward but this time the engine torque caused it to 'list' to one side with the result it moved sideways at the same time.
Never did cross the channel in an SRN4 or take a 'Bay of Biscay jolly' in Concorde come to that, both of which I never quite got to do. Ah! well. Opportunities missed.
|Thread: 2 or 3 questions please, need some wise advice|
I have my Dad's Drummond flat bed which he bought in 1928(ish) and it was second hand then!
In 1960's he managed to get the appropriate castings from Myford (they bought out Drummond just after the war) and make the necassary parts to convert his to the 'Admiralty' pattern (as used on wartime submarines) that gives a powered saddle and cross feed.
Apparently such Drummonds are rare as Myford insisted that all of them in naval service were officially scrapped post war to protect their business.
Yes they are delightful lathes. Soon it will officially be a family antique.
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