Post by dennisp on Sept 21, 2008 15:34:18 GMT 8
Drop tanks
Having made the decision to use the drop tanks for the air tanks, I also wanted the ability to access the air tank inside the drop tank which requires the cover of the drop tank to be removable. The obvious way is needless to say to use screws and the tried and tested method as devised by Robbe kits moons ago was put into practice.
You need some dowel wood I am using 1/8” and 3/8” which you can see in the picture, the ends are sharpened with a pencil sharpener, first a small hole is made using the 1/8” dowel gentle twist and push and you have a nice hole. The 3/8” dowel is then used to enlarge the hole, you will note that there are 4 (plugs) x 3/8” dowel pieces ¼ long two with a small centre hole and the other two with a clearance hole for the self tapping screw.
The plugs are then glued into the drop tanks ensuring they are in the correct order self tapping clearance hole plugs into the removable cover.
I have opted to go for the extra small Robart tanks as two of these has a similar volume to the standard tank for air up / down retracts, it saves cutting out some foam to get the bigger tank to fit inside the drop tank.
So now we have completed the basic build of the model, once the model returns from the beautician I will cover the final assembly.
Lessons learnt
Every model one builds is an experience and new methods are tried with and without success, and this build was a trial of glassing a large foam model using PVA paste, in the main I would say I have had a reasonable success with this build.
So here are my list of things that I learnt...
• Try to use 3/4 ounce cloth rather than 1 or 1 ½ cloth, it is easier to apply the paste and get the wrinkles out, it is better to go for two layers of ¾ ounce than one 1.5 once cloth. I used the 1 ½ ounce cloth for the wing bottom for additional strength and hind sight should have inserted carbon fibre spars in the wing to get the strength.
• The 60 / 40 mix of PVA and water seems to work fine for all cloths as it did with brown paper covering (BPC).
• A little drop of Tamiya acrylic paint (less than a teasthingy full) improves the hardness of the PBA coating and also adds a little colour so you can see where the paste is too thin or too thick. I used this technique on the fuselage shells.
• Use a soft brush to apply the paste to the glass cloth keeping the pressure light as the cloth will stretch with ease without you realising it.
• If doing a conversion in my case bigger retracts check everything first before you go mad and chop foam and make the necessary mounting plates.
• As this is a foam wing strength is required in the MLG wheel area and retract mount, always try to make / use a ‘D” box structure in the case of the wheel wells light 1/16” balsa adds loads of strength with very little weight increase. It is important to get the grain direction correct it should be from top to bottom. For the retract mounting plate if you are using several pieces of Lite ply then each piece should have the grain in the opposite direction again adds a lot of strength for no additional weight.
I will continue with the build in a few weeks time once the model returns from its facial..
Having made the decision to use the drop tanks for the air tanks, I also wanted the ability to access the air tank inside the drop tank which requires the cover of the drop tank to be removable. The obvious way is needless to say to use screws and the tried and tested method as devised by Robbe kits moons ago was put into practice.
You need some dowel wood I am using 1/8” and 3/8” which you can see in the picture, the ends are sharpened with a pencil sharpener, first a small hole is made using the 1/8” dowel gentle twist and push and you have a nice hole. The 3/8” dowel is then used to enlarge the hole, you will note that there are 4 (plugs) x 3/8” dowel pieces ¼ long two with a small centre hole and the other two with a clearance hole for the self tapping screw.
The plugs are then glued into the drop tanks ensuring they are in the correct order self tapping clearance hole plugs into the removable cover.
I have opted to go for the extra small Robart tanks as two of these has a similar volume to the standard tank for air up / down retracts, it saves cutting out some foam to get the bigger tank to fit inside the drop tank.
So now we have completed the basic build of the model, once the model returns from the beautician I will cover the final assembly.
Lessons learnt
Every model one builds is an experience and new methods are tried with and without success, and this build was a trial of glassing a large foam model using PVA paste, in the main I would say I have had a reasonable success with this build.
So here are my list of things that I learnt...
• Try to use 3/4 ounce cloth rather than 1 or 1 ½ cloth, it is easier to apply the paste and get the wrinkles out, it is better to go for two layers of ¾ ounce than one 1.5 once cloth. I used the 1 ½ ounce cloth for the wing bottom for additional strength and hind sight should have inserted carbon fibre spars in the wing to get the strength.
• The 60 / 40 mix of PVA and water seems to work fine for all cloths as it did with brown paper covering (BPC).
• A little drop of Tamiya acrylic paint (less than a teasthingy full) improves the hardness of the PBA coating and also adds a little colour so you can see where the paste is too thin or too thick. I used this technique on the fuselage shells.
• Use a soft brush to apply the paste to the glass cloth keeping the pressure light as the cloth will stretch with ease without you realising it.
• If doing a conversion in my case bigger retracts check everything first before you go mad and chop foam and make the necessary mounting plates.
• As this is a foam wing strength is required in the MLG wheel area and retract mount, always try to make / use a ‘D” box structure in the case of the wheel wells light 1/16” balsa adds loads of strength with very little weight increase. It is important to get the grain direction correct it should be from top to bottom. For the retract mounting plate if you are using several pieces of Lite ply then each piece should have the grain in the opposite direction again adds a lot of strength for no additional weight.
I will continue with the build in a few weeks time once the model returns from its facial..
