Why the Flamingo?
Last year there were a couple of articles in RCM&E which caught my eye, the first was an article about the Ecirtech Hexen slope soarer and on looking at the French website I found that I was drawn to the company’s Bannsperber vintage glider. The Bannsperber would make a great builder’s project but before I took the plunge there was another article in the RCM&E about the 1/5th scale Flamingo HW-4 slope soarer. I liked the idea of both models as they were going to provide a significant build project and after much ado about nothing I plumbed for the Flamingo as I thought it more suitable for the slope.The Flamingo was a Brazilian glider of 1947 vintage glider with a gull wing and high aspect ratio, the model I’m building will have a wingspan of 3.5m.
From the RCM&E article I had the free plan but it would have needed a significant amount of copying to make it useable to build from. Over the lockdown I ordered a laser cut short kit from Laser Cut Sailplanes (LCS) and a pack of additional spruce, balsa and plywood from Sarik hobbies. I went to LCS as the guy there was more forthcoming with information regarding the plan than I could glean from Sarik even though I phoned them up.
The wood that arrived from both companies is of good quality and a full size plan is thrown in free of charge by LCS. I’m sure the purist would ask why I am not cutting everything out myself but I have done that in the past and there is enough of a build so I make no apologies for having bought laser cut ribs, frames and other parts that need to be accurately cut out. One half of the fuselage is built over the plan, the whole then being completed by building the second side directly on to the first half.
The first part was to laydown the keel (no it's not a boat) and the first two parts supplied by LCS didn't match properly as shown below which would mean that the plywood to be fitted later would not connect to the frame properly.
So the build commenced:
I've been plodding along this last week as my motorcycle decided to play up big time (a sump full of fuel doesn't make life easy) and it's now in bits in the garage - more to do in the near future.
Back to the Flamingo, the build is progressing slowly as most of the tasks seem to be those where you do a little and wait a long time for glue to dry or wood to bend in water.
Since completing the fuselage frame I have completed the nose plywood planking and sanded down the balsa bracing and inter-frame pieces in readiness for the top 0.8mm plywood skin which has been cut to shape, bent and glued to the frame from frame F5 to F12 as per the photo. A lot of clamps are required even if the balsa has been pre-shaped.
It looks good though once the plywood is in place.
With the plywood in place the next job I did was to remove the three temporary frames (F2-F4) in readiness for a bit of fibre glassing.
In the mean time the plywood skin has been cut out to compete the top skinning from F12 to the tail. As I write the piece of plywood has been cut out and it is soaking in order to get it in the right shape as it becomes more difficult to bend it round a sharp curve the further back along the fuselage one goes.
7 June 2020
More progress to report. The top of the fuselage has now been competely covered in 0.8mm plywood. Working with plywood when some of the angles are very tight, particularly at the top and bottom of the fuselage is a challenge but leaving the plywood wrapped in damp clothes overnight does the trick.
And then the fuselage gets a nose.
Next came the tailplane, which is built upside down. Unfortunately the plan gives you one dimension but not the other, which is also true of the elevators and rudder so beware.
To get the right angle of dangle three tailplane holders are provided in the laser cut kit to hold the centre and end ribs in the correct position and then all you need is a weight to hold the tailplane down while the glue dries.
One tailplane securing bolt and captive nut ready for installation in the fuselage.
The elevator TE is made from no less than nine separate items per half elevator so I used cyno in this case as I needed them to dry flat and cyno seemed to be the best way of doing it. The TE is made of a plywood core surrounded above and below with balsa.
All the ribs need some adjustment even though they are laser cut as the laser cutting is square whereas from the picture above you can see the ribs attach at angles to the TE and LE.
22nd June
Slow progress recently thanks to many other things taking priority. The tailplane has been completed so too the fin, rudder and elevators. The fin is finished in plywood though each side is separately skinned so it's not too difficult. However, the elevator control linkage will be totally enclosed in the fuselage so before I want to or can finish putting the lower fuselage plywood skinning on it is a must that the elevator controls are installed.
The first job was to make the elevator horn, which is made from sheet brass with a 2mm od steel rod soldered together and bent slightly.
The horn is then screwed and glued to the elevator that's strengthened with ply.
As access is going to get more difficult as the fuselage is covered in plywood I decided that it was best to install the elevator and rudder servos and to connect them to their respective surfaces as it would be impossible to secure the bowden cable and outers within the fuselage at any point other than the extremes.
It might sound OTT but it took me about five hours to satisfy myself that the elevator linkage and servos were as I wanted them to be before I finalised everything and moved on.
After the elevator controls were connected the fin could be fitted to the rear of the fuselage for which I mounted a rule in the cockpit in order to check that the fin was vertical, I used the frame centre joint as my master reference.
The fin trailing edge is a substantial thickness (approx 18mm) and blocks access to the elevator control linkage, connecting the elevator control every time the model is put together at the flying field is going to be an interesting exercise.
29th June
Some more progress this week although if you look quickly you will wonder what I've been doing. The first item I worked on was the shroud that fits above the tailplane to form the lower part of the fin and is removable to allow the tailplane to be fitted and removed.
After the shroud I started bending and fitting 0.8mm thick plywood behind the cockpit to close out the lower half of the fuselage.The plan shows it being closed out with just two pieces on each side but on closer inspection the fuselage behind the cockpit can be split into three disinct sections:
- The first two frames have a curve in three dimensions with the keel in a gentle curve which stops and straightens aft of the second frame and to my mind created a natural break
- Behind the first two frames there is then a section that covers three frames ending in a change of lower keel angle, which takes you to the original designers break point
- The third section is the area to the rudder.
Another advantage of doing it in three sectiions is that the two rearmost sections can be done as a single piece wrapped over the keel and allows the front and rear sections to be fitted which still leaves access to the inside to secure the controls bowden cables inside the fuselage, which I did with some of my wife's cotton tied around the bowden cable and with a little application of cyno makes a secure fitting.
I've never worked so extensively with plywood and I'll be honest, it's been a challenge. I started by using steam and heat but I've found it best to prepare the plywood for bending by soaking it with water. A good overnight soaking with a wet rag wrapped around the plywood and using either rubber bands or tape to encourage it into the correct shape has proven to be my best approach.
I have found working with plywood very hard work but gives a very strong finish when done.
The next was to prepare the rudder controls, which means inserting a 6mm diameter dowl into the rudder LE to receive the 3mm control horn.
And then I connected the rudder control to the servo.
Now the fuselage has been skinned with plywood and the rudder shroud is in place I'm rapidly reaching the point to remove part of the lower keel in the wheel well so I can fit a wheel and the tail skid before applying car filler to create a smooth covering of the plywood planking around the cockpit and of course to fill the nose section with Isopon.
6th July
The wheelwell has now been created and the application of Isopon has begun. To be honest it's more a case of putting Isopon on and then spending four times longer taking it off to get a smooth finish. The first comment I must make though is that the nose takes a huge amount of Isopon and the 250ml tin of Isopon that I thought would do most of the nose only just filled the nose and that's after first adding four chunks of lead too. It's a messy job and it's best to have some overalls on with a face mask and to do it outside as it really smells if you try doing it indoors.
It's years since I used anything like Isopon, the great thing about it is that it hardens sufficiently to sand in around 20 minutes but the downside is that it has a very short working time so you have to work quickly. In fact the recommendation in the instructions is to mix a small amount and make more as necessary, something I've come to realise is very good advice.
When I took this photo I had already done alot of clearing up and this was after the third application of Isopon. I've shaped the nose with 80 grade sandpaper and I'm in the process of getting a smooth finish with 120 grade with the 320 grade awaiting its turn.
27th July
Time seems to have stood still recently and progress has been painfully slow. The shaping of the fuselage is mostly complete and in recent weeks I've been looking at starting the wing build, which is when a few issues appeared.
All the laser cut parts I bought fitted the templates on the plan but when I laid them over the plan I realised that some of the ribs and the aileron diagonals didn't fit the plan view of the wing. In addition I couldn't find any information on the plan to create the gullwing break nor the angles required - fairly basic information. Emailing the supplier of the kit and the designer illicited a pdf file with the wing support building supports and a comment "the information is on the plan". On my plan the information was missing though I did find it on the plan in the RCM&E December article. The saga continued as I then realised that my plan differs to the plan in the RCM&E in that the root chord and span are larger on mine. After much emailing and phone calls I received some recut aileron ribs and diagonals and a new plan from the designer. The plan is different again!!!! However, I now have enough to build a wing and parts coming out of my ears.
First thing you're supposed to do is pin the TE to the board and attach ribs to it and the lower main spar but if you don't lift the TE up 15mm the ribs won't sit on the spar properly.
Having fitted all the ribs (R1 - R9 on the TE and lower spar and R10 to R28 just on the spar) the assembly has to be lifted off the board and mounted on the wing supports. At this point I realised that another very important bit of information was not explicitly stated - the point at which the gull wing bend is. Initially I thought it was at R9 but on looking VERY closely at the designer's photos I saw that the peak of the supports was between R8 and R9 and about a cm from R9. R9 needs to be vertical to the spar so that the aileron which is immediately outboard fits against an upright component.
So far I've fitted the inter-rib webbing to R11, only got to fill in to R28. All webbing is in 0.8mm plywood.
While I've been waiting for the glue to dry I've started building the cockpit canopy, which is made by laminating 3mm x 6mm strips of spruce and bending to form the canopy side frames.
4th August
Progress is being made with the port wing slowly, I had to wait for the wing joiner metal work to arrive in stock and now I have it the wing joiner is in place and all the inter rib webbing has been cut and glued in place (all 28 of them). After the webbing and wing joiner had been fitted I was then able to cut the ribs to install the sub-spar top and bottom, the sub-spar going in front of the webbing to form an H section.
Sub-spar in place and gluing - I used aliphatic as it takes time to get the spar in place and it needs to be sanded, the top one I used clamps and my wife's clothes pegs but for the lower sub-spar I used tape - you choose which you think is best.
At the gull-break additional spars are fitted either side of the break within the D section and then the hidden LE is sanded prior to fitment of the top and bottom sheeting.
Another little job to do is to fit plywood stiffeners in the inner section of the wing.
The next job is to use a straight edge to ensure the wing TE in front of the aileron is straight prior to fitting the bottom sheeting on the bottom of the wing's D section.
12th August
This latest part of the wing build has turned out to be the most critical for making sure the wing takes the correct shape. The process has been to sheet the bottom of the wing's D section and the top sheeting between the ribs either side of the Gull break. Sheeting the bottom is straight forward though for my convenience I did it in three sections - under the ribs either side of the Gull break as it's a compound curve, inside that point to rib 1 and outside to the tip. The top of the Gull break is also a compound curve so it requires a little more time and care. Then the fun begins.
At this point all that's needed is for the top of the wing's D section to be sheeted but and this is the critical bit, the shape of the wing will then be fixed. Before you get carried away though stop and ensure everything that needs to be in rib 1 is in place i.e. the wing retaining hooks, the incidence pin socket, and a cable to pull aileron and spoiler servo cables through.
The approach is to mount the wing on the jig, they go under ribs 1, 8, 10, 18 & 26. The jig under rib 8 takes a lot of weight as it's the high point and it collapsed on me so I reinforced it with sections of balsa on its side. A good idea is to use something to stop the wing moving side to side too as it tends to move as you glue and fit the D section sheeting in place. Lots of weight you might ask - why? Well with the wing sitting on the jig you have to weigh the wing down to make it take the correct shape and to sit on the jigs. In my case all was OK except the jig under rib 10 wasn't taking any weight so I concluded the shape was incorrect, which is where the weights came in.
All in place ready for sheeting - retaining hooks, cable pull through, incidence pin.
Jig under rib 8 reinforced.
Jig in place.
Weighed down, the bottle on top is full!!
The final result, just the wing LE to fit and shape and sand the remainder. No servo mountings or spoiler installation yet.
6th September
Since I last updated this blog I have been busy even if I haven't been adding anything here as I didn't think you needed me to write about my building the starboard wing, which is a mirror image of the port. However, that's now done and I've moved on to the wing to fuselage joint, a critical activity.
On the plan it states that the mainplane should have an incidence of 1.5 to 2 degrees but it doesn't tell you what the incidence baseline is. In Chris Williams December 2019 article he stated that the reference is the tailplane - a pity it's not on the plan. He did confirm it to me by email.
Using the provided paper template I marked out the position for the mainplane joiner, which whilst important wasn't too difficult and I duly cut into the plywood sheeting behind the cockpit and inserted the steel joiner box and checked that it was parallel to the cockpit reference and while doing it eye-balled the tailplane to check it was also parallel.
Having borrowed an inclinometer from a club friend I fixed the elevator at its neutral position and then set the fuselage up till the tailplane was at zero degrees.
Having jigged the fuselage to set the tailplane to zero incidence I then realised I needed to sand the balsa doubler on the mainplane TE down to the spruce to give it the correct shape so I shaped a small section on each wing to enable me to check and set the mainplane incidences.
In fact I set the starboard wing using this method and then used the Mk 1 eye-ball to set the port wing so that it looked the same as the starboard side. During this activity the wing fuselage joint is a standoff holding a lightweight plywood rib template which is pinned in place using cyno to hold the incidence angle and then it has to be filled with scrap balsa as can be seen in the photo below but beware! I fell into the trap of filling the starboard side with scrap balsa without the wing in place and in my enthusiasm I distorted the lightweight ply rib such that the wing wouldn't sit squarely on the fuselage. I then fitted the wing in place as can be seen in the photo below and filled the joint with scrap balsa always checking the fuselage wing seat was square. One point point here is YOU NEED AN AWFUL LOT OF SCRAP BALSA.
Once the roots have been filled with balsa the roots are finished with Isopon or similar to get a smooth finish, a task I have yet to do. Ailerons yet to do, they are almost next after Isopon.
Having got this far I could not stop myself putting all the bits together to have a look at my handy work so far. I'm pleased with it though finishing is going to take some time yet as I want to get a really good finish and if that takes a few more months so be it.
5th October
Since my last post a month ago I have been flying when the weather allowed and with family duties progress hasn't been as fast as some would have been. So what have I been doing?
I have built the two ailerons which are over 36 inches long which means that standard lengths of balsa need to be extended. The LE is built from 6mm balsa at an angle to allow for downward aileron movement, the TE is spruce laminated with 6mm wide balsa and between the ribs are diagonals inserted last which stiffen the ailerons up by an incredible amount.
After the ailerons I've started applying Isopon 38 to smooth out the balsa infill and to create a smooth transition to the wing. In order to do that the wing was attached and the Isopon applied to the whole and when applied a knife run along the joint (before the Isopon hardens) to separate the wing from the root thus creating a nice join.
Whilst the Isopon was handy I also fitted the skid below the nose section; it's made from 10mm balsa sandwiched between 0.8mm ply sides and the whole smoothed with Isopon. Lastly the axle holes were drilled to take the single 60mm diameter wheel.
Next came the aero-tow hook and so I drilled a 10mm hole in the nose and mounted another servo in the cockpit.
The airbrakes have details for making the airbrake surfaces which are made from a sandwich of three pieces with the hinge held in a cutout in the centre piece. For all wing surface hinges I've use pin hinges. For the servo mounting there are no details just a photo of Chris' solution. Following a method I've built before in my Friendlito I cut a hole in the appropriate rib, lined the rib with 0.8mm ply on the servo side and backed it with 3mm light ply, I'll then connect the servo with a simple link to a horn I'll make attached to the under surface of the airbrake.
The ailerons have been mounted though not glued in position yet, the cabinets on the left and motorcycle on the right give scale to the photo of the wings ready for final sanding.
No comments:
Post a Comment