Warbird Replicas Ju88 Night Fighter build

[Jon H]

Ahh I see you have been infected by the 'to hell with the easy way, lets reinvent the wheel!' bug. Our build thread is full of it, and I don't think our standard of build is so far ahead. If you only you could hear the language that was required to build my flaps!

Anyway, I used a ply core in my Hurricane wingtips and it works a treat, I am also toying with doing the ailerons like yours but was thinking I might use some litho plate instead of balsa to cover the gap. I can cut it to the scale panel shape and them glue it on with contact adhesive.

That's my plan anyway, we will see what happens

[Geoff S]

Why top hinge the flaps when their movement is only going to be downwards? Wouldn't it be easier to bottom hinge them then they can go as far down as required (90 degrees maximum)? Your ply strip method could be used at the top to disguise the gap revealed as the flaps were deployed.

Building is to a standard I can only dream of

Geoff

[Ady Hayward]

Hi Geof

The kit is intended to be a simple build and as such the top hinge gives a very nice clean top surface for the airflow, and visually too. I had the same thoughts as you and have gone some way to deviate from the original plan. The prototype that I have seen can achieve around 30 degrees down flap which does slow the plane for landing so for club/ sport flying achieves a goal in simplicity yet still has benefit.

With my setup the top edge of the flap will be covered until around 25 degrees deflection after which a large gap will appear and to correct this would deviate too much from my build plan. The flap will still be able to go down as far as I want and as the gap will be visible only in flight which I think is acceptable. I am just showing some food for thought for other builders of this kit should it go into production which I hope it does

.

[Ady Hayward]

Hi Folks,

Not too much to report at this time. I have fixed the upper rear fairings on both nacelles in place and made the access tunnel and servo mounting points for both ailerons. The flaps are awaiting decision on the type of retract I will choose (But will probably remain the metal mechanical type supplied for this type of model).

The servo openings were simply probing the wing to get as close to the trailing edge but still having the wing depth to bury most of the servo.

The opening was cut out and the foam removed where necessary. I let some ply blocks into the mounting lug areas to give good support for the servo and a solid mounting

The lead access tunnel was made by cutting a slot around 12mm wide from the servo to the nacelle and around 1” (25mm) deep. A wooden stick (Lollypop/ Popsicle) was used with a sharpened end to “Chisel” away the foam so it lifted out in a strip with the foam attached to the veneer. The foam was cut back ½” (12mm) so when it was glued back in place it left a tunnel for the cable to pass through. The foam between the nacelle side plate and the cable access was pushed through with the stick to make a continuous hole through the wing.

I found the ply fairings quite a fiddly job to carry out having to adjust the top of the rear ply locking plate so the ply can curve around everything. Some light balsa block was glued in place behind the rear former to give a little more surface area for the glue to work upon.

The Starboard one was first and left dry. I found that it was tricky to hold it in contact with the wing surface despite loads of pins, tape weight and although the resin had a quick grab time it was still an overnight job to let it set and then I used some C/A to hold down any edges that had lifted. The Port one was done but with the plywood dampened on the outer surface to help it bend and make it a bit more supple. This time it was a lot easier and is definitely the way to go. A little lightweight filler completes the job for now.

 

​Adrian

Edited By Ady Hayward on 06/04/2016 17:30:15

Edited By Ady Hayward on 06/04/2016 17:32:16

[Ady Hayward]

Hi Folks,

A midnight oil burning session here and attention is on the flaps. Where the ailerons were recessed centre hinges these will be bottom hinged surfaces so they can deflect through a range from 0 degrees deflection to over 90 degrees if needed. I am using slightly smaller pin hinges than the ailerons but using 4 instead of the 3 used on the ailerons.

The first task was to mark out the positions of the hinges on the flap, followed by the drilling and dry fitting of the hinges. The angle is quite steep so that I can get a lot of balsa around the hinge for support but this required the last 1 or 2 segments of the hinge to be cut off so it does not protrude through the flap top surface. All hinges were pushed well in so that the hinge point is right over the edge of the flap.

The flap was offered in to its position on the wing with a 1/32” (0.8mm) spacer between the wing and the flap inboard end and the centres of the hinges were then marked onto the wing trailing edge. As for the flap the trailing edge was drilled and the holes opened to the correct diameter. (I found a square section file best to use). Test each hinge in place to ensure that the end will not protrude through the wing upper skin and cut the required amount off the hinge end as necessary.

When done the flap can be dry fitted in place and the range of movement tested and any adjustments made to get the flap to seat well in the up position and deflect to the desired range. Like the ailerons these will be left off until after the wing is skinned in glass fibre and painted.

Adrian

[Ady Hayward]

Hi Folks,

I have fixed the tailplane in position using a line from the nose centre to each trailing edge tip to ensure the tailplane is straight with regard to the centre line and made sure that the tailplane is square to the vertical plane. I made some check marks on both the fuselage and tailplane to ensure they go into the exact same place when glued, and of course used the line and square to check the angles.

Due to a slight difference in the bending ability of one of the fuselage sides in the tail area I had to insert a temporary block of balsa to hold the fuselage sides in the correct position for the tailplane glue to set. The block will stay in place until after the fin post is glued in place. The two tailplane profiled pieces of balsa were glued to the tailplane to level off the top of the tailplane to the end section of the fuselage ready for the fin assembly.

It was seen that the fin has only the fin post and the forward stump to hold it in place. To give a bit more support I made a small plate from soft 1/8” (3mm) balsa that had the front underside profiled to match the tailplane rear section and to fit flush within the rear fuselage sides so the fin is well and truly bonded in place.

Adrian

[Jon H]

Looking good! I was toying with the idea of using small servos like that for my hurricane but as they were just as expensive (if not more) than the normal ones and less able to handle the vibration of an ic engine i just went with hitec 311's all round.

[Enemy Ace]

This is a great looking model of a cool plane. It would be nice to have accessories for different varients. Maybe An ju 188 canopy and nose section or a fin and rudder combo to make into a ju88a? So many options!

[Ady Hayward]

Hi Jon,

The servos that I use are Tower-Pro MG90's These have been found to be very good and as yet I have not had a failure in the 30+ I have used over the past few years. They have a torque rating of 2kg/cm which is powerful enough for any of my applications and appear to take the abuse I give them and spares are available too come the time I strip a gear.

Enemy Ace, Thanks for looking in and the kind comments. I'm sure that your idea for accessories will be seen and considered as this aircraft can be converted to many variants with few mods so fingers crossed on that one. At this time I'm toying with doing this to the one that landed at Woodbridge in 1944 (4r+UR) so will have RAF markings.

Adrian

[Ady Hayward]

Hi Folks,

Its been a rather embarrassingly long time since the last build stage but the family taxi was needed and someone has to drive it. Also I spent a rather long time making servo mounts for the rudder, elevator and tailwheel operating servos. I ended up taking the easy option and putting the servos well forward and using snakes instead. Weight penalties were surprisingly close but simplicity won through in the end.

I will start with the elevators as they have to be done before the fin and tailwheel go in. Instead of using external control horns and elevators joined with piano wire I opted to source a wire joiner that has the control horn brazed on to it and bent the ends around a 5mm rod so not to stress the wire and have it break at the bend (As happened to the first one I tried). The bends were biased to the side so when fitted in place the horn is offset from centre so that it is very close to the fuselage side so that the tailwheel will not interfere.

The elevators were sanded to size and the locating hole was drilled and checked ready for the final fixing after covering. The top of the fuselage was filled where it was cut away to allow location of the joiner and the fin was fixed in place ensuring the fin post is vertical to the centre line. When the adhesive had set the fin plate was glued in place ready for shaping of the upper fuselage.

The closed loop guide tubes were also fitted at this time to the extreme rear of the fuselage.I utilised some small sections of snake inner cores for the closed loop guides. These were passed through holes drilled in the fuselage rear and glued in place ensuring that they are long enough to clear the tailwheel fuselage former.

A servo arm was utilised to become the rudder horn for the closed loop system to be used. A suitable void was cut into the rudder to allow seating in the correct place and when the arm was secured the balsa that was removed was then used to backfill and retain the original profile.

A control snake was secured to the elevator horn and the end of the outer was secured and routed so that it clears the tailwheel and runs without bends to the forward fuselage

Adrian

Edited By Ady Hayward on 19/04/2016 11:48:04

[Ady Hayward]

Hi Folks,

Time to sort the tailwheel. Where the standard kit has a fixed tailwheel that has the wire fixed to a ply plate which in turn is held within the rear fuselage. I have decided to go that bit extra and found a lightweight retract unit for a small model which proved ideal in size when compared to a mainwheel unit. It is not steerable but I think it will be ok in practice and aid tracking during the start of the takeoff run.

I split the mounting plate to make installation easier and after assembling the system positioned it in the best place so there is no conflict with any of the controls nearby and then opened a recess in the tailplane underside for the tailwheel to rest when retracted. When I was satisfied with the position it was glued into place.

The lower rear balsa block was glued in place closing the tail end and shaped roughly. The lower fuselage decking was then held in place with masking tape and the tailwheel bay opening was marked out and then cut out ready for the final shaping and fitting of the doors.

Adrian

[Jon H]

the tailwheel looks great and is very similar to how i do my retracting tail wheels.

The fixed wheel wont be a problem either and mine are either fixed or free castoring. If you are accurate with a dremel cutting wheel you can grind a very small slot round the wire leg and lock the point of the retaining grub screw into the slot without pinching up on the wire. This will allow it to rotate but not fall out.

My P40 and Sea Fury have tailwheels like this.

[David Humphreys]

I'm really enjoying your build, Adrian. Lots of inspiration for when I can get into the garage and make a start!

Cheers

David

[Ady Hayward]

Hi David,

Many thanks. It really makes my day to see/hear that the blogs both help and inspire other modellers. I hope your build goes well.

Jon, I was in two minds whether to have a castoring tailwheel and would have used the same methodology as you have. Unfortunately the trunnion does not allow the wire to pass through but holds it in place as a very tight push fit so I have Hobsons' choice of a fixed wheel on this one.

Adrian​

[Ady Hayward]

Hi All,

I’ve worked on a few bits and pieces left over before getting started on the engine mountings/ Nacelles. First was the Bottom decking where the foam/veneer section was glued to the fuselage and taped down until set then sanded to the fuselage profile.

Next was the rudder to make it look more scale like and this was by running two strips of triangular balsa each side of the fin trailing edge so that the rudder leading edge radius rotates nicely within and gives that nice socket type join between fin and rudder.

The picture also shows the closed loop tubes and rudder horn made from an X shape servo arm let into the rudder leading edge.

The ¼” (6mm) plywood rear wing fixing was glued into the rear fuselage against the former and two support pieces were fixed in place each side. This was set so that the plate was parallel to the lower wing surface so that the rear wing bolt washer and head sits flat to the wing.

The wing was then offered to the fuselage and aligned so it was straight and the rear fixing point was drilled through the wing perpendicular to the lower wing surface using a small drill to make a pilot hole. As the hole was on the centre line of the plate I then drilled the plate to accept a M6 T nut which was fixed in place using a steel M6 screw and penny washers.

The hole in the wing trailing edge was drilled 6.5mm and the fit checked with a nylon M6x60 screw. Whilst the wing was in position the two front mounting points were drilled through to mark the positions on the wing leading edges. These points were drilled through the leading edge when the wing was off the fuselage.

The two locating dowels were glued into the leading edge and the wing fixed back onto the fuselage so that the 15 minute epoxy would cure with the dowels in their correct positions. Needless to say all traces of surplus epoxy should be removed before refitting the wing.

The nacelle took a bit of time to get a paper template to fit around the formers but when it was completed the ply shell was cut to shape and glued to the nacelle frame.

The result looks nice with plenty of room for Lipos, ESC etc. I left plenty of overhang on each side to fix stiffeners and hinges for access hatches as necessary further on into the build.

Adrian

[Jon H]

plenty of space in there for almost anything, even fuel tanks

[Ady Hayward]

Hi Jon,

The engine nacelles have more than enough room for tanks etc. The design is just electric for now but with very little extra work could take ic engines for sure. The bays would need a fair amount of fuel proofer though.

Adrian

[Jon H]

A coat or 2 of thinned epoxy would sort that out. And I guess a pair of 25's would be plenty of power for it. Alas my hangar is packed so I need to get shot of something to make space for the hurricane.

And if Richard does a whirlwind in the end I will have to make more room again!

[Ady Hayward]

Hi Jon,

Yes, the epoxy does work well and I was thinking a pair of 40 sized 4 strokes would be nice. A whirlwind would be nice but there are many nice planes that could be done but so little building time between them all.

Ady

[Ady Hayward]

Hi Folks,

Onwards and upwards (Why is it that when I cut and paste text when I forget to relocate the cursor I get the next text typed runs backwards?).

The tailwheel doors were made from a lamination of 0.8mm ply and 3/16" balsa to give the doors a curved form. I them let points in the internal walls for hinges and fixed a ply strip to create pockets for the hinges which will be sunk slightly within the bay walls. This was much better than having the forward hinges fix only in the foam. The doors were slotted for the hinges also and were then fixed to the tailwheel bay with the hinges and then sanded to the fuselage profile.

The next item was a head scratcher in how do I sort out the tailwheel door open/ close system. After much deliberation I dropped the idea of servo operation within the bay. Sprung doors and a drawstring across the tailwheel leg to close the doors as the effort required was too great. I eventually made a compromise in that I made the already hinged doors so that they were held in the open position by using flexible hinging material as a spring and having a simple drawstring to a servo forwards in the fuselage.

In hindsight using the flexible hinging material from the start would have been the best solution.​

Adrian

Edited By Ady Hayward on 01/05/2016 13:15:48

[Ady Hayward]

Hi Again Folks,

This time I’m attacking the motor bay covers. The intention was to use the original ply pieces to make a cover that allowed access to the main bay. By whatever means I ended up (Like the prototype) with quite a large opening on top which allowed access to the spaces between the main supports and the ply sides of the cowl, ideal for inserting the esc and cables allowing the full internal space for batteries.

I made paper templates of the opening and cut 1/32” (0.8mm) ply sheet to suit trimming the ply to fit well with enough gap to allow finger nails to get purchase for opening the hatches.

I then put the ply pieces in a jug of boiling water for a few minutes until they went very pliable then rolled them up to give them a curved form when cooled. (In actual fact a bottle of around 75mm would have been ideal) As the picture shows it was very effective giving me a tightly rolled ply cover!

Fortunately careful teasing of the ply allowed it to uncurl and nearly conform to the shape required. I then made a set of formers as shown to hold the correct shape positioning them so that the rear was some 10mm from the rear edge and the front former almost touching the firewall. A little sanding here and there had all fitting very nicely. I then marked the position of the front peg onto the front former and cut it out and inserted a small 1/8” (3mm) ply locating peg

To the rear I added some balsa to the rear former each side to give the magnets a better seating and made a cut out for two magnets deep each side and glued a single magnet in the bottom of each cut out. The hatch was marked with the magnets position and the second magnet was glued onto the inner rim each side behind the former so that it matched the previously glued magnet perfectly making sure of course that the polarity is correct.

The rear was blended in to the existing airframe where required and the front of the hatches were levelled off flush to the firewall.

Adrian

Edited By Ady Hayward on 01/05/2016 17:06:18

[Ady Hayward]

Hi again Folks,

It has been a wee while again since the last update but has not been wasted as the whole airframe has now been covered with 18g/sq metre glass cloth affixed in place with a water based varnish. This provides a smooth light covering that gives a good base for the paint, hides little errors etc and also gives a little extra strength too for a small weight increase. I find that after covering the edges can be sanded down to nothing so with the weave filled gives the effect of a wrap around skin just what is wanted to represent a metal skinned airframe. The pictures show the smooth surface well.

When completed I moved on to the ABS nacelles and cut them roughly to shape and then carefully sanded the edges to conform to the wing profile.

Where these were a little short I stuck some plasticard to the edges to fill the gaps at the front. When completed a bit of glass cloth covering will have them looking the same as the rest of the airframe plus the ABS is less prone to cracking. I then fixed the nacelle mounting blocks in position, Two at the bulkhead and two at the rear end made from some scrap ¼” ply glued into a balsa mounting.

Adrian

[Ady Hayward]

Hi Folks,

Another wee while between posts unfortunately. The time has not been wasted as the wings, fuselage and control surfaces have all been filled, primed, cut back, primed again and finally panel lines scored into the surface. The idea being an empty ballpoint pen is used to make a small furrow into the surface of the glass fibre without breaking through. This will remain through the painting stage leaving a faint but visible line which looks quite convincing. A little black wash will bring these out where needed to give that extra emphasis on the panel and oil/ dirt staining.

The next operation is the colour along with the fitting of the retracts. The standard night fighter scheme for this airframe was RLM 75 Dark grey patches over an overall RLM 76 blue/grey.

The G versions of aircraft had the tail surfaces of the Ju-188 as well as doing away with the rear underside gunner/ gondola arrangement. For extra hitting power a gunpack with 4x cannon was fitted on the underside instead. This was fashioned from some old orange XPS foam and a skin of 25g glass fibre.

The cannon will be added later with the final detailing.

 

Adrian

Edited By Ady Hayward on 20/05/2016 18:01:23

Edited By Ady Hayward on 20/05/2016 18:07:06

[Jon H]

Looks nice. I will be doing something similar with my hurricane when it comes to panel lines. Currently I am at the never ending rubbing down stage

[Danny Fenton]

Looks great Adrian, coming along well. Though I am not sure I would like to indent the glass skin like this for panel lines, I am sure it is creating potential fracture lines?

I prefer the chart tape and primer approach personally

Cheers

Danny