Fokker V25

[Simon Chaddock]

Thr V25 was one of several prototype monoplane fighters Anthony Fokker produced for the final German Air Ministry fighter 'competions' in 1918.

It basically merged a Triplane type fuselage and engine with a plywood covered two spar cantelever wing.

With only a 110HP Oberursel it had a pretty good performance however at the time downward visibility was considered paramount so the similar DVIII but with a high mounted parasol wing was chosen although it was sightly slower and heavier.

One can only surmise that if the V25 had been chosen over the strut mounted wing of the DVIII the arrival of the classic low wing monoplane fighter might well occured 10 or more years earlier.

Anyway my intention is to build a scale electric 26" span V25 to see how it goes.

[PatMc]

The Fokker wasn't the first low wing monoplane fighter.

The Junkers developed a low wing monoplane from 1915 resulting in the D1 which was operational by the last month of the war. Only a few were supplied to the Western front where they weren't used in action. However some were used against Poland after the Armistice was signed.

There was also the Brandenberg W29 floatplane which was operational with the German navy from April 1918.

[bouncebounce crunch]

Very interesting Simon, that definately will make a nice scale model, and will this one be made of foam or balsa?

looking forward to this.

bbc

[Simon Chaddock]

PatMc

The Junkers was altogether a much bigger heavier machine and lacked the manoeuvrability considered essential for a fighter so had little impact on fighter design until all metal structures were required.

The Fokker was 1/3 the weight and very manoeuvrable. Had the low wing version gone into production I expect it would have made quite an impact on fighter design.

As far as I can tell the basically similar parasol wing DVIII was considered a bit of an oddity and the design was ignored by the allies although the French did continue with the principle but with a conventional strut braced wing.

bbc

At 26" span it will be Depron not only for weight but also the plywood covered wing really needs to be sheet covered to look right.

[Simon Chaddock]

First a 3 view.

I could not find one so I 'reverse engineered' one from the DVIII which was actually developed from the V25!

The V25's wing had slightly greater span and a constant taper to the root whereas the DVIII had a short parallel cord centre section.

The wing was pretty thick at the root and had noticeable under camber.

To create this the wing will be build over a tapered support block added onto the plan.

The bottom skin is formed to approximately the correct profile.

The root rib and shear web go on.

Only the underside of the rib has been cut to the correct profile and is then cut in two and glued either side of the shear web. Weights are applied to keep the lower skin on the under camber block. Each wing component created is duplicated so hopefully the other wing will come out the same.

With all the ribs added the wing can be lifted from the board and the top surface of the ribs carefully cut and sanded to shape using the shear web as a guide to thickness. Not quite a difficult as it sounds but it does need quite a bit of the mk1 eyeball!.

With aileron cut out the top skin is added.

One advantage of using UHU POR as a simple glue is take quite a while to grip hard so it gives plenty of time to get everything lined up and true.

The bare wing weighs 1/3oz.

[Colin Leighfield]

I will be interested to see what your conclusions on cg position will be with this one Simon.

[Simon Chaddock]

The wing halves joined.

As it has no spar there is no joiner but the whole joint will have a tissue bandage glued with PVA.

The double sided aileron horn also acts as the hinge pin support. The aileron has a leading edge radius.

The wing has a matching shroud.

The outboard end pivots on a pin driven through from the wing tip.

So far so good but it is rather slow going.

[Colin Leighfield]

By my standards, that's very fast.

[Peter Miller]

Now that is a most interesting subject. I love the fact that there are no struts. I hate struts!

[Martian]

I like the aileron hinge I will use that idea Simon thanks ,it is always interesting and informative to follow your builds

[Simon Chaddock]

Peter

No struts - yes, but there is still the undercarriage.

Of course the original used Fokker's 'sprung axle' inside the undercarriage fairing but as this is a small outdoor model I really want some thing that will take completely non scale loads and with plenty of 'give' but retaining a scale appearance and of course it has to be light.

I might have to get pretty creative!

Anyway the V25 of course used a rotary so that is the next task.

At this scale the bell of the out runner is exactly the diameter of the Oberursel's crankcase so the cylinders can simply be stuck on..

Each cylinder is a paper tube bound with cotton to simulate the fine fins..

With the valve push/pull rod and the inlet pipes added it can be given a coat of paint.

The front of the motor has 3 Depron inserts.

The Oberrursel URII was a direct copy of the LeRhone 9J which had characteristic copper inlet pipes. Copper was in short supply in Germany so on the URII they were made of aluminium.

A low speed run.

For a foam plane this is all getting a bit silly!

Edited By Simon Chaddock on 11/09/2013 14:34:33

[Simon Chaddock]

The fuselage is built as a hollow structure with the shape changing from the circular bulkhead at the front via a single former just behind the cockpit to a point at the rudder post. The original used a rectangular frame with fairing to achieve the required shape..

It is just resting on the wing.

The extra bit of top decking was a mistake. I cut it too short!.

The 'drum' mounting of the Emax 2205 is sandwiched (glued) between two 2mm Deprn sheets that makes up the front bulkhead.

There is just room between the bulkhead and the rear of the dummy rotary to access the securing grub screws.

The elevator servo mounted right up against the rear of the bulkhead with just its arm protruding.

The combined aileron/rudder servo is mounted in the wing leading edge with it single arm protruding below the surface.

The single closed loop cable that will connect it to both ailerons and the rudder will be over 6 feet long!

Simple foam plane? Yeah right!

 

Edited By Simon Chaddock on 13/09/2013 21:09:25

[Simon Chaddock]

The tail feathers in 2mm Depron although the tail plane itself has 0.8mm balsa edges.sanded to a half round to simulate the tubular construction of the original. .

The rudder has top and bottom 'pin' hinges.

The elevator has 4. The elevator halves are joined by a 2mm diam carbon rod which also acts as the 'pin' on the inner hinge.

The tailplane is braced with 3x1mm birch struts.

Next to consider is the battery, how to mount it and how to get it in and out.

[Simon Chaddock]

After some thought and testing it should be possible to insert the battery through the cockpit which will avoid having to create any hatches at all.

The Depron cockpit coaming.

The battery box.

The box is the full depth of the fuselage (it has a false floor) and runs forward to the bulkhead so adds significant rigidity of the motor mounting.

The drinking straw is to run the closed loop aileron/rudder cable across the fuselage.

The rotary and prop at full power.

The clicking is not the motor but a reaction from the camera to the ESC.

It draws 6A from a 2s LiPo.

[Simon Chaddock]

The cowling presented its own challenge.

In keeping with the very light weight of the rest of the plane it really need to be made of Depron but how?

I decided to try 'concentric rings'.

Starting from the flat nose disc each 'ring' is progressively wider and stepped over.

It is actually a very economical method of construction as each 'ring' is formed from a strip of 2mm Depron.

The steps on the inside can be left as long as it clears the rotary. The out surface is carefully sanded to right profile..

The sanded Depron gives a very open structure so neat PVA is painted over the surface to fill the surface and is sanded smooth when dry.

The cowling test fitted on the fuselage.

For rigidity it is still a full circle cowling. It will be cut to the correct shape only during final assembly.

[Martian]

looking good Simon,ingenious stuff

[Simon Chaddock]

Unfortunately my last Orange Rx has failed and the obvious cheap replacement from Hobby King is not in stock in the UK so it has to come from HK.

I was going to effectively build the Rx in but now it will have to be designed to to installed through the cockpit.

Using thw dud Rx as a test piece the first job is to make it smaller.

It is now also only 1/3 the weight!

The ESC lead had to be extended but now all can be connected to the Rx outside the cockpit and it then fed into a mount on the side of the fuselage.

This means the motor can be installed and the wing glued in place.

The undercarriage is next to go on.

It will use the same wire sprung system that I used on the Depron Super Cub.

The front U/C mounting plate.

Only the front strut provides springing. The rear is flexibly mounted and terminates in a Z bend.

The rear mounting plate goes into the wing and is glued to the side of a rib.

The complete U/C with Depron fairings.

It will have a dummy U/C 'wing' that still allows the appropriate movement.

Now to start thinking about the painting.

[Stephen Jones]

Wow ,

That is one very interesting build project you have there Simon ,

Keep up the good work

[Simon Chaddock]

With the structure complete it can be painted.

With hindsight dark green on white Depron was not ideal as even after two coats isome streaks still show through. It will be maidened with a 7x4 prop rather than the 8x4.3 as it doesn't need the thrust and the torque will be lower.

The Dutch orange marking have unfortunately turned out rather pink!

The control pull/pull cables have still to be added. One of the six tiny eyelets used to change the cable direction on the combined aileron/rudder loop.

The elevator pull/pull closed lioop is simple and direct.

[Martian]

looking fantastic,do you ever work out the cost of your planes ?

[Simon Chaddock]

The aileron/rudder closed loop circuit uses 6 tiny eyelets to change the direction of the cable.

The monofilament line to the top of the LH aileron.

The line runs through the tube to the other side of the fuselage before going back to the rudder.

The line on the under side that connect directly to the servo arm..

In comparison the elevator loop is simple and direct.

Complete.

Just waiting for the Rx to be delivered!

Martian

This one is particularly cheap as it was built specifically to demonstrate a low cost scale airframe.

It works out at about £6 and almost half of that is the UHU POR glue! - but there is enough sheet Depron left over to build another one.

Adding in the two servos (£2 each) the ESC (£5.50) Motor (£4.58) Rx (£3.88) Prop & adapter (£1.50) and battery (£3.79) the grand total including postage is close to £25.

But add in the hours to do it (at even the minimum wage) and it becomes extremely expensive!

[Martian]

thats brilliant Simon it certainly bring scale RC into anyones reach, I would like to try the depron building myself but will have to get it online there doesn't appear to be any suppliers round here,I've incorporated to of your ingeneous methods in my polystyrene da42 plane, any way loving the work

[Simon Chaddock]

Much to my annoyance the replacement Orange Rx bound once no problem but that was it. Now just both the orange and red LEDs show continuously which I think means it is terminal unless the chip can be reset.

So I have put in a 35mHz Corona 4ch as it is small enough.

The only problem was feeding the long aerial wire down the fuselage. It is so long I reckon in a tight loop there is a real danger it will chop its own aerial!

So it is now flight ready but the weather isn't so a video of short taxi.

It has masses of power as long as I can control the torque - and I don't mean just for take off!

[Simon Chaddock]

It does fly.

A very short maiden in far too much wind. It was tossed about all over the place so I could not really establish its handling characteristics.

Temporarily grounded until a much calmer day and then a video as well.

[Erfolg]

Simon

I am rather surprised that there has not been comment, with respect to safety. That is running a unsecured model in the home, where were the restraining stakes. Remember, rules is rules, one size fits all!

I am quite impressed that the UC is able to deal with the rather soft and undulating surface of a Duvet. Bodes very well for the grass.

Seriously looks a nice model. Although, if built as part of the D8 development programme, would it not have Balkenkreus or Iron Cross, rather than roundels?

Again being very serious, recently I have experienced annoyance with one of my models, where I needed to take the wing of to arm/disarm the battery. I do see this as a potential safety issue, particularly with more powerful motors, just because of the manhandling and the time required. I am planning a model at the moment, where I am considering using a arming plug, where one part would be in the pilots body, the other the model. The problem, is that this requires a robust model in the cockpit area if a Deans style plug is used. Have you thought of any similar lower force solutions? I am thinking along the lines that the model could be armed immediately before take off and after landing (having checked the model). Avoiding potentially having a live model in the pits area.