882 forum posts
There are a few things that can be mentioned about the tail feathers. I like built up fins, rudders and tailplanes but I also wanted Grumpy to have a solid look. The wings are fully sheeted on the top surface and mainly sheeted on the underside so I did get to fit a few cap strips which I also like doing. Any kind of multi-coloured covering with curves is easier over a sheeted surface because all the overlaps are fully supported.
The tail feathers were therefore built up and then sheeted. This does give a very strong structure.
First step is to draw the built up structure. Using a series of triangle makes the whole thing very stable. The area shaded red gives good support to the sections that will be glued. In an open structure this would give the covering something to stick to.
The slot in F8 has been deepened to locate the base of the fin and the post at the rear of the fin extends down through the fuselage. This makes the fin self-jigging when finally assembled.
Here the rudder has been given the same treatment and I try to get some sort of relationship with the fin. In this case it does not matter too much as it will be covered by sheeting but in an open structure it looks better. A copied section of the plan is now on the board ready to start building as soon as I have covered it with cling-film.
The tailplane ready as well. The drawing was photocopied twice and one flipped on the centreline to give the other half. The lines showed up well enough to trace them through.
The centre section is made with a generous allowance to again make sure the glue area has good support. If left an open structure this again provides a margin for covering.
The centre section being glued in using chocks and wedges to squeeze the joints together.
The rudder and fin framework is complete and the paper templates that were stuck on with Pritt Stick are release by lightly damping with water. Just enough to wet the paper but not enough to curl the balsa.
Using the rudder as an example (the elevators get the same treatment) one side of the sheeting has been stuck on for strength and the framework is sanded to a taper before applying the opposite sheeting.
882 forum posts
If my aircraft has a clear canopy then I like the cockpit to be occupied with something. I have not built a true scale plane yet so my "pilots" have not had to stick to any convention. I have carved up and reassembled ping pong balls, re-assigned Smurf fridge magnets and here is Spain, quails eggs are popular so I could easily end up with an eggshell egg-head wiggling the sticks.
My main beef with bought pilots is that they look so wooden - well plastic really! That straight ahead fixed gaze looks so rigid (plus if there were more goggles down pilots it would make painting a whole lot easier). If ever I get into 3D printing, pilots would be No 1 on the list along with printed fuel tanks.
Here is Grumpy's pilot straight from the box of potential aviators. OK some colours have to change and he may end up sporting a goatee but look, straight ahead, rigid and probably paralysed with fear from antics of the person holding the transmitter. Time for something more radical and for those of you with a sensitive disposition I suggest you look away now.
There were no witnesses but truly it was an odd feeling taking the razor saw to this poor fellow's neck.
Fortunately he survived surgery and recovery was quite quick with no major complications. After a short period of convalescence he should be fit for duty well before the date set for test flying.
There is only about 3 degrees of twist but now with his shoulders straight in the cockpit he is definitely looking at something.
Plastic but no longer wooden.
|Tim Ballinger||18/04/2018 12:54:40|
676 forum posts
Mine is still suffering from whiplash and slumped over his instruments. Needs some micro surgery to get some glue under his bottom again as canopy is still intact around him.
882 forum posts
Beware the compensation claim. Perhaps we should have some sort of personal medical / accident insurance before we get a stiff letter from their association.
Your post uncomfortably reminds me of an episode relating to superglue, shorts, bottoms and a chair. That is enough information.
882 forum posts
It hasn't only been light hearted stuff. I have been thing hard about the ailerons and flaps combining this with my mission to try something different on every build and stretch myself a bit. In this I have surely been influenced by Danny Fenton whose work I find truly aspirational.
I now have aircraft at roughly the same stage of build and ready for final details, covering and fitting out. Grumpy has finally caught up with Oodalally (both from the Peter Miller stable) and both share the same basic wing.
To start with I wanted to try out Danny's shrouded hinged surfaces. To date I have done hinges with the covering as well as conventional hinges and creating the clearance by putting a V on one or both edges. Many years ago I did some shrouded rudder hinges on a model sailing yacht.
The first stage was to cut a rebate in the trailing edge of the wing. This was done on the upper and lower surfaces for the ailerons and on the upper surface only for the flaps. Here we are looking at the aileron section of the port wing.
To do this and again following Danny's method I mas up a special sanding block in balsa. A strip of fairly coarse emery cloth was stuck to the block using Evostick with the width corresponding to the desired width of the recess. In this case it was 10mm. The rail is set at the same angle that occurs between the top sheeting and the trailing edge strip, in this case 94 degrees. This means that when both surfaces are sliding in contact with the wing the rebate will have reached the required depth to receive the 0.6mm ply strip. I chose the emery because it was thicker than the alternative sand paper and also I did not want it to wear out in the middle of the job. That would have made things tricky. On the first go it turned out that the rebate was slightly shallow but this was easily rectified by carefully sanding a bit off the block alongside the emery. This did the business and a few more passes allowed the ply to sit flush with the wing surface.
Just to remind you that I don't like sanding ply it had previously finish sanded the trailing edge of the wings so they only need "polishing" before covering.
Here the last tip section is about to be glued in. The dimples are from the clamps used while gluing the bottom strips in place. I took the swivelling feet off the clamps so the ends would bite into the balsa and not slide off the taper. You can see the end of some masking tape that was put on the bottom strip again to stop the clamps sliding.
To get even clamping pressure because 0.6mm ply is very bendy and especially so in its bendy direction. I placed a steel rule over the strip and clamped onto that.
The finished result was a trailing edge with about 3mm of recess. After dressing the edges with a long Permagrit I estimate the recess will reduce to around 2mm to suite the radius on the leading edge of the ailerons. I know, I did say I hated sanding ply but sometimes you just have to.
|Peter Miller||19/04/2018 08:05:02|
10504 forum posts
I like to see people experimenting and adding their own modifications to a structure.
882 forum posts
Finishing the ailerons is slightly different as it has to work partly inside the shrouds but the hinge line lies some way outside.
The leading edges are rounded off instead of having a V shape and the hinges (Robart type) have to be deeply recessed so that the centre of the hinge pin sits on the centre of the radius. This is where the overhang of the shroud is critical. Too much and the hinged surface will have very limited movement. Too little and the effect of closing the gap and having a neat hinge line is lost.
This will have to be a little bit trial and error for the first one and the overhangs may have to be reduced bit.
Here is a closer look at the recess. I did have to elongate the hole slightly to get the three hinges to line up exactly.
To be honest I have some trepidation about final assembly with the covering done and the glue in place. There is not much room for mistakes.
The tailplane and fin had similar treatment but instead of using ply strips, I extended the sheet a couple of mm past the trailing edges to create the shrouds. Before gluing I sanded a 45 degree angle on the inside face taking it to quite a sharp edge. This was then hardened with cyano to give the edges some durability.
Here you can just see the shroud made by the sheeting on the post of the fin.
Time now to get to grips with the flaps.
|Peter Miller||20/04/2018 08:32:16|
10504 forum posts
I have a special method for marking the holes for hinge points.
I have three 1"nails with the heads cut off and a small washer soldered on near the point.
I drill holes in one surface where the hinges will go and insert the nails. Then I lay the wing and control surface on a flat surface and push them together.
The points of the nails mark the exact spot to drill the other part.
882 forum posts
Nice one Peter.
I will make some up and use them on the tail feathers which haven't been done yet.
|Nigel R||20/04/2018 08:51:07|
3403 forum posts
Very neat. I like the rebating widget - must remember that one. And the wedges for lightly compressing the joints - clever.
I like sheet over framework tail feathers too, they have a habit of resisting warps quite nicely.
I guess you said a few choice words when you discovered the screwdriver stuck into your carefully built fuselage!
|McG 6969||20/04/2018 08:55:21|
2902 forum posts
Nice work over there, Lev.
I remember Danny's 'shrouds' on his Chippie. In fact, his build blog was the first one I followed entirely here at the forum and it convinced me to have a go with Peter's Ballerina.
Regarding your 'pin holes' for the control surfaces, here is what I used on the Bella.
It's exactly the same principle as Peter's method and it works perfectly.
Keep up the great job.
Edited By McG 6969 on 20/04/2018 09:02:55
882 forum posts
Thank you Nigel R and Chris
Somehow Chris I knew you would have beautifully engineered nails.
The basic flaps started life as two pieces of 2mm birch ply being the same thickness as the wing sheeting. As far as ply is concerned I am lucky in that the local model shop does have some nice flat pieces. My thinking at the time was that I might go for simple split flaps and these would have to be ply to get the stiffness at 2mm.
Then my thinking started to drift but to see how things might work out I made a little mock-up of the trailing edge to see how the hinges might work.
The ply on the left represents the flap and the balsa on the right is the trailing edge complete with the recess that was formed very early on in the wing construction.
The hinges are Robart points. The connection to the flap is horizontal made by the block and the connection to the wing is vertical going up through the wing. The block on the right hand side is simply a fairing piece and hides most of the hinge as well as giving a better appearance.
The trailing edge of the wing is of course tapered in plan form but the hinge pins have to align along the plane of the hinge joint otherwise they would bind. I wanted the fairing blocks however to align with the airflow so the hole in the flap block had to be drilled at an angle corresponding to the taper. The crude lower hinge is there just to make the mock-up stable and the different angle corresponds to the opposite wing.
The V between the blocks allows a maximum deflection of about 80 degrees which should be more than enough.
There are going to be six of these blocks so and the angle is quite critical so I made a drill jig.
The blocks are held in the angled supports and the jig itself is positioned so that the hole starts dead in the centre of the end of the block. The depth was set so the drill would not break through the sides.
By making sure the hole starts dead centre we only have to have one set-up for the whole batch as they can be handed left and right.
This is a Proxxon drill and one of my favourites along with the disc sander. It has an adjustable stop front to back and a channel on the right hand side. A strip of wood on the base of the jig locates in this channel and keeps everything accurately aligned from side to side.
Here is the jig in action and the block is just held in place by hand while drilling out the hole for the hinge point.
The patriotic tin in the background used to contain baked beans. Made in Italy, sold in Spain and liveried with the Union Flag. Yummy! My first choice for beans as they are less sweet than the Heinz originals which I suspect are pumped up with sugar for the Spanish market where things often seem to be very sweet or very salty. Watch a Spanish cookery programme!
Anyway back on topic.
This is a cross section of the mock-up in the raised position.
The thin ply shroud is visible on the top of the trailing edge and the aileron section is glued to the top of the flap. This is where I strayed from my original thoughts for a simple split.
The flap is now in the lowered position and with the hinge being further forward than the split line it makes the flap project lower into the airstream.
There was only one problem. I didn't like it. I was trying to achieve a sort of Fowler flap arrangement but it didn't work out. I think this is mainly due to the hinge being on the same level as the bottom of the wing. Not all has been wasted because I reckoned that if the aileron section was fixed to the trailing edge I could use the same arrangement but only hinge the ply, reverting to a split flap. This is what I am going to do on Oodalally and at the same time I will probably put the hinge a bit closer to the split line.
So back to the drawing board for Grumpy and this involved rethinking the hinge arrangement to get some rearward extension of the flap as well as the droop. I don't suppose all this will make the faintest bit of difference in real life but it is fun having a go.
882 forum posts
It was the hinge layout that as going to make the difference and I did make a couple of sketches to make some up out of aluminium. I pushed that idea to one side and it might surface again if I join one of Danny's masterclasses but in the meantime I needed something a bits quicker and easier.
Control horns! This might work. These are SLEC horns but I think they are fairly generic. The main thing was I have plenty of them.
Each hinge is made from three horns and handed flanges are removed from two of them. This as done by scoring a few times with a sharp scalpel and then quickly breaking away with a pair of pliers. Some needed a bit more persuasion with the knife but the cut ends up nice and clean. The centre part of the hinge is an unmodified horn.
The top hole of the horn was used as the pivot point. The other holes could be used but I wanted to project the hinge point as low as possible. The hinge pin is hard brass peened over small stainless steel washers. The length of the brass was found by trial and error. On the first attempts I had been a bit too generous and the pins bent as there was too much material to peen. No big problem as the heads are easily filed off to have another go. In the end I found about 1.5mm past the washers was about right.
The brass pins were peened until all the slack was taken out of the hinge but before it started to clamp up tight.
The finished result. There are three per flap and the double part of the hinge will be screwed to the wing (the blocks are already in place) and to make the base more secure extra holes were drilled to end up with four.
A very useful feature of the horns is the projection of the horn with the holes beyond the base. This means that when closed (as shown) the projections interlock making the hinge very stable. Clearly this starts to get lost when the flaps are lowered but there is still useful support at about 20 degrees. Fully extended they are on their own but have you ever seen the Fowler flaps flapping around when fully lowered on full size?
I am not sure if I am going to give them any fairing. At the moment they look quite large in comparison to the previous attempt. Anyway, another choice I don't have to make right now.
|285 forum posts|
I for one appreciate you taking the time and effort to share your tips and ideas, Fantastic - Brilliant
882 forum posts
Thank you for your very kind comments.
How are you getting on with yours? I saw you in the sign-up thread with an impressive collection of parts. I know you said you were not going to do a blog but it would be good to have some updates.
|285 forum posts|
Going to sound lame but work and home work projects have taken priority with snatched flying days eating up what little free time was left. That said yesterday I did dust it off and make a start on the nacelle assemblies so moving forward again.
882 forum posts
Progress slows down as bits get more fiddly and distractions start to creep in but at least I am getting some ideas about covering colours. In hindsight I may have used too soft a material for the planking so I may have to tissue or glass the nose which would commit me to painting the fuselage. I am not set against that but covering with film is quicker. The planking of the cockpit area is better protected and although it is fixed to the wing, it would still have to conform in colour and texture to the rest of the fuselage.
Anyway back the bits that are taxing my mind - the flaps.
Here the basic 2mm ply flaps have had the customary slimming treatment. The holes will be covered on the top surface by the aileron section so that the profile of the wing section is complete with the flap when raised.
The little 0.6mm ply pads are to match similar pads stop the hinges compressing into the balsa. I have been a bit lax about doing this on control horns so I may revisit some on my earlier builds to reinforce these points. It does make a considerable difference.
Using masking tape to make temporary handles for little pieces makes gluing and positioning much easier.
The aileron section is being glued to the flap. On the underside there is a piece of planed pine that keeps the flap dead straight while the glue dries as effectively this is making a lamination and adds useful stiffness.
The clamps were applied from one side as it helped to stop them sliding off the taper. I didn't protect the balsa under the clamps because 2mm will have to be sanded off later because we added the 2mm ply on the underside.
In this photo the hinges have been fitted using the plastic backing plates supplied with the horns. The aileron section had shallow slots cut out to go over the backing plates. The small gaps between the slots and the backing plates was filled with home made gunge comprising balsa dust and aliphatic. This is because I want the backing plates to be captive and hidden inside the flap itself.
The recess has been sanded off the top surface of the flap and later this will slide under the shroud on the wing.
Shown here being dry fitted. The shroud for the flaps is on the top surface only and is wider than the aileron shrouds because the flaps only have to hinge down. The wider shroud also keeps the flap covered for the early part of the extension for smoother airflow.
The backing plates are now covered and held fully captive by another balsa strip.
Now the fun starts with a lot of sanding and trimming to get the flap to mate with the wing.
882 forum posts
Some quick notes about the screws supplied with the horns. Definitely made of good stuff and much to hard to cut with side cutters which I normally use for trimming the brass bolts supplied with some horns.
The only way to cut them was with a Dremel.
There are lots of them so I found a scrap piece of balsa where the thickness equals the finished length of screw.
Fit the screw into the balsa (no pilot hole was needed) and they are held quite snugly while the Dremel chops them off at the surface. The nib that usually gets left behind is easily ground flush.
No more burnt fingers or trying to hold them in a pair of pliers and the balsa makes a useful holder until the screws get to be used.