Kits Black Horse Ju 87 Stuka

[les51]

Hi Guys
I am just starting to put together the BH Stuka it’s the early model, I have come up against 1 or 2 small issues which I have sorted but the instructions that came with the kit are basically just pictures so I expect to find more thing that need tweaking, does anyone know if a build guide has been posted anywhere or does anyone have experience building one of these that can pass on any advice.
One thing I do expect to have issues with is the mounting of the engine the kit suggests a 120 4 stroke, I have a NGH GF 38cc 4 stroke Petrol engine which is not going to match the markings on the firewall should I use the centre line that is marked on the firewall to centre the engine which is slightly to the right of the actual centre and mount the engine to that which may lead to cowling problems or mount the engine so that it sits squarely inside the cowling.
Any help greatly received
Les

 

[Smoggie]

For the engine mounting the important thing is that the prop shaft is where it's intended to be (on the centre of the fuselage) so if the mount has to be offset to allow the prop to be on centre then so be it.

I'm no expert on gas engine conversions but a 38cc gas engine seems to me like it will be MUCH bigger and heavier than the 120 (20cc) engine that the plane was intended to fly with? This is almost certainly going to cause big problems with fitting the engine in the cowl and CG (and overall weight).

 

[Tony]

What Smoggie stated is exactly what I was thinking. 38cc is a much larger and more importantly, heavier engine than the plane was designed to carry. It can be done, but do test fits first to make sure the cowl will still go on, that it still gets enough airflow to cool itself down and so on before you drill any holes. I would be looking up the weight of a 120 (1.2 cubic inch I think) engine and comparing it to the weight of the engine you have now. If the weight is close (don't see how it could be with all of that extra, cam, valves, pushrods, ignition box and so on) then you only have to worry about the size and getting it to fit.

Keep us posted and please post pictures of the progress. I'm interested in seeing this come together.

 

[les51]

Thanks to you both for your input, I have looked at the general weight of a 120 4 stroke engine which comes in around 1000g give or take depending on the exhaust used, my engine weighs 1310g plus another 270g for the electronics, the cables including the main spark plug cable are long enough to be able to mount them behind the CG obviously the overall weight is greater than with the 120 but I have been searching on line for any information to help me with the build and I have read that there have been problems with the plane being tail heavy and weight being added to correct the balance so it is possible that the weight issue may not be such a problem, I did take your advise about the engine being a problem fitting inside the cowl and temporarily fitted the engine on the mount and clamped it to the firewall and you were correct when I fitted the cowl over the engine it was about an inch away from the fixing point on the body this was caused by the engine hitting a part of the cowl preventing it from going further back this also prevented the prop shaft from fully exiting the front of the cowl so the prop and spinner could not be fitter ( see pictures ), this would be reasonably easy to sort by removing the section of cowl that is hitting the engine allowing the cowl back by the necessary amount this should solve both problems, there was also a problem with the carburettor touching the fire wall preventing the mounting from being flush to the firewall, again a small modification would sort this out. My only real concern would be modifying the cowl and spoiling the visual affect of the cowl.
I would be interested in any comments you guys may have.

I have taken some pictures of of my efforts so far and I have highlighted the small issues I have sorted out, I will post them shortly, should I add them to this post or should I start a new post.

Thanks again
Les

 

[Tony]

If they have to do with this plane, you can add them to this post. But if you want to make another one, feel free to do so.

And yea, just a little trimming and that should work out quite well. And very nice about the plane being a touch tail heavy, nothing better than adding weight to the nose in the forum of MORE POWER!!! lol.

 

[Smoggie]

Good point, better to have nose weight in the form of engine than in the form of lead! As long as you don't end up having to add tail weight because the weight increase really starts to add up. The physical fit of the engine doesn't look too bad all things considered.

 

[les51]

Hi All

I have just started to put together a Black Horse JU 87 Stuka ARTF kit most of the building has been done by the manufacturer but the assemble is still required and during this I have met some small issues which I have had to sort out.

I posted a question regarding the build so I thought I would post my progress.

I started by putting the servos into the wings and connecting them to the flaps and ailerons, the control horns are quite different to the usual type used and a lot stronger. Fig 1 & 2

Fig 1

Fig 2


The servos are fitted to a tray that is already setup in the wing there are 3 in each wing they are held in place temporarily by tape but will be finally held in place by a screw on each corner, each tray has fixing points glued in place ready for each servo the exit slot for the servo arm is covered and needs to be cut when the servos are fitted, it’s a quite large slot, I decided to modify it by filling the slot with scrap light ply before cutting the covering and cutting a smaller slot. Fig 3&4&5

Fig 3 Fig 4 Fig 5



The next job was fitting main landing gear onto the wings, the holes for the leg brace and the main leg fixing point are hidden under the wing covering as shown in the instruction, the small holes for the wire supports are easily found by feeling with your finger, I found that it was necessary to adjust the wire at the bends to allow the ends to fit into the holes easily, this wire is high tensile and I had to use a vice to hold it close to the bend that needed tweaking and use a hammer to make small adjustments, once the wire ends are correctly adjusted and fitted there is a plastic strap that is screwed down to hold the wire leg support in place. Fig 6

Fig 6 View attachment 19214


When I test fitted the suspension leg and plastic strap in place I found that the plastic strap was too wide and pushed the leg back against the wire which prevented the leg from raking forward and connecting with the 2 bracing straps, I solved this problem by making a smaller strap from some metal I had although smaller using metal has made it stronger, Fig 7

I also found that the 2 angled plates that hold the suspension leg to the wing were wider than the recess in the wing, I managed to slide one side between the wing surface and the ply fixing surface the other side I had to cut a recess in the wing surface to accommodate the extra length of the side angle plate. Fig 8


Fig 7

Fig 8 View attachment 19216

I next test fitted the wheel into the to the landing gear leg, again I needed to adjust things, firstly the 2 pieces of flat bent metal that form the brace between the wire and the leg were badly out of shape and needed twisting and the bends adjusting so that they met the U sides of the leg evenly, luckily the metal is mild steel so bending was quite easy. Fig 9
Fig 9 View attachment 19218


The wheel is held in place by a length if rod that is threaded at each end this is passed through the suspension frame and wheel there is a collar either side of the wheel which holds the wheel central these are held in place by grub screws, the rod is held in place by a nut at each end, when I test fitted this together I found that in order for the sprung leg to operate correctly the U section of the leg and the flat support pieces need to be able to move easily, I found for this to work correctly it required the nuts to be loosely tightened and they were only on the bolt by a couple of threads , obviously this is not acceptable the nuts would fall off during the first flight, the answer would be to use nilock nuts unfortunately the rod is not long enough to accommodate nilock nuts Fig 10
To get over this problem I used a bolt of the same thickness and ground the head of the bolt to reduce its size and cut it to the right length to use a nilock nut, to prevent the thread from wearing wheel centre I used an epoxy filler to fill the threads Fig 11
This worked quite well, the nilock nut should be shake free and the sprung leg moves freely Fig 12


Fig 10 View attachment 19219


View attachment 19220
Fig 11

Fig 12 View attachment 19221



The build is going well, I will post more in a day or two

 

[les51]

As you will have noticed my previous post is missing many of the pictures so I am posting from the point the pictures are missing again, hopefully everything will be ok this time

The next job was fitting main landing gear onto the wings, the holes for the leg brace and the main leg fixing point are hidden under the wing covering as shown in the instruction, the small holes for the wire supports are easily found by feeling with your finger, I found that it was necessary to adjust the wire at the bends to allow the ends to fit into the holes easily, this wire is high tensile and I had to use a vice to hold it close to the bend that needed tweaking and use a hammer to make small adjustments, once the wire ends are correctly adjusted and fitted there is a plastic strap that is screwed down to hold the wire leg support in place. Fig 6

Fig 6


When I test fitted the suspension leg and plastic strap in place I found that the plastic strap was too wide and pushed the leg back against the wire which prevented the leg from raking forward and connecting with the 2 bracing straps, I solved this problem by making a smaller strap from some metal I had although smaller using metal has made it stronger, Fig 7

I also found that the 2 angled plates that hold the suspension leg to the wing were wider than the recess in the wing, I managed to slide one side between the wing surface and the ply fixing surface the other side I had to cut a recess in the wing surface to accommodate the extra length of the side angle plate. Fig 8

Fig 7 Fig 8


I next test fitted the wheel into the to the landing gear leg, again I needed to adjust things, firstly the 2 pieces of flat bent metal that form the brace between the wire and the leg were badly out of shape and needed twisting and the bends adjusting so that they met the U sides of the leg evenly, luckily the metal is mild steel so bending was quite easy. Fig 9


Fig 9

The wheel is held in place by a length if rod that is threaded at each end this is passed through the suspension frame and wheel there is a collar either side of the wheel which holds the wheel central these are held in place by grub screws, the rod is held in place by a nut at each end, when I test fitted this together I found that in order for the sprung leg to operate correctly the U section of the leg and the flat support pieces need to be able to move easily, I found for this to work correctly it required the nuts to be loosely tightened and they were only on the bolt by a couple of threads , obviously this is not acceptable the nuts would fall off during the first flight, the answer would be to use nilock nuts unfortunately the rod is not long enough to accommodate nilock nuts Fig 10
To get over this problem I used a bolt of the same thickness and ground the head of the bolt to reduce its size and cut it to the right length to use a nilock nut, to prevent the thread from wearing wheel centre I used an epoxy filler to fill the threads Fig 11
This worked quite well, the nilock nut should be shake free and the sprung leg moves freely Fig 12


Fig 10

Fig 11
Fig 12


I have now started fitting the wheel and suspension covers, I noticed that the wheel boot was quite flimsy around the edge so I reinforced around the edge about 2 inches wide with fibre glass matting, it is now really strong and should withstand any landings that may end up in long grass etc Fig 13


Fig 13


The main wheel boot is a bit fiddle to get over the metal work but once over there is quite a bit of movement room, a bit of rubbing down of the edge of the wing fairing was needed to get it to fit to the wing shape as much as possible, once the wheel boot is slipped into the fairing there is plenty of adjustment to get the wheel central in the boot before gluing, one quite important part of finishing the suspension is final fitting of the wheel, the instruction manual shows the bolt being pushed into place over the edge of the boot Fig 14, I tried every way I could but was unable to manage to get the bolt in place like this, I eventually had to drill a hole in the boot to get the bolt in place, I’ll sort the hole later, the wheel is a snug fit in the boot but the suspension moves perfectly without snagging Fig15


Fig 14 Fig 15

 

[Jimbo]

Very nice.

Jim

 

[les51]

I have completed some more of my Stuka build


Now that all the wing servos are fitted and attached to their surfaces I have connected wire extensions where needed, as there are 3 servo cables per wing, to help to identify which cable goes to which servo I have put coloured heat shrink on the push rod and over the cable extension joint this links the servo to the joint and prevents the joint coming apart and then I put the same colour on the plug that will plug into the receiver so no chance of confusion Fig 16 & 17

Fig 16 Fig 17




I had previously looked at using the larger engine and posted asking for advice on this site which is at the beginning of this post, during my investigation I discovered that I would have to move the firewall back half inch to achieve this, so my first job was to remove the firewall and reinstall it further back I have taken some pictures showing how it went.


Fig 18 Fig 19 Fig 20

The firewall was made up of 3 sections glued together the outer layer was slotted into the side & top pieces Fig 19 & 23 I had to remove the triangular corner supports fig 21

Fig 21 Fig 22 Fig23

Once everything was removed I cut the side and top back to the level of the slots, I removed the protruding wood that had slotted into the sides and top from the firewall which now fitted between the sides. I glued the firewall between the sides flush with their front edge Fig 25


Fig 24 Fig 25

 

[les51]

I replaced the corner supports Fig 26 and glued the top in place and trimmed it flush with the front Fig 27. To replace the strength lost by cutting out the slots I drilled 3 holes down both sides into the firewall and glued in dowels Fig 28 & 29
Fig 26 Fig 27 Fig 28

Fig 29


More soon

 

[les51]

My next job was to install the engine and cowl

I started by temporarily fitting the engine mount that came with the model instead of the mount that came with the engine, I screwed the mount to the fire wall using the manufactures markings, the mounting is a 2 part type so can be used to accommodate a variety of engines, the fixing marks are for a 20cc engine which is too small for my 38cc engine so I checked the size between the fixing holes of my engine I marked the centre point between the mounting arms and then opened the arms of the mount equally from the centre mark they just fitted onto the firewall Fig 30
Fig 30

I put the engine onto the mount and found that one of the mounting legs was right in front of the throttle connection and the carburettor was also hitting the leg.
The engine mountings were made to be fitted either way round with the longer legs going up or down so I marked a line on the firewall level with the arms that the carburettor was sitting on I removed the mountings and marked a line vertically through both side screw holes to maintain the correct width then offered each mount up and lined up the fixing holes with the vertical lines and the arms with the horizontal line, I have ended up with the carburettor in exactly the same place but now the longer legs of the mount are now going in the opposite direction Fig 31 & 32
Fig 31 Fig 32


I put the carburettor onto the mount and the problem was solved, now that the carburettor was no longer hitting the mount the engine went slightly further back and just touched the firewall I just ground a dip in the firewall to allow the carburettor to be clear Fig 33
Fig 33


Now that the carburettor is nicely fitted I have drilled the holes in the mount to fix the carburettor in place fig 34


Fig34

Now that the carburettor is in position I am going to fit the cowl in place.


The cowl fits over the engine very well but does not go right back onto the plane body Fig 34 the engine hits the grill on the front of the cowl Fig 35

Fig 34 Fig 35

The only way around this is to cut out a section of the cowl Fig 36 this will allow the engine to come through and the cowl to go further back over the plane body Fig 37
Fig 36 Fig 37

Now that the cowl has been cut it fits very well Fig 38 and the spinner fits and looks great Fig 39

Fig 38
Fig 38 Fig 39

 

[les51]

The engine is quite large so the cut out is also large so I am going to use the cut out piece Fig 40 to build a cover over the engine, I used light ply to start to build a frame to support the cut out piece of cow Fig 41.
Fig 40 Fig 41


Fig 42 Fig 43

The idea was to replace the cut out in front of the engine and use the ply to slip into the hole either side of the engine then put balsa over the top of the engine I shaped the 2 side pieces of ply so that the unit fitted into the hole and the ply went either side of the engine without touching it, the cut out piece touched at several points around the cut out which held it in a good position then I glued strips of balsa around the top opening which further strengthened it, I wet a piece of balsa and rubber banded it to a can an let it dry I offered the curved balsa over the engine head and trimmed it so that it left an arch which angled down towards the back and glued it into place. I continued to trim away the excess balsa and tweak the fit Fig 42 to 47


Fig44 Fig 45

Fig 46 Fig 47

I filled in the front of the arch and raked it back to help with air flow Fig 48, I will look into if possible putting slits into this to match the ones below, I have filled in any gaps with filler Fig 49 to 51 which I will rub down and cover with fibreglass tissue and resin so that it will match the finish of the cowl.

Fig 48 Fig 49

 

[les51]

Fig 50 Fig 51

 

[les51]

I glued the finished section of cowl into place on the main cowl filled the joints and rubbed them down, I covered the new filler with fibreglass resin and rubbed if down smooth with wet and dry I then sprayed undercoat over the new area, flatted with wet and dry then gave it several coats .of yellow auto paint, the new colour is not exact so I will have to spray the cowl completely and then repaint the black areas which I will do by brush. I am happy with the mod to cover the engine and it is looking great now that it has been painted.

 

[Tony]

Dude, that looks absolutely fantastic!!! Most people just cut a huge hole and leave it. Can't wait to see the completed model!

 

[Smoggie]

Very nice work, i'd have most likely just chopped the hole and called it good but your modification is much better.

 

[D.O.G.]

WOW! I'm not a builder and into planes but I agree with Tony and Smoggie ...what an awesome job you are doing. I'm enjoying your pics les51 Keep up the good work and pics too. Thanks for sharing.

 

[Admiral]

Love the build, keep the photos coming.