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RBC Dornier 335

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Erfolg12/01/2020 23:37:52
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11797 forum posts
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In defense of RBC, I suspect that kits produced are small in number. I also guess that not many have been built by RBC. RBC probably supply models that are not mainstream, a bit quirky, they are far more interesting.

It would not surprise me that this is just one guy, who has to design, build the prototype, cut the kit, source all of the kit materials, package the kit, deal with the accounts (cash flow) and tax.

By ARTF standards, the total build cost is far higher.

As for the 335, it is bigger than i thought. It is worth doing, although my model will not be as scale and detailed as the French example. I just feel it will fly, probably quite well, look good in the air, to my eye.

The down side is, i do wish i had beefed up the UC mounting, as our field imparts a bit of pounding.

I do hope you find the build interesting, even my cock ups, I always manage a few.

Erfolg22/01/2020 12:31:16
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11797 forum posts
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Whilst I wait for suitable motors to become available I have turned my attention to the nose and tail mouldings where the motors will go.

The supplied moulding unfortunately are very flimsy, akin to those often found in some of the early cheap far eastern imported kits. Perhaps they could be of even poorer quality. Certainly the worst aspect of this kit.

What to do about it? In the past i have made similar cowlings by building up a nose area.

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Both of the cowls above were made by slightly different methods, they all work. All involve a layers of balsa wound onto formers then put in a drill an slowly sanded down, as in a crude cylindrical grinder.

In this case I have some mouldings which are a little less than I would really like. In this case I think I will give another method i have used in the past. Which is to use the mouldings as formers to create a mould. In the past i used Plaster of Paris, now finding a reasonable art shop requires me to travel. This time I decided to use finishing plaster as used on walls, I have used it previously for my grandkids school projects. The down side it does not set as fast, and probably uses more water. meaning it will be weeks before it is approaching dry, during the intervening time it's weak.

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The mouldings are so flimsy that I need to support them to make them concentric/round.

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I cut out corrugated cardboard discs which i inserted into the moulds whilst pouring, with internal weights to stop the mouldings floating.

I am not to concerned with the nose cone as it appears to be reasonably round and of the right shape. The rear cowling is another matter. I am not sure it is near enough to fit well, where its flimsy properties would possibly allow it to be pulled into shape. I also know i cannot mould this with to a heavy lay up, as weight at the back, has most unfortunate CG consequences.

In the case of the rear, I will try cutting and filing to get a good shape. If all else fails it will be a balsa and ply built up structure.

In the next week or so i will clean the inside of the mould out, then start wax polishing the inside. I the past i have found that 6 coats are over kill but work. I still have some old blue moulding PVA which I will try.

My intention has now moved to Polyester Resin, as I can buy a small quantity from Halfords.

 

Edited By Erfolg on 22/01/2020 12:32:33

Erfolg29/02/2020 18:33:47
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11797 forum posts
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The project had ground to a halt due to a number of circumstances, HK not having in stock the motors that I wanted. I have now forgotten which ones and why, it is an age thing. Then I have had one cold after another, that is three to date. A holiday in Lanzerote, glad I got back in the nick of time. Looking after a house rabbit, then a delinquent dog, that needed a lot of walking and of course Christmas.

In between I did what I could.

I also posted a number of threads with respect to moulding cowlings. From which I did get useful information, which to a large extent decided what I did.

In the dim and distant past, I have been involved in various GRP work. In addition in my early twenties I worked in a commercial plastic moulding company, that did injection, transfer, dough, and some steam moulding. Nearly every type of polymer you could think of was mixed, bought in etc. Of course I took a lot less notice than I thought. As a hobbyist I had some specialist tools for the stuff I did.

Today, the tools have gone, what I knew, is now forgotten.

I knew |I needed better cowlings than have been supplied with the kit, so the following is what I did.

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This is a pattern for something

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A length of hobby related cloth I purchased at 200 g per ft^2.

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I pre cut all of the laminations I wanted

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The mouldings as they have been pulled.

I may have described how I made the moulds, but here is a repeat. I made up a box to put the RBC cowls into. I then purchased some time expired plaster from B&Q. Filled the cavity and weighted the cowls down to prevent any lifting. Binned 90% of the plaster.

I then waxed the the moulds 6 times.

I then painted with blue PVA, the type used in moulding. It is 40 years old. Still works.

Debated if to used polyester or epoxy resin. I was convinced that Epoxy would be better. I purchased 500ml set. Ordering was a trial, then the order went missing. It was not Easy composites fault.

I found that what I once found to be no big deal, was for an old man, without any recent practice and remembered relevant knowledge.

What I learnt was (as recommended on another thread) weighing is much preferred to volumetric measuring. That I work a lot slower than I thought. That 60 ml goes of faster than i could work, approx 20 minutes. That for the cowling that 26 ml was just about ok. That the flexibility of Epoxy allowed me to ease the mouldings out of the mould, where with polyester it is far to stiff, for a similar moulding.

In the end I got there, but, golly gosh, it was a close thing a number of times.

Erfolg01/03/2020 15:21:00
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11797 forum posts
1346 photos

I have now done a little bit more, the emphasis on bit.

I do not like GRP mouldings with bits of random glass sticking out of them, as they are surprisingly prickly. On that basis I took some measurements from the supplied drawing and set about creating a cutting line.wp_20200301_12_14_43_pro.jpg

I taped a little masking tape in the area where the cut had to be made. Fortunately I have my fathers old scribing block. Again it just shows, do not throw out anything, even though you think you will not use it. I taped a pencil to the scriber as it marks more clearly than the scriber, with sufficient accuracy for what i need or can work to.

I was a little surprised and disappointed in that the rear cowl has virtually no waste on it.

I do not like GRP dust either so I donned my gardening gloves, coat, shoes and hat and headed outside. There I cut the waste of using a junior hacksaw. I did take a very fine (number of teeth) hacksaw blade, although it was not needed.

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First stage now done.

Before I move on, it is time to clean and tidy my modeling room. Then cogitate how to mount the cowls, consider motor cooling. Any one who saw my PM 1/4 scale Cassutt will be aware what inadequate cooling ( two blanked of galleries) can achieve.

Also this week I will consider the motor issue.

Erfolg08/03/2020 14:29:58
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11797 forum posts
1346 photos

After a little examination I found a problem with rear cowl. The problem being that the length of the cowl incorporated a little sweep upwards at the top and the bottom.

A little more scrutiny of the drawing indicated that the cowl is supposed to slip over the rear end of the Fuz. That may happen with the flimsy moulding supplied. With my light weight moulding that is is not going to happen, as it is to stiff, rigid. The other issue is that the supplied mould does not match well with rear bulkhead.

My solution is to lay up more laminations inside the problem areas, then sand the outer surfaces to shape.

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To mount the front cowl I have made up a inner ring of light ply which then has a few layers of glass cloth layed up on top. When I have satisfactorily centred the cowl I will then tack the two bits together,

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I ideally now need some motors. I was hoping to use Propdrive 35-42 at the front and a Turnigy D3536/6 at the rear (being fractionally lighter, although I am not sure the difference really matters). Both are out of stock. I considered a Turnigy 480L V-Spec, which is on offer, although due to a 23p excess over £15, could cost me over an additional £10, as has happened previously for 50p.

So I will now start looking for alternative motors which provide something like 1.3 kg static thrust (approx 2.5 kg combined).

Edited By Erfolg on 08/03/2020 14:31:06

Erfolg09/03/2020 14:32:32
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11797 forum posts
1346 photos

I have been looking more carefully at the rear moulding as supplied, and have come to the conclusion, it deviates from scale, noticeably. It is the sort of thing that passes me by, that is normally, not this time.

The full size aircraft had side opening doors for radiator cooling air. The kit omits these, but has potentially a large (ish) opening where the TE would be.

I am now thinking of opening this up for a cooling air outlet, then creating reverse side openings, to let air in.

As I am not a rivet counter, I can live with this non scale aberration, to scale aficionados.

I have noted a discrepancy with respect to the nose moulding, a radiator on the real thing. Again, practicalities matter more than absolute scale.

As it has now started raining, I will content myself in marking out where all the various holes should go. Then wait for a good day, to go outside to work on the GRP.

In the mean time I am still pondering suitable motors.

Erfolg11/03/2020 11:37:53
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11797 forum posts
1346 photos

I have been trawling through the HK site looking for suitable motors. They seem to have nothing remotely in the sizes I use. Although I have purchased one that may be OK. My present plan is to install motors that could do the job, although not as ideal as I would like, with a view to replacement in the future. To that end my motor fixings need to be easily replaced.

I have been waiting months for HK to restock, I suspect that motors are either in short supply in China, or that motors are not a high priority for HK, or there maybe a cash flow issue, where money is being directed to the highest margin and sales items.

In the mean time I am dealing with the things that appear to be wrong with the kit, or maybe how I have built it.

The first bit that seemed wrong was the cockpit area. Their was a curious bulge by the cockpit. I have poured over numerous pictures, my trusty Airfix model, on the full size it does not appear to be there. So I marked the line which appears to be near enough correct to my eye.

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Then just removed the offending material and re glued.

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I will now sit down and consider what should be my next logical things to do and the relationship or order. I have a feeling that much of the bare airframe is now done, but a lot of time consuming things need to identified and done. In my case not made easier by not always remembering what I have done and why, for the later stages of building. It all seems so logical at the time.sad

Erfolg18/03/2020 02:02:13
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11797 forum posts
1346 photos

This turning out to be a slow build. The lack of HK stock being one of the issues.

I have decided to go a slightly different way than intended and that is to use a motor combination that i have used previously. One of the motors coming from a TH Clean Sweep (which I crashed).

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These are high torque inrunners of relatively low Kv.

It was only after some lazy thinking, when it suddenly dawned on me, that I could have bent the motor shaft. On this type of motor, the shaft is not replaceable. Sticking on the original spinner on i could see that it was running out. But was it the shaft or the spinner? I have no fancy equipment that many model engineers have in their workshop, only some basic stuff. So I have to improvise.

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In this case some vee blocks to hold the motor, a DTI mounted on my scribing block. Everything was moving, so a couple of pieces of lead to keep stuff in place. There is a little run out, of a couple of thou, which is possibly the prop adapter. Running on the shaft, there appeared to be none, although the flat on the shaft complicated things, hence the adapter.

To mount the motor is less simple than with an outrunner, although I have two options I am considering. Both are not straight forward. Both use approx, the same stuff

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more work is required, although I have some confidence I can get it to work. Outrunners would be so much easier. This set up has ruined my plan of how to actuate the rudders. I think it will now be visually messy.

I will use the same motor as the pattern to make the front mounting, whilst I wait for the HK motor

Edited By Erfolg on 18/03/2020 02:06:01

alan p18/03/2020 09:10:13
288 forum posts
25 photos

Cincinnati machine tools a good old firm. Blast from the past

Erfolg19/03/2020 17:19:26
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11797 forum posts
1346 photos

After consideration of the planned method of mounting the rear motor, I came to the conclusion, although I believed I could make it work, with careful setting up and gluing, it would be clunky. I was not very happy.

Luckily I woke up, the next morning with a possible solution.

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Which is above. it works quite well, still more work to finish, including the purchase of a couple of spinners.

I intend installing the front motor in a similar way, although, the installation will be a little better, in that the motor assembly will not be cantilevered or overhung to the same degree. The only problem is that I am in the age group of self isolation, so cannot go out and buy an endcap, to modify.crying 2

Erfolg15/04/2020 11:06:23
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11797 forum posts
1346 photos

It probably seems that I have not been doing anything with this model. I have but it has been slow going.

The first thing I noticed that the rear cowl did not fit as well as even I like.Rectifying the issue took some time and work, Then I noticed that the thrust line may not have been as ideal as is necessary. Yet more time with the cowl. The thrust line is now pretty much along the centre line. Unfortunate the cowl is less than a perfect fit, it will have to do.

Next I noticed that the fins were not quite at 90 degrees to the tailplanes. Yet more work. To get the back end within acceptable limits seems to ba an iterative process, which is beyond me in single operations.

I have finally glassed the body with with 1.5 oz cloth. The fins, tailplane in 1/2 oz cloth. Does any one know the metric equivalent, as i will need to buy some more for the future. I used Ronsons Hardglaze as the varnish adhesive.

I am now waiting a motor for the back, now I have paid PO handling fee, plus about £4 in vat. It just occurred to me that most of the vat is the PO handling fee, as the motor was £16. I could not get what I wanted in the UK.

I will make a few bits of trims, then probably put it to one side, and work on it in bits, as we are now getting to the fiddly, slow bits.

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