Flight

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Flight is a Division B and Division C event for the 2024 season. Competitors must design and fly an aircraft powered by a rubber band with the objective of spending the longest time in flight. It is a combination of various previous flight events, such as Wright Stuff and Helicopter. This allows competitors to have greater freedom to design the aircraft they desire. However, only planes are viable this season due to the minimum weight of 8 grams. The event is sponsored by NFFS who have released resources pertaining to the event on their website.

Types of Aircraft

Fixed-Wing Aircraft

Fixed-wing aircraft are standard Wright Stuff planes.

Powered Rotorcraft

Helicopters.

Unpowered Rotorcraft

Elastic launched gliders.

Getting Started

The vast majority of fliers build their plane using a kit. Freedom Flight is generally regarded as the best quality but hardest to build, while J&H Aerospace's Stinger is of similar quality but easier to build. Freedom Flight works well as a first build as long as the instructions are read thoroughly, and takes around 4-6 hours to build. Using a cya applicator to apply glue allows for much greater control while adding less glue weight and is highly recommended. A toothpick also works.

It is useful to invest in a torque meter, such as the Simple Torque Meter, or the torque meters sold by Freedom Flight and J&H. It's necessary to have a winder, which can be purchased from the same place the plane kit was bought from. A rubber lubricant is also required. See "Rubber" for more details on this page.

Learn how to wind by watching Coach Brian's video as the difference between good and bad winding technique affects flight time greatly--sometimes as much as 30 seconds.

NFFS has released a wealth of resources for this event.

Parts of a Plane

A typical Flight airplane contains six major parts:

Wing assembly
A frame made of sticks of low-density balsa wood glued together, covered and glued with a thin covering made of paper or plastic. One or two sets of these are glued to tougher (higher-density balsa or basswood) sticks, and inserted into tubes on the fuselage of the airplane (so that the wings can be disassembled from the fuselage for storage/transportation). There are also other ways of mounting the wings on the motorstick besides the tubes. Sometimes, the tubes are attached to the wing for disassembly during travel. The sticks running perpendicular to the motorstick are called spars. The front spar is called the Leading edge and the back spar is the Trailing edge. The ones running parallel to the motorstick are called ribs, and are usually curved (cambered) to increase the lift of the wing. Ribs are usually created using a simplex foil. The higher the simplex, the harder it is for the plane to climb. The wing usually has a slightly higher simplex than the stab as well.
Motorstick ("MS" or "stick")
The fuselage or "body" of the plane. This is a length of fairly thick balsa wood. The motorstick serves to hold the twisted rubber between the propeller assembly (at the front) and the motor hook (at the back of the MS) and to hold the wing tubes.
Tailboom ("TB" or "boom")
The "tail" of the plane. This is another length of solid balsa, usually lighter than the MS and sometimes tapered to save weight. The boom serves to support the vertical and horizontal stabilizers. Since it doesn't have to support the rubber, it is usually lighter and weaker than the motorstick.
Propeller assembly ("prop")
The propeller, the thrust bearing (or plastic nose thing), and the wire propeller shaft.
Horizontal stabilizer
The horizontal stab has a similar structure to the wing with the exception that it's smaller. It is the second lifting surface and is usually located in the rear of the plane, except in canards.
Vertical stabilizer
Usually located near the horizontal stab, the vertical stab controls the yaw of a plane. It can act as a rudder to induce turn.

Construction Tips

Some people recommend using a cheap ceiling tile as a build surface. Foam boards work as well. Pins can then be used to secure parts in place before they are glued together.

Use a pit of wax or parchment paper under glue joins to ensure that pieces are not glued to the paper (optional, alternatively just glue better). A popular choice of glue is medium viscosity cyanoacrylate (CA). Try to fit all parts snugly. A joint with gaps will not be strong. With thin CA, the joint will not adhere, and with medium CA, the glue will act as a gap filler and add weight while being a weak joint. Taping down or otherwise securing components before gluing is helpful—especially wing and stabilizer spars. Use a "Cya Applicator". If glue is visible, it is likely that there is too much being used. Ensure that the building surface is flat, so flying surfaces will be, too. You can also use super glue accelerant to decrease the setting time of superglue to 1-2 seconds, but try to not use accelerant because it decreases joint strength. Do not put accelerant into a large amount of CA and then use your finger to touch it, as it can cause burns.

Care must be taken while covering flying surfaces. Mylar covering is the most common, although grocery bags and similar alternatives have been used in the past. The only adhesive used for covering is 3M Super 77 spray adhesive. Carry the flying surfaces outside or to a well-ventilated area, and spray lightly, following instructions on the bottle. Be sure to follow all safety regulations and wear a mask. The mylar is usually stretched over a frame with Vaseline on it, and pressed over the sprayed flying surfaces. However, some kits do not mention that after spraying the flying surfaces, you must bring them to another location before covering. If this step is not done, the covering will stick to the frame, but also the surface that was sprayed.

Most kits will have detailed instructions for the construction process. Read through them before starting.

Trimming a Plane

For inexperienced fliers, focus on building a working airplane to weight and trimming (adjusting) it until it flies around in circles before worrying too much about advanced techniques. A simple, well-trimmed plane with lots of practice flights will do better than a poorly trimmed pusher canard with a torque burner, flaring balsa propeller, and other bells and whistles.

The Basics

Plane stabilizer tilt.png

Turning

Plane stabilizer offset.png

There are, in general, three methods for controlling turn:

  • Tilting the horizontal stabilizer, causing the plane to roll. This works because the lift vectors are directly perpendicular to the surfaces that generate them. So, since the wing and stab are slanting in opposite directions, their lift vectors have components in opposite directions. Since they are on opposite ends of the fuselage, this causes the plane to turn.
  • Turning the rudder/vertical stabilizer so that the entire plane yaws. The plane is now moving forward, but pointing slightly to the side. One tip of the wing is now pointing more forwards than it was before. Dihedral causes that end of the wing to rise, which makes the plane roll. This is known as "slipping and sliding" because the plane is never pointed in the same direction that it is traveling in, so it is always skidding a little.
  • Controlling how much the propeller is angled compared to the motorstick. This is usually only necessary at very high torques.

If the plane is going straight or turning right, and all of these parameters seem correct, then something is likely broken.

Center of Gravity and Decalage

  • Center of Gravity (CG) - The balance point of the plane with the rubber motor and propeller attached, measured relative to the wing
    • Moving the CG forward relative to the wing increases stability, but reduces efficiency. Moving it back reduces stability, but may increase efficiency.
    • Moving the wing forward moves the CG back relative to the wing, and vice versa. Note that as the wing moves back, tail movement decreases, increasing difficulty when trimming the plane.
    • It's good to build underweight so that there will be clay added to the plane that can be used to move the CG without moving the wing
    • The CG may be moved forward to reduce stalling or moved back to reduce diving
  • Wing incidence - The angle of the wing relative to the motor stick, with positive being the leading edge higher than the trailing edge
    • Typically the leading edge is 3-6 mm higher than the trailing edge
  • Stabilizer Incidence - The angle of the stabilizer relative to the motor stick or tail boom, with positive being the leading edge higher than the trailing edge
    • Typically not adjustable and set to 0 degrees
  • Decalage - The difference between the wing incidence and stabilizer incidence
    • Decalage may be reduced to reduce stalling, or increased to reduce diving

Flight Characteristics

Stall

The wing of the plane reaches a high enough angle of attack that it fails to generate lift, and the nose of the plane drops. A stall may be induced by too much decalage or a center of gravity (CG) too far to the rear. To get rid of stall, the decalage can be reduced, usually by moving the front wing post down a little. Alternatively, the CG can be moved forwards by moving the wing backwards or moving some clay on the plane forwards.

Roll

The plane may rotate along the motorstick towards the left due to torque. Adding wing wash in by lowering the left TE of the wing can help as this increases incidence for the left side of the wing, increasing lift on the left side. However, this creates a lot of drag, so wash in should only be used if necessary. Adding left thrust can also help reduce roll. The 2024 Freedom Flight kit should not need any wash in.

Dive

The plane points down and dives, usually after hitting something. A stable plane will recover from a dive while an unstable plane won't. Both stable planes that try to get a good time by skimming the ceiling many times and unstable planes that are more efficient but can't afford to hit anything are good strategies. Stable planes are naturally less efficient than unstable planes. If the plane is diving at the start of a flight without hitting anything, then the CG needs to be moved back or the decalage needs to be increased, usually by moving the front wing post up a little.

Trimming the Characteristics

A plane should be trimmed to have a good cruise (when the plane stays at roughly the same height) and letdown (when the plane is coming back down). In Division C in the 2023 and 2024 seasons, it's been best to have the plane be on the verge of stalling when coming down or even stalling a tiny amount. Late flight characteristics can be observed by winding the rubber to 30-40% of max winds. 600 winds (300 done at full stretch and 300 while walking in with no backwinds) is a good amount for a rubber with a thickness of around .094". Use partial winds to trim the plane to near stalling before moving on to full winds.

Advanced Trimming

Propeller Pitch

Propeller (prop) pitch can be measured in degrees using a protractor or a pitch meter. The pitch angle refers to the angle of the prop blades as they rotate. At steeper pitch angle the prop will revolve at a slower rpm, and at a lower pitch angle the prop will speed up. Some broad blade props are designed to be natural flexing props, meaning that at high torque the blades will flex to a steeper pitch angle slowing the climb, while flexing to a lower pitch angle later in flight.

Rubber

Rubber is the source of potential energy that is transferred into thrust. The most common rubber used by competitors is FAI Tan Super Sport. Rubber is often measured with its cross section or density. A band with a bigger cross section will take less winds than a smaller band before it breaks. However, the bigger cross section will spin the prop faster. Matching a propeller pitch with cross section to make the longest endurance can take much testing.

A precise method of measuring rubber is by its density. When cutting motors to the desired weight with the same width, it may be noticed that the length of the rubber motor is different. This is due to the large variance in rubber batches. Similar to balsa density, rubber density can also vary significantly within the same batch or strand, affecting flight behavior. Since the effect on flight behavior is significant enough to affect performance, it is recommended to begin measuring rubber by density instead of cross-section. Use this rubber density and max turns calculator.

Lubricating the rubber with Armor-All, Dow Corning 33, or any similar silicone-based lubricant will greatly increase total amount of winds. Avoid petroleum-based lubricant, as that will degrade the rubber and cause eventual breakage. Without lubricant, the rubber will snap early from small nicks forming while being wound. This happens because rubber is coated in talc powder before being sold. Some fliers will wash their competition rubber with soap and water and apply lubricant. However, this is not necessary when practicing—lubricant will suffice. Motors are usually stored in coin envelopes or Ziploc bags.

Watch Calgoddard's video on tying a motor knot.

Most planes can likely add another 30 seconds of flight time by trimming propeller pitch and rubber density. More information can be found in this video.

Flying

Always have a toolkit for making minor repairs, so if something goes wrong your entire day won't go to waste. Also, regardless of how well your plane flies, keep a log. This is not only for competition purposes but also to help you decide what adjustments to make (winds, torque, rubber size) when flying in a new ceiling height at competition.

Finding a Flying Spot

Most people only have access to their school's gym. If you cannot find a gym, warehouses, auditoriums, cafeterias, band rooms, and even churches and universities have been used before. For states (and maybe nationals) if you live in the area and it is easy to get to the site of the competition, they will probably let you fly your plane if nothing else is going on in the building. Check with the site owner/manager, and if you are nice and explain your love for science, they may allow you in. Once inside, stay away from wires, hanging scoreboards, basketball hoops, and places where the rafters extend downward. Don't wind your plane up too much the first time you fly it, because if it gets stuck, you are out of luck. A leaf blower or very long pole can help you get the plane unstuck. Also note the radius of the circle in which your plane turns. Launch from a known location, and then use your steps to measure where the center of the plane's circle is relative to the launch location. Use this information to determine where to launch from. 50-60% of the room's shortest wall is a good circle size to aim for. A smaller circle loses some efficiency and flight time(energy is lost towards turning rather than staying aloft), but such a flight is far better than a large circling flight that hits a wall and never finishes.

You may want to try to find a model airplane group in your area if there is one. Often, they will get gym time from colleges or other places, and if you explain what you're doing, chances are they will let you join them.

Transporting Aircraft

A foam holder secures a plane in a box. The plane can be transported without fear of damage and without taking it apart.

Ideally, get a box that can fit your aircraft while it's assembled and use foam board to create a small jig that securely holds your aircraft inside the box. However, if your aircraft is too big and you don't want to buy a bigger box, you can disassemble your aircraft and transport it that way. If you have good trim, you should mark everything regardless of if you take your aircraft apart to transport it--especially remember to do this if you're going to take it apart, so you can replicate trim after assembling.

Winding Rubber

Use a hand cranked winder with a 10:1 or 15:1 ratio. When winding rubber, first stretch the rubber 5-8 times its original/relaxed length. Stretch distance depends on the number of flights the motor has been used for, the density/width of the motor, etc. After entering around half the desired winds, slowly move in, decreasing the length of the stretched rubber, while still putting in some more winds. The key to winding is to place as many winds as possible without the band breaking. It takes a true feel to know when you are on the edge and when you can still put in a few more winds, so practice helps. After one reaches the desired number of winds, dewinding might be useful. Dewinding decreases the launch torque so you can avoid hitting the hazardous ceiling. It may sound counterintuitive to remove winds, but dewinding takes advantage of a property known as rubber hysteresis. For example, winding to 0.35oz torque will yield less turns than winding to a higher torque and dewinding to 0.35oz. It is highly recommended that you use a torque meter when winding.

Additionally, a good single person winding process is to construct a winding jig with a holder for the winder and a torque meter. Another setup is to clamp the torque meter to a table. Some competitions will not provide tables--if unsure of whether they will do so, reach out to the director or Event Supervisor just to confirm. Especially if you fly solo, it may be necessary to bring a table.

Launching a Plane

Indoor planes are not meant to be thrown, just released. Simply walk with the plane to its normal flight speed, and release. In small ceilings, launch your plane with a lower torque than in high ceilings. Also, it may be beneficial to launch your plane while kneeling on the floor. That way, you may be able to add 3-5 feet to the ceiling height. However, in very high ceilings, it may be more beneficial to stand and launch to gain more height. In settings with very strong air conditioning, it may even be dangerous to launch close to the floor. The AC could push the plane down and cause it to hit the floor.

Launching a Helicopter

Hold both the top and bottom. Let go of the top and sweep your arm away before immediately letting go of the bottom.

Launching a Glider

https://scioly.org/wiki/index.php/Elastic_Launched_Glider#The_Launch

Logs

Serious indoor fliers keep very accurate logs so they can test and record what makes their plane most efficient. A log is also required by the rules. Some suggested data are rubber weight, number of dewinds, launch torque, circle radius, max height, number of winds left, prop diameter/pitch/width, duration time, etc.

Scoring

The final score of a team is determined by the better flight time of their two flights, plus bonus. A complete flight log is a 20% bonus while a partial flight log is a 10% bonus. In previous years, you'd get a bonus for coloring in part of your wing and a deduction for incomplete or nonexistent flight logs; however, the color bonus was removed and the deduction was changed to a bonus.

Past Results

2023 Nationals Division B
Place School Time
1st Sierra Vista Middle School 4:10
2nd Beckendorff Junior High School 4:05
3rd Solon Middle School 3:26
4th Kennedy Middle School --
5th Timberline Middle School --
6th Clague Middle School 3:05

2023 Nationals Division C

Place School Time
1st Ed W. Clark High School 3:00
2nd William P. Clements High School 2:57
3rd Mason High School 2:39
4th Castro Valley High School 2:39
5th* Solon High School 2:38
6th Pioneer High School 2:34

*Boca Raton also got around 2:38 but got an incomplete flight log deduction (10% off).

Useful Resources

Resources

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