HELP DIRECTORY - 9-F


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• TOPIC LISTINGS :
  Filler Tips
  When balancing your aircraft fill your fuel tank HALF full. It helps on both end of the spectrum of  a plane being nose heavy or tail heavy when the tank is Full for flight.
  Cheap Filler  If you want to fill a gap and you're wondering what to use, go over to the clothes dryer, get some lint, and mix it with epoxy. It works great, and you can’t beat the price.
  Alan Cox

  ---

  Film canister uses
  1. Makes a great glo plug storage container.
  2. Makes an even better container for small screws and other hardware.
  3. You can drill a small hole in the lid and use as an overflow catch can when fueling your planes.
  4. Cut the bottom out and use to keep charger cords rolled up in.
  5. Cut a hole in the bottom and glue it to your flight box for a glow plug igniter holder.
  
  Firewall Fuelproofing
  Firewall Fuelproofing  Firewalls of planes are normally coated with epoxy to help prevent fuel and oil damage to the wood. On planes with no cowling, apply a coat of epoxy on the firewall after you cover the plane with film covering. Make sure the film overlaps a little onto the firewall. This way the epoxy seals the edges of the film covering. Besides, most film adheres better to wood than epoxy, so that's another plus.

• ---

  Flight Box Tips
  RADIO FLYER TYPE WAGONS
  Build or Put your Flight Box in a Radio Flyer type wagon sold at most toy stores. 
  There was substantial surface area inside the wagon to accommodate all the "stuff" you need in a field box.

Field Box Leads  by Futaba Inc
 

• ---

  Flight Logs
  Flight Log for models & motors - Freeware Download

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  Flight Theory
  Theory of Flight

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  Flaps and Flaperons
  
  Flap systems
   

  There are a many types of flap systems but if flaps are used at all, in ultralights or other light aircraft, then only the simpler devices shown at left are needed.
  
  The most common [because of its simplicity] is the plain flap which might provide a 0.5 increase in C_Lmax with a large increase in drag when fully deflected. The split flap provides slightly more increase in lift but a larger increase in drag and is more difficult to construct and thus probably not worth the effort.
  
  The slot incorporated into the junction between the main wing and the plain flap in the slotted flap arrangement allows airflow from under the wing to energise [i.e. accelerate and smooth] the turbulent boundary layer flow over the upper surface of the lowered flap, providing better downstream boundary layer adherence, and thus allowing a larger angle of attack to be achieved before stall with higher C_L and lower drag than the plain flap. Ailerons may also be 'slotted' for improved performance.
  
  The rearward extension of the Fowler flap as it is deflected increases wing area as well as camber so it provides the best increase in lift of all the simpler systems — although perhaps even a single element Fowler flap like that shown is not that simple to construct.

  Summary — flap effect on coefficient of lift

  In the diagram above it can be seen that the deflection of flaps provides an increase in C_L of about 0.4 at all angles of attack. This is probably representative of plain flaps extending along 50% of the wing trailing edge with chord equivalent to about 20% of the wing chord and deflected 30°. The attainable C_L increase depends on flap span, chord and degrees deflected plus the complexity of the flap system — C_L increase of 0.8 might be achieved with long span Fowler flaps deflected to 35°. Incorporating slots into plain or Fowler flaps increases C_L.

  Advantages of using flaps

  If flaps are fitted a small flap deflection, say 10°, might be used for safer take-off, due to the lower lift-off speed available but half to full flap deflection is always used for landing to provide:
   

  • lower safe approach and touch-down speeds
  • a nose down attitude for a better view of the landing area
  • a steeper approach path (because of the degraded L/D) for better obstacle clearance, which can be controlled at will
  • a shorter 'float' after rounding out because of increased drag
  • a shorter ground roll, if flaps are left fully extended until the aircraft has exited the runway.

  And flaps enable the approach to be made with engine power well above idle, which is beneficial to the engine, allows power changes to either increase or decrease the rate of sink and provides better engine response in case of a go-around. Of course if the aircraft is fitted with an unreliable engine which necessitates glide approaches then flaps are unsuitable.

  Flaperons

  In some light aircraft designs, particularly those with STOL (short take-off & landing) capability it has been found expedient to incorporate the aileron and a plain flap into one control surface which extends the full length of the wing trailing edge. The different functional movements are sorted out by a control mixer mechanism. Usually the flaperon is not integral with the wing but bracketed to the underwing to provide a slotted flap — acting like an external aerofoil flying in close formation with the main wing. Although the C_L increase attainable might be 1.0 there are drawbacks to this arrangement which particularly exacerbate low speed aileron drag.
  Flaperons - Ailerons Can be Flaps, Too!

  Reflex flaps

  Some aircraft [particularly sailplanes] are fitted with flaps that also can be deflected upward 5° or 10° above the normal neutral or stowed position in addition to the normal downward deflection positions described above. Upward deflection of flaps is done at cruising speed, increasing the maximum cruise speed perhaps 5% by reflexing camber and reducing drag and is often associated with aerofoils that have good laminar flow.

  Flaperons is a term used when one uses strip ailerons as flaps.
  Using ailerons as flaps can be done mechanically or with the use of some  radios that allow the mixing of
  servos.
  Flaperons when applied add drag and lift to your aircraft, but not without problems.
  
  1. Usually there is adverse Yaw when the flaps are in the down position.
  
  2. There are pitch trim problems that are natural when lowering these flaps.

  ADVERSE YAW :  With both ailerons down, any aileron deflection will cause more drag on the rising wing - the one on the outside of the intended turn. Note fig. 1; to roll to the right, the right flaperon is raised, decreasing drag on the right wing - and drag on the left wing is increased as that flaperon is dropped further. This imbalance of drag on the wings will try to yaw, or turn, the plane to the left, opposite our intended right turn.

  Adverse yaw effects are worsened by a long wing (high aspect ratio), or by shorter tails and smaller fin/rudder areas. Small Rudders make it nearly impossible to counter act this yaw , but it can be managable..

  PITCH TRIM : The reaction may be  negligible to violent, either up or down, depending on the plane.
  Generally , planes with long tails and large stabilizers, and high-aspect ratio wings, will tend to pitch up with flaps down. But aircraft with smaller stabs and shorter tails, and low aspect ratio wings, may very well pitch down.
  
  Ailerons must be configured to handle normal aileron deflection, PLUS any flap deflection.
  
  Use only strip ailerons. This is because lowering flaperons effectively raises the angle of incidence. Any
  other configuration can result in stalls as it affects airflow over the wings.

  ---

  Flutter
  Generally .. on ailerons occurs at the end of the aileron out at the wing tip.
  If you will allow about 3 to 4 inches from the tip, any flutter tendency goes away.
  Other conditions that create flutter are loose linkages and Gaps between the ailerons and the wing.
  Keep all the edges sharp and all lines straight.
  Another point to consider is that  flutter loves nice rounded edges and curving surfaces,
  but it hates straight lines and sharp edges.  
  It is not necessary to taper the trailing edges on rudders.
  Flutter is usually not noticable in slow flight but when you hear a buzz after recovering from a dive then you
  know you got flutter problems.
  Mass balancing for Larger aircraft is common.
  Check out the link below for diagrams on how they mass balance these ailerons.
  
  Other Links concerning Flutter
  Mass Balance Control Surfaces - prevent Flutter.
   IMAA High Flight article
  Flutter - Curing flutter by Ed Moorman  
  Mass Balance Control Surfaces - prevent Flutter.

  ---

    Flight Box customizing    Flight boxes can be customized in lots of different ways. If you drill small holes around the fuel bottle hold down bracket you can store long screwdrivers and hex wrenches. Two eye bolts can be used to hold your 4 way wrench. Velcro can be used to hold any number of things to and in the box

  {If you use a piece of Velcro on the back of the drawer and on the back wall of the hole the drawer fits into it will keep your drawer from sliding out. A bolt and wing nut can hold spare props on the side of your box. If your box keeps getting heavier and heavier, try to find a smaller fuel bottle. It is unlikely that you will ever use a gallon of fuel on one trip to the field, a quart is plenty. Fuel is light and air sensitive also so the less you carry around with you the better.}

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  Flying Wings
  Flying Wing Models - Basic design
  Flying Wings - Trimming
  Flying Wings - Trimming

  ---

  
  Foam Applications
   

The Basics of Foam Wings

Foam wings are simple. An airfoil shape is cut from a block of foam and then sheeted. The two halves are joined and a strip of fiberglass is applied around the joint. The foam provides the shape and is relatively strong in compression and shear. There is little strength in the foam for tension or bending. When a wing is under load, one surface is in tension and the other is in compression. For a positive G load, the lower skin is in tension and the upper skin is in compression. The tension loads are easier to withstand than the compression loads. A balsa skin with glass at the center joint is usually strong enough for the tension loads. The compression of the skin is not that difficult to withstand. Fortunately, balsa is adequate in both tension and compression. A side effect of compression is buckling. This buckling is more difficult to withstand. Balsa by itself is not that great, it will tend to buckle if it is not supported. That is the reason for the foam core. The foam holds the skins stable in compression so they don't buckle under load. The skin is the primary strength member, so use the lightest foam you can find.

I usually add a little carbon fiber between the skins and the core to help on a fast or heavy plane. Be sure to use a strip wide enough so that a good glue joint will result. A thin strip can pull away by failing the glue joint.

 

Aircraft Spruce Is one supplier of foam blocks. They can also be found a home insulation specialty stores.

 

Cautions for Foam Wing Construction

Do NOT attempt to hot wire cut polyurethane foam. This type foam is identifiable by its lack of beads and it's coarse appearance. It is available in green and other colors and is sold for use in floral arrangements. The fumes from cutting this foam are TOXIC. The easy way to check for this type of foam is to see if polyester resin will dissolve it. If not, then it is polyurethane.

Always cut cores in a well ventallated area. Don't overtly try to inhale the fumes that come off while cutting.

Tools for Foam Wing Construction

You will need a power supply, a bow, nichrome wire, a very flat surface and foam blanks.

Power Supply

I use an electrical transformer called a Variac for this. It is AC current, but it is insulated. It is sold for electrical power tools use, and other for other electrical devices that need to be slowed down. These are available from Aircraft Spruce. I have heard that a model train transformer will work, as will a car battery with a resistor, but I have no experience with those. Always start with it set in the lowest setting and slowly increase power until it cuts.

Bow

I made a simple bow from a lenght of 1x2 pine with 2 12 in long pieces of 5/32 music wire on the ends. The music wire has a notch filed on the end on the outer side. This allows the cutting wire to be attached. The music wire protrudes through the 1x2 about 1 in and the power supply is connected there with alligator clips.

Twist a loop in one end of your cutting wire and place it on one of the music wires. Bend the other music wire in about an inch and use this length to twist a looop in the other end of the cutting wire. Slip this on the other music wire and it will hold tension in the wire for cutting.

Make two bows, one about 12 in wide and one long enough for the longest wing panel you'll cut.

Supplies

Cutting Wire

I use Nichrome wire that is available from several sources. RCM used to sell it, Wing Manufacturing, sig Manufacturing and others.

Aircraft Spruce also sells it. You can also buy a big wire wound resistor and break it open to get the wire. I have heard that stainless steel safety wire from the aerospace industry works too, but I have never tried it.

Check out Epic R/C's Web Page. They are a supplier for the wire, and their page offers a lot of technical info on cutting foam wings too.

Cut 2 pieces of 5/16 dowel about 1 in long. Drill a hole through it lengthwise and slip the wire through them before attaching it to the bow. These will be used as guides for precise cutting. One dowel on each end of the bow is used as a handle for precise control. This is, or course, not required. It can help if cutting a complex shape.

Foam

Is available from several sources. Use white bead foam. It is sold as insulation for buildings at specialty stores (not home warehouse type stores). I have bought pieces 4 in thick and 4 feet by 8 feet.

Extruded polystyrene foam can also be used. It is usually blue or pink and is sold as home insulation. This foam has a "grain" appearance. It is acceptable, but is much heavier than the white bead foam. Extruded foam can be hot wire cut.

Making Templates

There are two methods for making templates. You can make a single template the shape of the airfoil, or you can make seperate templates for the upper and lower surface. The two part templates are the best because you can set the washout (or lack of) precisely each time.

Draw the airfoil section on paper at the correct angle. Check to see if it will fit on the thickness of foam you have. Draw the bottom of the foam block and then cut out the pattern. Cut it from door skin ply when satisfied. You will need one set of templates for each section. If it is a constant chord wing you'll need two identical sets. If it is a tapered, wing you'll need an inboard and an outboard set. If you are careful in the placement of the templates, you can cut in the correct dihedral at the same time.

 

Note the "lead in" at the LE and TE to allow the wire to smoothly transition. Mark number stations along the template equidistant from the LE to the TE on all templates, both sides. With a tapered wing, you will put the same number of marks with a smaller spacing on the smaller template. These marks are used for alignment during cutting.

Foam Preparation

You must cut the block to the planform of the wing first. I invented a method for this to make it easy and repeatable. Lay out the plan for the wing. Take several yardsticks and lay them on the plan so that they form a "picture frams" with the outside edge exactly on the outline of the core. Overlap the corners and cut and glue the frame together. Make two of these. Take your sheet of foam and place one of the frames on top and the other on the bottom exactly aligned. Use your small bow and cut the foam using the top and bottom frames as guides. When you are done, the "core blank" will be exact, and so will subsequant ones you make. You could also make two templates out of plywood for the same purpose.

Set your power supply to the lowest setting and turn it on. Slowly increase the power and push a test piece of foam into the wire. It should be hot enough to cut about 1 inch every 1 to 2 seconds. Don't push too hard or you'll stretch the wire. Cut the core blanks, turning the power supply off after each cut. If not, the wire will get too hot. Cut the core blank out one side at a time.

Cutting Cores

Attach the upper surface template to the end of the core blank on each end. Place it on a FLAT table. Test cut a scrap piece of foam the same length as the core and find the correct power setting. You can start at either end, I like to start at the LE in case the wire dosent exit the foam at the same time the error will be less. Position the bow on the lead-ins. Turn on the power supply and have your helper pull the wire into the core at the same time (faster at the longer template). Keep the wire at the same station calling them out as you go. Slow down at the short template as required. Exit the core and turn the power off. Any ridges can be sanded off.

Sheeting the Core

Foam cores can be sheeted with balsa, cardboard, glass, or other materials. Balsa is easiest to work with, and leans toward iron on covering material.

1. Sand the proper dihedral angle in the root chord of the core.
2. Edge glue your 1/16 balsa sheets after true cutting the edges with a straight edge. The sheet should be at least 1/2 in larger than the core. Use the lightest wood you can find, especially for the smaller planes.
3. Block sand both sides with 240 then 400 grit sandpaper.
4. Dry wipe and vacuum both sides.
5. Place the core "beds" on a flat table. 6. Apply 3 hour cure epoxy to one side of the skin. Apply only enough the wet the balsa. About 1 oz for a .40 size wing. Squeege it all over the core. Place it on the core bed with the epoxy side up.
7. Place a strip of dry carbon fibre tow at 30% chord. The tow should be long enough to extend to the other tip in one piece. Apply epoxy to the top of the carbon.
8. Place the core on the skin.
9. Repeat for the top applying the carbon to the core first.
10. Place the top core bed on the skin and place a large flat board on it. Load bricks or books on the board.
11. Allow to cure over night.
12. Remove the weights and the core beds. Place the other panel's core bed next to the panel and block up the wing panel to match the core bed and block up the tip to the proper dihedral. Secure the wing panel.
13. Repeat the process this time aligning the carbon strips so that they align straight tip to tip.
14. Let it cure overnight.
15. Remove the wing and aply a 2 oz strip of glass/epoxy, 2 in wide to the center section. Use 4 oz cloth for larger planes.
 

Glassing Foam Cores

I have never done this but it is worth trying. Follow the above with one exception: Use 2 oz glass cloth and epoxy for covering.

1. Use contact cement and attach thin, smooth sheets of sheet aluminum to the core beds. Mylar, or other semi-rigid plastic will also work.
2. Polish the surface to a high gloss. These surfaces will be the mold for the wing skin.
3. Apply the epoxy resin to the mold surface and apply the cloth. Apply any carbon fiber strips.
4. Place the core on the glass.
5. Repeat the glass proceedure for the other core bed and place it on top of the core.
6. Apply weights to the core beds until the epoxy has cured.
7. After cure, remove the mold forms and finish the wings.
 

• FOAM WING ADVANTAGES

• Shorter building time. This may be arguable, but most builders feel that building a foam wing is quicker, less tedious, than conventional construction.
• Manufacturing ease. Once the proper cutting jigs and equipment is on hand, foam cores can be cut in great numbers with minimal effort. The foam wing certainly requires less work in drawing plans; the whole concept is far simpler.
• Strength/Stiffness. This is an area where the foam wing really shines. Foam wings tend to be very stiff - they resist bending and twisting far better than the conventional design. For high performance aircraft, this is essential; most pattern planes, larger aerobatic planes, and ducted fan/turbine planes use the foam wing exclusively.
• Accurate, Smooth Shapes. A conventionally built up wing that is not fully skinned will have slight irregularities where the open spaces meet solid structure. And the covering will have slight concavities in the open areas. The fully skinned foam wing will be smooth, and accurately follow the airfoil shape throughout the entire structure.
• Tapered Wings are easily Reproduced. All that is required for the foam wing is the shape of the root and the tip airfoils to accurately scale everything in between.
• Washout or Twist is Easily Incorporated. Positioning of the root and tip templates during foam core cutting will determine any twist or washout in the final completed wing. Aerodynamic washout (ie. progressing to a more stall resistant airfoil shape out toward the wingtips) is just as easily accomplished in the cutting process.
   

• FOAM WING DISADVANTAGES
  Weight. The completed foam wing will generally be slightly heavier than a comparable wing of conventional construction. This will vary with the choice of wingskin weights, the type and amount of bonding glue used, and other construction considerations.

• The technique of building a foam wing is very different than conventional wing construction; this is only a problem if the builder is intimidated by learning new building methods.
• Covering. Applying covering requires more care - the foam core or the bonding agent may be damaged by the use of too much heat in the covering process. If the model is to be painted, however, this is considerably eased by the full skin.
• Hard Points. Attaching or mounting landing gear or servos to a foam wing is trickier - there just isn't much in the way of solid structure to bolt on a landing gear, for instance. Properly designed mounts must be built into the wing to carry the appropriate loads.
• Repairs? A damaged foam wing may be difficult to repair - there are techniques to do this but its more difficult and time consuming than just splinting a couple of ribs or spars on a conventional wing structure.
• SO- are foam wings for you? Like so many other things in the world of model aviation, it all depends. It depends on just how strong your model must be. The importance of a totally accurate shape. How heavy is permissable. Your building preferences. Or, maybe that's just what came with the kit!
  REFERENCE LINKS
  Foam Wing Analysis - Are They as Great as Everyone Says?? 
  Gyros Frequently Asked Questions (FAQ)

•  Foam Cutters 
  REFERENCE LINKS

• TRANSLATION

       

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