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Warbird Replicas Ju88 Night Fighter build


Ady Hayward

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Hi Folks. Me again
Following the build of the Mk9 Spitfire from Warbird replicas UK, I have taken the plunge to carry out a Beta build of one their twin engine projects.
This one will be a Ju88-G6 Night Fighter built using a mix of ABS, Foam/ veneer and balsa/ plywood. At 74" wingspan it looks quite huge and will utilise the same motors as used in the Spitfire. It has a massive clear canopy which will suit those that like their scale detail and will use 6 channels for the primary flight controls and flaps/ undercarriage. A friend (ZeroG_RC) will also be building one and he intends to go to town on his build and having seen some of his models will enhance the model no end. Here are some pictures of the kit as it was found and ZeroG Has kindly provided a wide angle shot of his pack of bits which shows well how much stuff is crammed into the box.

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Adrian

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Now started the build with the fuselage. The fuselage is very long requiring the front section to be spliced onto the rear fuselage side. When done the ply doublers are glued in place ensuring they fix along the lower part of the fuselage side leaving a small gap along the upper edge for the fuselage crutch to seat.

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Front side section glued on

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Ply doubler glued in place

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Sorted

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Hi again,

Continuing with the fuselage build and adding formers to the front and rear fuselage ply crutches. Ensure that the formers are perpendicular at all times otherwise the formers will not locate as intended into the slots in the fuselage side doublers and to this end I marked the former positions on to both fuselage sides.

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I decided to add the fuselage sides at this stage, and maybe should have added the lower square section longerons first. In the end it has made little difference but if the longerons are added first then they must be accurately placed or the formers will not fit when the fuselage sides are added to the crutch assembly. It would appear that the best method of assembly would be to fit the front crutch assembly first, then the main rear section as I found it a little tricky to get Former 2 in position. I clamped and taped the sides in position and left them weighted down on the bench for several hours for the PVA to set to ensure that the fuselage was straight and the main crutch was flat on the bench.

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I then added the rear balsa fuselage doublers making sure that they matched the tailplane seat followed by the square section longerons again making sure that they seated fully in the slots and rear doublers.

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The final job of this section of build was to cut and fit the wing seating triangular sections to the fuselage sides. Again, it is debatable whether they could be fitted before the sides were added but in any case I used a razor saw to cut many slots around 2/3 of the thickness to enable the sectioned balsa to bend around the wing seating aperture. I made sure that PVA was pushed into the slots before they were glued in place and held with clamps or pins as needed. The whole was then left overnight to dry completely.

Adrian

 

 

Edited By Ady Hayward on 22/03/2016 15:18:40

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That's not fair Jon Mine will only have wooden guns! LoL

Yesterdays work commenced with the former for locating the ABS nose sections.

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This former is glued to the forward end of the fuselage to give a firm seating for the ABS nose shell. I angled the edges slightly so that the shell will easily take form when it is finally glued in place. There needs to be a ½” overhang for the bottom fuselage sheeting.

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I commenced work on the tailplane whilst the glue was setting on the fuselage by fixing the leading and trailing edges followed at the end by the wingtips. The centre section joining tape which will be fixed using wbpu. The fin had the same treatment carried out

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Two short pieces of ½” triangular balsa were glued into the front upper corners of the forward fuselage so to have some extra meat there for when the corners are sanded down to conform to the ABS nose shell.

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The rear of the fuselage crutch needs to be cut at an angle to suit the shape of the tailplane leading edge when it is fitted in place.

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I then sanded down the top of the fuselage crutch to make sure that the top decking will seat correctly and then fixed both pieces of the top decking in place with PVA and held it in firm contact until the glue had set. A quick check of the fin/ tailplane fit was made validating the decking position.

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I then returned to the nose section and cut off the surplus plastic from the rear fuselage nose shell and carefully sanded the edges down until the faint cut line was reached. A test fit to the ply former showed it to be a good tight fit. I then glued the ABS shell in place using an ABS formulated adhesive and held it in place with masking tape.

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Edited By Ady Hayward on 24/03/2016 06:19:30

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Hi Ady what a luxury to have a Ju88 kit to work with. I had to scratch build mine. I am intrigued by the build materials and concept. Are you planning to install retracts? How about propulsion, electric or ICE? From my experience I would advise a serious effort to keep the rear end light as there is not a lot of room to put ballast in the nose. Mine is powered by three 4S batteries (in parallel) all in the forward section under the canopy and they are accompanied by a lead weight . Mine is an A4 but with your Nachtjager you might have some additional space in the nose for ballast.

Looking ahead to flying I quickly discovered that despite having props running in opposite rotation there was serious yaw instability in the early phase of the take off roll. This necessitated a rudder gyro which can be switched off once airborne as once trimmed and the plane fly's fast and true. Landing is also pretty hot, probably because mine is a bit heavy due to my overbuilding a few areas.

Looking forward to seeing your results. I have some pics in one of my posts if you are interested.

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Hi John,

Many thanks. I am very glad that you have looked at this blog as it has shown where I have been somewhat remiss and have not stated the power system. This one is intended for electric power although there will be scope for using IC engines as well. I am using the manufacturers specified motors here: **LINK** These turn the Dynam 3 blade props 13x7 and look very scale like. The motors have their own 4 cell 3000+ MAh Lipos that are placed behind each motor in the nacelles. There is a detachable front section of the nose moulding to allow fitment of a larger lipo in the fuselage if desired. I have no idea of the flying weight of this one but I am hoping for less than around 3.5Kg 7.5lbs. The prototype did not show any vices but we will have to see when the maiden comes around. Please feel free to add your pics here to show different ideas.

Adrian

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Hello From Me smiley

I just thought id pop in and let you know I'm not just a figment of Adrian's imagination
So far Adrian is ahead of me in this build as he is an incredibly fast builder. I tend to be much slower! I haven't posted any pictures or thoughts yet simply because Adrian is ahead of me and pretty much covered all I could say or show. This is a pretty straight forward build and considering the fact its a pre production kit with no instructions and no indication for things like battery placement, servo placement etc is going together very nicely. For my pennies worth after a conversation with Adrian, I decided that I'm going to put the rudder and elevator servos in the tail so I can hide the linkages to keep a more scale appearance. I suspect the production kit will be using snake/pushrods with the servos in a more traditional place like under the wing seat for ease of access, and as I will be posting pictures as I go along with these little alterations it will serve as a "ready made guide" for those who wish to do the same. I have chosen this route because I intend to do most of my hard work after the bulk of the model is finished. I will be adding as much scale detail as I can possibly manage. That is where I come in on the blog later on . I hope this makes sense, this is the first time I have posted properly on a build blog (except for the odd question on other peoples!).
See You soon

Zero
(Paul)

Edited By zeroG_RC on 26/03/2016 15:07:24

Edited By zeroG_RC on 26/03/2016 15:08:04

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Hi Folks and Happy Easter to you all.

Many thanks Paul and I will be looking forwards to your detail work.

The build has been progressing with work done on the fuselage, wings and control surfaces. I started with the wing and bored a hole of around 1/2" diameter from the root to the nacelle centre line some 4" (100mm) rearwards of the leading edge. This will be used for the wiring needing to go to the motor, servos etc. and its position marked on the wing surface. Unfortunately the tube I had was only just long enough to reach the nacelle but it will be suggested for the future production (Should it go ahead) to have a hole through the entire wing. The wing halves were joined together with 15 minute epoxy and left to set ensuring the panels were symmetrical to each other.

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I then turned on to the leading edges and glued the centre section leading edge in place so it bridges the centre break adding to the overall strength in that area. One the PVA (Aliphatic resin) had set I then chamfered the ends to match the outer panel and glued the outer leading edge section in place.

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I decided to leave the leading edge in one piece as the slight change in angle of the outboard section is easily accommodated by bending the wood and taping it down well. The adhesive was spread liberally as both the foam and balsa will absorb some of the adhesive but not so much as it would ooze out everywhere. The same was repeated for the other leading edge.

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I then did the same with the trailing edge but had a simple overlapping join at the centre. Like the leading edge the changes in wing taper were taken care of by use of lots of masking tape pulling the leading/ trailing edges in firm in place.

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Adrian.

Edited By Ady Hayward on 27/03/2016 17:46:36

Edited By Ady Hayward on 27/03/2016 18:17:06

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Hi,

Following swiftly after, I turned my attentions to the control surfaces which need leading edges attaching. This was a simple job where I simply glued each one in place on the strip of leading edge balsa supplied. Again plenty of tape was used to hold them in good contact with the balsa.

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Finally I assembled the engine mount frames. These are nicely cut by laser and all parts fitted well. I took the trouble to remove the burned wood from the scorched edges so that the adhesive has the best surface to hold well. The frames are handed so care must be taken to ensure that they are built as left and right assemblies.

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The leading edge profiles on each plate end either at the bulkhead (Inboard section) or stands off by around 1/2" (12.5mm) which is the outboard section. Now on to sanding everything on the wings and tail to shape crook

Adrian

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Hi All,

Getting on towards the interesting bits now. All of the control surfaces have been sanded to shape and have been set aside for later. I have decided to fit the engine/ motor mounts as it seems about the right time in the build.

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On the prototype these were simply glued into place onto the veneer and locked to the wing by a plate located behind the top mount bulkhead to another plate let into the wing running span-wise so that the mount is anchored in place. Simple but effective. At this time I have just glued the mounts in place as the motors show.

Adrian

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Thanks Ady

Slightly off topic but this is my tail as installed on the model

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I am building this model as part of my clubs winter warbird build to help populate our 'Warbird Wednesdays' events. Long story short, we all turn up at about 6pm with our warbirds and have at it. The winter build was to help bring new people into building, and into the event from a social side. Its proven quite successful and we have a build log (covering 4 of the 6 models under construction) here **LINK**

Assuming you have some free time while your epoxy dries have a little read!

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Hi All,

Well, following on from Jons build I see I will have to bring my building up a notch or three to match Jons build standard and what a great way to get folks interested in building their planes!!!

Although the thread went a bit quiet it has not been through lack of thoughts on the build process.

I did find that the nacelle frames were not very stiff in torsion and one test had some of a couple of glue joints give. I re-glued the offending joints and added some triangular section balsa along the wing/ nacelle frame areas. I found that the nacelles stiffened up considerably as well as gaining a lot of strength on the nacelle/ wing joints.

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The next job was to let in the ply plate to the rear of the nacelle top and to add the locking plate using epoxy resin for strength.

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Work on the nacelles stops here for a bit as I am undecided whether to try and use dsr’s with a 90 degree twist for scale realism or just opt for the simple solution and have the wheels recess into the wing and show slightly past the nacelle underside.

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Hi All

The wing tips were next. The kit provides some lovely soft and light ¾” (21mm) balsa block for each wing tip. I was cautioned about the thin tips being prone to crushing if the wing is stored standing on the wing tip and also general damage as the section is quite thin.

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My solution was to laminate some soft 3/16” and ¼” balsa around a 1/16” ply section The crossing grain patterns and the ply made the tip very stiff with a weight increase before sanding of 7g and 8g for each wing tip over the original supplied so not a great increase overall.

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I left a small section of ply protruding from the tip root to provide a key into the foam wing tip. This requires a small slot to be cut to provide the key and aid alignment.

​Adrian

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Hi Folks,

Whatever transpires will be shown later but focus is now on to the ailerons and flaps. The prototype had top hinged control surfaces which are a really simple and effective way to fix the ailerons and elevators. The flaps too are top hinged but this does limit the flap movement to around 30 degrees downward deflection which is ok and recommended for most. All that needs doing is to sand back the leading edge of the control surface so it is full thickness at the top, and around 1/16” (1.5mm) thick at the lower edge. If more downward travel is needed then the same is repeated on the wing trailing edge. The pictures show the general idea.

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Me, being the person I am, cannot leave the control surfaces like that and so have opted for a slightly different approach to have the control surfaces look closer to scale with closed hinges. I first cut two strips of 1/32” (0.8mm) ply ½” (12mm) wide that will run from flap root to wing tip around 32” (815mm) in length. If this is not possible then two pieces each as long as the control surface plus an extra ¼” (6mm) to each length. A thin sliver of balsa10mm wide and 1/32” deep is then cut from the tops of the wing trailing edges to allow the flush fixing of the ply strip.

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With the ply strip in place the aileron can be presented to the wing and the leading edge rounded so that the aileron sits under the ply strip and is flush with the lower wing surface.

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The hinges are first dry fitted to the ailerons with the hinge point at the centre of the leading edge profile.The hinges are recessed quite deep into the control surface so that the hinge centre is in line with the radius of the leading edges.

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The aileron should be able to rotate around with the leading edge being just covered by the ply strip. If need be then the strip can be trimmed back a little to give full range of movement of the aileron. The same procedure will apply to the flaps except that they will only be needed to lower and back to the neutral position.

Adrian

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