Three videos - well worthwhile watching if you are building lightweight rubber power scale models for indoor or outdoor use.
Part 1
Part 2
Part 3
Diary of a Dedicated Aeromodeller
Showing posts with label Construction Techniques. Show all posts
Showing posts with label Construction Techniques. Show all posts
Wednesday, 13 July 2016
Lavoie method of building Stick Model Aircraft Fuselages
Posting this for posterity so that I don't lose these links again. I use a derivative of this method and as time moves on I use more of the ideas presented.
Three videos - well worthwhile watching if you are building lightweight rubber power scale models for indoor or outdoor use.
Part 1
Part 2
Part 3
Highly recommended
Three videos - well worthwhile watching if you are building lightweight rubber power scale models for indoor or outdoor use.
Part 1
Part 2
Part 3
Tuesday, 14 June 2016
Making Polyester Plastic Fuselages
By Pham Anh Tuan
This article was lifted from the Aeromodeller Annual 1972-73 - advanced at the time and still a good reference today.
The modellers who are prepared to make their own polyester fuselages know the type of aircraft they want to build, so we will assume they can carve the master and cast the female mould. We must now consider the question of actual lay-up of the fuselage.
The aim of this article is to give readers as many hints as possible to enable them to go ahead without further undue difficulty.
Moulds are made of the same material as the fuselage, i.e.
1. a base resin,
2. the gel coat,
3. the release agent,
4. the glass-fibre (medium weave: about one mm thick).
The fuselage should be built in a well-aired room. A workshop is the most suitable, but if one is not available, use a room with large windows which can be opened fully.
The principle of construction is as follows:
The fuselage mould is in two halves. The two halves are joined together with bolts, and a band of glass-fibre matting is used to reinforce the seam.
The object is to put a smooth piece of cloth (or mat) over the release agent inside the two halves of the mould. First spread the release agent generously over the joint area, making sure the surface is coveted with release agent and that no excess builds up inside the mould. Leave it to dry for at least one hour. The release agent must be completely dry.
After this, prepare a dose of gel coat and add to this the catalyst. Using a paint brush, apply an even coat of gel over the dry release agent. Too thick a layer of gel coat will impair the solidity of the fuselage.
Leave it to dry for about half an hour, until the gel coat is tacky. While waiting, cut the fibreglass into two pieces sufficient to cover each of the insides of the moulds, leaving a few inches for overlap.
The fibreglass is then applied to the gel coat in the two halves of the mould. Gently rub the fibreglass to ensure perfect adhesion to the gel coat; this will determine the final finish of the fuselage.
Now, prepare a larger quantity of base resin, adding less catalyst.
Using a paint brush, spread the base resin evenly over the fibreglass, paying particular attention to the seam (make sure the fibreglass does not bubble at this place), and other areas such as the wing supporting flairs, fin leading edge, etc.
Reinforce the fibreglass in those places which are more susceptible to damage, i.e., the nose of the fuselage, the wing supporting fairings and the fin, etc.
Have a sharp knife at hand. When the resin has almost set (when it is firm] cut away the excess fibreglass. The two halves of the fuselage, though stuck together in the moulds, are now ready.
Now, the two halves must be joined securely.
We have already said it is very difficult to make at clean join at the fin without taking special precautions. Cut bands of fibreglass approximately one and a half inches wide; these are for the seams.
Cut a small and of fibreglass for the tail fin leading edge. Dip the band in base resin, put it on one side of the tail fin and curve it along the leading edge.
Do the same with the other inaccessible parts, i.e., the inside of the fuselage near the tail fin.
Work through the apertures left at the base of the fuselage for the wing, and at the rear of the fin, using sticks as spatulas and a long-handled paint brush. The fibreglass band must be moved into position while the resin is still fluid.
With the two halves assembled, the job is now three-quarters completed. All that remains to be done is to apply the fibreglass strip to the other seams.
This is a difficult operation due to the lack of access. The band must be rolled up, soaked in resin, placed on the accessible pan of the seam, and unrolled with the aid of a long and curved spatula.
The second “trick” is to put the resin impregnated strip on to a piece of balsa, slide this into the fuselage and tum it upside down so that that strip drops onto the seam.
Once this strip is in position, cut off any excess material.
Leave the fuselage for several hours so that the resin is perfectly dry before taking away the moulds.
Unscrew the mould retaining bolts. With the aid of a screwdriver gently pride the two halves of the mould apart, paying careful attention not to damage the joining surfaces of the moulds.
Gently press away any excess fibreglass along the seam of the fuselage, then wash of the release agent with water.
You now have a fibreglass fuselage.
The back of the fin should be blocked with a piece of balsa and fixed with resin. This will provide a firm mount for fixing hinges. On the inside of the fuselage, cross ply the matting to aid strength
One might imagine a great deal of work being involved in all this. In fact, the opposite is true!
Once the formers and engine mount are installed, the rest is easy. Bearing in mind the precision of the mould, the formers can be cut and pierced beforehand - this is, of course, a great advantage.
The fuselage should be rubbed down with a fine wet abrasive material (grade 400) before being painted with Epoxy.
With a little experience. it is possible to build a fuselage in one evening. Cost is relatively little. With this type of material it is possible to build models weighing less than 6.5 lbs, quite suitable for competition flying. The two main advantages, therefore, are speed and cheapness, and also versatility of fuselages thus made. Rounded curves, aerodynamic forms, wing supporting flairs, etc, are difficult to realise: when using only balsa for construction.
Many people decry the use of polyester plastics for fuselages. They say that this type of material gives rise to vibration and interferes with the radio equipment. We do not agree with their views. Vibration has never given any trouble. During many months of flying the author had no trouble at all. The servos were simply stuck to the side of the fuselage on rubber mounts. Reasoning is quite simple: the sides are fairly resilient and quite elastic in themselves.
Although the text has so far dealt exclusively with a radio controlled subject, application of the same method could produce fuselages for other types ranging from team racers to slope soaring gliders. In fact, the control line models have a lot in common with the radio example except that they are in general smaller. For some subjects it will he necessary to add extra reinforcement, around tho nose of a glider for example, and also to prepare for removable hatches which will have to he cut away.
As a club project, the polyester fuselage has a lot to commend it. Shared cost of the original carved or plaster shaped master, and the preparation of the moulds, will result in production line procedures which bring satisfaction to a whole group of clubsters. Moreover, it introduces a club “shape" of model - a uniformity that some people like to adopt for identification on the field.
This article was lifted from the Aeromodeller Annual 1972-73 - advanced at the time and still a good reference today.
The modellers who are prepared to make their own polyester fuselages know the type of aircraft they want to build, so we will assume they can carve the master and cast the female mould. We must now consider the question of actual lay-up of the fuselage.
The aim of this article is to give readers as many hints as possible to enable them to go ahead without further undue difficulty.
Moulds are made of the same material as the fuselage, i.e.
1. a base resin,
2. the gel coat,
3. the release agent,
4. the glass-fibre (medium weave: about one mm thick).
The fuselage should be built in a well-aired room. A workshop is the most suitable, but if one is not available, use a room with large windows which can be opened fully.
The principle of construction is as follows:
The fuselage mould is in two halves. The two halves are joined together with bolts, and a band of glass-fibre matting is used to reinforce the seam.
The object is to put a smooth piece of cloth (or mat) over the release agent inside the two halves of the mould. First spread the release agent generously over the joint area, making sure the surface is coveted with release agent and that no excess builds up inside the mould. Leave it to dry for at least one hour. The release agent must be completely dry.
After this, prepare a dose of gel coat and add to this the catalyst. Using a paint brush, apply an even coat of gel over the dry release agent. Too thick a layer of gel coat will impair the solidity of the fuselage.
Leave it to dry for about half an hour, until the gel coat is tacky. While waiting, cut the fibreglass into two pieces sufficient to cover each of the insides of the moulds, leaving a few inches for overlap.
The fibreglass is then applied to the gel coat in the two halves of the mould. Gently rub the fibreglass to ensure perfect adhesion to the gel coat; this will determine the final finish of the fuselage.
Now, prepare a larger quantity of base resin, adding less catalyst.
Using a paint brush, spread the base resin evenly over the fibreglass, paying particular attention to the seam (make sure the fibreglass does not bubble at this place), and other areas such as the wing supporting flairs, fin leading edge, etc.
Reinforce the fibreglass in those places which are more susceptible to damage, i.e., the nose of the fuselage, the wing supporting fairings and the fin, etc.
Have a sharp knife at hand. When the resin has almost set (when it is firm] cut away the excess fibreglass. The two halves of the fuselage, though stuck together in the moulds, are now ready.
Now, the two halves must be joined securely.
We have already said it is very difficult to make at clean join at the fin without taking special precautions. Cut bands of fibreglass approximately one and a half inches wide; these are for the seams.
Cut a small and of fibreglass for the tail fin leading edge. Dip the band in base resin, put it on one side of the tail fin and curve it along the leading edge.
Do the same with the other inaccessible parts, i.e., the inside of the fuselage near the tail fin.
Work through the apertures left at the base of the fuselage for the wing, and at the rear of the fin, using sticks as spatulas and a long-handled paint brush. The fibreglass band must be moved into position while the resin is still fluid.
With the two halves assembled, the job is now three-quarters completed. All that remains to be done is to apply the fibreglass strip to the other seams.
This is a difficult operation due to the lack of access. The band must be rolled up, soaked in resin, placed on the accessible pan of the seam, and unrolled with the aid of a long and curved spatula.
The second “trick” is to put the resin impregnated strip on to a piece of balsa, slide this into the fuselage and tum it upside down so that that strip drops onto the seam.
Once this strip is in position, cut off any excess material.
Leave the fuselage for several hours so that the resin is perfectly dry before taking away the moulds.
Unscrew the mould retaining bolts. With the aid of a screwdriver gently pride the two halves of the mould apart, paying careful attention not to damage the joining surfaces of the moulds.
Gently press away any excess fibreglass along the seam of the fuselage, then wash of the release agent with water.
You now have a fibreglass fuselage.
The back of the fin should be blocked with a piece of balsa and fixed with resin. This will provide a firm mount for fixing hinges. On the inside of the fuselage, cross ply the matting to aid strength
One might imagine a great deal of work being involved in all this. In fact, the opposite is true!
Once the formers and engine mount are installed, the rest is easy. Bearing in mind the precision of the mould, the formers can be cut and pierced beforehand - this is, of course, a great advantage.
The fuselage should be rubbed down with a fine wet abrasive material (grade 400) before being painted with Epoxy.
With a little experience. it is possible to build a fuselage in one evening. Cost is relatively little. With this type of material it is possible to build models weighing less than 6.5 lbs, quite suitable for competition flying. The two main advantages, therefore, are speed and cheapness, and also versatility of fuselages thus made. Rounded curves, aerodynamic forms, wing supporting flairs, etc, are difficult to realise: when using only balsa for construction.
Many people decry the use of polyester plastics for fuselages. They say that this type of material gives rise to vibration and interferes with the radio equipment. We do not agree with their views. Vibration has never given any trouble. During many months of flying the author had no trouble at all. The servos were simply stuck to the side of the fuselage on rubber mounts. Reasoning is quite simple: the sides are fairly resilient and quite elastic in themselves.
Gliders, Control-Line and other types
Although the text has so far dealt exclusively with a radio controlled subject, application of the same method could produce fuselages for other types ranging from team racers to slope soaring gliders. In fact, the control line models have a lot in common with the radio example except that they are in general smaller. For some subjects it will he necessary to add extra reinforcement, around tho nose of a glider for example, and also to prepare for removable hatches which will have to he cut away.
As a club project, the polyester fuselage has a lot to commend it. Shared cost of the original carved or plaster shaped master, and the preparation of the moulds, will result in production line procedures which bring satisfaction to a whole group of clubsters. Moreover, it introduces a club “shape" of model - a uniformity that some people like to adopt for identification on the field.
Tuesday, 30 June 2015
Incidence Measuring Tool
Being a fairly recent adopter of Smart Phones, I was delighted to discover that there are several rather useful applications that can be adapted for Aeromodelling.
One of these is a 'Bubble app', freely available for iPhones and Androids.
I have started to use this extensively on my Kwik Fli build but what I really needed was an Incidence Measuring Tool. I have put off buying a commercial tool due to the relative high cost, mainly I suspect, due to the cost of the meter. The Bubble App has a resolution of 0.1 degrees and appears to be quite repeatable - i.e. the results are consistent which is very reassuring.
This, therefore is my Incidence Tool. I make no excuse - the basis of the design is a copy of those commercially available, however, I made mine in an evening from (mainly) offcuts of builders ply that I had lying round. It only cost me my time.
It comprises of one fixed leg, the other is free to slide down the beam. My beam is 450mm long - this means that I can separate the legs by 390mm - about 15" - which is large enough for the foreseeable future. The legs and beam are 35mm wide, the leg length is 190mm long (top to bottom)
The legs are reinforced on each side by 2 laminations of 3.6mm ply - 100mm long. On the diagram, the left leg is glued firmly into place, the right leg slides up and down the beam. It needs to slide quite freely but without being too loose. Before the right leg was glued up (PVA), I lubricated the beam with Beeswax. This prevent glue sticking to it and allows a nice smooth action.
The platform is a simple (in my case iPhone4 sized) ply platform inlaid into the top of the beam. Again, this needs to be parallel with the beam. I pinned it into place with a couple of panel pins and ensured that it was square by using balsa triangle section on each side of the joint between the beam and the platform.
Make sure the VEEs are the same length and size. Note, it is more important that these are square with each other rather than the legs being the same length.
Weighted down while the glue dried
This shot shows the doublers in place. These were sanded down with a nice curved edge when the glue dried
This shows the general arrangement quite well (even though the photo is on its side). The elastic band pulls the legs together when its in use
The Smartphone platform inlaid into the top of the beam
Calibrate the Tool.
Place the model in a stand so that it is held quite firmly, it needs to be approximately level, but it's not critical.
Place the Jig on the wing, place the smartphone on the platform and zero the Application. Reverse the tool on the wing and without altering the Smartphone calibration, the incidence axis should still be zero degrees. If its not then you have an error in your construction and will need to make an alteration to the centre line of one of the two Vees. Over 300mm, an error of 0.1 degrees is about 0.5mm out..
Using the Tool
On most (not all) models the tailplane is set at 0 (zero) degrees to the Fuselage Datum. This is the case with the Kwik Fli used for the demonstration. If the tailplane is not set with the datum, then you will need to zero the application on the Datum first, then measure the wing and tail separately to find the Decalage. (The difference between the incidences of the wing and tail or upper and lower wings in a biplane)
Place the smartphone on the tailplane and press the calibrate button. This will zero the bubble and X and Y should be set to 0.0 degrees.
Place the tool so that it is clamped between the LE and TE, somewhere near the wing root although it could be anywhere down the wing
Transfer the phone from the tailplane to the platform and measure the incidence. On this app, its the 'Y' axis that shows we have 0.4 degrees positive incidence. Check that its positive by lifting the phone very slightly at the LE side and the value should increase without going through zero first.
One of these is a 'Bubble app', freely available for iPhones and Androids.
I have started to use this extensively on my Kwik Fli build but what I really needed was an Incidence Measuring Tool. I have put off buying a commercial tool due to the relative high cost, mainly I suspect, due to the cost of the meter. The Bubble App has a resolution of 0.1 degrees and appears to be quite repeatable - i.e. the results are consistent which is very reassuring.
This, therefore is my Incidence Tool. I make no excuse - the basis of the design is a copy of those commercially available, however, I made mine in an evening from (mainly) offcuts of builders ply that I had lying round. It only cost me my time.
Design Overview
The design is quite straightforward:
It comprises of one fixed leg, the other is free to slide down the beam. My beam is 450mm long - this means that I can separate the legs by 390mm - about 15" - which is large enough for the foreseeable future. The legs and beam are 35mm wide, the leg length is 190mm long (top to bottom)
Construction Notes
The really critical part of the tool is the length of the leg to the centre of the 'VEE' which locate on the LE and TE of the wing. The legs need to be at 90 degrees to the beam and the VEE must be at the came distance or the platform will not be level. It is quite easy to check when assembled, but if it is wrong, it much more difficult to correct.The legs are reinforced on each side by 2 laminations of 3.6mm ply - 100mm long. On the diagram, the left leg is glued firmly into place, the right leg slides up and down the beam. It needs to slide quite freely but without being too loose. Before the right leg was glued up (PVA), I lubricated the beam with Beeswax. This prevent glue sticking to it and allows a nice smooth action.
The platform is a simple (in my case iPhone4 sized) ply platform inlaid into the top of the beam. Again, this needs to be parallel with the beam. I pinned it into place with a couple of panel pins and ensured that it was square by using balsa triangle section on each side of the joint between the beam and the platform.
Make sure the VEEs are the same length and size. Note, it is more important that these are square with each other rather than the legs being the same length.
Weighted down while the glue dried
This shot shows the doublers in place. These were sanded down with a nice curved edge when the glue dried
This shows the general arrangement quite well (even though the photo is on its side). The elastic band pulls the legs together when its in use
The Smartphone platform inlaid into the top of the beam
Using the Incidence Meter with a Smartphone
Download and install the App from your favourite App Store. I have the free version of 'Surface Level' which is one of a suite of potentially useful measuring tools. The little banner at the bottom of the App had adverts running all the time which the commercial version doesn't have.Calibrate the Tool.
Place the model in a stand so that it is held quite firmly, it needs to be approximately level, but it's not critical.
Place the Jig on the wing, place the smartphone on the platform and zero the Application. Reverse the tool on the wing and without altering the Smartphone calibration, the incidence axis should still be zero degrees. If its not then you have an error in your construction and will need to make an alteration to the centre line of one of the two Vees. Over 300mm, an error of 0.1 degrees is about 0.5mm out..
Using the Tool
On most (not all) models the tailplane is set at 0 (zero) degrees to the Fuselage Datum. This is the case with the Kwik Fli used for the demonstration. If the tailplane is not set with the datum, then you will need to zero the application on the Datum first, then measure the wing and tail separately to find the Decalage. (The difference between the incidences of the wing and tail or upper and lower wings in a biplane)
Place the smartphone on the tailplane and press the calibrate button. This will zero the bubble and X and Y should be set to 0.0 degrees.
Place the tool so that it is clamped between the LE and TE, somewhere near the wing root although it could be anywhere down the wing
Transfer the phone from the tailplane to the platform and measure the incidence. On this app, its the 'Y' axis that shows we have 0.4 degrees positive incidence. Check that its positive by lifting the phone very slightly at the LE side and the value should increase without going through zero first.
Measure Washout or Washin
Simply by measuring the incidence at the root then measuring again at the wingtip, the difference determines any warps (intentional or otherwise). With the wing the right way up, less incidence at the tip means that the wing is washed out. You do need to ensure that the weight of the Incidence tool is not causing the wing to bend or twist.
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