It has to be easy and good value.
11395 forum posts
I have had a break from building a RMC Dornier 335. The reason being is fear and I have doubts if it will be robust enough for me.
I also have regrets, last week was our club auction, stupidly I missed out on a motor that I probably needed, just because I was not interested in a pile of others that came with it, they all went for in reality nothing. Otherwise this blog would have been about a Mercury kits Aeronca Sedan. Instead it is about a set of foam wings, that I bought for very little.
The wings came with a plan of one of favourite designers, David Boddington. On refection i came to the conclusion that it was not one of his better designs.
I then thought I personally value robust models, that I can fly in most weathers. No race horse for me, or Lutus Cars, rather a Shire horse, or BMW. Something that does the job, many see as boring, but solidly made, functional.
My wife has said I mean with myself, as i wont buy an expensive ARTF model, that cost thousands. I prefer a good value model.
So using the wings as the starting point, with the work horse in mind I set about designing a minimalist model,
This is the basic design, as simple as I could make it, using minimal materials, as less is more. It owes a little to my NitroModels Do 335, in that I have tried to get the drag and thrust lines pretty much balance, to avoid down or other thrust.
I have started to create the servo lead passage in the wings on the "Neutral Axis". Which reminds me that a good few years back, when I was asked what I did for a living, i said I was an engineer. What sought came the next question, I am a Diploma or CEng I said. Ah, perhaps you could fix our lawn mower came the response, only my husband is a Professional, in insurance you know, practical things are not his forte. I sighed and said, i cannot fix lawn mowers, fridges are more my thing. Turned out he sold the thing called insurance.
I have created a passage so far half way down the wing, using an old arrow shaft.
So its back to fixing fridges, until i have made some progress.
Edited By Erfolg on 11/10/2019 20:47:41
11395 forum posts
As with many projects, I have considered a few issues and then made changes.
The obvious one is that the wing was cut with a slight amount of dihedral. I think that this unnecessary, with a high winger, that should be as happy upside down as normal. So I have made the aileron cable route go from one end to the other. The boring method i have used has worked with a high degree of accuracy, a little to my surprise. Initially i had twisted the arrow shaft by hand. But it was time consuming. I then tried using my electric brill/screwdriver, set for screws. This worked both fast and easier to control direction etc. A first for me.
If you look carefully you can just see the arrow shaft at each end.
This picture was supposed to show the passage way right through with the room lighting showing at the other end. It did using my eyes, not so the camera.
I am now joining the wing panels. I do not use GF cloth or anything like it, as it is pants to my mind. My hobby background is thermal gliders. I have a bible, which I refer to often, written by George Stringwell, titled "Thermal Gliders". Now George provides more methods for joining wing panels than you can shake a stick at. Pre moulded FG models, George provided all the answers you would ever need. In the case of foam cut wings veneered, Georges simplest way is essentially ply brace. The simplest does not even face the the ends with balsa sheet. Although George did shape his braces option to better distribute stresses into the materials. I have not bothered, as braces does a far better job of that aspect than most peoples GF bandage method. Although my brace does show what George advocates in Green.
I just carefully mark out the wing both sides, work from either side as advocated, then open up progressively with saw blades.
I have now inserted the braces using PVA, this will take some time to set, probably days.
I have increased the height of the UC, as I realised, what I have drawn is fine take off, but limits the AOA when landing, probably preventing a good flare.
11395 forum posts
I would not be surprised that many modelers also started building rubber jobbies, using a double edged, used Gillette razor blade. Not for me a single edged, NEW, razor blade. I made do, as I still do with dress makers pins of various vintages. Everything else relied on my teeth to chew through thicker balsa.
For years i have shown and registered contempt for those with a gadget for this, another for that. I made do. However in more recent times i have acquired various gadgets, often recommended in our posts.
Perhaps the first that really has improved both my quality of output in finish and accuracy is this £30 sander from lidl. I know at least one person paid even less.
What is perhaps not obvious it has mitred the leading edge balsa perfectly.
although the picture quality is pants, trust me, the joints are perfect, two 45 degree scarfs.
My latest Gizmo came in at £26, from HK. Previously for cutting strip wood I used a SLEC stripping device, it at best produced a passable strip. I have used it so far on some 1/8" ply, and to strip of the leading edge strips and 3/16" longerons. Now the longerons are perfect, just what the doctor ordered. Long ply pushes its capabilities. In case of balsa no problems.
I have now started on the body.
Edited By Erfolg on 16/10/2019 14:09:41
|Nigel R||16/10/2019 14:16:15|
3102 forum posts
Quick work Erfolg. Looks kind of Rival-ish for the fuselage. Should go nicely.
"My latest Gizmo came in at £26, from HK"
It appears to be a small table saw, correct me if I am wrong. I did not know they sold these.
I have made a captive blade stripper in the past, it works ok - providing the grain is perfectly straight. If the grain is not, the wood can compress behind the blade, leading to wobbly cuts. I have had to throw an otherwise usable sheet or two of wood because I could not keep the cut straight. The HK kit looks like a useful widget to have on hand for making strips.
Edited By Nigel R on 16/10/2019 14:18:49
964 forum posts
Erfolg. Easton Xx75 autumn gold. Also very useful for cutting holes in ribs for aileron/flap/etc leads and for lining wing bolt holes
|Rich too||16/10/2019 17:40:12|
3052 forum posts
11395 forum posts
Nigel, it is a small saw table. In the past I have been put of some models, as they needed quite a lot of strip wood. As proportionally it is expensive, I have gone in for baulks of balsa. As I inferred, the SLEC stripper provided OK results after quite a bit of time and care.
I had considered the Proxon saw table, again I was put of by the price, my age, in that I would never see value for money from it.
Seeing the HK device for £26, I thought worth a try. I have been very surprised at how good a job it does and also so quick. My only concern is safety, the blade in use is not protected. On that basis extreme care is required, and constant thought of where my fingers are, and what could go wrong, to avoid injury.
As a builder I am slow, Sloth like, no pretensions to being a trades man.
As to what the model looks like. That has been dictated by the foam veneer wing. The body is just a 36" sheet, that is 3" wide. Being an ex engineer, I like straight lines, no fancy curves. As one of the Chief engineers said, in a meeting, when I hear you designers and architects talk about aesthetics and form, I see piles of money being stacked up and set on fire. Everything is simple with minimum wastage. If it turns out like something else, they just implemented the concept before me.
To keep both of the frame sides separate, I use bits of old plastic sheet, in this case a food packaging.
the position of the support for the tray when finished is to accommodate any servo from standard to 9g types
I was going to have a ply doubler that was full depth. I changed my mind on the basis it is the bottom of the model that constantly see the most forces and hence stress. I also pre-bend to make the next phase easier in my jig.
|Nigel R||17/10/2019 14:48:30|
3102 forum posts
Thanks Erf. It sounds pretty good for our needs.
Build is proceeding pretty quickly despite your protestations!
11395 forum posts
I do not know about others, my building sessions start when I have nothing else to do and finish often when my old fashioned PVA needs to dry. There is another criteria, there is always 30 minutes spent on my modeling room when East Enders comes on.
I realise that these breaks are great, especially over night ones. As many of my decisions and thoughts occur whilst not fully asleep. Todays revolved around the motor. My drawing is based on the use of a Turnigy 35** type of motor. On reflection , I have a number of motors already, some possibly suitable.
The extreme right motor is more than powerful enough, from experience. For the moment I have gone for the motor to the right. I know little about its technical detail, as it came out of my Parkzone Reliant, when the wing started stalling even at speed, and I found I could not buy a replacement one.
I have set up my jig and assembled the stick fuz in it. It is now out, at present I am sticking cross grain balsa across the top and bottom. Then with a reasonably stiff fuz i will stick on the side panels.
this picture shows how the fuz has designed itself, being based on a standard 36" balsa sheet.
Edited By Erfolg on 19/10/2019 16:57:33
11395 forum posts
I now have a basic body.
My thoughts are now turning to both the tailplane and fin.
In essence the tailplane will have a fixed part of 18"*4". the moving bit probably 1" or maybe something a little bigger. Dependent on the % of wing area it comes out at. In the case of the fin, I am now thinking a triangle is probably the simplest, although, it all depends on what is left from the build so far and what I have lying about. I tend to like a bit of fin/rudder area, seems to little harm if generous, bit of a directional issue when a little small.
11395 forum posts
Although the weather is leapt forward to winter, I have had little time for any building.
I have spent the last week walking a dog, which i have been baby sitting, whilst my daughter No.1 went on holiday to Iceland. The grand kids complained on their return, it was so cold, no snow. I thought the name should give a clue. Any way two walks a day, over an hour each.. Still, I now have walked the beach in the depth of winter, seen the sea, in all of its, well, wetness.
I spent some time on the wing, comparing the nose section with NACA 0015, the drawing that came with the model. What ever the section is does not seem to be NACA, complicating matters the foam wing is not quite the same as the drawing. The complication being that a template made from the drawing, did not seem to fit, nor did a NACA print out.
In the end I compromised and made a template, that was a blend of NACA and the section as cut.
I must admit, being historically a glider guider, I was obssive with respect to wing profiles. I have made a lot of wings, and have my own believes, as do most guiders. I know that Clary Y, although apparently similar to E205, they behave differently, E205 will penetrate with little height loss and will also loiter at low speed with little height loss. The percentage thickness being about 9-10%. I built heavily under-cambered wings, and flattish bottomed wings with a large camber. The experiments have gone on to thin percentage wings HLG 5 and MH32 for example. Played with nose radiuses and so on.
You cannot believe how much concern I have had with discovering the wing is 15%. I have built symmetrical wings relative recently.
This wing is NACA 9%
Where if memory serves me well this is NACA 0008
I found that my ancient and now in bits KK Specter was NACA 0018.
I find that very thick wings require a lot of power to go fastish. Although the well rounded nose of the NACA 0000 series stall in a mush, seemingly holding high AoA beyond the section data suggest they are capable. In the case of the Specter, the high profile drag meant it did not accelerate much down hill.
As unhappy as I am, I have what I have. Time will tell how much of an issue the section really is.
I had to stick on a extra piece of wood to get a good nose radius.
All the major bits are now made.
Everything from now on is about the detail bits and assembly.
As a point of interest, counter to a lot of people, who fly aerobatics, I do not set my symmetrical sections at 0-0 to the tailplane, I set the wing 0-0 line at +2 degrees, to the tailplane and the body set at the position I want it to fly at under level flight. Otherwise the model will have to fly slightly tail down by about 2 degrees. It seems to work for me. With the convectional sections, typically set on the 0-0 line the section is still generating lift, which is not so with symmetrical sections.
Edited By Erfolg on 29/10/2019 15:17:18
11395 forum posts
The vast majority of all the basic detail work has now been completed.
There is a torsion bar UC, a steerable tail wheel. The mountings for the wing servos have been made and fitted. Wing tips shaped and glassed. I have given the veneered wing a coating of WBV, to aid film adhesion. The battery hatch just needs a little more work.
Most importantly I now have an idea with respect to the CG balance point. That is using either a 3s or 4s 2200 Lipo. It will need lead to bring the CG to the 25% chord point. I will run the basic design through a CG calculator, to get an idea how sensitive it would be at 30% chord.
The issue now is about covering the model.
I have toyed with using Christmas, present, type wrapping paper. I almost certainly will stick to China film. I have one major issue, that is my checker film has no adhesive on the film. I have only one pot of Balsaloc. I see that % star sell something called Coverloc, that appears to do the same thing, at a slightly higher price than Balsaloc sold for. Is there anything else that will do the same job?
I will move onto a Lipo tray and Servo tray whilst I ponder the covering issues with respect to the checked covering for the wing and tailplane underside.
I will have to probably change my plans with respect to the servo tray. I had intended to mount the Rx at the forward end, with space to the side for a giro. The giro will eventually be for experimentation, as I want to build either a Gee Bee r1/2 or a QED, and feel a giro would make life potentially easier, providng longevity to the model. Plus a bit of knowledge and experience is always nice.
The table also urgently needs a tidy up.
Edited By Erfolg on 08/11/2019 19:58:33
11395 forum posts
I used to think when I had reached this stage, covering, that the model was very near to finished. With the advent of ARTF models, I now know that I am some distance away.
The odds and ends have taken much more time than you tend to think. The motor hatch has taken much longer than i would have thought.
It has taken me a day just to cover the underside of the model, goodness knows how long it will take for the rest.
Slow or what?
|Bruce Collinson||14/11/2019 21:15:13|
|404 forum posts|
Erf, Solarfilm had Balsaloc fairly recently.
|Geoff Sleath||14/11/2019 21:52:43|
3429 forum posts
Airtek Hobbies sell something called MD Balsa Bond. No idea what it's like but I ordered some when I also orederd some Oratex for my Pup. It's at the bottom of the page.
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