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Member postings for Simon Chaddock

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: Round the pole
29/03/2020 18:59:57

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.

RTPpup

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.

SC-Triplane-1c.jpg

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.

Triplaneconstruction1

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.

SC-Triplane-2.jpg

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. wink 2.

That's quite enough of my reminiscing!

 

Edited By Simon Chaddock on 29/03/2020 19:00:54

Thread: Composite wing ribs
29/03/2020 14:14:47

David

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.

Tigermothwing

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. wink 2

28/03/2020 20:48:30

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.

RibShearweb

This rib weighs 0.5 g

Larger ribs can be reinforced with diagonal cross bracinglightrib.jpg

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.

 

ribset1-12.jpg

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. wink 2

 

Edited By Simon Chaddock on 28/03/2020 20:50:32

Thread: Cheetah
27/03/2020 11:35:51

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.

Center3

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.

TrailingEdge2

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. wink 2

The trailing edge extensions with the aileron cut out.

Extensions1

Aileron servos next.

Thread: 2 or 3 questions please, need some wise advice
25/03/2020 14:48:21

011hillclimber

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.

Wing tissue and ESC

.Rather important if you are trying to build a scale twin EDF under 250 g. wink 2

Thread: Cheetah
24/03/2020 22:36:57

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.

RibShearweb

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.

Center2

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
24/03/2020 22:07:00

Steve

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.wink 2

23/03/2020 23:07:38

The Gnat has had a rather chequed career so far and all of it my fault. smile o

First attempt result.

08mar20a

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. sad

A completely rebuilt nose.

Nose on1

A week later complete and ready to go again.

New Nose Cmplt

Second attempt.smile o

16mar20a

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. crook

3 days later.

19mar20a

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. wink 2

Edited By Simon Chaddock on 23/03/2020 23:14:29

Thread: Cheetah
23/03/2020 10:55:27

Hi Steve

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! wink 2

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. smile o

 

 

 

Edited By Simon Chaddock on 23/03/2020 13:24:25

Thread: I never thought it would come to this....
23/03/2020 10:10:58

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. wink 2

Thread: Cheetah
22/03/2020 22:19:22

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.

Foldprop1

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.

orange

At 890 mm span it looks to have a limited wing area for a electric RC conversion.

parts 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.

Thread: Hovercraft
21/03/2020 23:59:49

Martian

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.
21/03/2020 12:37:57

David

I think your motor is a Cyclon Twister 29 of 2000 vintage

cyclontwister29

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.

Thread: Hovercraft
21/03/2020 12:09:21

Robert

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! smile o

SC1a

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.

SC1d

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. wink 2

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
18/03/2020 15:49:38

011hillclimber

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. wink 2

Thread: Drone crashes are now investigated by the AAIB
15/03/2020 20:17:51

The interesting bit to me was in the January report there were also quite a list of commercial quad crashes (DJI Matrice) and almost all were caused by either motor or ESC failure which resulted in an uncontrolled descent by 5 kg quad directly into the ground.

The AAIB pointed out that to the unprotected (no hard hat) this could be a potentially lethal situation. They also commented that the same failure in a plane would be unlikely to have the same outcome.

They made no recommendation on this subject but the inference is clear.

Thread: 2 or 3 questions please, need some wise advice
14/03/2020 18:17:27

911hillclimber

Rather than change the set up of the tx it would be easier to leave the tx in normal Mode 2 (throttle/rudder on LH stick, aileron/elevator on RH) and then simply plug the rudder servo into the unused aileron port on the rx. This will transfer the left/right on the elevator stick to the rudder. Left/right on the throttle stick will then do nothing.

Remember the rx just takes the tx signals and directs then to a specific servo port. Which control surface that servo moves is entirely up to you. wink 2

II have done this very thing on a 3 ch plane that was to be flown by someone who could only fly "rudder on the right". It only took a few seconds to do.

12/03/2020 20:42:40

911Hillclimber

I am left handed (well like you not for everything) and fly mode 2. As I also flew full size gliders it seemed quite natural to me.

Then I discover the benefit of hand launching with my 'good' arm and still having aileron/elevator control instantly available. wink 2

Thread: Bind to a second Model
12/03/2020 14:00:46

P J Hearne

Yes you can bind as many rx to one model memory as you like BUT as Peter points out they will all have the same settings.

Now if you are used to basic 35 meg gear where you have to mechanically set up every plane so all the servos work the same way and the neutral trim positions are basically the same them no problem.

I have more planes than the 10 model memory on my DX6i so I have a few 'doubles' and give the memory a title that reminds me which two they are.wink 2

Thread: 2 or 3 questions please, need some wise advice
11/03/2020 21:01:52

911hillclimber

Just to be sure you can use the DX6 'monitor' feature to display exactly what signal the tx thinks it is sending for each stick and on which channel.

I presume you are using the ESC BEC to power the rx and servos.

If so the fact the rx 'powers up' means the ESC plug to the rx must be in the right way round but not necessarily in the right port for the throttle. wink 2

Does the ESC make the 'arming' beeps? If it doesn't then the motor will never turn.

If the ESC is in the right rx port then is the throttle stick at minimum when you connect the battery? As a safety feature the ESC will not arm unless the throttle is at minimum. The ESC may just repeat single beep as a warning. Some ESCs actually need the throttle trim to be set at minimum as well.

It is a good idea to un plug the servos until you have the ESC arming and the motor working (prop off). Then connect one servo and get that working before connecting the next.

It pays to go one step at a time.

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