MiG-21 MF/MA/R 1/72 3in1 Joy Pack by Kovozavody Prostejov (KPM0105) has butt jointed wings.

[WhiskySierraKilo]

Good afternoon.

I bought a 3in1 Joy Pack of 1/72 MiG-21s by Kovozavody Prostejov (KPM0105).

The main wings and rear horizontal stabilizers are butt joined to the fuselage.

I'm not sure how I'm going to strengthen this ?  Surely cyano alone won't be sufficient ?

Advice please.

Kind regards, w.

[malpaso]

I have just butt-jointed Spitfire tail planes with Tamiya extra thin which works but as you say not very confidence inspiring!  I have occasionally reinforced such butt joints with pins from wire, but it's a bit of a job to line up both sides, especially on tail planes which are very thin!

Cheers 

Will 

[Giorgio N]

Best way to deal with this kind of joints is to reinforce them using metal rods. The system is relatively simple:

Step 1: find a suitable metal rod. I use brass rod sold at hobby shops but unfolding a paper clip of the appropriate size is a good and cheap source of metal rods...

Step 2: drill in the wing surface a hole deep "enough"... how do you know if enough is enough ? The hole will have to accomodate the rod for a length sufficient to give some support, for a full wing on a 1/72 Mig-21 you may want to have say 4-5 mm, if the wing is larger and heavier you may want something even deeper.

Step 3: cut a length of rod... how long ? You want the rod to go fully inside the wing and then have around the same length or more to go into the fuselage.

Step 4: fix the rod into the wing. You may simply push the rod in the wing if the hole is of the same diameter, but you may also use CA to fix it in place.

Step 5: locate the point where the rod will enter the fuselage and drill a hole there. Now generally I drill the hole in the fuselage a bit larger so that I can adjust the location of the wing relative to the fuselage if I haven't drilled the hole in the perfect place.

Step 6: when it's time to glue the wing in place, add plenty of CA or, even better, 2-component epoxy in the hole you made in the fuselage.

At the end of this you will have a much stronger joint !

 

Now there are some variations on the system that may be even better in some cases... One is to drill the holes in the fuselage first and have a single rod crossing the fuselage. This makes for an even more robust joint but it's not always possible. In this case it's better to drill the holes in the wings after the ones in the fuselage,

One other variation, and one that I used on your same kit, is to have two rods along the length of the wing root. In this case it's more difficult to locate the holes in the fuselage correctly, so it is important to drill these a bit larger.

Whatever the variation, I strongly suggest to prepare the holes and the rods before starting the assembly of the kit.

 

Now some pictures to show the proces....

The basic system, here on a resin 1/144 Il-62... now this is larger and heavier than a 1/72 MiG-21. Each wing is one solid chunk of resin... notice the length of the rods

You can also see that on the fin I glued metal rods ready to accept the tailplanes.

 

 

Now an unusual solution I had to use on a 1/72 A-35, with a variation on the "rod through the fuselage" system. Here passing a straight rod through the fuselage was not possible because of the shape of the wing leading edges and  because the cockpit was in the way, so I inserted a straight rod farther forward and then bent this

 

 

 

Now a MiG-21, not the wings but the tailplanes... here the length of rod inside the fuselage had to be short because of the presence of the afterburner section. The system still worked pretty well and gave me a robust joint, I also use this method to replace the kit tabs when I want to reporoduce all-flying tailplanes deflected

 

 

As mentioned before, I built the same RV/KP kit you have and I used this system for both wings and tailplanes. Requires some work but in the end gives pretty good results

Edited January 26, 2021 by Giorgio N

[WhiskySierraKilo]

@malpaso  @Giorgio N :

Chaps, I was discouraged at first .

Glad I asked in this forum.

 

 I reckon even I can do this   .

Thank you for the rapid and complete advice.

 

Cheers, William.
 

[Giorgio N]

William, I'm sure you'll have no problem ! There is mainly one step where caution is needed: drilling the hole in the wing (or tailplane).

Here it's important to be very patient, use a good drill bit in a pin vice and choose a diameter that will "fit comfortably" in the thickness of the plastic.

The risk of using an excessively large drill bit can be seen in the picture I posted of the MiG-21 tailplane: you can see a whitish mark on the surface that is the result of the drill bit "pushing" the plastic out. The bit must be kept perfectly perpendicular to the mating surface as if it takes an angle there's the possibility of cutting through the surface of the plastic, that is not good.

Using a particularly thick metal rod is not necessary as metal is pretty stiff anyway. You can use a clothes pin for example, that is very thin but will still be strong and stiff enough for the wing-fuselage junction of a MiG-21. The problem with using very thin rods or pins is not with them, it's with the drill bit: using a very thin bit to drill a relatively deep hole without breaking the bit is a bit more difficult than using a larger bit.

To give you a rough idea, on my KP MiG I used a 0.8 mm rod for the wings (two per wing). It's a size that I know I can drill easily in the wings of that kit without damaging them.

For the tailplanes I used a smaller rod, IIRC 0.5 mm or maybe 0.4. In this case the hole in the tailplanes was not particularly deep, only a couple mm, as these parts are much lighter.

[RidgeRunner]

Great advice, Giorgio. I'd add that you should start with a pilot hole. So, for example, if you are going for a 0.8mm ultimate rod start with a 0.3 or 0.5mm drill. Once you have the pilot hole okay you can drill it out to take the rod. I was concerned that you mentioned "cyano" in your first post. That wouldnot hold for the long term even with tabs. For styrene to styrene using Extra Thin or regular plastic cement.

 

Oh, one more thign ..... never be tempted to use a powered drill for any of these jobs. You have less control and the plastic could melt.

 

Martin

 

 

[Giorgio N]

16 minutes ago, RidgeRunner said:

Great advice, Giorgio. I'd add that you should start with a pilot hole. So, for example, if you are going for a 0.8mm ultimate rod start with a 0.3 or 0.5mm drill. Once you have the pilot hole okay you can drill it out to take the rod. I was concerned that you mentioned "cyano" in your first post. That wouldnot hold for the long term even with tabs. For styrene to styrene using Extra Thin or regular plastic cement.

 

Oh, one more thign ..... never be tempted to use a powered drill for any of these jobs. You have less control and the plastic could melt.

 

Martin

 

 

 

I should have been a bit more clear,,. when I mention CA or epoxy glue I mean to use these only on the metal pins and relative holes, the rest of the joint should be glued with whatever standard polystirene glue one prefers. For the metal pins I prefer to use 2-component epoxy because sets slower, so giving time to align everything properly, and also because it can be used to really fill the larger hole I usually drill in the fuselage, so trapping the pin.

Regarding the use of pilot holes, I usually don't bother too much if I'm using a 0.8 mm, I usually locate the drilling point with a steel pin though, to avoid having the drillbit slipping when I start drilling

[MigModeller]

Thank you Giorgio 

 

I'll avoid KP Mig-21s in future.  Thankfully the type is proving popular given its shape and distribution.

 

Let's boycott kits that require butt gluing for wings/tailplanes.

 

Giorgio, what's the square addition to vertical tail plane in your pic?  Noticeable because it's white 

[Giorgio N]

The white square was IIRC an antenna that I made with plasticard. That subject (a Croatian MiG-21 Bis) featured a number of updates like new antennas and reinforcement plates, so I had to add these to the base model (the Zvezda 1/72 kit).

[Giorgio N]

On the RV/KP kits, IMHO the lack of alignment pins and tabs in the wing and tailplanes may be an annoying feature but there are others that I consider worse, for example the heavy framing on the windscreen, that does not look very good. Even when it comes to assembly, I found other areas that were more annoying than the wings, for example putting together the cockpit tub with the nose wheel well/radome assembly, and then locating this into the fuselage. Can be done but all locations are pretty vague and the contact surfaces are not very wide so it becomes one of those jobs that need 3 or 4 hands....

With the Eduard kits around today the RV/KP ones can now be left on the shelves... however it should be said that they often have very interesting markings and the joypack is always something interesting pricewise for modellers who already have decals

[RidgeRunner]

1 hour ago, Giorgio N said:

With the Eduard kits around today the RV/KP ones can now be left on the shelves... however it should be said that they often have very interesting markings and the joypack is always something interesting pricewise for modellers who already have decals

Agreed, Giorgio

[Paul Thompson]

14 hours ago, MigModeller said:

 

Let's boycott kits that require butt gluing for wings/tailplanes.

 

 

Let's not, or 99% of my collection of WW1 and between-the-wars aircraft will disappear, and I'm not that fond of scratch building.

 

Paul.

Edited February 1, 2021 by Paul Thompson
senior moment, corrected.

[72modeler]

Excellent techniques, @Giorgio N and @RidgeRunner! I have a suggestion that might help with the alignment of the holes to be drilled between the two mating surfaces. Drill a hole just big enough to fit the wire/rod being used in the wing/fin/tail plane. Then mix a little black paint with some white (PVA) glue and put a blob in the hole so that some sticks out. Press the flying surface against the fuselage where it needs to go; the paint blob will be deposited in the correct spot  for the second hole to be drilled. A little warm water and a brush will remove the blobs; cement the wire/rod of choice into the hole drilled in the flying surface, and Bob's your Uncle, as they say! BTW, Giorgio, pretty clever engineering on that Vengeance- have to remember that one! 

Mike

Edited February 8, 2021 by 72modeler
corrected spelling

[Mr T]

On 31/01/2021 at 11:22 PM, MigModeller said:

Let's boycott kits that require butt gluing for wings/tailplanes.

Well that most of my vacforms gone then. Not only do they not have convienent slots and tabs, they have to be cut from a backing sheet etc, and horror of horrors have vacform canopies. 😉🛩️✂️

[alt-92]

I prefer my options not to be limited.

And really, what's the problem with a butt-join, between friends?

 /coat

[rossm]

On 2/2/2021 at 5:50 PM, 72modeler said:

Excellent techniques, @Giorgio N and @RidgeRunner! I have a suggestion that might help with the alignment of the holes to be drilled between the two mating surfaces. Drill a hole just big enough to fit the wire/rod being used in the wing/fin/tail plane. Them mix a little black paint with some white (PVA) glue and put a blob in the hole so that some sticks out. Press the flying surface against the fuselage where it needs to go; the paint blob will be deposited in the correct spot  for the second hole to be drilled. A little warm water and a brush will remove the blobs; cement the wire/rod of choice into the hole drilled in the flying surface, and Bob's your Uncle, as they say! BTW, Giorgio, pretty clever engineering on that Vengeance- have to remember that one! 

Mike

I like that idea - I've always drilled the fuselage and then tried to hold the wing in place to mark through the hole with the drill. It usually works but your method sounds better.