Tricks of the Trade
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I have included a few 'handy hints' on this page, things I have tried that work or that I haven't seen elsewhere.
Throw Gauge :- make your own throw gauge and set up controls accurately and precisely. Wing boring :- how to bore neat holes for servo wires in a foam core Leaky tank :- how to test a fuel tank of any variety for even tiny leaks. Super Scales:- using your prop balancer to weigh out very small amounts of epoxy. Smooth Operator :- How to keep your covering iron gliding (with out strapping 100" wings to it). Lateral Balance :- or the ancient Chinese art of 6 inch nails. Aerial antics: - Neat ways to run your receiver aerial out of the model Perfect wing seating: Give your wing and fuselage a nice snug fit Namby pamby electric fliers need not bother reading the next three.............!! Oil Removal:- How to remove oil from balsa wood. (See leaky tank for how to get oil into balsa wood in the first place!) Oil Removal 2: Keeping the outside clean Oil Removal 3: Keep your motor clean
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Wing boring
When boring a hole in a foam wing for servo wires etc. it can be difficult to ensure the hole follows the intended path. The method I use is illustrated in the diagram.
I make a ‘Vee block’ from scrap wood, either balsa or ply depending what is at hand. I fix this on a board or the bench relative to the wing core such that the boring tube will be at the correct height and position. If necessary support the wing on scrap blocks. If it is a kit keep the scrap polystyrene the core is cut from and use this a support. If the is wing is tapered root to tip adjust tip height if necessary so that tube will run down the centre line. Secure wing to the board when correct orientation is achieved.
To actually bore the hole I use a metal tube (13mm copper water pipe), and gently heat the end with a gas torch, and then use that to ‘melt’ my way into the core. If you want to go to a particular depth mark the tube with masking tape. Don’t overheat the tube; if you only use gently heat the tube won’t blast a huge great hole. You have been warned! The advantage of the Vee block is that as the tube cools it can be retracted, re-heated, and pushed back in while following the exact same line. You can also use the Vee block and a serrated end tube and ‘cut’ your way in by turning the tube. In my experience this never leaves a neat job.
Finally to finish the job, I make a paper tube by pasting a couple of layers of paper over a well-greased example of the same size tube. Wall paper paste and photocopier paper work well. When this is dry slide it off the former (this is usually hard work so make sure the paste is well dry) and then glue the paper tube into the foam with PVA. This not only strengthens the ‘hole’ but also keeps your PVC servo wires away from the polystyrene foam (they can interact to the determent of your servo wires).
Wing boring:Leaky tank:Super Scales:Oil Removal:Smooth Operator :Lateral Balance :Aerial antics: Perfect wing seating: Oil Removal 2:Oil Removal 3: Back to the Top
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Checking fuel tanks for leaks.
Having discovered fuel had leaked from the tank installed in my Acrowot I needed to determine if the leak was curable (i.e. a loose screw in the front bung) or terminal (i.e. a split seam). The leak was not large and therefore not obvious. This technique can also be used for checking new tanks prior to installation, and is good for all tank types.
Take the tank to be tested and seal all the outlets. I normally end up linking two with a single piece of fuel tube, and fitting a piece of blocked tube to the third. Immerse the whole tank in hot but not boiling water. As hot as you can stand with rubber gloved hands is more than sufficient.
As the air in the tank expands due to the heat from the water you will see a small stream of bubbles from the offending leak. If it is around the bung tighten the screw until the leak stops. If its is a split seam throw the tank away!
I now check all tanks prior to installation with this method. Wing boring:Leaky tank:Super Scales:Oil Removal:Smooth Operator :Lateral Balance :Aerial antics: Perfect wing seating: Oil Removal 2:Oil Removal 3: Back to the Top
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Super Scales
I often find myself needing to mix small quantities of epoxy resin, less than 1/2oz. With quantities that small it can be difficult to gauge the correct mix of resin and hardener. If the mix is incorrect the resin may not reach full strength or fail to cure completely.
To overcome this problem I have pressed my magnetic prop balancer into service as a precision set of scales. The accompanying sketch shows the details. Nothing is critical, just keep everything as light as possible. The cross piece can be 3mm lite-ply or hard balsa and should be a good fit on the balance shaft. On mine the cross piece is about 200mm long. Adjust the wire pan supports so that the pan sits horizontal with the pivot point above the pan centre, and give yourself some clearance above the bench, 10mm should be sufficient. click for larger image To mix the resins I use a small pot cut from the bottom of a plastic aspirin pot or small yoghurt pot. Make sure the plastic is compatible with the resin system. A small quantity of tin foil would also be suitable.
Before adding the resin etc. place the pot on one pan and balance with blue tack before adding your measuring weight. I use 1p pieces as medium weights (they are circa 1/8oz) and M5 or M4 nuts for small quantities. If you want to be really fussy use the same item for both resin and hardener, balancing between with more blue tack.
Note that if you need to mix unequal quantities a second balance point can be added as shown. The quantities will be mixed in the ratio of pivot point positions e.g. 5:1 as shown. Again before adding resin balance the pot plus hardener with blue tack, with the measuring weight off the pan.
My prop balancer is the magnetic type and hence will only cope with a total suspended weight of about 3oz; I suspect that other mechanical types would serve a similar roll and cope with larger masses. With mine I can easily see the difference of ‘one M3 nut’ in weight; as I have found that circa 22 M3 nuts equals 1/4oz this equates to a precision of 0.01oz. Wing boring:Leaky tank:Super Scales:Oil Removal:Smooth Operator :Lateral Balance :Aerial antics: Perfect wing seating: Oil Removal 2:Oil Removal 3: Back to the Top
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Oil Removal
While refurbishing my trusty old Acrowot I noticed that oil/fuel had soaked into one side of the fuselage around the tank bay. It must have represented a slow leak over the years as it was only on one side, and the wood was basically still sound. As the structure and joints where still in good condition I needed something to remove the oil with out having to replace the wood. The method I adopted was as follows:
Mix a quantity of talcum powder with methylated spirits to a fine creamy paste, sufficient to cover the effected area to a depth of 6mm or so. (Use up all that all smelly stuff your Gran or Auntie gave you for Christmas!). Spread this paste liberally over the effected area and leave over night to dry.
In the morning break off and scrape out the talcum powder that remains. It will break up easily, turning back into powder with little effort. This can be a bit fiddly but it’s a lot quicker than a re-build! Finally clean out with a Hoover or similar. You should find that the oil has been absorbed by the talcum mix and is no longer resident in your precious balsa wood.
I wouldn’t recommend this where there has been a major ingress of oil that has weakened the wood and joints. Of course having cleaned the area up ensure the cause of the leak is found and cured before using the model again. Wing boring:Leaky tank:Super Scales:Oil Removal:Smooth Operator :Lateral Balance :Aerial antics: Perfect wing seating: Oil Removal 2:Oil Removal 3: Back to the Top
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Smooth Operator
In my experience even a Teflon coated covering iron eventually looses it ability to slide smoothly over the coverings. This seem to be especially true if you use Solarfilm and related products where the adhesive and colour layers separate when being applied. You can restore the iron's smooth operation by spraying with a car interior cleaners that are silicone based. Products such as 'Back to Black' and 'Cockpit Shine' are suitable.
With the iron at operating temperature clean the adhesive and colour residue off the iron sole with a fairly aggressive solvent. I use cellulose cleaners or car paint cleaner. Then spray a liberal coating of 'Cockpit Shine' onto the iron. Wait a few seconds for most of the solvents to evaporate and then wipe of any excess. You will now find your irons glides effortlessly over the model.
I have been using this for several years (and several models) and have found no adverse effects on the covering or its ability to stick to itself when overlapping Wing boring:Leaky tank:Super Scales:Oil Removal:Smooth Operator :Lateral Balance :Aerial antics: Perfect wing seating: Oil Removal 2:Oil Removal 3: Back to the Top
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Lateral Balance
NB Lateral balance is either side of the fuselage centre line to determine if one wing is heavy.
We all pay attention to the fore and aft balance of a model (or suffer the consequences if we don't) but how many worry about the lateral balance? Certainly anybody involved in performance aerobatics does but what about the rest of us? In my experience even high wing trainer type models benefit from getting the lateral balance right. Also it can be surprising how 'out of balance' a model can be, particularly if you mount the engine on its side.
To achieve the balance either support the model on the engine prop shaft (threaded part) and the tail wheel/fin or suspend the model on string at these two points. Provided the model is free to pivot you should find one side is heavy, normally the side the engine hangs out. If you don't suspect that your pivot is inadequate not that the model is perfectly balanced! Now take some 6inch nails; saw off the head, and bang them into the light weight wing until balance is achieved. If your wing is built up instead of foam you would have been better balancing before covering. However this technique can still work provided you find a suitable place to push the nail in.
To avoid wing flutter due to mass imbalance make sure the additional weights are forward of the 1/3 chord point if you can.
In practise I usually experiment by placing the nails on the wing until I get a balance and then driving them home. That way you can cut nails down when you need less than a full one to achieve balance.
6 inch nails may sound extreme but in my experience a side mounted .60- .90 2 stroke in a 50-60inch span model requires between 1 and 2 nails to achieve balance Wing boring:Leaky tank:Super Scales:Oil Removal:Smooth Operator :Lateral Balance :Aerial antics: Perfect wing seating: Oil Removal 2:Oil Removal 3: Back to the Top
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Aerial antics
When you bring your receiver aerial out through the fuselage make a small 3 mm dia hole in the fuse. and then glue a brass servo eyelet into the hole on either side. These make the hole entry exit smooth and neat (particularly on the outside though the covering).
To secure the aerial at the rear take a short length (1/2 inch or 12mm) of silicone fuel tubing. Push the aerial wire through the tubing and then push a servo fixing screw through the tube, avoiding the aerial wire. Now screw into the rear of the fuselage until the head compresses the tube and holds the aerial. This gives sufficient 'friction' to hold the aerial in place, but should you prang it (when you prang it!) the aerial can pull out without damage. It also saves knotting the aerial as the case with the ubiquitous 'small rubber' band method of securing.
Wing boring:Leaky tank:Super Scales:Oil Removal:Smooth Operator :Lateral Balance :Aerial antics: Perfect wing seating: Oil Removal 2:Oil Removal 3: Back to the Top
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Perfect wing seating
To achieve a good seal between the wing and the fuselage without stick on foam tape (which I find eventually becomes stick off tape) I use the following. It will also cope with very small gaps that tape would be too thick for.
Having made and covered the model and ensured the wing seats OK, take some cling film and cover the portion of the wings that seat against the fuselage. Keep this covering as smooth as possible (not always easy). Now run a bead of silicone sealant (bathroom sealant) along the fuselage wing seat. Must be silicone and if you can get a colour match so much the better. The amount you need will depend on the gap that needs to be filled but don't worry about over doing it. Now fit the wing and screw or band it into position. Wipe any excess sealant off from the outside. Set the plane aside for at least 24 hours for the sealant to cure.
When the sealant has cured remove wings and peel off the clingfilm. You may find that the sealant is still a little tacky in the middle, particularly if you have a thick section. Don't worry, either let it cure in the air or dust some talcum powder over it with a small brush to take off the tackiness. Now trim back the excess inside and out with a 'very' sharp knife or scissors and Hey Presto a perfect fit wing seat Wing boring:Leaky tank:Super Scales:Oil Removal:Smooth Operator :Lateral Balance :Aerial antics: Perfect wing seating: Oil Removal 2:Oil Removal 3: Back to the Top
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Oil Removal 2 : Cleaning the aircraft after a flying session.
Having tried various commercial cleaners and home made concoctions of detergents etc. I now use "Baby Wipes". These are alcohol impregnated clothes that get the oil and dirty off both the model and your hands very efficiently. Just buy the cheap 'stores own brand' types; unless your model has sensitive skin off course!
The bay wipes do leave a slight film of very fine 'baby oil' behind. If you want to get rid off this as well then occasionally wipe the model down with straight methylated spirits. Pour some into a trigger spray bottle as supplied with many household cleaners these days and just spray meths. onto the model and wipe off. Works extremely well even in low temperatures and leaves the model grease and dirt free.
CAUTION: Can effect some paint surfaces, even those that are fuel proof, but in my experience the effect is minimal.
SAFETY WARNING: DO NOT SPRAY NEAR A NAKED FLAME OR WHEN SMOKING Wing boring:Leaky tank:Super Scales:Oil Removal:Smooth Operator :Lateral Balance :Aerial antics: Perfect wing seating: Oil Removal 2:Oil Removal 3: Back to the Top
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Oil Removal 3: Keep your motor clean
To remove the brown film (black film if you leave it long enough!) that inevitably accumulates on your engine just immerse it in methanol for a period. Old fuel that is a bit too suspect to risk running through the engine will be fine. Depending on the thickness and stubbornness of the deposits this may require several days and a few intermediate scrubs with a stiff toothbrush or similar. The nice thing about it is that it does not attack the aluminium as aggressive detergents and caustic products do and is easier (but slower) than using paint stripper. It may not get all the very heavy burnt on stuff off, but you shouldn't let it get that bad in the first place
Wing boring:Leaky tank:Super Scales:Oil Removal:Smooth Operator :Lateral Balance :Aerial antics: Perfect wing seating:
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