$50.00 Scratch Build Contest - Fokker V25
Well if Chellie has started........
The V25 was a one off prototype built by Anthony Fokker in 1918 for the last series of the German fighter competitions.
Basically it used the Triplane fuselage and engine but with a low mounted all plywood covered wing.
At the time downward visibility was considered of vital importance so the Fokker DVIII with a parasol wing was chosen although it was actually a bit heavier so had a slightly lower climb rate.
The fact that it had an all sheet wing will lend itself to being made from Depron.
OK. I wont actually start building until the 6th.
But I assume I can draw! ;)
I will use this 3 view that I have 'adjusted' from a DVIII fuselage (it was almost identical) and with a slightly enlarged wing as the V25 had a span of 8.73m whereas the DVIII's was only 8.34.
For comparison I will keep it to the same scale as my 24" Sopwith Pup so it will have a span of 26" but it will turn an 8" prop! :eek:
That's about as far as my thinking goes at the moment.
As far as I can tell although the V25 in production would have had two Spandau guns like the DVIII but there is no picture of them ever being fitted.
Phew! I don't have to do the guns but it does look like it had the standard 'lozenge' paint finish, at least on the fabric covered bits. :concern:
This view seems to suggest the undercarriage was not cross wire braced but used struts instead.
One of the penalties of modelling a one off prototype is there is very little information, just 3 pictures and no drawings.
If I ever fit the guns I hope it would look a bit more scale than that model!
The guns in the otherwise identical DVIII fuselage.
Note the huge ammunition box. It could hold 650 rounds per gun although the performance suffered at this load. Apparently the spent cartridge cases were ejected overboard although the links were returned to the ammo box for re-use.
6th Sept so I am starting.
First job is to print out the 3 view to the required size.
It makes a tidy little plane. That's a 2 foot rule.
Despite Chellie's rather, dare I say, lax ;) rules this will be a true scratch build.
One big sheet of 2mm Depron - you can see the plans underneath.
Apart from some hardware bits that should be all the construction material it will take!
My intention is to use a further development of a micro pull/pull control system I have used on some other (but non scale) small planes.
Most Fokker planes of the period had a notoriously small fin (if any!) and rudder so I may have to use a 'coupled' aileron and rudder to keep the adverse yaw under control.
Weight? Lets say a target of 7oz with an 800mAh 2s.
Of course the biggest challenge will be that Oberursel in its 'horse shoe' cowling! :eek:
The start of the build proper.
The rather unusual wing section, quite thick with noticeable under camber.
To incorporate the under camber a tapered wedge has to be glued to the plan.
And the lower skin 'formed' to a bit over the required shape so when the ribs are placed on and held down they will form the skin to the exact profile - I hope. :concern:
At this scale the exact wing section is rather less important than the fact that both side are exactly the same! ;)
To aid the flying characteristics the under camber will gradually disappear toward the tips to provide a degree of aerodynamic washout.
Finally to save weight this wing will have no spar and rely entirely on the skin for all bending and torsional loads.
The build actually starts. The first rib goes on.
This is a truly crazy way of making a wing. Only the underside of the rib is cut to shape and it is then cut in two and glued in place either side of the shear web.
When all the ribs are in place the under camber is fixed and the very wobbly wing can be lifted from the board and the top of the ribs cut and sanded to the correct profile using the shear web to set the wing thickness.
It needs care and plenty of the mk1 eyeball to get right.
At this stage the aileron is cut out which will be built separately using the cut out bits.
Working with the wing still over the under camber support on the plan the top skin is added. Like the bottom skin it is preformed to slightly more than the correct shape so it does not distort the wing.
UHU POR is a normally a contact adhesive but if used a simple glue it allows plenty of 'adjustment' to ensure the wing is flat and true before it sets firm.
It weighs 1/3oz (9gm)
The final wing root section.
A strip of Depron will be glued along the leading edge and sanded to shape.
As I have gone along I have cut out all the duplicate parts for the other wing so hopefully it will end up exactly the same :concern: and it should be a bit quicker to make.
So far the the material for the complete 26" wing has used this amount of the $5 sheet of Depron. ;)
The glue used probably cost almost as much!
Thats looking great, Keep up the nice work :$
The two halves of the iwng joined.
As it has no spar it needs no joiner but the whole joint will be bandaged with a strip of Modelspan tissue glued on with PVA.
The next bit gets tricky. As the pull/pull system is under some tension the aileron has to have 'pin' hinges that can take the load without adding too much friction.
The one piece horn and pin support on the inboard end of the aileron. It seats into a hole in a small plastic plate glued on the wing.
The aileron has a proper rounded leading edge and mates with a matching shape in the wing.
The outboard hinge is similar, but obviously no horns, with the pin (and it is an actual pin!) pushed in from the wing tip to permit assembly.
The aileron fitted.
So far so good but I keep asking myself is it worth all the effort for what is basically a cheap foamie. ????
Nice work indeed. I'm amazed by the detail you put into this small build. Are the pull-pull cables going to run outside the wing?
Yes the cables will run over the top and bottom surface of the wing although to call them 'cables' gives the wrong impression as they will be 1.7lb mono filament fishing line.
You have to get the light 'right' to be able to even see it so external runs are really the only way to rig it!
It is however flexible & slippery enough not to need pulleys but it can be run through tiny metal eyes.
This even smaller Depron plane has its ailerons done that way although here the lines run along in front of the leading edge.
I fear building the Depron is going to be the easy bit! :<:
The V25 of course has a rotary engine so the next task is to build that.
At this scale the bell of the 28mm diam out runner is exactly the size of the Oberursel's crankcase so the cylinders are simply stuck directly on.
Each cylinder is a paper tube wound with cotton to simulate the cooling fins which were actually very shallow.
With the push rod and inlet duct added it gets a coat of paint.
The engine was unusual in that valve gear and the inlet manifold emanated from the rear of the engine rather than the front and it used a single push/pull rod to open the inlet and exhaust valves.
The URII was a direct copy of the Le Rhone 9J. Oberursel did take out a licence just before the beginning of the war but I doubt they actually paid the Société des Moteurs Gnome et Rhône for the German war time production!
The Le Rhone 9J had characteristic copper inlet manifolds.
Copper was scarce in Germany so on the Oberursel URII they were made of aluminium.
A low power test tun.
Next comes the fuselage.
That is sweet!
Thats neet :ws: Very Creative :$
As this is just a simple (ha!) foam plane the fuselage is built as a single skin monocoque unlike the original which was a rectangular structure with fairings added.
Just balanced together but it gives me an idea of it actual size.
The additional top deck in the picture is a simple mistake - I cut the cockpit in the wrong place. :mad: Fortunately I spotted it before it was glued on!
The basic fuselage is extraordinarily light at just 0.28oz (8g).
I will now have to built a control system "rig" to make sure it actually works as planned. Once it is all built in it will be very hard to modify anything.
The simple geometrically similar control test rig.
All driven from a single 3.7g servo I wanted to make sure it would actually work, which it does!
Even on this small plane the aileron/rudder pull/pull line is 6ft long!
But can you spot the fundamental error!;)
Rudder is moving in the wrong direction with the ailerons!
I love that motor!:) [popcorn]
Having proved that technically the pull/pull system will at least move the control surfaces the aileron/rudder servo can be mounted in the wing leading edge.
The elevator servo will be mounted in the fuselage with just its arm protruding.
The 'drum' motor mount fixed (glued!) in the bulkhead.
It is actually sandwiched between two layers of 2mm Depron.
There is just room between the back of the dummy rotary and the bulkhead to access the grub screws.
Like all rotary engined fighters of the period the engine was relatively very heavy (1/3 of the empty weight - about the same as an electric motor and battery!) so the noses were very short.
As I can't put any ballast in the cowl it means everything else has to be crammed right up behind the bulkhead.
I don't mind even if it comes out a bit nose heavy as it is easy to bring it back with a tiny bit of tail weight.
I have now cut out all the basic airframe components from the $5 Depron sheet with just the cowling still to do.
On this plane I don't think the $50 limit will be problem! ;)
Looking good there quorneng, very clever.
Rather fiddly bits today so there is not much to show for many hours work.
The elevator servomounted right up behind the bulkhead.
The Oberursel mounted just to make sure it actually fits.
I made it slightly under diameter to allow for a non scale thickness Depron cowling. In fact it could be a couple of mm larger diameter.
The tail feathers.
Still all 2mm Depron however the tailplane itself has a 0.8mm balsa LE and TE sanded to a radius to simulate the full sized tubular frame. The rudder has top and bottom hinges whereas the elevator has 4 with the two halves joined by a CF rod which also acts as the 'pin' for the inner pair of hinges.
The tail plane is braced with 3x0.8mm birch struts.
The complete bare airframe with 2 servos but less undercarriage weighs 1.6oz (46g).
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